The origin of oil in the Cretaceous succession from the South Pars Oil Layer of the Persian Gulf

NASA Astrophysics Data System (ADS)

Rahmani, Omeid; Aali, Jafar; Junin, Radzuan; Mohseni, Hassan; Padmanabhan, Eswaran; Azdarpour, Amin; Zarza, Sahar; Moayyed, Mohsen; Ghazanfari, Parviz

2013-07-01

The origin of the oil in Barremian-Hauterivian and Albian age source rock samples from two oil wells (SPO-2 and SPO-3) in the South Pars oil field has been investigated by analyzing the quantity of total organic carbon (TOC) and thermal maturity of organic matter (OM). The source rocks were found in the interval 1,000-1,044 m for the Kazhdumi Formation (Albian) and 1,157-1,230 m for the Gadvan Formation (Barremian-Hauterivian). Elemental analysis was carried out on 36 samples from the source rock candidates (Gadvan and Kazhdumi formations) of the Cretaceous succession of the South Pars Oil Layer (SPOL). This analysis indicated that the OM of the Barremian-Hauterivian and Albian samples in the SPOL was composed of kerogen Types II and II-III, respectively. The average TOC of analyzed samples is less than 1 wt%, suggesting that the Cretaceous source rocks are poor hydrocarbon (HC) producers. Thermal maturity and Ro values revealed that more than 90 % of oil samples are immature. The source of the analyzed samples taken from Gadvan and Kazhdumi formations most likely contained a content high in mixed plant and marine algal OM deposited under oxic to suboxic bottom water conditions. The Pristane/nC17 versus Phytane/nC18 diagram showed Type II-III kerogen of mixture environments for source rock samples from the SPOL. Burial history modeling indicates that at the end of the Cretaceous time, pre-Permian sediments remained immature in the Qatar Arch. Therefore, lateral migration of HC from the nearby Cretaceous source rock kitchens toward the north and south of the Qatar Arch is the most probable origin for the significant oils in the SPOL.

A four-dimensional petroleum systems model for the San Joaquin Basin Province, California: Chapter 12 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

USGS Publications Warehouse

Peters, Kenneth E.; Magoon, Leslie B.; Lampe, Carolyn; Scheirer, Allegra Hosford; Lillis, Paul G.; Gautier, Donald L.

2008-01-01

A calibrated numerical model depicts the geometry and three-dimensional (3-D) evolution of petroleum systems through time (4-D) in a 249 x 309 km (155 x 192 mi) area covering all of the San Joaquin Basin Province of California. Model input includes 3-D structural and stratigraphic data for key horizons and maps of unit thickness, lithology, paleobathymetry, heat flow, original total organic carbon, and original Rock-Eval pyrolysis hydrogen index for each source rock. The four principal petroleum source rocks in the basin are the Miocene Antelope shale of Graham and Williams (1985; hereafter referred to as Antelope shale), the Eocene Kreyenhagen Formation, the Eocene Tumey formation of Atwill (1935; hereafter referred to as Tumey formation), and the Cretaceous to Paleocene Moreno Formation. Due to limited Rock-Eval/total organic carbon data, the Tumey formation was modeled using constant values of original total organic carbon and original hydrogen index. Maps of original total organic carbon and original hydrogen index were created for the other three source rocks. The Antelope shale was modeled using Type IIS kerogen kinetics, whereas Type II kinetics were used for the other source rocks. Four-dimensional modeling and geologic field evidence indicate that maximum burial of the three principal Cenozoic source rocks occurred in latest Pliocene to Holocene time. For example, a 1-D extraction of burial history from the 4-D model in the Tejon depocenter shows that the bottom of the Antelope shale source rock began expulsion (10 percent transformation ratio) about 4.6 Ma and reached peak expulsion (50 percent transformation ratio) about 3.6 Ma. Except on the west flank of the basin, where steep dips in outcrop and seismic data indicate substantial uplift, little or no section has been eroded. Most petroleum migration occurred during late Cenozoic time in distinct stratigraphic intervals along east-west pathways from pods of active petroleum source rock in the Tejon and Buttonwillow depocenters to updip sandstone reservoirs. Satisfactory runs of the model required about 18 hours of computation time for each simulation using parallel processing on a Linux-based cluster.

Aquifers survey in the context of source rocks exploitation: from baseline acquisition to long term monitoring

NASA Astrophysics Data System (ADS)

Garcia, Bruno; Rouchon, Virgile; Deflandre, Jean-Pierre

2017-04-01

Producing hydrocarbons from source rocks (like shales: a mix of clays, silts, carbonate and sandstone minerals containing matured organic matter, i.e. kerogen oil and gas, but also non-hydrocarbon various species of chemical elements including sometimes radioactive elements) requires to create permeability within the rock matrix by at least hydraulically fracturing the source rock. It corresponds to the production of hydrocarbon fuels that have not been naturally expelled from the pressurized matured source rock and that remain trapped in the porosity or/and kerogen porosity of the impermeable matrix. Azimuth and extent of developed fractures can be respectively determined and mapped by monitoring the associated induced microseismicity. This allows to have an idea of where and how far injected fluids penetrated the rock formation. In a geological context, aquifers are always present in the vicinity -or on fluid migration paths- of such shale formations: deep aquifers (near the shale formation) up to sub-surface and potable (surface) aquifers. Our purpose will be to track any unsuitable invasion or migration of chemicals specifies coming from matured shales of production fluids including both drilling and fracturing ones into aquifers. Our objective is to early detect and alarm of any anomaly to avoid any important environmental issue. The approach consists in deploying a specific sampling tool within a well to recover formation fluids and to run a panoply of appropriate laboratory tests to state on fluid characteristics. Of course for deep aquifers, such a characterization process may consider aquifer properties prior producing shale oil and gas, as they may contain naturally some chemical species present in the source rocks. One can also consider that a baseline acquisition could be justified in case of possible previous invasion of non-natural fluids in the formation under survey (due to any anthropogenic action at surface or in the underground). The paper aims at presenting the protocol and routine test we propose to make our early detection approach efficient for production of shale hydrocarbon fluids, in considering the source-rock reservoir itself, the aquifers, and also the chemical species present in the fluids that are used for hydraulic fracturing operations.

Studying physical properties of deformed intact and fractured rocks by micro-scale hydro-mechanical-seismicity model

NASA Astrophysics Data System (ADS)

Raziperchikolaee, Samin

The pore pressure variation in an underground formation during hydraulic stimulation of low permeability formations or CO2 sequestration into saline aquifers can induce microseismicity due to fracture generation or pre-existing fracture activation. While the analysis of microseismic data mainly focuses on mapping the location of fractures, the seismic waves generated by the microseismic events also contain information for understanding of fracture mechanisms based on microseismic source analysis. We developed a micro-scale geomechanics, fluid-flow and seismic model that can predict transport and seismic source behavior during rock failure. This model features the incorporation of microseismic source analysis in fractured and intact rock transport properties during possible rock damage and failure. The modeling method considers comprehensive grains and cements interaction through a bonded-particle-model. As a result of grain deformation and microcrack development in the rock sample, forces and displacements in the grains involved in the bond breakage are measured to determine seismic moment tensor. In addition, geometric description of the complex pore structure is regenerated to predict fluid flow behavior of fractured samples. Numerical experiments are conducted for different intact and fractured digital rock samples, representing various mechanical behaviors of rocks and fracture surface properties, to consider their roles on seismic and transport properties of rocks during deformation. Studying rock deformation in detail provides an opportunity to understand the relationship between source mechanism of microseismic events and transport properties of damaged rocks to have a better characterizing of fluid flow behavior in subsurface formations.

Source rock contributions to the Lower Cretaceous heavy oil accumulations in Alberta: a basin modeling study

USGS Publications Warehouse

Berbesi, Luiyin Alejandro; di Primio, Rolando; Anka, Zahie; Horsfield, Brian; Higley, Debra K.

2012-01-01

The origin of the immense oil sand deposits in Lower Cretaceous reservoirs of the Western Canada sedimentary basin is still a matter of debate, specifically with respect to the original in-place volumes and contributing source rocks. In this study, the contributions from the main source rocks were addressed using a three-dimensional petroleum system model calibrated to well data. A sensitivity analysis of source rock definition was performed in the case of the two main contributors, which are the Lower Jurassic Gordondale Member of the Fernie Group and the Upper Devonian–Lower Mississippian Exshaw Formation. This sensitivity analysis included variations of assigned total organic carbon and hydrogen index for both source intervals, and in the case of the Exshaw Formation, variations of thickness in areas beneath the Rocky Mountains were also considered. All of the modeled source rocks reached the early or main oil generation stages by 60 Ma, before the onset of the Laramide orogeny. Reconstructed oil accumulations were initially modest because of limited trapping efficiency. This was improved by defining lateral stratigraphic seals within the carrier system. An additional sealing effect by biodegraded oil may have hindered the migration of petroleum in the northern areas, but not to the east of Athabasca. In the latter case, the main trapping controls are dominantly stratigraphic and structural. Our model, based on available data, identifies the Gordondale source rock as the contributor of more than 54% of the oil in the Athabasca and Peace River accumulations, followed by minor amounts from Exshaw (15%) and other Devonian to Lower Jurassic source rocks. The proposed strong contribution of petroleum from the Exshaw Formation source rock to the Athabasca oil sands is only reproduced by assuming 25 m (82 ft) of mature Exshaw in the kitchen areas, with original total organic carbon of 9% or more.

An integrated study of geochemistry and mineralogy of the Upper Tukau Formation, Borneo Island (East Malaysia): Sediment provenance, depositional setting and tectonic implications

NASA Astrophysics Data System (ADS)

Nagarajan, Ramasamy; Roy, Priyadarsi D.; Kessler, Franz L.; Jong, John; Dayong, Vivian; Jonathan, M. P.

2017-08-01

An integrated study using bulk chemical composition, mineralogy and mineral chemistry of sedimentary rocks from the Tukau Formation of Borneo Island (Sarawak, Malaysia) is presented in order to understand the depositional and tectonic settings during the Neogene. Sedimentary rocks are chemically classified as shale, wacke, arkose, litharenite and quartz arenite and consist of quartz, illite, feldspar, rutile and anatase, zircon, tourmaline, chromite and monazite. All of them are highly matured and were derived from a moderate to intensively weathered source. Bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic-ultramafic rocks. The chondrite normalized REE signature indicates the presence of felsic rocks in the source region. Zircon geochronology shows that the samples were of Cretaceous and Triassic age. Comparable ages of zircon from the Tukau Formation sedimentary rocks, granitoids of the Schwaner Mountains (southern Borneo) and Tin Belt of the Malaysia Peninsular suggest that the principal provenance for the Rajang Group were further uplifted and eroded during the Neogene. Additionally, presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the Rajang Group. From a tectonic standpoint, the Tukau Formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings. Our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern Borneo as described in the literature.

Temperature and petroleum generation history of the Wilcox Formation, Louisiana

USGS Publications Warehouse

Pitman, Janet K.; Rowan, Elisabeth Rowan

2012-01-01

A one-dimensional petroleum system modeling study of Paleogene source rocks in Louisiana was undertaken in order to characterize their thermal history and to establish the timing and extent of petroleum generation. The focus of the modeling study was the Paleocene and Eocene Wilcox Formation, which contains the youngest source rock interval in the Gulf Coast Province. Stratigraphic input to the models included thicknesses and ages of deposition, lithologies, amounts and ages of erosion, and ages for periods of nondeposition. Oil-generation potential of the Wilcox Formation was modeled using an initial total organic carbon of 2 weight percent and an initial hydrogen index of 261 milligrams of hydrocarbon per grams of total organic carbon. Isothermal, hydrous-pyrolysis kinetics determined experimentally was used to simulate oil generation from coal, which is the primary source of oil in Eocene rocks. Model simulations indicate that generation of oil commenced in the Wilcox Formation during a fairly wide age range, from 37 million years ago to the present day. Differences in maturity with respect to oil generation occur across the Lower Cretaceous shelf edge. Source rocks that are thermally immature and have not generated oil (depths less than about 5,000 feet) lie updip and north of the shelf edge; source rocks that have generated all of their oil and are overmature (depths greater than about 13,000 feet) are present downdip and south of the shelf edge. High rates of sediment deposition coupled with increased accommodation space at the Cretaceous shelf margin led to deep burial of Cretaceous and Tertiary source rocks and, in turn, rapid generation of petroleum and, ultimately, cracking of oil to gas.

Total petroleum systems of the Bonaparte Gulf Basin area, Australia; Jurassic, Early Cretaceous-Mesozoic; Keyling, Hyland Bay-Permian; Milligans-Carboniferous, Permian

USGS Publications Warehouse

Bishop, M.G.

1999-01-01

The Bonaparte Gulf Basin Province (USGS #3910) of northern Australia contains three important hydrocarbon source-rock intervals. The oldest source-rock interval and associated reservoir rocks is the Milligans-Carboniferous, Permian petroleum system. This petroleum system is located at the southern end of Joseph Bonaparte Gulf and includes both onshore and offshore areas within a northwest to southeast trending Paleozoic rift that was initiated in the Devonian. The Milligans Formation is a Carboniferous marine shale that sources accumulations of both oil and gas in Carboniferous and Permian deltaic, marine shelf carbonate, and shallow to deep marine sandstones. The second petroleum system in the Paleozoic rift is the Keyling, Hyland Bay-Permian. Source rocks include Lower Permian Keyling Formation delta-plain coals and marginal marine shales combined with Upper Permian Hyland Bay Formation prodelta shales. These source-rock intervals provide gas and condensate for fluvial, deltaic, and shallow marine sandstone reservoirs primarily within several members of the Hyland Bay Formation. The Keyling, Hyland Bay-Permian petroleum system is located in the Joseph Bonaparte Gulf, north of the Milligans-Carboniferous, Permian petroleum system, and may extend northwest under the Vulcan graben sub-basin. The third and youngest petroleum system is the Jurassic, Early Cretaceous-Mesozoic system that is located seaward of Joseph Bonaparte Gulf on the Australian continental shelf, and trends southwest-northeast. Source-rock intervals in the Vulcan graben sub-basin include deltaic mudstones of the Middle Jurassic Plover Formation and organic-rich marine shales of the Upper Jurassic Vulcan Formation and Lower Cretaceous Echuca Shoals Formation. These intervals produce gas, oil, and condensate that accumulates in, shallow- to deep-marine sandstone reservoirs of the Challis and Vulcan Formations of Jurassic to Cretaceous age. Organic-rich, marginal marine claystones and coals of the Plover Formation (Lower to Upper Jurassic), combined with marine claystones of the Flamingo Group and Darwin Formation (Upper Jurassic to Lower Cretaceous) comprise the source rocks for the remaining area of the system. These claystones and coals source oil, gas, and condensate accumulations in reservoirs of continental to marine sandstones of the Plover Formation and Flamingo Group. Shales of the regionally distributed Lower Cretaceous Bathurst Island Group and intraformational shales act as seals for hydrocarbons trapped in anticlines and fault blocks, which are the major traps of the province. Production in the Bonaparte Gulf Basin Province began in 1986 using floating production facilities, and had been limited to three offshore fields located in the Vulcan graben sub-basin. Cumulative production from these fields totaled more than 124 million barrels of oil before the facilities were removed after production fell substantially in 1995. Production began in 1998 from three offshore wells in the Zone of Cooperation through floating production facilities. After forty years of exploration, a new infrastructure of pipelines and facilities are planned to tap already discovered offshore reserves and to support additional development.

Marine and nonmarine gas-bearing rocks in Upper Cretaceous Blackhawk and Neslen Formations, eastern Uinta Basin, Utah: sedimentology, diagenesis, and source rock potential

USGS Publications Warehouse

Pitman, Janet K.; Franczyk, K.J.; Anders, D.E.

1987-01-01

Thermogenic gas was generated from interbedded humic-rich source rocks. The geometry and distribution of hydrocarbon source and reservoir rocks are controlled by depositional environment. The rate of hydrocarbon generation decreased from the late Miocene to the present, owing to widespread cooling that occurred in response to regional uplift and erosion associated with the development of the Colorado Plateau. -from Authors

HYDROCARBON SOURCE ROCK EVALUATION OF MIDDLE PROTEROZOIC SOLOR CHURCH FORMATION, NORTH AMERICAN MID-CONTINENT RIFT SYSTEM, RICE COUNTY, MINNESOTA.

USGS Publications Warehouse

Hatch, J.R.; Morey, G.B.

1985-01-01

Hydrocarbon source rock evaluation of the Middle Proterozoic Solor Church Formation (Keweenawan Supergroup) as sampled in the Lonsdale 65-1 well, Rice County, shows that: the rocks are organic matter lean; the organic matter is thermally post-mature, probably near the transition between the wet gas phase of catagenesis and metagenesis; and the rocks have minimal potential for producing additional hydrocarbons. The observed thermal maturity of the organic matter requires significantly greater burial depths, a higher geothermal gradient, or both. It is likely, that thermal maturation of the organic matter in the Solor Church took place relatively early, and that any hydrocarbons generated during this early phase were probably lost prior to deposition of the overlying formation.

Oil-source correlations between the Mississippian Heath Shales and the reservoired oils in the Pennsylvanian Tyler Sands, Montana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cole, G.A.; Drozd, R.J.; Daniel, J.A.

The Mississippi Heath Formation exposed in Fergus County, central Montana, is comprised predominantly of nearshore, marine, black, calcareous shales and carbonates with minor anhydrite and coal beds. The black shales and limestones have been considered as sources for shale oil via Fischer Assay and pyrolysis analysis. These shales are potential source units for the oils reservoired in the overlying Pennsylvanian Tyler Formation sands located 50 mi (80 km) to the east of the Fergus County Heath sediment studied. Heath Formation rocks from core holes were selectively sampled in 2-ft increments and analyzed for their source rock characteristics. Analyses include percentmore » total organic carbon (%TOC), Rock-Eval pyrolysis, pyrolysis-gas chromatography, and characterization of the total soluble extracts using carbon isotopes and gas chromatography-mass Spectrometry. Results indicated that the Heath was an excellent potential source unit that contained oil-prone, organic-rich (maximum of 17.6% TOC), calcareous, black shale intervals. The Heath and Tyler formations also contained intervals dominated by gas-prone, organic-rich shales of terrestrial origin. Three oils from the Tyler Formation sands in Musselshell and Rosebud counties were characterized by similar methods as the extracts. The oils were normally mature, moderate API gravity, moderate sulfur, low asphaltene crudes. Oil to source correlations between the Heath shale extracts and the oils indicated the Heath was an excellent candidate source rock for the Tyler reservoired oils. Conclusions were based on excellent matches between the carbon isotopes of the oils and the kerogen-kerogen pyrolyzates, and from the biomarkers.« less

The influence of shale depositional fabric on the kinetics of hydrocarbon generation through control of mineral surface contact area on clay catalysis

NASA Astrophysics Data System (ADS)

Rahman, Habibur M.; Kennedy, Martin; Löhr, Stefan; Dewhurst, David N.; Sherwood, Neil; Yang, Shengyu; Horsfield, Brian

2018-01-01

Accurately assessing the temperature and hence the depth and timing of hydrocarbon generation is a critical step in the characterization of a petroleum system. Clay catalysis is a potentially significant modifier of hydrocarbon generation temperature, but experimental studies of clay catalysis show inconsistent or contradictory results. This study tests the hypothesis that source rock fabric itself is an influence on clay mineral catalysis as it controls the extent to which organic matter and clay minerals are physically associated. Two endmember clay-organic fabrics distinguish the source rocks studied: (1) a particulate fabric where organic matter is present as discrete, >5 μm particles and (2) a nanocomposite fabric in which amorphous organic matter is associated with clay mineral surfaces at sub-micron scale. High-resolution electron imaging and bulk geochemical characterisation confirm that samples of the Miocene Monterey Formation (California) are representative of the nanocomposite source rock endmember, whereas samples from the Permian Stuart Range Formation (South Australia) represent the particulate source rock endmember. Kinetic experiments are performed on paired whole rock and kerogen isolate samples from these two formations using open system, non-isothermal pyrolysis at three different heating rates (0.7, 2 and 5 K/min) to determine the effects of the different shale fabrics on hydrocarbon generation kinetics. Extrapolation to a modelled geological heating rate shows a 20 °C reduction in the onset temperature of hydrocarbon generation in Monterey Formation whole rock samples relative to paired kerogen isolates. This result is consistent with the Monterey Formations's nanocomposite fabric where clay catalysis can proceed because reactive clay minerals are intimately associated with organic matter. By contrast, there is no significant difference in the modelled hydrocarbon generation temperature of paired whole rock and kerogen isolates from the Stuart Range Formation. This is consistent with its particulate fabric, where relatively large, discrete organic particles have limited contact with the mineral matrix and the clay minerals are mainly diagenetic and physically segregated within pores. While heating rate may have a control on mineral matrix effects, this result shows that the extent to which organic matter and clay minerals are physically associated could have a significant effect on the timing of hydrocarbon generation, and is a function of the depositional environment and detrital vs diagenetic origin of clay minerals in source rocks.

Quarries of Culture: An Ethnohistorical and Environmental Account of Sacred Sites and Rock Formations in Southern California's Mission Indian Country

ERIC Educational Resources Information Center

Karr, Steven M.

2005-01-01

Sacred sites and Rock Formations throughout Southern California's India Country are described by Indians as ancestral markers, origin and place-name locales, areas of deity habitation, and power sources. Early ethnographers were keen to record the traditional stories and meanings related to them by their Native collaborators. Rock formations…

Geochemistry of the Upper Triassic black mudstones in the Qiangtang Basin, Tibet: Implications for paleoenvironment, provenance, and tectonic setting

NASA Astrophysics Data System (ADS)

Wang, Zhongwei; Wang, Jian; Fu, Xiugen; Zhan, Wangzhong; Armstrong-Altrin, John S.; Yu, Fei; Feng, Xinglei; Song, Chunyan; Zeng, Shengqiang

2018-07-01

The Qiangtang Basin is the largest Mesozoic marine basin in the Tibetan Plateau. The Upper Triassic black mudstones are among the most significant hydrocarbon source rocks in this basin. Here, we present geochemical data for the Upper Triassic black mudstones to determine their paleoenvironment conditions, provenance, and tectonic setting. To achieve these, 30 black mudstones formed in various sedimentary environments were collected from the Zangxiahe, Zana, and Bagong formations. The results show that the total REE concentrations of mudstones from these formations range from 169 to 214 ppm, 204 to 220 ppm, and 141 to 194 ppm, respectively. All samples have chondrite-normalized REE patterns with enrichment of LREE, depletion of HREE and negative Eu and Ce anomalies. Specifically, mudstones from the Bagong Formation exhibit higher negative Eu anomalies and lower REE contents than those from the Zangxiahe and Zana formations. Mudstones from the Zangxiahe and Zana formations with low Sr/Ba and Sr/Cu ratios indicate the humid climate, whereas the high Sr/Ba and Sr/Cu ratios of rocks from the Bagong Formation suggest the arid climate. The low U/Th, (Cu + Mo)/Zn, V/Cr and Ni/Co ratios of rocks from the Zangxiahe, Zana, and Bagong formations are indicators of oxidized conditions. The bivariate diagrams (TiO2 vs. Al2O3, TiO2 vs. Zr, La/Th vs. Hf, and Co/Th vs. La/Sc) reveal that mudstones from the Zangxiahe and Zana formations were potentially derived from intermediate igneous rocks, whereas mudstones from the Bagong Formation were probably sourced from felsic igneous rocks. Their source rocks are mostly deposited in the collisional setting. REE of mudstones from the Zangxiahe, Zana, and Bagong formations were possibly originated from terrigenous detritus, with minor non-terrigenous contributions into the Zana samples. The REE contents of these mudstones are controlled mainly by terrigenous detrital minerals, rather than by the paleoclimate, paleoredox conditions, or organic matter. However, calcite minerals could dilute REE. Therefore, the REE contents of the Bagong Formation mudstones are significant lower than those of the Zangxiahe and Zana formations mudstones.

Geochemistry, palynology, and regional geology of worldclass Upper Devonian source rocks in the Madre de Dios basin, Bolivia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, K.E.; Conrad, K.T.; Carpenter, D.G.

Recent exploration drilling indicates the existence of world-class source rock in the Madre de Dios basin, Bolivia. In the Pando-1 X and -2X wells, over 200 m of poorly bioturbated, organic-rich (TOC = 3-16 wt.%) prodelta to shelf mudstones in the Frasnian-Famennian Tomachi Formation contain oil-prone organic matter (hydrogen index = 400-600 mg HC/g TOC). Our calculated source prolificity indices for this interval in these wells (SPI = 15-18 tons of hydrocarbons per square meter of source rock) exceed that for the Upper Jurassic in Central Saudi Arabia. The Tomachi interval is lithologically equivalent to the Colpacucho Formation in themore » northern Altiplano, the Iquiri Formation in the Cordillera Oriental, and is coeval with other excellent source rocks in North America, Africa, and Eurasia. All of these rocks were deposited under conditions favorable for accumulation of organic matter, including a global highstand and high productivity. However, the Madre de Dios basin was situated at high latitude during the Late Devonian and some of the deposits are interpreted to be of glacial origin, indicating conditions not generally associated with organic-rich deposition. A biomarker and palynological study of Upper Devonian rocks in the Pando-1X well suggests deposition under conditions similar to certain modern fjords. High productivity resulted in preservation of abundant organic matter in the bottom sediments despite a cold, toxic water column. Low-sulfur crude oil produced from the Pando-1X well is geochemically similar to, but more mature than, extracts from associated organic-rich Tomachi samples, and was generated from deeper equivalents of these rocks.« less

Provenance and tectonic setting of the Neoproterozoic clastic rocks hosting the Banana Zone Cu-Ag mineralisation, northwest Botswana

NASA Astrophysics Data System (ADS)

Kelepile, Tebogo; Bineli Betsi, Thierry; Franchi, Fulvio; Shemang, Elisha; Suh, Cheo Emmanuel

2017-05-01

Petrographic and geochemical data were combined in order to decipher the petrogenesis of the Neoproterozoic sedimentary succession associated with the Banana Zone Cu-Ag mineralisation (northwest Botswana), in the Kalahari Copperbelt. The investigated Neoproterozoic sedimentary succession is composed of two formations including the Ngwako Pan and the D'kar Formations. The Ngwako Pan Formation is made up of continental siliciclastic sediments, mainly sandstones interbedded with siltstones and mudstones, whereas the D'kar Formation is comprised of shallow marine laminated siltstones, sandstones and mudstones, with subordinate limestone. Copper-Ag mineralisation is essentially confined at the base of the D'kar Formation, which bears reduced organic components, likely to have controlled Cu-Ag precipitation. Sandstones of both the Ngwako Pan and the D'kar Formations are arkoses and subarkoses, composed of quartz (Q), feldspars (F) and lithic fragments (L). Moreover, geochemically the sandstones are considered as potassic and classified as arkoses. On the other hand, mudrocks of the D'kar Formation are finely laminated and are dominated by muscovite, sericite, chlorite and quartz. The modified chemical index of weathering (CIW‧) values indicated an intense chemical weathering of the source rock. The dominance of detrital quartz and feldspar grains coupled with Al2O3/TiO2 ratios (average 29.67 and 24.52 for Ngwako Pan and D'kar Formations, respectively) and Ni and Cr depletion in the sandstones, suggest a dominant felsic source. However, high concentrations of Ni and Cr and a low Al2O3/TiO2 ratio (<20) in the mudrocks of the D'kar Formation indicate a mixed source. Provenance of the investigated sandstones and mudrocks samples is further supported by the REE patterns, the size of Eu anomaly as well as La/Co, Th/Co, Th/Cr and Cr/Th ratios, which show a felsic source for the sandstones of both the Ngwako Pan and D'kar Formations and an intermediate source for the mudrocks of the D'kar Formation. Detrital modes (QFL diagrams) and geochemical characteristics of the sandstones of both the Ngwako Pan and D'kar Formations indicate that the detritus were probably supplied from a heavily weathered felsic continental block and deposited in a continental rift setting (passive margin) in a humid environment. The source rocks might have been the Palaeoproterozoic basement rocks (granitoids and granitic gneiss) and the Mesoproterozoic Kgwebe volcanic rocks exposed north of the study area.

Marine petroleum source rocks and reservoir rocks of the Miocene Monterey Formation, California, U.S.A

USGS Publications Warehouse

Isaacs, C.M.

1988-01-01

The Miocene Monterey Formation of California, a biogenous deposit derived mainly from diatom debris, is important both as a petroleum source and petroleum reservoir. As a source, the formation is thought to have generated much of the petroleum in California coastal basins, which are among the most prolific oil provinces in the United States. Oil generated from the Monterey tends to be sulfur-rich and heavy (<20° API), and has chemical characteristics that more closely resemble immature source extracts than "normal" oil. Thermal-maturity indicators in Monterey kerogens appear to behave anomalously, and several lines of evidence indicate that the oil is generated at lower than expected levels of organic metamorphism. As a reservoir, the Monterey is important due both to conventional production from permeable sandstone beds and to fracture production from fine-grained rocks with low matrix permeability. Fractured reservoirs are difficult to identify, and conventional well-log analysis has not proven to be very useful in exploring for and evaluating these reservoirs. Lithologically similar rocks are broadly distributed throughout the Circum-Pacific region, but their petroleum potential is unlikely to be realized without recognition of the distinctive source and reservoir characteristics of diatomaceous strata and their diagenetic equivalents.

Assessment of Coalbed Gas Resources in Cretaceous and Tertiary Rocks on the North Slope, Alaska, 2006

USGS Publications Warehouse

Roberts, Steve; Barker, Charles E.; Bird, Kenneth J.; Charpentier, Ronald R.; Cook, Troy; Houseknecht, David W.; Klett, Timothy R.; Pollastro, Richard M.; Schenk, Christopher J.

2006-01-01

The North Slope of Alaska is a vast area of land north of the Brooks Range, extending from the Chukchi Sea eastward to the Canadian border. This Arctic region is known to contain extensive coal deposits; hypothetical coal resource estimates indicate that nearly 4 trillion short tons of coal are in Cretaceous and Tertiary rocks. Because of the large volume of coal, other studies have indicated that this region might also have potential for significant coalbed gas resources. The present study represents the first detailed assessment of undiscovered coalbed gas resources beneath the North Slope by the USGS. The assessment is based on the total petroleum system (TPS) concept. Geologic elements within a TPS relate to hydrocarbon source rocks (maturity, hydrocarbon generation, migration), the characteristics of reservoir rocks, and trap and seal formation. In the case of coalbed gas, the coal beds serve as both source rock and reservoir. The Brookian Coalbed Gas Composite TPS includes coal-bearing rocks in Cretaceous and Tertiary strata underlying the North Slope and adjacent Alaska State waters. Assessment units (AUs) within the TPS (from oldest to youngest) include the Nanushuk Formation Coalbed Gas AU, the Prince Creek and Tuluvak Formations Coalbed Gas AU, and the Sagavanirktok Formation Coalbed Gas AU.

Geochemistry of approximately 1.9 Ga sedimentary rocks from northeastern Labrador, Canada

NASA Technical Reports Server (NTRS)

Hayashi, K. I.; Fujisawa, H.; Holland, H. D.; Ohmoto, H.

1997-01-01

Fifty-eight rock chips from fifteen samples of sedimentary rocks from the Ramah Group (approximately 1.9 Ga) in northeastern Labrador, Canada, were analyzed for major and minor elements, including C and S, to elucidate weathering processes on the Earth's surface about 1.9 Ga ago. The samples come from the Rowsell Harbour, Reddick Bight, and Nullataktok Formations. Two rock series, graywackes-gray shales of the Rowsell Harbour, Reddick Bight and Nullataktok Formations, and black shales of the Nullataktok Formation, are distinguishable on the basis of lithology, mineralogy, and major and trace element chemistry. The black shales show lower concentrations than the graywackes-gray shales in TiO2 (0.3-0.7 wt% vs. 0.7-1.8 wt%), Al2O3 (9.5-20.1 wt% vs. 13.0-25.0 wt%), and sigma Fe (<1 wt% vs. 3.8-13.9 wt% as FeO). Contents of Zr, Th, U, Nb, Ce, Y, Rb, Y, Co, and Ni are also lower in the black shales. The source rocks for the Ramah Group sediments were probably Archean gneisses with compositions similar to those in Labrador and western Greenland. The major element chemistry of source rocks for the Ramah Group sedimentary rocks was estimated from the Al2O3/TiO2 ratios of the sedimentary rocks and the relationship between the major element contents (e.g., SiO2 wt%) and Al2O3/TiO2 ratios of the Archean gneisses. This approach is justified, because the Al/Ti ratios of shales generally retain their source rock values; however, the Zr/Al, Zr/Ti, and Cr/Ni ratios fractionate during the transport of sediments. The measured SiO2 contents of shales in the Ramah Group are generally higher than the estimated SiO2 contents of source rocks by approximately 5 wt%. This correction may also have to be applied when estimating average crustal compositions from shales. Two provenances were recognized for the Ramah Group sediments. Provenance I was comprised mostly of rocks of bimodal compositions, one with SiO2 contents approximately 45 wt% and the other approximately 65 wt%, and was the source for most sedimentary rocks of the Ramah Group, except for black shales of the Nullataktok Formation. The black shales were apparently derived from Provenance II that was comprised mostly of felsic rocks with SiO2 contents approximately 65 wt%. Comparing the compositions of the Ramah Group sedimentary rocks and their source rocks, we have recognized that several major elements, especially Ca and Mg, were lost almost entirely from the source rocks during weathering and sedimentation. Sodium and potassium were also leached almost entirely during the weathering of the source rocks. However, significant amounts of Na were added to the black shales and K to all the rock types during diagenesis and/or regional metamorphism. The intensity of weathering of source rocks for the Ramah Group sediments was much higher than that of typical Phanerozoic sediments, possibly because of a higher PCO2 in the Proterozoic atmosphere. Compared to the source rock values, the Fe3+/Ti ratios of many of the graywackes and gray shales of the Ramah Group are higher, the Fe2+/Ti ratios are lower, and the sigma Fe/Ti ratios are the same. Such characteristics of the Fe geochemistry indicate that these sedimentary rocks are comprised of soils formed by weathering of source rocks under an oxygen-rich atmosphere. The atmosphere about 1.9 Ga was, therefore, oxygen rich. Typical black shales of Phanerozoic age exhibit positive correlations between the organic C contents and the concentrations of S, U, and Mo, because these elements are enriched in oxygenated seawater and are removed from seawater by organic matter in sediments. However, such correlations are not found in the Ramah Group sediments. Black shales of the Ramah Group contain 1.7-2.8 wt% organic C, but are extremely depleted in sigma Fe (<1 wt% as FeO), S (<0.3 wt%), U (approximately l ppm), Mo (<5 ppm), Ni (<2 ppm), and Co (approximately 0 ppm). This lack of correlation, however, does not imply that the approximately 1.9 Ga atmosphere-ocean system was anoxic. Depletion of these elements from the Ramah Group sediments may have occurred during diagenesis.

Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

NASA Astrophysics Data System (ADS)

Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

2004-04-01

A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that collided with the Sino-Korea plate towards the end of the Early Paleozoic or during the Devonian. A prominent feature in the detrital zircon age structure of the Huyoufang Formation is the Neoproterozoic detritus, which could be derived only from the Yangtze Craton. Reasonable interpretation of the two distinct source materials for the Huyoufang Formation is that the two plates were juxtaposed through collision before the late Carboniferous.

Age and origin of the Merrimack terrane, southeastern New England: A detrital zircon U-Pb geochronology study

NASA Astrophysics Data System (ADS)

Sorota, Kristin

Metasedimentary rocks of the Merrimack terrane (MT) originated as a thick cover sequence on Ganderia consisting of sandstones, calcareous sandstones, pelitic rocks and turbidites. In order to investigate the age, provenance and stratigraphic order of these rocks and correlations with adjoining terranes, detrital zircon suites from 7 formations across the MT along a NNE-trending transect from east-central Massachusetts to SE New Hampshire were analyzed by U-Pb LA-ICP-MS methods on 90-140 grains per sample. The youngest detrital zircons in the western units, the Worcester, Oakdale and Paxton Formations, are ca. 438 Ma while those in the Kittery, Eliot and Berwick Formations in the northeast are ca. 426 Ma. The Tower Hill Formation previously interpreted to form the easternmost unit of the MT in MA, has a distinctly different zircon distribution with its youngest zircon population in the Cambrian. All samples except for the Tower Hill Formation have detrital zircon age distributions with significant peaks in the mid-to late Ordovician, similar abundances of early Paleozoic and late Neoproterozoic zircons, significant input from ˜1.0 to ˜1.8 Ga sources and limited Archean grains. The similarities in zircon provenance suggest that all units across the terrane, except for the Tower Hill Formation, belong to a single sequence of rocks, with similar sources and with the units in the NE possibly being somewhat younger than those in east-central Massachusetts. The continuous zircon age distributions observed throughout the Mesoproterozoic and late Paleoproterozoic are consistent with an Amazonian source. All samples, except the Tower Hill Formation, show sedimentary input from both Ganderian and Laurentian sources and suggest that Laurentian input increases as the maximum depositional age decreases.

New insight on petroleum system modeling of Ghadames basin, Libya

NASA Astrophysics Data System (ADS)

Bora, Deepender; Dubey, Siddharth

2015-12-01

Underdown and Redfern (2008) performed a detailed petroleum system modeling of the Ghadames basin along an E-W section. However, hydrocarbon generation, migration and accumulation changes significantly across the basin due to complex geological history. Therefore, a single section can't be considered representative for the whole basin. This study aims at bridging this gap by performing petroleum system modeling along a N-S section and provides new insights on source rock maturation, generation and migration of the hydrocarbons using 2D basin modeling. This study in conjunction with earlier work provides a 3D context of petroleum system modeling in the Ghadames basin. Hydrocarbon generation from the lower Silurian Tanezzuft formation and the Upper Devonian Aouinet Ouenine started during the late Carboniferous. However, high subsidence rate during middle to late Cretaceous and elevated heat flow in Cenozoic had maximum impact on source rock transformation and hydrocarbon generation whereas large-scale uplift and erosion during Alpine orogeny has significant impact on migration and accumulation. Visible migration observed along faults, which reactivated during Austrian unconformity. Peak hydrocarbon expulsion reached during Oligocene for both the Tanezzuft and the Aouinet Ouenine source rocks. Based on modeling results, capillary entry pressure driven downward expulsion of hydrocarbons from the lower Silurian Tanezzuft formation to the underlying Bir Tlacsin formation observed during middle Cretaceous. Kinetic modeling has helped to model hydrocarbon composition and distribution of generated hydrocarbons from both the source rocks. Application of source to reservoir tracking technology suggest some accumulations at shallow stratigraphic level has received hydrocarbons from both the Tanezzuft and Aouinet Ouenine source rocks, implying charge mixing. Five petroleum systems identified based on source to reservoir correlation technology in Petromod*. This Study builds upon the original work of Underdown and Redfern, 2008 and offers new insights and interpretation of the data.

Timing of oil and gas generation of petroleum systems in the Southwestern Wyoming Province

USGS Publications Warehouse

Roberts, L.N.R.; Lewan, M.D.; Finn, T.M.

2004-01-01

Burial history, thermal maturity, and timing of petroleum generation were modeled for eight key source-rock horizons at seven locations throughout the Southwestern Wyoming Province. The horizons are the bases of the Lower Permian Phosphoria Formation, the Upper Cretaceous Mowry Shale, Niobrara Formation, Baxter Shale (and equivalents), upper part of the Mesaverde Group, Lewis Shale, Lance Formation, and the Tertiary (Paleocene) Fort Union Formation. Burial history locations include three in the deepest parts of the province (Adobe Town in the Washakie Basin, Eagles Nest in the Great Divide Basin, and Wagon Wheel in the northern Green River Basin); two at intermediate basin depths (Federal 31-1 and Currant, Creek in the central and southern parts of the Green River Basin, respectively); and two relatively shallow locations (Bear 1 on the southeastern margin of the Sand Wash Basin and Bruff 2 on the Moxa arch). An overall ranking of the burial history locations in order of decreasing thermal maturity is Adobe Town > Eagles Nest > Wagon Wheel > Currant Creek > Federal 31-1 > Bear-1 > Bruff 2. The results of the models indicate that peak petroleum generation from Cretaceous oil- and gas-prone source rocks in the deepest parts of the province occurred from Late Cretaceous through middle Eocene. At the modeled locations, peak oil generation from source rocks of the Phosphoria Formation, which contain type-IIS kerogen, occurred in the Late Cretaceous (80 to 73 million years ago (Ma)). Gas generation from the cracking of Phosphoria oil reached a peak in the late Paleocene (57 Ma) only in the deepest parts of the province. The Mowry Shale, Niobrara Formation, and Baxter Shale (and equivalents) contain type-IIS or a mix of type-II and type-III kerogens. Oil generation from these units, in the deepest parts of the province, reached peak rates during the latest Cretaceous to early Paleocene (66 to 61 Ma). Only at these deepest locations did these units reach peak gas generation from the cracking of oil, which occurred in the early to late Eocene (52 to 41 Ma). For the Mesaverde Group, which also contains a mix of type-II and type-III kerogen, peak oil generation occurred only in the deepest parts of the province during middle Eocene (50 to 41 Ma). Only at Adobe Town did cracking of oil occur and gas generation reach peak in the earliest Oligocene (33 Ma). Gas-prone source rocks (type-III kerogen) of the Mowry and Baxter (and equivalents) Shales reached peak gas generation in the latest Cretaceous (66 Ma) in the deepest parts of the province. At the shallower Bear 1 location, the Mancos Shale (Baxter equivalent) source rocks reached peak gas generation at about this same time. Gas generation from the gas-prone Mesaverde source rocks started at all of the modeled locations, but reached peak generation at only the deepest locations in the early Eocene (54 to 49 Ma). The Lewis Shale, Lance Formation, and Fort Union Formation all contain gas-prone source rocks with type-III kerogen. Peak generation of gas from the Lewis Shale occurred only at Eagles Nest and Adobe Town in the early Eocene (52 Ma). Source rocks of the Lance reached peak gas generation only at the deepest locations during the middle Eocene (48 to 45 Ma) and the Fort Union reached peak gas generation only at Adobe Town also in the middle Eocene (44 Ma).

Petroleum Systems and Assessment of Undiscovered Oil and Gas in the Raton Basin - Sierra Grande Uplift Province, Colorado and New Mexico - USGS Province 41

USGS Publications Warehouse

Higley, Debra K.

2007-01-01

Introduction The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The USGS recently completed an assessment of undiscovered oil and gas resources of the Raton Basin-Sierra Grande Uplift Province of southeastern Colorado and northeastern New Mexico (USGS Province 41). The Cretaceous Vermejo Formation and Cretaceous-Tertiary Raton Formation have production and undiscovered resources of coalbed methane. Other formations in the province exhibit potential for gas resources and limited production. This assessment is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). The USGS used this geologic framework to define two total petroleum systems and five assessment units. All five assessment units were quantitatively assessed for undiscovered gas resources. Oil resources were not assessed because of the limited potential due to levels of thermal maturity of petroleum source rocks.

Integrated system for investigating sub-surface features of a rock formation

DOEpatents

Vu, Cung Khac; Skelt, Christopher; Nihei, Kurt; Johnson, Paul A.; Guyer, Robert; Ten Cate, James A.; Le Bas, Pierre -Yves; Larmat, Carene S.

2015-08-18

A system for investigating non-linear properties of a rock formation around a borehole is provided. The system includes a first sub-system configured to perform data acquisition, control and recording of data; a second subsystem in communication with the first sub-system and configured to perform non-linearity and velocity preliminary imaging; a third subsystem in communication with the first subsystem and configured to emit controlled acoustic broadcasts and receive acoustic energy; a fourth subsystem in communication with the first subsystem and the third subsystem and configured to generate a source signal directed towards the rock formation; and a fifth subsystem in communication with the third subsystem and the fourth subsystem and configured to perform detection of signals representative of the non-linear properties of the rock formation.

Fractal Nature of Porosity in Volcanic Tight Reservoirs of the Santanghu Basin and its Relationship to Pore Formation Processes

NASA Astrophysics Data System (ADS)

Wang, Weiming; Wang, Zhixuan; Chen, Xuan; Long, Fei; Lu, Shuangfang; Liu, Guohong; Tian, Weichao; Su, Yue

In this paper, in a case study of Santanghu Basin in China, the morphological characteristics and size distribution of nanoscale pores in the volcanic rocks of the Haerjiawu Formation were investigated using the results of low temperature nitrogen adsorption experiments. This research showed that within the target layer, a large number of nanoscale, eroded pores showed an “ink bottle” morphology with narrow pore mouths and wide bodies. The fractal dimension of pores increases gradually with increasing depth. Moreover, as fractal dimension increases, BET-specific surface area gradually increases, average pore diameter decreases and total pore volume gradually increases. The deeper burial of the Haerjiawu volcanic rocks in the Santanghu Basin leads to more intense erosion by organic acids derived from the basin’s source rocks. Furthermore, the internal surface roughness of these corrosion pores results in poor connectivity. As stated above, the corrosion process is directly related to the organic acids generated by the source rock of the interbedded volcanic rocks. The deeper the reservoir, the more the organic acids being released from the source rock. However, due to the fact that the Haerjiawu volcanic rocks are tight reservoirs and have complicated pore-throat systems, while organic acids dissolve unstable minerals such as feldspars which improve the effective reservoir space; the dissolution of feldspars results in the formation of new minerals, which cannot be expelled from the tight reservoirs. They are instead precipitated in the fine pore throats, thereby reducing pore connectivity, while enhancing reservoir micro-preservation conditions.

Geochemical characteristics of igneous rocks associated with epithermal mineral deposits—A review

USGS Publications Warehouse

du Bray, Edward A.

2017-01-01

Newly synthesized data indicate that the geochemistry of igneous rocks associated with epithermal mineral deposits varies extensively and continuously from subalkaline basaltic to rhyolitic compositions. Trace element and isotopic data for these rocks are consistent with subduction-related magmatism and suggest that the primary source magmas were generated by partial melting of the mantle-wedge above subducting oceanic slabs. Broad geochemical and petrographic diversity of individual igneous rock units associated with epithermal deposits indicate that the associated magmas evolved by open-system processes. Following migration to shallow crustal reservoirs, these magmas evolved by assimilation, recharge, and partial homogenization; these processes contribute to arc magmatism worldwide.Although epithermal deposits with the largest Au and Ag production are associated with felsic to intermediate composition igneous rocks, demonstrable relationships between magmas having any particular composition and epithermal deposit genesis are completely absent because the composition of igneous rock units associated with epithermal deposits ranges from basalt to rhyolite. Consequently, igneous rock compositions do not constitute effective exploration criteria with respect to identification of terranes prospective for epithermal deposit formation. However, the close spatial and temporal association of igneous rocks and epithermal deposits does suggest a mutual genetic relationship. Igneous systems likely contribute heat and some of the fluids and metals involved in epithermal deposit formation. Accordingly, deposit formation requires optimization of source metal contents, appropriate fluid compositions and characteristics, structural features conducive to hydrothermal fluid flow and confinement, and receptive host rocks, but not magmas with special compositional characteristics.

SW New Mexico Oil Well Formation Tops

DOE Data Explorer

Shari Kelley

2015-10-21

Rock formation top picks from oil wells from southwestern New Mexico from scout cards and other sources. There are differing formation tops interpretations for some wells, so for those wells duplicate formation top data are presented in this file.

Origin of sulfur for elemental sulfur concentration in salt dome cap rocks, Gulf Coast Basin, USA

NASA Astrophysics Data System (ADS)

Hill, J. M.; Kyle, R.; Loyd, S. J.

2017-12-01

Calcite cap rocks of the Boling and Main Pass salt domes contain large elemental sulfur accumulations. Isotopic and petrographic data indicate complex histories of cap rock paragenesis for both domes. Whereas paragenetic complexity is in part due to the open nature of these hydrodynamic systems, a comprehensive understanding of elemental sulfur sources and concentration mechanisms is lacking. Large ranges in traditional sulfur isotope compositions (δ34S) among oxidized and reduced sulfur-bearing phases has led some to infer that microbial sulfate reduction and/or influx of sulfide-rich formation waters occurred during calcite cap rock formation. Ultimately, traditional sulfur isotope analyses alone cannot distinguish among local microbial or exogenous sulfur sources. Recently, multiple sulfur isotope (32S, 33S, 34S, 36S) studies reveal small, but measurable differences in mass-dependent behavior of microbial and abiogenic processes. To distinguish between the proposed sulfur sources, multiple-sulfur-isotope analyses have been performed on native sulfur from the Boling and Main Pass cap rocks. Similarities or deviations from equilibrium relationships indicate which pathways were responsible for native sulfur precipitation. Pathway determination provides insight into Gulf Coast cap rock development and potentially highlights the conditions that led to anomalous sulfur enrichment in Boling and Main Pass Domes.

Change of Conditions of the Formation of the Karelian Province of the Baltic Shield Continental Crust during Transition from Meso- to Neoarchean: Geochemical Study Results

NASA Astrophysics Data System (ADS)

Chekulaev, V. P.; Arestova, N. A.; Egorova, Yu. S.; Kucherovskii, G. A.

2018-05-01

The compositions of the tonalite-trondhjemite-granodiorite (TTG) assemblage and volcanic rocks of the Archaean greenstone belts from different domains of the Karelian province of the Baltic Shield are compared. Neoarchean medium felsic volcanic rocks and TTG of the Central Karelian domain drastically differ from analogous Mesoarchean rocks of the neighboring Vodlozero and West Karelian domains in higher Rb, Sr, P, La, and Ce contents and, correspondingly, values of Sr/Y, La/Yb, and La/Sm, and also in a different REE content distribution owing to different rock sources of these domains. This fact is confirmed by differences in the composition and the nature of the REE distribution in the basic and ultrabasic volcanic rocks making up the greenstone belts of these domains. It is established that the average compositions of Mesoarchean TTG rocks and volcanic rocks of the Karelian province differ markedly from those of plagiogranitoids and volcanic rocks of the recent geotectonic environments in high Mg (mg#) and Sr contents. Neoarchean volcanic rocks of Karelia differ from recent island-arc volcanic rocks, but are similar in composition to recent volcanic rocks of the continental arcs. On the basis of the cumulative evidence, the Karelian province of the Baltic Shield was subject to dramatic changes in the crust formation conditions at the beginning of the Neoarchean at the turn of about 2.75-2.78 Ga. These changes led to formation of volcano-sedimentary and plutonic rock complexes, different in composition from Mesoarchean rocks, and specific complexes of intrusive sanukitoids and granites. Changes and variations in the rock composition were related to the mixing of plume sources with continental crust and/or lithospheric mantle material, likely as a result of the combined effect of plumes and plate tectonics. This process resulted in formation of a younger large fragment of the Archean crust such as the Central Karelian domain which factually connected more ancient fragments of the crust and likely contributed to development of the Neoarchean Kenorland Supercontinent.

Reservoirs and petroleum systems of the Gulf Coast

USGS Publications Warehouse

Pitman, Janet K.

2010-01-01

This GIS product was designed to provide a quick look at the ages and products (oil or gas) of major reservoir intervals with respect to the different petroleum systems that have been identified in the Gulf Coast Region. The three major petroleum source-rock systems are the Tertiary (Paleocene-Eocene) Wilcox Formation, Cretaceous (Turonian) Eagle Ford Formation, and Jurassic (Oxfordian) Smackover Formation. The ages of the reservoir units extend from Jurassic to Pleistocene. By combining various GIS layers, the user can gain insights into the maximum extent of each petroleum system and the pathways for petroleum migration from the source rocks to traps. Interpretations based on these data should improve development of exploration models for this petroleum-rich province.

In search of a Silurian total petroleum system in the Appalachian basin of New York, Ohio, Pennsylvania, and West Virginia: Chapter G.11 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Ryder, Robert T.; Swezey, Christopher S.; Trippi, Michael H.; Lentz, Erika E.; Avary, K. Lee; Harper, John A.; Kappel, William M.; Rea, Ronald G.; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

Although the TOC analyses in this study indicate that good to very good source rocks are present in the Salina Group and Wills Creek Formation of southwestern Pennsylvania and northern West Virginia, data are insufficient to propose a new Silurian total petroleum system in the Appalachian basin. However, the analytical results of this investigation are encouraging enough to undertake more systematic studies of the source rock potential of the Salina Group, Wills Creek Formation, and perhaps the Tonoloway Formation (Limestone) and McKenzie Limestone (or Member).

Comparison of the petroleum systems of East Venezuela in their tectonostratigraphic context

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stronach, N.J.; Kerr, H.M.; Scotchmer, J.

1996-08-01

The Maturin and Guarico subbasins of East Venezuela record the transition from Cretaceous passive margin to Tertiary foreland basin with local post-orogenic transtensional basins. Petroleum is reservoired in several units ranging from Albian (El Cantil Formation) to Pliocene (Las Piedras Formation) age. Source rocks are principally in the Upper Cretaceous (Querecual Formation), and Miocene (Carapita Formation) in the Maturin subbasin and in the Upper Cretaceous (Tigre Formation) and Oligocene (Roblecito and La Pascua Formations) in the Guarico subbasin. An extensive well database has been used to address the distribution and provenance of hydrocarbons in the context of a tectonostratigraphic modelmore » for the evolution of the East Venezuela basin. Nine major plays have been described, comprising thirteen petroleum systems. The principal factors influencing the components of individual petroleum systems are as follows: (1) structural controls on Upper Cretaceous source rock distribution, relating to block faulting on the proto-Caribbean passive margin; (2) paleoenvironmental controls on source rock development within the Oligocene-Miocene foreland basin; and (3) timing of subsidence and maturation within the Oligocene-Upper Miocene foreland basin and the configuration of the associated fold and thrust belt, influencing long range and local migration routes (4) local development of Pliocene post-orogenic transtensional basins, influencing hydrocarbon generation, migration and remigration north of the Pirital High.« less

The Influence of Lithology on the Formation of Reaction Infiltration Instabilities in Mantle Rocks

NASA Astrophysics Data System (ADS)

Pec, M.; Holtzman, B. K.; Zimmerman, M. E.; Kohlstedt, D. L.

2017-12-01

The formation of oceanic plates requires extraction of large volumes of melt from the mantle. Several lines of evidence suggest that melt extraction is rapid and, therefore, necessitates high-permeability pathways. Such pathways may form as a result of melt-rock reactions. We report the results of a series of Darcy-type experiments designed to study the development of channels due to melt-solid reactions in mantle lithologies. We sandwiched a partially molten rock between a melt source and a porous sink and annealed it at high pressure (P = 300 MPa) and high temperatures (T = 1200° or 1250°C) with a controlled pressure gradient (∂P/∂z = 0-100 MPa/mm). To study the influence of lithology on the channel formation, we synthesized partially molten rocks of harzburgitic (40:40:20 Ol - Opx - basalt), wehrlitic (40:40:20 Ol - Cpx - basalt) and lherzolitic (65:25:10 Ol - Opx - Cpx) composition. The melt source was a disk of alkali basalt. In all experiments, irrespective of the exact mineralogy, melt - undersaturated in silica - from the source dissolved pyroxene in the partially molten rock and precipitated olivine ( Fo82), thereby forming a dunite reaction layer at the interface between the source and the partially molten rock. In samples annealed under a small pressure gradient, the reaction layer was roughly planar. However, if the velocity of melt due to porous flow exceeded 0.1 µm/s, the reaction layer locally protruded into the partially molten rock forming finger-like, melt-rich channels in rocks of wehrlitic and harzburgitic composition. The lherzolitic rocks were generally impermeable to the melt except at highest-pressure gradients where a narrow fracture developed, forming a dyke which drained the melt reservoir. Three-dimensional reconstructions using micro-CT images revealed clear differences between the dyke (a narrow, through-going planar feature) and the channels formed by reactive infiltration (multiple sinuous finger-like features). Apparently, the fraction of soluble minerals together with the melt fraction in the partially molten rock control whether dykes or reactive channels develop. Our experiments demonstrate that melt-rock reactions can lead to channelization in mantle lithologies, and the observed lithological transformations broadly agree with those observed in nature

Chapter 5: Geologic Assessment of Undiscovered Petroleum Resources in the Waltman Shale Total Petroleum System,Wind River Basin Province, Wyoming

USGS Publications Warehouse

Roberts, Steve B.; Roberts, Laura N.R.; Cook, Troy

2007-01-01

The Waltman Shale Total Petroleum System encompasses about 3,400 square miles in the Wind River Basin Province, Wyoming, and includes accumulations of oil and associated gas that were generated and expelled from oil-prone, lacustrine shale source rocks in the Waltman Shale Member of the Paleocene Fort Union Formation. Much of the petroleum migrated and accumulated in marginal lacustrine (deltaic) and fluvial sandstone reservoirs in the Shotgun Member of the Fort Union, which overlies and intertongues with the Waltman Shale Member. Additional petroleum accumulations derived from Waltman source rocks are present in fluvial deposits in the Eocene Wind River Formation overlying the Shotgun Member, and also might be present within fan-delta deposits included in the Waltman Shale Member, and in fluvial sandstone reservoirs in the uppermost part of the lower member of the Fort Union Formation immediately underlying the Waltman. To date, cumulative production from 53 wells producing Waltman-sourced petroleum exceeds 2.8 million barrels of oil and 5.8 billion cubic feet of gas. Productive horizons range from about 1,770 feet to 5,800 feet in depth, and average about 3,400 to 3,500 feet in depth. Formations in the Waltman Shale Total Petroleum System (Fort Union and Wind River Formations) reflect synorogenic deposition closely related to Laramide structural development of the Wind River Basin. In much of the basin, the Fort Union Formation is divided into three members (ascending order): the lower unnamed member, the Waltman Shale Member, and the Shotgun Member. These members record the transition from deposition in dominantly fluvial, floodplain, and mire environments in the early Paleocene (lower member) to a depositional setting characterized by substantial lacustrine development (Waltman Shale Member) and contemporaneous fluvial, and marginal lacustrine (deltaic) deposition (Shotgun Member) during the middle and late Paleocene. Waltman Shale Member source rocks have total organic carbon values ranging from 0.93 to 6.21 weight percent, averaging about 2.71 weight percent. The hydrocarbon generative potential of the source rocks typically exceeds 2.5 milligrams of hydrocarbon per gram of rock and numerous samples had generative potentials exceeding 6.0 milligrams of hydrocarbon per gram of rock. Waltman source rocks are oil prone, and contain a mix of Type-II and Type-III kerogen, indicating organic input from a mix of algal and terrestrial plant matter, or a mix of algal and reworked or recycled material. Thermal maturity at the base of the Waltman Shale Member ranges from a vitrinite reflectance value of less than 0.60 percent along the south basin margin to projected values exceeding 1.10 percent in the deep basin west of Madden anticline. Burial history reconstructions for three wells in the northern part of the Wind River Basin indicate that the Waltman Shale Member was well within the oil window (Ro equal to or greater than 0.65 percent) by the time of maximum burial about 15 million years ago; maximum burial depths exceeded 10,000 feet. Onset of oil generation calculated for the base of the Waltman Shale member took place from about 49 million years ago to about 20 million years ago. Peak oil generation occurred from about 31 million years ago to 26 million years ago in the deep basin west of Madden anticline. Two assessment units were defined in the Waltman Shale Total Petroleum System: the Upper Fort Union Sandstones Conventional Oil and Gas Assessment Unit (50350301) and the Waltman Fractured Shale Continuous Oil Assessment Unit (50350361). The conventional assessment unit primarily relates to the potential for undiscovered petroleum accumulations that are derived from source rocks in the Waltman Shale Member and trapped within sandstone reservoirs in the Shotgun Member (Fort Union Formation) and in the lower part of the overlying Wind River Formation. The potential for Waltman-sourced oil accumulations in fan-delta depos

Burial history, thermal maturity, and oil and gas generation history of petroleum systems in the Wind River Basin Province, central Wyoming: Chapter 6 in Petroleum systems and geologic assessment of oil and gas resources in the Wind River Basin Province, Wyoming

USGS Publications Warehouse

Roberts, Laura N.R.; Finn, Thomas M.; Lewan, Michael D.; Kirschbaum, Mark A.

2007-01-01

Burial history, thermal maturity, and timing of oil and gas generation were modeled for eight key source rock units at nine well locations throughout the Wind River Basin Province. Petroleum source rocks include the Permian Phosphoria Formation, the Cretaceous Mowry Shale, Cody Shale, and Mesaverde, Meeteetse, and Lance Formations, and the Tertiary (Paleocene) Fort Union Formation, including the Waltman Shale Member. Within the province boundary, the Phosphoria is thin and only locally rich in organic carbon. Phosphoria oil produced from reservoirs in the province is thought to have migrated from the Wyoming and Idaho thrust belt. Locations (wells) selected for burial history reconstructions include three in the deepest parts of the province (Adams OAB-17, Bighorn 1-5, and Coastal Owl Creek); three at intermediate depths (Hells Half Acre, Shell 33X-10, and West Poison Spider); and three at relatively shallow locations (Young Ranch, Amoco Unit 100, and Conoco-Coal Bank). The thermal maturity of source rocks is greatest in the deep northern and central parts of the province and decreases to the south and east toward the basin margins. The results of the modeling indicate that, in the deepest areas, (1) peak petroleum generation from Cretaceous rocks occurred from Late Cretaceous through middle Eocene time, and (2) onset of oil generation from the Waltman Shale Member occurred from late Eocene to early Miocene time. Based on modeling results, gas generation from the cracking of Phosphoria oil reservoired in the Park City Formation reached a peak in the late Paleocene/early Eocene (58 to 55 Ma) only in the deepest parts of the province. The Mowry Shale and Cody Shale (in the eastern half of the basin) contain a mix of Type-II and Type-III kerogens. Oil generation from predominantly Type-II source rocks of these units in the deepest parts of the province reached peak rates during the latest Cretaceous to early Eocene (65 to 55 Ma). Only in these areas of the basin did these units reach peak gas generation from the cracking of oil, which occurred in the early to middle Eocene (55 to 42 Ma). Gas-prone source rocks of the Mowry and Cody Shales (predominantly Type-III kerogen), and the Mesaverde, Meeteetse, Lance, and Fort Union Formations (Type –III kerogen) reached peak gas generation in the latest Cretaceous to late Eocene (67 to 38 Ma) in the deepest parts of the province. Gas generation from the Mesaverde source rocks started at all of the modeled locations but reached peak generation at only the deepest locations and at the Hells Half Acre location in the middle Paleocene to early Eocene (59 to 48 Ma). Also at the deepest locations, peak gas generation occurred from the late Paleocene to the early Eocene (57 to 49 Ma) for the Meeteetse Formation, and during the Eocene for the Lance Formation (55 to 48 Ma) and the Fort Union Formation (44 to 38 Ma). The Waltman Shale Member of the Fort Union Formation contains Type-II kerogen. The base of the Waltman reached a level of thermal maturity to generate oil only at the deep-basin locations (Adams OAB-17 and Bighorn 1-5 locations) in the middle Eocene to early Miocene (36 to 20 Ma).

Variability over time in the sources of South Portuguese Zone turbidites: evidence of denudation of different crustal blocks during the assembly of Pangaea

NASA Astrophysics Data System (ADS)

Pereira, M. F.; Ribeiro, C.; Vilallonga, F.; Chichorro, M.; Drost, K.; Silva, J. B.; Albardeiro, L.; Hofmann, M.; Linnemann, U.

2014-07-01

This study combines geochemical and geochronological data in order to decipher the provenance of Carboniferous turbidites from the South Portuguese Zone (SW Iberia). Major and trace elements of 25 samples of graywackes and mudstones from the Mértola (Visean), Mira (Serpukhovian), and Brejeira (Moscovian) Formations were analyzed, and 363 U-Pb ages were obtained on detrital zircons from five samples of graywackes from the Mira and Brejeira Formations using LA-ICPMS. The results indicate that turbiditic sedimentation during the Carboniferous was marked by variability in the sources, involving the denudation of different crustal blocks and a break in synorogenic volcanism. The Visean is characterized by the accumulation of immature turbidites (Mértola Formation and the base of the Mira Formation) inherited from a terrane with intermediate to mafic source rocks. These source rocks were probably formed in relation to Devonian magmatic arcs poorly influenced by sedimentary recycling, as indicated by the almost total absence of pre-Devonian zircons typical of the Gondwana and/or Laurussia basements. The presence of Carboniferous grains in Visean turbidites indicates that volcanism was active at this time. Later, Serpukhovian to Moscovian turbiditic sedimentation (Mira and Brejeira Formations) included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism. The abundance of Precambrian and Paleozoic zircons reveals strong recycling of the Gondwana and/or Laurussia basements. A peri-Gondwanan provenance is indicated by zircon populations with Neoproterozoic (Cadomian-Avalonian and Pan-African zircon-forming events), Paleoproterozoic, and Archean ages. The presence of late Ordovician and Silurian detrital zircons in Brejeira turbidites, which have no correspondence in the Gondwana basement of SW Iberia, indicates Laurussia as their most probable source.

The cretaceous source rocks in the Zagros Foothills of Iran: An example of a large size intracratonic basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bordenave, M.L.; Huc, A.Y.

1993-02-01

The Zagros orogenic belt of Iran is one of the world most prolific petroleum producing area. However, most of the oil production is originated from a relatively small area, the 60,000 km[sup 2] wide Dezful Embayment which contains approximately 12% of the proven oil global reserves. The distribution of the oil and gas fields results from the area extent of six identified source rock layers, their thermal history and reservoir, cap rock and trap availability. In this paper, the emphasis is three of the layers of Cretaceous sources rocks. The Garau facies was deposited during the Neocomian to Albian intervalmore » over Lurestan, Northeast Khuzestan and extends over the extreme northeast part of Fars, the Kazhdumi source rock which deposited over the Dezful Embayment, and eventually the Senonian Gurpi Formation which has marginal source rock characteristics in limited areas of Khuzestan and Northern Fars. The deposition environment of these source rock layers corresponds to semipermanent depressions, included in an overall shallow water intracratonic basin communicating with the South Tethys Ocean. These depressions became anoxic when climatic oceanographical and geological conditions were adequate, i.e., humid climate, high stand water, influxes of fine grained clastics and the existence of sills separating the depression from the open sea. Distribution maps of these source rock layers resulting from extensive field work and well control are also given. The maturation history of source rocks is reconstructed from a set of isopachs. It was found that the main contributor to the oil reserves is the Kazhdumi source rock which is associated with excellent calcareous reservoirs.« less

Isotopic data for Late Cretaceous intrusions and associated altered and mineralized rocks in the Big Belt Mountains, Montana

USGS Publications Warehouse

du Bray, Edward A.; Unruh, Daniel M.; Hofstra, Albert H.

2017-03-07

The quartz monzodiorite of Mount Edith and the concentrically zoned intrusive suite of Boulder Baldy constitute the principal Late Cretaceous igneous intrusions hosted by Mesoproterozoic sedimentary rocks of the Newland Formation in the Big Belt Mountains, Montana. These calc-alkaline plutonic masses are manifestations of subduction-related magmatism that prevailed along the western edge of North America during the Cretaceous. Radiogenic isotope data for neodymium, strontium, and lead indicate that the petrogenesis of the associated magmas involved a combination of (1) sources that were compositionally heterogeneous at the scale of the geographically restricted intrusive rocks in the Big Belt Mountains and (2) variable contamination by crustal assimilants also having diverse isotopic compositions. Altered and mineralized rocks temporally, spatially, and genetically related to these intrusions manifest at least two isotopically distinct mineralizing events, both of which involve major inputs from spatially associated Late Cretaceous igneous rocks. Alteration and mineralization of rock associated with the intrusive suite of Boulder Baldy requires a component characterized by significantly more radiogenic strontium than that characteristic of the associated igneous rocks. However, the source of such a component was not identified in the Big Belt Mountains. Similarly, altered and mineralized rocks associated with the quartz monzodiorite of Mount Edith include a component characterized by significantly more radiogenic strontium and lead, particularly as defined by 207Pb/204Pb values. The source of this component appears to be fluids that equilibrated with proximal Newland Formation rocks. Oxygen isotope data for rocks of the intrusive suite of Boulder Baldy are similar to those of subduction-related magmatism that include mantle-derived components; oxygen isotope data for altered and mineralized equivalents are slightly lighter.

Grains of Nonferrous and Noble Metals in Iron-Manganese Formations and Igneous Rocks of Submarine Elevations of the Sea of Japan

NASA Astrophysics Data System (ADS)

Kolesnik, O. N.; Astakhova, N. V.

2018-01-01

Iron-manganese formations and igneous rocks of submarine elevations in the Sea of Japan contain overlapping mineral phases (grains) with quite identical morphology, localization, and chemical composition. Most of the grains conform to oxides, intermetallic compounds, native elements, sulfides, and sulfates in terms of the set of nonferrous, noble, and certain other metals (Cu, Zn, Sn, Pb, Ni, Mo, Ag, Pd, and Pt). The main conclusion that postvolcanic hydrothermal fluids are the key sources of metals is based upon a comparison of the data of electron microprobe analysis of iron-manganese formations and igneous rocks dredged at the same submarine elevations in the Sea of Japan.

Rock flows

NASA Technical Reports Server (NTRS)

Matveyev, S. N.

1986-01-01

Rock flows are defined as forms of spontaneous mass movements, commonly found in mountainous countries, which have been studied very little. The article considers formations known as rock rivers, rock flows, boulder flows, boulder stria, gravel flows, rock seas, and rubble seas. It describes their genesis as seen from their morphological characteristics and presents a classification of these forms. This classification is based on the difference in the genesis of the rubbly matter and characterizes these forms of mass movement according to their source, drainage, and deposit areas.

The upper limit of maturity of natural gas generation and its implication for the Yacheng formation in the Qiongdongnan Basin, China

NASA Astrophysics Data System (ADS)

Su, Long; Zheng, Jianjing; Chen, Guojun; Zhang, Gongcheng; Guo, Jianming; Xu, Yongchang

2012-08-01

Vitrinite reflectance (VR, Ro%) measurements from residual kerogen of pyrolysis experiments were performed on immature Maoming Oil Shale substituted the samples for the gas-prone source rocks of Yacheng formation of the Qiongdongnan Basin in the South China Sea. The work was focused on determination an upper limit of maturity for gas generation (ULMGG) or "the deadline of natural gas generation". Ro values at given temperatures increase with increasing temperature and prolonged heating time, but ΔRo-value, given a definition of the difference of all values for VR related to higher temperature and adjacent lower temperature in open-system non-isothermal experiment at the heating rate of 20 °C/min, is better than VR. And representative examples are presented in this paper. It indicates that the range of natural gas generation for Ro in the main gas generation period is from 0.96% to 2.74%, in which ΔRo is in concordance with the stage for the onset and end of the main gas generation period corresponding to 0.02% up to 0.30% and from 0.30% up to 0.80%, respectively. After the main gas generation period of 0.96-2.74%, the evolution of VR approach to the ULMGG of the whole rock for type II kerogen. It is equal to 4.38% of VR, where the gas generation rates change little with the increase of maturation, ΔRo is the maximum of 0.83% corresponding to VR of 4.38%Ro, and the source rock does not nearly occur in the end process of hydrocarbon gas generation while Ro is over 4.38%. It shows that it is the same the ULMGG from the whole rock for type II kerogen as the method with both comparison and kinetics. By comparing to both the conclusions of pyrolysis experiments and the data of VR from the source rock of Yacheng formation on a series of selected eight wells in the shallow-water continental shelf area, it indicate that the most hydrocarbon source rock is still far from reaching ULMGG from the whole rock for type II kerogen. The source rock of Yacheng formation in the local areas of the deepwater continental slope basin have still preferable natural gas generative potential, especially in the local along the central depression belt (namely the Ledong, Lingshui, Songnan and Baodao sags from southwest to northeast) from the depocenter to both the margin and its adjacent areas. It help to evaluate the resource potential for oil and gas of the hydrocarbon source rock in the deepwater continental slope of the Qiongdongnan Basin or other basins with lower exploration in the northern of the South China Sea and to reduce the risk in exploration.

Egret-Hibernia(!), a significant petroleum system, northern Grand Banks area, offshore eastern Canada

USGS Publications Warehouse

Magoon, L.B.; Hudson, T.L.; Peters, K.E.

2005-01-01

Egret-Hibernia(!) is a well-explored petroleum system (3.25 billion barrels oil equivalent [BOE]) located in the Jeanne d'Arc Basin on the Labrador - Newfoundland shelf. Rifting and sediment fill began in the Late Triassic. Egret source rock was deposited in the Late Jurassic at about 153 Ma. After this time, alternating reservoir rock and seal rock were deposited with some syndepositional faulting. By the end of the Early Cretaceous, faults and folds had formed numerous structural traps. For the next 100 m.y., overburden rock thermally matured the source rock when it reached almost 4 km (2.5 mi) burial depth. For 2 km (1.25 mi) below this depth, oil and gas were expelled, until the source was depleted. The expelled petroleum migrated updip to nearby faulted, anticlinal traps, where much of it migrated across faults and upsection to the Hibernia Formation (44% recoverable oil) and Avalon Formation (28%). Accumulation size decreased, and gas content increased from west to east, independent of trap size. These changes correspond to a decrease in source rock richness and quality from west to east. Almost all (96%) of the discovered petroleum resides in the Lower Cretaceous or older reservoir rock units. All accumulations found to date are normally pressured in structural traps. Fifty-two exploration wells found eighteen discoveries. Their size ranges from 1.2 to 0.01 billion BOE. Most discoveries were made between 1979 and 1991. The discovery cycle began with larger accumulations and progressed to smaller accumulations. The estimated sizes of the larger accumulations have grown since 1990. Estimated mean value for undiscovered hydrocarbons is 3.8 billion BOE, thereby raising the ultimate size of Egret-Hibernia(!) to 6.19 billion BOE. Copyright ?? 2005. The American Association of Petroleum Geologists. All rights reserved.

Aerial radiometric and magnetic reconnaissance survey of portions of Arizona, Idaho, Montana, New Mexico, South Dakota and Washington. Volume 2-F. Lewistown Quadrangle. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1979-06-01

Results of a high-sensitivity, aerial, gamma-ray spectrometer and magnetometer survey of the Lewistown Quadrangle, Montana, are presented. Instrumentation and methods are described in Volume 1 of this final report. Statistical and geological analysis of the radiometric data revealed 58 uranium anomalies worthy of field-checking as possible prospects. One anomaly may be associated with the Cambrian Flathead Quartzite that may contain deposits similar to the Blind River and Rand uranium deposits. Three anomalies may be indicative of sandstone-type deposits in Jurassic rocks, particularly the Morrison Formation, which hosts uranium mineralization elsewhere. One of the latter anomalies is also related to rocksmore » of the Mississippian Madison Group, and this suggests the possible presence of uranium in limestones of the Mission Canyon Formation. There are 45 anomalies related to the Cretaceous rocks. Lignite in the Hell Creek and Judith River formations and Eagle Sandstone may have caused the formation of 22 epigenetic uranium deposits. Many anomalies occur in the Bearpaw Shale and Claggett Formation. However, only five are considered significant of the remainder are expected to be caused by large amounts of radioactive bentonite or bentonitic shale. Two other Cretaceous units that may host sandstone-type deposits are the Colorado Shale and Kootenai Formation that register 16 and two anomalies respectively. Only one anomaly pertains to Tertiary rocks, and it may be indicative of vein-type deposits in the intrusives of the Judith Mountains. These rocks may also act as source rocks for deposits surrounding the Judith Mountains. Eight anomalies related only to Quaternary units may be demonstrative of uranium-rich source rocks that could host uranium mineralization.Several anomalies are located close to oil fields and may have been cause by radium-rich oil-field brines.« less

Magma genesis at Gale Crater: Evidence for Pervasive Mantle Metasomatism

NASA Astrophysics Data System (ADS)

Filiberto, J.

2017-12-01

Basaltic rocks have been analyzed at Gale Crater with a larger range in bulk chemistry than at any other landing site [1]. Therefore, the rocks may have experienced significantly different formation conditions than those experienced by magmas at Gusev Crater or Meridiani Planum. Specifically, the rocks at Gale Crater have higher potassium than other Martian rocks, with a potential analog of the Nakhlite parental magma, and are consistent with forming from a metasomatized mantle source [2-4]. Mantle metasomatism would not only affect the bulk chemistry but mantle melting conditions, as metasomatism fluxes fluids into the source region. Here I will combine differences in bulk chemistry between Martian basalts to calculate formation conditions in the interior and investigate if the rocks at Gale Crater experienced magma genesis conditions consistent with metasomatism - lower temperatures and pressures of formation. To calculate average formation conditions, I rely on experimental results, where available, and silica-activity and Mg-exchange thermometry calculations for all other compositions following [5, 6]. The results show that there is a direct correlation between the calculated mantle potential temperature and the K/Ti ratio of Gale Crater rocks. This is consistent with fluid fluxed metasomatism introducing fluids to the system, which depressed the melting temperature and fluxed K but not Ti to the system. Therefore, all basalts at Gale Crater are consistent with forming from a metasomatized mantle source, which affected not only the chemistry of the basalts but also the formation conditions. References: [1] Cousin A. et al. (2017) Icarus. 288: 265-283. [2] Treiman A.H. et al. (2016) Journal of Geophysical Research: Planets. 121: 75-106. [3] Treiman A.H. and Medard E. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10.1130/abs/2016AM-285851. [4] Schmidt M.E. et al. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10.1130/abs/2016AM-285651. [5] Filiberto J. and Dasgupta R. (2011) Earth and Planetary Science Letters. 304: 527-537. [6] Filiberto J. and Dasgupta R. (2015) Journal of Geophysical Research: Planets. 120: DOI: 10.1002/2014JE004745.

Application of Fusion Gyrotrons to Enhanced Geothermal Systems (EGS)

NASA Astrophysics Data System (ADS)

Woskov, P.; Einstein, H.; Oglesby, K.

2013-10-01

The potential size of geothermal energy resources is second only to fusion energy. Advances are needed in drilling technology and heat reservoir formation to realize this potential. Millimeter-wave (MMW) gyrotrons and related technologies developed for fusion energy research could contribute to enabling EGS. Directed MMW energy can be used to advance rock penetration capabilities, borehole casing, and fracking. MMWs are ideally suited because they can penetrate through small particulate extraction plumes, can be efficiently guided long distances in borehole dimensions, and continuous megawatt sources are commercially available. Laboratory experiments with a 10 kW, 28 GHz CPI gyrotron have shown that granite rock can be fractured and melted with power intensities of about 1 kW/cm2 and minute exposure times. Observed melted rock MMW emissivity and estimated thermodynamics suggest that penetrating hot, hard crystalline rock formations may be economic with fusion research developed MMW sources. Supported by USDOE, Office of Energy Efficiency and Renewable Energy and Impact Technologies, LLC.

Families of miocene monterey crude oil, seep, and tarball samples, coastal California

USGS Publications Warehouse

Peters, K.E.; Hostettler, F.D.; Lorenson, T.D.; Rosenbauer, R.J.

2008-01-01

Biomarker and stable carbon isotope ratios were used to infer the age, lithology, organic matter input, and depositional environment of the source rocks for 388 samples of produced crude oil, seep oil, and tarballs to better assess their origins and distributions in coastal California. These samples were used to construct a chemometric (multivariate statistical) decision tree to classify 288 additional samples. The results identify three tribes of 13C-rich oil samples inferred to originate from thermally mature equivalents of the clayey-siliceous, carbonaceous marl and lower calcareous-siliceous members of the Monterey Formation at Naples Beach near Santa Barbara. An attempt to correlate these families to rock extracts from these members in the nearby COST (continental offshore stratigraphic test) (OCS-Cal 78-164) well failed, at least in part because the rocks are thermally immature. Geochemical similarities among the oil tribes and their widespread distribution support the prograding margin model or the banktop-slope-basin model instead of the ridge-and-basin model for the deposition of the Monterey Formation. Tribe 1 contains four oil families having geochemical traits of clay-rich marine shale source rock deposited under suboxic conditions with substantial higher plant input. Tribe 2 contains four oil families with traits intermediate between tribes 1 and 3, except for abundant 28,30-bisnorhopane, indicating suboxic to anoxic marine marl source rock with hemipelagic input. Tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher plant input. Tribes 1 and 2 occur mainly south of Point Conception in paleogeographic settings where deep burial of the Monterey source rock favored petroleum generation from all three members or their equivalents. In this area, oil from the clayey-siliceous and carbonaceous marl members (tribes 1 and 2) may overwhelm that from the lower calcareous-siliceous member (tribe 3) because the latter is thinner and less oil-prone than the overlying members. Tribe 3 occurs mainly north of Point Conception where shallow burial caused preferential generation from the underlying lower calcareous-siliceous member or another unit with similar characteristics. In a test of the decision tree, 10 tarball samples collected from beaches in Monterey and San Mateo counties in early 2007 were found to originate from natural seeps representing different organofacies of Monterey Formation source rock instead from one anthropogenic pollution event. The seeps apparently became more active because of increased storm activity. Copyright ?? 2008. The American Association of Petroleum Geologists. All rights reserved.

Origin of a Tertiary oil from El Mahafir wildcat & geochemical correlation to some Muglad source rocks, Muglad basin, Sudan

NASA Astrophysics Data System (ADS)

Fadul Abul Gebbayin, Omer. I. M.; Zhong, Ningning; Ali Ibrahim, Gulfan; Ali Alzain, Mohamed

2018-01-01

Source rock screening analysis was performed on four stratigraphic units from the Muglad basin namely; Abu Gabra, Zarqa, Ghazal, and Baraka formations using pyrolysis and Vitrinite Reflectance (Ro). Results, integrated with the chromatographic and isotopic data from these rocks extracts and a Tertiary oil from El Mahafir-1 wild cat, were used to determine the origin of the oil. A good organic source within the Middle Abu Gabra Formation is observed in wells El Toor-6 and Neem Deep-1 (TOC, 1.0-2.0% & S2 5.0-10.0 mg C/g rock), with mixed kerogens I, II, & III, and thermally mature (% Ro = 0.74-0.94). The Campanian-Early Maastrichtian sequence, i.e. Zarqa and Ghazal formations are generally poor (TOC, <0.5% & S2 <2.5 mg C/g rock), dominated by type III kerogens, and immature at the studied locations. The Baraka shale nevertheless, is good at El Mahafir-1 well (avg. TOC 1.8% & S2 5.0-10.0 mg C/g rock) and fair at Timsah-1 well (Avg. TOC 0.69% & S2 2.5-5.0 mg C/g rock) with a Kerogen that is predominantly Sapropellic at the former, and an exclusively Humic at the later. The formation is mature at Timsah (% Ro = 0.77-1.16) and early mature at El Mahafir-1 (% Ro = 0.64-0.81). Consistent with the pyrolysis, chromatographic data of the rock extracts confirms the mixed source nature of the Abu Gabra Formation which consists of both algal [prominent LMW n-alkanes & elevated C27 steranes (36-47%)], as well as terrigenous material [higher diasterane/regular sterane ratios (0.50-0.56), abundant rearranged hopanes, & relatively high CPIs (1.22-1.9)], accumulated in an oxic to sub-oxic environment (Pr/Ph, 1.3-3.0). Abu Gabra further shows low C29/C30 hopanes (0.45-0.54), low C28 steranes (21-26%) with high Gammacerane index (20.3). In contrast, the environment during the Late Cretaceous was strongly reducing (Pr/Ph, 0.37-1.0), associated with a wide organic diversity, both in space and time and is characterized by dominant algal input at some areas and or stratigraphic intervals [Elevated tricyclics, higher C29/C30 hopanes (0.5-1.14), and relatively low Gammacerane indices (4.6-14.4)], while mixed with abundant terrigenous material at others. A direct correlation between El Mahafir oil and the Abu Gabra extracts is thus inferred based on: its mixed organic source nature, oxic to sub-oxic depositional environment (Pr/Ph 1.22), relatively low C29/C30 hopanes (0.54), low C28 steranes (29%), and a high gammacerane index (20.5). This is largely supported by the maturity modeling results which suggest generation is only from the Abu Gabra at this location.

Early Tertiary Exhumation, Erosion, and Sedimentation in the Central Andes, NW Argentina

NASA Astrophysics Data System (ADS)

Carrapa, B.; Decelles, P. G.; Gerhels, G.; Mortimer, E.; Strecker, M. R.

2006-12-01

Timing of deformation and resulting sedimentation patterns in the Altiplano-Puna Plateau-Eastern Cordillera of the southern Central Andes are the subject of ongoing controversial debate. In the Bolivian Altiplano, sedimentation into a foreland basin system commenced during the Paleocene. Farther south in the Puna and Eastern Cordillera of NW Argentina, a lack of data has precluded a similar interpretation. Early Tertiary non-marine sedimentary rocks are preserved within the present day Puna Plateau and Eastern Cordillera of NW Argentina. The Salar de Pastos Grandes basin in the Puna Plateau contains more than 2 km of Eocene alluvial and fluvial strata in the Geste Formation, deposited in close proximity to orogenic source terrains. Sandstone and conglomerate petrographic data document Ordovician quartzites and minor phyllites and schists as the main source rocks. Detrital zircon U-Pb ages from both the Geste Formation and from underlying Ordovician quartzite cluster in the 900-1200 Ma (Grenville) and late Precambrian-Cambrian (Panafrican) ranges. Sparse late Eocene (~37-34 Ma) grains are also present; their large size, euhedral shape, and decreasing mean ages upsection suggest that these grains are volcanogenic (i.e. ash fall contamination), derived from an inferred magmatic arc to the west. The Eocene ages corroborate mammalian paleontological dates, defining the approximate begin of deposition of the Geste Formation. Alternatively, these young zircons could be of plutonic origin; however, no Eocene plutons are present in the surrounding source rocks and this interpretation is not likely. From W to E, fluvial rocks of the Quebrada de los Colorados Formation show similar sedimentological features as those observed for the Geste Formation, suggesting a genetic link between the two. Detrital zircon U-Pb data show mainly Panafrican ages, with sparse ages in the 860-935 Ma range and a few mid-Proterozoic ages. More importantly, a significant number of late Eocene-Oligocene ages (ca. 37-32 Ma) are also present, suggesting a similar volcanogenic origin for these grains and time-stratigraphic equivalence to the Geste Formation. The upper conglomeratic part of this formation records western sources mainly composed of volcanic, granitic and quartzitic rocks derived from the proto-Eastern Cordillera. Detrital apatite fission track (AFT) data from the Geste Formation document strong Paleocene and early Eocene signals suggesting active exhumation of western sources. This corroborates AFT data from the Cordillera Domeyko (northern Chile) to the west and the proto-Eastern Cordillera to the east of the study area documenting cooling and exhumation at this time. Combined, these data indicate active Paleocene to Eocene deformation, exhumation, erosion, and sedimentation within the region that corresponds to the present-day Puna Plateau and the Eastern Cordillera.

Geochemical Analysis of Parasequences within the Productive Middle Member of the Eagle Ford Formation at Lozier Canyon near Del Rio, Texas

NASA Astrophysics Data System (ADS)

Shane, Timothy E.

The middle member of the Eagle Ford formation is a heterogeneous, carbonate-shale unit that is a focus of unconventional oil and gas exploration in southern Texas. Exploration results have been mixed because of the apparent heterogeneity of the member. In this study, the extent of heterogeneities in the Eagle Ford on the "bedding-scale" were examined by evaluating changes in organic and inorganic geochemistry. Samples were collected vertically in outcrop covering four non-consecutive parasequences. These samples were analyzed using a Rock Eval 6 Analyzer(TM) to determine source rock generative potential and a Niton(TM) XRF to evaluate inorganic geochemistry to identify changes in paleoredox conditions, paleoproductivity, and clastic influx. From pyrolysis data, it is determined that Parasequence 1 potentially displays an increase in source rock potential, Parasequence 2 potentially displays a constant source rock potential, and Parasequences 3 and 4 potentially display overall decreases in source rock potential during deposition. From the inferred paleoredox conditions, paleoproductivity, and clastic influx, it is determined that Parasequence 1 experienced a potential increase in oxygen abundance, Parasequence 2 experienced a potential decrease in oxygen abundance, and Parasequences 3 and 4 potentially experienced increases in oxygen abundance during deposition. It is concluded that geochemical heterogeneities do exist on a bedding scale within the parasequences of the middle member of the Eagle Ford. Additional comprehensive sampling and analysis is recommended in the future in order to tie these data to subsurface data for economic application.

Hydrocarbons in recent sediment of the Monterey Bay National Marine Sanctuary

USGS Publications Warehouse

Kvenvolden, K.A.; Hostettler, F.D.; Rosenbauer, R.W.; Lorenson, T.D.; Castle, W.T.; Sugarman, S.

2002-01-01

A complex mixture of hydrocarbons is present in the recent sediment of the Monterey Bay National Marine Sanctuary. Eighteen samples from the continental shelf between San Francisco and Monterey contain aliphatic and aromatic hydrocarbons showing biological contributions from both marine and terrigenous sources, with the terrigenous indicators more pronounced near Monterey. Of particular interest, however, is a low-level background of petroleum-related compounds, including 28,30-bisnorhopane and 18??+??(H)-oleanane, which are characteristic of many crude oils from the Monterey Formation of California. Thus, the sediments are overprinted by a regional chemical signature which may be derived from eroded Monterey Formation rocks and from onshore and offshore seeps releasing petroleum from Monterey Formation source rocks. ?? 2002 Elsevier Science B.V. All rights reserved.

Petrophysical Rock Typing of Unconventional Shale Plays: A Case Study for the Niobrara Formation of the Denver-Julesburg (DJ) Basin

NASA Astrophysics Data System (ADS)

Kamruzzaman, A.; Prasad, M.

2015-12-01

The hydrocarbon-rich mudstone rock layers of the Niobrara Formation were deposited in the shallow marine environment and have evolved as overmature oil- or gas-prone source and reservoir rocks. The hydrocarbon production from its low-porosity, nano-darcy permeability and interbedded chalk-marl reservoir intervals is very challenging. The post-diagenetic processes have altered the mineralogy and pore structure of its sourcing and producing rock units. A rock typing analysis in this play can help understand the reservoir heterogeneity significantly. In this study, a petrophysical rock typing workflow is presented for the Niobrara Formation by integrating experimental rock properties with geologic lithofacies classification, well log data and core study.Various Niobrara lithofacies are classified by evaluating geologic depositional history, sequence stratigraphy, mineralogy, pore structure, organic content, core texture, acoustic properties, and well log data. The experimental rock measurements are conducted on the core samples recovered from a vertical well from the Wattenberg Field of the Denver-Julesburg (DJ) Basin. Selected lithofacies are used to identify distinct petrofacies through the empirical analysis of the experimental data-set. The grouped petrofacies are observed to have unique mineralogical properties, pore characteristics, and organic contents and are labelled as discrete Niobrara rock types in the study area.Micro-textural image analysis (FESEM) is performed to qualitatively examine the pore size distribution, pore types and mineral composition in the matrix to confirm the classified rock units. The principal component analysis and the cluster analysis are carried out to establish the certainty of the selected rock types. Finally, the net-to-pay thicknesses of these rock units are compared with the cumulative production data from the field to further validate the chosen rock types.For unconventional shale plays, the rock typing information can be used to locate hydrocarbon sweetspots, facilitate the placement of the horizontal section of the wells along the sweetspots, and can augment engineers' abilities on suitable well placement considerations. It can also help enhancing the effectiveness of the hydraulic fracture stimulation and completion operation.

Geochemical typification of kimberlite and related rocks of the North Anabar region, Yakutia

NASA Astrophysics Data System (ADS)

Kargin, A. V.; Golubeva, Yu. Yu.

2017-11-01

The results of geochemical typification of kimberlites and related rocks (alneites and carbonatites) of the North Anabar region are presented with consideration of the geochemical specification of their source and estimation of their potential for diamonds. The content of representative trace elements indicates the predominant contribution of an asthenospheric component (kimberlites and carbonatites) in their source, with a subordinate contribution of vein metasomatic formations containing Cr-diopside and ilmenite. A significant contribution of water-bearing potassium metasomatic parageneses is not recognized. According to the complex of geochemical data, the studied rocks are not industrially diamondiferous.

Hydrocarbon source-rock evaluation - Solor Church Formation (middle Proterozoic, Keweenawan Supergroup), southeastern Minnesota

USGS Publications Warehouse

Hatch, J.R.; Morey, G.B.

1984-01-01

In the type section (Lonsdale 65-1 core, Rice County, Minnesota) the Solor Church Formation (Middle Proterozoic, Keweenawan Supergroup) consists primarily of reddish-brown mudstone and siltstone and pale reddish-brown sandstone. The sandstone and siltstone are texturally and mineralogically immature. Hydrocarbon source-rock evaluation of bluish-gray, greenish-gray and medium-dark-gray to grayish-black beds, which primarily occur in the lower 104 m (340 ft) of this core, shows: (1) the rocks have low organic carbon contents (<0.5 percent for 22 of 25 samples); (2) the organic matter is thermally very mature (Tmax = 494°C, sample 19) and is probably near the transition between the wet gas phase of catagenesis and metagenesis (dry gas zone); and (3) the rocks have minimal potential for producing additional hydrocarbons (genetic potential <0.30 mgHC/gm rock). Although no direct evidence exists from which to determine maximum depths of burial, the observed thermal maturity of the organic matter requires significantly greater depths of burial and(or) higher geothermal gradients. It is likely, at least on the St. Croix horst, that thermal alteration of the organic matter in the Solor Church took place relatively early, and that any hydrocarbons generated during this early thermal alteration were probably lost prior to deposition of the overlying Fond du Lac Formation (Middle Proterozoic, Keweenawan Supergroup).

Hydrocarbon source rock evaluation: Solor Church Formation. (Middle Proterozoic, Keweenawan Supergroup) southeastern Minnesota

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hatch, J.R.; Morey, G.B.

In the type section (Lonsdale 65-1 core, Rice County, Minnesota) the Solar Church Formation (Middle Proterozoic, Keweenawan Supergroup) consists primarily of reddish-brown mudstone and siltstone and pale reddish-brown sandstone. The sandstone and siltstone are texturally and mineralogically immature. Hydrocarbon source-rock evaluation of bluish-gray, greenish-gray and medium-dark-gray to grayish-black beds, which primarily occur in the lower 104 m (340 ft) of this core, shows: (1) the rocks have low organic carbon contents (<0.5% for 22 of 25 samples); (2) the organic matter is thermally very mature (T/sub max/ = 494/sup 0/C, sample 19) and is probably near the transition between themore » wet gas phase of catagenesis and metagenesis (dry gas zone); and (3) the rocks have minimal potential for producing additional hydrocarbons (genetic potential <0.30 mgHC/gm rock). Although no direct evidence exists from which to determine maximum depths of burial, the observed thermal maturity of the organic matter requires significantly greater depths of burial and(or) higher geothermal gradients. It is likely, at least on the St. Croix horst, that thermal alteration of the organic matter in the Solor Church took place relatively early, and that any hydrocarbons generated during this early thermal alteration were probably lost prior to deposition of the overlying Fond du Lac Formation (Middle Proterozoic, Keweenawan Supergroup). 5 figs., 2 tabs.« less

Geologically Controlled Isotope-Time Patterns Reveal Early Differentiation and Crust Formation Processes

NASA Astrophysics Data System (ADS)

Bennett, V. C.; Nutman, A. P.

2014-12-01

The mechanisms of continental crust production and evolution in the early Earth remain controversial, as are questions of the relative roles of early differentiation versus subsequent tectonic procssing in creating Earth's chemical signatures. Here we present geologic observations integrated with whole rock major, trace element and Sm-Nd isotopic signatures and combined with U-Pb and Lu-Hf isotopic compositions of zircon populations from the same rocks, from the most extensive early rock record comprising the 3.9 Ga to 3.6 Ga terranes of southwest Greenland. These data reveal repeated patterns of formation of juvenile TTG crust and associated mafic and ultramafic rocks in convergent margin settings followed by formation of more evolved granites [1]. Our new zircon Lu-Hf data from rare 3.6-3.7 Ga tonalites within the Itsaq Gneiss Complex, obtained from single component, non-migmatitic gneisses with simple zircon populations, limited within sample Hf isotopic variability and accurate U-Pb ages, now document extraction of juvenile tonalites from a near chondritic mantle source between 3.9 Ga and 3.6 Ga. The more evolved, granitic rocks in each area show slightly negative initial ɛHf in accord with crustal reworking of the older (3.8-3.9 Ga) gniesses. There is no evidence for Hadean material in the sources of the granitoids. The Hf isotope-time patterns are consistent with juvenile crust production from a mantle source that experienced only modest amounts of prior crustal extraction. They are distinct from those predicted by reprocessing of an enriched Hadean mafic crust, as has been proposed for this region [2] and for the source of the Hadean Jack Hills zircons [3]. The well-documented, time decreasing, positive 142Nd anomalies [e.g., 4] from these rocks are further evidence of crustal derivation from a convecting mantle source, rather than reworking of an enriched mafic lithosphere. The 143Nd isotopic -time patterns are more complex, reflecting the interplay between early Sm/Nd fractionation processes as required by the 142Nd data, juvenile crustal growth and in some cases geologic disturbance of the whole rock Sm-Nd system. [1] Nutman, et al, (2013) Amer. Jour. Sci. 313, 877-911. [2] Naeraa et al.. (2012) Nature 485, 627-631. [3] Kemp et al., (2010) EPSL 296, 45-56. [4] Bennett et al., (20070 Science 318, 1907.

System and method for investigating sub-surface features of a rock formation with acoustic sources generating coded signals

DOEpatents

Vu, Cung Khac; Nihei, Kurt; Johnson, Paul A; Guyer, Robert; Ten Cate, James A; Le Bas, Pierre-Yves; Larmat, Carene S

2014-12-30

A system and a method for investigating rock formations includes generating, by a first acoustic source, a first acoustic signal comprising a first plurality of pulses, each pulse including a first modulated signal at a central frequency; and generating, by a second acoustic source, a second acoustic signal comprising a second plurality of pulses. A receiver arranged within the borehole receives a detected signal including a signal being generated by a non-linear mixing process from the first-and-second acoustic signal in a non-linear mixing zone within the intersection volume. The method also includes-processing the received signal to extract the signal generated by the non-linear mixing process over noise or over signals generated by a linear interaction process, or both.

Geologic framework of oil and gas genesis in main sedimentary basins from Romania Oprea Dicea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ionescu, N.; Morariu, C.D.

1991-03-01

Oil and gas fields located in Moldavic nappes are encompassed in Oligocene and lower Miocene formations, mostly in the marginal folds nappe, where Kliwa Sandstone sequences have high porosity, and in the Black Sea Plateau. The origin of the hydrocarbon accumulations from the Carpathian foredeep seems to be connected to the Oligocene-lower Miocene bituminous formations of the marginal folds and sub-Carpathian nappes. In the Gethic depression, the hydrocarbon accumulations originate in Oligocene and Miocene source rocks and host in structural, stratigraphical, and lithological traps. The accumulations connected with tectonic lines that outline the areal extension of the Oligocene, Miocene, andmore » Pliocene formations are in the underthrusted Moesian platform. The hydrocarbon accumulations related to the Carpathian foreland represent about 40% of all known accumulations in Romania. Most of them are located in the Moesian platform. In this unit, the oil and gas fields present a vertical distribution at different stratigraphic levels, from paleozoic to Neogene, and in all types of reservoirs, suggesting multicycles of oleogenesis, migration, accumulation, and sealing conditions. The hydrocarbon deposits known so far on the Black Sea continental plateau are confined in the Albian, Cenomanian, Turonian-Senonian, and Eocene formations. The traps are of complex type structural, lithologic, and stratigraphic. The reservoirs are sandstones, calcareous sandstones, limestones, and sands. The hydrocarbon source rocks are pelitic and siltic Oligocene formations. Other older source rocks are probably Cretaceous.« less

Uranium enrichment in lacustrine oil source rocks of the Chang 7 member of the Yanchang Formation, Erdos Basin, China

NASA Astrophysics Data System (ADS)

Yang, Hua; Zhang, Wenzheng; Wu, Kai; Li, Shanpeng; Peng, Ping'an; Qin, Yan

2010-09-01

The oil source rocks of the Chang 7 member of the Yanchang Formation in the Erdos Basin were deposited during maximum lake extension during the Late Triassic and show a remarkable positive uranium anomaly, with an average uranium content as high as 51.1 μg/g. Uranium is enriched together with organic matter and elements such as Fe, S, Cu, V and Mo in the rocks. The detailed biological markers determined in the Chang 7 member indicate that the lake water column was oxidizing during deposition of the Chang 7 member. However, redox indicators for sediments such as S 2- content, V/Sc and V/(V + Ni) ratios demonstrate that it was a typical anoxic diagenetic setting. The contrasted redox conditions between the water column and the sediment with a very high content of organic matter provided favorable physical and chemical conditions for syngenetic uranium enrichment in the oil source rocks of the Chang 7 member. Possible uranium sources may be the extensive U-rich volcanic ash that resulted from contemporaneous volcanic eruption and uranium material transported by hydrothermal conduits into the basin. The uranium from terrestrial clastics was unlike because uranium concentration was not higher in the margin area of basin where the terrestrial material input was high. As indicated by correlative analysis, the oil source rocks of the Chang 7 member show high gamma-ray values for radioactive well log data that reflect a positive uranium anomaly and are characterized by high resistance, low electric potential and low density. As a result, well log data can be used to identify positive uranium anomalies and spatial distribution of the oil source rocks in the Erdos Basin. The estimation of the total uranium reserves in the Chang 7 member attain 0.8 × 10 8 t.

Petroleum systems and geologic assessment of undiscovered oil and gas, Cotton Valley group and Travis Peak-Hosston formations, East Texas basin and Louisiana-Mississippi salt basins provinces of the northern Gulf Coast region. Chapters 1-7.

USGS Publications Warehouse

,

2006-01-01

The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The USGS recently completed an assessment of undiscovered oil and gas potential of the Cotton Valley Group and Travis Peak and Hosston Formations in the East Texas Basin and Louisiana-Mississippi Salt Basins Provinces in the Gulf Coast Region (USGS Provinces 5048 and 5049). The Cotton Valley Group and Travis Peak and Hosston Formations are important because of their potential for natural gas resources. This assessment is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). The USGS used this geologic framework to define one total petroleum system and eight assessment units. Seven assessment units were quantitatively assessed for undiscovered oil and gas resources.

An overview on source rocks and the petroleum system of the central Upper Rhine Graben

NASA Astrophysics Data System (ADS)

Böcker, Johannes; Littke, Ralf; Forster, Astrid

2017-03-01

The petroleum system of the Upper Rhine Graben (URG) comprises multiple reservoir rocks and four major oil families, which are represented by four distinct source rock intervals. Based on geochemical analyses of new oil samples and as a review of chemical parameter of former oil fields, numerous new oil-source rock correlations were obtained. The asymmetric graben resulted in complex migration pathways with several mixed oils as well as migration from source rocks into significantly older stratigraphic units. Oldest oils originated from Liassic black shales with the Posidonia Shale as main source rock (oil family C). Bituminous shales of the Arietenkalk-Fm. (Lias α) show also significant source rock potential representing the second major source rock interval of the Liassic sequence. Within the Tertiary sequence several source rock intervals occur. Early Tertiary coaly shales generated high wax oils that accumulated in several Tertiary as well as Mesozoic reservoirs (oil family B). The Rupelian Fish Shale acted as important source rock, especially in the northern URG (oil family D). Furthermore, early mature oils from the evaporitic-salinar Corbicula- and Lower Hydrobienschichten occur especially in the area of the Heidelberg-Mannheim-Graben (oil family A). An overview on potential source rocks in the URG is presented including the first detailed geochemical source rock characterization of Middle Eocene sediments (equivalents to the Bouxwiller-Fm.). At the base of this formation a partly very prominent sapropelic coal layer or coaly shale occurs. TOC values of 20-32 % (cuttings) and Hydrogen Index (HI) values up to 640-760 mg HC/g TOC indicate an extraordinary high source rock potential, but a highly variable lateral distribution in terms of thickness and source rock facies is also supposed. First bulk kinetic data of the sapropelic Middle Eocene coal and a coaly layer of the `Lymnäenmergel' are presented and indicate oil-prone organic matter characterized by low activation energies. These sediments are considered as most important source rocks of numerous high wax oils (oil family B) in addition to the coaly source rocks from the (Lower) Pechelbronn-Schichten (Late Eocene). Migration pathways are significantly influenced by the early graben evolution. A major erosion period occurred during the latest Cretaceous. The uplift center was located in the northern URG area, resulting in SSE dipping Mesozoic strata in the central URG. During Middle Eocene times a second uplift center in the Eifel area resulted in SW-NE-directed shore lines in the central URG and contemporaneous south-southeastern depocenters during marine transgression from the south. This structural setting resulted in a major NNW-NW-directed and topography-driven migration pattern for expelled Liassic oil in the fractured Mesozoic subcrop below sealing Dogger α clays and basal Tertiary marls.

Analysis of Shublik Formation rocks from Mt. Michelson quadrangle, Alaska

USGS Publications Warehouse

Detterman, Robert L.

1970-01-01

Analysis of 88 samples from the Shublik formation on Fire Creek, Mt. Michelson Quadrangle, Alaska, are presented in tabular form. The results include the determination of elements by semiquantitative spectrographic analysis, phosphate by X-ray fluorescence, carbon dioxide by acid decomposable carbonate, total carbon by induction furnace, carbonate carbon by conversion using the conversion factor of 0.2727 for amount of carbon in carbon dioxide, and organic carbon by difference. A seven- cycle semilogarithmic chart presents the data graphically and illustrates the range, mode, and mean for some of the elements. The chart shows, also, the approximate concentration of the same elements in rocks similar to the black shale and limestone of the Shublik Formation. Each sample represents 5 feet of section and is composed of rock chips taken at 1 - foot intervals. The samples are keyed into a stratigraphic column of the formation. Rocks of the Shublik Formation contain anomalously high concentrations of some of the elements. These same elements might be expected to be high in some of the petroleum from northern Alaska if the Shublik Formation is a source for this petroleum. Several of the stratigraphic intervals may represent, also, a low-grade phosphate deposit.

Geochemical Analyses of Rock, Sediment, and Water from the Region In and Around the Tuba City Landfill, Tuba City, Arizona

USGS Publications Warehouse

Johnson, Raymond H.; Wirt, Laurie

2009-01-01

The Tuba City Landfill (TCL) started as an unregulated waste disposal site in the 1940s and was administratively closed in 1997. Since the TCL closure, radionuclides have been detected in the shallow ground water. In 2006, the Bureau of Indian Affairs (BIA) contracted with the U.S. Geological Survey (USGS) to better understand the source of radionuclides in the ground water at the TCL compared to the surrounding region. This report summarizes those data and presents interpretations that focus on the geochemistry in the rocks and water from the Tuba City region. The TCL is sited on Navajo Sandstone above the contact with the Kayenta Formation. These formations are not rich in uranium but generally are below average crustal abundance values for uranium. Uranium ores in the area were mined nearby in the Chinle Formation and processed at the Rare Metals mill (RMM). Regional samples of rock, sediment, leachates, and water were collected in and around the TCL site and analyzed for major and minor elements, 18O, 2H, 3H, 13C, 14C,34S, 87Sr, and 234U/238U, as appropriate. Results of whole rock and sediment samples, along with leachates, suggest the Chinle Formation is a major source of uranium and other trace elements in the area. Regional water samples indicate that some of the wells within the TCL site have geochemical signatures that are different from the regional springs and surface water. The geochemistry from these TCL wells is most similar to leachates from the Chinle Formation rocks and sediments. Isotope samples do not uniquely identify TCL-derived waters, but they do provide a useful indicator for shallow compared to deep ground-water flow paths and general rock/water interaction times. Information in this report provides a comparison between the geochemistry within the TCL and in the region as a whole.

1-D/3-D geologic model of the Western Canada Sedimentary Basin

USGS Publications Warehouse

Higley, D.K.; Henry, M.; Roberts, L.N.R.; Steinshouer, D.W.

2005-01-01

The 3-D geologic model of the Western Canada Sedimentary Basin comprises 18 stacked intervals from the base of the Devonian Woodbend Group and age equivalent formations to ground surface; it includes an estimated thickness of eroded sediments based on 1-D burial history reconstructions for 33 wells across the study area. Each interval for the construction of the 3-D model was chosen on the basis of whether it is primarily composed of petroleum system elements of reservoir, hydrocarbon source, seal, overburden, or underburden strata, as well as the quality and areal distribution of well and other data. Preliminary results of the modeling support the following interpretations. Long-distance migration of hydrocarbons east of the Rocky Mountains is indicated by oil and gas accumulations in areas within which source rocks are thermally immature for oil and (or) gas. Petroleum systems in the basin are segmented by the northeast-trending Sweetgrass Arch; hydrocarbons west of the arch were from source rocks lying near or beneath the Rocky Mountains, whereas oil and gas east of the arch were sourced from the Williston Basin. Hydrocarbon generation and migration are primarily due to increased burial associated with the Laramide Orogeny. Hydrocarbon sources and migration were also influenced by the Lower Cretaceous sub-Mannville unconformity. In the Peace River Arch area of northern Alberta, Jurassic and older formations exhibit high-angle truncations against the unconformity. Potential Paleozoic though Mesozoic hydrocarbon source rocks are in contact with overlying Mannville Group reservoir facies. In contrast, in Saskatchewan and southern Alberta the contacts are parallel to sub-parallel, with the result that hydrocarbon source rocks are separated from the Mannville Group by seal-forming strata within the Jurassic. Vertical and lateral movement of hydrocarbons along the faults in the Rocky Mountains deformed belt probably also resulted in mixing of oil and gas from numerous source rocks in Alberta.

System and method for investigating sub-surface features of a rock formation using compressional acoustic sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vu, Cung Khac; Skelt, Christopher; Nihei, Kurt

A system and method for investigating rock formations outside a borehole are provided. The method includes generating a first compressional acoustic wave at a first frequency by a first acoustic source; and generating a second compressional acoustic wave at a second frequency by a second acoustic source. The first and the second acoustic sources are arranged within a localized area of the borehole. The first and the second acoustic waves intersect in an intersection volume outside the borehole. The method further includes receiving a third shear acoustic wave at a third frequency, the third shear acoustic wave returning to themore » borehole due to a non-linear mixing process in a non-linear mixing zone within the intersection volume at a receiver arranged in the borehole. The third frequency is equal to a difference between the first frequency and the second frequency.« less

Petrography and geochemistry characteristics of the lower Cretaceous Muling Formation from the Laoheishan Basin, Northeast China: implications for provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Song, Yu; Liu, Zhaojun; Meng, Qingtao; Wang, Yimeng; Zheng, Guodong; Xu, Yinbo

2017-06-01

The petrography, mineralogy and geochemistry of sedimentary rocks from the lower Cretaceous Muling Formation (K1ml) in the Laoheishan basin, northeast (NE) China are studied to determine the weathering intensity, provenance and tectonic setting of the source region. Petrographic data indicate the average quartz-feldspar-lithic fragments (QFL) of the sandstone is Q = 63 %, F = 22 %, and L = 15 %. Lithic fragments mainly contain volcanic clasts that derived from surrounding basement. X-ray diffraction (XRD) data reveal abundant clay and detrital minerals (e.g. quartz), as well as minor calcite in the fine-grained sediments. The Hf contents and element concentration ratios such as Al2O3/TiO2, Co/Th, La/Sc, and La/Th are comparable to sediments derived from felsic and intermediate igneous rocks. The strong genetic relationship with the igneous rocks from the northwest and northeast areas provides evidence that the sediments of the Muling Formation (K1ml) in the Laoheishan basin have been derived from this area. The chemical index of alteration (CIA) and index of chemical variability (ICV) reveal an intensive weathering in the source region of the sediments. The multidimensional tectonic discrimination diagrams indicate that the source rocks of K1ml are mainly derived from the collision system. However, they may also comprise sediments derived from the continental rift system. The results are consistent with the geology of the study area.

Clay mineralogy, strontium and neodymium isotope ratios in the sediments of two High Arctic catchments (Svalbard)

NASA Astrophysics Data System (ADS)

Hindshaw, Ruth S.; Tosca, Nicholas J.; Piotrowski, Alexander M.; Tipper, Edward T.

2018-03-01

The identification of sediment sources to the ocean is a prerequisite to using marine sediment cores to extract information on past climate and ocean circulation. Sr and Nd isotopes are classical tools with which to trace source provenance. Despite considerable interest in the Arctic Ocean, the circum-Arctic source regions are poorly characterised in terms of their Sr and Nd isotopic compositions. In this study we present Sr and Nd isotope data from the Paleogene Central Basin sediments of Svalbard, including the first published data of stream suspended sediments from Svalbard. The stream suspended sediments exhibit considerable isotopic variation (ɛNd = -20.6 to -13.4; 87Sr / 86Sr = 0.73421 to 0.74704) which can be related to the depositional history of the sedimentary formations from which they are derived. In combination with analysis of the clay mineralogy of catchment rocks and sediments, we suggest that the Central Basin sedimentary rocks were derived from two sources. One source is Proterozoic sediments derived from Greenlandic basement rocks which are rich in illite and have high 87Sr / 86Sr and low ɛNd values. The second source is Carboniferous to Jurassic sediments derived from Siberian basalts which are rich in smectite and have low 87Sr / 86Sr and high ɛNd values. Due to a change in depositional conditions throughout the Paleogene (from deep sea to continental) the relative proportions of these two sources vary in the Central Basin formations. The modern stream suspended sediment isotopic composition is then controlled by modern processes, in particular glaciation, which determines the present-day exposure of the formations and therefore the relative contribution of each formation to the stream suspended sediment load. This study demonstrates that the Nd isotopic composition of stream suspended sediments exhibits seasonal variation, which likely mirrors longer-term hydrological changes, with implications for source provenance studies based on fixed end-members through time.

Evidence for Cambrian petroleum source rocks in the Rome trough of West Virginia and Kentucky, Appalachian basin: Chapter G.8 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Ryder, Robert T.; Harris, David C.; Gerome, Paul; Hainsworth, Timothy J.; Burruss, Robert A.; Lillis, Paul G.; Jarvie, Daniel M.; Pawlewicz, Mark J.; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

The bitumen extract from the Rogersville Shale compares very closely with oils or condensates from Cambrian reservoirs in the Carson Associates No. 1 Kazee well, Homer gas field, Elliott County, Ky.; the Inland No. 529 White well, Boyd County, Ky.; and the Miller No. 1 well, Wolfe County, Ky. These favorable oil-source rock correlations suggest a new petroleum system in the Appalachian basin that is characterized by a Conasauga Group source rock and Rome Formation and Conasauga Group reservoirs. This petroleum system probably extends along the Rome trough from eastern Kentucky to at least central West Virginia.

Application of uniaxial confining-core clamp with hydrous pyrolysis in petrophysical and geochemical studies of source rocks at various thermal maturities

USGS Publications Warehouse

Lewan, Michael D.; Birdwell, Justin E.; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

2013-01-01

Understanding changes in petrophysical and geochemical parameters during source rock thermal maturation is a critical component in evaluating source-rock petroleum accumulations. Natural core data are preferred, but obtaining cores that represent the same facies of a source rock at different thermal maturities is seldom possible. An alternative approach is to induce thermal maturity changes by laboratory pyrolysis on aliquots of a source-rock sample of a given facies of interest. Hydrous pyrolysis is an effective way to induce thermal maturity on source-rock cores and provide expelled oils that are similar in composition to natural crude oils. However, net-volume increases during bitumen and oil generation result in expanded cores due to opening of bedding-plane partings. Although meaningful geochemical measurements on expanded, recovered cores are possible, the utility of the core for measuring petrophysical properties relevant to natural subsurface cores is not suitable. This problem created during hydrous pyrolysis is alleviated by using a stainless steel uniaxial confinement clamp on rock cores cut perpendicular to bedding fabric. The clamp prevents expansion just as overburden does during natural petroleum formation in the subsurface. As a result, intact cores can be recovered at various thermal maturities for the measurement of petrophysical properties as well as for geochemical analyses. This approach has been applied to 1.7-inch diameter cores taken perpendicular to the bedding fabric of a 2.3- to 2.4-inch thick slab of Mahogany oil shale from the Eocene Green River Formation. Cores were subjected to hydrous pyrolysis at 360 °C for 72 h, which represents near maximum oil generation. One core was heated unconfined and the other was heated in the uniaxial confinement clamp. The unconfined core developed open tensile fractures parallel to the bedding fabric that result in a 38 % vertical expansion of the core. These open fractures did not occur in the confined core, but short, discontinuous vertical fractures on the core periphery occurred as a result of lateral expansion.

Geology and hydrocarbon potential of the Hartford-Deerfield Basin, Connecticut and Massachusetts

USGS Publications Warehouse

Coleman, James

2016-01-01

The Hartford-Deerfield basin, a Late Triassic to Early Jurassic rift basin located in central Connecticut and Massachusetts, is the northernmost basin of the onshore Mesozoic rift basins in the eastern United States. The presence of asphaltic petroleum in outcrops indicates that at least one active petroleum system has existed within the basin. However, to-date oil and gas wells have not been drilled in the basin to test any type of petroleum trap. There are good to excellent quality source rocks (up to 3.8% present day total organic carbon) within the Jurassic East Berlin and Portland formations. While these source rock intervals are fairly extensive and at peak oil to peak gas stages of maturity, individual source rock beds are relatively thin (typically less than 1 m) based solely on outcrop observations. Potential reservoir rocks within the Hartford-Deerfield basin are arkosic conglomerates, pebbly sandstones, and finer grained sandstones, shales, siltstones, and fractured igneous rocks of the Triassic New Haven and Jurassic East Berlin and Portland formations (and possibly other units). Sandstone porosity data from 75 samples range from less than 1% to 21%, with a mean of 5%. Permeability is equally low, except around joints, fractures, and faults. Seals are likely to be unfractured intra-formational shales and tight igneous bodies. Maturation, generation, and expulsion likely occurred during the late synrift period (Early Jurassic) accentuated by an increase in local geothermal gradient, igneous intrusions, and hydrothermal fluid circulation. Migration pathways were likely along syn- and postrift faults and fracture zones. Petroleum resources, if present, are probably unconventional (continuous) accumulations as conventionally accumulated petroleum is likely not present in significant volumes.

Some Cenozoic hydrocarbon basins on the continental shelf of Vietnam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dien, P.T.

1994-07-01

The formation of the East Vietnam Sea basins was related to different geodynamic processes. The pre-Oligocene basement consists of igneous, metamorphic, and metasediment complexes. The Cretaceous-Eocene basement formations are formed by convergence of continents after destruction of the Tethys Ocean. Many Jurassic-Eocene fractured magmatic highs of the Cuulong basin basement constitute important reservoirs that are producing good crude oil. The Paleocene-Eocene formations are characterized by intramountain metamolasses, sometimes interbedded volcanic rocks. Interior structures of the Tertiary basins connect with rifted branches of the widened East Vietnam Sea. Bacbo (Song Hong) basin is predominated by alluvial-rhythmic clastics in high-constructive deltas, whichmore » developed on the rifting and sagging structures of the continental branch. Petroleum plays are constituted from Type III source rocks, clastic reservoirs, and local caprocks. Cuulong basin represents sagging structures and is predominated by fine clastics, with tidal-lagoonal fine sandstone and shalestone in high-destructive deltas that are rich in Type II source rocks. The association of the pre-Cenozoic fractured basement reservoirs and the Oligocene-Miocene clastic reservoir sequences with the Oligocene source rocks and the good caprocks is frequently met in petroleum plays of this basin. Nan Conson basin was formed from complicated structures that are related to spreading of the oceanic branch. This basin is characterized by Oligocene epicontinental fine clastics and Miocene marine carbonates that are rich in Types I, II, and III organic matter. There are both pre-Cenozoic fractured basement reservoirs, Miocene buildup carbonate reservoir rocks and Oligocene-Miocene clastic reservoir sequences, in this basin. Pliocene-Quaternary sediments are sand and mud carbonates in the shelf facies of the East Vietnam Sea back-arc basin. Their great thickness provides good conditions for maturation and trapping.« less

Petrogenesis and tectonics of the Acasta Gneiss Complex derived from integrated petrology and 142Nd and 182W extinct nuclide-geochemistry

NASA Astrophysics Data System (ADS)

Reimink, Jesse R.; Chacko, Thomas; Carlson, Richard W.; Shirey, Steven B.; Liu, Jingao; Stern, Richard A.; Bauer, Ann M.; Pearson, D. Graham; Heaman, Larry M.

2018-07-01

The timing and mechanisms of continental crust formation represent major outstanding questions in the Earth sciences. Extinct-nuclide radioactive systems offer the potential to evaluate the temporal relations of a variety of differentiation processes on the early Earth, including crust formation. Here, we investigate the whole-rock 182W/184W and 142Nd/144Nd ratios and zircon Δ17O values of a suite of well-studied and lithologically-homogeneous meta-igneous rocks from the Acasta Gneiss Complex, Northwest Territories, Canada, including the oldest-known zircon-bearing rocks on Earth. In the context of previously published geochemical data and petrogenetic models, the new 142Nd/144Nd data indicate that formation of the Hadean-Eoarchean Acasta crust was ultimately derived from variable sources, both in age and composition. Although 4.02 Ga crust was extracted from a nearly bulk-Earth source, heterogeneous μ142Nd signatures indicate that Eoarchean rocks of the Acasta Gneiss Complex were formed by partial melting of hydrated, Hadean-age mafic crust at depths shallower than the garnet stability field. By ∼3.6 Ga, granodioritic-granitic rocks were formed by partial melting of Archean hydrated mafic crust that was melted at greater depth, well into the garnet stability field. Our 182W results indicate that the sources to the Acasta Gneiss Complex had homogeneous, high-μ182W on the order of +10 ppm-a signature ubiquitous in other Eoarchean terranes. No significant deviation from the terrestrial mass fractionation line was found in the triple oxygen isotope (16O-17O-18O) compositions of Acasta zircons, confirming homogeneous oxygen isotope compositions in Earth's mantle by 4.02 Ga.

Birth and demise of the Rheic Ocean magmatic arc(s): Combined U-Pb and Hf isotope analyses in detrital zircon from SW Iberia siliciclastic strata

NASA Astrophysics Data System (ADS)

Pereira, M. F.; Gutíerrez-Alonso, G.; Murphy, J. B.; Drost, K.; Gama, C.; Silva, J. B.

2017-05-01

Paleozoic continental reconstructions indicate that subduction of Rheic oceanic lithosphere led to collision between Laurussia and Gondwana which was a major event in the formation of the Ouachita-Appalachian-Variscan orogenic belt and the amalgamation of Pangea. However, arc systems which record Rheic Ocean subduction are poorly preserved. The preservation of Devonian detrital zircon in Late Devonian-Early Carboniferous siliciclastic rocks of SW Iberia, rather than arc-related igneous rocks indicates that direct evidence of the arc system may have been largely destroyed by erosion. Here we report in-situ detrital zircon U-Pb isotopic analyses of Late Devonian-Early Carboniferous siliciclastic rocks from the Pulo do Lobo Zone, which is a reworked Late Paleozoic suture zone located between Laurussia and Gondwana. Detrital zircon age spectra from the Pulo do Lobo Zone Frasnian formations show striking similarities, revealing a wide range of ages dominated by Neoproterozoic and Paleoproterozoic grains sourced from rocks typical of peri-Gondwanan terranes, such as Avalonia, the Meguma terrane and the Ossa-Morena Zone. Pulo do Lobo rocks also include representative populations of Mesoproterozoic and Early Silurian zircons that are typical of Avalonia and the Meguma terrane which are absent in the Ossa-Morena Zone. The Famennian-Tournaisian formations from the Pulo do Lobo Zone, however, contain more abundant Middle-Late Devonian zircon indicating the contribution from a previously unrecognized source probably related to the Rheic Ocean magmatic arc(s). The Middle-Late Devonian to Early Carboniferous zircon ages from the siliciclastic rocks of SW Iberia (South Portuguese, Pulo do Lobo and Ossa-Morena zones) have a wide range in εHfT values (- 8.2 to + 8.3) indicating the likely crystallization from magmas formed in a convergent setting. The missing Rheic Ocean arc was probably built on a Meguma/Avalonia type basement. We propose for the Pulo do Lobo Zone that the Frasnian sedimentation occurred through the opening of a back-arc basin formed along the Laurussian active margin during Rheic Ocean subduction, as has been recently proposed for the Rhenohercynian Zone in Central Europe. Detrital zircon ages in the Frasnian siliciclastic rocks indicate provenance in the Meguma terrane, Avalonia and Devonian Rheic Ocean arc(s). As a result of back-arc basin inversion, the Frasnian formations underwent deformation, metamorphism and denudation and were unconformably overlain by Famennian to Visean siliciclastic strata (including the Phyllite-Quartzite Formation of the South Portuguese Zone). The Latest Devonian-Early Carboniferous detritus were probably shed to the Pulo do Lobo Zone (Represa and Santa Iria formations) by recycling of Devonian siliciclastic rocks, from the South Portuguese Zone (Meguma terrane) and from a new distinct source with Baltica/Laurentia derivation (preserved in the Horta da Torre Formation and Alajar Mélange).

Geochemistry of sandstones from the Pliocene Gabir Formation, north Marsa Alam, Red Sea, Egypt: Implication for provenance, weathering and tectonic setting

NASA Astrophysics Data System (ADS)

Zaid, Samir M.

2015-02-01

Petrographic, major and trace element compositions of sandstones from the Pliocene Gabir Formation, Central Eastern Desert, Egypt have been investigated to determine their provenance, intensity of paleo-weathering of the source rocks and their depositional tectonic setting. Gabir Formation is composed mainly of sandstones alternating with limestone and shale beds. The Gabir sandstone is yellowish gray to yellowish brown color, calcareous and fossiliferous. The composition of this formation refers to shallow warm agitated marine conditions. Texturally, Gabir sandstones are immature, poorly sorted and grain supported. Abundance of feldspars indicates rapid deposition of sediments from a nearby source rocks. Their average modal composition (Q71.35F16.6L12.05), classifies them as sublitharenite and arkose with subordinate litharenite and subarkose, which is also supported by geochemical study. Chemical analyses revealed that sandstones have high SiO2, K2O > Na2O, and low Fe2O3 values, which are consistent with the modal data. Also, sandstone samples are enriched in most trace elements such as Ba, Sr, Ni, Cr and Zr and depleted in U and Th. The petrography and geochemistry suggest that Gabir sandstones were deposited in an active continental margin basin. They were mainly derived from granitic and low grade metamorphic sources. The CIA values (41.69-74.84) of the Gabir sandstones indicate low to moderate degree of chemical weathering, which may reflect cold and/or arid climate conditions in the source area. The source rocks are probably identified to be Proterozoic granites, metagabbros and metavolcanics, which must have been exposed during rifting, initiated during Oligocene and continued till post Miocene.

Alteration of immature sedimentary rocks on Earth and Mars. Recording Aqueous and Surface-atmosphere Processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cannon, Kenneth M.; Mustard, John F.; Salvatore, Mark R.

The rock alteration and rind formation in analog environments like Antarctica may provide clues to rock alteration and therefore paleoclimates on Mars. Clastic sedimentary rocks derived from basaltic sources have been studied in situ by martian rovers and are likely abundant on the surface of Mars. Moreover, how such rock types undergo alteration when exposed to different environmental conditions is poorly understood compared with alteration of intact basaltic flows. Here we characterize alteration in the chemically immature Carapace Sandstone from Antarctica, a terrestrial analog for martian sedimentary rocks. We employ a variety of measurements similar to those used on previousmore » and current Mars missions. Laboratory techniques included bulk chemistry, powder X-ray diffraction (XRD), hyperspectral imaging and X-ray absorption spectroscopy. Through these methods we find that primary basaltic material in the Carapace Sandstone is pervasively altered to hydrated clay minerals and palagonite as a result of water–rock interaction. A thick orange rind is forming in current Antarctic conditions, superimposing this previous aqueous alteration signature. The rind exhibits a higher reflectance at visible-near infrared wavelengths than the rock interior, with an enhanced ferric absorption edge likely due to an increase in Fe 3+ of existing phases or the formation of minor iron (oxy)hydroxides. This alteration sequence in the Carapace Sandstone results from decreased water–rock interaction over time, and weathering in a cold, dry environment, mimicking a similar transition early in martian history. This transition may be recorded in sedimentary rocks on Mars through a similar superimposition mechanism, capturing past climate changes at the hand sample scale. These results also suggest that basalt-derived sediments could have sourced significant volumes of hydrated minerals on early Mars due to their greater permeability compared with intact igneous rocks.« less

Stratigraphic variations in the biomarker distribution of the Moreno Formation: Their correlation with San Joaquin basin oils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bac, M.G.; Schulein, B.J.

1990-05-01

Variability in the biomarker compositions of petroleums is typically employed in the recognition and distinction of contributions from different source rocks. We demonstrate that the fluctuations in the biomarker distributions of different intervals within a single source rock sequence appear to account for specific compositional differences in a suite of oils from the San Joaquin basin California. Rock-Eval pyrolysis studies of a 100-m-thick immature, laminated, marine shale sequence within the Upper Cretaceous lo lower Paleocene portion of the Moreno Formation reveals TOC (total organic carbon) contents consistently around 2% and moderate hydrogen indices (i.e., 175-300 mg HC/g org. C) characteristicsmore » suggestive of a uniform depositional sequence with source rock potential. Analyses of the extractable aliphatic hydrocarbons of cored samples taken at approximately 10-m intervals from the sequence reveal significant variability in biomarker distributions. Such differences are exemplified by the triterpenoids (as seen in m/z 191 chromatograms from GC-MS and GC-MS/MS analyses) where the dominant component fluctuates from a 17{alpha}(h),21{beta}(H)-30-norhopane to 28,30-l8{alpha}(H)-bisnorhopane to 20S and 20R danunar-13(17)-enes. Some components are dominant in one interval, but are not detected in others, suggesting discrete stratigraphic variations in the biomarker characteristics of the Moreno. Similar discrepancies in biomarker distributions are evident in the aliphatic hydrocarbons of the suite of oils. The three petroleums reservoired in the San Carlos sandstone member of the Lodo Formation which directly overlies the Moreno, reflect biomarker contributions from a Moreno source, including compound distributions, and the occurrence of both alkanes (e.g., 28.30-bisnorhopane) and alkenes (e.g.. danunarenes and diasterenes).« less

Total petroleum systems of the Paleozoic and Jurassic, Greater Ghawar Uplift and adjoining provinces of central Saudi Arabia and northern Arabian-Persian Gulf

USGS Publications Warehouse

Pollastro, Richard M.

2003-01-01

Oil of the Arabian Sub-Basin Tuwaiq/Hanifa-Arab TPS is sourced by organic-rich, marine carbonates of the Jurassic Tuwaiq Mountain and Hanifa Formations. These source rocks were deposited in two of three intraplatform basins during the Jurassic and, where thermally mature, have generated a superfamily of oils with distinctive geochemical characteristics. Oils were generated and expelled from these source rocks beginning in the Cretaceous at about 75 Ma. Hydrocarbon production is from 3 cyclic carbonate-rock reservoirs of the Arab Formation that are sealed by overlying anhydrite. Several giant and supergiant fields, including the world's largest oil field at Ghawar, Saudi Arabia, produce mostly from the Arab carbonate-rock reservoirs. Two assessment units are also recognized in the Arabian Sub-Basin Tuwaiq/Hanifa-Arab TPS that are similarly related to structural trap style and presence of underlying Infracambrian salt: (1) an onshore Horst-Block Anticlinal Oil AU, and (2) a mostly offshore Salt-Involved Structural Oil AU. The mean total volume of undiscovered resource for the Arabian Sub-Basin Tuwaiq/Hanifa-Arab TPS is estimated at about 49 billion barrels of oil equivalent (42 billion barrels of oil, 34 trillion feet of gas, and 1.4 billion barrels of natural gas liquids).

Origin and accumulation mechanisms of petroleum in the Carboniferous volcanic rocks of the Kebai Fault zone, Western Junggar Basin, China

NASA Astrophysics Data System (ADS)

Chen, Zhonghong; Zha, Ming; Liu, Keyu; Zhang, Yueqian; Yang, Disheng; Tang, Yong; Wu, Kongyou; Chen, Yong

2016-09-01

The Kebai Fault zone of the West Junggar Basin in northwestern China is a unique region to gain insights on the formation of large-scale petroleum reservoirs in volcanic rocks of the western Central Asian Orogenic Belt. Carboniferous volcanic rocks are widespread in the Kebai Fault zone and consist of basalt, basaltic andesite, andesite, tuff, volcanic breccia, sandy conglomerate and metamorphic rocks. The volcanic oil reservoirs are characterized by multiple sources and multi-stage charge and filling history, characteristic of a complex petroleum system. Geochemical analysis of the reservoir oil, hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source, the petroleum filling history, and the dominant mechanisms controlling the petroleum accumulation. Reservoir oil geochemistry indicates that the oil contained in the Carboniferous volcanic rocks of the Kebai Fault zone is a mixture. The oil is primarily derived from the source rock of the Permian Fengcheng Formation (P1f), and secondarily from the Permian Lower Wuerhe Formation (P2w). Compared with the P2w source rock, P1f exhibits lower values of C19 TT/C23 TT, C19+20TT/ΣTT, Ts/(Ts + Tm) and ααα-20R sterane C27/C28 ratios but higher values of TT C23/C21, HHI, gammacerane/αβ C30 hopane, hopane (20S) C34/C33, C29ββ/(ββ + αα), and C29 20S/(20S + 20R) ratios. Three major stages of oil charge occurred in the Carboniferous, in the Middle Triassic, Late Triassic to Early Jurassic, and in the Middle Jurassic to Late Jurassic periods, respectively. Most of the oil charged during the first stage was lost, while moderately and highly mature oils were generated and accumulated during the second and third stages. Oil migration and accumulation in the large-scale stratigraphic reservoir was primarily controlled by the top Carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity. Secondary dissolution pores and fractures are the two major reservoir storage-space types in the reservoirs. Structural highs and reservoirs near the unconformity are two favorable oil accumulation places. The recognition of the large-scale Carboniferous volcanic reservoirs in the Kebai Fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces, and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings.

Petroleum systems of the San Joaquin Basin Province -- geochemical characteristics of gas types: Chapter 10 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

USGS Publications Warehouse

Lillis, Paul G.; Warden, Augusta; Claypool, George E.; Magoon, Leslie B.

2008-01-01

The San Joaquin Basin Province is a petroliferous basin filled with predominantly Late Cretaceous to Pliocene-aged sediments, with organic-rich marine rocks of Late Cretaceous, Eocene, and Miocene age providing the source of most of the oil and gas. Previous geochemical studies have focused on the origin of the oil in the province, but the origin of the natural gas has received little attention. To identify and characterize natural gas types in the San Joaquin Basin, 66 gas samples were analyzed and combined with analyses of 15 gas samples from previous studies. For the purpose of this resource assessment, each gas type was assigned to the most likely petroleum system. Three general gas types are identified on the basis of bulk and stable carbon isotopic composition—thermogenic dry (TD), thermogenic wet (TW) and biogenic (B). The thermogenic gas types are further subdivided on the basis of the δ13C values of methane and ethane and nitrogen content into TD-1, TD-2, TD-Mixed, TW-1, TW-2, and TW-Mixed. Gas types TD-1 and TD-Mixed, a mixture of biogenic and TD-1 gases, are produced from gas fields in the northern San Joaquin Basin. Type TD-1 gas most likely originated from the Late Cretaceous to Paleocene Moreno Formation, a gas-prone source rock. The biogenic component of the TD-Mixed gas existed in the trap prior to the influx of thermogenic gas. For the assessment, these gas types were assigned to the Winters- Domengine Total Petroleum System, but subsequent to the assessment were reclassified as part of the Moreno-Nortonville gas system. Dry thermogenic gas produced from oil fields in the southern San Joaquin Basin (TD-2 gas) most likely originated from the oil-prone source rock of Miocene age. These samples have low wetness values due to migration fractionation or biodegradation. The thermogenic wet gas types (TW-1, TW-2, TW-Mixed) are predominantly associated gas produced from oil fields in the southern and central San Joaquin Basin. Type TW-1 gas most likely originates from source rocks within the Eocene Kreyenhagen Formation or the Eocene Tumey formation of Atwill (1935). Type TW-2 gas most likely originates from the Miocene Monterey Formation and equivalents. TW-Mixed gas is likely a mixture of biogenic and wet thermogenic gas (TW-1 or TW-2) derived from source rocks mentioned above. The thermogenic wet gas types are included in the corresponding Eocene or Miocene total petroleum systems. Type B gas is a dry, nonassociated gas produced from the Pliocene San Joaquin Formation in the central and southern San Joaquin Basin. This gas type most likely originated from Pliocene marine source rocks as a product of methanogenesis, and defines the Neogene Nonassociated Gas Total Petroleum System.

The Birth of a Cratonic Core: Petrologic Evolution of the Hadean-Eoarchean Acasta Gneiss Complex

NASA Astrophysics Data System (ADS)

Reimink, J. R.; Chacko, T.; Davies, J.; Pearson, D. G.; Stern, R. A.; Heaman, L. M.; Carlson, R.; Shirey, S. B.

2016-12-01

Granitoid magmatism within the 4.02-3.6 Ga Acasta Gneiss Complex records distinct whole-rock compositional changes during the building the Slave Craton. Previously1,2 we suggested that these signatures implied petrologic changes from initiation of evolved crust formation in an Iceland-like setting to partial melting of hydrated mafic crust at increasing depth through time, culminating in relatively voluminous magmatism at 3.6 Ga. Increasing La/Yb in these rocks suggest increasing depth of melting (and increasing residual garnet content) with time, ending in emplacement of rocks comparable to other Archean TTG suites3, with both high pressure (high La/Yb) and low pressure (low La/Yb) rocks represented at 3.6 Ga. Data from rocks with variable La/Yb that crystallized 3.6 Ga allow us to evaluate potential mechanisms for formation of rocks of this age such as subduction/accretion or intracrustal melting/delamination. Despite major and trace element compositional and age variability, zircon oxygen isotope compositions from a wide variety of rocks are extremely consistent (+6.0-6.5 ‰ from 3.9-2.9 Ga), implying a similar source, one that had been altered by surface waters1. Potential source rocks include the upper portion of oceanic crust, which contains a large portion of mafic crust that had been altered at low temperatures (e.g., 4). Paired whole rock and zircon radiogenic isotopic data are especially sensitive to the extent of pre-existing felsic material in the region, as well as the longevity of primary, basaltic rocks prior to their reworking into more evolved crust. New paired zircon Hf and whole rock Nd isotope data collected from these samples show variably unradiogenic signatures and allow an exploration of similarities and disparities between crust formation in the Acasta Gneiss Complex and other Paleoarchean-Mesoarchean crustal blocks. [1] Reimink et al., 2016. Precambrian Research 281, 453-472. [2] Reimink et al., 2014 Nature Geoscience 7, 529-533. [3] Moyen and Martin, 2012 Lithos 148, 312-348. [4] Eiler, J.M., 2001 Reviews in Mineralogy and Geochemistry 43, 319-364.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Copuroglu, Oguzhan, E-mail: O.Copuroglu@CiTG.TUDelft.NL; Andic-Cakir, Ozge; Broekmans, Maarten A.T.M.

In this paper, the alkali-silica reaction performance of a basalt rock from western Anatolia, Turkey is reported. It is observed that the rock causes severe gel formation in the concrete microbar test. It appears that the main source of expansion is the reactive glassy phase of the basalt matrix having approximately 70% of SiO{sub 2}. The study presents the microstructural characteristics of unreacted and reacted basalt aggregate by optical and electron microscopy and discusses the possible reaction mechanism. Microstructural analysis revealed that the dissolution of silica is overwhelming in the matrix of the basalt and it eventually generates four consequences:more » (1) Formation of alkali-silica reaction gel at the aggregate perimeter, (2) increased porosity and permeability of the basalt matrix, (3) reduction of mechanical properties of the aggregate and (4) additional gel formation within the aggregate. It is concluded that the basalt rock is highly prone to alkali-silica reaction. As an aggregate, this rock is not suitable for concrete production.« less

Formation resistivity as an indicator of oil generation in black shales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hester, T.C.; Schmoker, J.W.

1987-08-01

Black, organic-rich shales of Late Devonian-Early Mississippi age are present in many basins of the North American craton and, where mature, have significant economic importance as hydrocarbon source rocks. Examples drawn from the upper and lower shale members of the Bakken Formation, Williston basin, North Dakota, and the Woodford Shale, Anadarko basin, Oklahoma, demonstrate the utility of formation resistivity as a direct in-situ indicator of oil generation in black shales. With the onset of oil generation, nonconductive hydrocarbons begin to replace conductive pore water, and the resistivity of a given black-shale interval increases from low levels associated with thermal immaturitymore » to values approaching infinity. Crossplots of a thermal-maturity index (R/sub 0/ or TTI) versus formation resistivity define two populations representing immature shales and shales that have generated oil. A resistivity of 35 ohm-m marks the boundary between immature and mature source rocks for each of the three shales studied. Thermal maturity-resistivity crossplots make possible a straightforward determination of thermal maturity at the onset of oil generation, and are sufficiently precise to detect subtle differences in source-rock properties. For example, the threshold of oil generation in the upper Bakken shale occurs at R/sub 0/ = 0.43-0.45% (TTI = 10-12). The threshold increases to R/sub 0/ = 0.48-0.51% (TTI = 20-26) in the lower Bakken shale, and to R/sub 0/ = 0.56-0.57% (TTI = 33-48) in the most resistive Woodford interval.« less

Age and source of terrigenous rocks of the turan group of the bureya terrane of the eastern part of the central Asian foldbelt: Results of geochemical (Sm-Nd) and geochronological (U-Pb LA-ICP-MS) studies

NASA Astrophysics Data System (ADS)

Sorokin, A. A.; Smirnov, Yu. V.; Kotov, A. B.; Kovach, V. P.

2014-06-01

According to Sm-Nd isotopic-geochemical studies, the t Nd(DM) of the terrigenous rocks of the Turan Group of the Bureya terrane is 1.4-1.5 Ga and their sources are Precambrian rocks and (or) younger effusive rocks, the formation of which is related to the reworking of the Late Precambrian continental crust. The U-Pb LA-ICP-MS geochronological studies indicate dominant Vendian-Cambrian (588-483 Ma) and Late Riphean (865-737 Ma) detrital zircons. Our data point to their accumulation at the beginning of the Paleozoic rather than in the Precambrian as is accepted in modern stratigraphic schemes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sari, A.; Geze, Y.

The studied area is a lake basin located in Bolu basin in Turkey. In the basin, from Upper Cretaceous to Upper Miocene 3,000-m thickness sediments were deposited. Upper Miocene Himmetoglu formation consisted of sandstone, claystone, and marl. To the middle level of the formation are located coal, bituminous limestone, and bituminous shales. In the basin, there are two coal beds whose thicknesses range from 1 to 13 m. The coals are easily breakable and black in color. In the coal beds exists some bituminous limestone and bituminous shales, and their thicknesses are between 5 and 45 cm. The amount ofmore » organic matter of the bituminous rocks from the Upper Miocene Himmetoglu formation are between 6.83 and 56.34 wt%, and the amount of organic matter of the bituminous limestone from the formation are between 13.58 and 57.16 wt%. These values indicate that these rocks have very good source potential. According to hydrogen index (HI), S2/S3, HI-T{sub max}, and HI-OI (oxygen index) parameters, kerogen types of the bituminous rocks and coals belonging to Upper Miocene Himmetoglu formation are Type I, Type II, and Type III. In accordance with HI, S2/S3, HI-T{sub max}, and HI-OI parameters, the bituminous rocks and coals from the Upper Miocene Himmetoglu formation are mostly immature.« less

Intermittent inflations recorded by broadband seismometers prior to caldera formation at Miyake-jima volcano in 2000

NASA Astrophysics Data System (ADS)

Kobayashi, Tomokazu; Ohminato, Takao; Ida, Yoshiaki; Fujita, Eisuke

2012-12-01

Very-long-period (VLP) pulses with widths of 20 s on velocity seismograms were observed during volcanic activity at Miyake-jima Volcano, Japan in 2000. The VLP events occurred repeatedly during a few days prior to caldera formation and essentially vanished following the onset of caldera collapse. Waveform inversions of the pulse-like signals point to a source offset 3.5 km beneath and 1 km south of the summit. A candidate for the source mechanism is the inflation of an elliptical cylinder with axis tilted 20-30° from vertical and major axis of the elliptical cross section oriented northeast-southwest. The inferred mechanism appears consistent with a step-like pressurization of a magma reservoir impacted by a falling rock mass in response to gravitational instability. The repeated occurrences of the rock collapses lead to the caldera formation at Miyake-jima.

Age, geochemical and Sr Nd Pb isotopic constraints for mantle source characteristics and petrogenesis of Teru Volcanics, Northern Kohistan Terrane, Pakistan

NASA Astrophysics Data System (ADS)

Khan, S. D.; Stern, R. J.; Manton, M. I.; Copeland, P.; Kimura, J. I.; Khan, M. A.

2004-11-01

This paper presents new geochemical and geochronology data for the Teru Volcanic Formation (previously known as the Shamran Volcanics) exposed west of Gilgit in the Kohistan terrane of the Pakistani Himalayas. The Teru Volcanic Formation ranges from basalt through andesite to rhyolite and has subalkaline and midalkaline affinities. Trace-element compositions and isotopic characteristics suggest these magmas were formed in a subduction zone setting; isotopic studies also support this conclusion. It is suggested that these lavas originated from a depleted mantle source, which experienced contamination by variable subduction components. Model mixing calculations using 87Sr/ 86Sr and 143Nd/ 144Nd data suggest that addition of 0.2-0.6% of Indus margin sediments and/or 2-4% of fluids derived from Indus margin sediment can generate the compositional variation of the Teru Volcanic Formation. Two samples from the Teru Volcanic Formation yielded 40Ar/ 39Ar ages of 43.8+0.5 and 32.5+0.4 Ma. These ages make the volcanic rocks of the Teru Volcanic Formation the youngest reported in the Kohistan terrane. These volcanic rocks unconformably overly the Shunji Pluton, which has a 65 Ma Rb-Sr whole-rock isochron age. The results of this research suggest that subduction-related volcanism was active until 33 Ma in the India-Asia collision zone.

In search of a Silurian Total Petroleum System in the Appalachian Basin of New York, Ohio, Pennsylvania, and West Virginia

USGS Publications Warehouse

Ryder, Robert T.; Swezey, Christopher S.; Trippi, Michael H.; Lentz, Erika E.; Avary, K. Lee; Harper, John A.; Kappel, William M.; Rea, Ronald G.

2007-01-01

This report provides an evaluation of the source rock potential of Silurian strata in the U.S. portion of the northern Appalachian Basin, using new TOC and RockEval data. The study area consists of all or parts of New York, Ohio, Pennsylvania, and West Virginia. The stratigraphic intervals that were sampled for this study are as follows: 1) the Lower Silurian Cabot Head Shale, Rochester Shale, and Rose Hill Formation; 2) the Lower and Upper Silurian McKenzie Limestone, Lockport Dolomite, and Eramosa Member of the Lockport Group; and 3) the Upper Silurian Wills Creek Formation, Tonoloway Limestone, Salina Group, and Bass Islands Dolomite. These Silurian stratigraphic intervals were chosen because they are cited in previous publications as potential source rocks, they are easily identified and relatively continuous across the basin, and they contain beds of dark gray to black shale and (or) black argillaceous limestone and dolomite.

Total Petroleum Systems of the North Carpathian Province of Poland, Ukraine, Czech Republic, and Austria

USGS Publications Warehouse

Pawlewicz, Mark

2006-01-01

Three total petroleum systems were identified in the North Carpathian Province (4047) that includes parts of Poland, Ukraine, Austria, and the Czech Republic. They are the Isotopically Light Gas Total Petroleum System, the Mesozoic-Paleogene Composite Total Petroleum System, and the Paleozoic Composite Total Petroleum System. The Foreland Basin Assessment Unit of the Isotopically Light Gas Total Petroleum System is wholly contained within the shallow sedimentary rocks of Neogene molasse in the Carpathian foredeep. The biogenic gas is generated locally as the result of bacterial activity on dispersed organic matter. Migration is also believed to be local, and gas is believed to be trapped in shallow stratigraphic traps. The Mesozoic-Paleogene Composite Total Petroleum System, which includes the Deformed Belt Assessment Unit, is structurally complex, and source rocks, reservoirs, and seals are juxtaposed in such a way that a single stratigraphic section is insufficient to describe the geology. The Menilite Shale, an organic-rich rock widespread throughout the Carpathian region, is the main hydrocarbon source rock. Other Jurassic to Cretaceous formations also contribute to oil and gas in the overthrust zone in Poland and Ukraine but in smaller amounts, because those formations are more localized than the Menilite Shale. The Paleozoic Composite Total Petroleum System is defined on the basis of the suspected source rock for two oil or gas fields in western Poland. The Paleozoic Reservoirs Assessment Unit encompasses Devonian organic-rich shale believed to be a source of deep gas within the total petroleum system. East of this field is a Paleozoic oil accumulation whose source is uncertain; however, it possesses geochemical similarities to oil generated by Upper Carboniferous coals. The undiscovered resources in the North Carpathian Province are, at the mean, 4.61 trillion cubic feet of gas and 359 million barrels of oil. Many favorable parts of the province have been extensively explored for oil and gas. The lateral and vertical variability of the structure, the distribution and complex geologic nature of source rocks, and the depths of potential exploration targets, as well as the high degree of exploration, all indicate that future discoveries in this province are likely to be numerous but in small fields.

Total petroleum systems of the Pelagian Province, Tunisia, Libya, Italy, and Malta; the Bou Dabbous, Tertiary and Jurassic-Cretaceous composite

USGS Publications Warehouse

Klett, T.R.

2001-01-01

Undiscovered conventional oil and gas resources were assessed within total petroleum systems of the Pelagian Province (2048) as part of the U.S. Geological Survey World Petroleum Assessment 2000. The Pelagian Province is located mainly in eastern Tunisia and northwestern Libya. Small portions of the province extend into Malta and offshore Italy. Although several petroleum systems may exist, only two ?composite? total petroleum systems were identified. Each total petroleum system comprises a single assessment unit. These total petroleum systems are called the Bou Dabbous?Tertiary and Jurassic-Cretaceous Composite, named after the source-rock intervals and reservoir-rock ages. The main source rocks include mudstone of the Eocene Bou Dabbous Formation; Cretaceous Bahloul, Lower Fahdene, and M?Cherga Formations; and Jurassic Nara Formation. Known reservoirs are in carbonate rocks and sandstone intervals throughout the Upper Jurassic, Cretaceous, and Tertiary sections. Traps for known accumulations include fault blocks, low-amplitude anticlines, high-amplitude anticlines associated with reverse faults, wrench fault structures, and stratigraphic traps. The estimated means of the undiscovered conventional petroleum volumes in total petroleum systems of the Pelagian Province are as follows: [MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids] Total Petroleum System MMBO BCFG MMBNGL Bou Dabbous?Tertiary 667 2,746 64 Jurassic-Cretaceous Composite 403 2,280 27

Evaluation of hydrocarbon potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cashman, P.H.; Trexler, J.H. Jr.

1992-09-30

Task 8 is responsible for assessing the hydrocarbon potential of the Yucca Mountain vincinity. Our main focus is source rock stratigraphy in the NTS area in southern Nevada. (In addition, Trexler continues to work on a parallel study of source rock stratigraphy in the oil-producing region of east central Nevada, but this work is not funded by Task 8.) As a supplement to the stratigraphic studies, we are studying the geometry and kinematics of deformation at NTS, particularly as these pertain to reconstructing Paleozoic stratigraphy and to predicting the nature of the Late Paleozoic rocks under Yucca Mountain. Our stratigraphicmore » studies continue to support the interpretation that rocks mapped as the {open_quotes}Eleana Formation{close_quotes} are in fact parts of two different Mississippian units. We have made significant progress in determining the basin histories of both units. These place important constraints on regional paleogeographic and tectonic reconstructions. In addition to continued work on the Eleana, we plan to look at the overlying Tippipah Limestone. Preliminary TOC and maturation data indicate that this may be another potential source rock.« less

Mutagens from the cooking of food. III. Survey by Ames/Salmonella test of mutagen formation in secondary sources of cooked dietary protein.

PubMed

Bjeldanes, L F; Morris, M M; Felton, J S; Healy, S; Stuermer, D; Berry, P; Timourian, H; Hatch, F T

1982-08-01

A survey of mutagen formation during the cooking of a variety of protein-rich foods that are minor sources of protein intake in the American diet is reported (see Bjeldanes, Morris, Felton et al. (1982) for survey of major protein foods). Milk, cheese, tofu and organ meats showed negligible mutagen formation except following high-temperature cooking for long periods of time. Even under the most extreme conditions, tofu, cheese and milk exhibited fewer than 500 Ames/Salmonella typhimurium revertants/100 g equivalents (wet weight of uncooked food), and organ meats only double that amount. Beans showed low mutagen formation after boiling and boiling followed by frying (with and without oil). Only boiling of beans followed by baking for 1 hr gave appreciable mutagenicity (3650 revertants/100g equivalents). Seafood samples gave a variety of results: red snapper, salmon, trout, halibut and rock cod all gave more than 1000 revertants/100 g wet weight equivalents when pan-fried or griddle-fried for about 6 min/side. Baked or poached rock and deep-fried shrimp showed no significant mutagen formation. Broiled lamb chops showed mutagen formation similar to that in red meats tested in the preceding paper: 16,000 revertants/100 g equivalents. These findings show that as measured by bioassay in S. typhimurium, most of the foods that are minor sources of protein in the American diet are also minor sources of cooking-induced mutagens.

Deciphering fluid sources of hydrothermal systems: A combined Sr- and S-isotope study on barite (Schwarzwald, SW Germany)

USGS Publications Warehouse

Staude, S.; Gob, S.; Pfaff, K.; Strobele, F.; Premo, W.R.; Markl, G.

2011-01-01

Primary and secondary barites from hydrothermal mineralizations in SW Germany were investigated, for the first time, by a combination of strontium (Sr) isotope systematics (87Sr/86Sr), Sr contents and δ34S values to distinguish fluid sources and precipitation mechanisms responsible for their formation. Barite of Permian age derived its Sr solely from crystalline basement rocks, whereas all younger barite also incorporate Sr from formation waters of the overlying sediments. In fact, most of the Sr in younger barite is leached from Lower and Middle Triassic sediments. In contrast, most of the sulfur (S) of Permian, Jurassic and northern Schwarzwald Miocene barite originated from basement rocks. The S source of Upper Rhinegraben (URG)-related Paleogene barite differs depending on geographic position: for veins of the southern URG, it is the Oligocene evaporitic sequence, while central URG mineralizations derived its S from Middle Triassic evaporites. Using Sr isotopes of barite of known age combined with estimates on the Sr contents and Sr isotopic ratios of the fluids' source rocks, we were able to quantify mixing ratios of basement-derived fluids and sedimentary formation waters for the first time. These calculations show that Jurassic barite formed by mixing of 75–95% ascending basement-derived fluids with 5–25% sedimentary formation water, but that only 20–55% of the Sr was brought by the basement-derived fluid to the depositional site. Miocene barite formed by mixing of an ascending basement-derived brine (60–70%) with 30–40% sedimentary formation waters. In this case, only 8–15% of the Sr was derived from the deep brine. This fluid-mixing calculation is an example for deposits in which the fluid source is known. This method applied to a greater number of deposits formed at different times and in various geological settings may shed light on more general causes of fluid movement in the Earth's crust and on the formation of hydrothermal ore deposits.

High resolution study of petroleum source rock variation, Lower Cretaceous (Hauterivian and Barremian) of Mikkelsen Bay, North Slope, Alaska

USGS Publications Warehouse

Keller, Margaret A.; Macquaker, Joe H.S.; Lillis, Paul G.

2001-01-01

Open File Report 01-480 was designed as a large format poster for the Annual Meeting of the American Association of Petroleum Geologists and the Society for Sedimentary Geology in Denver Colorado in June 2001. It is reproduced here in digital format to make widely available some unique images of mudstones. The images include description, interpretation, and Rock-Eval data that resulted from a high-resolution study of petroleum source rock variation of the Lower Cretaceous succession of the Mobil-Phillips Mikkelsen Bay State #1 well on the North Slope of Alaska. Our mudstone samples with Rock-Eval data plus color images are significant because they come from one of the few continuously cored and complete intervals of the Lower Cretaceous succession on the North Slope. This succession, which is rarely preserved in outcrop and very rarely cored in the subsurface, is considered to include important petroleum source rocks that have not previously been described nor explained Another reason these images are unique is that the lithofacies variability within mudstone dominated successions is relatively poorly known in comparison with that observed in coarser clastic and carbonate successions. They are also among the first published scans of thin sections of mudstone, and are of excellent quality because the sections are well made, cut perpendicular to bedding, and unusually thin, 20 microns. For each of 15 samples, we show a thin section scan (cm scale) and an optical photomicrograph (mm scale) that illustrates the variability present. Several backscattered SEM images are also shown. Rock-Eval data for the samples can be compared with the textures and mineralogy present by correlating sample numbers and core depth.

Geochemistry of the Archean Yellowknife Supergroup

NASA Astrophysics Data System (ADS)

Jenner, G. A.; Fryer, B. J.; McLennan, S. M.

1981-07-01

The Archean Yellowknife Supergroup (Slave Structural Province. Canada) is composed of a thick sequence of supracrustal rocks, which differs from most Archean greenstone belts in that it contains a large proportion ( ~ 80%) of sedimentary rocks. Felsic volcanics of the Banting Formation are characterized by HREE depletion without Eu-anomalies, indicating an origin by small degrees of partial melting of a mafic source, with minor garnet in the residua. Granitic rocks include synkinematic granites [HREE-depleted; low ( 87Sr /86Sr ) I], post-kinematic granites [negative Eu-anomalies, high ( 87Sr /86Sr ) I] and granitic gneisses with REE patterns similar to the post-kinematic granites. Sedimentary rocks (turbidites) of the Burwash and Walsh Formations have similar chemical compositions and were derived from 20% mafic-intermediate volcanics, 55% felsic volcanics and 25% granitic rocks. Jackson Lake Formation lithic wackes can be divided into two groups with Group A derived from 50% mafic-intermediate volcanics and 50% felsic volcanics and Group B, characterized by HREE depletion, derived almost exclusively from felsic volcanics. REE patterns of Yellowknife sedimentary rocks are similar to other Archean sedimentary REE patterns, although they have higher La N/Yb N. These patterns differ significantly from typical post-Archean sedimentary REE patterns, supporting the idea that Archean exposed crust had a different composition than the present day exposed crust.

Distribution, richness, quality, and thermal maturity of source rock units on the North Slope of Alaska

USGS Publications Warehouse

Peters, K.E.; Bird, K.J.; Keller, M.A.; Lillis, P.G.; Magoon, L.B.

2003-01-01

Four source rock units on the North Slope were identified, characterized, and mapped to better understand the origin of petroleum in the area: Hue-gamma ray zone (Hue-GRZ), pebble shale unit, Kingak Shale, and Shublik Formation. Rock-Eval pyrolysis, total organic carbon analysis, and well logs were used to map the present-day thickness, organic quantity (TOC), quality (hydrogen index, HI), and thermal maturity (Tmax) of each unit. To map these units, we screened all available geochemical data for wells in the study area and assumed that the top and bottom of the oil window occur at Tmax of ~440° and 470°C, respectively. Based on several assumptions related to carbon mass balance and regional distributions of TOC, the present-day source rock quantity and quality maps were used to determine the extent of fractional conversion of the kerogen to petroleum and to map the original organic richness prior to thermal maturation.

System and method for investigating sub-surface features and 3D imaging of non-linear property, compressional velocity VP, shear velocity VS and velocity ratio VP/VS of a rock formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vu, Cung Khac; Skelt, Christopher; Nihei, Kurt

A system and a method for generating a three-dimensional image of a rock formation, compressional velocity VP, shear velocity VS and velocity ratio VP/VS of a rock formation are provided. A first acoustic signal includes a first plurality of pulses. A second acoustic signal from a second source includes a second plurality of pulses. A detected signal returning to the borehole includes a signal generated by a non-linear mixing process from the first and second acoustic signals in a non-linear mixing zone within an intersection volume. The received signal is processed to extract the signal over noise and/or signals resultingmore » from linear interaction and the three dimensional image of is generated.« less

New data supporting a Sm-146,147-Nd-142,143 formation interval for the lunar mantle

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Wiesmann, H.; Bansal, B. M.; Shih, C.-Y.

1994-01-01

Very small variations in Nd-142 abundance in SNC meteorites lunar basalts, and a terrestrial supracrustal rock, have been attributed to the decay of 103 Ma Sm-146 initially present in basalt source regions in varying abundances as a result of planetary differentiation. We previously interpreted variations in Nd-142 abundances in two Apollo 17 high-Ti basalts, three Apollo 12 low-Ti basalts, and two KREEP basalts as defining an isochron giving a formation interval of approximately 94 Ma for the lunar mantle. Here we report new data for a third Apollo 17 high-Ti basalt, two Apollo 15 low-Ti basalts, the VLT basaltic lunar meteorite A881757 (formerly Asuka 31), basalt-like KREEP impact melt rocks 14310 and 14078, and three terrestrial rock standards. Those lunar samples which were not exposed to large lunar surface thermal neutron fluences yield a revised mantle formation interval of 237 +/- 64 Ma.

Evaluating Re-Os systematics in organic-rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments

USGS Publications Warehouse

Rooney, A.D.; Selby, D.; Lewan, M.D.; Lillis, P.G.; Houzay, J.-P.

2012-01-01

Successful application of the 187Re–187Os geochronometer has enabled the determination of accurate and precise depositional ages for organic-rich sedimentary rocks (ORS) as well as establishing timing constraints of petroleum generation. However, we do not fully understand the systematics and transfer behaviour of Re and Os between ORS and petroleum products (e.g., bitumen and oil). To more fully understand the behaviour of Re–Os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks: the Permian Phosphoria Formation (TOC = 17.4%; Type II-S kerogen) and the Jurassic Staffin Formation (TOC = 2.5%; Type III kerogen). The laboratory-based hydrous pyrolysis experiments were carried out for 72 h at 250, 300, 325 and 350 °C. These experiments provided us with whole rock, extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of Re–Os isotopic and elemental abundance. The data from these experiments demonstrate that the majority (>95%) of Re and Os are housed within extracted rock and that thermal maturation does not result in significant transfer of Re or Os from the extracted rock into organic phases. Based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of Re and Os than sulphides. Across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187Re/188Os ratios show small variations (3.3% and 4.7%, for Staffin, respectively and 6.3% and 4.9% for Phosphoria, respectively). Similarly, the 187Os/188Os ratios show only minor variations for the Staffin and Phosphoria whole rock and extracted rock samples (0.6% and 1.4% and 1.3% and 2.2%). These isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the Re–Os systematics in ORS as supported by various studies on natural systems. The elemental abundance data reveal limited transfer of Re and Os into the bitumen from a Type III kerogen in comparison to Type II-S kerogen (0.02% vs. 3.7%), suggesting that these metals are very tightly bound in Type III kerogen structure. The 187Os/188Os data from the pyrolysis generated Phosphoria bitumens display minor variation (4%) across the experimental temperatures, with values similar to that of the source rock. This indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation. These data further support the premise that the Os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks. Oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of Re or Os (~120 and ~3 ppt, respectively), in contrast to natural oils (2–50 ppb and 34–288 ppt for Re and Os, respectively), which may suggest that kinetic parameters are fundamental to the transfer of Re and Os from source rocks to oils. From this we hypothesise that, at the temperatures employed in hydrous pyrolysis, Re and Os are assimilated into the extracted rock as a result of cross-linking reactions.

Evaluating Re-Os systematics in organic-rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments

NASA Astrophysics Data System (ADS)

Rooney, Alan D.; Selby, David; Lewan, Michael D.; Lillis, Paul G.; Houzay, Jean-Pierre

2012-01-01

Successful application of the 187Re-187Os geochronometer has enabled the determination of accurate and precise depositional ages for organic-rich sedimentary rocks (ORS) as well as establishing timing constraints of petroleum generation. However, we do not fully understand the systematics and transfer behaviour of Re and Os between ORS and petroleum products (e.g., bitumen and oil). To more fully understand the behaviour of Re-Os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks: the Permian Phosphoria Formation (TOC = 17.4%; Type II-S kerogen) and the Jurassic Staffin Formation (TOC = 2.5%; Type III kerogen). The laboratory-based hydrous pyrolysis experiments were carried out for 72 h at 250, 300, 325 and 350 °C. These experiments provided us with whole rock, extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of Re-Os isotopic and elemental abundance. The data from these experiments demonstrate that the majority (>95%) of Re and Os are housed within extracted rock and that thermal maturation does not result in significant transfer of Re or Os from the extracted rock into organic phases. Based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of Re and Os than sulphides. Across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187Re/188Os ratios show small variations (3.3% and 4.7%, for Staffin, respectively and 6.3% and 4.9% for Phosphoria, respectively). Similarly, the 187Os/188Os ratios show only minor variations for the Staffin and Phosphoria whole rock and extracted rock samples (0.6% and 1.4% and 1.3% and 2.2%). These isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the Re-Os systematics in ORS as supported by various studies on natural systems. The elemental abundance data reveal limited transfer of Re and Os into the bitumen from a Type III kerogen in comparison to Type II-S kerogen (0.02% vs. 3.7%), suggesting that these metals are very tightly bound in Type III kerogen structure. The 187Os/188Os data from the pyrolysis generated Phosphoria bitumens display minor variation (4%) across the experimental temperatures, with values similar to that of the source rock. This indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation. These data further support the premise that the Os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks. Oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of Re or Os (∼120 and ∼3 ppt, respectively), in contrast to natural oils (2-50 ppb and 34-288 ppt for Re and Os, respectively), which may suggest that kinetic parameters are fundamental to the transfer of Re and Os from source rocks to oils. From this we hypothesise that, at the temperatures employed in hydrous pyrolysis, Re and Os are assimilated into the extracted rock as a result of cross-linking reactions.

Sequence and petrogenesis of the Jurassic volcanic rocks (Yeba Formation) in the Gangdese arc, southern Tibet: Implications for the Neo-Tethyan subduction

NASA Astrophysics Data System (ADS)

Liu, Zhi-Chao; Ding, Lin; Zhang, Li-Yun; Wang, Chao; Qiu, Zhi-Li; Wang, Jian-Gang; Shen, Xiao-Li; Deng, Xiao-Qin

2018-07-01

The Yeba Formation volcanic rocks in the Gangdese arc recorded important information regarding the early history of the Neo-Tethyan subduction. To explore their magmatic evolution and tectonic significance, we performed a systematic petrological, geochronological and geochemical study on these volcanic rocks. Our data indicated that the Yeba Formation documents a transition from andesite-dominated volcanism (which started before 182 Ma and continued until 176 Ma) to bimodal volcanism ( 174-168 Ma) in the earliest Middle Jurassic. The early-stage andesite-dominated volcanics are characterized by various features of major and trace elements and are interpreted as the products of interactions between mantle-derived arc magmas and lower crustal melts. Their positive εNd(t) and εHf(t) values suggest a significant contribution of asthenosphere-like mantle. The late-stage bimodal volcanism is dominated by felsic rocks with subordinate basalts. Geochemical signatures of the basalts indicate a composite magma source that included a "subduction component", an asthenosphere-like upper mantle domain and an ancient subcontinental lithospheric mantle component. The felsic rocks of the late stage were produced mainly by the melting of juvenile crust, with some ancient crustal materials also involved. We suggest that the occurrence and preservation of the Yeba Formation volcanic rocks were tied to a tectonic switch from contraction to extension in the Gangdese arc, which probably resulted from slab rollback of the subducting Neo-Tethyan oceanic slab during the Jurassic.

Strontium and neodymium isotope systematics of target rocks and impactites from the El'gygytgyn impact structure: Linking impactites and target rocks

NASA Astrophysics Data System (ADS)

Wegner, Wencke; Koeberl, Christian

2016-12-01

The 3.6 Ma El'gygytgyn structure, located in northeastern Russia on the Chukotka Peninsula, is an 18 km diameter complex impact structure. The bedrock is formed by mostly high-silica volcanic rocks of the 87 Ma old Okhotsk-Chukotka Volcanic Belt (OCVB). Volcanic target rocks and impact glasses collected on the surface, as well as drill core samples of bedrock and impact breccias have been investigated by thermal ionization mass spectrometry (TIMS) to obtain new insights into the relationships between these lithologies in terms of Nd and Sr isotope systematics. Major and trace element data for impact glasses are added to compare with the composition of target rocks and drill core samples. Sr isotope data are useful tracers of alteration processes and Nd isotopes reveal characteristics of the magmatic sources of the target rocks, impact breccias, and impact glasses. There are three types of target rocks mapped on the surface: mafic volcanics, dacitic tuff and lava of the Koekvun' Formation, and dacitic to rhyolitic ignimbrite of the Pykarvaam Formation. The latter represents the main contributor to the impact rocks. The drill core is divided into a suevite and a bedrock section by the Sr isotope data, for which different postimpact alteration regimes have been detected. Impact glasses from the present-day surface did not suffer postimpact hydrothermal alteration and their data indicate a coherent alteration trend in terms of Sr isotopes with the target rocks from the surface. Surprisingly, the target rocks do not show isotopic coherence with the Central Chukotka segment of the OCVB or with the Berlozhya magmatic assemblage (BMA), a late Jurassic felsic volcanic suite that crops out in the eastern part of the central Chukotka segment of the OCVB. However, concordance for these rocks exists with the Okhotsk segment of the OCVB. This finding argues for variable source magmas having contributed to the build-up of the OCVB.

Provenance, tectonic setting and age of the sediments of the Upper Disang Formation in the Phek District, Nagaland

NASA Astrophysics Data System (ADS)

Imchen, Watitemsu; Thong, Glenn T.; Pongen, Temjenrenla

2014-07-01

Integrated petrographic and geochemical studies of sandstones, and geochemical studies of shales of turbidites from the Upper Disang Formation, Phek district, Nagaland have been carried out to determine their provenance, weathering conditions and tectonic setting. Paleomagnetic studies were carried out for magnetostratigraphic purposes. Studies indicate that most of these sediments were derived from felsic and mafic sources with minor contribution from low to medium grade metamorphic rocks. Most of the felsic components have been transported from distant sources as evidenced from extensive reworking of grains. The most likely source rocks are the granite/granite gneiss of the Karbi Anglong crystalline complex to the west of the study area. However, the bulk of the sediments have been contributed from nearby basic and ultrabasic sources. This would correspond to the fast rising Naga Ophiolite, which probably emerged above sea level during the Mid-Eocene. Prevailing high temperatures and humid climate caused intense chemical weathering of the source rocks. The sediments from the west were transported great distances by turbidity currents into an easterly deepening basin. Sediments from the nearby east were rapidly dumped on the seafloor causing rapid mixing, leading to textural and chemical immaturity. Paleomagnetic studies endorse published paleontological evidence to indicate that most of the sediments of the Upper Disang Formation were deposited during the Late Eocene. Deposition took place in a westward-migrating accretionary-prism complex in an active-margin setting at the convergence of the Indian and Burma plates. This was a rapidly-closing basin where anoxic conditions prevailed. Towards the end of the Eocene this basin closed completely with the destruction of the Tethyan Ocean.

Timing and petroleum sources for the Lower Cretaceous Mannville Group oil sands of northern Alberta based on 4-D modeling

USGS Publications Warehouse

Higley, D.K.; Lewan, M.D.; Roberts, L.N.R.; Henry, M.

2009-01-01

The Lower Cretaceous Mannville Group oil sands of northern Alberta have an estimated 270.3 billion m3 (BCM) (1700 billion bbl) of in-place heavy oil and tar. Our study area includes oil sand accumulations and downdip areas that partially extend into the deformation zone in western Alberta. The oil sands are composed of highly biodegraded oil and tar, collectively referred to as bitumen, whose source remains controversial. This is addressed in our study with a four-dimensional (4-D) petroleum system model. The modeled primary trap for generated and migrated oil is subtle structures. A probable seal for the oil sands was a gradual updip removal of the lighter hydrocarbon fractions as migrated oil was progressively biodegraded. This is hypothetical because the modeling software did not include seals resulting from the biodegradation of oil. Although the 4-D model shows that source rocks ranging from the Devonian-Mississippian Exshaw Formation to the Lower Cretaceous Mannville Group coals and Ostracode-zone-contributed oil to Mannville Group reservoirs, source rocks in the Jurassic Fernie Group (Gordondale Member and Poker Chip A shale) were the initial and major contributors. Kinetics associated with the type IIS kerogen in Fernie Group source rocks resulted in the early generation and expulsion of oil, as early as 85 Ma and prior to the generation from the type II kerogen of deeper and older source rocks. The modeled 50% peak transformation to oil was reached about 75 Ma for the Gordondale Member and Poker Chip A shale near the west margin of the study area, and prior to onset about 65 Ma from other source rocks. This early petroleum generation from the Fernie Group source rocks resulted in large volumes of generated oil, and prior to the Laramide uplift and onset of erosion (???58 Ma), which curtailed oil generation from all source rocks. Oil generation from all source rocks ended by 40 Ma. Although the modeled study area did not include possible western contributions of generated oil to the oil sands, the amount generated by the Jurassic source rocks within the study area was 475 BCM (2990 billion bbl). Copyright ?? 2009. The American Association of Petroleum Geologists. All rights reserved.

Assessment of Undiscovered Oil and Gas Resources of the Uinta-Piceance Province of Colorado and Utah, 2002

USGS Publications Warehouse

,

2002-01-01

The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the UintaPiceance Province of northwestern Colorado and northeastern Utah (fig. 1). The assessment of the Uinta-Piceance Province is geology based and uses the Total Petroleum System concept. The geologic elements of Total Petroleum Systems include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy, petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined five Total Petroleum Systems and 20 Assessment Units within these Total Petroleum Systems, and quantitatively estimated the undiscovered oil and gas resources within each Assessment Unit (table 1).

Mesozoic–Cenozoic Climate and Neotectonic Events as Factors in Reconstructing the Thermal History of the Source-Rock Bazhenov Formation, Arctic Region, West Siberia, by the Example of the Yamal Peninsula

NASA Astrophysics Data System (ADS)

Isaev, V. I.; Iskorkina, A. A.; Lobova, G. A.; Starostenko, V. I.; Tikhotskii, S. A.; Fomin, A. N.

2018-03-01

Schemes and criteria are developed for using the measured and modeled geotemperatures for studying the thermal regime of the source rock formations, as well as the tectonic and sedimentary history of sedimentary basins, by the example of the oil fields of the Yamal Peninsula. The method of paleotemperature modeling based on the numerical solution of the heat conduction equation for a horizontally layered solid with a movable upper boundary is used. The mathematical model directly includes the climatic secular trend of the Earth's surface temperature as the boundary condition and the paleotemperatures determined from the vitrinite reflectance as the measurement data. The method does not require a priori information about the nature and intensities of the heat flow from the Earth's interior; the flow is determined by solving the inverse problem of geothermy with a parametric description of the of the sedimentation history and the history of the thermophysical properties of the sedimentary stratum. The rate of sedimentation is allowed to be zero and negative which provides the possibility to take into account the gaps in sedimentation and denudation. The formation, existence, and degradation of the permafrost stratum and ice cover are taken into account as dynamical lithological-stratigraphic complexes with anomalously high thermal conductivity. It is established that disregarding the paleoclimatic factors precludes an adequate reconstruction of thermal history of the source-rock deposits. Revealing and taking into account the Late Eocene regression provided the computationally optimal and richest thermal history of the source-rock Bazhenov Formation, which led to more correct volumetric-genetic estimates of the reserves. For estimating the hydrocarbon reserves in the land territories of the Arctic region of West Siberia by the volumetric-genetic technique, it is recommended to use the Arctic secular trend of temperatures and take into account the dynamics of the Neoplesitocene permafrost layers 300-600 m thick. Otherwise, the calculated hydrocarbon reserves could be underestimated by up to 40%.

A summary of the occurrence and development of ground water in the southern High Plains of Texas

USGS Publications Warehouse

Cronin, J.G.; Myers, B.N.

1964-01-01

The Southern High Plains of Texas occupies an area of about 22,000 square miles in n'Orthwest Texas, extending fr'Om the Canadian River southward. about 250 miles and fr'Om the New Mexico line eastward an average distance of about 120 miles. The economy of the area is dependent largely upon irrigated agriculture, and in 1958 about 44,000 irrigation wells were in operation. The economy of the area is also dependent upon the oil industry either in the f'Orm of oil and gas production or in the form of industries based on the producti'On of petroleum. The Southern High Plains of Tems is characterized. 'by a nearly flat land surface sloping gently toward. the southeast at an average of 8 to 10 feet per mile. Shallow undrained depressions or playas are characteristic of the plains surface, and during periods of heavy rainfall, runoff collects in the depressions to form temporary ponds or lakes. Stream drainage 'On the plains surface is poorly developed; water discharges over the eastern escarpment off the plains only during periods of excessive rainfall. The climate of the area is semiarid; the average annual precipitation is about 20 inches. About 70 percent of the precipitation falls during the growing season from April to September. Rocks of Permian age underlie the entire area and consist chiefly of red sandstone and shale containing nUmerous beds of gypsum and dolomite. The Permian rocks are not a source of water in the Southern High Plains, and any water in these rocks would probably be saline. The Triassic rocks underlying the 'S'Outhern Hi'gh Plains consist of three formations of the Dockum group: the Tecovas formation, the Santa Rosa sandstone. and the Chinle formation equivalent. The Tecovas and Chinle formation equivalent both consist chiefly of shale and sandy shale; however, the Santa Rosa sandstone consists mainly of medium to coarse conglomeratic sandstone containing some shale. Tbe formations of the Dockum group are capable of yielding small to moderate quantities of water in many parts of the Southern High Pl'ains; however, in practically all places the water is rather saline and pr

Provenance of Jurassic sediments in the Hefei Basin, east-central China and the contribution of high-pressure and ultrahigh-pressure metamorphic rocks from the Dabie Shan

NASA Astrophysics Data System (ADS)

Li, Renwei; Wan, Yusheng; Cheng, Zhenyu; Zhou, Jianxiong; Li, Shuangying; Jin, Fuquan; Meng, Qingren; Li, Zhong; Jiang, Maosheng

2005-03-01

The provenance of the Jurassic sediments in the Hefei Basin is constrained by compositions of the detrital K-white micas and garnets, and SHRIMP dating of the detrital zircons, which can help to understand the evolution and to reconstruct the paleogeographic distribution of HP-UHP rocks in the Jurassic Dabie Shan. (1) For the oldest Mesozoic sediments at the bottom of the Fanghushan Formation ( J1), the predominance of the early Paleozoic and Luliang (1700-1900 Ma) zircons indicates a major source from the North China Block. However, Neoproterozoic zircons as the major component in other Jurassic sediments indicate that the source rocks were mainly derived from the exhumed Yangtze Block in the Dabie Shan. (2) The co-occurrence of high-Si phengites and Triassic zircons provides stratigraphic evidence that the first exposure of the UHP rocks at the Earth's surface in the Dabie Shan occurred in the Early Jurassic during deposition of the Fanghushan Formation. (3) From the east to the west of the Hefei Basin, there is a spatial variation in the compositions for detrital micas and garnets, and in the U-Pb ages of detrital zircons. Evidently, HP-UHP rocks were widely distributed at outcrop in the eastern Dabie Shan. In contrast, they were less important in the western Dabie Shan during the Jurassic.

Provenance from zircon U-Pb age distributions in crustally contaminated granitoids

NASA Astrophysics Data System (ADS)

Bahlburg, Heinrich; Berndt, Jasper

2016-05-01

The basement of sedimentary basins is often entirely covered by a potentially multi-stage basin fill and therefore removed from direct observation and sampling. Melts intruding through the basin stratigraphy at a subsequent stage in the geological evolution of a region may assimilate significant volumes of country rocks. This component may be preserved in the intrusive body either as xenoliths or it may be reflected only by the age spectrum of incorporated zircons. Here we present the case of an Ordovician calc-alkaline intrusive belt in NW Argentina named the "Faja Eruptiva de la Puna Oriental" (Faja Eruptiva), which in the course of intrusion sampled the unexposed and unknown basement of the Ordovician basin in this region, and parts of the basin stratigraphy. We present new LA-ICP-MS U-Pb ages on zircons from 9 granodiorites and granites of the Faja Eruptiva. The main part of the Faja Eruptiva intruded c. 445 Ma in the Late Ordovician. The zircon ages obtained from the intrusive rocks have a large spread between 2683.5 ± 21.6 and 440.0 ± 4.9 Ma and reflect the underlying crust and may be interpreted in several ways. The inherited zircons may have been derived from the oldest known unit in the region, the thick siliciclastic turbidite successions of the upper Neoproterozoic-lower Cambrian Puncoviscana Formation, which is inferred to represent the basement of the NW Argentina. The basement to the Puncoviscana Formation is not known. Alternatively, the inherited zircons may reflect the geochronological structure of the entire unexposed Early Paleozoic crust underlying this region of which the Puncoviscana Formation was only one component. This crust likely contained rocks pertaining to and detritus derived from earlier orogenic cycles of the southwestern Amazonia craton, including sources of Early Meso- and Paleoproterozoic age. Detritus derived, in turn, from the Faja Eruptiva intrusive belt reflects the origin of the granitoids as well as the inherited geochronological and isotope geochemical structure of either the basement and/or distant sources having supplied material to the basement rocks. If unrecognized, sediment formed from such granitoid sources may erroneously be used to infer the exposure of, and direct detrital contributions from, a variety of older source rocks in fact not directly involved in the studied source-sink system.

A molecular and isotopic study of the organic matter from the Paris Basin, France

NASA Technical Reports Server (NTRS)

Lichtfouse, E.; Albrecht, P.; Behar, F.; Hayes, J. M.

1994-01-01

Thirteen Liassic sedimentary rocks of increasing depth and three petroleums from the Paris Basin were studied for 13C/12C isotopic compositions and biological markers, including steranes, sterenes, methylphenanthrenes, methylanthracenes, and triaromatic steroids. The isotopic compositions of n-alkanes from mature sedimentary rocks and petroleums fall in a narrow range (2%), except for the deepest Hettangian rock and the Trias petroleum, for which the short-chain n-alkanes are enriched and depleted in 13C, respectively. Most of the molecular parameters increase over the 2000-2500 m depth range, reflecting the transformation of the organic matter at the onset of petroleum generation. In this zone, carbonate content and carbon isotopic composition of carbonates, as well as molecular parameters, are distinct for the Toarcian and Hettangian source rocks and suggest a migration of organic matter from these two formations. Two novel molecular parameters were defined for this task: one using methyltriaromatic steroids from organic extracts; the other using 1-methylphenanthrene and 2-methylanthracene from kerogen pyrolysates. The anomalous high maturity of the Dogger petroleum relative to the maturity-depth trend of the source rocks is used to estimate the minimal vertical distance of migration of the organic matter from the source rock to the reservoir.

Stratigraphy of the Morrison and related formations, Colorado Plateau region, a preliminary report

USGS Publications Warehouse

Craig, Lawrence C.; ,

1955-01-01

Three subdivisions of the Jurassic rocks of the Colorado Plateau region are: the Glen Canyon group, mainly eolian and fluvial sedimentary rocks; the San Rafael group, marine and marginal marine sedimentary rocks; and the Morrison formation, fluvial and lacustrine sedimentary rocks. In central and eastern Colorado the Morrison formation has not been differ- entiated into members. In eastern Utah, northeastern Arizona, northwestern New Mexico, and in part of western Colorado, the Morrison may be divided into a lower part and an upper part; each part has two members which are di1Ierentiated on a lithologic basis. Where differentiated, the lower part of the Morrison consists either of the Salt Wash member or the Recapture member or both; these are equivalent in age and inter tongue and intergrade over a broad area in the vicinity of the Four Corners area of New Mexico, Colorado, Arizona, and Utah. The Salt Wash member is present in eastern Utah and parts of western Colorado, north- eastern Arizona, and northwestern New Mexico. It was formed as a large alluvial plain or 'fan' by an aggrading system of braided streams diverging to the north and east from an apex in south-central Utah. The major source area of the Salt Wash was to the southwest of south-central Utah, probably in west-central Arizona and southeastern California. The member was derived mainly from sedimentary rocks. The Salt Wash deposits grade from predomi- nantly coarse texture at the apex of the 'fan' to predominantly flne texture at the margin of the 'fan'. The Salt Wash member has been arbitrarily divided into four facies: a con- glomera tic sandstone facies, a sandstone and mudstone facies, a claystone and lenticular sandstone facies, and a claystone and limestone facies. The Recapture member of the Morrison formation is present in northeastern Arizona, northwestern New Mexico, and small areas of southeastern Utah and southwestern Colorado near the Four Corners. It was formed as a large alluvial plain or 'fan' by an aggrading system of braided streams. The Recap- ture deposits grade from predominantly coarse texture sedimentary rocks to predominantly fine texture and have been arbitrarily divided into three facies: a conglomeratic sandstone facies, a sandstone facies, and a claystone and sandstone facies. The distribution of the facies indicates that the major source area of the Recapture was south of Gallup, N. Mex., probably in west-central New Mexico. The Recapture was derived from an area of intrusive and extrusive igneous rocks, metamorphic rocks, and sedimentary rocks. The upper part of the Morrison formation consists of the Westwater Canyon member and the Brushy Basin member. The Westwater Canyon member forms the lower portion of the upper part of the Morrison in northeastern Arizona, northwestern New Mexico, and places in southeastern Utah and southwestern Colorade near the Four Corners, and it intertongues and intergrades northward into the Brushy Basin member. The Westwater Canyon member was formed as a large alluvial plain or 'fan' by an aggrading system of braided streams. The Westwater deposits grade from predominantly coarse-textured sedimentary rocks to somewhat finer textured sedimentary rocks, and have been arbitrarily divided into two facies: a conglomeratic sandstone facies and a sandstone facies. The distribution of the facies indicates that the major source area of the Westwater was south of Gallup, N. Mex., probably in west-central New Mexico. The Westwater was derived from an area of intrusive and extrusive igneous rocks, metamorphic rocks, and sedimentary rocks. The similarity of the distribution and composition of the Westwater to the Recapture indicates that the Westwater represents essentially a continuation of deposition on the Recapture 'fan'; the Westwater contains, however, considerably coarser materials. Whereas the S

Major Element Analysis of the Target Rocks at Meteor Crater, Arizona

NASA Technical Reports Server (NTRS)

See, Thomas H.; Hoerz, Friedrich; Mittlefehldt, David W.; Varley, Laura; Mertzman, Stan; Roddy, David

2002-01-01

We collected approximately 400 rock chips in continuous vertical profile at Meteor Crater, Arizona, representing, from bottom to top, the Coconino, Toroweap, Kaibab, and Moenkopi Formations to support ongoing compositional analyses of the impact melts and their stratigraphic source depth(s) and other studies at Meteor Crater that depend on the composition of the target rocks. These rock chips were subsequently pooled into 23 samples for compositional analysis by XRF (x ray fluorescence) methods, each sample reflecting a specific stratigraphic "subsection" approximately 5-10 in thick. We determined the modal abundance of quartz, dolomite, and calcite for the entire Kaibab Formation at vertical resolutions of 1-2 meters. The Coconino Formation composes the lower half of the crater cavity. It is an exceptionally pure sandstone. The Toroweap is only two inches thick and compositionally similar to Coconino, therefore, it is not a good compositional marker horizon. The Kaibab Formation is approximately 80 in thick. XRD (x ray diffraction) studies show that the Kaibab Formation is dominated by dolomite and quartz, albeit in highly variable proportions; calcite is a minor phase at best. The Kaibab at Meteor Crater is therefore a sandy dolomite rather than a limestone, consistent with pronounced facies changes in the Permian of SE Arizona over short vertical and horizontal distances. The Moenkopi forms the 12 in thick cap rock and has the highest Al2O3 and FeO concentrations of all target rocks. With several examples, we illustrate how this systematic compositional and modal characterization of the target ideologies may contribute to an understanding of Meteor Crater, such as the depth of its melt zone, and to impact cratering in general, such as the liberation of CO2 from shocked carbonates.

Gold in the Black Hills, South Dakota, and how new deposits might be found

USGS Publications Warehouse

Norton, James Jennings

1974-01-01

Of the recorded production of 34,694,552 troy ounces of gold mined in South Dakota through 1971, about 90 percent has come from Precambrian ore bodies in the Homestake mine at Lead in the northern Black Hills. Most of the rest has come from ore deposited in the Deadwood Formation (Cambrian) by hydrothermal replacement during early Tertiary igneous activity. About 99 percent of the total production has been within a radius of 5 miles (8 km) of Lead. Elsewhere, prospecting has been intense, both in the Precambrian rocks, which are exposed over an area 61 by 26 miles (98 by 42 km), and in nearby Paleozoic rocks. All the known ore bodies have been found either at the surface or in subsurface workings of operating mines. Efforts to find totally new deposits have been modest and sporadic; no comprehensive and systematic program has ever been attempted. Obviously, any exploration program should be aimed at finding a new deposit resembling the Homestake in the Precambrian, but discovery in the Deadwood of a new group of ore bodies containing several hundred thousand ounces of gold would certainly be worthwhile. Evidence has long been available that the Deadwood deposits and the Homestake deposit are somehow related. Current opinion is that (1) the Homestake ore is mainly Precambrian, (2) a trivial amount of Homestake ore is Tertiary, (3)gold in Deadwood basal conglomerate is largely of placer origin, and (4) the gold of replacement deposits in the Deadwood and in other rock units came originally from sources similar to the Homestake deposit or its parent materials. Homestake ore is virtually entirely contained in a unit of iron-formation locally known as the Homestake Formation, which seemingly had more gold in the original sediments than similar rocks exposed elsewhere in the Black Hills. Gold, sulfur, and other constituents were subsequently concentrated in ore shoots in zones of dilation caused by cross folds that deformed earlier major folds. These ore shoots are in metamorphic rocks of a grade just above the garnet isograd, in a zone where the principal iron-magnesium mineral of the iron-formation changes from a carbonate (sideroplesite) to a silicate (cummingtonite). This metamorphic reaction would release carbon dioxide to the fluid that presumably formed the ore bodies. In short, three controls over localization of the ore have been identified: (1) the cross folds; (2) the so-called Homestake Formation, which passes beneath Paleozoic rocks north of Lead and has not been proved to reappear anywhere else in the Black Hills (Other units of iron-formation less enriched in gold might locally become more like the Homestake Formation beneath the cover of Paleozoic rocks.}; (3} proximity to the garnet isograd--nearly all the exposed Precambrian rocks in the Black Hills are at a metamorphic grade higher than this isograd--and occurrence of this isograd zone mostly beneath Paleozoic rocks. In searching for new deposits, one can guess from existing data where Precambrian rocks of suitable nature may be concealed. The usefulness of such guesses can be increased if they are made with information about the distribution of gold in younger rocks. Gold in the Deadwood basal conglomerate would be the simplest indicator of a deposit once exposed on the pre-Deadwood surface. Tertiary replacement deposits in the Deadwood or other rocks, which obtained their gold from Precambrian sources that may be nearby or far away, can also be helpful; they, like anomalies found by geochemical sampling, at least outline the regions of mineralizing activity. A suitable approach to exploration is to make a thorough study of the stratigraphy, the structure, and the metals geochemistry of the Deadwood Formation and associated rocks, chiefly in the northern Black Hills but to a lesser extent elsewhere in localities where the Precambrian geology seems promising and where gold has been found nearby. Such a program, even if it does not yield

DOE Office of Scientific and Technical Information (OSTI.GOV)

Molina, J.

The Chipaque-Lower Carbonera({circ}) Petroleum System of the northernmost Llanos Basin of Colombia, covers 11,100 km{sup 2} and includes two major oil fields: Caho Limon in Colombia, and Guafita in Venezuela, jointly with three more relatively small fields in Colombia: Redondo, Cano Rondon, and Jiba. Ultimate recoverable reserves are in the order of 1.4 BBO. The sedimentary section penetrated in the Northern Llanos has been informally subdivided into four Cretaceous formations: K3, K2B, K2A, and Lower K1 deposited during the Albian-Senonian, and into four Tertiary formations: Lower Carbonera, Upper Carbonera, Leon, and Guayabo deposited during the Late Eocene to Pliocene time.more » The main reservoir is the Lower Carbonera Formation, which contains 81% of the total reserves. The Cretaceous K2A and Lower K1 reservoirs contain 6% and 8%, respectively of the reserves. Minor reserves are accumulated in the discontinuous sandstones of the Oligocene Upper Carbonera Formation Geochemical analyses of the Cano Limon/Guafita oils indicate that these are aromatic intermediate to paraffinic-naphthenic, non degradated, genetically related to a common marine-derived type of kerogen. These oils were generated by a mature, marine clastic source rock with a small contribution of continental organic matter. The geochemistry of the hydrocarbon suggest a genetic relationship with the shales of the Chipaque formation, basin-ward equivalent of the K2 Formation, which presents kerogen type II organic matter and has been recognized as a good source rock. The petroleum system is hypothetical because a definite oil-source rock correlation is lacking. The development of the petroleum system is directly related to the history of movement of the Santa Maria, La Yuca, Caho Limon, and Matanegra wrench faults. It has been determined that these faults of pre-Cretaceous rifting origin, created the Santa Maria Graben of which the Espino Graben is the continuation in Venezuela.« less

Similarity and Differences of Cretaceous Magmatism in the Arctic Region

NASA Astrophysics Data System (ADS)

Peyve, A. A.

2018-03-01

The paper considers Cretaceous magmatism at the continental margin of the Arctic Region. It is shown that Cretaceous igneous rocks of this region are rather heterogeneous in age, composition, and geodynamic formation setting. This differentiates them from rocks of typical large igneous provinces (LIPs). Local areas of magmatic activity, their substantial remoteness them from one another, and significant distinctions in age, composition of rocks, and formation conditions prevent us from unreservedly combining all occurrences of Cretaceous magmatism at the continental margin of the Arctic Region into a common igneous province. The stage of tholeiitic magmatism in the Svalbard Archipelago, Franz Josef Land, Arctic Canada, and the Alpha-Mendeleev Rise, which can be considered an LIP, began in the Early Cretaceous and continued for a long time, at least until the Campanian. The magmatism apparently had a plume source and was caused by extension during opening of the Canada Basin. Tholeiitic magmatism gave way to the alkaline magmatism stage from the Campanian to the onset of the Paleocene, related to continental rifting at the initial stage of formation of Eurasian Basin in the Arctic Region. No convincing evidence for a genetic link between Early Cretaceous tholeiitic and Late Cretaceous alkaline magmatism is known at present, nor for the alkaline magmatism belonging to a plume source.

High Resolution Biostratigraphy and the Origin of the Basal Cambrian Bedded Chert from the Aksu Area (Tarim Block, Northwestern China)

NASA Astrophysics Data System (ADS)

Wang, Z.; Liu, H.; Dong, L.

2017-12-01

The early Cambrian Yurtus Formation in the Aksu area (Tarim block, northwestern China) consists of two lithostratigraphic units, lower black shale with interbedded chert unit and upper siltstone/carbonate unit. This time period represents the most important Proterozoic- Phanerozoic transition in earth's history. In recent years, the black shale has been confirmed to have high hydrocarbon generation potential. However, the depositional environment of the Yurtus Formation remains controversial and the biostratigraphic constrains are rather poor. The chert that is interbedded with black shale in the Yurtus Formation provides an exceptional taphonomic window to capture the diversity of the early Cambrian microfossils. Meanwhile, the origin of the bedded chert would give us some insight into the environmental background when the source rock was deposited. Therefore, in this research, we focus on the chert in the lower Yurtus formation and our purpose is to establish high resolution biostratigraphic framework and to better understand the depositional environment of the source rock. We investigated 4 sections in the Tarim basin: Kungaikuotan, Sugaite, Kule, and Yurtus VI. Abundant acritarch fossils have been identified, including Heliosphaeridium ampliatum, Yurtusia uniformis, and Comasphaeridium annulare. The tubular fossil Megathrix longus is also very common in this formation. In addition, two new types of specimens have been discovered, sheet-like encrolled fossils ( 0.5 mm in size) and regular spindle-like double layered microfossils ( 10μm in diameter). All of these fossils have constant occurrences in the studied sections, and can be well correlated with those yielded from the equivalent interval in South China. The biostratigraphic work suggests the source rock in the lower unit of the Yurtus Formation could be correlated with the Meishucunian small shelly fossil assemblage I and II. The Gemenium/Silicon ratio of the Yurtus chert is less than 1μmol/mol, suggesting the primary Si source is from normal sea water instead of hydrothermal fluids. The sea water origin and petrological evidence also indicate that the chert is unlikely mainly from the replacement of carbonate. This recognition fundamentally challenges the previous interpretation of the depositional environment.

Mantle sources and origin of the Middle Paleoproterozoic Jatulian Large Igneous Province of the Fennoscandian shield: evidence from isotope geochemical data on the Kuetsjarvi volcanics, Kola Craton

NASA Astrophysics Data System (ADS)

Bogina, Maria; Zlobin, Valeriy; Chistyakov, Alexeii; Evgenii, Sharkov

2014-05-01

Paleoproterozoic is one of the most important stages in the Earth's evolution as marking a cardinal change in a style of tectonomagmatic processes at 2.2-2.0 Ga, which corresponds to the formation of the Jatulian Large Igneous Province at the Fennoscandian Shield. The fragment of this province is represented by the volcanics of the Kuetsjarvi Group in the Kola Craton. These rocks differ in the extremely wide rock diversity and prominent role of alkaline rocks, the extremely rare rocks in the Precambrian. The rocks of the group are subdivided into the alkaline and tholeiitic basaltic series. The tholeiites are highly fractionated (mg# 38) high-Ti rocks enriched in HFSE. The alkaline series show wider mg# variations (32-52), which is inconsistent with a single fractionation sequence of these series. All rocks have high HFSE, at extremely wide LILE variations. Tholeiites show moderate LREE fractionation pattern at practically flat HREE: La/YbN = 3.6-4.5; La/SmN = 2.2-2.4, Gd/YbN = 1.5-1.7 and slight Eu anomaly (Eu/Eu* = 0.80-0.85). The alkaline rocks display much more fractionated LREE and fractionated HREE (La/YbN = 43.9-5.8; La/SmN = 2.2-2.4, Gd/YbN = 2.04-3.92) patterns at Eu anomaly varying from 0.53 to 1. The spidergrams of both series reveal negative Nb and Sr anomalies at sign-variable Ti anomaly. The alkaline rocks are enriched relative to tholeiites in U, Th, and Nb. Examination of behavior of incompatible trace elements offers an opportunity to compare the conditions of generation of parental mantle magmas of the studied series. In particular, the tholeiitic basalts have higher Zr/Nb ratios than the alkaline rocks, which in combination with their lower La/Yb ratios indicates their formation under the higher melting degree of mantle source as compared to the alkaline rocks. Simultaneous increase in Ce/Y ratio in the alkaline rocks may indicate their formation at greater depths. Tholeiitic basalts have lower Nb/U ratio, which testifies some crustal contamination of the melts. In addition, they have low Ti/Y (323-449) ratios and high Lu/Hf (0.11-0.16), which is typical of the rocks formed by melting of spinel peridotites. The alkaline basalts were derived from a deeper garnet-bearing mantle source (Ti/Y = 640-1140, Lu/Hf = 0.03-0.05). Isotope-geochemical study showed that these rocks have very similar Nd isotope composition ((eNd (2200) = +1.5 in the alkaline basalt and +1.9 in the tholeiites). It was found that the studied alkaline rocks are similar in composition to the OIB-type Tristan da Kunha basalts, while tholeiites are closer to the high-Ti rocks of the Parana plateau, which experienced significant lithospheric contribution. Obtained data confirm the within-plate setting at the Jatulian stage of the Fennoscandian Shield. The Kutesjarvi Group consists of two rock types: OIB-type alkaline and E-MORB-type tholeiitic, which is typical of most Phanerozoic large igneous provinces. However, unlike the latters, the rocks of this area were too much tectonized and eroded to compile a systematic sequence. But, the Kuetsjarvi Group may be considered as the fragment of the oldest large igneous province.

Enhanced late gas generation potential of petroleum source rocks via recombination reactions: Evidence from the Norwegian North Sea

NASA Astrophysics Data System (ADS)

Erdmann, Michael; Horsfield, Brian

2006-08-01

Gas generation in the deep reaches of sedimentary basins is usually considered to take place via the primary cracking of short alkyl groups from overmature kerogen or the secondary cracking of petroleum. Here, we show that recombination reactions ultimately play the dominant role in controlling the timing of late gas generation in source rocks which contain mixtures of terrigeneous and marine organic matter. These reactions, taking place at low levels of maturation, result in the formation of a thermally stable bitumen, which is the major source of methane at very high maturities. The inferences come from pyrolysis experiments performed on samples of the Draupne Formation (liptinitic Type II kerogen) and Heather Formation (mixed marine-terrigeneous Type III kerogen), both Upper Jurassic source rocks stemming from the Norwegian northern North Sea Viking Graben system. Non-isothermal closed system micro scale sealed vessel (MSSV) pyrolysis, non-isothermal open system pyrolysis and Rock Eval type pyrolysis were performed on the solvent extracted, concentrated kerogens of the two immature samples. The decrease of C 6+ products in the closed system MSSV pyrolysis provided the basis for the calculation of secondary gas (C 1-5) formation. Subtraction of the calculated secondary gas from the total observed gas yields a "remaining" gas. In the case of the Draupne Formation this is equivalent to primary gas cracked directly from the kerogen, as detected by a comparison with multistep open pyrolysis data. For the Heather Formation the calculated remaining gas formation profile is initially attributable to primary gas but there is a second major gas pulse at very high temperature (>550 °C at 5.0 K min -1) that is not primary. This has been explained by a recondensation process where first formed high molecular weight compounds in the closed system yield a macromolecular material that undergoes secondary cracking at elevated temperatures. The experiments provided the input for determination of kinetic parameters of the different gas generation types, which were used for extrapolations to a linear geological heating rate of 10 -11 K min -1. Peak generation temperatures for the primary gas generation were found to be higher for Heather Formation ( Tmax = 190 °C, equivalent to Ro appr. 1.7%) compared to Draupne Formation ( Tmax = 175 °C, equivalent to appr. Ro 1.3%). Secondary gas peak generation temperatures were calculated to be 220 °C for the Heather Formation and 205 to 215 °C for the Draupne Formation, respectively, with equivalent vitrinite reflectance values ( Ro) between 2.4% and 2.0%. The high temperature secondary gas formation from cracking of the recombination residue as detected for the Heather Formation is quantitatively important and is suggested to occur at very high temperatures ( Tmax approx. 250 °C) for geological heating rates. The prediction of a significant charge of dry gas from the Heather Formation at very high maturity levels has important implications for petroleum exploration in the region, especially to the north of the Viking Graben where Upper Jurassic sediments are sufficiently deep buried to have experienced such a process.

Structural evolution and petroleum productivity of the Baltic basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulmishek, G.F.

The Baltic basin is an oval depression located in the western part of the Russian craton; it occupies the eastern Baltic Sea and adjacent onshore areas. The basin contains more than 5,000 m of sedimentary rocks ranging from latest Proterozoic to Tertiary in age. These rocks consist of four tectonostratigraphic sequences deposited during major tectonic episodes of basin evolution. Principal unconformities separate the sequences. The basin is underlain by a rift probably filled with Upper Proterozoic rocks. Vendian and Lower Cambrian rocks (Baikalian sequence) form two northeast-trending depressions. The principal stage of the basin development was during deposition of amore » thick Middle Cambrian-Lower Devonian (Caledonian) sequence. This stage was terminated by the most intense deformations in the basin history. The Middle Devonian-Carboniferous (Hercynian) and Permian-Tertiary (Kimmerian-Alpine) tectonic and depositional cycles only slightly modified the basin geometry and left intact the main structural framework of underlying rocks. The petroleum productivity of the basin is related to the Caledonian tectonostratigraphic sequence that contains both source rocks and reservoirs. However, maturation of source rocks, migration of oil, and formation of fields took place mostly during deposition of the Hercynian sequence.« less

Distinct Igneous APXS Rock Compositions on Mars from Pathfinder, MER and MSL

NASA Technical Reports Server (NTRS)

Gellert, Ralf; Arvidson, Raymond; Clark, Benton, III; Ming, Douglas W.; Morris, Richard V.; Squyres, Steven W.; Yen, Albert S.

2015-01-01

The alpha particle x-ray spectrometer (APXS) on all four Mars Rovers returned geochemical data from about 1000 rocks and soils along the combined traverses of over 50 kilometers. Here we discuss rocks likely of igneous origin, which might represent source materials for the soils and sediments identified along the traverses. Adirondack-type basalts, abundant in the plains of Gusev Crater, are primitive, olivine bearing basalts. They resemble in composition the basaltic soils encountered at all landing sites, except the ubiquitous elevated S, Cl and Zn in soils. They have been postulated to represent closely the average Martian crust composition. The recently identified new Martian meteorite Black Beauty has similar overall geochemical composition, very distinct from the earlier established SNC meteorites. The rim of the Noachian crater Endeavour, predating the sulfate-bearing Burns formation at Meridiani Planum, also resembles closely the composition of Adirondack basalts. At Gale Crater, the MSL Curiosity rover identified a felsic rock type exemplified by the mugearitic float rock JakeM, which is widespread along the traverse at Gale. While a surprise at that time, possibly related more evolved, alkaline rocks had been previously identified on Mars. Spirit encountered the Wishstone rocks in the Columbia Hills with approx. 6% Na2O+K2O, 15 % Al2O3 and low 12% FeO. Pathfinder rocks with elevated K and Na and >50% SiO2 were postulated to be andesitic. Recently Opportunity encountered the rock JeanBaptisteCharbonneau with >15% Al2O3, >50% SiO2 and approx. 10% FeO. A common characteristic all these rocks is the very low abundance of Cr, Ni and Zn, and an Fe/Mn ratio of about 50, indicating an unaltered Fe mineralogy. Beside these likely igneous rock types, which occurred always in several rocks, a few unique rocks were encountered, e.g. Bounce Rock, a pyroxene-bearing ejecta rock fragment resembling the Shergottite EETA 79001B meteorite. The APXS data can be used to relate the findings of all 4 landing sites, constrain the water to rock ratio of sediments or imply source rock provenance. Beyond that the capability to quantify important volatile elements like P, S, Cl, and Br have provided new insights into the chemistry and the environment present during the formation of the sediments.

Volcanostratigraphy, petrography and petrochemistry of Late Cretaceous volcanic rocks from the Görele area (Giresun, NE Turkey)

NASA Astrophysics Data System (ADS)

Oguz, Simge; Aydin, Faruk; Baser, Rasim

2015-04-01

In this study, we have reported for lithological, petrographical and geochemical features of late Cretaceous volcanic rocks from the Çanakçı and the Karabörk areas in the south-eastern part of Görele (Giresun, NE Turkey) in order to investigate their origin and magmatic evolution. Based on the previous ages and recent volcano-stratigraphic studies, the late Cretaceous time in the study area is characterized by an intensive volcanic activity that occurred in two different periods. The first period of the late Cretaceous volcanism (Cenomanian-Santonian; 100-85 My), conformably overlain by Upper Jurassic-Lower Cretaceous massive carbonates (Berdiga Formation), is represented by bimodal units consisting of mainly mafic rock series (basaltic-andesitic lavas and hyaloclastites, dikes and sills) in the lower part (Çatak Formation), and felsic rock series (dacitic lavas and hyaloclastites, crystal- and pyrite-bearing tuffs) in the upper part (Kızılkaya Formation). The second period of the late Cretaceous volcanism (Santonian-Late Campanian; 85-75 Ma) is also represented by bimodal character and again begins with mafic rock suites (basaltic-basaltic andesitic lavas and hyaloclastites) in the lower part (Çağlayan Formation), and grades upward into felsic rock suites (biotite-bearing rhyolitic lavas, ignimbrites and hyaloclastites) through the upper part (Tirebolu Formation). These bimodal units are intercalated with volcanic conglomerates-sandstones, claystones, marl and red pelagic limestones throughout the volcanic sequence, and the felsic rock series have a special important due to hosting of volcanogenic massive sulfide deposits in the region. All volcano-sedimentary units are covered by Tonya Formation (Late Campanian-Paleocene) containing calciturbidites, biomicrites and clayey limestones. The mafic rocks in the two volcanic periods generally include basalt, basaltic andesite and minor andesite, whereas felsic volcanics of the first period mainly consists of dacite but those of the second period have biotite-bearing rhyolite. The basalts and basaltic andesites exhibit subaphyric to porphyritic texture with phenocrysts of calcic plagioclase and augite in a fine-grained to microcrystalline groundmass, consisting of plag+cpx+mag. Andesite samples display a porphyritic texture with phenocrysts of calcic to sodic plagioclase and augite in a hyalopilitic matrix of plag+cpx±amph+mag. Zircon and magnetite are common accessory minerals, whereas chlorite, epidote and calcite are typical alteration products. On the other hand, the dacitic and rhyolitic rocks commonly show a porphyritic texture with predominant feldspar, quartz and some biotite phenocrysts. The microgranular to felsophyric groundmass is mainly composed of aphanitic plagioclase, K-feldspar and quartz. Accessory minerals include zircon, apatite and magnetite. Typical alteration minerals include late-formed sericite, albite and clay minerals. Late Cretaceous mafic and felsic volcanic rocks have a largely sub-alkaline character with typical arc geochemical signatures. N-MORB-normalised multi-element patterns show that all rock samples are enriched in LILEs (e.g. Rb, Ba, Th) but depleted in Nb and Ti. The chondrite-normalized REE patterns are concave shapes with low to medium enrichment, suggesting a common mantle source for the studied bimodal rock series. All geochemical data reflecting typical characteristics of subduction-related magmas are commonly attributed to a depleted mantle source, which has been previously enriched by fluids or sediments. Acknowledgments This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK, grant 112Y365)

Rock glaciers originating from mass movements: A new model based on field data

NASA Astrophysics Data System (ADS)

Reitner, J. M.; Gruber, A.

2009-04-01

The morphological and geological conditions for the formation of rock glaciers in Alpine environments seem to be clear according to our present knowledge (BARSCH, 1996; HAEBERLI et al. 2006). All known examples derive from porous more or less coarse grained sedimentary bodies, either from moraines or, in most cases, from talus fans. In the latter case the debris accumulation originates overwhelmingly from physical weathering, rock falls or rock avalanches in proximity to rockwalls. However, in the course of geological mapping in the crystalline areas of Eastern and Northern Tyrol (Schober Gruppe, Tuxer Alpen) we found an additional setting. Some relict rock glaciers occur directly at the bulging toe of bedrock slopes, which had been affected by deep-seated gravitational slope deformations (REITNER, 2003; GRUBER, 2005). Furthermore rock glaciers are also present in ridge-top depressions and similar graben-like features that originated from gravitational processes in jointed bedrock. In all these cases talus fans with debris accumulation are missing in the source area of those rock glaciers. According to our model the disintegration of jointed rocks by creeping mass movements resulted in an increased volume of joint space. This enabled the formation of interstitial ice under permafrost conditions. Increased ice saturation led to the reduction of the angle of internal friction and finally to the initial formation of a rock glacier. Abundant material was provided for the further movement and thus for formation of quite large rock glaciers due to the previous and maybe still ongoing slope deformation. Most rock glaciers of this type originated from mass movements of sagging -type (Sackung sensu ZISCHINSKY, 1966), which illustrates the continuous transition from gravitational to periglacial creep process in high Alpine areas. All studied examples are of Lateglacial age according to the altitude in correspondence to the known amount of permafrost depression compared to modern time. Thus, on the one hand such rock glaciers postdate the formation of the mass movements, which enable a chronological constraint of this phenomenon on the base of our knowledge of climate history. On the other hand, those examples with rock glaciers linked at various altitudes with mass movements also mirror former stepwise permafrost degradation, where rock glacier formation moved to higher altitudes. In this respect, and envisaging a rising permafrost boundary, rock glacier formation on slopes affected by mass movements should be anticipated for the future. References: BARSCH, D. (1996): Rockglaciers. - Springer Verlag, Berlin. GRUBER, A. (2005) Bericht 2004 über geologische Aufnahmen im Quartär der Nördlichen Tuxer Alpen auf Blatt 148 Brenner.- Jahrbuch der Geologischen Bundesanstalt, 145, 337-343, Wien. HAEBERLI, W. et al. (2006): Permafrost Creep and Rock Glacier Dynamics.- Permafrost and Periglac. Process., 17, 189-214 (2006), Wiley Interscience, New York REITNER, J. M. (2003a): Bericht 1998-99 über geologische Aufnahmen im Quartär und Kristallin auf Blatt 179 Lienz.- Jahrbuch der Geologischen Bundesanstalt., 143, 514-522, Wien. ZISCHINSKY, U. (1966): On the deformation of high slopes. Proc.-1st Int. Conf.Soc.Rock Mech. Lisbon, 179-185.

Abiogenic formation of alkanes in the Earth's crust as a minor source for global hydrocarbon reservoirs.

PubMed

Sherwood Lollar, B; Westgate, T D; Ward, J A; Slater, G F; Lacrampe-Couloume, G

2002-04-04

Natural hydrocarbons are largely formed by the thermal decomposition of organic matter (thermogenesis) or by microbial processes (bacteriogenesis). But the discovery of methane at an East Pacific Rise hydrothermal vent and in other crustal fluids supports the occurrence of an abiogenic source of hydrocarbons. These abiogenic hydrocarbons are generally formed by the reduction of carbon dioxide, a process which is thought to occur during magma cooling and-more commonly-in hydrothermal systems during water-rock interactions, for example involving Fischer-Tropsch reactions and the serpentinization of ultramafic rocks. Suggestions that abiogenic hydrocarbons make a significant contribution to economic hydrocarbon reservoirs have been difficult to resolve, in part owing to uncertainty in the carbon isotopic signatures for abiogenic versus thermogenic hydrocarbons. Here, using carbon and hydrogen isotope analyses of abiogenic methane and higher hydrocarbons in crystalline rocks of the Canadian shield, we show a clear distinction between abiogenic and thermogenic hydrocarbons. The progressive isotopic trends for the series of C1-C4 alkanes indicate that hydrocarbon formation occurs by way of polymerization of methane precursors. Given that these trends are not observed in the isotopic signatures of economic gas reservoirs, we can now rule out the presence of a globally significant abiogenic source of hydrocarbons.

Reconnaissance studies of potential petroleum source rocks in the Middle Jurassic Tuxedni Group near Red Glacier, eastern slope of Iliamna Volcano

USGS Publications Warehouse

Stanley, Richard G.; Herriott, Trystan M.; LePain, David L.; Helmold, Kenneth P.; Peterson, C. Shaun

2013-01-01

Previous geological and organic geochemical studies have concluded that organic-rich marine shale in the Middle Jurassic Tuxedni Group is the principal source rock of oil and associated gas in Cook Inlet (Magoon and Anders, 1992; Magoon, 1994; Lillis and Stanley, 2011; LePain and others, 2012; LePain and others, submitted). During May 2009 helicopter-assisted field studies, 19 samples of dark-colored, fine-grained rocks were collected from exposures of the Red Glacier Formation of the Tuxedni Group near Red Glacier, about 70 km west of Ninilchik on the eastern flank of Iliamna Volcano (figs. 1 and 3). The rock samples were submitted to a commercial laboratory for analysis by Rock-Eval pyrolysis and to the U.S. Geological Survey organic geochemical laboratory in Denver, Colorado, for analysis of vitrinite reflectance. The results show that values of vitrinite reflectance (percent Ro) in our samples average about 2 percent, much higher than the oil window range of 0.6–1.3 percent (Johnsson and others, 1993). The high vitrinite reflectance values indicate that the rock samples experienced significant heating and furthermore suggest that these rocks may have generated oil and gas in the past but no longer have any hydrocarbon source potential. The high thermal maturity of the rock samples may have resulted from (1) the thermaleffects of igneous activity (including intrusion by igneous rocks), (2) deep burial beneath Jurassic, Cretaceous, and Tertiary strata that were subsequently removed by uplift and erosion, or (3) the combined effects of igneous activity and burial.

Catagenesis of organic matter of oil source rocks in Upper Paleozoic coal formation of the Bohai Gulf basin (eastern China)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, R.X.; Li, Y.Z.; Gao, Y.W.

2007-05-15

The Bohai Gulf basin is the largest petroliferous basin in China. Its Carboniferous-Permian deposits are thick (on the average, ca. 600 m) and occur as deeply as 5000 m. Coal and carbonaceous shale of the Carboniferous Taiyuan Formation formed in inshore plain swamps. Their main hydrocarbon-generating macerals are fluorescent vitrinite, exinite, alginite, etc. Coal and carbonaceous shale of the Permian Shanxi Formation were deposited in delta-alluvial plain. Their main hydrocarbon-generating macerals are vitrinite, exinite, etc. The carbonaceous rocks of these formations are characterized by a high thermal maturity, with the vitrinite reflectance R{sub 0} > 2.0%. The Bohai Gulf basinmore » has been poorly explored so far, but it is highly promising for natural gas.« less

Isotopic studies of mariposite-bearing rocks from the south- central Mother Lode, California.

USGS Publications Warehouse

Kistler, R.W.; Dodge, F.C.W.; Silberman, M.L.

1983-01-01

Gold-bearing vein formation in the Mother Lode belt of the study area apparently occurred during the Early Cretaceous between 127 and 108 m.y. B.P. The hydrothermal fluids that carried the gold precipitated quartz and mariposite at approx 320oC, similar to the T of precipitation of gold-bearing quartz veins in the Allegheny district. The O- and H-isotopic composition calculated for the fluid indicate that it was similar to formation water or was metamorphic in origin. If the carbonate in the veins was in isotopic equilibrium with this same fluid, it apparently precipitated at a higher T of approx 400oC. The Sr in the carbonate is much less radiogenic than that in any known marine carbonate, but is similar in isotopic composition to that in metamorphosed mafic volcanic rocks of the general region. These mafic rocks could have been the source for the Sr in the hydrothermal veins. This observation supports the contention that the gold-mariposite-quartz-carbonate rocks were formed as an alteration product of serpentinite and other mafic igneous rocks.-A.P.

Uranium favorability of the San Rafael Swell area, east-central Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mickle, D G; Jones, C A; Gallagher, G L

1977-10-01

The San Rafael Swell project area in east-central Utah is approximately 3,000 sq mi and includes the San Rafael Swell anticline and the northern part of the Waterpocket Fold monocline at Capitol Reef. Rocks in the area are predominantly sedimentary rocks of Pennsylvanian through Cretaceous age. Important deposits of uranium in the project area are restricted to two formations, the Chinle (Triassic) and Morrison (Jurassic) Formations. A third formation, the White Rim Sandstone (Permian), was also studied because of reported exploration activity. The White Rim Sandstone is considered generally unfavorable on the basis of lithologic characteristics, distance from a possiblemore » source of uranium, lack of apparent mineralization, and the scarcity of anomalies on gamma-ray logs or in rock, water, and stream-sediment samples. The lower Chinle from the Moss Back Member down to the base of the formation is favorable because it is a known producer. New areas for exploration are all subsurface. Both Salt Wash and Brushy Basin Members of the Morrison Formation are favorable. The Salt Wash Member is favorable because it is a known producer. The Brushy Basin Member is favorable as a low-grade resource.« less

Geology, thermal maturation, and source rock geochemistry in a volcanic covered basin: San Juan sag, south-central Colorado

USGS Publications Warehouse

Gries, R.R.; Clayton, J.L.; Leonard, C.

1997-01-01

The San Juan sag, concealed by the vast San Juan volcanic field of south-central Colorado, has only recently benefited from oil and gas wildcat drilling and evaluations. Sound geochemical analyses and maturation modeling are essential elements for successful exploration and development. Oil has been produced in minor quantities from an Oligocene sill in the Mancos Shale within the sag, and major oil and gas production occurs from stratigraphically equivalent rocks in the San Juan basin to the south-west and in the Denver basin to the northeast. The objectives of this study were to identify potential source rocks, assess thermal maturity, and determine hydrocarbon-source bed relationships. Source rocks are present in the San Juan sag in the upper and lower Mancos Shale (including the Niobrara Member), which consists of about 666 m (2184 ft) of marine shale with from 0.5 to 3.1 wt. % organic carbon. Pyrolysis yields (S1 + S2 = 2000-6000 ppm) and solvent extraction yields (1000-4000 ppm) indicate that some intervals within the Mancos Shale are good potential source rocks for oil, containing type II organic matter, according to Rock-Eval pyrolysis assay. Oils produced from the San Juan sag and adjacent part of the San Juan basin are geochemically similar to rock extracts obtained from these potential source rock intervals. Based on reconstruction of the geologic history of the basin integrated with models of organic maturation, we conclude that most of the source rock maturation occurred in the Oligocene and Miocene. Little to no maturation took place during Laramide subsidence of the basin, when the Animas and Blanco Basin formations were deposited. The timing of maturation is unlike that of most Laramide basins in the Rocky Mountain region, where maturation occurred as a result of Paleocene and Eocene basin fill. The present geothermal gradient in the San Juan sag is slightly higher (average 3.5??C/100 m; 1.9??F/100 ft) than the regional average for southern Rocky Mountain basins; however, although the sag contains intrusives and a volcanic cover, the gradient is significantly lower than that reported for parts of the adjacent San Juan basin (4.7??C/100 m; 2.6??F/100 ft). Burial depth appears to be a more important controlling factor in the thermal history of the source rocks than local variations in the geothermal gradient due to volcanic activity. Interestingly, the thick overburden of volcanic rocks appears to have provided the necessary burial depth for maturation.

Provenance and paleogeography of the Devonian Durazno Group, southern Parana Basin in Uruguay

NASA Astrophysics Data System (ADS)

Uriz, N. J.; Cingolani, C. A.; Basei, M. A. S.; Blanco, G.; Abre, P.; Portillo, N. S.; Siccardi, A.

2016-03-01

A succession of Devonian cover rocks occurs in outcrop and in the subsurface of central-northern Uruguay where they were deposited in an intracratonic basin. This Durazno Group comprises three distinct stratigraphic units, namely the Cerrezuelo, Cordobés and La Paloma formations. The Durazno Group does not exceed 300 m of average thickness and preserves a transgressive-regressive cycle within a shallow-marine siliciclastic shelf platform, and is characterized by an assemblage of invertebrate fossils of Malvinokaffric affinity especially within the Lower Devonian Cordobés shales. The sedimentary provenance of the Durazno Group was determined using petrography, geochemistry, and morphological studies of detrital zircons as well as their U-Pb ages. Sandstone petrography of Cerrezuelo and La Paloma sequences shows that they have a dominantly quartz-feldspathic composition with a minor contribution of other minerals. Whole-rock geochemical data indicate that alteration was strong in each of the three formations studied; chondritic-normalized REE patterns essentially parallel to PAAS, the presence of a negative Eu-anomaly, and Th/Sc and La/Hf ratios point to an average source composition similar to UCC or slightly more felsic. Within the Cerrezuelo Formation, recycling of older volcano-metasedimentary sources is interpreted from Zr/Sc ratios and high Hf, Zr, and REE concentrations. U-Pb detrital zircon age populations of the Cerrezuelo and La Paloma formations indicate that the principal source terranes are of Neoproterozoic age, but include also minor populations derived from Mesoproterozoic and Archean-Paleoproterozoic rocks. A provenance from the Cuchilla Dionisio-Dom Feliciano, Nico Pérez and Piedra Alta terranes of Uruguay and southern Brazil is likely. This study establishes an intracratonic extensional tectonic setting during Durazno time. Considering provenance age sources, regional paleocurrent distributions and the established orogenic history recorded in SW Gondwana, we suggest that the basin fill was derived from paleohighs located in what is currently SE Uruguay.

Near-Infrared Imaging for Spatial Mapping of Organic Content in Petroleum Source Rocks

NASA Astrophysics Data System (ADS)

Mehmani, Y.; Burnham, A. K.; Vanden Berg, M. D.; Tchelepi, H.

2017-12-01

Natural gas from unconventional petroleum source rocks (shales) plays a key role in our transition towards sustainable low-carbon energy production. The potential for carbon storage (in adsorbed state) in these formations further aligns with efforts to mitigate climate change. Optimizing production and development from these resources requires knowledge of the hydro-thermo-mechanical properties of the rock, which are often strong functions of organic content. This work demonstrates the potential of near-infrared (NIR) spectral imaging in mapping the spatial distribution of organic content with O(100µm) resolution on cores that can span several hundred feet in depth (Mehmani et al., 2017). We validate our approach for the immature oil shale of the Green River Formation (GRF), USA, and show its applicability potential in other formations. The method is a generalization of a previously developed optical approach specialized to the GRF (Mehmani et al., 2016a). The implications of this work for spatial mapping of hydro-thermo-mechanical properties of excavated cores, in particular thermal conductivity, are discussed (Mehmani et al., 2016b). References:Mehmani, Y., A.K. Burnham, M.D. Vanden Berg, H. Tchelepi, "Quantification of organic content in shales via near-infrared imaging: Green River Formation." Fuel, (2017). Mehmani, Y., A.K. Burnham, M.D. Vanden Berg, F. Gelin, and H. Tchelepi. "Quantification of kerogen content in organic-rich shales from optical photographs." Fuel, (2016a). Mehmani, Y., A.K. Burnham, H. Tchelepi, "From optics to upscaled thermal conductivity: Green River oil shale." Fuel, (2016b).

Petrography and geochemistry of Jurassic sandstones from the Jhuran Formation of Jara dome, Kachchh basin, India: Implications for provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Periasamy, V.; Venkateshwarlu, M.

2017-06-01

Sandstones of Jhuran Formation from Jara dome, western Kachchh, Gujarat, India were studied for major, trace and rare earth element (REE) geochemistry to deduce their paleo-weathering, tectonic setting, source rock characteristics and provenance. Petrographic analysis shows that sandstones are having quartz grains with minor amount of K-feldspar and lithic fragments in the modal ratio of Q 89:F 7:L 4. On the basis of geochemical results, sandstones are classified into arkose, sub-litharenite, wacke and quartz arenite. The corrected CIA values indicate that the weathering at source region was moderate to intense. The distribution of major and REE elements in the samples normalized to upper continental crust (UCC) and chondrite values indicate similar pattern of UCC. The tectonic discrimination diagram based on the elemental concentrations and elemental ratios of Fe2O3 + MgO vs. TiO2, SiO2 vs. log(K2O/Na2O), Sc/Cr vs. La/Y, Th-Sc-Zr/10, La-Th-Sc plots Jhuran Formation samples in continental rift and collision settings. The plots of Ni against TiO2, La/Sc vs. Th/Co and V-Ni-Th ∗10 reveals that the sediments of Jhuran Formation were derived from felsic rock sources. Additionally, the diagram of (Gd/Yb) N against Eu/Eu ∗ suggest the post-Archean provenance as source possibly Nagar Parkar complex for the studied samples.

Ground-based hyperspectral imaging and terrestrial laser scanning for fracture characterization in the Mississippian Boone Formation

NASA Astrophysics Data System (ADS)

Sun, Lei; Khan, Shuhab D.; Sarmiento, Sergio; Lakshmikantha, M. R.; Zhou, Huawei

2017-12-01

Petroleum geoscientists have been using cores and well logs to study source rocks and reservoirs, however, the inherent discontinuous nature of these data cannot account for horizontal heterogeneities. Modern exploitation requires better understanding of important source rocks and reservoirs at outcrop scale. Remote sensing of outcrops is becoming a first order tool for reservoir analog studies including horizontal heterogeneities. This work used ground-based hyperspectral imaging, terrestrial laser scanning (TLS), and high-resolution photography to study a roadcut of the Boone Formation at Bella Vista, northwest Arkansas, and developed an outcrop model for reservoir analog analyses. The petroliferous Boone Formation consists of fossiliferous limestones interbedded with chert of early Mississippian age. We used remote sensing techniques to identify rock types and to collect 3D geometrical data. Mixture tuned matched filtering classification of hyperspectral data show that the outcrop is mostly limestones with interbedded chert nodules. 1315 fractures were classified according to their strata-bounding relationships, among these, larger fractures are dominantly striking in ENE - WSW directions. Fracture extraction data show that chert holds more fractures than limestones, and both vertical and horizontal heterogeneities exist in chert nodule distribution. Utilizing ground-based remote sensing, we have assembled a virtual outcrop model to extract mineral composition as well as fracture data from the model. We inferred anisotropy in vertical fracture permeability based on the dominancy of fracture orientations, the preferential distribution of fractures and distribution of chert nodules. These data are beneficial in reservoir analogs to study rock mechanics and fluid flow, and to improve well performances.

Source rock potential of middle cretaceous rocks in Southwestern Montana

USGS Publications Warehouse

Dyman, T.S.; Palacas, J.G.; Tysdal, R.G.; Perry, W.J.; Pawlewicz, M.J.

1996-01-01

The middle Cretaceous in southwestern Montana is composed of a marine and nonmarine succession of predominantly clastic rocks that were deposited along the western margin of the Western Interior Seaway. In places, middle Cretaceous rocks contain appreciable total organic carbon (TOC), such as 5.59% for the Mowry Shale and 8.11% for the Frontier Formation in the Madison Range. Most samples, however, exhibit less than 1.0% TOC. The genetic or hydrocarbon potential (S1+S2) of all the samples analyzed, except one, yield less than 1 mg HC/g rock, strongly indicating poor potential for generating commercial amounts of hydrocarbons. Out of 51 samples analyzed, only one (a Thermopolis Shale sample from the Snowcrest Range) showed a moderate petroleum potential of 3.1 mg HC/g rock. Most of the middle Cretaceous samples are thermally immature to marginally mature, with vitrinite reflectance ranging from about 0.4 to 0.6% Ro. Maturity is high in the Pioneer Mountains, where vitrinite reflectance averages 3.4% Ro, and at Big Sky Montana, where vitrinite reflectance averages 2.5% Ro. At both localities, high Ro values are due to local heat sources, such as the Pioneer batholith in the Pioneer Mountains.

Geology and hydrocarbon potential of the Dead Sea Rift Basins of Israel and Jordan

USGS Publications Warehouse

Coleman, James; ten Brink, Uri S.

2016-01-01

Geochemical analyses indicate that the source of all oils, asphalts, and tars recovered in the Lake Lisan basin is the Ghareb Formation. Geothermal gradients along the Dead Sea fault zone vary from basin to basin. Syn-wrench potential reservoir rocks are highly porous and permeable, whereas pre-wrench strata commonly exhibit lower porosity and permeability. Biogenic gas has been produced from Pleistocene reservoirs. Potential sealing intervals may be present in Neogene evaporites and tight lacustrine limestones and shales. Simple structural traps are not evident; however, subsalt traps may exist. Unconventional source rock reservoir potential has not been tested.

The Cannery Formation--Devonian to Early Permian arc-marginal deposits within the Alexander Terrane, Southeastern Alaska

USGS Publications Warehouse

Karl, Susan M.; Layer, Paul W.; Harris, Anita G.; Haeussler, Peter J.; Murchey, Benita L.

2011-01-01

The Cannery Formation consists of green, red, and gray ribbon chert, siliceous siltstone, graywacke-chert turbidites, and volcaniclastic sandstone. Because it contains early Permian fossils at and near its type area in Cannery Cove, on Admiralty Island in southeastern Alaska, the formation was originally defined as a Permian stratigraphic unit. Similar rocks exposed in Windfall Harbor on Admiralty Island contain early Permian bryozoans and brachiopods, as well as Mississippian through Permian radiolarians. Black and green bedded chert with subordinate lenses of limestone, basalt, and graywacke near Kake on Kupreanof Island was initially correlated with the Cannery Formation on the basis of similar lithology but was later determined to contain Late Devonian conodonts. Permian conglomerate in Keku Strait contains chert cobbles inferred to be derived from the Cannery Formation that yielded Devonian and Mississippian radiolarians. On the basis of fossils recovered from a limestone lens near Kake and chert cobbles in the Keku Strait area, the age of the Cannery Formation was revised to Devonian and Mississippian, but this revision excludes rocks in the type locality, in addition to excluding bedded chert on Kupreanof Island east of Kake that contains radiolarians of Late Pennsylvanian and early Permian age. The black chert near Kake that yielded Late Devonian conodonts is nearly contemporaneous with black chert interbedded with limestone that also contains Late Devonian conodonts in the Saginaw Bay Formation on Kuiu Island. The chert cobbles in the conglomerate in Keku Strait may be derived from either the Cannery Formation or the Saginaw Bay Formation and need not restrict the age of the Cannery Formation, regardless of their source. The minimum age of the Cannery Formation on both Admiralty Island and Kupreanof Island is constrained by the stratigraphically overlying fossiliferous Pybus Formation, of late early and early late Permian age. Because bedded radiolarian cherts on both Admiralty and Kupreanof Islands contain radiolarians as young as Permian, the age of the Cannery Formation is herein extended to Late Devonian through early Permian, to include the early Permian rocks exposed in its type locality. The Cannery Formation is folded and faulted, and its stratigraphic thickness is unknown but inferred to be several hundred meters. The Cannery Formation represents an extended period of marine deposition in moderately deep water, with slow rates of deposition and limited clastic input during Devonian through Pennsylvanian time and increasing argillaceous, volcaniclastic, and bioclastic input during the Permian. The Cannery Formation comprises upper Paleozoic rocks in the Alexander terrane of southeastern Alaska. In the pre-Permian upper Paleozoic, the tectonic setting of the Alexander terrane consisted of two or more evolved oceanic arcs. The lower Permian section is represented by a distinctive suite of rocks in the Alexander terrane, which includes sedimentary and volcanic rocks containing early Permian fossils, metamorphosed rocks with early Permian cooling ages, and intrusive rocks with early Permian cooling ages, that form discrete northwest-trending belts. After restoration of 180 km of dextral displacement of the Chilkat-Chichagof block on the Chatham Strait Fault, these belts consist, from northeast to southwest, of (1) bedded chert, siliceous argillite, volcaniclastic turbidites, pillow basalt, and limestone of the Cannery Formation and the Porcupine Slate of Gilbert and others (1987); (2) greenschist-facies Paleozoic metasedimentary and metavolcanic rocks that have Permian cooling ages; (3) silty limestone and calcareous argillite interbedded with pillow basalt and volcaniclastic rocks of the Halleck Formation and the William Henry Bay area; and (4) intermediate-composition and syenitic plutons. These belts correspond to components of an accretionary complex, contemporary metamorphic rocks, forearc-basin deposits,

Geochemical characterization of the siliciclastic rocks of Chitravati Group, Cuddapah Supergroup: Implications for provenance and depositional environment

NASA Astrophysics Data System (ADS)

Somasekhar, V.; Ramanaiah, S.; Sarma, D. Srinivasa

2018-06-01

Petrological and geochemical studies have been carried out on Pulivendla and Gandikota Quartzite from Chitravati Group of Cuddapah Supergroup to decipher the provenance and depositional environment. Both the units are texturally mature with sub-rounded to well-rounded and moderately to well-sorted grains. Majority of the framework grains are quartz, in the form of monocrystalline quartz, followed by feldspars (K-feldspar and plagioclase), mica, rock fragments, heavy minerals, with minor proportion of the matrix and cement. Based on major element geochemical classification diagram, Pulivendla Quartzite is considered as quartz-arenite and arkose to sub-arkose, whereas Gandikota Quartzite falls in the field of lith-arenite and arkose to sub-arkose. Weathering indices like CIA, PIA, CIW, ICV, Th/U ratio and A-CN-K ternary diagram suggest moderate to intense chemical weathering of the source rocks of these quartzites. Whole rock geochemistry of quartzites indicate that they are primarily from the first-cycle sediments, along with some minor recycled components. Also their sources were mostly intermediate-felsic igneous rocks of Archean age. The tectonic discrimination plots, Th-Sc-Zr/10 of both these formations reflect active to passive continental margin setting. Chondrite-normalized rare earth element (REE) patterns, and various trace element ratios like Cr/Th, Th/Co, La/Sc and Th/Cr indicate dominantly felsic source with minor contribution from mafic source. Th/Sc ratios of Pulivendla and Gandikota Quartzite are in close proximity with average values of 2.83, 3.45 respectively, which is higher than AUCC (Th/Sc=0.97), demonstrating that the contributions from more alkali source rocks than those that contributed to AUCC.

Thermal Maturity Data Used by the U.S. Geological Survey for the U.S. Gulf Coast Region Oil and Gas Assessment

USGS Publications Warehouse

Dennen, Kristin O.; Warwick, Peter D.; McDade, Elizabeth Chinn

2010-01-01

The U.S. Geological Survey is currently assessing the oil and natural gas resources of the U.S. Gulf of Mexico region using a total petroleum system approach. An essential part of this geologically based method is evaluating the effectiveness of potential source rocks in the petroleum system. The purpose of this report is to make available to the public RockEval and vitrinite reflectance data from more than 1,900 samples of Mesozoic and Tertiary rock core and coal samples in the Gulf of Mexico area in a format that facilitates inclusion into a geographic information system. These data provide parameters by which the thermal maturity, type, and richness of potential sources of oil and gas in this region can be evaluated.

Central Antarctic provenance of Permian sandstones in Dronning Maud Land and the Karoo Basin: Integration of U Pb and TDM ages and host-rock affinity from detrital zircons

NASA Astrophysics Data System (ADS)

Veevers, J. J.; Saeed, A.

2007-12-01

In conjugate SE Africa and Antarctica, Early Permian sandstones of the Swartrant Formation of the Ellisras Basin, Vryheid Formation of the Karoo Basin, and Amelang Plateau Formation of Dronning Maud Land (DML) were deposited after Gondwanan glaciation on a westward paleoslope. We analysed detrital zircons for U-Pb ages by a laser ablation microprobe-inductively coupled plasma mass spectrometer (LAM-ICPMS) and attached age significance only to clusters of three or more overlapping analyses. We analysed Hf-isotope compositions by a multi-collector spectrometer (LAM-MC-ICPMS) and trace elements by electron microprobe (EMP) and ICPMS. These analyses indicate the rock type and source (whether crustal or juvenile mantle) of the host magma, and a "crustal" model age ( TDMC). The integrated analysis gives a more distinctive, and more easily interpreted, picture of crustal evolution in the provenance area than age data alone. Zircons from the Ellisras Basin are aged 2700-2540 Ma with minor populations about 2815 Ma and 2040 Ma, which correspond with the ages of the upslope parts of the proximal Kaapvaal Craton and Limpopo Belt. Mafic rock is the dominant host rock, and it reflects the Archean granite-greenstone terrane of the Kaapvaal Craton. The three Karoo Basin samples and the two DML samples have zircons with these common properties: (1) 1160-880 Ma, host magma mafic granitoid (< 65% SiO 2) derived from juvenile depleted mantle sources ( ɛHf positive) at 1.65 Ga and 1.35 Ga, with TDMC of 2.0-0.9 Ga; (2) 760 to 480 Ma, host magma granitoid and low-heavy rare earth element rock (?alkaline rock-carbonatite), derived from mixed crustal and juvenile depleted mantle sources ( ɛHf positive and negative) at 1.50 Ga and 1.35 Ga, with TDMC of 2.0-0.9 Ga. Together with similar detrital zircons in Triassic sandstone of SE Australia, these properties reflect those in upslope central Antarctica, indicating a provenance of ˜ 1000 Ma (Grenville) cratons embedded in 700-500 Ma (Pan-Gondwanaland) fold belts. Detrital zircons in Cambrian sediments of the Ellsworth-Whitmore Mountains block and Cambrian metasediments of the Welch Mountains with comparable properties suggest that the central Antarctic provenance operated also in the ˜ 500 Ma Cambrian.

National Assessment of Oil and Gas Project: petroleum systems and geologic assessment of oil and gas in the Southwestern Wyoming Province, Wyoming, Colorado and Utah

USGS Publications Warehouse

,

2005-01-01

The U.S. Geological Survey (USGS) completed an assessment of the undiscovered oil and gas potential of the Southwestern Wyoming Province of southwestern Wyoming, northwestern Colorado, and northeastern Utah (fig. 1). The USGS Southwestern Wyoming Province for this assessment included the Green River Basin, Moxa arch, Hoback Basin, Sandy Bend arch, Rock Springs uplift, Great Divide Basin, Wamsutter arch, Washakie Basin, Cherokee ridge, and the Sand Wash Basin. The assessment of the Southwestern Wyoming Province is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation, and migration), reservoir rocks (sequence stratigraphy, petrophysical properties), and hydrocarbon traps (trap types, formation, and timing). Using this geologic framework, the USGS defined 9 total petroleum systems (TPS) and 23 assessment units (AU) within these TPSs, and quantitatively estimated the undiscovered oil and gas resources within 21 of the 23 AUs.

Evaluation of kinetic uncertainty in numerical models of petroleum generation

USGS Publications Warehouse

Peters, K.E.; Walters, C.C.; Mankiewicz, P.J.

2006-01-01

Oil-prone marine petroleum source rocks contain type I or type II kerogen having Rock-Eval pyrolysis hydrogen indices greater than 600 or 300-600 mg hydrocarbon/g total organic carbon (HI, mg HC/g TOC), respectively. Samples from 29 marine source rocks worldwide that contain mainly type II kerogen (HI = 230-786 mg HC/g TOC) were subjected to open-system programmed pyrolysis to determine the activation energy distributions for petroleum generation. Assuming a burial heating rate of 1??C/m.y. for each measured activation energy distribution, the calculated average temperature for 50% fractional conversion of the kerogen in the samples to petroleum is approximately 136 ?? 7??C, but the range spans about 30??C (???121-151??C). Fifty-two outcrop samples of thermally immature Jurassic Oxford Clay Formation were collected from five locations in the United Kingdom to determine the variations of kinetic response for one source rock unit. The samples contain mainly type I or type II kerogens (HI = 230-774 mg HC/g TOC). At a heating rate of 1??C/m.y., the calculated temperatures for 50% fractional conversion of the Oxford Clay kerogens to petroleum differ by as much as 23??C (127-150??C). The data indicate that kerogen type, as defined by hydrogen index, is not systematically linked to kinetic response, and that default kinetics for the thermal decomposition of type I or type II kerogen can introduce unacceptable errors into numerical simulations. Furthermore, custom kinetics based on one or a few samples may be inadequate to account for variations in organofacies within a source rock. We propose three methods to evaluate the uncertainty contributed by kerogen kinetics to numerical simulations: (1) use the average kinetic distribution for multiple samples of source rock and the standard deviation for each activation energy in that distribution; (2) use source rock kinetics determined at several locations to describe different parts of the study area; and (3) use a weighted-average method that combines kinetics for samples from different locations in the source rock unit by giving the activation energy distribution for each sample a weight proportional to its Rock-Eval pyrolysis S2 yield (hydrocarbons generated by pyrolytic degradation of organic matter). Copyright ?? 2006. The American Association of Petroleum Geologists. All rights reserved.

Microseismicity of Blawan hydrothermal complex, Bondowoso, East Java, Indonesia

NASA Astrophysics Data System (ADS)

Maryanto, S.

2018-03-01

Peak Ground Acceleration (PGA), hypocentre, and epicentre of Blawan hydrothermal complex have been analysed in order to investigate its seismicity. PGA has been determined based on Fukushima-Tanaka method and the source location of microseismic estimated using particle motion method. PGA ranged between 0.095-0.323 g and tends to be higher in the formation that containing not compacted rocks. The seismic vulnerability index region indicated that the zone with high PGA also has a high seismic vulnerability index. This was because the rocks making up these zones were inclined soft and low-density rocks. For seismic sources around the area, epicentre and hypocentre, have estimated base on seismic particle motion method of single station. The stations used in this study were mobile stations identified as BL01, BL02, BL03, BL05, BL06, BL07 and BL08. The results of the analysis particle motion obtained 44 points epicentre and the depth of the sources about 15 – 110 meters below ground surface.

Petrology of arkosic sandstones, Pennsylvanian Minturn Formation and Pennsylvanian and Permian Sangre de Cristo Formation, Sangre de Cristo Range, Colorado - data and preliminary interpretations

USGS Publications Warehouse

Lindsey, D.A.

2000-01-01

This report describes the mineral and chemical composition of immature, arkosic sandstones of the Pennsylvanian Minturn and Pennsylvanian and Permian Sangre de Cristo Formations, which were derived from the Ancestral Rocky Mountains. Located in the Sangre de Cristo Range of southern Colorado, the Minturn and Sangre de Cristo Formations contain some of the most immature, sodic arkoses shed from the Ancestral Rocky Mountains. The Minturn Formation was deposited as fan deltas in marine and alluvial environments; the Sangre de Cristo Formation was deposited as alluvial fans. Arkoses of the Minturn and Sangre de Cristo Formations are matrix-rich and thus may be properly considered arkosic wackes in the terminology of Gilbert (Williams and others, 1954). In general, potassium feldspar and plagioclase are subequal in abundance. Arkose of the Sangre de Cristo Formation is consistently plagioclase-rich; arkose from the Minturn Formation is more variable. Quartz and feldspar grains are accompanied by a few percent rock fragments, consisting mostly of intermediate to granitic plutonic rocks, gneiss, and schist. All of the rock fragments seen in sandstone are present in interbedded conglomerate, consistent with derivation from a Precambrian terrane of gneiss and plutonic rocks much like that exposed in the present Sangre de Cristo Range. Comparison of mineral and major oxide abundances reveals a strong association of detrital quartz with SiO2, all other detrital minerals (totaled) with Al2O3, potassium feldspar plus mica with K2O, and plagioclase with Na2O. Thus, major oxide content is a good predictor of detrital mineralogy, although contributions from matrix and cement make these relationships less than perfect. Detrital minerals and major oxides tend to form inverse relationships that reflect mixtures of varying quantities of minerals; when one mineral is abundant, the abundance of others declines by dilution. In arkose of the Minturn and Sangre de Cristo Formations, the abundance of quartz (and SiO2) is enhanced by weathering and transport, which destroys feldspar and rock fragments. Weathering also preferentially destroys plagioclase (and removes Na2O) over potassium feldspar. Thus, as fresh sodic arkose detritus is weathered and transported in the fluvial environment, it becomes potassic and quartz-rich. Stratigraphic profiles of mineral and major oxide abundance reveal that weathering and transport, including reworking by marine currents, was most effective in reducing plagioclase and enhancing quartz content of arkosic sediment in the Minturn Formation near Marble Mountain. In general, the quartz-poor, sodic arkoses of the Sangre de Cristo Formation indicate little weathering in the source area or during transport. Iron-titanium oxides and other heavy minerals, notably zircon and sphene, tend to be most abundant in the Sangre de Cristo Formation. Although concentrated locally as fluvial placers, the overall abundance of heavy minerals probably reflects lack of weathering and proximity to source. The degree of weathering and destruction of unstable grains (feldspar and rock fragments) in the Minturn and Sangre de Cristo Formations of the Sangre de Cristo Range was dependent on rates of uplift and erosion as much as climate (wet versus dry). Reworking by marine currents further reduced the proportion of unstable grains during Minturn time. Sodic (plagioclase-rich), quartz-poor arkose in the coarse, conglomeratic Sangre de Cristo Formation is the product of rapid uplift and erosion.

Total Petroleum Systems of the Northwest Shelf, Australia: The Dingo-Mungaroo/Barrow and the Locker-Mungaroo/Barrow

USGS Publications Warehouse

Bishop, Michele G.

1999-01-01

The Northwest Shelf Province (U.S.G.S. #3948) of Australia contains two important hydrocarbon source-rock intervals and numerous high quality reservoir intervals. These are grouped into two petroleum systems, Dingo-Mungaroo/Barrow and Locker-Mungaroo/Barrow, where the Triassic Mungaroo Formation and the Early Cretaceous Barrow Group serve as the major reservoir rocks for the Jurassic Dingo Claystone and Triassic Locker Shale source rocks. The primary source rock, Dingo Claystone, was deposited in restricted marine conditions during the Jurassic subsidence of a regional sub-basin trend. The secondary source rock, Locker Shale, was deposited in terrestrially-influenced, continental seaway conditions during the Early Triassic at the beginning of the breakup of Pangea. These systems share potential reservoir rocks of deep-water, proximal and distal deltaic, marginal marine, and alluvial origins, ranging in age from Late Triassic through Cretaceous. Interformational seals and the regional seal, Muderong Shale, along with structural and stratigraphic traps account for the many types of hydrocarbon accumulations in this province. In 1995, the Northwest Shelf produced 42% of the hydrocarbon liquids in Australia, and in 1996 surpassed the Australian Bass Straits production, with 275,000 barrels per day (bpd) average. This region is the major producing province of Australia. Known reserves as of 1995 are estimated at 11.6 billion of barrels of oil equivalent (BBOE)(Klett and others, 1997) . Although exploration has been conducted since 1955, many types of prospects have not been targeted and major reserves continue to be discovered.

Earth's first stable continents did not form by subduction

NASA Astrophysics Data System (ADS)

Johnson, Tim; Brown, Michael; Gardiner, Nicholas; Kirkland, Christopher; Smithies, Hugh

2017-04-01

The geodynamic setting in which Earth's first stable cratonic nuclei formed remains controversial. Most exposed Archaean continental crust comprises rocks of the tonalite-trondhjemite-granodiorite (TTGs) series that were produced from partial melting of low magnesium basaltic source rocks and have 'arc-like' trace element signatures that resemble continental crust produced in modern supra-subduction zone settings. The East Pilbara Terrane, Western Australia, is amongst the oldest fragments of preserved continental crust of Earth. Low magnesium basalts of the Paleoarchaean Coucal Formation, at the base of the Pilbara Supergroup, have trace element compositions consistent with the putative source rocks for TTGs. These basalts may be remnants of the ≥35 km-thick pre-3.5 Ga plateau-like basaltic crust that is predicted to have formed if mantle temperatures were much hotter than today. Using phase equilibria modelling of an average uncontaminated Coucal basalt, we confirm their suitability as TTG source rocks. The results suggest that TTGs formed by 20-30% melting along high geothermal gradients (≥700 °C/GPa), which accord with apparent geotherms recorded by >95% of Archaean rocks worldwide. Moreover, the trace element composition of the Coucal basalts demonstrates that they were derived from an earlier generation of mafic/ultramafic rocks, and that the arc-like signature in Archaean TTGs was inherited through an ancestral source lineage. The protracted multistage process required for production and stabilisation of Earth's first continents, coupled with the high geothermal gradients, are incompatible with modern-style subduction and favour a stagnant lid regime in the early Archaean.

Simulation of geochemical processes responsible for the formation of the Zhezqazghan deposit

NASA Astrophysics Data System (ADS)

Ryzhenko, B. N.; Cherkasova, E. V.

2014-05-01

Physicochemical computer simulation of water-rock systems at a temperature of 25-150°C and under a pressure of up to 600 bar has been carried out for quantitative description of the mineralization formation conditions at sandstone- and shale-hosted copper deposits. The simulation is based on geological and geochemical information concerning the Zhezqazghan deposit and considers (i) a source of ore matter, (ii) composition of the fluid that transfers ore matter to the ore formation zone, and (iii) factors of ore concentration. It has been shown that extraction of copper from minerals of rocks and its accumulation in aqueous solution are optimal at a high mass ratio of rock to water (R/W > 10), Eh of +200 to -100 mV, and an obligatory content of chloride ions in the aqueous phase. The averaged ore-bearing fluid Cl95SO44//Ca50(Na + K)30Mg19 (eq %), pH ˜ 4, mineralization of up to 400 g/L, is formed by the interaction of red sandstone beds with a sedimentogenic brine (a product of metamorphism of seawater in carbonate rocks enriched in organic matter). The ore concentration proceeds in the course of cooling from 150 to 50°C during filtration of ore-bearing fluid through red sandstone beds in the rock-water system thermodynamically opened with respect to the reductive components.

The calc-alkaline and adakitic volcanism of the Sabzevar structural zone (NE Iran): Implications for the Eocene magmatic flare-up in Central Iran

NASA Astrophysics Data System (ADS)

Moghadam, Hadi Shafaii; Rossetti, Federico; Lucci, Federico; Chiaradia, Massimo; Gerdes, Axel; Martinez, Margarita Lopez; Ghorbani, Ghasem; Nasrabady, Mohsen

2016-04-01

A major magmatic flare-up is documented along the Bitlis-Zagros suture zone in Eocene-Oligocene times. The Cenozoic magmatism of intraplate Central Iran is an integrant part of this tectono-magmatic scenario. The Cenozoic magmatism of the Sabzevar structural zone consists of mostly intermediate to felsic intrusions and volcanic products. These igneous rocks have calc-alkaline and adakitic geochemical signatures, with nearly coincident zircon U-Pb and mica Ar-Ar ages of ca. 45 Ma. Adakitic rocks have quite low HREE and high Sr/Y ratio, but share most of their geochemical features with the calc-alkaline rocks. The Sabzevar volcanic rocks have similar initial Sr, Nd and Pb isotope ratios, showing their cogenetic nature. Nd model ages cluster tightly around 0.2-0.3 Ga. The geochemistry of the Sabzevar volcanic rocks, along with their isotopic signatures, might strangle that an upper mantle source, metasomatized by slab-derived melts was involved in generating the Sabzevar calc-alkaline rocks. A bulk rock trace element modeling suggests that amphibole-plagioclase-titanite-dominated replenishment-fractional crystallization (RFC) is further responsible for the formation of the middle Eocene Sabzevar adakitic rocks. Extensional tectonics accompanied by lithospheric delamination, possibly assisted by slab break-off and melting at depth was responsible for the Eocene formation of the Sabzevar magmatic rocks and, more in general, for the magmatic "flare-up" in Iran.

Campanian-Maastrichtian phosphorites of Iraq

NASA Astrophysics Data System (ADS)

Al-Bassam, K. S.; Al-Dahan, A. A.; Jamil, A. K.

1983-08-01

Bedded marine sedimentary phosphate rocks of Campanian-Maastrichtian age are exposed in the Western Desert of Iraq, forming part of the Tethyan phosphate province. The studied phosphorites are found in three horizons within carbonate rocks; they are mostly pelletal in texture, associated with bone fragments and detrital quartz grains, and cemented by calcite or chert. The mineralogy of the phosphate is dominated by carbonate-fluorapatite. The phosphate and the associated carbonate rocks are relatively enriched with Cr, Ni, Cu, Zn, V, and organic matter. The apatite is enriched with isotopically light carbon and heavy sulfur. The mode of phosphorite formation seems to have included syngenetic deposition of phosphate under reducing, slightly alkaline conditions in shallow marine environment. Decomposition of organic phosphatic remnants appear to have been the local source of phosphorus enrichment. However, the major tectonic and paleogeographic development of the Tethys Sea during Upper Cretaceous have probably played an important role in providing suitable setting for large scale formation of phosphorite.

Hydrocarbons related to early Cretaceous source rocks, reservoirs and seals, trapped in northeastern Neuqun basin, Argentina

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gulisano, C.; Minniti, S.; Rossi, G.

1996-08-01

The Jurassic-Cretaceous backarc Neuqun Basin, located in the west central part of Argentina, is currently the most prolific oil basin of the country. The primary objective of this study is to evaluate an Early Cretaceous to Tertiary petroleum system in the northeastern portion of the basin, where oil and gas occurrences (e.g., Puesto Hernandez, Chihuido de la Sierra Negra, El Trapial and Filo Morado oil fields, among others) provide 82 MMBO/yr comprising 67% of the basin oil production and 31% of Argentina. The source rocks are represented by two thick sections of basinal kerogen type I and II organic-rich shales,more » deposited during transgressive peaks (Agrio Formation), with TOC content up to 5.1%. Lowstand sandstones bodies, 10 to 100 m thick, are composed of eolian and fluvial facies with good reservoir conditions (Avil and Troncoso Sandstones). The seals are provided by the organic-rich shales resting sharply upon the Avil Sandstone and a widespread Aptian-Albian evaporitic event (Huitrin Formation) on top of the Troncoso reservoir. Tertiary structural traps (duplex anticlines) are developed in the outer foothills, whereas structural, combined and stratigraphic traps are present in the adjacent stable structural platform. Oil-to-source rock and oil-to-oil correlation by chromatographic and biomarker fingerprints, carbon isotopic composition and the geological evidences support the proposed oil system.« less

Effects of smectite on the oil-expulsion efficiency of the Kreyenhagen Shale, San Joaquin Basin, California, based on hydrous-pyrolysis experiments

USGS Publications Warehouse

Lewan, Michael D.; Dolan, Michael P.; Curtis, John B.

2014-01-01

The amount of oil that maturing source rocks expel is expressed as their expulsion efficiency, which is usually stated in milligrams of expelled oil per gram of original total organic carbon (TOCO). Oil-expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water (i.e., hydrous pyrolysis) at temperatures between 350°C and 365°C for 72 hr. This pyrolysis method generates oil that is compositionally similar to natural crude oil and expels it by processes operative in the subsurface. Consequently, hydrous pyrolysis provides a means to determine oil-expulsion efficiencies and the rock properties that influence them. Smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous-pyrolysis study involving a representative sample of smectite-rich source rock from the Eocene Kreyenhagen Shale in the San Joaquin Basin of California. Smectite is the major clay mineral (31 wt. %) in this thermally immature sample, which contains 9.4 wt. % total organic carbon (TOC) comprised of type II kerogen. Compared to other immature source rocks that lack smectite as their major clay mineral, the expulsion efficiency of the Kreyenhagen Shale was significantly lower. The expulsion efficiency of the Kreyenhagen whole rock was reduced 88% compared to that of its isolated kerogen. This significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix. Within the interlayers, much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking. As a result, smectite does not promote oil generation but inhibits it. Bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet. This change prevents potassium ion (K+) transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite. As a result, illitization only reaches 35% to 40% at 310°C for 72 hr and remains unchanged to 365°C for 72 hr. Bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite-rich source rock to determine its expulsion efficiency. Complete illitization prior to bitumen generation is common for Paleozoic source rocks (e.g., Woodford Shale and Retort Phosphatic Shale Member of the Phosphoria Formation), and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis. Conversely, smectite is more common in Cenozoic source rocks like the Kreyenhagen Shale, and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface.

Stratigraphic reconnaissance of the Middle Jurassic Red Glacier Formation, Tuxedni Group, at Red Glacier, Cook Inlet, Alaska

USGS Publications Warehouse

LePain, David L.; Stanley, Richard G.

2015-01-01

The Alaska Division of Geological & Geophysical Surveys (DGGS) and U.S. Geological Survey (USGS) are implementing ongoing programs to characterize the petroleum potential of Cook Inlet basin. Since 2009 this program has included work on the Mesozoic stratigraphy of lower Cook Inlet, including the Middle Jurassic Tuxedni Group between Tuxedni and Iniskin bays (LePain and others, 2013; Stanley and others, 2013; fig. 5-1). The basal unit in the group, the Red Glacier Formation (fig. 5-2), is thought to be the principal source rock for oil produced in upper Cook Inlet, and available geochemical data support this contention (Magoon and Anders, 1992; Magoon, 1994). Despite its economic significance very little has been published on the formation since Detterman and Hartsock’s (1966) seminal contribution on the geology of the Iniskin–Tuxedni area nearly 50 years ago. Consequently its stratigraphy, contact relations with bounding formations, and source rock characteristics are poorly known. During the 2014 field season, a nearly continuous stratigraphic section through the Red Glacier Formation in its type area at Red Glacier was located and measured to characterize sedimentary facies and to collect a suite of samples for analyses of biostratigraphy, Rock-Eval pyrolysis, vitrinite reflectance, and sandstone composition (fig. 5-3).The poorly known nature of the Red Glacier Formation is likely due to its remote location, steep terrain, and the fact that the type section is split into two segments that are more than 3 km apart. The lower 375 m segment of the formation is on the ridge between Red Glacier and Lateral Glacier and the upper 1,009 m segment is on the ridge between Red Glacier and Boulder Creek (fig. 5-3). Structural complications in the area add to the difficulty in understanding how these two segments fit together.

Early Triassic wrinkle structures on land: stressed environments and oases for life

NASA Astrophysics Data System (ADS)

Chu, Daoliang; Tong, Jinnan; Song, Haijun; Benton, Michael J.; Bottjer, David J.; Song, Huyue; Tian, Li

2015-06-01

Wrinkle structures in rocks younger than the Permian-Triassic (P-Tr) extinction have been reported repeatedly in marine strata, but rarely mentioned in rocks recording land. Here, three newly studied terrestrial P-Tr boundary rock succession in North China have yielded diverse wrinkle structures. All of these wrinkles are preserved in barely bioturbated shore-shallow lacustrine siliciclastic deposits of the Liujiagou Formation. Conversely, both the lacustrine siliciclastic deposits of the underlying Sunjiagou Formation and the overlying Heshanggou Formation show rich bioturbation, but no wrinkle structures or other microbial-related structures. The occurrence of terrestrial wrinkle structures in the studied sections reflects abnormal hydrochemical and physical environments, presumably associated with the extinction of terrestrial organisms. Only very rare trace fossils occurred in the aftermath of the P-Tr extinction, but most of them were preserved together with the microbial mats. This suggests that microbial mats acted as potential oases for the surviving aquatic animals, as a source of food and oxygen. The new finds suggests that extreme environmental stresses were prevalent both in the sea and on land through most of the Early Triassic.

Slides showing quantitative models for mineral-resource assessment of the Rolla 1 degree x 2 degrees Quadrangle, Missouri

USGS Publications Warehouse

Walker, Kim-Marie; Jenson, S.K.; Francica, J.R.; Hastings, D.A.; Trautwein, C.M.; Pratt, W.P.

1983-01-01

Th.is report consists of nineteen 35-mm color slides sh.owing digital synthesis and quantitative modeling of five geologic recognition criteria for assessment of Mississippi Valley-type resource potential in the Rolla 1° x 2° quadrangle, Missouri. The digital synthesis and quantitative modeling (Pratt and others, 1982) was done to supplement an earlier manual synthesis and evaluation (Pratt, 1981). The five criteria synthesized in this study, and the sources of data used, are that most known deposits are: In dolomite of the Bonneterre Formation, near the limestone-dolomite interface, which is defined as ls:dol = 1:16 (Thacker and Anderson, 1979; Kisvarsanyi, 1982);Near areas where insoluble residues of "barren" Bonneterre Formation contain anomalously high amounts of base metals (Erickson and others, 1978);Near areas of faults and fractures in the Bonneterre Formation or in underlying rocks (Pratt, 1982);In "brown rock" (finely crystalline brown dolomite) near the interface with "white rock" (coarsely recrystallized, white or very light gray, vuggy, illite-bearing dolomite) (Kisvarsanyi, 1982);Near or within favorably situated digitate reef-complex facies (Kisvarsanyi , 1982).

Evaluation of the rhenium-osmium geochronometer in the Phosphoria petroleum system, Bighorn Basin of Wyoming and Montana, USA

USGS Publications Warehouse

Lillis, Paul G.; Selby, David

2013-01-01

Rhenium-osmium (Re-Os) geochronometry is applied to crude oils derived from the Permian Phosphoria Formation of the Bighorn Basin in Wyoming and Montana to determine whether the radiogenic age reflects the timing of petroleum generation, timing of migration, age of the source rock, or the timing of thermochemical sulfate reduction (TSR). The oils selected for this study are interpreted to be derived from the Meade Peak Phosphatic Shale and Retort Phosphatic Shale Members of the Phosphoria Formation based on oil-oil and oil-source rock correlations utilizing bulk properties, elemental composition, δ13C and δ34S values, and biomarker distributions. The δ34S values of the oils range from -6.2‰ to +5.7‰, with oils heavier than -2‰ interpreted to be indicative of TSR. The Re and Os isotope data of the Phosphoria oils plot in two general trends: (1) the main trend (n = 15 oils) yielding a Triassic age (239 ± 43 Ma) with an initial 187Os/188Os value of 0.85 ± 0.42 and a mean square weighted deviation (MSWD) of 1596, and (2) the Torchlight trend (n = 4 oils) yielding a Miocene age (9.24 ± 0.39 Ma) with an initial 187Os/188Os value of 1.88 ± 0.01 and a MSWD of 0.05. The scatter (high MSWD) in the main-trend regression is due, in part, to TSR in reservoirs along the eastern margin of the basin. Excluding oils that have experienced TSR, the regression is significantly improved, yielding an age of 211 ± 21 Ma with a MSWD of 148. This revised age is consistent with some studies that have proposed Late Triassic as the beginning of Phosphoria oil generation and migration, and does not seem to reflect the source rock age (Permian) or the timing of re-migration (Late Cretaceous to Eocene) associated with the Laramide orogeny. The low precision of the revised regression (±21 Ma) is not unexpected for this oil family given the long duration of generation from a large geographic area of mature Phosphoria source rock, and the possible range in the initial 187Os/188Os values of the Meade Peak and Retort source units. Effects of re-migration may have contributed to the scatter, but thermal cracking and biodegradation likely have had minimal or no effect on the main-trend regression. The four Phosphoria-sourced oils from Torchlight and Lamb fields yield a precise Miocene age Re-Os isochron that may reflect the end of TSR in the reservoir due to cooling below a threshold temperature in the last 10 m.y. from uplift and erosion of overlying rocks. The mechanism for the formation of a Re-Os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process. Bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer, and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187Re/188Os values from an oil family.

Provenance of sediments from Sumatra, Indonesia

NASA Astrophysics Data System (ADS)

Liebermann, Christof; Hall, Robert; Gough, Amy

2017-04-01

The island of Sumatra is situated at the south-western margin of the Indonesian archipelago. Sumatra is affected by active continental margin volcanism along the Sunda Trench, west of Sumatra as a result of active northeast subduction of the Indian plate under the Eurasian plate. Exposures of the Palaeozoic meta-sedimentary basement are mainly limited in extent to the northeast-southwest trending Barisan Mountain chain. The younger Cenozoic rocks are widespread across Sumatra, but can be grouped into structurally subdivided 'fore-arc', 'intramontane', and 'back-arc' basins. However, the formation of the basins pre-dates the current magmatic arc, thus a classical arc-related generation model can not be applied. The Cenozoic formations are well studied due to hydrocarbon enrichment, but little is known about their provenance history. A comprehensive sedimentary provenance study of the Cenozoic formations can aid in the wider understanding of Sumatran petroleum plays, can contribute to palaeographic reconstruction of western SE Asia, and might help to simplify the overall stratigraphy of Sumatra. This work represents a multi-proxy provenance study of sedimentary rocks from the main Cenozoic basins of Sumatra, alongside sediment from present-day river systems. The project refines the provenance in two ways: first, by studying the heavy mineral assemblages of the targeted formations, and secondly, by U-Pb detrital zircon dating using LA-ICP-MS to identify the age-range of the potential sediment sources. Preliminary U-Pb zircon age-data of >1500 concordant grains (10% discordant cut-off), heavy mineral compositions, and thin section analysis from two fieldwork seasons indicate a mixed provenance model, with a proximal igneous source, and mature basement rocks. An increase of the proximal signature in Lower-Miocene strata indicated by the occurrence of unstable heavy mineral phases such as apatite, and clinopyroxene suggests a major change of the source at the Oligocene-Miocene boundary. This can be interpreted as a pulse in the uplift of the Barisan Mountains. The presence of volcanic quartz in thin section supports this hypothesis. On the contrary, older sedimentary strata are characterised by ultra-stable heavy minerals such as zircon, tourmaline, and rutile; the presence of garnet in both pre-, and post-uplift affected strata indicates a contribution from metamorphic basement rocks, either from the local Sumatran basement or the Malay-Peninsula. Detrital zircon ages as old as Archean are present in all sedimentary formations; a prominent Triassic age group can be correlated with the Main Range Province granitoids reported from the Malay-Peninsula. It is noteworthy that zircon age spectra from Sumatra lack some diagnostic age groups commonly found in central- and western SE Asia, such as Cretaceous ages, correlated with igneous rock in the Schwaner Mountains, SW Borneo. The analysis of modern river sands suggests that the current sedimentary fluvial systems are mainly sourced from the recent Barisan-related volcanic arc. Zircon age patterns of the modern river sands resemble the populations found in the sedimentary strata, whereas, the heavy mineral composition is highly diluted by the recent igneous sources.

Analytical volcano deformation source models

USGS Publications Warehouse

Lisowski, Michael; Dzurisin, Daniel

2007-01-01

Primary volcanic landforms are created by the ascent and eruption of magma. The ascending magma displaces and interacts with surrounding rock and fluids as it creates new pathways, flows through cracks or conduits, vesiculates, and accumulates in underground reservoirs. The formation of new pathways and pressure changes within existing conduits and reservoirs stress and deform the surrounding rock. Eruption products load the crust. The pattern and rate of surface deformation around volcanoes reflect the tectonic and volcanic processes transmitted to the surface through the mechanical properties of the crust.

Geology and ground-water resources of the Rawlins area, Carbon County, Wyoming

USGS Publications Warehouse

Berry, Delmar W.

1960-01-01

The Rawlins area in west-central Carbon County, south-central Wyoming includes approximately 634 square miles of plains and valleys grading into relatively rugged uplifts. The climate is characterized by low precipitation, rapid evaporation, and a wide range of temperature. Railroading and ranching are the principal occupations in the area. The exposed rocks in the area range in age from Precambrian through Recent. The older formations are exposed in the uplifted parts, the oldest being exposed along the apex of the Rawlins uplift. The formations dip sharply away from the anticlines and other uplifts and occur in the subsurface throughout the remainder of the area. The Cambrian rocks (undifferentiated), Madison limestone, Tensleep sandstone, Sun dance formation, Cloverly formation, Frontier formation, and Miocene and Pliocene rocks (undifferentiated) yield water to domestic and stock wells in the area. In the vicinity of the Rawlins uplift, the rocks of Cambrian age, Madison limestone, and Tensleep sandstone yield water to a few public-supply wells. The Cloverly formation yields water to public-supply wells in the Miller Hill and Sage Creek basin area. Wells that tap the Madison limestone, Tensleep sandstone, and Cloverly formation yield water under sufficient artesian pressure to flow at the land surface. The Browns Park formation yields water to springs that supply most of the Rawlins city water and supply water for domestic and stock use. Included on the geologic map are location of wells and test wells, depths to water below land surface, and location of springs. Depths to water range from zero in the unconsolidated deposits along the valley of Sugar Creek at the southern end of the Rawlins uplift to as much as 129 feet below the land surface in the Tertiary sedimentary rocks along the Continental Divide in the southern part of the area. The aquifers are recharged principally by precipitation that falls upon the area, by percolation from streams and ponds, and by movement of ground water from adjacent areas. Water is discharged from the ground-water reservoir by evaporation and transpiration, by seeps and springs, through wells, and by underflow out of the area. Although most water supplies in the area are obtained from springs, some domestic, stock, and public supplies are obtained from drilled wells, many yielding water under artesian pressure, and some flowing. Dissolved solids in the water from several geologic sources, ranging from 181 to 6,660 parts per million (ppm), indicate the varied chemical quality of ground water in the Rawlins area. Water from the Cambrian rocks, Tensleep sandstone, Cloverly formation, Frontier formation, Browns Park formation, and Miocene and Pliocene rocks is generally suitable for domestic and stock use. However, water yielded to the only well sampled in the lower part of the Frontier formation contained a high concentration of fluoride. Water from the rocks mentioned above contains less than 1,000 ppm of dissolved solids but in some places may contain iron in troublesome amounts. Water from the Madison limestone and Tensleep sandstone combined, Permian rocks, and Sundance formation contains more than 1,000 ppm of dissolved solids. Water in the Sundance, Cloverly, and Frontier :formations is very soft. More ground water can be obtained in the Rawlins area than is now being used. Many springs are undeveloped, and water can be obtained from additional wells without unduly lowering ground-water levels.

Assessment of undiscovered oil and gas resources of the Williston Basin Province of North Dakota, Montana, and South Dakota, 2010

USGS Publications Warehouse

,

2011-01-01

Using a geology-based assessment method, the U.S. Geological Survey estimated mean undiscovered volumes of 3.8 billion barrels of undiscovered oil, 3.7 trillion cubic feet of associated/dissolved natural gas, and 0.2 billion barrels of undiscovered natural gas liquids in the Williston Basin Province, North Dakota, Montana, and South Dakota. The U.S. Geological Survey (USGS) recently completed a comprehensive oil and gas assessment of the Williston Basin, which encompasses more than 90 million acres in parts of North Dakota, eastern Montana, and northern South Dakota. The assessment is based on the geologic elements of each total petroleum system (TPS) defined in the province, including hydrocarbon source rocks (source-rock maturation, hydrocarbon generation, and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined 11 TPS and 19 Assessment Units (AU).

National Assessment of Oil and Gas Project: Petroleum Systems and Geologic Assessment of Undiscovered Oil and Gas, Hanna, Laramie, and Shirley Basins Province, Wyoming

USGS Publications Warehouse

U.S. Geological Survey Hanna, Laramie

2007-01-01

INTRODUCTION The purpose of the U.S. Geological Survey?s (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the Hanna, Laramie, and Shirley Basins Province in Wyoming and northeastern Colorado. The assessment is based on the geologic elements of each total petroleum system (TPS) defined in the province, including hydrocarbon source rocks (source-rock maturation, hydrocarbon generation, and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined three TPSs and seven assessment units (AUs) within them; undiscovered resources for three of the seven AUs were quantitatively assessed.

Executive Summary -- assessment of undiscovered oil and gas resources of the San Joaquin Basin Province of California, 2003: Chapter 1 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

USGS Publications Warehouse

Gautier, Donald L.; Scheirer, Allegra Hosford; Tennyson, Marilyn E.; Peters, Kenneth E.; Magoon, Leslie B.; Lillis, Paul G.; Charpentier, Ronald R.; Cook, Troy A.; French, Christopher D.; Klett, Timothy R.; Pollastro, Richard M.; Schenk, Christopher J.

2007-01-01

In 2003, the U.S. Geological Survey (USGS) completed an assessment of the oil and gas resource potential of the San Joaquin Basin Province of California (fig. 1.1). The assessment is based on the geologic elements of each Total Petroleum System defined in the province, including hydrocarbon source rocks (source-rock type and maturation and hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined five total petroleum systems and ten assessment units within these systems. Undiscovered oil and gas resources were quantitatively estimated for the ten assessment units (table 1.1). In addition, the potential was estimated for further growth of reserves in existing oil fields of the San Joaquin Basin.

Jurassic-Cretaceous Composite Total Petroleum System and Geologic Assessment of Oil and Gas Resources of the North Cuba Basin, Cuba

USGS Publications Warehouse

,

2008-01-01

The purpose of the U.S. Geological Survey's (USGS) World Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the world. The U.S. Geological Survey (USGS) completed an assessment of the undiscovered oil and gas potential of the North Cuba Basin. The assessment is based on the geologic elements of the total petroleum system (TPS) defined in the province, including petroleum source rocks (source-rock maturation, generation, and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and petroleum traps (Trap formation and timing). Using this geologic framework, the USGS defined a Jurassic-Cretaceous Total Petroleum System in the North Cuba Basin Province. Within this TPS, three assessment units were defined and assessed for undiscovered oil and gas resources.

Petrography and geochemistry of clastic sedimentary rocks as evidences for provenance of the Lower Cambrian Lalun Formation, Posht-e-badam block, Central Iran

NASA Astrophysics Data System (ADS)

Etemad-Saeed, N.; Hosseini-Barzi, M.; Armstrong-Altrin, John S.

2011-09-01

Petrography and geochemistry (major, trace and rare earth elements) of clastic rocks from the Lower Cambrian Lalun Formation, in the Posht-e-badam block, Central Iran, have been investigated to understand their provenance. Petrographical analysis suggests that the Lalun conglomerates are dominantly with chert clasts derived from a proximal source, probably chert bearing Precambrian Formations. Similarly, purple sandstones are classified as litharenite (chertarenite) and white sandstones as quartzarenite types. The detrital modes of purple and white sandstones indicate that they were derived from recycled orogen (uplifted shoulders of rift) and stable cratonic source. Most major and trace element contents of purple sandstones are generally similar to upper continental crust (UCC) values. However, white sandstones are depleted in major and trace elements (except SiO 2, Zr and Co) relative to UCC, which is mainly due to the presence of quartz and absence of other Al-bearing minerals. Shale samples have considerably lower content in most of the major and trace elements concentration than purple sandstones, which is possibly due to intense weathering and recycling. Modal composition (e.g., quartz, feldspar, lithic fragments) and geochemical indices (Th/Sc, La/Sc, Co/Th, Cr/Th, Cr/V and V/Ni ratios) of sandstones, and shales (La/Sc and La/Cr ratios) indicate that they were derived from felsic source rocks and deposited in a passive continental margin. The chondrite-normalized rare earth element (REE) patterns of the studied samples are characterized by LREE enrichment, negative Eu anomaly and flat HREE similar to an old upper continental crust composed chiefly of felsic components in the source area. The study of paleoweathering conditions based on modal composition, chemical index of alteration (CIA), plagioclase index of alteration (PIA) and A-CN-K (Al 2O 3 - CaO + Na 2O - K 2O) relationships indicate that probably chemical weathering in the source area and recycling processes have been more important in shale and white sandstones relative to purple sandstones. The results of this study suggest that the main source for the Lalun Formation was likely located in uplifted shoulders of a rifted basin (probably a pull-apart basin) in its post-rift stage (Pan-African basement of the Posht-e-badam block).

Dominant factors in controlling marine gas pools in South China

USGS Publications Warehouse

Xu, S.; Watney, W.L.

2007-01-01

In marine strata from Sinian to Middle Triassic in South China, there develop four sets of regional and six sets of local source rocks, and ten sets of reservoir rocks. The occurrence of four main formation periods in association with five main reconstruction periods, results in a secondary origin for the most marine gas pools in South China. To improve the understanding of marine gas pools in South China with severely deformed geological background, the dominant control factors are discussed in this paper. The fluid sources, including the gas cracked from crude oil, the gas dissolved in water, the gas of inorganic origin, hydrocarbons generated during the second phase, and the mixed pool fluid source, were the most significant control factors of the types and the development stage of pools. The period of the pool formation and the reconstruction controlled the pool evolution and the distribution on a regional scale. Owing to the multiple periods of the pool formation and the reconstruction, the distribution of marine gas pools was complex both in space and in time, and the gas in the pools is heterogeneous. Pool elements, such as preservation conditions, traps and migration paths, and reservoir rocks and facies, also served as important control factors to marine gas pools in South China. Especially, the preservation conditions played a key role in maintaining marine oil and gas accumulations on a regional or local scale. According to several dominant control factors of a pool, the pool-controlling model can be constructed. As an example, the pool-controlling model of Sinian gas pool in Weiyuan gas field in Sichuan basin was summed up. ?? Higher Education Press and Springer-Verlag 2007.

A gas sampling system for withdrawing humid gases from deep boreholes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rousseau, J.P.; Thordarson, W.; Kurzmack, M.A.

A gas sampling system, designed to withdraw nearly vapor-saturated gases (93 to 100% relative humidity) from deep, unsaturated zone boreholes, was developed by the U.S. Geological Survey for use in the unsaturated zone borehole instrumentation and monitoring program at Yucca Mountain, Nye County, Nevada. This gas sampling system will be used to: (1) sample formation rock gases in support of the unsaturated zone hydrochemical characterization program; and (2) verify downhole, thermocouple psychrometer measurements of water potential in support of the unsaturated zone borehole instrumentation and monitoring program. Using this sampling system, nearly vapor-saturated formation rock-gases can be withdrawn from deepmore » boreholes without condensing water vapor in the sampling tubes, and fractionating heavy isotopes of oxygen, hydrogen, and carbon. The sampling system described in this paper uses a dry carrier-gas (nitrogen) to lower the dew point temperature of the formation rock-gas at its source. Mixing of the dry carrier gas with the source gas takes place inside a specially designed downhole instrument station apparatus (DISA). Nitrogen inflow is regulated in a manner that lowers the dew point temperature of the source gas to a temperature that is colder than the coldest temperature that the mixed gas will experience in moving from warmer, deeper depths, to colder, shallower depths near the land surface. A test of this gas sampling system was conducted in December, 1992, in a 12.2 meter deep borehole that was instrumented in October, 1991. The water potential calculated using this system reproduced in-situ measurements of water potential to within five percent of the average value, as recorded by two thermocouple psychrometers that had been in operation for over 12 months.« less

Petroleum source potential of the Lower Cretaceous mudstone succession of the NPRA and Colville Delta area, North Slope Alaska, based on sonic and resistivity logs

USGS Publications Warehouse

Keller, Margaret A.; Bird, Kenneth J.

2003-01-01

Resource assessment of the North Slope of Alaska by the U. S. Geological Survey includes evaluation of the petroleum source potential of Mesozoic and Cenozoic rocks using the delta log R technique (Passey and others, 1990). Porosity and resistivity logs are used in combination with thermal maturity data to produce a continuous profile of total organic carbon content in weight % (TOC). From the pattern and amount of TOC in the profile produced, the depositional setting and thus the petroleum source-rock potential (kerogen type) of the organic matter can be inferred and compared to interpretations from other data such as Rock-Eval pyrolysis. TOC profiles determined by this technique for the contiguous interval of pebble shale unit, Hue Shale (including the Gamma Ray Zone or GRZ), and lower part of the Torok Formation indicate important potential for petroleum generation in the Tunalik 1, Inigok 1, N. Inigok 1, Kuyanak 1, Texaco Colville Delta 1, Nechelik 1, and Bergschrund 1 wells of the western North Slope region. TOC profiles suggest that this interval contains both type II and III kerogens – consistent with proposed depositional models -- and is predominantly greater than 2 wt. % TOC (cut-off used for effective source potential). Average TOC for the total effective section of the pebble shale unit + Hue Shale ranges from 2.6 to 4.1 wt % TOC (values predominantly 2-8% TOC) over 192-352 ft. Source potential for the lower Torok Formation, which also has interbedded sandstone and lean mudstone, is good to negligible in these 7 wells.

Kerogen maturation and incipient graphitization of hydrocarbon source rocks in the Arkoma Basin, Oklahoma and Arkansas: A combined petrographic and Raman spectrometric study

USGS Publications Warehouse

Spotl, C.; Houseknecht, D.W.; Jaques, R.C.

1998-01-01

Dispersed kerogen of the Woodford-Chattanooga and Atoka Formations from the subsurface of the Arkoma Basin show a wide range of thermal maturities (0.38 to 6.1% R(o)) indicating thermal conditions ranging from diagenesis to incipient rock metamorphism. Raman spectral analysis reveals systematic changes of both the first- and second-order spectrum with increasing thermal maturity. These changes include a pronounced increase in the D/O peak height ratio accompanied by a narrowing of the D peak, a gradual decrease in the D/O peak width ratio, and a shift of both peaks toward higher wave numbers. Second-order Raman peaks, though less intensive, also show systematic peak shifting as a function of R(o). These empirical results underscore the high potential of Raman spectrometry as a fast and reliable geothermometer of mature to supermature hydrocarbon source rocks, and as an indicator of thermal maturity levels within the anchizone.Dispersed kerogen of the Woodford-Chattanooga and Atoka Formations from the subsurface of the Arkoma Basin show a wide range of thermal maturities (0.38 to 6.1% Ro) indicating thermal conditions ranging from diagenesis to incipient rock metamorphism. Raman spectral analysis reveals systematic changes of both the first- and second-order spectrum with increasing thermal maturity. These changes include a pronounced increase in the D/O peak height ratio accompanied by a narrowing of the D peak, a gradual decrease in the D/O peak width ratio, and a shift of both peaks toward higher wave numbers. Second-order Raman peaks, though less intensive, also show systematic peak shifting as a function of Ro. These empirical results underscore the high potential of Raman spectrometry as a fast and reliable geothermometer of mature to supermature hydrocarbon source rocks, and as an indicator of thermal maturity levels within the anchizone.

Distribution of organic carbon and petroleum source rock potential of Cretaceous and lower Tertiary carbonates, South Florida Basin: preliminary results

USGS Publications Warehouse

Palacas, James George

1978-01-01

Analyses of 134 core samples from the South Florida Basin show that the carbonates of Comanchean age are relatively richer in average organic carbon (0.41 percent) than those of Coahuilan age (0.28 percent), Gulfian age (0.18 percent) and Paleocene age (0.20 percent). They are also nearly twice as rich as the average world, wide carbonate (average 0.24 percent). The majority of carbonates have organic carbons less than 0.30 percent but the presence of many relatively organic rich beds composed of highly bituminous, argillaceous, highly stylolitic, and algal-bearing limestones and dolomites accounts for the higher percentage of organic carbon in some of the stratigraphic units. Carbonate rocks that contain greater than 0.4 percent organic carbon and that might be considered as possible petroleum sources were noted in almost each subdivision of the Coahuilan and Comanchean Series but particularly the units of Fredericksburg 'B', Trinity 'A', Trinity 'F', and Upper Sunniland. Possible source rocks have been ascribed by others to the Lower Sunniland, but lack of sufficient samples precluded any firm assessment in this initial report. In the shallower section of the basin, organic-rich carbonates containing as much as 3.2 percent organic carbon were observed in the lowermost part of the Gulfian Series and carbonate rocks with oil staining or 'dead' and 'live oil' were noted by others in the uppermost Gulfian and upper Cedar Keys Formation. It is questionable whether these shallower rocks are of sufficient thermal maturity to have generated commercial oil. The South Florida basin is still sparsely drilled and produces only from the Sunniland Limestone at an average depth of 11,500 feet (3500 m). Because the Sunniland contains good reservoir rocks and apparently adequate source rocks, and because the success rate of new oil field discoveries has increased in recent years, the chances of finding additional oil reserves in the Sunniland are promising. Furthermore, the presence of possible source rocks in many of the other stratigraphic units, in particular, the Fredericksburg, should give further impetus to exploring for other productive horizons.

Petroleum systems of the San Joaquin Basin Province, California -- geochemical characteristics of oil types: Chapter 9 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

USGS Publications Warehouse

Lillis, Paul G.; Magoon, Leslie B.

2007-01-01

New analyses of 120 oil samples combined with 139 previously published oil analyses were used to characterize and map the distribution of oil types in the San Joaquin Basin, California. The results show that there are at least four oil types designated MM, ET, EK, and CM. Most of the oil from the basin has low to moderate sulfur content (less than 1 weight percent sulfur), although a few unaltered MM oils have as much as 1.2 weight percent sulfur. Reevaluation of source rock data from the literature indicate that the EK oil type is derived from the Eocene Kreyenhagen Formation, and the MM oil type is derived, in part, from the Miocene to Pliocene Monterey Formation and its equivalent units. The ET oil type is tentatively correlated to the Eocene Tumey formation of Atwill (1935). Previous studies suggest that the CM oil type is derived from the Late Cretaceous to Paleocene Moreno Formation. Maps of the distribution of the oil types show that the MM oil type is restricted to the southern third of the San Joaquin Basin Province. The composition of MM oils along the southern and eastern margins of the basin reflects the increased contribution of terrigenous organic matter to the marine basin near the Miocene paleoshoreline. EK oils are widely distributed along the western half of the basin, and ET oils are present in the central and west-central areas of the basin. The CM oil type has only been found in the Coalinga area in southwestern Fresno County. The oil type maps provide the basis for petroleum system maps that incorporate source rock distribution and burial history, migration pathways, and geologic relationships between hydrocarbon source and reservoir rocks. These petroleum system maps were used for the 2003 U.S. Geological Survey resource assessment of the San Joaquin Basin Province.

Quantification of Organic richness through wireline logs: a case study of Roseneath shale formation, Cooper basin, Australia

NASA Astrophysics Data System (ADS)

Ahmad, Maqsood; Iqbal, Omer; Kadir, Askury Abd

2017-10-01

The late Carboniferous-Middle Triassic, intracratonic Cooper basin in northeastern South Australia and southwestern Queensland is Australia's foremost onshore hydrocarbon producing region. The basin compromises Permian carbonaceous shale like lacustrine Roseneath and Murteree shale formation which is acting as source and reservoir rock. The source rock can be distinguished from non-source intervals by lower density, higher transit time, higher gamma ray values, higher porosity and resistivity with increasing organic content. In current dissertation we have attempted to compare the different empirical approaches based on density relation and Δ LogR method through three overlays of sonic/resistivity, neutron/resistivity and density/resistivity to quantify Total organic content (TOC) of Permian lacustrine Roseneath shale formation using open hole wireline log data (DEN, GR, CNL, LLD) of Encounter 1 well. The TOC calculated from fourteen density relations at depth interval between 3174.5-3369 meters is averaged 0.56% while TOC from sonic/resistivity, neutron/resistivity and density/resistivity yielded an average value of 3.84%, 3.68%, 4.40%. The TOC from average of three overlay method is yielded to 3.98%. According to geochemical report in PIRSA the Roseneath shale formation has TOC from 1 - 5 wt %.There is unpromising correlations observed for calculated TOC from fourteen density relations and measured TOC on samples. The TOC from average value of three overlays using Δ LogR method showed good correlation with measured TOC on samples.

The Red Sea Basin Province: Sudr-Nubia(!) and Maqna(!) Petroleum Systems

USGS Publications Warehouse

Lindquist, Sandra J.

1999-01-01

The Sudr-Nubia(!) oil-prone total petroleum system dominates the densely explored Gulf of Suez part of the rifted Red Sea Basin Province. Upper Cretaceous to Eocene source rocks, primarily the Senonian Sudr Formation, are organic-rich, areally uniform marine carbonates that have generated known ultimate recoverable reserves exceeding 11 BBOE. The name Nubia is used for sandstone reservoirs with a wide range of poorly constrained, pre-rift geologic ages ranging from Early Paleozoic to Early Cretaceous. Syn- and post-rift Tertiary reservoirs, especially the Kareem Formation, also contain significant reserves. Partly overlapping Sudr-Nubia(!) is the areally larger and geochemically distinct, oil-and-gas-prone Maqna(!) total petroleum system within the southern Gulf of Suez basin and the sparsely explored remaining Red Sea basin. Known ultimate recoverable reserves are 50-100 MMBOE and more than 900 MMBOE, respectively, in those areas. Both the source and reservoir rocks in this petroleum system are Tertiary, dominantly Miocene, in age. Maqna(!) has the greater potential for future resource development.

Origin, mode of emplacement, and trace element geochemistry of albertite at the type locality, Albert Mines, southeastern New Brunswick, Canada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farrell, K.P.J.; Mossman, D.J.

1995-07-01

Fracturing of oil shale was coeval with albertite vein formation at Albert Mines early in the diagenetic history of the Lower Carboniferous (Tourmasian) Albert Formation. Albertite of this type locality is a pre-oil bitumen produced as a result of overpressuring due to a high rate of hydrocarbon generation and, as such, is largely preserved in an immature source rock. Dolomite precipitated in albertite during emplacement of the latter, and was sourced from an accompanying CO{sub 2}-rich fluid phase. Trace element contents of albertite are within the range of selected other major bitumen occurrences and, except for nickel, are lower thanmore » those of the host rock. Ratios of Ni/V are elevated in comparison with the host oil shale and with other bitumen occurrences. Carbon isotope values for albertite range from 27.92 to 30.80 {per_thousand}, {delta} {sup 13}C, within the range of most conventional crudes.« less

Regional Surface Waves from Mesabi Range Mine Blasts (Northern Minnesota)

DTIC Science & Technology

1991-10-29

rocks within the Archean basement which underlies the Animikie basin near the source areas. The final analysis was two dimensional raytracing which...overlying the Archean basement. Overlying the Pokegama Quartzite is the Biwabik Iron Formation and the Virginia Formation (Morey, 1983, Southwick and others...composed of intercalated mudstone and siltstone turbidite deposits which thicken and coarsen progressively from north to south across the basin (Morey and

Three ancient Montana fluvial systems: Pennsylvanian Tyler, Lower Cretaceous Muddy, and Upper Cretaceous Eagle - their reservoir and source rock distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shepard, B.

The importance of using Holocene geology as a model in mapping reservoir and source rock distribution is demonstrated in three Montana river-related systems: alluvial valley, barrier bar, and distributary channel-prodelta. The Pennsylvanian Tyler Formation was deposited by a westward-flowing meandering-stream system controlled by an east-west-trending rift valley, and surrounded by backswamp deposits. It is underlain by its probable hydrocarbon source, the marine Mississippian Heath shale and limestone, and overlain locally by the lagoonal Pennsylvanian Bear Gulch Limestone. To date, about 90 million bbl of recoverable oil have been found in Tyler sands. The oil-producing Lower Cretaceous Muddy sandstones in themore » northern Powder River basin are considered to be barrier bars, encased in organic-rich shales, which are most probably the source rock. The Upper Cretaceous Eagle Sandstone in north-central Montana is a distributary channel system, similar to that of the modern Mississippi, which dumped highly carbonaceous materials into an organic-rich delta system. The Eagle now contains possibly enormous amounts of biogenic methane. By using Galveston Island and the modern Mississippi delta as models, in conjunction with employing electric log shapes and porosity logs, it is possible to map ancient fluvial patterns in the study areas. One can then predict the location of possible hydrocarbon accumulations in porous and permeable sand bodies, along with their encasing hydrocarbon source rocks.« less

U-pb zircon age of metafelsite from the pinney hollow formation: Implications for the development of the vermont Appalachians

USGS Publications Warehouse

Walsh, G.J.; Aleinikoff, J.N.

1999-01-01

The Pinney Hollow Formation of central Vermont is part of a rift-clastic to drift-stage sequence of cover rocks deposited on the Laurentian margin during the development of the Iapetan passive margin in Late Proterozoic to Cambrian time. Conventional U-Pb zircon data indicate an age of 571 ?? 5 Ma for a metafelsite from the Pinney Hollow Formation. Geochemical data indicate that the protolith for the metafelsite, now a quartz-albite gneiss or granofels, was rhyolite from a source that was transitional between a witnin-plate granite and ocean-ridge granite setting and probably came through partially distended continental crust The transitional setting is consistent with previous data from metabasalts in the Pinney Hollow Formation and supports the idea that the source magma came through continental crust on the rifted margin of the Laurentian craton. The 571 ?? 5 Ma age provides the first geochronologic age from the rift-clastic cover sequence in New England and establishes a Late Proterozoic age for the Pinney Hollow Formation. The Late Proterozoic age of the Pinney Hollow confirms the presence of a significant mapped thrust fault between the autochthonous and para-autochthonous rocks of the cover sequence. These findings support the interpretation that the Taconic root zone is located in the hinterland of the Vermont Appalachians on the eastern side of the Green Mountain massif.

Undiscovered hydrocarbon resources in the U.S. Gulf Coast Jurassic Norphlet and Smackover Formations

USGS Publications Warehouse

Pearson, Ofori N.

2011-01-01

The U.S. Geological Survey has completed assessments of undiscovered technically recoverable oil and gas resources in the Jurassic Norphlet and Smackover formations of the onshore coastal plain and State waters of the U.S. Gulf Coast. The Norphlet Formation consists of sandstones and interbedded shales and siltstones deposited during a marine transgression. Along its northeast margin, deposition of the Norphlet was in alluvial fans, fluvial systems, and dune and clastic sabkha environments. Mudstones of the underlying Smackover Formation act as source rocks for Norphlet reservoirs. The Norphlet was divided into the following three assessment units (AUs): the Norphlet Salt Basins and Updip AU, the Norphlet Mobile Bay Deep Gas AU, and the Norphlet South Texas Gas AU. The lower part of the Smackover consists primarily of dark carbonate mudstone and argillaceous limestone deposited in low-energy environments, and is one of the Gulf of Mexico Basin’s major source rocks. The upper part of the Smackover is comprised primarily of grain-supported carbonates deposited in high-energy environments. The Smackover was divided into the following four AUs: the Smackover Updip and Peripheral Fault Zone AU, the Smackover Salt Basin AU, the Smackover South Texas AU, and the Smackover Downdip Continuous Gas AU. Although the Norphlet and Smackover formations have been the focus of extensive exploration and production, they probably still contain significant undiscovered oil and gas resources.

Contributions to the geology of uranium and thorium by the United States Geological Survey and Atomic Energy Commission for the United Nations International Conference on Peaceful Uses of Atomic Energy, Geneva, Switzerland, 1955

USGS Publications Warehouse

Page, Lincoln R.; Stocking, Hobart E.; Smith, Harriet B.

1956-01-01

Within the boundaries of the United States abnormal amounts of uranium have been found in rocks of nearly all geologic ages and lithologic types. Distribution of ore is more restricted. On the Colorado Plateau, the Morrison formation of Jurassic age yields 61.4 percent of the ore produced in the United States, and the Chinle conglomerate and Shinarump formation of Triassic age contribute 26.0 and 5.8 percent, respectively. Clastic, carbonaceous, and carbonate sedimentary rocks of Tertiary, Mesozoic, and Paleozoic ages and veins of Tertiary age are the source of the remaining 6.8 percent.

Role of melting process and melt-rock reaction in the formation of Jurassic MORB-type basalts (Alpine ophiolites)

NASA Astrophysics Data System (ADS)

Renna, Maria Rosaria; Tribuzio, Riccardo; Sanfilippo, Alessio; Thirlwall, Matthew

2018-04-01

This study reports a geochemical investigation of two thick basalt sequences, exposed in the Bracco-Levanto ophiolite (northern Apennine, Italy) and in the Balagne ophiolite (central-northern Corsica, France). These ophiolites are considered to represent an oceanward and a continent-near paleogeographic domain of the Jurassic Liguria-Piedmont basin. Trace elements and Nd isotopic compositions were examined to obtain information about: (1) mantle source and melting process and (2) melt-rock reactions during basalt ascent. Whole-rock analyses revealed that the Balagne basalts are slightly enriched in LREE, Nb, and Ta with respect to the Bracco-Levanto counterparts. These variations are paralleled by clinopyroxene chemistry. In particular, clinopyroxene from the Balagne basalts has higher CeN/SmN (0.4-0.3 vs. 0.2) and ZrN/YN (0.9-0.6 vs. 0.4-0.3) than that from the Bracco-Levanto basalts. The basalts from the two ophiolites have homogeneous initial Nd isotopic compositions (initial ɛ Nd from + 8.8 to + 8.6), within typical depleted mantle values, thereby excluding an origin from a lithospheric mantle source. These data also reject the involvement of contaminant crustal material, as associated continent-derived clastic sediments and radiolarian cherts have a highly radiogenic Nd isotopic fingerprint ( ɛ Nd at the time of basalt formation = - 5.5 and - 5.2, respectively). We propose that the Bracco-Levanto and the Balagne basalts formed by partial melts of a depleted mantle source, most likely containing a garnet-bearing enriched component. The decoupling between incompatible elements and Nd isotopic signature can be explained either by different degrees of partial melting of a similar asthenospheric source or by reaction of the ascending melts with a lower crustal crystal mush. Both hypotheses are reconcilable with the formation of these two basalt sequences in different domains of a nascent oceanic basin.

Mineralogy and geochemistry of the Lower Cretaceous siliciclastic rocks of the Morita Formation, Sierra San José section, Sonora, Mexico

NASA Astrophysics Data System (ADS)

Madhavaraju, J.; Pacheco-Olivas, S. A.; González-León, Carlos M.; Espinoza-Maldonado, Inocente G.; Sanchez-Medrano, P. A.; Villanueva-Amadoz, U.; Monreal, Rogelio; Pi-Puig, T.; Ramírez-Montoya, Erik; Grijalva-Noriega, Francisco J.

2017-07-01

Clay mineralogy and geochemical studies were carried out on sandstone and shale samples collected from the Sierra San José section of the Morita Formation to infer the paleoclimate and paleoweathering conditions that prevailed in the source region during the deposition of these sediments. The clay mineral assemblages (fraction < 2 μm) of the Sierra San José section are composed of chlorite and illite. The abundance of illite and chlorite in the studied samples suggest that the physical weathering conditions were dominant over chemical weathering. Additionally, the illite and chlorite assemblages reflect arid or semi-arid climatic conditions in the source regions. K2O/Al2O3 ratio of shales vary between 0.15 and 0.26, which lie in the range of values for clay minerals, particularly illite composition. Likewise, sandstones vary between 0.06 and 0.13, suggesting that the clay minerals are mostly kaolinte and illite types. On the chondrite-normalized diagrams, sandstone and shale samples show enriched light rare earth elements (LREE), flat heavy rare earth elements (HREE) patterns and negative Eu anomalies. The CIA and PIA values and A-CN-K plot of shales indicate low to moderate degree of weathering in the source regions. However, the sandstones have moderate to high values of CIA and PIA suggesting a moderate to intense weathering in the source regions. The SiO2/Al2O3 ratios, bivariate and ternary plots, discriminant function diagram and elemental ratios indicate the felsic source rocks for sandstone and shale of the Morita Formation.

Sources of Hydrogen as Food for Deep Microbial Communities

NASA Technical Reports Server (NTRS)

Freund, Friedemann; Fonda, Mark (Technical Monitor)

1998-01-01

To survive in deep subsurface environments autolithotrophic microbial communities require a sustainable food supply. One possible source is H2 which forms when H2O reacts with ferrous iron at rock surfaces or mineral grain boundaries to produce H2 plus ferric iron. The amount of H2 that can be supplied in this way, however, is relatively small and may not last for more than a few hundred or thousand years. A much larger reservoir of H2 exists in the rocks, inside mineral grains, arising from an as yet little-known redox conversion that affects OH- in nominally anhydrous minerals. These OH- represent small amounts of "water" that become incorporated during crystallization in H2O-laden environments. A corollary of the H2 formation from OH- is the formation of peroxy, an oxidized form of oxygen. While the peroxy become part of the mineral structure, the H2 molecules are diffusively mobile and can escape from within the mineral grains, entering the intergranular space. Assuming cautiously realistic number densities of OH- undergoing the in situ redox conversion to H2 plus peroxy, a 10 km deep rock column is expected to contain enough H2 to allow for a constant degassing rate of 50-100 nmole H2 per day per sq cm over 30 million years.

Reconnaissance stratigraphy of the Red Glacier Formation (Middle Jurassic) near Hungryman Creek, Cook Inlet basin, Alaska

USGS Publications Warehouse

LePain, D.L.; Stanley, Richard G.; Helmold, K.P.

2016-01-01

Geochemical data suggest the source of oil in upper Cook Inlet fields is Middle Jurassic organic-rich shales in the Tuxedni Group (Magoon and Anders, 1992; Lillis and Stanley, 2011; LePain and others, 2012, 2013). Of the six formations in the group (Detterman, 1963), the basal Red Glacier Formation is the only unit that includes fine-grained rocks in outcrop that appear to be organic-rich (fig. 3-1). In an effort to better understand the stratigraphy and source-rock potential of the Red Glacier Formation, the Alaska Division of Geological & Geophysical Surveys, in collaboration with the Alaska Division of Oil and Gas and the U.S. Geological Survey, has been investigating the unit in outcrop between Tuxedni Bay and the type section at Lateral and Red glaciers (Stanley and others, 2013; LePain and Stanley, 2015; Helmold and others, 2016 [this volume]). Fieldwork in 2015 focused on a southeast-trending ridge south of Hungryman Creek, where the lower 60–70 percent of the formation (400–500 m) is exposed and accessible, except for the near-vertical faces of three segments near the southeast end of the ridge (figs. 3-2 and 3-3). Three stratigraphic sections were measured along the ridge to document facies and depositional environments (figs. 3-3 and 3-4). Steep terrain precluded study of the upper part of the formation exposed east of the ridge. This report includes a preliminary summary of findings from the 2015 field season.

Petroleum systems of Zhu III depression in Pearl River Mouth Basin, South China Sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weilin, Zhu; Li Mingbi; Wu Peikang

Zhu III depression is located in the west part of Pearl River Mouth Basin, and covers an area of 11,000 sq km. Until now more than twenty wells have been drilled in the depression and its surrounding area, and all oil-gas fields and oil-gas discoveries are concentrated inside the depression. Integrated study indicates that there are two petroleum systems in Zhu III depression. One is Wenchang - Zhuhai, Zhujiang oil system which is mainly distributed in Wenchang B sag in the southwest part of the depression. Its source rock, the Wenchang formation is mainly composed of dark mudstone of lacustrinemore » facies, with thicknesses up to more than 1000 m. Its reservoir includes tidal sandstone of transitional facies of Zhuhai formation and neritic sandstone of the lower part of Zhujiang formation. Through bounding faults and margin coarse sediment zone, oil generated from the Wenchang formation migrated into overlying sandstone of Zhuhai formation, which was overlaid by mudstone beds of bay facies of Zhuhai formation or neritic facies of Zhujiang formation, and formed oil accumulations. The other system is Enping - Zhuhai gas system, distributed in Wenchang A sag in the northeast part of the depression, whose source rock in the Enping formation deposited in the contracting stage of the lake, dominated by swamp coal measure in lithology and terrestrial plant clastics in kerogen components. The gas generated from Enping formation directly migrated into overlying tidal sandstone of Zhuhai formation and formed gas accumulations. Therefore, exploration in Wenchang A sag in the northeast part of the depression is for gas accumulations, and oil accumulations in Wenchang B sag in the southwest part of the depression, while oil-gas mixed accumulations are likely to be found in the transitional area of two systems.« less

Chemical variations in Yellowknife Bay formation sedimentary rocks analyzed by ChemCam on board the Curiosity rover on Mars

USGS Publications Warehouse

Mangold, Nicolas; Forni, Olivier; Dromart, G.; Stack, K.M.; Wiens, Roger C.; Gasnault, Olivier; Sumner, Dawn Y.; Nachon, Marion; Meslin, Pierre-Yves; Anderson, Ryan B.; Barraclough, Bruce; Bell, J.F.; Berger, G.; Blaney, D.L.; Bridges, J.C.; Calef, F.; Clark, Brian R.; Clegg, Samuel M.; Cousin, Agnes; Edgar, L.; Edgett, Kenneth S.; Ehlmann, B.L.; Fabre, Cecile; Fisk, M.; Grotzinger, John P.; Gupta, S.C.; Herkenhoff, Kenneth E.; Hurowitz, J.A.; Johnson, J. R.; Kah, Linda C.; Lanza, Nina L.; Lasue, Jeremie; Le Mouélic, S.; Lewin, Eric; Malin, Michael; McLennan, Scott M.; Maurice, S.; Melikechi, Noureddine; Mezzacappa, Alissa; Milliken, Ralph E.; Newsome, H.L.; Ollila, A.; Rowland, Scott K.; Sautter, Violaine; Schmidt, M.E.; Schroder, S.; D'Uston, C.; Vaniman, Dave; Williams, R.A.

2015-01-01

The Yellowknife Bay formation represents a ~5 m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the Curiosity rover in Gale crater, Mars. Previous works have mainly focused on the mudstones that were drilled by the rover at two locations. The present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures. Results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column. Though the chemistry of the sediments does not vary much in the lower part of the stratigraphy, the variations in alkali elements indicate variations in the source material and/or physical sorting, as shown by the identification of alkali feldspars. The sandstones contain similar relative proportions of hydrogen to the mudstones below, suggesting the presence of hydrous minerals that may have contributed to their cementation. Slight variations in magnesium correlate with changes in textures suggesting that diagenesis through cementation and dissolution modified the initial rock composition and texture simultaneously. The upper part of the stratigraphy (~1 m thick) displays rocks with different compositions suggesting a strong change in the depositional system. The presence of float rocks with similar compositions found along the rover traverse suggests that some of these outcrops extend further away in the nearby hummocky plains.

Anorogenic nature of magmatism in the Northern Baikal volcanic belt: Evidence from geochemical, geochronological (U-Pb), and isotopic (Pb, Nd) data

USGS Publications Warehouse

Neymark, L.A.; Larin, A.M.; Nemchin, A.A.; Ovchinnikova, G.V.; Rytsk, E. Yu

1998-01-01

The Northern Baikal volcanic belt has an age of 1.82-1.87 Ga and extends along the boundary between the Siberian Platform and the Baikal foldbelt. The volcanic belt is composed of volcanics of the Akitkan Group and granitic rocks of the Irel and Primorsk complexes. The geochemistry of the rocks points to the intraplate anorogenic nature of the belt. U-Pb zircon dating of the Chuya granitoids revealed that they are older (2020-2060 Ma) than the Northern Baikal volcanic belt and, thus, cannot be regarded as its component. Data on the Pb isotopic system of feldspars from the granitoids confirm the contemporaneity of all volcanic rocks of the belt except the volcanics of the upper portion of the Akitkan Group (Chaya Formation). Our data suggest its possibly younger (???1.3 Ga) age. The isotopic Nd and Pb compositions of the acid volcanic rocks provide evidence of the heterogeneity of their crustal protoliths. The volcanics of the Malaya Kosa Formation have ??Nd(T) = -6.1, ??2 = 9.36, and were most probably produced with the participation of the U-depleted lower continental crust of Archean age. Other rocks of the complex show ??Nd(T) from -0.1 to -2.4, ??2 = 9.78, and could have been formed by the recycling of the juvenile crust. The depletion of the Malaya Kosa volcanics in most LILEs and HFSEs compared with other acid igneous rocks of the belt possibly reflects compositional differences between the Late Archean and Early Proterozoic crustal sources. The basaltic rocks of the Malaya Kosa Formation (??Nd varies from -4.6 to -5.4) were produced by either the melting of the enriched lithospheric mantle or the contamination of derivatives of the depleted mantle by Early Archean lower crustal rocks, which are not exposed within the area. Copyright ?? 1998 by MAEe Cyrillic signK Hay??a/Interperiodica Publishing.

Provenance and sedimentary environments of the Proterozoic São Roque Group, SE-Brazil: Contributions from petrography, geochemistry and Sm-Nd isotopic systematics of metasedimentary rocks

NASA Astrophysics Data System (ADS)

Henrique-Pinto, R.; Janasi, V. A.; Tassinari, C. C. G.; Carvalho, B. B.; Cioffi, C. R.; Stríkis, N. M.

2015-11-01

The Proterozoic metasedimentary sequences exposed in the São Roque Domain (Apiaí Terrane, Ribeira Belt, southeast Brazil) consist of metasandstones and meta-felspathic wackes with some volcanic layers of within-plate geochemical signature (Boturuna Formation), a passive margin turbidite sequence of metawackes and metamudstones (Piragibu Formation), and volcano-sedimentary sequences with MORB-like basalts (Serra do Itaberaba Group; Pirapora do Bom Jesus Formation). A combination of zircon provenance studies in metasandstones, whole-rock geochemistry and Sm-Nd isotopic systematics in metamudstones was used to understand the provenance and tectonic significance of these sequences, and their implications to the evolution of the Precambrian crust in the region. Whole-rock geochemistry of metamudstones, dominantly from the Piragibu Formation, points to largely granitic sources (as indicated for instance by LREE-rich moderately fractionated REE patterns and subtle negative Eu anomalies) with some mafic contribution (responding for higher contents of Fe2O3, MgO, V, and Cr) and were subject to moderate weathering (CIA - 51 to 85). Sm-Nd isotope data show three main peaks of Nd TDM ages at ca. 1.9, 2.1 and 2.4 Ga; the younger ages define an upper limit for the deposition of the unit, and reflect greater contributions from sources younger than the >2.1 Ga basement. The coincident age peaks of Nd TDM and U-Pb detrital zircons at 2.1-2.2 Ga and 2.4-2.5 Ga, combined with the possible presence of a small amount of zircons derived from mafic (gabbroid) sources with the same ages, as indicated by a parallel LA-ICPMS U-Pb dating study in metapsammites, are suggestive that these were major periods of crustal growth in the sources involving not only crust recycling but also some juvenile addition. A derivation from similar older Proterozoic sources deposited in a passive margin basin is consistent with the main sedimentary sequences in the São Roque Domain being broadly coeval and in part laterally continuous. The coincident age, Sm-Nd isotope signature and geographic proximity make the exposures of basement orthogneisses in the Apiaí Terrane candidates for source material to the São Roque Domain. Additional sources with younger Nd TDM could be juvenile 2.2 Ga basement from the southern portion of the São Francisco Craton and its marginal belts (e.g., Mineiro Belt and Juiz de Fora Complex).

Simulation and Characterization of Methane Hydrate Formation

NASA Astrophysics Data System (ADS)

Dhakal, S.; Gupta, I.

2017-12-01

The ever rising global energy demand dictates human endeavor to explore and exploit new and innovative energy sources. As conventional oil and gas reserves deplete, we are constantly looking for newer sources for sustainable energy. Gas hydrates have long been discussed as the next big energy resource to the earth. Its global occurrence and vast quantity of natural gas stored is one of the main reasons for such interest in its study and exploration. Gas hydrates are solid crystalline substances with trapped molecules of gas inside cage-like crystals of water molecules. Gases such as methane, ethane, propane and carbon dioxide can form hydrates but in natural state, methane hydrates are the most common. Subsurface geological conditions with high pressure and low temperature favor the formation and stability of gas hydrates. While the occurrence and potential of gas hydrates as energy source has long been studied, there are still gaps in knowledge, especially in the quantitative research of gas hydrate formation and reservoir characterization. This study is focused on exploring and understanding the geological setting in which gas hydrates are formed and the subsequent changes in rock characteristics as they are deposited. It involves the numerical simulation of methane gas flow through fault to form hydrates. The models are representative of the subsurface geologic setting of Gulf of Mexico with a fault through layers of shale and sandstone. Hydrate formation simulated is of thermogenic origin. The simulations are conducted using TOUGH+HYDRATE, a numerical code developed at the Lawrence Berkley National Laboratory for modeling multiphase flow through porous medium. Simulation results predict that as the gas hydrates form in the pores of the model, the porosity, permeability and other rock properties are altered. Preliminary simulation results have shown that hydrates begin to form in the fault zone and gradually in the sandstone layers. The increase in hydrate saturation is followed by decrease in the porosity and permeability of the reservoir rock. Sensitivities on flow rates of gas and water are simulated, using different reservoir properties, fault angles and grid sizes to study the properties of hydrate formation and accumulation in the subsurface.

Earth’s first stable continents did not form by subduction

NASA Astrophysics Data System (ADS)

Johnson, Tim E.; Brown, Michael; Gardiner, Nicholas J.; Kirkland, Christopher L.; Smithies, R. Hugh

2017-02-01

The geodynamic environment in which Earth’s first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have ‘arc-like’ signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today’s. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG ‘parents’, and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents—coupled with the high geothermal gradients—is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.

Earth's first stable continents did not form by subduction.

PubMed

Johnson, Tim E; Brown, Michael; Gardiner, Nicholas J; Kirkland, Christopher L; Smithies, R Hugh

2017-03-09

The geodynamic environment in which Earth's first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have 'arc-like' signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today's. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG 'parents', and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents-coupled with the high geothermal gradients-is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.

Chabazite and dolomite formation in a dolocrete profile: An example of a complex alkaline paragenesis in Lanzarote, Canary Islands

NASA Astrophysics Data System (ADS)

Alonso-Zarza, Ana M.; Bustamante, Leticia; Huerta, Pedro; Rodríguez-Berriguete, Álvaro; Huertas, María José

2016-05-01

This paper studies the weathering and soil formation processes operating on detrital sediments containing alkaline volcanic rock fragments of the Mirador del Río dolocrete profile. The profile consists of a lower horizon of removilised weathered basalts, an intermediate red sandy mudstones horizon with irregular carbonate layers and a topmost horizon of amalgamated carbonate layers with root traces. Formation occurred in arid to semiarid climates, giving place to a complex mineralogical association, including Mg-carbonates and chabazite, rarely described in cal/dolocretes profiles. Initial vadose weathering processes occurred in the basalts and in directly overlying detrital sediments, producing (Stage 1) red-smectites and dolomicrite. Dominant phreatic (Stage 2) conditions allowed precipitation of coarse-zoned dolomite and chabazite filling porosities. In Stages 3 and 4, mostly pedogenic, biogenic processes played an important role in dolomite and calcite accumulation in the profile. Overall evolution of the profile and its mineralogical association involved initial processes dominated by alteration of host rock, to provide silica and Mg-rich alkaline waters, suitable for chabazite and dolomite formation, without a previous carbonate phase. Dolomite formed both abiogenically and biogenically, but without a previous carbonate precursor and in the absence of evaporites. Dominance of calcite towards the profile top is the result of Mg/Ca decrease in the interstitial meteoric waters due to decreased supply of Mg from weathering, and increased supply of Ca in aeolian dust. Meteoric origin of the water is confirmed by C and O isotope values, which also indicate lack of deep sourced CO2. The dolocrete studied and its complex mineral association reveal the complex interactions that occur at surface during weathering and pedogenesis of basalt-sourced rocks.

Depositional environments, provenance and paleoclimatic implications of Ordovician siliciclastic rocks of the Thango Formation, Spiti Valley, Tethys Himalaya, northern India

NASA Astrophysics Data System (ADS)

Rashid, Shaik A.; Ganai, Javid A.

2018-05-01

Recently published findings indicate that the Ordovician period has been much more dynamic than previously anticipated thus making this period significant in geological time. The Ordovician of India can best be studied in the Spiti region because the Spiti basin records the complete uninterrupted history of excellent marine sedimentary rocks starting from Cambrian to Paleogene which were deposited along the northern margin of India. Due to these reasons the geochemical data on the Ordovician rocks from the Spiti region is uncommon. The present geochemical study on the Ordovician Thango Formation (Sanugba Group) is mainly aimed to understand the provenance and the paleoclimatic conditions. The sandstones are the dominant lithology of the Thango Formation with intercalations of minor amount of shales. Detailed petrographic and sedimentological analysis of these rocks suggest that three major depositional environments, viz., fluvial, transitional and marine prevailed in the basin representing transgressive and regressive phases. The major and trace element ratios such as SiO2/Al2O3, K2O/Na2O and La-Th- Sc discrimination diagram suggest that these rocks were deposited in passive margin tectonic settings. Various geochemical discriminants and elemental ratios such as K2O/Na2O, Al2O3/TiO2, La/Sc, Th/Sc, Cr/Th, Zr/Sc, (Gd/Yb)N and pronounced negative Eu anomalies indicate the rocks to be the product of weathering of post-Archean granites. The striking similarities of the multi-elemental spider diagrams of the studied sediments and the Himalayan granitoids indicate that sediments are sourced from the Proterozoic orogenic belts of the Himalayan region. Chemical index of alteration (CIA) values of the studied sediments (55-72) suggest that the source rocks underwent low to moderate degree of chemical weathering. The span of the CIA values (55-72) recorded in the sediments from the Spiti region may have resulted from varying degrees of weathering conditions in the source area. This, in turn, reflects variable climatic conditions prevailing during the Ordovician period, which is consistent with the global studies. The high CIA values observed by numerous studies on siliciclastic sediments may imply warm paleoclimate attributed to an increase in atmospheric carbon dioxide and/or methane levels inducing an acidic weathering environment and enhanced silicate weathering. While the low CIA values indicates prevalence of arid-glacial conditions where negligible chemical alteration is possible. This study documents the noteworthy events like fluctuating (rise and fall) atmospheric CO2 and sea levels during the Ordovician period, a conclusion which is consistent with the other such studies on the Phanerozoic glaciation (or mass extinction) events on Gondwana supercontinent.

Clastic dikes of Heart Mountain fault breccia, northwestern Wyoming, and their significance

USGS Publications Warehouse

Pierce, W.G.

1979-01-01

Structural features in northwestern Wyoming indicate that the Heart Mountain fault movement was an extremely rapid, cataclysmic event that created a large volume of carbonate fault breccia derived entirely from the lower part of the upper plate. After fault movement had ceased, much of the carbonate fault breccia, here called calcibreccia, lay loose on the resulting surface of tectonic denudation. Before this unconsolidated calcibreccia could be removed by erosion, it was buried beneath a cover of Tertiary volcanic rocks: the Wapiti Formation, composed of volcanic breccia, poorly sorted volcanic breccia mudflows, and lava flows, and clearly shown in many places by inter lensing and intermixing of the calcibreccia with basal volcanic rocks. As the weight of volcanic overburden increased, the unstable water-saturated calcibreccia became mobile and semifluid and was injected upward as dikes into the overlying volcanic rocks and to a lesser extent into rocks of the upper plate. In some places the lowermost part of the volcanic overburden appears to have flowed with the calcibreccia to form dike like bodies of mixed volcanic rock and calcibreccia. One calcibreccia dike even contains carbonized wood, presumably incorporated into unconsolidated calcibreccia on the surface of tectonic denudation and covered by volcanic rocks before moving upward with the dike. Angular xenoliths of Precambrian rocks, enclosed in another calcibreccia dike and in an adjoining dikelike mass of volcanic rock as well, are believed to have been torn from the walls of a vent and incorporated into the basal part of the Wapiti Formation overlying the clastic carbonate rock on the fault surface. Subsequently, some of these xenoliths were incorporated into the calcibreccia during the process of dike intrusion. Throughout the Heart Mountain fault area, the basal part of the upper-plate blocks or masses are brecciated, irrespective of the size of the blocks, more intensely at the base and in places extending upward for several tens of meters. North of Republic Mountain a small 25-m-high upper-plate mass, brecciated to some degree throughout, apparently moved some distance along the Heart Mountain fault as brecciated rock. Calcibreccia dikes intrude upward from the underlying 2 m of fault breccia into the lower part of the mass and also from its top into the overlying volcanic rocks; an earthquake-related mechanism most likely accounts for the observed features of this deformed body. Calcibreccia dikes are more common within the bedding-plane phase of the Heart Mountain fault but also occur in its transgressive and former land-surface phases. Evidence that the Wapiti Formation almost immediately buried loose, unconsolidated fault breccia that was the source of the dike rock strongly suggests a rapid volcanic deposition over the area in which clastic dikes occur, which is at least 75 km long. Clastic dikes were injected into both the upper-plate and the volcanic rocks at about the same time, after movement on the Heart Mouuntain fault had ceased, and therefore do not indicate a fluid-flotation mechanism for the Heart Mountain fault. The difference between contacts of the clastic dikes with both indurated and unconsolidated country rock is useful in field mapping at localities where it is difficult to distinguish between volcanic rocks of the Cathedral Cliffs and Lamar River Formations, and the Wapiti Formation. Thus, calcibreccia dikes in the Cathedral Cliffs and Lamar River Formations show a sharp contact because the country rock solidified prior to fault movement, whereas calcibreccia dikes in the Wapiti Formation in many instances show a transitional or semifluid contact because the country rock was still unconsolidated or semifluid at the time of dike injection.

Age and speciation of iodine in groundwater and mudstones of the Horonobe area, Hokkaido, Japan: Implications for the origin and migration of iodine during basin evolution

NASA Astrophysics Data System (ADS)

Togo, Yoko S.; Takahashi, Yoshio; Amano, Yuki; Matsuzaki, Hiroyuki; Suzuki, Yohey; Terada, Yasuko; Muramatsu, Yasuyuki; Ito, Kazumasa; Iwatsuki, Teruki

2016-10-01

This paper reports the concentration, speciation and isotope ratio (129I/127I) of iodine from both groundwater and host rocks in the Horonobe area, northern Hokkaido, Japan, to clarify the origin and migration of iodine in sedimentary rocks. Cretaceous to Quaternary sedimentary rocks deposited nearly horizontally in Tenpoku Basin and in the Horonobe area were uplifted above sea level during active tectonics to form folds and faults in the Quaternary. Samples were collected from the Pliocene Koetoi and late Miocene Wakkanai formations (Fms), which include diatomaceous and siliceous mudstones. The iodine concentration in groundwater, up to 270 μmol/L, is significantly higher than that of seawater, with the iodine enrichment factor relative to seawater reaching 800-1500. The iodine concentration in the rocks decreases from the Koetoi to Wakkanai Fms, suggesting that iodine was released into the water from the rocks of deeper formations. The iodine concentration in the rocks is sufficiently high for forming iodine-rich groundwater as found in this area. X-ray absorption near edge structure (XANES) analysis shows that iodine exists as organic iodine and iodide (I-) in host rocks, whereas it exists mainly as I- in groundwater. The isotope ratio is nearly constant for iodine in the groundwater, at [0.11-0.23] × 10-12, and it is higher for iodine in rocks, at [0.29-1.1] × 10-12, giving iodine ages of 42-60 Ma and 7-38 Ma, respectively. Some iodine in groundwater must have originated from Paleogene and even late Cretaceous Fms, which are also considered as possible sources of oil and gas, in view of the old iodine ages of the groundwater. The iodine ages of the rocks are older than the depositional ages, implying that the rocks adsorbed some iodine from groundwater, which was sourced from greater depths. The iodine concentration in groundwater decreases with decreasing chlorine concentration due to mixing of iodine-rich connate water and meteoric water. A likely scenario is that iodine-rich brine formed during the long-term basin evolution from the Cretaceous to Quaternary and that this brine was diluted by mixing with meteoric water during uplifting and denudation of the area.

What is shale gas and why is it important?

EIA Publications

2012-01-01

Shale gas refers to natural gas that is trapped within shale formations. Shales are fine-grained sedimentary rocks that can be rich sources of petroleum and natural gas. Over the past decade, the combination of horizontal drilling and hydraulic fracturing has allowed access to large volumes of shale gas that were previously uneconomical to produce. The production of natural gas from shale formations has rejuvenated the natural gas industry in the United States.

Mrar formation of western Libya - evolution of an early Carboniferous delta system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitbread, T.; Kelling, G.

1982-08-01

The Lower Carboniferous Mrar Formation is exposed extensively along the southern margin of the Ghadames basin in northwest Libya. The basal part of the Mrar forms the cap rock and possible hydrocarbon source for many of the producing reservoirs in the underlying Tahara sandstones. Furthermore, the Mrar itself is known to contain significant gas shows southwest of the outcrop, associated with some oil potential. The Mrar formation was deposited in a deltaic environment which developed on the northern part of the stable Saharan platform. The history of the Mrar formation's deposition is discussed. (JMT)

Assessment of Undiscovered Technically Recoverable Oil and Gas Resources of the Bakken Formation, Williston Basin, Montana and North Dakota, 2008

USGS Publications Warehouse

Pollastro, R.M.; Roberts, L.N.R.; Cook, T.A.; Lewan, M.D.

2008-01-01

The U.S. Geological Survey (USGS) has completed an assessment of the undiscovered oil and associated gas resources of the Upper Devonian to Lower Mississippian Bakken Formation in the U.S. portion of the Williston Basin of Montana and North Dakota and within the Williston Basin Province. The assessment is based on geologic elements of a total petroleum system (TPS), which include (1) source-rock distribution, thickness, organic richness, maturation, petroleum generation, and migration; (2) reservoir-rock type (conventional or continuous), distribution, and quality; and (3) character of traps and time of formation with respect to petroleum generation and migration. Framework studies in stratigraphy and structural geology and modeling of petroleum geochemistry, combined with historical exploration and production analyses, were used to estimate the undiscovered, technically recoverable oil resource of the Bakken Formation. Using this framework, the USGS defined a Bakken-Lodgepole TPS and seven assessment units (AU) within the system. For the Bakken Formation, the undiscovered oil and associated gas resources were quantitatively estimated for six of these AUs.

Petrogenesis of meta-volcanic rocks from the Maimón Formation (Dominican Republic): Geochemical record of the nascent Greater Antilles paleo-arc

NASA Astrophysics Data System (ADS)

Torró, Lisard; Proenza, Joaquín A.; Marchesi, Claudio; Garcia-Casco, Antonio; Lewis, John F.

2017-05-01

Metamorphosed basalts, basaltic andesites, andesites and plagiorhyolites of the Early Cretaceous, probably pre-Albian, Maimón Formation, located in the Cordillera Central of the Dominican Republic, are some of the earliest products of the Greater Antilles arc magmatism. In this article, new whole-rock element and Nd-Pb radiogenic isotope data are used to give new insights into the petrogenesis of the Maimón meta-volcanic rocks and constrain the early evolution of the Greater Antilles paleo-arc system. Three different groups of mafic volcanic rocks are recognized on the basis of their immobile element contents. Group 1 comprises basalts with compositions similar to low-Ti island arc tholeiites (IAT), which are depleted in light rare earth elements (LREE) and resemble the forearc basalts (FAB) and transitional FAB-boninitic basalts of the Izu-Bonin-Mariana forearc. Group 2 rocks have boninite-like compositions relatively rich in Cr and poor in TiO2. Group 3 comprises low-Ti island arc tholeiitic basalts with near-flat chondrite-normalized REE patterns. Plagiorhyolites and rare andesites present near-flat to subtly LREE-depleted chondrite normalized patterns typical of tholeiitic affinity. Nd and Pb isotopic ratios of plagiorhyolites, which are similar to those of Groups 1 and 3 basalts, support that these felsic lavas formed by anatexis of the arc lower crust. Geochemical modelling points that the parental basic magmas of the Maimón meta-volcanic rocks formed by hydrous melting of a heterogeneous spinel-facies mantle source, similar to depleted MORB mantle (DMM) or depleted DMM (D-DMM), fluxed by fluids from subducted oceanic crust and Atlantic Cretaceous pelagic sediments. Variations of subduction-sensitive element concentrations and ratios from Group 1 to the younger rocks of Groups 2 and 3 generally match the geochemical progression from FAB-like to boninite and IAT lavas described in subduction-initiation ophiolites. Group 1 basalts likely formed at magmatic stages transitional between FAB and first-island arc magmatism, whereas Group 2 boninitic lavas resulted from focused flux melting and higher degrees of melt extraction in a more mature stage of subduction. Group 3 basalts probably represent magmatism taking place immediately before the establishment of a steady-state subduction regime. The relatively high extents of flux melting and slab input recorded in the Maimón lavas support a scenario of hot subduction beneath the nascent Greater Antilles paleo-arc. Paleotectonic reconstructions and the markedly depleted, though heterogeneous character of the mantle source, indicate the rise of shallow asthenosphere which had sourced mid-ocean ridge basalts (MORB) and/or back-arc basin basalts (BABB) in the proto-Caribbean domain prior to the inception of SW-dipping subduction. Relative to the neighbouring Aptian-Albian Los Ranchos Formation, we suggest that Maimón volcanic rocks extruded more proximal to the vertical projection of the subducting proto-Caribbean spreading ridge.

Estimation of subsurface formation temperature in the Tarim Basin, northwest China: implications for hydrocarbon generation and preservation

NASA Astrophysics Data System (ADS)

Liu, Shaowen; Lei, Xiao; Feng, Changge; Hao, Chunyan

2016-07-01

Subsurface formation temperature in the Tarim Basin, northwest China, is vital for assessment of hydrocarbon generation and preservation, and of geothermal energy potential. However, it has not previously been well understood, due to poor data coverage and a lack of highly accurate temperature data. Here, we combined recently acquired steady-state temperature logging data with drill stem test temperature data and measured rock thermal properties, to investigate the geothermal regime and estimate the subsurface formation temperature at depth in the range of 1000-5000 m, together with temperatures at the lower boundary of each of four major Lower Paleozoic marine source rocks buried in this basin. Results show that heat flow of the Tarim Basin ranges between 26.2 and 66.1 mW/m2, with a mean of 42.5 ± 7.6 mW/m2; the geothermal gradient at depth of 3000 m varies from 14.9 to 30.2 °C/km, with a mean of 20.7 ± 2.9 °C/km. Formation temperature estimated at the depth of 1000 m is between 29 and 41 °C, with a mean of 35 °C, while 63-100 °C is for the temperature at the depth of 3000 m with a mean of 82 °C. Temperature at 5000 m ranges from 97 to 160 °C, with a mean of 129 °C. Generally spatial patterns of the subsurface formation temperature at depth are basically similar, characterized by higher temperatures in the uplift areas and lower temperatures in the sags, which indicates the influence of basement structure and lateral variations in thermal properties on the geotemperature field. Using temperature to identify the oil window in the source rocks, most of the uplifted areas in the basin are under favorable condition for oil generation and/or preservation, whereas the sags with thick sediments are favorable for gas generation and/or preservation. We conclude that relatively low present-day geothermal regime and large burial depth of the source rocks in the Tarim Basin are favorable for hydrocarbon generation and preservation. In addition, it is found that the oil and gas fields discovered in the Tarim Basin are usually associated with relatively high-temperature anomalies, and the upward migration and accumulation of hot geofluids along faults as conduit from below could explain this coincidence. Accordingly, this thermal anomaly could be indicative of hydrocarbon exploration targets in the basin.

Uranium migration and favourable sites of potential radioelement concentrations in Gabal Umm Hammad area, Central Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Youssef, Mohamed A. S.; Sabra, Mohamed Elsadek M.; Abdeldayem, Abdelaziz L.; Masoud, Alaa A.; Mansour, Salah A.

2017-12-01

Airborne gamma-ray spectrometric data, covering Gabal Umm Hammad area, near Quseir City, in the Eastern Desert of Egypt, has been utilized to identify the uranium migration path, and U, Th and K-favorability indices. The following of the uranium migration technique enabled estimation of the amount of migrated uranium, in and out of the rock units. Investigation of the Taref Formation, Nakhil Formation, Tarawan Formation and Dawi Formation shows large negative amount of uranium migration, indicating that uranium leaching is outward from the geologic body toward surrounding rock units. Moreover, calculation of the U, Th and K-favorability indices has been carried out for the various rock units to locate the rocks having the highest radioelement potentialities. The rock units that possess relatively major probability of uranium potentiality include Mu‧tiq Group, weakly deformed granitic rocks, and Trachyte plugs and sheets. Meanwhile, the rock units with major potential of Th-index are Taref Formation, Quseir Formation and Dawi Formation. The rock units with major potential of K-index are Dokhan volcanic and Mu‧tiq group.

3D pore-type digital rock modeling of natural gas hydrate for permafrost and numerical simulation of electrical properties

NASA Astrophysics Data System (ADS)

Dong, Huaimin; Sun, Jianmeng; Lin, Zhenzhou; Fang, Hui; Li, Yafen; Cui, Likai; Yan, Weichao

2018-02-01

Natural gas hydrate is being considered as an alternative energy source for sustainable development and has become a focus of research throughout the world. In this paper, based on CT scanning images of hydrate reservoir rocks, combined with the microscopic distribution of hydrate, a diffusion limited aggregation (DLA) model was used to construct 3D hydrate digital rocks of different distribution types, and the finite-element method was used to simulate their electrical characteristics in order to study the influence of different hydrate distribution types, hydrate saturation and formation of water salinity on electrical properties. The results show that the hydrate digital rocks constructed using the DLA model can be used to characterize the microscopic distribution of different types of hydrates. Under the same conditions, the resistivity of the adhesive hydrate digital rock is higher than the cemented and scattered type digital rocks, and the resistivity of the scattered hydrate digital rock is the smallest among the three types. Besides, the difference in the resistivity of the different types of hydrate digital rocks increases with an increase in hydrate saturation, especially when the saturation is larger than 55%, and the rate of increase of each of the hydrate types is quite different. Similarly, the resistivity of the three hydrate types decreases with an increase in the formation of water salinity. The single distribution hydrate digital rock constructed, combined with the law of microscopic distribution and influence of saturation on the electrical properties, can effectively improve the accuracy of logging identification of hydrate reservoirs and is of great significance for the estimation of hydrate reserves.

Generation of Hydrogen and Methane during Experimental Low-Temperature Reaction of Ultramafic Rocks with Water

NASA Astrophysics Data System (ADS)

McCollom, Thomas M.; Donaldson, Christopher

2016-06-01

Serpentinization of ultramafic rocks is widely recognized as a source of molecular hydrogen (H2) and methane (CH4) to support microbial activity, but the extent and rates of formation of these compounds in low-temperature, near-surface environments are poorly understood. Laboratory experiments were conducted to examine the production of H2 and CH4 during low-temperature reaction of water with ultramafic rocks and minerals. Experiments were performed by heating olivine or harzburgite with aqueous solutions at 90°C for up to 213 days in glass bottles sealed with butyl rubber stoppers. Although H2 and CH4 increased steadily throughout the experiments, the levels were very similar to those found in mineral-free controls, indicating that the rubber stoppers were the predominant source of these compounds. Levels of H2 above background were observed only during the first few days of reaction of harzburgite when CO2 was added to the headspace, with no detectable production of H2 or CH4 above background during further heating of the harzburgite or in experiments with other mineral reactants. Consequently, our results indicate that production of H2 and CH4 during low-temperature alteration of ultramafic rocks may be much more limited than some recent experimental studies have suggested. We also found no evidence to support a recent report suggesting that spinels in ultramafic rocks may stimulate H2 production. While secondary silicates were observed to precipitate during the experiments, formation of these deposits was dominated by Si released by dissolution of the glass bottles, and reaction of the primary silicate minerals appeared to be very limited. While use of glass bottles and rubber stoppers has become commonplace in experiments intended to study processes that occur during serpentinization of ultramafic rocks at low temperatures, the high levels of H2, CH4, and SiO2 released during heating indicate that these reactor materials are unsuitable for this purpose.

Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane

NASA Astrophysics Data System (ADS)

Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan

2017-05-01

Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

U.S.A. National Surface Rock Density Map - Part 2

NASA Astrophysics Data System (ADS)

Winester, D.

2016-12-01

A map of surface rock densities over the USA has been developed by the NOAA-National Geodetic Survey (NGS) as part of its Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Program. GRAV-D is part of an international effort to generate a North American gravimetric geoid for use as the vertical datum reference surface. As a part of modeling process, it is necessary to eliminate from the observed gravity data the topographic and density effects of all masses above the geoid. However, the long-standing tradition in geoid modeling, which is to use an average rock density (e.g. 2.67 g/cm3), does not adequately represent the variety of lithologies in the USA. The U.S. Geological Survey has assembled a downloadable set of surface geologic formation maps (typically 1:100,000 to 1:500, 000 scale in NAD27) in GIS format. The lithologies were assigned densities typical of their rock type (Part 1) and these variety of densities were then rasterized and averaged over one arc-minute areas. All were then transformed into WGS84 datum. Thin layers of alluvium and some water bodies (interpreted to be less than 40 m thick) have been ignored in deference to underlying rocks. Deep alluvial basins have not been removed, since they represent significant fraction of local mass. The initial assumption for modeling densities will be that the surface rock densities extend down to the geoid. If this results in poor modeling, variable lithologies with depth can be attempted. Initial modeling will use elevations from the SRTM DEM. A map of CONUS densities is presented (denser lithologies are shown brighter). While a visual map at this scale does show detailed features, digital versions are available upon request. Also presented are some pitfalls of using source GIS maps digitized from variable reference sources, including the infamous `state line faults.'

Northwest Africa 8535 and Northwest Africa 10463: New Insights into the Angrite Parent Body

NASA Technical Reports Server (NTRS)

Santos, A. R.; Agee, C. B.; Shearer, C. K.; McCubbin, F. M.

2016-01-01

The angrite meteorites are valuable samples of igneous rocks formed early in Solar System history (approx.4.56 Ga, summarized in [1]). This small meteorite group (approx.24 individually named specimens) consists of rocks with somewhat exotic mineral compositions (e.g., high Ca olivine, Al-Ti-bearing diopside-hedenbergite, calcium silico-phosphates), resulting in exotic bulk rock compositions. These mineral assemblages remain fairly consistent among angrite samples, which suggests they formed due to similar processes from a single mantle source. There is still debate over the formation process for these rocks (see summary in [1]), and analysis of additional angrite samples may help to address this debate. Toward this end, we have begun to study two new angrites, Northwest Africa 8535, a dunite, and Northwest Africa 10463, a basaltic angrite.

A detrital zircon provenance study of the Lower Carboniferous sequences in the East Fife section of the Midland Valley of Scotland

NASA Astrophysics Data System (ADS)

Murchie, Sean; Robinson, Ruth, ,, Dr; Lancaster, Penelope, ,, Dr

2014-05-01

Detrital zircons from the Lower Carboniferous clastic rocks of the Midland Valley of Scotland have been dated using U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to determine which source areas contributed sediment to the basin during its development, and to investigate whether provenance changed during deposition of these units. Specific provenance detection using U/Pb dating of zircons has never been attempted in these rocks, and there are uncertainties remaining about the regional paleogeographic setting for the Midland Valley. Four samples from the Dinantian Strathclyde Group have been analysed, and the units are locally known as the Fife Ness, Anstruther, Pittenweem, Sandy Craig, and Pathhead formations. The formations are composed of shallow marine, deltaic, fluvial and floodplain deposits and these predominantly siliciclastic sedimentary rocks are interbedded with thin fossiliferous carbonate bands. The samples are quartz arenitic, sub-arkosic and lithic arkosic medium-grained sandstones, predominantly from a fluvial origin. The British Geological Survey developed a lithostratigraphy which is the most used framework for the Strathclyde Group (Browne et al., 1997), but a different biostratigraphical framework based on palynology has been proposed by Owens et al. (2005). In addition to identifying provenance, the zircon age populations for each formation are compared to test which stratigraphic framework is correct. More broadly, the provenance data provides a way to improve the regional palaeogeographic setting for the Midland Valley. Zircon ages in the Strathclyde Group are dominated by Late Mesoproterozoic to Late Palaeoproterozoic (0.9 - 2.0 Ga) and Early Palaeozoic (350 - 450 Ma) ages which reflect Caledonide (Laurentian-Baltica margin including Scotland, Scandinavia, Greenland, Newfoundland), Grampian and internal Midland Valley source areas. Notable peaks occur at 400 Ma, 1.0 --1.1 Ga, 1.3 Ga, 1.6 - 1.7 Ga, and 2.7 Ga, and the Proterozoic age peaks are consistent with a Dalradian source. Although the age spectra for each formation are broadly similar, the proportions of age populations differ and age peaks present in the Anstruther Formation are absent in other formations. For instance, the Anstruther Formation has a significantly larger proportion of Archaean-aged zircons compared to the Pittenweem Formation, and contains a 1.3 Ga peak which is absent in the other formations. This suggests that source areas evolved throughout the deposition of the Strathclyde Group. The dominance of Mesoproterozoic and Palaeoproterozoic ages relative to Palaeozoic ages contrasts to similar ages units in the Pennine Basin and offshore North Sea, where the latter dominate the age spectra (Hallsworth et al., 2000; Morton et al., 2001). This may reflect the proximity of the Dalradian terrane and organisation of river systems draining into the Fife section of the Midland Valley during the Dinantian. References: Browne, M.A. et al. (1997). A lithostratigraphical framework for the Carboniferous rocks of the Midland Valley of Scotland. BGS Technical Report WA/96/29 Owens, B. et al. (2005). Reappraisal of the Mississippian palynostratigraphy of the East Fife coast, Scotland, United Kingdom. Palynology, 29, 23-47 Hallsworth et al (2000). Carboniferous sand provenance in the Pennine Basin. Sedimentary Geology, 137, 137-145 Morton et al (2001). Zircon age and heavy mineral constraints on provenance of North Sea Carboniferous sandstones. Marine and petroleum geology, 18, 319-337

Petroleum geology and resources of the Nepa-Botuoba High, Angara-Lena Terrace, and Cis-Patom Foredeep, southeastern Siberian Craton, Russia

USGS Publications Warehouse

Ulmishek, Gregory F.

2001-01-01

Three structural provinces of this report, the Nepa-Botuoba High, the Angara-Lena Terrace, and the Cis-Patom Foredeep, occupy the southeastern part of the Siberian craton northwest of the Baikal-Patom folded region (fig. 1). The provinces are similar in many aspects of their history of development, stratigraphic composition, and petroleum geology characteristics. The sedimentary cover of the provinces overlies the Archean?Lower Proterozoic basement of the Siberian craton. Over most of the area of the provinces, the basement is covered by Vendian (uppermost Proterozoic, 650?570 Ma) clastic and carbonate rocks. Unlike the case in the more northwestern areas of the craton, older Riphean sedimentary rocks here are largely absent and they appear in the stratigraphic sequence only in parts of the Cis-Patom Foredeep province. Most of the overlying sedimentary section consists of Cambrian and Ordovician carbonate and clastic rocks, and it includes a thick Lower Cambrian salt-bearing formation. Younger rocks are thin and are present only in marginal areas. 1 A single total petroleum system (TPS) embraces all three provinces. The TPS is unique in two aspects: (1) its rich hydro-carbon reserves are derived from Precambrian source rocks and (2) preservation of oil and gas fields is extremely long owing to the presence of the Lower Cambrian undeformed salt seal. Discovered reserves of the TPS are about 2 billion barrels of oil and more than 30 trillion cubic feet of gas. The stratigraphic distribution of oil and gas reserves is narrow; all fields are in Vendian to lowermost Cambrian clastic and carbonate reservoirs that occur below Lower Cambrian salt. Both structural and stratigraphic traps are known. Source rocks are absent in the sedimentary cover of the provinces, with the possible exception of a narrow zone on the margin of the Cis-Patom Foredeep province. Source rocks are interpreted here to be Riphean and Vendian organic-rich shales of the Baikal-Patom folded region. These rocks presently are deformed and metamorphosed, but they generated oil and gas before the deformation occurred in Late Silurian and Devonian time. Generated hydrocarbons migrated updip onto the craton margin. The time of migration and formation of fields is constrained by the deposition of Lower Cambrian salt and by the Late Silurian or Devonian metamorphism of source rocks. This time frame indicates that the TPS is one of the oldest petroleum systems in the world. All three provinces are exploration frontiers, and available geologic data are limited; therefore, only one assessment unit has been identified. The largest undiscovered hydrocarbon resources are expected to be in Vendian clastic reservoirs in both structural and stratigraphic traps of the Nepa-Botuoba High province. The petroleum potential of Vendian?lowermost Cambrian carbonate reservoirs is smaller. Nevertheless, these reservoirs may contain significant resources. Gas is expected to dominate over oil in the resource base.

Uranium favorability of tertiary rocks in the Badger Flats, Elkhorn Thrust Area, Park and Teller Counties, Colorado

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, P.; Mickle, D.G.

1976-10-01

Uranium potential of Tertiary rocks in the Badger Flats--Elkhorn Thrust area of central Colorado is closely related to a widespread late Eocene erosion surface. Most uranium deposits in the area are in the Eocene Echo Park Alluvium and Oligocene Tallahassee Creek Conglomerate, which were deposited in paleodrainage channels on or above this surface. Arkosic detritus within the channels and overlying tuffaceous sedimentary rocks of the Antero and Florissant Formations of Oligocene age and silicic tuffs within the volcanic units provide abundant sources of uranium that could be concentrated in the channels where carbonaceous debris facilitates a reducing environment. Anomalous soil,more » water, and stream-sediment samples near the Elkhorn Thrust and in Antero basin overlie buried channels or are offset from them along structural trends; therefore, uranium-bearing ground water may have moved upward from buried uranium deposits along faults. The area covered by rocks younger than the late Eocene erosion surface, specifically the trends of mapped or inferred paleochannels filled with Echo Park Alluvium and Tallahassee Creek Conglomerate, and the Antero Formation are favorable for the occurrence of uranium deposits.« less

Petrogenesis of incipient charnockite in the Ikalamavony sub-domain, south-central Madagascar: New insights from phase equilibrium modeling

NASA Astrophysics Data System (ADS)

Endo, Takahiro; Tsunogae, Toshiaki; Santosh, M.; Shaji, E.; Rambeloson, Roger A.

2017-06-01

Incipient charnockites representing granulite formation on a mesoscopic scale occur in the Ambodin Ifandana area of Ikalamavony sub-domain in south-central Madagascar. Here we report new petrological data from these rocks, and discuss the process of granulite formation on the basis of petrography, mineral equilibrium modeling, and fluid inclusion studies. The incipient charnockites occur as brownish patches, lenses, and layers characterized by an assemblage of biotite + orthopyroxene + K-feldspar + plagioclase + quartz + magnetite + ilmenite within host orthopyroxene-free biotite gneiss with an assemblage of biotite + K-feldspar + plagioclase + quartz + magnetite + ilmenite. Lenses and layers of calc-silicate rock (clinopyroxene + garnet + plagioclase + quartz + titanite + calcite) are typically associated with the charnockite. Coarse-grained charnockite occurs along the contact between the layered charnockite and calc-silicate rock. The application of mineral equilibrium modeling on the mineral assemblages in charnockite and biotite gneiss employing the NCKFMASHTO system as well as fluid inclusion study on coarse-grained charnockite defines a P-T range of 8.5-10.5 kbar and 880-900 °C, which is nearly consistent with the inferred P-T condition of the Ikalamavony sub-domain (8.0-10.5 kbar and 820-880 °C). The result of T versus H2O activity (a(H2O)) modeling demonstrates that orthopyroxene-bearing assemblage in charnockite is stable under relatively low a(H2O) condition of 0.42-0.43, which is consistent with the popular models of incipient-charnockite formation related to the lowering of water activity and stabilization of orthopyroxene through dehydration of biotite. The occurrence of calc-silicate rocks adjacent to the charnockite suggests that the CO2-bearing fluid that caused dehydration and incipient-charnockite formation might have been derived through decarbonation of calc-silicate rocks during the initial stage of decompression slightly after the peak metamorphism. The calc-silicate rocks might have also behaved as a cap rock that trapped CO2 infiltrated from an external source. 'CO2-rich fluid ponds' formed beneath calc-silicate layers could have enhanced dehydration of biotite to orthopyroxene, and produced layers of coarse-grained charnockite adjacent to calc-silicate layers.

Uranium-lead isotope systematics of Mars inferred from the basaltic shergottite QUE 94201

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaffney, A M; Borg, L E; Connelly, J N

2006-12-22

Uranium-lead ratios (commonly represented as {sup 238}U/{sup 204}Pb = {mu}) calculated for the sources of martian basalts preserve a record of petrogenetic processes that operated during early planetary differentiation and formation of martian geochemical reservoirs. To better define the range of {mu} values represented by the source regions of martian basalts, we completed U-Pb elemental and isotopic analyses on whole rock, mineral and leachate fractions from the martian meteorite Queen Alexandra Range 94201 (QUE 94201). The whole rock and silicate mineral fractions have unradiogenic Pb isotopic compositions that define a narrow range ({sup 206}Pb/{sup 204}Pb = 11.16-11.61). In contrast, themore » Pb isotopic compositions of weak HCl leachates are more variable and radiogenic. The intersection of the QUE 94201 data array with terrestrial Pb in {sup 206}Pb/{sup 204}Pb-{sup 207}Pb/{sup 204}Pb-{sup 208}Pb/{sup 204}Pb compositional space is consistent with varying amounts of terrestrial contamination in these fractions. We calculate that only 1-7% contamination is present in the purified silicate mineral and whole rock fractions, whereas the HCl leachates contain up to 86% terrestrial contamination. Despite the contamination, we are able to use the U-Pb data to determine the initial {sup 206}Pb/{sup 204}Pb of QUE 94201 (11.086 {+-} 0.008) and calculate the {mu} value of the QUE 94201 mantle source to be 1.823 {+-} 0.008. This is the lowest {mu} value calculated for any martian basalt source, and, when compared to the highest values determined for martian basalt sources, indicates that {mu} values in martian source reservoirs vary by at least 100%. The range of source {mu} values further indicates that the {mu} value of bulk silicate Mars is approximately three. The amount of variation in the {mu} values of the mantle sources ({mu} {approx} 2-4) is greater than can be explained by igneous processes involving silicate phases alone. We suggest the possibility that a small amount of sulfide crystallization may generate large extents of U-Pb fractionation during formation of the mantle sources of martian basalts.« less

Detrital-zircon fission-track geochronology of the Lower Cenozoic sediments, NW Himalayan foreland basin: Clues for exhumation and denudation of the Himalaya during the India-Asia collision

NASA Astrophysics Data System (ADS)

Jain, A.; Lal, N.; Suelmani, B.; Awasthi, A. K.; Singh, S.; Kumar, R.

2007-12-01

Detrital-zircon fission-track geochronology of the synorogenically-deposited Subathu-Dagshai-Kasauli-Lower Siwalik Formations of the Sub-Himalayan Lower Cenozoic foreland basin reflects progressive effects of the Himalayan tectonometamorphic events on the Proterozoic-Paleozoic source rock as a consequence of the India-Asia collision. The oldest transgressive marine Subathu Formation (57.0-41.5 Ma) contains a very dominant 302.4 ± 21.9 Ma old detrital zircon FT suite with a few determinable 520.0 Ma grains. This old suite was derived by mild erosion of the Zircon Partially Annealed Zone (ZPAZ) of 240-180 oC, which affected the Himalayan Proterozoic basement and its Tethyan sedimentary cover as a consequence of first imprint of the collision. In addition, 50.0 Ma old detrital zircons in this formation were derived possibly from the Indus Tsangpo Suture Zone and the Trans-Himalayan Ladakh Batholith. Sudden source rock changes and unroofing are manifested in the overlying fluvial Dagshai (~30-20 Ma) and Kasauli (20-13 Ma) molassic sediments, which are characterised by dominant 30.0 and 25.0 Ma old youngest zircon FT peaks, respectively. A distinct unconformity spanning for about 10 Myr gets established between the Subathu-Dagshai formations on the basis of detrital- zircon FT ages. Molassic sedimentation since ~30 Ma coincides with the depletion of detritus from the suture zone, and the bulk derivation from the main Higher Himalayan source rock, which has undergone sequentially the UHP-HP-amphibolite facies metamorphism (53-40 Ma) in the extreme north and widespread Eo- and Neo-Himalayan tectonothermal events in the middle. Strength of the Pre-Himalayan Peaks (PHP) >50 Ma in these younger sediments gradually decreases with the intensification of the Himalayan thermal events till the end of the Kasauli sedimentation. Widespread Eo- and Neo-Himalayan metamorphic events (40.0-30.0 and 25.0-15.0 Ma) have almost remobilised the provenance and obliterated most of the evidences of the Pre-Himalayan Peaks in zircon FT ages and appear to be responsible for incoming of the Himalayan (HP) ~30.0 Ma and Young Himalayan Peaks (YHP) of ~15.0 Ma, respectively; the latter appears only between 13.0 and 11.0 Ma sedimentation of the Lower Siwalik Formation. Three distinct metamorphic events get recognised in source area of the Himalayan Metamorphic Belt. Though the Dagshai-Kasauli-Lower Siwalik sequence records uninterrupted fluvial sedimentation since 30 Ma, distinct breaks in zircon FT ages ~5.0-7.0 Myr at the beginning of each formation records pulsative exhumation of the source area in response to the collision between India and Asia.

Geologic Assessment of Undiscovered, Technically Recoverable Coalbed-Gas Resources in Cretaceous and Tertiary Rocks, North Slope and Adjacent State Waters, Alaska

USGS Publications Warehouse

Roberts, Stephen B.

2008-01-01

The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geology-based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States, focusing on the distribution, quantity, and availability of oil and natural gas resources. The USGS has completed an assessment of the undiscovered, technically recoverable coalbed-gas resources in Cretaceous and Tertiary rocks underlying the North Slope and adjacent State waters of Alaska (USGS Northern Alaska Province 5001). The province is a priority Energy Policy and Conservation Act (EPCA) province for the National Assessment because of its potential for oil and gas resources. The assessment of this province is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (stratigraphy, sedimentology, petrophysical properties), and hydrocarbon traps (trap formation and timing). In the Northern Alaska Province, the USGS used this geologic framework to define one composite coalbed gas total petroleum system and three coalbed gas assessment units within the petroleum system, and quantitatively estimated the undiscovered coalbed-gas resources within each assessment unit.

Maximum sedimentation ages and provenance of metasedimentary rocks from Tinos Island, Cycladic blueschist belt, Greece

NASA Astrophysics Data System (ADS)

Hinsken, Tim; Bröcker, Michael; Berndt, Jasper; Gärtner, Claudia

2016-10-01

U-Pb zircon ages of five metasedimentary rocks from the Lower Unit on Tinos Island (Cycladic blueschist belt, Greece) document supply of detritus from various Proterozoic, Paleozoic and Mesozoic source rocks as well as post-depositional metamorphic zircon formation. Essential features of the studied zircon populations are Late Cretaceous (70-80 Ma) maximum sedimentation ages for the lithostratigraphic succession above the lowermost dolomite marble, significant contributions from Triassic to Neoproterozoic source rocks, minor influx of detritus recording Paleoproterozoic and older provenance (1.9-2.1, 2.4-2.5 and 2.7-2.8 Ga) and a lack or paucity of zircons with Mesoproterozoic ages (1.1-1.8 Ga). In combination with biostratigraphic evidence, the new dataset indicates that Late Cretaceous or younger rocks occur on top of or very close to the basal Triassic metacarbonates, suggesting a gap in the stratigraphic record near the base of the metamorphic succession. The time frame for sediment deposition is bracketed by the youngest detrital zircon ages (70-80 Ma) and metamorphic overgrowths that are related to high-pressure/low-temperature overprinting in the Eocene. This time interval possibly indicates a significant difference to the sedimentation history of the southern Cyclades, where Late Cretaceous detrital zircons have not yet been detected.

World class Devonian potential seen in eastern Madre de Dios basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, K.E.; Wagner, J.B.; Carpenter, D.G.

The Madre de Dios basin in northern Bolivia contains thick, laterally extensive, organic-rich Upper Devonian source rocks that reached the oil-generative stage of thermal maturity after trap and seal formation. Despite these facts, less than one dozen exploration wells have been drilled in the Madre de Dios basin, and no significant reserves have been discovered. Mobil geoscientists conducted a regional geological, geophysical, and geochemical study of the Madre de Dios basin. The work reported here was designed to assess the distribution, richness, depositional environment, and thermal maturity of Devonian source rocks. It is supported by data from over 3,000 mmore » of continuous slimhole core in two of the five Mobil wells in the basin. Source potential also exists in Cretaceous, Mississippian, and Permian intervals. The results of this study have important implications for future exploration in Bolivia and Peru.« less

Observations on the geology and petroleum potential of the Cold Bay-False Pass area, Alaska Peninsula

USGS Publications Warehouse

McLean, Hugh James

1979-01-01

Upper Jurassic strata in the Black Hills area consist mainly of fossiliferous, tightly cemented, gently folded sandstone deposited in a shallow marine environment. Upper Cretaceous strata on Sanak Island are strongly deformed and show structural features of broken formations similar to those observed in the Franciscan assemblage of California. Rocks exposed on Sanak Island do not crop out on the peninsular mainland or on Unimak Island, and probably make up the acoustic and economic basement of nearby Sanak basin. Tertiary sedimentary rocks on the outermost part of the Alaska Peninsula consist of Oligocene, Miocene, and lower Pliocene volcaniclastic sandstone, siltstone, and conglomerate deposited in nonmarine and very shallow marine environments. Interbedded airfall and ash-flow tuff deposits indicate active volcanism during Oligocene time. Locally, Oligocene strata are intruded by quartz diorite plutons of probable Miocene age. Reservoir properties of Mesozoic and Tertiary rocks are generally poor due to alteration of chemically unstable volcanic rock fragments. Igneous intrusions have further reduced porosity and permeability by silicification of sandstone. Organic-rich source rocks for petroleum generation are not abundant in Neogene strata. Upper Jurassic rocks in the Black Hills area have total organic carbon contents of less than 0.5 percent. Deep sediment-filled basins on the Shumagin Shelf probably contain more source rocks than onshore correlatives, but reservoir quality is not likely to be better than in onshore outcrops. The absence of well-developed folds in most Tertiary rocks, both onshore and in nearby offshore basins, reduces the possibility of hydrocarbon entrapment in anticlines.

The Nahuel Niyeu basin: A Cambrian forearc basin in the eastern North Patagonian Massif

NASA Astrophysics Data System (ADS)

Greco, Gerson A.; González, Santiago N.; Sato, Ana M.; González, Pablo D.; Basei, Miguel A. S.; Llambías, Eduardo J.; Varela, Ricardo

2017-11-01

Early Paleozoic basement of the eastern North Patagonian Massif includes low- and high grade metamorphic units, which consist mainly of alternating paraderived metamorphic rocks (mostly derived from siliciclastic protoliths) with minor intercalations of orthoderived metamorphic rocks. In this contribution we provide a better understanding of the tectonic setting in which the protoliths of these units were formed, which adds to an earlier suggested idea. With this purpose, we studied the metasedimentary rocks of the low-grade Nahuel Niyeu Formation from the Aguada Cecilio area combining mapping and petrographic analysis with U-Pb geochronology and characterization of detrital zircon grains. The results and interpretations of this unit, together with published geological, geochronological and geochemical information, allow us to interpret the sedimentary and igneous protoliths of all metamorphic units from the massif as formed in a forearc basin at ∼520-510 Ma (Nahuel Niyeu basin). It probably was elongated in the ∼NW-SE direction, and would have received detritus from a proximal source area situated toward its northeastern side (present coordinates). The basin might be related to an extensional tectonic regime. Most likely source rocks were: (1) 520-510 Ma, acidic volcanic rocks (an active magmatic arc), (2) ∼555->520 Ma, acidic plutonic and volcanic rocks (earlier stages of the same arc), and (3) latest Ediacaran-Terreneuvian, paraderived metamorphic rocks (country rocks of the arc). We evaluate the Nahuel Niyeu basin considering the eastern North Patagonian Massif as an autochthonous part of South America, adding to the discussion of the origin of Patagonia.

Petroleum Systems and Geologic Assessment of Oil and Gas Resources in the Wind River Basin Province, Wyoming

USGS Publications Warehouse

,

2007-01-01

The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the Wind River Basin Province which encompasses about 4.7 million acres in central Wyoming. The assessment is based on the geologic elements of each total petroleum system (TPS) defined in the province, including hydrocarbon source rocks (source-rock maturation, hydrocarbon generation, and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined three TPSs: (1) Phosphoria TPS, (2) Cretaceous-Tertiary TPS, and (3) Waltman TPS. Within these systems, 12 Assessment Units (AU) were defined and undiscovered oil and gas resources were quantitatively estimated within 10 of the 12 AUs.

Petroleum Systems and Geologic Assessment of Undiscovered Oil and Gas, Navarro and Taylor Groups, Western Gulf Province, Texas

USGS Publications Warehouse

,

2006-01-01

The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The USGS recently completed an assessment of undiscovered oil and gas potential of the Late Cretaceous Navarro and Taylor Groups in the Western Gulf Province in Texas (USGS Province 5047). The Navarro and Taylor Groups have moderate potential for undiscovered oil resources and good potential for undiscovered gas resources. This assessment is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). The USGS used this geologic framework to define one total petroleum system and five assessment units. Five assessment units were quantitatively assessed for undiscovered oil and gas resources.

Sources of Matter and Ore-Producing Fluid of the Tamunyer Gold-Sulfide Deposit (Northern Urals): Isotope Results

NASA Astrophysics Data System (ADS)

Zamyatina, D. A.; Murzin, V. V.

2018-02-01

The Tamunyer deposit is a typical example of gold-sulfide mineralization located in the lower lithologic-stratigraphic unit (S2-D1) of the Auerbach volcanic-plutonic belt. The latter comprises island-arc andesitic volcano-sediments, volcanics, and comagmatic intrusive formations. Carbonates have demonstrated intermediate values of δ13C between marine limestone and mantle. The quartz δ18O is in the range of 15.3-17.2‰. The δ34S of sulfides from the beresitized volcano-sedimentary rocks and ores varies widely from -7.5 to 12‰. The calculated isotope compositions of H2O, CO2, and H2S of the ore-bearing fluid imply two major sources of matter contributing to ore genesis: local rocks and foreign fluid. The ore-bearing fluid was formed by interaction and isotope equilibration between a deep magmatic fluid and marine carbonates (W/R 1), with the contribution of sulfur from the volcano-sedimentary rocks.

National Assessment of Oil and Gas Project: Geologic Assessment of Undiscovered Oil and Gas Resources of the Eastern Great Basin Province, Nevada, Utah, Idaho, and Arizona

USGS Publications Warehouse

,

2007-01-01

Introduction The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the Eastern Great Basin Province of eastern Nevada, western Utah, southeastern Idaho, and northwestern Arizona. This assessment is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). The USGS used this geologic framework to define one total petroleum system and three assessment units. All three assessment units were quantitatively assessed for undiscovered oil and gas resources.

Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation

PubMed Central

Carlson, Richard W.; Borg, Lars E.; Gaffney, Amy M.; Boyet, Maud

2014-01-01

New Rb-Sr, 146,147Sm-142,143Nd and Lu-Hf isotopic analyses of Mg-suite lunar crustal rocks 67667, 76335, 77215 and 78238, including an internal isochron for norite 77215, were undertaken to better define the time and duration of lunar crust formation and the history of the source materials of the Mg-suite. Isochron ages determined in this study for 77215 are: Rb-Sr=4450±270 Ma, 147Sm-143Nd=4283±23 Ma and Lu-Hf=4421±68 Ma. The data define an initial 146Sm/144Sm ratio of 0.00193±0.00092 corresponding to ages between 4348 and 4413 Ma depending on the half-life and initial abundance used for 146Sm. The initial Nd and Hf isotopic compositions of all samples indicate a source region with slight enrichment in the incompatible elements in accord with previous suggestions that the Mg-suite crustal rocks contain a component of KREEP. The Sm/Nd—142Nd/144Nd correlation shown by both ferroan anorthosite and Mg-suite rocks is coincident with the trend defined by mare and KREEP basalts, the slope of which corresponds to ages between 4.35 and 4.45 Ga. These data, along with similar ages for various early Earth differentiation events, are in accord with the model of lunar formation via giant impact into Earth at ca 4.4 Ga. PMID:25114305

Geologic history of the Neogene “Qena Lake” developed during the evolution of the Nile Valley: A sedimentological, mineralogical and geochemical approach

NASA Astrophysics Data System (ADS)

Philobbos, Emad R.; Essa, Mahmoud A.; Ismail, Mustafa M.

2015-01-01

Siliciclastic and carbonate sediments were laid down in southern Wadi Qena and around the Qena Nile bend (Middle Egypt) in a lacustrine-alluvial environment which dominated a relatively wide lake, the "Qena Lake" that interrupted the Nile course during the Neogene time. These sediments are represented mainly by the oldest dominantly lacustrine chocolate brown mudstones of the Khuzam Formation that accumulated nearer to the center of that lake (now forming a 185 m terrace above sea level), overlain by the dominantly lacustrine carbonates and marls of the Durri Formation which accumulated during semi-arid conditions, mainly nearer to the periphery of the lake (now forming 170, 180 and 185 m terraces a.s.l. in the studied sections). The water level of the "Qena Lake" reached 240 m. above sea level, as indicated by the maximum carbonate elevation reached in the region. Finally fanglomerates of the Higaza Formation with its chert and limestone conglomerates accumulated during torrential periods at higher elevations (forming 240, 300 and 400 m terraces a.s.l.). These three formations accumulated in this particular area before and during the unroofing of the basement rocks of the Eastern Desert, west of the watershed. According to the known Early Miocene initial development of the Nile Valley, beside the occurrence of similar deposits of Oligocene age along the eastern side of the basement range, the earlier known Pliocene age given for these sediments in the Qena area is here questioned. It might belong to earlier Miocene?-Pliocene times. As the basement rocks of the Eastern Desert were still covered by Cretaceous-Paleogene sedimentary rocks while the Khuzam, Durri and Higaza Formations were accumulating in the Qena Lake region, it is believed, contrary to the belief of some authors, that the basement rocks of the Eastern Desert were not the source of these sediments. The carbonate petrographic study, beside the X-ray, and the11 major oxides and 22 trace elements analyses, all point to that the mudrock sediments of the oldest Neogene Khuzam and Durri Formations of the "Qena Lake" phase were carried out and entered the area of southern Wadi Qena and around the Qena Nile bend mainly from the south. The intermediate igneous rocks of southern Egypt and northern Sudan were the main source areas. Additional contributions had possibly come from the weathering of the non-marine to brackish Cretaceous (pre-Campanian) shales of southern Egypt. Accumulation of conglomerates with mixed igneous and sedimentary clasts followed (forming 7 terraces in Wadi Qena, ranging from 240 m in the north to 140 m a.s.l. in the south), constituting the newly introduced Late Pliocene formation; El Heita Formation. These conglomerates were mainly drained from the then exposed basement rocks of the middle parts of Wadi Qena, and cut through the older Neogene sediments. Later on, after the lake became connected to the northern parts of the Nile Valley, the lake water level was lowered to 180 m a.s.l., and another lake with this lower level was formed (Isawiyya Lake). With the successive lowering of water level the younger well known Issawia, Qena, Abbassia and Dandara Formations accumulated successively; nearer to, and within, the present Nile Valley.

Detrital zircon geochronology of the Adams Argillite and Nation River Formation, east-central Alaska, U.S.A

USGS Publications Warehouse

Gehrels, G.E.; Johnsson, M.J.; Howell, D.G.

1999-01-01

The Cambrian Adams Argillite and the Devonian Nation River Formation are two sandstone-bearing units within a remarkably complete Paleozoic stratigraphic section in east-central Alaska. These strata, now foreshortened and fault-bounded, were originally contiguous with miogeoclinal strata to the east that formed as a passive-margin sequence along the northwestern margin of the North American continent. Seventy-five detrital zircon grains from the Adams Argillite and the Nation River Formation were analyzed in an effort to provide constraints on the original sources of the grains, and to generate a detrital zircon reference for miogeoclinal strata in the northern Cordillera. Thirty-five single zircon grains from a quartzite in the Adams Argillite yield dominant age clusters of 1047-1094 (n = 6), 1801-1868 (n = 10), and 2564-2687 (n = 5) Ma. Forty zircons extracted from a sandstone in the Nation River Formation yield clusters primarily of 424-434 (n = 6), 1815-1838 (n = 6), 1874-1921 (n = 7), and 2653-2771 (n = 4) Ma. The Early Proterozoic and Archean grains in both units probably originated in basement rocks in a broad region of the Canadian Shield. In contrast, the original igneous sources for mid-Protcrozoic grains in the Adams Argillite and ??? 430 Ma grains in the Nation River Formation are more difficult to identify. Possible original sources for the mid-Proterozoic grains include: (1) the Grenville Province of eastern Laurentia, (2) the Pearya terrane along the Arctic margin, and (3) mid-Proterozoic igneous rocks that may have been widespread along or outboard of the Cordilleran margin. The ??? 430 Ma grains may have originated in: (1) arc-type sources along the Cordilleran margin, (2) the Caledonian orogen, or (3) a landmass, such as Pearya, Siberia, or crustal fragments now in northern Asia, that resided outboard of the Innuitian orogen during mid-Paleozoic time. Copyright ?? 1999, SEPM (Society for Sedimentary Geology).

Stratigraphy and sediment provenance of the Karoo Supergroup in Southern Botswana using geochemical indicators

NASA Astrophysics Data System (ADS)

Diskin, Sorcha; Wendorff, Marek; Lasarwe, Reneilwe

2010-05-01

The Karoo Supergroup of Botswana unconformably overlies Archaean and Proterozoic rocks. They are however, poorly exposed being in turn overlain by up to 200m of Kalahari Beds. This Carboniferous - Jurassic succession comprises sequences of sedimentary and volcanic rocks which are spread across southern Africa. In Botswana, rock complexes have been correlated between widely spaced boreholes based on macroscopically similar appearance and similar position in the succession. In neighbouring South Africa and Namibia these rocks are well exposed and the lithostratigraphy is well constrained by the fossil record. The Karoo units of Botswana have been correlated with these more precisely defined successions on the basis of lithostratigraphy only and are unsupported by other criteria and as such are limited; especially considering the different depositional settings between Botswana and South Africa. Here we present the results of a study of the heavy whole rock geochemistry in an attempt to provide additional, chemostratigraphic criteria for the lower and middle part of the Karoo suite, the Dwyka and Ecca Groups. Analysis of 60 samples for major and trace (including REE) element composition shows a close relation between the geochemical characteristics and stratigraphy. Major elements show that the deltaic material of the Kweneng Formation and Boritse Formation was sourced from recycled continental crust. The basinal mudstone and siltstone below and above fall into an intermediate-mafic igneous field. Most samples have distinct negative europium anomalies (Eu/Eu*=0.49-1.27; av. = 0. 75) and most values are characteristic of sediments of cratonic derivation. A clear shift in (Gd/Yb)N in the basinal pro-delta shales (the Bori Formation) is generally 2.0 or greater, which is typical of an Archean signature, whereas post-Archean rocks usually have (Gd/Yb)N 1.0 - 2.0 as seen for the strata above the delta mouth bars and channels (average 1.6). In a diagram in which (La/Yb)N plotted against CeN shows a relationship between REE fractionation and provenance, the samples from the Ecca's lacustrine Kwetla Formation and Bori Formation fall into the Intermediate Igneous Provenance Field along with data from the Dwyka, whereas the deltaic Kweneng and Boritse Formation belong to the quartzose provenance field. This agrees with indicators from the major element discriminators.

Metamorphism and plutonism around the middle and south forks of the Feather River, California

USGS Publications Warehouse

Hietanen, Anna Martta

1976-01-01

The area around the Middle and South Forks of the Feather River provides information on metamorphic and igneous processes that bear on the origin of andesitic and granitic magmas in general and on the variation of their potassium content in particular. In the north, the area joins the Pulga and Bucks Lake quadrangles studied previously. Tectonically, this area is situated in the southern part of an arcuate segment of the Nevadan orogenic belt in the northwestern Sierra Nevada. The oldest rocks are metamorphosed calcalkaline island-arc-type andesite, dacite, and sodarhyolite with interbedded tuff layers (the Franklin Canyon Formation), all probably correlative with Devonian rocks in the Klamath Mountains. Younger rocks form a sequence of volcanic, volcaniclastic, and sedimentary rocks including some limestone (The Horseshoe Bend Formation), probably Permian in age. All the volcanic and sedimentary rocks were folded and recrystallized to the greenschist facies during the Nevadan (Jurassic) orogeny and were invaded by monzotonalitic magmas shortly thereafter. A second lineation and metamorphism to the epidote-amphibolite facies developed in a narrow zone around the plutons. In light of the concept of plate tectonics, it is suggested that the early (Devonian?) island-arc-type andesite, dacite, and sodarhyolite (the Franklin Canyon Formation) were derived from the mantle above a Benioff zone by partial melting of peridotite in hydrous conditions. The water was probably derived from an oceanic plate descending to the mantle. Later (Permian?) magmas were mainly basaltic; some discontinuous layers of potassium-rich rhyolite indicate a change into anhydrous conditions and a deeper level of magma generation. The plutonic magmas that invaded the metamorphic rocks at the end of the Jurassic may contain material from the mantle, the subducted oceanic lithosphere, and the downfolded metamorphic rocks. The ratio of partial melts from these three sources may have changed with time, giving rise to the diversity in composition of magmas.

The potential source of lead in the Permian Kupferschiefer bed of Europe and some selected Paleozoic mineral deposits in the Federal Republic of Germany

USGS Publications Warehouse

Wedepohl, K.H.; Delevaux, M.H.; Doe, B.R.

1978-01-01

New lead isotopic compositions have been measured for Paleozoic bedded and vein ore deposits of Europe by the high precision thermal emission (triple filament) technique. Eleven samples have been analyzed from the Upper Permian Kupferschiefer bed with representatives from Poland to England, three samples from the Middle Devonian Rammelsberg deposit and one from the Middle Devonian Meggen deposit, both of which are conformable ore lenses and are in the Federal Republic of Germany (FRG); and also two vein deposits from the FRG were analyzed, from Ramsbeck in Devonian host rocks and from Grund in Carboniferous host rocks. For Kupferschiefer bed samples from Germany, the mineralization is of variable lead isotopic composition and appears to have been derived about 250 m.y. ago from 1700 m.y. old sources, or detritus of this age, in Paleozoic sedimentary rocks. Samples from England, Holland, and Poland have different isotopic characteristics from the German samples, indicative of significantly different source material (perhaps older). The isotopic variability of the samples from the Kupferschiefer bed in Germany probably favors the lead containing waters coming from shoreward (where poor mixing is to be expected) rather than basinward (where better mixing is likely) directions. The data thus support the interpretation of the metal source already given by Wedepohl in 1964. Data on samples from Rammelsberg and Meggen tend to be slightly less radiogenic than for the Kupferschiefer, about the amount expected if the leads were all derived from the same source material but 100 to 150 m.y. apart in time. The vein galena from Ramsbeck is similar to that from Rammelsberg conformable ore lenses, both in rocks of Devonian age; vein galena from Grund in Upper Carboniferous country rocks is similar to some bedded Kupferschiefer mineralization in Permian rocks, as if the lead composition was formed at about the same time and from similar source material as the bedded deposits. Although heat has played a more significant role in the formation of some of these deposits (veins and Rammelsberg-Meggen) than in others (Kupferschiefer), there is no indication of radically different sources for the lead, all apparently coming from sedimentary source material containing Precambrian detritus. One feldspar lead sample from the Brocken-Oker Granite is not the same in isotopic composition as any of the ores analyzed. ?? 1978 Springer-Verlag.

Geology of the Cooper Ridge NE Quadrangle, Sweetwater County, Wyoming

USGS Publications Warehouse

Roehler, Henry W.

1979-01-01

The Cooper Ridge NE 7?-minute quadrangle is 18 miles southeast of Rock Springs, Wyo., on the east flank of the Rock Springs uplift. Upper Cretaceous rocks composing the Rock Springs Formation, Ericson Sandstone, Almond Formation, Lewis Shale, Fox Hills Sandstone, and Lance Formation, Paleocene rocks composing the Fort Union Formation, and Eocene rocks composing the Wasatch Formation are exposed and dip 5?-8? southeast. Outcrops are unfaulted and generally homoclinal, but a minor cross-trending fold, the Jackknife Spring anticline, plunges southeastward and interrupts the northeast strike of beds. Older rocks in the subsurface are faulted and folded, especially near the Brady oil and gas field. Coal beds are present in the Almond, Lance, and Fort Union Formations. Coal resources are estimated to be more than 762 million short tons in 16 beds more than 2.5 feet thick, under less than 3,000 ft of overburden. Nearly 166 million tons are under less than 200 ft of overburden and are recoverable by strip mining. Unknown quantities of oil and gas are present in the Cretaceous Rock Springs, Blair, and Dakota Formations, Jurassic sandstone (Entrada Sandstone of drillers), Jurassic(?) and Triassic(?) Nugget Sandstone, Permian Park City Formation, and Pennsylvanian and Permian Weber Sandstone at the Brady field, part of which is in the southeast corner of the quadrangle, and in the Dakota Sandstone at the Prenalta Corp. Bluewater 33-32 well near the northern edge of the quadrangle. Other minerals include uranium in the Almond Formation and titanium in the Rock Springs Formation.

U-Th-Pb, Rb-Sr, and Sm-Nd isotopic systematics of lunar troctolitic cumulate 76535 - Implications on the age and origin of this early lunar, deep-seated cumulate

NASA Technical Reports Server (NTRS)

Premo, Wayne R.; Tatsumoto, M.

1992-01-01

The U-Th-Pb, Rb-Sr, and Sm-Nd isotopic systematics of four lightly leached residues of pristine, high-Mg, troctolitic cumulate 76535 were analyzed in order to determine their ages and magma sources. The data indicate that the cumulate was in isotopic equilibrium with a fluid or magma characterized by a high U-238/Pb-204 (mu) value of 600 at 4.236 Ga. Two and three stage Pb evolution calculations define even greater source mu values of about 1000, assuming low lunar initial mu values between 5 and 40 prior to about 4.43 Ga. These results are similar to mu values for KREEP sources and are also consistent with values from 78235, suggesting that at least some high-Mg suite rocks were derived from magma sources with high-mu values similar to KREEP, and support that idea that these rocks postdate primary lunar differentiation and formation of ferroan anorthosites.

Geologic framework, age, and lithologic characteristics of the North Park Formation in North Park, north-central Colorado

USGS Publications Warehouse

Shroba, Ralph R.

2016-10-18

Deposits of the North Park Formation of late Oligocene and Miocene age are locally exposed at small, widely spaced outcrops along the margins of the roughly northwest-trending North Park syncline in the southern part of North Park, a large intermontane topographic basin in Jackson County in north-central Colorado. These outcrops suggest that rocks and sediments of the North Park Formation consist chiefly of poorly consolidated sand, weakly cemented sandstone, and pebbly sandstone; subordinate amounts of pebble conglomerate; minor amounts of cobbly pebble gravel, siltstone, and sandy limestone; and rare beds of cobble conglomerate and altered tuff. These deposits partly filled North Park as well as a few small nearby valleys and half grabens. In North Park, deposits of the North Park Formation probably once formed a broad and relatively thick sedimentary apron composed chiefly of alluvial slope deposits (mostly sheetwash and stream-channel alluvium) that extended, over a distance of at least 150 kilometers (km), northwestward from the Never Summer Mountains and northward from the Rabbit Ears Range across North Park and extended farther northwestward into the valley of the North Platte River slightly north of the Colorado-Wyoming border. The maximum preserved thickness of the formation in North Park is about 550 meters near the southeastern end of the North Park syncline.The deposition of the North Park Formation was coeval in part with local volcanism, extensional faulting, development of half grabens, and deposition of the Browns Park Formation and Troublesome Formation and was accompanied by post-Laramide regional epeirogenic uplift. Regional deposition of extensive eolian sand sheets and loess deposits, coeval with the deposition of the North Park Formation, suggests that semiarid climatic conditions prevailed during the deposition of the North Park Formation during the late Oligocene and Miocene.The North Park Formation locally contains a 28.1-mega-annum (Ma, million years ago) ash-flow tuff near its base at Owl Ridge and is interbedded with 29-Ma rhyodacite lava flows and volcanic breccia at Owl Mountain. The formation locally contains vertebrate fossils at least as young as Barstovian age (about 15.9–12.6 Ma) and overlies rocks as young as the White River Formation, which contains vertebrate fossils of Chadronian age (about 37–33.8 Ma) in North Park and a bed of 36.0-Ma volcanic ash in the upper part of the Laramie River valley about 30 km northeast of Walden, Colorado. Based on the ages of the vertebrate fossils, folding of the rocks and sediments in the North Park syncline may be much younger than about 16 Ma.Bedding characteristics of the North Park Formation suggest that (1) some or much of the sand, sandstone, and pebbly sandstone may have been deposited as sheetwash alluvium; (2) much of the siltstone may have been deposited as sheetwash alluvium or ephemeral pond or marsh deposits; (3) beds of sandy limestone probably were deposited as ephemeral pond or marsh deposits; and (4) altered tuff probably was deposited in ephemeral ponds or marshes. Most of the conglomerate and gravel in the North Park Formation are stream-channel deposits that were deposited by high-energy ephemeral or intermittent streams that issued from volcanic terrain rather than debris-flow deposits in relatively near-source fan deposits dominated by sediment gravity flow. Laccolithic doming, uplift, and tilting in the Never Summer Mountains near the Mount Richthofen stock, as well as the formation of volcanic edifices in the Never Summer Mountains and the Rabbit Ears Range during the late Oligocene and Miocene, significantly steepened stream gradients and greatly increased the erosive power and transport capacity of streams that transported large rock fragments and finer sediment eroded from volcanic and sedimentary sources and deposited them in the North Park Formation.Much of the material that makes up the rocks and sediments of the North Park Formation was derived from the erosion of volcanic, intrusive, and sedimentary rocks. Clasts in the North Park Formation were derived chiefly from the erosion of volcanic and intrusive igneous rocks of late Oligocene and Miocene age that range in composition from rhyolite to trachybasalt. These rocks are locally exposed along the west flank of the Never Summer Mountains, the north flank of the Rabbit Ears Range, and the east flank of the Park Range at and near Rabbit Ears Peak. The minor amount of igneous and metamorphic clasts of Proterozoic age in the North Park Formation are commonly composed of durable rock types that are resistant to both physical and chemical weathering. Many of these clasts may have been derived from the erosion of conglomerate and conglomeratic sandstone in the Coalmont Formation rather than from basement rocks currently at or near the ground surface in the Never Summer Mountains. Much of the sand and finer grained particles in the North Park Formation probably were derived from the erosion of sandstone, shale, and sandy claystone of the Coalmont Formation. Likewise, much of the abundant sand-sized quartz and feldspar in sand, sandstone, and pebbly sandstone of the North Park Formation probably was derived from the erosion of sandstone, conglomeratic sandstone, and conglomerate of the Coalmont Formation. Some of the fine sand, very fine sand, and silt in very fine grained sandstone and siltstone of the North Park Formation may be derived from the erosion of coeval eolian sand and loess in the Browns Park Formation that was transported across the Park Range by westerly or southwesterly winds.

Importance of dust storms in the diagenesis of sandstones: a case study, Entrada sandstone in the Ghost Ranch area, New Mexico, USA

NASA Astrophysics Data System (ADS)

Orhan, Hükmü

1992-04-01

The importance of dust storms on geological processes has only been studied recently. Case-hardening, desert-varnish formation, duricrust development, reddening and cementation of sediments and caliche formation, are some important geological processes related to dust storms. Dust storms can also be a major source for cements in aeolian sandstones. The Jurassic aeolian Entrada Formation in the Ghost Ranch area is composed of quartz with minor amounts of feldspar and rock fragments, and is cemented with smectite as grain coatings and calcite and kaolinite as pore fillings. Smectite shows a crinkly and honeycomb-like morphology which points to an authigenic origin. The absence of smectite as framework grains and the presence of partially dissolved grains, coated with smectite and smectite egg-shells, indicate an external source. Clay and fine silt-size particles are believed to be the major source for cements, smectite and calcite in the Entrada Formation. The common association of kaolinite with altered feldspar, and the absence of kaolinite in spots heavily cemented with calcite, lead to the conclusions that the kaolinite formation postdates carbonates and that framework feldspar grains were the source of kaolinite.

Chronostratigraphy and hydrocarbon habitat associated with the Jurassic carbonates of Abu Dhabi, United Arab Emirates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alsharahan, A.S.; Whittle, G.L.

1995-08-01

Deposition of Jurassic epeiric shelf carbonates and evaporates were controlled by epeirogenic movement and sea level fluctuations which formed an excellent combination of source rocks, reservoirs and seats in Abu Dhabi. At the end of the Triassic, a relative drop in sea level, caused by eustatic sea level lowering in conjunction with minor tectonic uplift, resulted in non-deposition or erosion. In the Toarcian, deposition of carbonates and terrigenous, clastics produced the Marrat Formation. In the mid-Aalenian, a drop in sea level eroded much of the Marrat and some of the Triassic in offshore U.A.E. The deposition of the Hamlah Formationmore » followed, under neritic, well-oxygenated conditions. The Middle Jurassic was characterized by widespread, normal marine shelf carbonates which formed the cyclic Izhara and Araej formations (reservoirs). In the Upper Jurassic, the carbonate shelf became differentiated into a broad shelf with a kerogen-rich intrashelf basin, formed in response to a eustatic rise coupled with epeirogenic downwarping and marine flooding. The intrashelf basin fill of muddy carbonate sediments constitutes the Diyab Formation and its onshore equivalent, the Dukhan Formation (source rocks). In the late Upper Jurassic, the climate became more arid and cyclic deposition of carbonates and evaporates prevailed, forming alternating peritidal anhydrite, dolomite and limestone in the Arab Formation (reservoir). Arid conditions continued into the Tithonian, fostering the extensive anhydrite of the Hith Formation (seal) in a sabkha/lagoonal setting on the shallow peritidal platform, the final regressive supratidal stage of this major depositional cycle.« less

Sea Level and Paleoenvironment Control on Late Ordovician Source Rocks, Hudson Bay Basin, Canada

NASA Astrophysics Data System (ADS)

Zhang, S.; Hefter, J.

2009-05-01

Hudson Bay Basin is one of the largest Paleozoic sedimentary basins in North America, with Southampton Island on its north margin. The lower part of the basin succession comprises approximately 180 to 300 m of Upper Ordovician strata including Bad Cache Rapids and Churchill River groups and Red Head Rapids Formation. These units mainly comprise carbonate rocks consisting of alternating fossiliferous limestone, evaporitic and reefal dolostone, and minor shale. Shale units containing extremely high TOC, and interpreted to have potential as petroleum source rocks, were found at three levels in the lower Red Head Rapids Formation on Southampton Island, and were also recognized in exploration wells from the Hudson Bay offshore area. A study of conodonts from 390 conodont-bearing samples from continuous cores and well cuttings from six exploration wells in the Hudson Bay Lowlands and offshore area (Comeault Province No. 1, Kaskattama Province No. 1, Pen Island No. 1, Walrus A-71, Polar Bear C-11 and Narwhal South O-58), and about 250 conodont-bearing samples collected from outcrops on Southampton Island allows recognition of three conodont zones in the Upper Ordovician sequence, namely (in ascendant sequence) Belodina confluens, Amorphognathus ordovicicus, and Rhipidognathus symmetricus zones. The three conodont zones suggest a cycle of sea level changes of rising, reaching the highest level, and then falling during the Late Ordovician. Three intervals of petroleum potential source rock are within the Rhipidognathus symmetricus Zone in Red Head Rapids Formation, and formed in a restricted anoxic and hypersaline condition during a period of sea level falling. This is supported by the following data: 1) The conodont Rhipidognathus symmetricus represents the shallowest Late Ordovician conodont biofacies and very shallow subtidal to intertidal and hypersaline condition. This species has the greatest richness within the three oil shale intervals to compare other parts of Red Head Rapids Formation. 2) Type I kerogen is normally formed in quiet, oxygen-deficient, shallow water environment. Rock-Eval6 data from 40 samples of the three oil shale intervals, collected from outcrops on Southampton Island, demonstrate that the proportion of Type I kerogen gradually increases in the mixed Type I-Type II kerogen from the lower to upper oil shale intervals. 3) Pristane/phytane ratio can be used as a paleoenvironment indicator. The low ratios in the three oil shale intervals range from 0.5 to 0.9 and indicate anoxic and hypersaline conditions. In addition, the presence of isorenieratene derivatives from green phototrophic sulfur bacteria (Chlorobiaceae), with highest relative concentrations in the lower oil shale intervals, points to anoxia reaching into the photic zone of the water column.

Evaluation of stress and saturation effects on seismic velocity and electrical resistivity - laboratory testing of rock samples

NASA Astrophysics Data System (ADS)

Vilhelm, Jan; Jirků, Jaroslav; Slavík, Lubomír; Bárta, Jaroslav

2016-04-01

Repository, located in a deep geological formation, is today considered the most suitable solution for disposal of spent nuclear fuel and high-level waste. The geological formations, in combination with an engineered barrier system, should ensure isolation of the waste from the environment for thousands of years. For long-term monitoring of such underground excavations special monitoring systems are developed. In our research we developed and tested monitoring system based on repeated ultrasonic time of flight measurement and electrical resistivity tomography (ERT). As a test site Bedřichov gallery in the northern Bohemia was selected. This underground gallery in granitic rock was excavated using Tunnel Boring Machine (TBM). The seismic high-frequency measurements are performed by pulse-transmission technique directly on the rock wall using one seismic source and three receivers in the distances of 1, 2 and 3 m. The ERT measurement is performed also on the rock wall using 48 electrodes. The spacing between electrodes is 20 centimeters. An analysis of relation of seismic velocity and electrical resistivity on water saturation and stress state of the granitic rock is necessary for the interpretation of both seismic monitoring and ERT. Laboratory seismic and resistivity measurements were performed. One series of experiments was based on uniaxial loading of dry and saturated granitic samples. The relation between stress state and ultrasonic wave velocities was tested separately for dry and saturated rock samples. Other experiments were focused on the relation between electrical resistivity of the rock sample and its saturation level. Rock samples with different porosities were tested. Acknowledgments: This work was partially supported by the Technology Agency of the Czech Republic, project No. TA 0302408

Generation of felsic rocks of bimodal volcanic suites from thinned and rifted continental margins: Geochemical and Nd, Sr, Pb-isotopic evidence from Haida Gwaii, British Columbia, Canada

NASA Astrophysics Data System (ADS)

Dostal, Jaroslav; Hamilton, Tark S.; Shellnutt, J. Gregory

2017-11-01

The compositionally bimodal volcanic rocks of the Eocene-Miocene Masset Formation from Queen Charlotte basin, Haida Gwaii, British Columbia, Canada, underlie an area greater than 5000 km2 where their exposed sections are up to 1.6 km thick. The suite of mafic and felsic rocks (dacites and rhyolites) that erupted closely spaced in time, in both submarine and subaerial conditions, was associated with significant crustal extension and thin continental crust ( 19-24 km thick), with volcanism persisting for 35 Ma (from 46 to 11 Ma). Predominant mafic types (mafic:felsic 2:1) are moderately enriched mid-ocean-ridge-like basalts that were derived by a partial melting of a heterogeneous spinel peridotite source. Felsic rocks are plagioclase-phyric, two pyroxene-bearing, mainly peraluminous types which have Nd, Pb and Sr isotopic compositions overlapping those of basalts including high positive ƐNd(t) values (up to >+6). The chondrite-normalized REE patterns show light REE enrichment but flat heavy REE along with a variable negative Eu anomaly. Mineralogy, major and trace elements, Nd-Sr-Pb isotopic data and model calculations using MELTS are consistent with a derivation of felsic rocks from the basalts by fractional crystallization. The intercalation of basaltic and felsic rocks suggests the existence of separate, simultaneously active plumbing and feeder systems and relatively stable magma chamber(s) to generate large volumes of differentiated felsic magmas by fractional crystallization. The Masset rocks provide an example for the generation of felsic magmas of bimodal volcanic suites during rifting along a thinned continental margin. Appendix 1b Representative analyses of minerals of the Masset Formation felsic rocks

Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydrothermal processes

NASA Astrophysics Data System (ADS)

Waite, J. Hunter; Glein, Christopher R.; Perryman, Rebecca S.; Teolis, Ben D.; Magee, Brian A.; Miller, Greg; Grimes, Jacob; Perry, Mark E.; Miller, Kelly E.; Bouquet, Alexis; Lunine, Jonathan I.; Brockwell, Tim; Bolton, Scott J.

2017-04-01

Saturn’s moon Enceladus has an ice-covered ocean; a plume of material erupts from cracks in the ice. The plume contains chemical signatures of water-rock interaction between the ocean and a rocky core. We used the Ion Neutral Mass Spectrometer onboard the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument’s open-source mode, background processes of hydrogen production in the instrument were minimized and quantified, enabling the identification of a statistically significant signal of hydrogen native to Enceladus. We find that the most plausible source of this hydrogen is ongoing hydrothermal reactions of rock containing reduced minerals and organic materials. The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium that favors the formation of methane from CO2 in Enceladus’ ocean.

Modal petrology of six soils from Apollo 16 double drive tube core 64002

NASA Technical Reports Server (NTRS)

Houck, K. J.

1982-01-01

Petrographic data form six size fractions for six samples of Apollo 16 drive tube section 64002 show source rocks similar to those of core 60009. Analysis of modal data from the 64002 core show that the upper three and lowest core soils are mature and have similar maturation histories, while the two middle soils are submature and have histories that are similar to each other but unlike those from the aforementioned soils. In all of these soils, mixing has dominated over reworking, and appears to involve two mature soils distinguished by differing source rocks and an immature, plagioclase-rich soil which is correlated with larger clasts of chalky, friable breccia. These breccias and the plagioclase-rich soil are tentatively associated with the Descartes Formation.

Dynamics of metasomatic transformation of lithospheric mantle rocks under Siberian Craton

NASA Astrophysics Data System (ADS)

Sharapov, Victor; Perepechko, Yury; Tomilenko, Anatoly; Chudnenko, Konstantin; Sorokin, Konstantin

2014-05-01

Numerical problem for one- and two-velocity hydrodynamics of heat and mass transfer in permeable zones over 'asthenospheric lenses' (with estimates for dynamics of non-isothermal metasomatosis of mantle rocks, using the approximation of flow reactor scheme) was formulated and solved based on the study of inclusion contents in minerals of metamorphic rocks of the lithosphere mantle and earth crust, estimates of thermodynamic conditions of inclusions appearance, and the results of experimental modeling of influence of hot reduced gases on rocks and minerals of xenoliths in mantle rocks under the cratons of Siberian Platform (SP): 1) the supply of fluid flows of any composition from upper mantle magma sources results in formation of zonal metasomatic columns in ultrabasic lithosphere mantle in permeable zones of deep faults; 2) when major element or petrogenetic components are supplied from magma source, depleted ultrabasic rocks of the lithosphere mantle are transformed into substrates which can be regarded as deep analogs of crust rodingites; 3) other fluid compositions cause deep calcinations and noticeable salination of metasomated substrate, or garnetization (eclogitization) of primary ultrabasic matrix develops; 4) above these zones the zone of basification appears; it is changed by the area of pyroxenitization, amphibolization, and biotitization; 5) modeling of thermo and mass exchange for two-velocity hydrodynamic problem showed that hydraulic approximation increases velocities of heat front during convective heating and decreases pressure in fluid along the flow. It was shown that grospydites, regarded earlier as eclogites, in permeable areas of lithosphere mantle, are typical zones draining upper mantle magma sources of metasomatic columns. As a result of the convective melting the polybaric magmatic sources may appear. Thus the formation of the (kimberlites?) melilitites or carbonatites is possible at the base of the lithospheric plates. It is shown that the physico - chemical conditions of the carbonation of the depleted mantle peridotites refer to the narrow interval of the possible fluid compositions. The bulk fluid content near 4 weight % with the SiO2 CaO 0.5 - 0.1 molar volumes the 1) the Si/Ca molar ratio is < 1; 2) in the C-H-O system the molar ration should be 1/2/3 - 2/1/2; 3) the pO2 variations should be -8 < lg pO2 < -11; 4) in the fluid the CO2 content is twice higher than H2O and Cl essentially prevail under F. In the system with smaller fraction of the fluid phase less increased by the major element rock components the carbonation is more intensive when the Ca content decrease. The fusions of the basic magmas are possible within the wehrlitization zones. The work is supported by RFBR grant 12-05-00625.

Methane clumped isotopes in the Songliao Basin (China): New insights into abiotic vs. biotic hydrocarbon formation

NASA Astrophysics Data System (ADS)

Shuai, Yanhua; Etiope, Giuseppe; Zhang, Shuichang; Douglas, Peter M. J.; Huang, Ling; Eiler, John M.

2018-01-01

Abiotic hydrocarbon gas, typically generated in serpentinized ultramafic rocks and crystalline shields, has important implications for the deep biosphere, petroleum systems, the carbon cycle and astrobiology. Distinguishing abiotic gas (produced by chemical reactions like Sabatier synthesis) from biotic gas (produced from degradation of organic matter or microbial activity) is sometimes challenging because their isotopic and molecular composition may overlap. Abiotic gas has been recognized in numerous locations on the Earth, although there are no confirmed instances where it is the dominant source of commercially valuable quantities in reservoir rocks. The deep hydrocarbon reservoirs of the Xujiaweizi Depression in the Songliao Basin (China) have been considered to host significant amounts of abiotic methane. Here we report methane clumped-isotope values (Δ18) and the isotopic composition of C1-C3 alkanes, CO2 and helium of five gas samples collected from those Xujiaweizi deep reservoirs. Some geochemical features of these samples resemble previously suggested identifiers of abiotic gas (13C-enriched CH4; decrease in 13C/12C ratio with increasing carbon number for the C1-C4 alkanes; abundant, apparently non-biogenic CO2; and mantle-derived helium). However, combining these constraints with new measurements of the clumped-isotope composition of methane and careful consideration of the geological context, suggests that the Xujiaweizi depression gas is dominantly, if not exclusively, thermogenic and derived from over-mature source rocks, i.e., from catagenesis of buried organic matter at high temperatures. Methane formation temperatures suggested by clumped-isotopes (167-213 °C) are lower than magmatic gas generation processes and consistent with the maturity of local source rocks. Also, there are no geological conditions (e.g., serpentinized ultramafic rocks) that may lead to high production of H2 and thus abiotic production of CH4 via CO2 reduction. We propose that the Songliao gas is representative of an atypical type of thermogenic gas that can be mistaken for abiotic gas. Such gases may be encountered more frequently in future exploration of deep or over-mature petroleum systems.

Geology and sequence stratigraphy of undiscovered oil and gas resources in conventional and continuous petroleum systems in the Upper Cretaceous Eagle Ford Group and related strata, U.S. Gulf Coast Region

USGS Publications Warehouse

Dubiel, Russell F.; Pearson, Ofori N.; Pitman, Janet K.; Pearson, Krystal M.; Kinney, Scott A.

2012-01-01

The U.S. Geological Survey (USGS) recently assessed the technically recoverable undiscovered oil and gas onshore and in State waters of the Gulf Coast region of the United States. The USGS defined three assessment units (AUs) with potential undiscovered conventional and continuous oil and gas resources in Upper Cretaceous (Cenomanian to Turonian) strata of the Eagle Ford Group and correlative rocks. The assessment is based on geologic elements of a total petroleum system, including hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and traps (formation, timing, and seals). Conventional oil and gas undiscovered resources are in updip sandstone reservoirs in the Upper Cretaceous Tuscaloosa and Woodbine Formations (or Groups) in Louisiana and Texas, respectively, whereas continuous oil and continuous gas undiscovered resources reside in the middip and downdip Upper Cretaceous Eagle Ford Shale in Texas and the Tuscaloosa marine shale in Louisiana. Conventional resources in the Tuscaloosa and Woodbine are included in the Eagle Ford Updip Sandstone Oil and Gas AU, in an area where the Eagle Ford Shale and Tuscaloosa marine shale display vitrinite reflectance (Ro) values less than 0.6%. The continuous Eagle Ford Shale Oil AU lies generally south of the conventional AU, is primarily updip of the Lower Cretaceous shelf edge, and is defined by thermal maturity values within shales of the Eagle Ford and Tuscaloosa that range from 0.6 to 1.2% Ro. Similarly, the Eagle Ford Shale Gas AU is defined downdip of the shelf edge where source rocks have Ro values greater than 1.2%. For undiscovered oil and gas resources, the USGS assessed means of: 1) 141 million barrels of oil (MMBO), 502 billion cubic feet of natural gas (BCFG), and 4 million barrels of natural gas liquids (MMBNGL) in the Eagle Ford Updip Sandstone Oil and Gas AU; 2) 853 MMBO, 1707 BCFG, and 34 MMBNGL in the Eagle Ford Shale Oil AU; and 3) 50,219 BCFG and 2009 MMBNGL in the Eagle Ford Shale Gas AU.

The Santa Cruz - Tarija Province of Central South America: Los Monos - Machareti(!) Petroleum System

USGS Publications Warehouse

Lindquist, Sandra J.

1999-01-01

The Los Monos - Machareti(!) total petroleum system is in the Santa Cruz - Tarija Province of Bolivia, Argentina and Paraguay. Province history is that of a Paleozoic, intracratonic, siliciclastic rift basin that evolved into a Miocene (Andean) foreland fold and thrust belt. Existing fields are typified by alternating reservoir and seal rocks in post-Ordovician sandstones and shales on anticlines. Thick Devonian and Silurian shale source rocks, depositionally and erosionally confined to this province, at a minimum have generated 4.1 BBOE known ultimate recoverable reserves (as of 1995, 77% gas, 15% condensate, 8% oil) into dominantly Carboniferous reservoirs with average 20% porosity and 156 md permeability. Major detachment surfaces within the source rocks contributed to the thin-skinned and laterally continuous nature of the deformation. Tertiary foreland burial adequate for significant source maturation coincided with the formation of compressional traps. Further hydrocarbon discovery in the fold and thrust belt is expected. In the foreland basin, higher thermal gradients and variable burial history - combined with the presence of unconformity and onlap wedges - create potential there for stratigraphic traps and pre-Andean, block-fault and forced-fold traps.

Geochemical Aspects of Formation of Large Oil Deposits in the Volga-Ural Sedimentary Basin

NASA Astrophysics Data System (ADS)

Plotnikova, I.; Nosova, F.; Pronin, N.; Nosova, J.; Budkevich, T.

2012-04-01

The study of the rocks domanikoid type in the territory of the Ural-Volga region has an almost century-long history, beginning with the first studies of A.D. Archangelsky in the late 20's of last century. But nevertheless the question of the source of oil that formed the industrial deposits of Volga-Ural oil and gas province (OGP), where Romashkinskoye oil field occupies a special place, remains unresolved and topical. According to the sedimentary-migration theory of origin of oil and gas, it is supposed that the primary source of hydrocarbons in this area are the deposits of domanikoid type that contain a large ammount of sapropel organic matter (OM). Semiluki (domanik) horizon of srednefranski substage of the Upper Devonian is considered to be a typical domanikoid stratum. Investigation of the OM of the rocks and oils of the sedimentary cover on the basis of chromato-mass spectrometry method allows us to study the correlations between rock and oil and to assess the location (or absence) of the sources of hydrocarbons in the Paleozoic sedimentary cover. The results of geochemical study of dispersed organic matter (DOM) of rocks from Semiluksky horizon of the Upper Devonian and of the oil from Pashiysky horizon of the Middle Devonian form the basis of this paper. The objectives of this study were the following: to determine the original organic matter of the rocks, which would indicate the conditions of sedimentation of the supposed rock-oil sources; the study of chemofossils (biomarkers) in oil from Pashiyskiy horizon; and the identification of genetic association of DOM rocks from Semiluksky horizon with this oil on the basis of the oil-DOM correlation. The study of biomarkers was carried out with the help of chromato-mass spectrometry in the Laboratory of Geochemistry of Fossil Fuels (Kazan Federal University). In this study we used several informative parameters characterizing the depositional environment, the type of source OM and its maturity: STER / PENT, hC35/hC34, GAM / HOP, S27/S28/S29 (steranes), DIA / REG, Ts / Tm, MOR / HOP, NOR / HOP, TET / TRI, C29SSR, C29BBAA, C31HSR, S30STER, TRI / PENT, TRI / HOP. Comparison in the rock-oil system was performed primarily according to the parameters indicating the depositional environment of the source rock that contains syngenetic DOM - according to the coefficients that determine lithological conditions for the formation of the supposed oil-source bed strata (DIA / REG, Ts / Tm, NOR / HOP, TRI / HOP and STER / PENT). Biomarker ratios indicate a different type of sedimentation basins. Sediments, which accumulated DOM from Semilukskiy horizon, can be characterized by low clay content, or its absence, that is consistent with the carbonate type of cut of the horizon. The bacterial material that was accumulated under reducing conditions of sedimentation appeared to be the source of syngenetic OM. Chemofossils found in oils from Pashiyskiy horizon are typical of sedimentary strata that contain clay - for clastic rocks, which in the study area are mainly represented by deposits and Eyfel Givetian layers of the Middle Devonian and lowfransk substage of the Upper Devonian. The study of correlations obtained for the different coefficients of OM and oils showed that only the relationships between Ts/Tm and DIA/REG and between NOR/HOP and TRI/HOP are characteristic of close, almost similar values of correlation both for the dispersed organic matter and for oil. In all other cases, the character of the correlation of OM is significantly different from that of oil. The differences in values and ranges of biomarker ratios as well as the character of their correlation indicates the absence of genetic connection between the oil from Pashiyskiy horizon for the dispersed organic matter from Semilukskiy horizon. This conclusion is based on the study of five biomarker parameters (DIA/REG, Ts/Tm, NOR/HOP, TRI/HOP and STER/PENT). The research results described in the article clearly indicate the need for further studies of geochemical features of the organic matter of the Paleozoic mantle rocks and the underlying sedimentary and crystalline complexes of Precambrian.

Sources of metals in the Porgera gold deposit, Papua New Guinea: Evidence from alteration, isotope, and noble metal geochemistry

NASA Astrophysics Data System (ADS)

Richards, Jeremy P.; McCulloch, Malcolm T.; Chappell, Bruce W.; Kerrich, Robert

1991-02-01

The Porgera gold deposit is spatially and temporally associated with the Late Miocene, mafic, alkalic, epizonal Porgera Intrusive Complex (PIC), located in the highlands of Papua New Guinea (PNG). The highlands region marks the site of a Tertiary age continent-island-arc collision zone, located on the northeastern edge of the Australasian craton. The PIC was emplaced within continental crust near the Lagaip Fault Zone, which represents an Oligocene suture between the craton and volcano-sedimentary rocks of the Sepik terrane. Magmatism at Porgera probably occurred in response to the Late Miocene elimination of an oceanic microplate, and subsequent Early Pliocene collision between the craton margin and an arc system located on the Bismarck Sea plate. Gold mineralization occurred within 1 Ma of the time of magmatism. Metasomatism accompanying early disseminated Au mineralization in igneous host rocks resulted in additions of K, Rb, Mn, S, and CO 2, and depletions of Fe, Mg, Ca, Na, Ba, and Sr; rare-earth and high-field-strength elements remained largely immobile. Pervasive development of illite-K-feldspar-quartz-carbonate alteration assemblages suggests alteration by mildly acidic, 200 to 350°C fluids, at high water/ rock ratios. Strontium and lead isotopic compositions of minerals from early base-metal sulphide veins associated with K-metasomatism, and later quartz-roscoelite veins carrying abundant free gold and tellurides, are remarkably uniform (e.g., 87Sr /86Sr = 0.70745 ± 0.00044 [n = 10] , 207Pb /204Pb = 15.603 ± 0.004 [n = 15] ). These compositions fall between those of unaltered igneous and sedimentary host rocks, and specifically sedimentary rocks from the Jurassic Om Formation which underlies the deposit (igneous rocks: 87Sr /86Sr ≈ 0.7035 , 207Pb /204Pb ≈ 15.560 ; Om Formation: 87Sr /86Sr |t~ 0.7153 , 207Pb /204Pb ≈ 15.636 ). It is therefore suggested that the hydrothermal fluids acquired their Sr and Pb isotopic signatures by interaction with, or direct derivation from, a plutonic root of the PIC and host sedimentary rocks of the Om Formation. It is likely that Au was also derived from one or both of these two sources. Concentrations of Au in unaltered igneous and sedimentary rocks from Porgera (≤10 ppb Au) do not indicate that either lithology represents a significantly enriched protore, although Au and platinum-group element (PGE) abundances in the igneous rocks suggest a mild primary magmatic enrichment of Au relative to the PGE (average [ Au/( Pt + Pd)] mantlenormalized = 14.0 ± 6.5 [ n = 8]). Evidence that the Porgera magmas were rich in volatiles permits speculation that Au may have been concentrated in a magmatic fluid phase, but alternative possibilities such as derivation of Au by hydrothermal leaching of solidified igneous materials or sedimentary rocks cannot be excluded at this time.

A chemical and thermodynamic model of oil generation in hydrocarbon source rocks

NASA Astrophysics Data System (ADS)

Helgeson, Harold C.; Richard, Laurent; McKenzie, William F.; Norton, Denis L.; Schmitt, Alexandra

2009-02-01

Thermodynamic calculations and Gibbs free energy minimization computer experiments strongly support the hypothesis that kerogen maturation and oil generation are inevitable consequences of oxidation/reduction disproportionation reactions caused by prograde metamorphism of hydrocarbon source rocks with increasing depth of burial.These experiments indicate that oxygen and hydrogen are conserved in the process.Accordingly, if water is stable and present in the source rock at temperatures ≳25 but ≲100 °C along a typical US Gulf Coast geotherm, immature (reduced) kerogen with a given atomic hydrogen to carbon ratio (H/C) melts incongruently with increasing temperature and depth of burial to produce a metastable equilibrium phase assemblage consisting of naphthenic/biomarker-rich crude oil, a type-II/III kerogen with an atomic hydrogen/carbon ratio (H/C) of ˜1, and water. Hence, this incongruent melting process promotes diagenetic reaction of detritus in the source rock to form authigenic mineral assemblages.However, in the water-absent region of the system CHO (which is extensive), any water initially present or subsequently entering the source rock is consumed by reaction with the most mature kerogen with the lowest H/C it encounters to form CO 2 gas and a new kerogen with higher H/C and O/C, both of which are in metastable equilibrium with one another.This hydrolytic disproportionation process progressively increases both the concentration of the solute in the aqueous phase, and the oil generation potential of the source rock; i.e., the new kerogen can then produce more crude oil.Petroleum is generated with increasing temperature and depth of burial of hydrocarbon source rocks in which water is not stable in the system CHO by a series of irreversible disproportionation reactions in which kerogens with higher (H/C)s melt incongruently to produce metastable equilibrium assemblages consisting of crude oil, CO 2 gas, and a more mature (oxidized) kerogen with a lower H/C which in turn melts incongruently with further burial to produce more crude oil, CO 2 gas, and a kerogen with a lower H/C and so forth.The petroleum generated in the process progresses from heavy naphthenic crude oils at low temperatures to mature petroleum at ˜150 °C. For example, the results of Computer Experiment 27 (see below) indicate that the overall incongruent melting reaction in the water-absent region of the system C-H-O at 150 °C and a depth of ˜4.3 km of an immature type-II/III kerogen with a bulk composition represented by C 292H 288O 12(c) to produce a mature (oxidized) kerogen represented by C 128H 68O 7(c), together with a typical crude oil with an average metastable equilibrium composition corresponding to C 8.8H 16.9 (C 8.8H 16.9(l)) and CO 2 gas (CO 2(g)) can be described by writing CHO (kerogen,H/C=0.99O/C=0.041) →1.527CHO(kerogen,H/C=0.53O/C=0.055) +10.896CH(crude oil,H/C=1.92)+0.656CO which corresponds to a disproportionation reaction in the source rock representing the sum of a series of oxidation/reduction conservation reactions. Consideration of the stoichiometries of incongruent melting reactions analogous to Reaction (A) for reactant kerogens with different (H/C)s and/or atomic oxygen to carbon ratios (O/C)s, together with crude oil compositions corresponding to Gibbs free energy minima at specified temperatures and pressures permits calculation of the volume of oil (mole of reactant organic carbon (ROC)) -1 that can be generated in, as well as the volume of oil (mol ROC) -1 which exceeds the volume of kerogen pore space produced that must be expelled from hydrocarbon source rocks as a function of temperature, pressure, and the H/C and O/C of the reactant kerogen. These volumes and the reaction coefficients (mol ROC) -1 of the product kerogen, crude oil, and CO 2 gas in the incongruent melting reaction are linear functions of the H/C and O/C of the reactant kerogen at a given temperature and pressure. The slopes of the isopleths can be computed from power functions of temperature along a typical US Gulf Coast geotherm. All of these reactions and relations are consistent with the well-known observations that (1) the relative abundance of mature kerogen increases, and that of immature kerogen decreases with increasing burial of hydrocarbon source rocks and (2) that the volume of oil generated in a given source rock increases with increasing weight percent total organic carbon (TOC) and the H/C and (to a lesser extent) the O/C of the immature kerogen. They are also compatible with preservation of biomarkers and other polymerized hydrocarbons during the incongruent melting process. It can be deduced from Reaction (A) that nearly 11 mol of crude oil are produced from one mole of the reactant kerogen (rk), which increases to ˜39.5 mol (mol rk) -1 as the carbon content and H/C of the reactant kerogen increase to that in the hydrogen-rich type-I kerogen represented by C 415H 698O 22(c). The secondary porosities created in source rocks by Reaction (A) and others like it are of the order of 75-80 vol % of the oil generated, which requires expulsion of the remainder, together with the CO 2 gas produced by the reaction. The expulsion of the CO 2 gas and excess crude oil from the hydrocarbon source rock is facilitated by their buoyancy and the fact that the pressure in the source rocks is ⩾ the fluid pressure in the adjoining formations during progressive generation of the volume of crude oil that exceeds the kerogen pore volume produced by the incongruent melting process. The expelled CO 2 gas lowers the pH of the surrounding formation waters, which promotes the development of secondary porosity and diagenetic reaction of detrital silicates to form authigenic mineral assemblages. Hence, the expulsion process facilitates initial upward migration of the oil, which is further enhanced by expansion of the oil and its reaction with H 2O at the oil-water interface to generate methane gas. Mass transfer calculations indicate that the minimal volume of crude oil expelled into these formations is comparable to, or exceeds the volume of oil produced and in proven reserves in major oil fields such as the North Sea, the Paris and Los Angeles Basins, and those in Kuwait, Saudi Arabia, and elsewhere in the Middle East. For example, taking account of the average weight percent ( W%) organic carbon in the immature kerogen (3.4 wt%) with an average H/C of ˜1.04 in the hydrocarbon source rocks in Saudi Arabia, which have an average thickness of ˜43 m, it can be shown (see below) that all of the oil (and oil equivalent of natural gas) produced and in proven reserves in Saudi Arabia (374 billion barrels of oil or ˜1.9 million barrels of oil km -2) can be accounted for by minimal expulsion from the source rocks of oil generated at ˜125 °C solely by the incongruent melting process. Computer experiments indicate that this process can also account for all the petroleum that can be, and has been generated in the world's hydrocarbon source rocks. Of the latter, as much as 75-80% may still remain in these rocks.

Acoustic reflection log in transversely isotropic formations

NASA Astrophysics Data System (ADS)

Ronquillo Jarillo, G.; Markova, I.; Markov, M.

2018-01-01

We have calculated the waveforms of sonic reflection logging for a fluid-filled borehole located in a transversely isotropic rock. Calculations have been performed for an acoustic impulse source with the characteristic frequency of tens of kilohertz that is considerably less than the frequencies of acoustic borehole imaging tools. It is assumed that the borehole axis coincides with the axis of symmetry of the transversely isotropic rock. It was shown that the reflected wave was excited most efficiently at resonant frequencies. These frequencies are close to the frequencies of oscillations of a fluid column located in an absolutely rigid hollow cylinder. We have shown that the acoustic reverberation is controlled by the acoustic impedance of the rock Z = Vphρs for fixed parameters of the borehole fluid, where Vph is the velocity of horizontally propagating P-wave; ρs is the rock density. The methods of waveform processing to determine the parameters characterizing the reflected wave have been discussed.

Potential for deep basin-centered gas accumulation in Travis Peak (Hosston) Formation, Gulf Coastal Basin

USGS Publications Warehouse

Bartberger, Charles E.; Dyman, Thaddeus S.; Condon, Steven M.

2003-01-01

The potential of Lower Cretaceous sandstones of the Travis Peak Formation in the northern Gulf Coast Basin to harbor a basin-centered gas accumulation was evaluated by examining (1) the depositional and diagenetic history and reservoir properties of Travis Peak sandstones, (2) the presence and quality of source rocks for generating gas, (3) the burial and thermal history of source rocks and time of gas generation and migration relative to tectonic development of Travis Peak traps, (4) gas and water recoveries from drill-stem and formation tests, (5) the distribution of abnormal pressures based on shut-in-pressure data, and (6) the presence or absence of gas-water contacts associated with gas accumulations in Travis Peak sandstones. The Travis Peak Formation (and correlative Hosston Formation) is a basinward-thickening wedge of terrigenous clastic sedimentary rocks that underlies the northern Gulf Coast Basin from eastern Texas across northern Louisiana to southern Mississippi. Clastic infl ux was focused in two main fl uvial-deltaic depocenters?one located in northeastern Texas and the other in southeastern Mississippi and northeastern Louisiana. Across the main hydrocarbon-productive trend in eastern Texas and northern Louisiana, the Travis Peak Formation is about 2,000 ft thick. Most Travis Peak hydrocarbon production in eastern Texas comes from drilling depths between 6,000 and 10,000 ft. Signifi cant decrease in porosity and permeability occurs through that depth interval. Above 8,000-ft drilling depth in eastern Texas, Travis Peak sandstone matrix permeabilities often are signifi cantly higher than the 0.1-millidarcy (mD) cutoff that characterizes tight-gas reservoirs. Below 8,000 ft, matrix permeability of Travis Peak sandstones is low because of pervasive quartz cementation, but abundant natural fractures impart signifi cant fracture permeability. Although pressure data within the middle and lower Travis Peak Formation are limited in eastern Texas, overpressured reservoirs caused by thermal generation of gas, typical of basin-centered gas accumulations, are not common in the Travis Peak Formation. Signifi cant overpressure was found in only one Travis Peak sandstone reservoir in 1 of 24 oil and gas fi elds examined across eastern Texas and northern Louisiana. The presence of gas-water contacts is perhaps the most defi nitive criterion indicating that a gas accumulation is conventional rather than a ?sweet spot? within a basin-centered gas accumulation. Hydrocarbon-water contacts within Travis Peak sandstone reservoirs were documented in 17 fi elds and probably occur in considerably more fi elds across the productive Travis Peak trend in eastern Texas and northern Louisiana. All known hydrocarbon-water contacts in Travis Peak reservoirs in eastern Texas, however, occur within sandstones in the upper 500 ft of the formation. Although no gas-water contacts have been reported within the lower three-fourths of the Travis Peak Formation in northeastern Texas, gas production from that interval is limited. The best available data suggest that most middle and lower Travis Peak sandstones are water bearing in northeastern Texas. Insuffi cient hydrocarbon charge relative to permeability of Travis Peak reservoirs might be responsible for lack of overpressure and basin-centered gas within the Travis Peak Formation. Shales interbedded with Travis Peak sandstones in eastern Texas are primarily oxidized fl ood-plain deposits with insuffi cient organic-carbon content to be signifi cant sources of oil and gas. The most likely source rocks for hydrocarbons in Travis Peak reservoirs are two stratigraphically lower units, the Jurassic-age Bossier Shale of the Cotton Valley Group, and laminated, lime mudstones of the Jurassic Smackover Formation. Hydrocarbon charge, therefore, might be suffi cient for development of conventional gas accumulations, but it is insuffi cient for

Petrogenesis of siliceous high-Mg series rocks as exemplified by the Early Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched mantle versus crustal contamination

NASA Astrophysics Data System (ADS)

Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii

2015-04-01

The Early Paleoproterozoic stage in the Earth's evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of mantle melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted mantle melts, and by generation from a mantle source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the rocks show no correlation between Th/Ta and La/Yb, (Nb/La)pm ratio and Th content, and eNd and (Nb/La)N ratio. At the same time, some correlation observed in the eNd-Mg# and (La/Sm)N-(Nb/La)N diagrams in combination with the presence of inherited zircons in the rocks does not allow us to discard completely the crustal contamination. Examination of Sm/Yb-La/Sm relations and the comparison with model melting curves for garnet and spinel lherzolites showed that the parental melts of the rocks were derived by 10-30% mantle melting at garnet-spinel facies transition. Two stage model can be proposed to explain such remarkable isotope-geochemical homogeneity of the mafic volcanic rocks over a large area: (1) ubiquitous emplacement of large volumes of sanukitoid melts in the lower crust of the shield at 2.7 Ga; (2) underplating of plume-derived DM melts at the crust-mantle boundary, melting of the lower crust of sanukitoid composition, and subsequent mixing of these melts with formation of SHMS melts at 2.4 Ga. A simple mixing model showed that in this case the Nd isotope composition of obtained melts remained practically unchanged at variable amounts of contaminant (up to 30%). This work was supported by the RFBR no. 14-05-00458.

Jurassic rifting at the Eurasian Tethys margin: Geochemical and geochronological constraints from granitoids of North Makran, southeastern Iran

NASA Astrophysics Data System (ADS)

Hunziker, Daniela; Burg, Jean-Pierre; Bouilhol, Pierre; von Quadt, Albrecht

2015-03-01

This study focuses on an east-west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern Dur Kan Complex, a continental slice outcropping to the north of the exposed Makran accretionary wedge in southeastern Iran. Field observations, petrographic descriptions, trace element, and isotope analyses combined with U-Pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks. Results document three magmatic episodes with different melt sources for (1) granites, (2) a diorite-trondhjemite-plagiogranite sequence, and (3) diabases and lavas. Granites, dated at 170-175 Ma, represent crystallized melt with a strong continental isotopic contribution. The diorite-trondhjemite-plagiogranite sequence is 165-153 Ma old and derives from a mantle magma source with minor continental contribution. East-west trending diabase dikes and bodies intruded the granitoids, which were eroded and then covered by Valanginian (140-133 Ma) alkaline lavas and sediments. Alkaline dikes and lavas have a mantle isotopic composition. Temporal correlation with plutonites of the Sanandaj-Sirjan Zone to the northwest defines a narrow, NW-SE striking and nearly 2000 km long belt of Jurassic intrusions. The increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling/decompression melting. Accordingly, the formation of the studied igneous rocks is related to the extension of the Iranian continental margin, which ultimately led to the formation of the Tethys-related North Makran Ophiolites.

Chemistry of surface water at a volcanic summit area, Norikura, central Japan: multivariate statistical approach.

PubMed

Anazaw, K; Ohmori, L H

2001-11-01

Many hydrochemical studies on chemical formation of shallow ground water have been reported as results of water-rock interaction, and contamination of paleo-brine or human activities, whereas the preliminary formation of precipitation source in the recharged region has not been established yet. The purpose of this research work is to clarify the geochemical process of water formation from a water source unpolluted by seawater or human activity. Norikura volcano, located in western part of central Japan provided a suitable source for this research purpose, and hence chemical compositions of water samples from the summit and the mountainside area of Norikura volcano were determined. Most samples in the summit area showed very low electrical conductivity, and lower than 12 microS/cm. On the basis of the chemical compositions, principal component analysis (PCA) and factor analysis (FA), such as kinds of multivariate statistical techniques were used to extract geochemical factors affecting hydrochemical process. As a result, three factors were extracted. The first factor showed high loading on K+, Ca2+, SO2 and SiO2, and this factor was interpreted due to influence of the chemical interaction between acidic precipitated water and rocks. The second factor showed high loading on Na+ and Cl-, and it was assumed to be an influence of seawater salt. The third factor showed loading on NO3-, and it was interpreted to be caused by biochemical effect of vegetation. The proportionate contributions of these factors to the evolution of water chemical composition were found to be 45%, 20%, and 10% for factors 1, 2 and 3, respectively. The same exploration at the mountainside of Norikura volcano revealed that the chemical variances of the non-geothermal water samples were highly influenced by water-rock interactions. The silicate dissolution showed 45% contribution for all chemical variances, while the adsorption of Ca2+ and Mg2+ by precipitation or ion exchange showed 20% contribution. The seawater salt influence or biochemical effect was statistically negligible in this area. The clear differentiation of geochemical process on water formation was found between the summit area and the mountainside area.

Sulfur, carbon, hydrogen, and oxygen isotope geochemistry of the Idaho cobalt belt

USGS Publications Warehouse

Johnson, Craig A.; Bookstrom, Arthur A.; Slack, John F.

2012-01-01

Cobalt-copper ± gold deposits of the Idaho cobalt belt, including the deposits of the Blackbird district, have been analyzed for their sulfur, carbon, hydrogen, and oxygen isotope compositions to improve the understanding of ore formation. Previous genetic hypotheses have ranged widely, linking the ores to the sedimentary or diagenetic history of the host Mesoproterozoic sedimentary rocks, to Mesoproterozoic or Cretaceous magmatism, or to metamorphic shearing. The δ34S values are nearly uniform throughout the Blackbird dis- trict, with a mean value for cobaltite (CoAsS, the main cobalt mineral) of 8.0 ± 0.4‰ (n = 19). The data suggest that (1) sulfur was derived at least partly from sedimentary sources, (2) redox reactions involving sulfur were probably unimportant for ore deposition, and (3) the sulfur was probably transported to sites of ore for- mation as H2S. Hydrogen and oxygen isotope compositions of the ore-forming fluid, which are calculated from analyses of biotite-rich wall rocks and tourmaline, do not uniquely identify the source of the fluid; plausible sources include formation waters, metamorphic waters, and mixtures of magmatic and isotopically heavy meteoric waters. The calculated compositions are a poor match for the modified seawaters that form vol- canogenic massive sulfide (VMS) deposits. Carbon and oxygen isotope compositions of siderite, a mineral that is widespread, although sparse, at Blackbird, suggest formation from mixtures of sedimentary organic carbon and magmatic-metamorphic carbon. The isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin. Several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper, so its significance for the ore-forming event is uncertain. From the stable isotope perspective, the mineral deposits of the Idaho cobalt belt contrast with typical VMS and sedimentary exhalative deposits. They show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes, although the isotopic evidence for magmatic components is relatively weak.

Petrography and stratigraphy of productive beds in the Morgan Formation, Church Buttes Unit No. 19, southwest Wyoming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Picard, M.D.

1977-01-01

The combination stratigraphic and structural traps in the Morgan Formation of Pennsylvanian age of Church Buttes, Butcher Knife, and Bruff that produce gas and condensate are directly related to folding of the Church Buttes Arch in SW. Wyoming and NE. Utah. Present knowledge indicates that the Morgan gas and condensate originated in source beds in the lower Morgan formation west of the present Church Buttes Arch and were trapped mainly in porous barrier deposits in the Morgan. Folding of the Church Buttes Arch liberated these accumulations and they migrated updip in their present traps. This work summarizes the sedimentary petrographymore » of the productive beds in the Morgan Formation at the Church Buttes Unit No. 19 (SEC. 8, T 16 N, R 112 W), Uinta County, Wyoming. The stratigraphy is outlined for the whole region and the productive interval at Church Buttes is correlated with other rock units. Nearly all of the rocks studied are dolomite, which is difficult to interpret because of pronounced diagenesis. 33 references.« less

Post-emplacement history of the Zambales Ophiolite Complex: Insights from petrography, geochronology and geochemistry of Neogene clastic rocks

NASA Astrophysics Data System (ADS)

Dimalanta, C. B.; Salapare, R. C.; Faustino-Eslava, D. V.; Ramos, N. T.; Queaño, K. L.; Yumul, G. P.; Yang, T. F.

2015-05-01

The Zambales Ophiolite Complex in Luzon, Philippines is made up of two blocks with differing geochemical signatures and ages - the Middle Jurassic to Early Cretaceous Acoje Block-San Antonio Massif that is of island arc tholeiite composition and the Eocene Coto Block-Cabangan Massif which is of transitional mid-ocean ridge basalt-island arc tholeiite affinity. These ophiolitic bodies are overlain by Miocene to Pliocene sedimentary units whose petrochemistry are reported here for the first time. Varying degrees of influences from ophiolitic detritus and from arc volcanic materials, as shown by petrography and indicator elements including Cr, Co and Ni, are observed in these sedimentary formations from north to south and from the oldest to the youngest. The Early to Middle Miocene Cabaluan Formation, whose outcrops are found to overlie only the Acoje Block, registers a more dominant ophiolitic signature as compared to the Late Miocene to Pliocene Santa Cruz Formation. The Santa Cruz Formation is generally characterized by fewer ophiolitic clasts and higher amounts of felsic components. Additionally, within this formation itself, a pronounced compositional change is observed relative to its spatial distribution. From the south to the north, an increase in ophiolitic components and a relative decrease in felsic signature is noted in units of the Santa Cruz Formation. It is therefore inferred that changes in the petrochemistry of rocks from the older Cabaluan to the younger Santa Cruz sedimentary formations record a decline in the influx of ophiolitic detritus or, conversely, the introduction of more diverse sediment sources as the deposition progressed. Detrital zircon U-Pb ages from the Santa Cruz Formation, with peaks at 46.73 ± 0.94 and 5.78 ± 0.13 Ma, reflects this change in provenance from the unroofing of an Early Eocene oceanic crust to fresh contributions from an active volcanic arc during the Late Miocene. The contrast in compositions of the southern and northern Santa Cruz Formation also indicates a closer proximity of the southern units to the source of these non-ophiolitic sources, which most likely corresponds to the Pliocene volcanoes of the West Luzon Arc.

Mechanical study of the Chartreuse Fold-and-Thrust Belt: relationships between fluids overpressure and decollement within the Toarcian source-rock

NASA Astrophysics Data System (ADS)

Berthelon, Josselin; Sassi, William; Burov, Evgueni

2016-04-01

Many source-rocks are shale and constitute potential detachment levels in Fold-and-Thrust Belts (FTB): the toarcian Schistes-Cartons in the French Chartreuse FTB for example. Their mechanical properties can change during their burial and thermal maturation, as for example when large amount of hydrocarbon fluids are generated. A structural reconstruction of the Chartreuse FTB geo-history places the Toarcian Formation as the major decollement horizon. In this work, a mechanical analysis integrating the fluids overpressuring development is proposed to discuss on the validity of the structural interpretation. At first, an analogue of the Chartreuse Toarcian Fm, the albanian Posidonia Schist, is documented as it can provide insights on its initial properties and composition of its kerogen content. Laboratory characterisation documents the vertical evolution of the mineralogical, geochemical and mechanical parameters of this potential decollement layer. These physical parameters (i.e. Total Organic Carbon (TOC), porosity/permeability relationship, friction coefficient) are used to address overpressure buildup in the frontal part of the Chartreuse FTB with TEMISFlow Arctem Basin modelling approach (Faille et al, 2014) and the structural emplacement of the Chartreuse thrust units using the FLAMAR thermo-mechanical model (Burov et al, 2014). The hydro-mechanical modeling results highlight the calendar, distribution and magnitude of the overpressure that developed within the source-rock in the footwall of a simple fault-bend fold structure localized in the frontal part of the Chartreuse FTB. Several key geological conditions are required to create an overpressure able to fracture the shale-rocks and induce a significant change in the rheological behaviour: high TOC, low permeability, favourable structural evolution. These models highlight the importance of modeling the impact of a diffuse natural hydraulic fracturing to explain fluids propagation toward the foreland within the decollement layer. In turn, with the FLAMAR geo-mechanical models it is shown that for key mechanical parameters within the Chartreuse mechanical stratigraphy (such as friction coefficient, cohesion and viscosity properties), the mechanical boundary conditions to activate, localize and propagate shear thrust in the toarcian source-rock can be found to discuss on the hydro-mechanics of the structural evolution: the very weak mechanical properties that must be attributed to the source-rock to promote the formation of a decollement tend to justify the hypothesis of high fluids pressures in it. In FLAMAR, the evolution of the toarcian source-rock mechanical properties, calibrated on the temperature of kerogen-to-gas transformation, can be introduced to allow its activation as a decollement at a burial threshold. However, without hydro-mechanical coupling, it is not possible to predict where the overpressured regions that localised these changes are positioned. As such, this work also highlights the need for a fully-coupled hydro-mechanical model to further investigate the relationship between fluids and deformations in FTB and accretionary prisms. Burov, E., Francois, T., Yamato, P., & Wolf, S. (2014). Mechanisms of continental subduction and exhumation of HP and UHP rocks. Gondwana Research, 25(2), 464-493. Faille, I., Thibaut, M., Cacas, M.-C., Havé, P., Willien, F., Wolf, S., Agelas, L., Pegaz-Fiornet, S., 2014. Modeling Fluid Flow in Faulted Basins. Oil Gas Sci. Technol. - Rev. d'IFP Energies Nouv. 69, 529-553.

Formation and propagation of Love waves in a surface layer with a P-wave source. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Florence, A.L.; Miller, S.A.

The objective of this research is to investigate experimentally, and support with theoretical calculations, the formation and propagation of Love waves from a P-wave source due to scattering at material heterogeneities. The P-wave source is a spherical piezoelectric crystal cast in a surface layer of rock simulant overlaying a higher impedance granite substrate. Excitation of the piezoelectric crystal with a known voltage applies a spherical compressional pulse of known amplitude to the surrounding medium. Lateral heterogeneities cast in the surface layer convert incident P-wave energy into shear waves. The horizontally polarized shear waves (SH waves) trapped in the surface layermore » wave guide are the Love waves we will measure at the surface.« less

Geochemical Analysis for Sedimentary Emerald Mineralization in Western Emerald belt, Colombia

NASA Astrophysics Data System (ADS)

Nino Vasquez, Gabriel Felipe; Song, Sheng-Rong

2017-04-01

1Gabriel Felipe Nino Vasquez and 1Sheng-Rong Song 1Department of Geosciences, National Taiwan University Colombia hosts a large quantity of mineral resources due to its complex tectonic arrangement, and emerald deposits are one of the most representatives for the country. Emeralds in Colombia occur mainly in black shale, and are located in eastern Andes Cordillera with two parallel belts separated by approximately 130 Km: the Western belt (WB) and the Eastern belt (EB). The geological, mineralogical and tectonic features from these belts are quite similar (Buenaventura 2002). Previous researchers concluded that emeralds in Colombia came from hydrothermal sedimentary processes without any magmatic influence, and suggested that the source of Cr, V and Be (which are important components of the beryl) was the host rock. According to their results, the process which allowed the shale to release these cations was the metasomatism (albitization and carbonization), which was resulted from the interaction between the rocks and the alkaline brines. Fractures and fault planes originated by these tectonic movements were fulfilled by enriched fluids, which they allowed emeralds and the other minerals precipitation with decreasing alkalinity and pressure (Giuliani et al. 1994). However, there were several pitfalls of conclusions drawn from previous researches. Firstly, Cr and V were widely distributed and come from mafic and ultramafic rocks, and Be was mostly found in pegmatites, finding these elements in sedimentary rocks suggest that probably the ultramafic rocks occurred not far from the deposits. Secondly, there was an inconsistency in the estimated temperatures of emeralds formation, i.e. temperature of hydrothermal sedimentary deposits was only 200° C, while laboratory analysis showed that the formation of emeralds was higher than 300° C. Therefore, there might still be an allocthonus influence on emerald formation that significantly increases the temperature. This research is going to contribute information in order to clarify these inconsistencies, We have done the O and C isotopes in calcite and S isotope in pyrite and shale from different mines along the (WB) in order to determine the main fluid source of the mineralization. Selected samples will also be analyzed with EDS, RAMAN and ICP-MS methods to obtain the exact compositions of elements with extremely low concentrations in host rock, metazomatized host rock and mineralization (productive and not productive veins); the main purpose is to measure how strong were the fluid-rock interaction to leach elements out from the black shale. Thin sections from the altered shale and vein have been analyzed with the purpose of identify paragenesis and microstructures in the mineralization. Finally, we would like to gather the results from different sectors and compare it with the previous studies.

The genesis of Mo-Cu deposits and mafic igneous rocks in the Senj area, Alborz magmatic belt, Iran

NASA Astrophysics Data System (ADS)

Nabatian, Ghasem; Li, Xian-Hua; Wan, Bo; Honarmand, Maryam

2017-11-01

The geochemical and isotopic investigations were provided on the Upper Eocene Senj mafic intrusion and Mo-Cu mineralization to better understand the tectono-magmatic evolution and metallogeny of the central part of the Alborz magmatic belt. The Senj mafic intrusion is composed of gabbro to monzodiorite and monzonite in lithology, and intruded as a sill into volcano-sedimentary rocks of the Eocene Karaj Formation. The Karaj Formation consists of volcano-sedimentary rocks, such as altered crystalline to shaly tuffs. The Senj intrusion (39.7 ± 0.4 Ma) shows LILE and LREE enrichment and negative anomaly of Nb, Ta and Ti, the geochemical signatures similar to those from subduction-related mafic magmas. The Hf-O zircon analyses yield ɛHf(t) values of + 4.1 to + 11.1 and δ18O values of + 4.8 to + 6.2‰. The zircon isotopic signatures together with shoshonitic affinity in the Senj mafic samples suggest partial melting of an enriched lithospheric mantle that had already been metasomatized by slab-derived melts and fluids. The Mo-Cu mineralization mainly occurs as veins and veinlets in the volcano-sedimentary rocks of the Karaj Formation and is dominated by molybdenite with minor amounts of chalcopyrite, bornite, pyrite and tetrahedrite-tennantite. The associated gangue minerals are tremolite, actinolite, quartz, calcite, chlorite and epidote. The Senj Mo-Cu deposit formed in volcano-sedimentary rocks following the emplacement of the Late Eocene Senj sill. The source of molybdenite in the Senj deposit is dominantly from crustal materials as it is revealed by Re contents in the molybdenite minerals (0.5 to 0.7 ppm). In fact, the molybdenite occurrence may be a remobilization process related to the emplacement of the Senj mafic magma.

Geological and geochemical investigations of uranium occurrences in the Arrastre Lake area of the Medicine Bow Mountains, Wyoming

USGS Publications Warehouse

Miller, W. Roger; Houston, R.S.; Karlstrom, K.E.; Hopkins, D.M.; Ficklin, W.H.

1977-01-01

Metasedimentary rocks of Precambrian X age in and near the Snowy Range wilderness study area of southeastern Wyoming are lithologically and chronologically similar to those on the north shore of Lake Huron in Canada. The rocks in Canada contain major deposits of uranium in quartz-pebble conglomerates near the base of the metasedimentary sequence. Similar conglomerates in the Deep Lake Formation in the Medicine Bow Mountains of southeastern Wyoming are slightly radioactive and may contain deposits of uranium and other valuable heavy metals. During the summer of 1976, a geological and geochemical pilot study was conducted in the vicinity of Arrastre Lake in the Medicine Bow Mountains to determine the most effective exploration methods for evaluating the uranium potential of the Snowy Range wilderness study area. The area around Arrastre Lake was selected because of the presence of a radioactive lens within a quartz-pebble conglomerate of the Deep Lake Formation. The results of the survey indicate possible uranium mineralization in the subsurface rocks of this formation. The radon content of the dilute waters of the area is much higher than can be accounted for by the uranium content of the surface rocks. Two sources for the high content of the radon are possible. In either case, the high values of radon obtained in this study are a positive indication of uranium mineralization in the subsurface rocks. The determination of the radon content of water samples is the recommended geochemical technique for uranium exploration in the area. The determination of uranium in water and in organic-rich bog material is also recommended.

Reservoir Characterization for Unconventional Resource Potential, Pitsanulok Basin, Onshore Thailand

NASA Astrophysics Data System (ADS)

Boonyasatphan, Prat

The Pitsanulok Basin is the largest onshore basin in Thailand. Located within the basin is the largest oil field in Thailand, the Sirikit field. As conventional oil production has plateaued and EOR is not yet underway, an unconventional play has emerged as a promising alternative to help supply the energy needs. Source rocks in the basin are from the Oligocene lacustrine shale of the Chum Saeng Formation. This study aims to quantify and characterize the potential of shale gas/oil development in the Chum Saeng Formation using advanced reservoir characterization techniques. The study starts with rock physics analysis to determine the relationship between geophysical, lithological, and geomechanical properties of rocks. Simultaneous seismic inversion is later performed. Seismic inversion provides spatial variation of geophysical properties, i.e. P-impedance, S-impedance, and density. With results from rock physics analysis and from seismic inversion, the reservoir is characterized by applying analyses from wells to the inverted seismic data. And a 3D lithofacies cube is generated. TOC is computed from inverted AI. Static moduli are calculated. A seismic derived brittleness cube is calculated from Poisson's ratio and Young's modulus. The reservoir characterization shows a spatial variation in rock facies and shale reservoir properties, including TOC, brittleness, and elastic moduli. From analysis, the most suitable location for shale gas/oil pilot exploration and development are identified. The southern area of the survey near the MD-1 well with an approximate depth around 650-850 m has the highest shale reservoir potential. The shale formation is thick, with intermediate brittleness and high TOC. These properties make it as a potential sweet spot for a future shale reservoir exploration and development.

Role of water in hydrocarbon generation from Type-I kerogen in Mahogany oil shale of the Green River Formation

USGS Publications Warehouse

Lewan, M.D.; Roy, S.

2011-01-01

Hydrous and anhydrous closed-system pyrolysis experiments were conducted on a sample of Mahogany oil shale (Eocene Green River Formation) containing Type-I kerogen to determine whether the role of water had the same effect on petroleum generation as reported for Type-II kerogen in the Woodford Shale. The experiments were conducted at 330 and 350??C for 72h to determine the effects of water during kerogen decomposition to polar-rich bitumen and subsequent bitumen decomposition to hydrocarbon-rich oil. The results showed that the role of water was more significant in bitumen decomposition to oil at 350??C than in kerogen decomposition to bitumen at 330??C. At 350??C, the hydrous experiment generated 29% more total hydrocarbon product and 33% more C15+ hydrocarbons than the anhydrous experiment. This is attributed to water dissolved in the bitumen serving as a source of hydrogen to enhance thermal cracking and facilitate the expulsion of immiscible oil. In the absence of water, cross linking is enhanced in the confines of the rock, resulting in formation of pyrobitumen and molecular hydrogen. These differences are also reflected in the color and texture of the recovered rock. Despite confining liquid-water pressure being 7-9 times greater in the hydrous experiments than the confining vapor pressure in the anhydrous experiments, recovered rock from the former had a lighter color and expansion fractures parallel to the bedding fabric of the rock. The absence of these open tensile fractures in the recovered rock from the anhydrous experiments indicates that water promotes net-volume increase reactions like thermal cracking over net-volume decrease reactions like cross linking, which results in pyrobitumen. The results indicate the role of water in hydrocarbon and petroleum formation from Type-I kerogen is significant, as reported for Type-II kerogen. ?? 2010.

Very early Archean crustal-accretion complexes preserved in the North Atlantic craton

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nutman, A.P.; Collerson, K.D.

1991-08-01

The North Atlantic craton contains very early Archean supracrustal rocks, orthogneisses, and massive ultramafic rocks. Most units of supracrustal rocks are dominated by mafic volcanic rocks, layered gabbros, and banded iron formations, bust some also contain abundant felsic volcanic-sedimentary rocks, quartzites, and marbles. Some quartzites contain detrital zircons derived from rocks identical in age to felsic volcanic-sedimentary rocks in these sequences (ca. 3800 Ma) and also from older (ca. 3850 Ma) sources. The presence of the ca. 3850 Ma detrital zircons suggests that the supracrustal units containing them were deposited on, or close to, ca. 3850 Ma sialic crust. Themore » massive ultramafic rocks have chemical affinities to upper mantle rocks. The voluminous suites of tonalitic gneisses are dominated by 3700-3730 Ma bodies that intrude the supracrustal sequences, but they also locally contain components with ages between 3820 and 3920 Ma. The diverse supracrustal units, upper mantle rocks, and {ge} 3820 Ma components in the gneisses were tectonically interleaved in very early Archean convergent plate boundaries, giving rise to accretion complexes. In the period 3700-3730 Ma, voluminous tonalitic magmas produced by partial melting of predominantly mafic rocks in the base of the accretion complexes were emplaced at higher levels, forming juvenile continental crust and leaving behind a refractory lower crustal to upper mantle substrate.« less

Sembar Goru/Ghazij Composite Total Petroleum System, Indus and Sulaiman-Kirthar Geologic Provinces, Pakistan and India

USGS Publications Warehouse

Wandrey, C.J.; Law, B.E.; Shah, Haider Ali

2004-01-01

Geochemical analyses of rock samples and produced oil and gas in the Indus Basin have shown that the bulk of the hydrocarbons produced in the Indus Basin are derived from the Lower Cretaceous Sembar Formation and equivalent rocks. The source rocks of the Sembar are composed of shales that were deposited in shallow marine environments, are of mixed type-II and type-III kerogen, with total organic carbon (TOC) content ranging from less than 0.5 percent to more than 3.5 percent; the average TOC of the Sembar is about 1.4 percent. Vitrinite reflectance (Ro) values range from immature (1.35 percent Ro). Thermal generation of hydrocarbons in the Sembar Formation began 65 to 40 million years ago, (Mya) during Paleocene to Oligocene time. Hydrocarbon expulsion, migration, and entrapment are interpreted to have occurred mainly 50 to 15 Mya, during Eocene to Miocene time, prior to and contemporaneously with the development of structural traps in Upper Cretaceous and Tertiary reservoirs. The principal reservoirs in the Sembar-Goru/Ghazij Composite Total Petroleum System are Upper Cretaceous through Eocene sandstones and limestones.

Soda Lake-Painted Rock(!) Petroleum System in the Cuyama Basin, California, U.S.A.

USGS Publications Warehouse

Lillis, Paul G.

1994-01-01

The Cuyama basin, located in the central California Coast Ranges, was formed by extension during early Miocene time and was filled with a variety of nonmarine, marginal marine, and neritic to bathyal marine sediments. Low sulfur oil is produced primarily from the lower Miocene Painted Rock Sandstone Member of the Vaqueros Formation along a structural trend parallel to the Russell fault, which was active from 23 to 5 Ma. A major fold and thrust belt beginning about 3 Ma formed the Caliente and Sierra Madre ranges and partially obscures the Miocene extensional basin. Stable carbon isotope and biomarker data indicate that the lower Miocene Soda Lake Shale Member of the Vaqueros Formation is the predominant source rock for the oil in the Cuyama area. Burial and thermal history modeling shows that oil generation began in middle-late Miocene time and that oil migrated into existing traps. Younger traps that formed in the overthrust are barren of oil because migration occurred prior to the development of the fold and thrust belt or because subthrust oil was unable to migrate into the overthrust.

Petrogenesis of Cretaceous volcanic-intrusive complex from the giant Yanbei tin deposit, South China: Implication for multiple magma sources, tin mineralization, and geodynamic setting

NASA Astrophysics Data System (ADS)

Li, Qian; Zhao, Kui-Dong; Lai, Pan-Chen; Jiang, Shao-Yong; Chen, Wei

2018-01-01

The giant Yanbei tin ore deposit is the largest porphyry-type tin deposit in South China. The orebodies are hosted by the granite porphyry in the central part of the Yanbei volcanic basin in southern Jiangxi Province. The Yanbei volcanic-intrusive complex mainly consists of dacitic-rhyolitic volcanic rocks, granite, granite porphyry and diabase dikes. In previous papers, the granite porphyry was considered as subvolcanic rocks, which came from the same single magma chamber with the volcanic rocks. In this study, zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemical and Sr-Nd isotopic compositions of different magmatic units in the Yanbei complex are reported. Geochronologic results show that various magmatic units have different formation ages. The dacite yielded a zircon U-Pb age of 143 ± 1 Ma, and the granite porphyry has the emplacement age of 138 ± 1 Ma. Diabase dikes which represented the final stage of magmatism, yielded a zircon U-Pb age of 128 ± 1 Ma. Distinctive whole rock Sr-Nd and zircon Hf isotopic compositions suggest that these magmatic units were derived from different magma sources. The volcanic rocks were mainly derived from the partial melting of Paleoproterozoic metasedimentary rocks without additions of mantle-derived magma. The granite porphyry has an A-type geochemical affinity, and was derived from remelting of Paleo-Mesoproterozoic crustal source with involvement of a subordinate mantle-derived magma. The granite porphyry is also a typical stanniferous granite with high F (4070-6090 ppm) and Sn (7-39 ppm) contents. It underwent strongly crystal fractionation of plagioclase, K-feldspar, and accessory minerals (like apatite, Fe-Ti oxides), which may contribute to the tin mineralization. The diabase was derived by partial melting of enriched lithospheric mantle which had been metasomatised by slab-derived fluids. The change of magmatic sources reflected an increasing extensional tectonic environment, perhaps induced by slab rollback of subducted paleo-Pacific plate.

Formative Assessment Probes: Is It a Rock? Continuous Formative Assessment

ERIC Educational Resources Information Center

Keeley, Page

2013-01-01

A lesson plan is provided for a formative assessment probe entitled "Is It a Rock?" This probe is designed for teaching elementary school students about rocks through the use of a formative assessment classroom technique (FACT) known as the group Frayer Model. FACT activates students' thinking about a concept and can be used to…

Origin of dolomitic rocks in the lower Permian Fengcheng formation, Junggar Basin, China: evidence from petrology and geochemistry

NASA Astrophysics Data System (ADS)

Zhu, Shifa; Qin, Yi; Liu, Xin; Wei, Chengjie; Zhu, Xiaomin; Zhang, Wei

2017-04-01

Although dolomitization of calcite minerals and carbonatization of volcanic rocks have been studied widely, the extensive dolomitic rocks that originated from altered volcanic and volcaniclastic rocks have not been reported. The dolomitic rocks of the Fengcheng Formation in the Junggar Basin of China appear to be formed under unusual geologic conditions. The petrological and geochemical characteristics indicate that the dolomitizing host rock is devitrified volcanic tuff. After low-temperature alteration and calcitization, these tuffaceous rocks are replaced by Mg-rich brine to form massive dolomitic tuffs. We propose that the briny (with -2 ‰ 6 ‰ of δ13CPDB and -5 ‰ 4 ‰ of δ18OPDB) and Mg-rich marine formation water (with 0.7060 0.7087 of 87Sr/86Sr ratio), the thick and intermediate-mafic volcanic ashes, and the tectonically compressional movement may have favored the formation of the unusual dolomitic rocks. We conclude that the proposed origin of the dolomitic rocks can be extrapolated to other similar terranes with volcaniclastic rocks, seabed tuffaceous sediment, and fracture filling of sill.

Stratigraphy, structure and regional correlation of eastern Blue Ridge sequences in southern Virginia and northwestern North Carolina: an interim report from new USGS mapping

USGS Publications Warehouse

Carter, Mark W.; Merschat, Arthur J.

2014-01-01

The contact between eastern Blue Ridge stratified rocks above Mesoproterozoic basement rocks is mostly faulted (Gossan Lead and Red Valley). The Callaway fault juxtaposes Ashe and Lynchburg rocks above Wills Ridge Formation. Alligator Back Formation rocks overlie Ashe and Lynchburg rocks along the Rock Castle Creek fault, which juxtaposes rocks of different metamorphism. The fault separates major structural domains: rocks with one penetrative foliation in the footwall, and pin-striped recrystallized compositional layering, superposed penetrative foliations, and cleavage characterize the hanging wall. These relationships are ambiguous along strike to the southwest, where the Ashe and Alligator Back formations are recrystallized at higher metamorphic grades.

The evolution of Gondwana: U-Pb, Sm-Nd, Pb-Pb and geochemical data from Neoproterozoic to Early Palaeozoic successions of the Kango Inlier (Saldania Belt, South Africa)

NASA Astrophysics Data System (ADS)

Naidoo, Thanusha; Zimmermann, Udo; Chemale, Farid

2013-08-01

The provenance of Neoproterozoic to Early Palaeozoic rocks at the southern margin of the Kalahari craton reveals a depositional setting and evolution with a significant position in the formation of Gondwana. The sedimentary record shows a progression from immature, moderately altered rocks in the Ediacaran Cango Caves Group; to mature, strongly altered rocks in the Early Palaeozoic Kansa Group and overlying formations; culminating below very immature quartzarenites of Ordovician age. Petrographic and geochemical observations suggest the evolution of a small restricted basin with little recycling space towards a larger continental margin where substantial turbidite deposition is observed. For the southern Kalahari craton, a tectonic evolution comparable to supracrustal rocks in southern South America, Patagonia and Antarctica is supported by similarities in U-Pb ages of detrital zircons (Mesoproterozoic, Ediacaran and Ordovician grain populations); Sm-Nd isotopes (TDM: 1.2-1.8 Ga); and Pb-Pb isotopes. The maximum depositional age of the Huis Rivier Formation (upper Cango Caves Group) is determined at 644 Ma, but a younger age is still possible due to the limited zircon yield. The Cango Caves Group developed in a retro-arc foreland basin syntectonically to the Terra Australis Orogeny, which fringed Gondwana. The Kansa Group and overlying Schoemanspoort Formation are related to an active continental margin developed after the Terra Australis Orogen, with Patagonia being the ‘missing link’ between the Central South American arc and Antarctica during the Ordovician. This explains the occurrence of Ordovician detritus in these rocks, as a source rock of this age has not been discovered in South Africa. The absence of arc characteristics defines a position distal to the active continental margin, in a retro-arc foreland basin. The similarity of isotope proxies to major tectonic provinces in Antarctica and Patagonia, with those on the margins of the Kalahari craton, also points to a common geological evolution during the Mesoproterozoic and highlights the global relevance of this study.

Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation.

PubMed

Carlson, Richard W; Borg, Lars E; Gaffney, Amy M; Boyet, Maud

2014-09-13

New Rb-Sr, (146,147)Sm-(142,143)Nd and Lu-Hf isotopic analyses of Mg-suite lunar crustal rocks 67667, 76335, 77215 and 78238, including an internal isochron for norite 77215, were undertaken to better define the time and duration of lunar crust formation and the history of the source materials of the Mg-suite. Isochron ages determined in this study for 77215 are: Rb-Sr=4450±270 Ma, (147)Sm-(143)Nd=4283±23 Ma and Lu-Hf=4421±68 Ma. The data define an initial (146)Sm/(144)Sm ratio of 0.00193±0.00092 corresponding to ages between 4348 and 4413 Ma depending on the half-life and initial abundance used for (146)Sm. The initial Nd and Hf isotopic compositions of all samples indicate a source region with slight enrichment in the incompatible elements in accord with previous suggestions that the Mg-suite crustal rocks contain a component of KREEP. The Sm/Nd-(142)Nd/(144)Nd correlation shown by both ferroan anorthosite and Mg-suite rocks is coincident with the trend defined by mare and KREEP basalts, the slope of which corresponds to ages between 4.35 and 4.45 Ga. These data, along with similar ages for various early Earth differentiation events, are in accord with the model of lunar formation via giant impact into Earth at ca 4.4 Ga. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Terrestrial rock glaciers: a potential analog for Martian lobate flow features (LFF)

NASA Astrophysics Data System (ADS)

Sinha, Rishitosh K.; Vijayan, Sivaprahasam; Bharti, Rajiv R.

2016-05-01

Rock glaciers, regarded as cryospheric ice/water resource in the terrestrial-glacial systems based on their tongue/lobate-shaped flow characteristic and subsurface investigation using ground-penetrating radar. We examined the subsurface, geomorphology, climate-sensitivity and thermophysical properties of a Lobate Flow Feature (LFF) on Mars (30°-60° N and S hemispheres) to compare/assess the potentials of rock glaciers as an analog in suggesting LFFs to be a source of subsurface ice/water. LFFs are generally observed at the foot of impact craters' wall. HiRISE/CTX imageries from MRO spacecraft were used for geomorphological investigation of LFF using ArcMap-10.0 and subsurface investigation was carried out using data from MRO-SHARAD (shallow radar) after integrating with SiesWare-8.0. ENVI-5.0 was used to retrieve thermophysical properties of LFF from nighttime datasets (12.57 μm) acquired by THEMIS instrument-onboard the Mars Odyssey spacecraft and derive LFFs morphometry from MOLA altimeter point tracks onboard MGS spacecraft. Integrating crater chronology tool (Craterstats) with Arc Map, we have derived the formation age of LFF. Our investigation and comparison of LFF to rock glaciers revealed: (1) LFFs have preserved ice at depth 50m as revealed from SHARAD radargram and top-layer composed of rocky-debris material with thermal inertia ( 300-350 Jm-2 K-1s-1/2). (2) LFF formation age ( 10-100 Ma) corresponds to moderate scale debris covered glaciation of a shorter-span suggesting high sensitivity to obliquity-driven climatic shifts. (3) Presence of polygon cracks and high linear-arcuate furrow-and-ridges on the surface indicates presence of buried ice. This work is a significant step towards suggesting LFF to be a potential source of present-day stored ice/water on Mars.

The Haselgebirge evaporitic mélange in central Northern Calcareous Alps (Austria): Part of the Permian to Lower Triassic rift of the Meliata ocean?

PubMed

Schorn, Anja; Neubauer, Franz; Genser, Johann; Bernroider, Manfred

2013-01-11

For the reconstruction of Alpine tectonics of the Eastern Alps, the evaporitic Permian to Lower Triassic Haselgebirge Formation plays a key role in (1) the origin of Haselgebirge bearing nappes, (2) the inclusion of magmatic and metamorphic rocks revealing tectonic processes not preserved in other units, and (3) the debated mode of emplacement of the nappes, namely gravity-driven or tectonic. Within the Moosegg quarry of the central Northern Calcareous Alps gypsum/anhydrite bodies are tectonically mixed with lenses of sedimentary rocks and decimeter- to meter-sized tectonic clasts of plutonic and subvolcanic rocks and rare metamorphics. We examined various types of (1) widespread biotite-diorite, meta-syenite, (2) meta-dolerite and rare ultramafic rocks (serpentinite, pyroxenite) as well as (3) rare metamorphic banded meta-psammitic schists and meta-doleritic blueschists. The apparent 40 Ar/ 39 Ar biotite ages from three biotite-diorite, meta-dolerite and meta-doleritic blueschist samples with variable composition and fabrics range from 248 to 270 Ma (e.g., 251.2 ± 1.1 Ma) indicating a Permian age of cooling after magma crystallisation or metamorphism. The chemical composition of biotite-diorite and meta-syenite indicates an alkaline trend interpreted to represent a rift-related magmatic suite. These, as well as Permian to Jurassic sedimentary rocks, were incorporated during Cretaceous nappe emplacement forming the sulphatic Haselgebirge mélange. The scattered 40 Ar/ 39 Ar white mica ages of a meta-doleritic blueschist (of N-MORB origin) and banded meta-psammitic schist are ca. 349 and 378 Ma, respectively, proving the Variscan age of pressure-dominated metamorphism. These ages are similar to detrital white mica ages reported from the underlying Rossfeld Formations, indicating a close source-sink relationship. According to our new data, the Haselgebirge bearing nappe was transported over the Lower Cretaceous Rossfeld Formations, which include many clasts derived from the Haselgebirge Formation and its exotic blocks deposited in front of the incoming nappe comprising the Haselgebirge Formation.

Coatings on Atacama Desert Basalt: A Possible Analog for Coatings on Gusev Plains Basalt

NASA Technical Reports Server (NTRS)

Sutter, B.; Golden, D. C.; Amundson, R.; Chong-Diaz, G.; Ming, D. W.

2007-01-01

Surface coatings on Gusev Plains basalt have been observed and may contain hematite and nanophase Fe-oxides along with enrichments in P, S, Cl, and K relative to the underlying rock. The Gusev coatings may be derived from the dissolution of adhering soil and/or parent rock along with the addition of S and Cl from outside sources. Transient water for dissolution could be sourced from melting snow during periods of high obliquity, acid fog, and/or ground water (Haskin et al., 2005). Coatings on basalt in the hyper-arid (less than 2mm y(sup -1)) Atacama Desert may assist in understanding the chemistry, mineralogy and formation mechanisms of the Gusev basalt coatings. The Atacama Desert climate is proposed to be analogous to a paleo-Mars climate that was characterized by limited aqueous activity when the Gusev coatings could have formed. The objectives of this work are to (i) determine the chemical nature and extent of surface coatings on Atacama Desert basalt, and (ii) assess coating formation mechanisms in the Atacama Desert. Preliminary backscattered electron imaging of Atacama basalt thin-sections indicated that the coatings are as thick as 20 m. The boundary between the coating and the basalt labradorite, ilmenite, and augite grains was abrupt indicating that the basalt minerals underwent no chemical dissolution. The Atacama coatings have been added to the basalt instead of being derived from basalt chemical weathering. Semi-quantitative energy dispersive spectroscopy shows the coatings to be chemically homogeneous. The coating is depleted in Ca (0.9 wt% CaO) and enriched in K (1.3 wt.% K2O) and Si (69.1 wt.% SiO2) relative to the augite and labradorite grains. A dust source enriched in Si (e.g., poorly crystalline silica) and K and depleted in Ca appears to have been added to the basalt surface. Unlike the Gusev coatings, no P, S, and Cl enrichment was observed. However, Fe (3.2 wt.% FeO) was present in the Atacama coatings suggesting the present of Fe-oxides. While the chemistry of Atacama coating does not mirror the Gusev coating, the coating formation mechanism may be similar. The Atacama coatings of surface basalt are derived completely from exogenous sources. If surface Mars rocks have experienced limited wetting conditions as in the Atacama, then Mars coatings may be derived only from dissolution of material adhering to rock.

Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydrothermal processes.

PubMed

Waite, J Hunter; Glein, Christopher R; Perryman, Rebecca S; Teolis, Ben D; Magee, Brian A; Miller, Greg; Grimes, Jacob; Perry, Mark E; Miller, Kelly E; Bouquet, Alexis; Lunine, Jonathan I; Brockwell, Tim; Bolton, Scott J

2017-04-14

Saturn's moon Enceladus has an ice-covered ocean; a plume of material erupts from cracks in the ice. The plume contains chemical signatures of water-rock interaction between the ocean and a rocky core. We used the Ion Neutral Mass Spectrometer onboard the Cassini spacecraft to detect molecular hydrogen in the plume. By using the instrument's open-source mode, background processes of hydrogen production in the instrument were minimized and quantified, enabling the identification of a statistically significant signal of hydrogen native to Enceladus. We find that the most plausible source of this hydrogen is ongoing hydrothermal reactions of rock containing reduced minerals and organic materials. The relatively high hydrogen abundance in the plume signals thermodynamic disequilibrium that favors the formation of methane from CO 2 in Enceladus' ocean. Copyright © 2017, American Association for the Advancement of Science.

Petrology and physical conditions of metamorphism of calcsilicate rocks from low- to high-grade transition area, Dharmapuri District, Tamil Nadu

NASA Technical Reports Server (NTRS)

Narayana, B. L.; Natarajan, R.; Govil, P. K.

1988-01-01

Calc-silicate rocks comprising quartz, plagioclase, diopside, sphene, scapolite, grossularite-andradite and wollastonite occur as lensoid enclaves within the greasy migmatitic and charnockitic gneisses of the Archaean amphibolite- to granulite-facies transition zone in Dharmapuri district, Tamil Nadu. The calc-silicate rocks are characterized by the absence of K-feldspar and primary calcite, presence of large modal quartz and plagioclase and formation of secondary garnet and zoisite rims around scapolite and wollastonite. The mineral distributions suggest compositional layering. The chemical composition and mineralogy of the calc-silicate rocks indicate that they were derived from impure silica-rich calcareous sediments whose composition is similar to that of pelite-limestone mixtures. From the mineral assemblages the temperature, pressure and fluid composition during metamorphism were estimated. The observed mineral reaction sequences require a range of X sub CO2 values demonstrating that an initially CO2-rich metamorphic fluid evolved with time towards considerably more H2O-rich compositions. These variations in fluid composition suggest that there were sources of water-rich fluids external to the calc-silicate rocks and that mixing of these fluids with those of calc-silicate rocks was important in controlling fluid composition in calc-silicate rocks and some adjacent rock types as well.

Chapter 1: Executive Summary - 2003 Assessment of Undiscovered Oil and Gas Resources in the Upper Cretaceous Navarro and Taylor Groups, Western Gulf Province, Gulf Coast Region, Texas

USGS Publications Warehouse

,

2006-01-01

The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the Upper Cretaceous Navarro and Taylor Groups in the Western Gulf Province of the Gulf Coast region (fig. 1) as part of a national oil and gas assessment effort (USGS Navarro and Taylor Groups Assessment Team, 2004). The assessment of the petroleum potential of the Navarro and Taylor Groups was based on the general geologic elements used to define a total petroleum system (TPS), including hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). Using this geologic framework, the USGS defined five assessment units (AU) in the Navarro and Taylor Groups as parts of a single TPS, the Smackover-Austin-Eagle Ford Composite TPS: Travis Volcanic Mounds Oil AU, Uvalde Volcanic Mounds Gas and Oil AU, Navarro-Taylor Updip Oil and Gas AU, Navarro-Taylor Downdip Gas and Oil AU, and Navarro-Taylor Slope-Basin Gas AU (table 1).

Rock magnetic characterization of faulted sediments with associated magnetic anomalies in the Albuquerque Basin, Rio Grande rift, New Mexico

USGS Publications Warehouse

Hudson, M.R.; Grauch, V.J.S.; Minor, S.A.

2008-01-01

Variations in rock magnetic properties are responsible for the many linear, short-wavelength, low-amplitude magnetic anomalies that are spatially associated with faults that cut Neogene basin sediments in the Rio Grande rift, including the San Ysidro normal fault, which is well exposed in the northern part of the Albuquerque Basin. Magnetic-susceptibility measurements from 310 sites distributed through a 1200-m-thick composite section of rift-filling sediments of the Santa Fe Group and prerift Eocene and Cretaceous sedimentary rocks document large variations of magnetic properties juxtaposed by the San Ysidro fault. Mean volume magnetic susceptibilities generally increase upsection through eight map units: from 1.7 to 2.2E-4 in the prerift Eocene and Cretaceous rocks to 9.9E-4-1.2E-3 in three members of the Miocene Zia Formation of the Santa Fe Group to 1.5E-3-3.5E-3 in three members of the Miocene-Pleistocene Arroyo Ojito Formation of the Santa Fe Group. Rock magnetic measurements and petrography indicate that the amount of detrital magnetite and its variable oxidation to maghemite and hematite within the Santa Fe Group sediments are the predominant controls of their magnetic property variations. Magnetic susceptibility increases progressively with sediment grain size within the members of the Arroyo Ojito Formation (deposited in fluvial environments) but within members of the Zia Formation (deposited in mostly eolian environments) reaches highest values in fine to medium sands. Partial oxidation of detrital magnetite is spatially associated with calcite cementation in the Santa Fe Group. Both oxidation and cementation probably reflect past flow of groundwater through permeable zones. Magnetic models for geologic cross sections that incorporate mean magnetic susceptibilities for the different stratigraphic units mimic the aeromagnetic profiles across the San Ysidro fault and demonstrate that the stratigraphic level of dominant magnetic contrast changes with different exposure levels into the fault. These data indicate that tectonic juxtaposition of primary variations of magnetic properties of strata across the fault is the source of the associated magnetic anomaly. This study indicates that magnetic anomalies over faults and folds can be generated by sediments (1) deposited within tectonic basins having volcanic or basement source areas rich in magnetite, (2) having depositional environments with sufficient but varying energy to transport dense magnetic minerals and cause stratigraphic changes of magnetic properties, and (3) having magnetic minerals preserved owing to their youth or nonreactive geochemical environments. ?? 2007 Geological Society of America.

Generation of Hydrogen and Methane during Experimental Low-Temperature Reaction of Ultramafic Rocks with Water.

PubMed

McCollom, Thomas M; Donaldson, Christopher

2016-06-01

Serpentinization of ultramafic rocks is widely recognized as a source of molecular hydrogen (H2) and methane (CH4) to support microbial activity, but the extent and rates of formation of these compounds in low-temperature, near-surface environments are poorly understood. Laboratory experiments were conducted to examine the production of H2 and CH4 during low-temperature reaction of water with ultramafic rocks and minerals. Experiments were performed by heating olivine or harzburgite with aqueous solutions at 90°C for up to 213 days in glass bottles sealed with butyl rubber stoppers. Although H2 and CH4 increased steadily throughout the experiments, the levels were very similar to those found in mineral-free controls, indicating that the rubber stoppers were the predominant source of these compounds. Levels of H2 above background were observed only during the first few days of reaction of harzburgite when CO2 was added to the headspace, with no detectable production of H2 or CH4 above background during further heating of the harzburgite or in experiments with other mineral reactants. Consequently, our results indicate that production of H2 and CH4 during low-temperature alteration of ultramafic rocks may be much more limited than some recent experimental studies have suggested. We also found no evidence to support a recent report suggesting that spinels in ultramafic rocks may stimulate H2 production. While secondary silicates were observed to precipitate during the experiments, formation of these deposits was dominated by Si released by dissolution of the glass bottles, and reaction of the primary silicate minerals appeared to be very limited. While use of glass bottles and rubber stoppers has become commonplace in experiments intended to study processes that occur during serpentinization of ultramafic rocks at low temperatures, the high levels of H2, CH4, and SiO2 released during heating indicate that these reactor materials are unsuitable for this purpose. Serpentinization-Hydrogen generation-Abiotic methane synthesis. Astrobiology 16, 389-406.

The Shublik Formation and adjacent strata in northeastern Alaska description, minor elements, depositional environments and diagenesis

USGS Publications Warehouse

Tourtelot, Harry Allison; Tailleur, Irvin L.

1971-01-01

The Shublik Formation (Middle and Late Triassic) is widespread in the surface and subsurface of northern Alaska. Four stratigraphic sections along about 70 miles of the front of the northeastern Brooks Range east of the Canning giver were examined and sampled in detail in 1968. These sections and six-step spectrographic and carbon analyses of the samples combined with other data to provide a preliminary local description of the highly organic unit and of the paleoenvironments. Thicknesses measured between the overlying Kingak Shale of Jurassic age and the underlying Sadlerochit Formation of Permian and Triassic age range from 400 to more than 800 feet but the 400 feet, obtained from the most completely exposed section, may be closer to the real thickness across the region. The sections consist of organic-rich, phosphatic, and fossiliferous muddy, silty, or carbonate rocks. The general sequence consists, from the bottom up, of a lower unit of phosphatic siltstone, a middle unit of phosphatic carbonate rocks, and an upper unit of shale and carbonate rocks near the Canning River and shale, carbonate rocks, and sandstone to the east. Although previously designated a basal member of the Kingak Shale (Jurassic), the upper unit is here included with the Shublik on the basis of its regional lithologic relation. The minor element compositions of the samples of the Shublik Formation are consistent with their carbonaceous and phosphatic natures in that relatively large amounts of copper, molybdenum, nickel, vanadium and rare earths are present. The predominantly sandy rocks of the underlying Sadlerochit Formation (Permian and Triassic) have low contents of most minor elements. The compositions of samples of Kingak Shale have a wide range not readily explicable by the nature of the rock: an efflorescent sulfate salt contains 1,500 ppm nickel and 1,500 ppm zinc and large amounts of other metals derived from weathering of pyrite and leaching of local shale. The only recorded occurrence of silver and 300 ppm lead in gouge along a shear plane may be the result of metals introduced from an extraneous source. The deposits reflect a marine environment that deepened somewhat following deposition of the Sadlerochit Formation and then shoaled during deposition of the upper limestone-siltstone unit. This apparently resulted from a moderate transgression and regression of the sea with respect to a northwest-trending line between Barrow and the Brooks Range at the International Boundary. Nearer shore facies appear eastward. The phosphate in nodules, fossil molds and oolites, appears to have formed diagenetically within the uncompacted sediment.

Salt deposits in Los Medanos area, Eddy and Lea counties, New Mexico

USGS Publications Warehouse

Jones, C.L.; with sections on Ground water hydrology, Cooley; and Surficial Geology, Bachman

1973-01-01

The salt deposits of Los Medanos area, in Eddy and Lea Counties, southeastern New Mexico, are being considered for possible use as a receptacle for radioactive wastes in a pilot-plant repository. The salt deposits of the area. are in three evaporite formations: the Castile, Salado, and Rustler Formations, in ascending order. The three formations are dominantly anhydrite and rock salt, but some gypsum, potassium ores, carbonate rock, and fine-grained clastic rocks are present. They have combined thicknesses of slightly more than 4,000 feet, of which roughly one-half belongs to the Salado. Both the Castile and the Rustler are-richer in anhydrite-and poorer in rock salt-than the Salado, and they provide this salt-rich formation with considerable Protection from any fluids which might be present in underlying or overlying rocks. The Salado Formation contains many thick seams of rock salt at moderate depths below the surface. The rock salt has a substantial cover of well-consolidated rocks, and it is very little deformed structurally. Certain geological details essential for Waste-storage purposes are unknown or poorly known, and additional study involving drilling is required to identify seams of rock salt suitable for storage purposes and to establish critical details of their chemistry, stratigraphy, and structure.

Evidence for Seismogenic Hydrogen Gas, a Potential Microbial Energy Source on Earth and Mars.

PubMed

McMahon, Sean; Parnell, John; Blamey, Nigel J F

2016-09-01

The oxidation of molecular hydrogen (H2) is thought to be a major source of metabolic energy for life in the deep subsurface on Earth, and it could likewise support any extant biosphere on Mars, where stable habitable environments are probably limited to the subsurface. Faulting and fracturing may stimulate the supply of H2 from several sources. We report the H2 content of fluids present in terrestrial rocks formed by brittle fracturing on fault planes (pseudotachylites and cataclasites), along with protolith control samples. The fluids are dominated by water and include H2 at abundances sufficient to support hydrogenotrophic microorganisms, with strong H2 enrichments in the pseudotachylites compared to the controls. Weaker and less consistent H2 enrichments are observed in the cataclasites, which represent less intense seismic friction than the pseudotachylites. The enrichments agree quantitatively with previous experimental measurements of frictionally driven H2 formation during rock fracturing. We find that conservative estimates of current martian global seismicity predict episodic H2 generation by Marsquakes in quantities useful to hydrogenotrophs over a range of scales and recurrence times. On both Earth and Mars, secondary release of H2 may also accompany the breakdown of ancient fault rocks, which are particularly abundant in the pervasively fractured martian crust. This study strengthens the case for the astrobiological investigation of ancient martian fracture systems. Deep biosphere-Faults-Fault rocks-Seismic activity-Hydrogen-Mars. Astrobiology 16, 690-702.

Phosphate rock formation and marine phosphorus geochemistry: the deep time perspective.

PubMed

Filippelli, Gabriel M

2011-08-01

The role that phosphorite formation, the ultimate source rock for fertilizer phosphate reserves, plays in the marine phosphorus (P) cycle has long been debated. A shift has occurred from early models that evoked strikingly different oceanic P cycling during times of widespread phosphorite deposition to current thinking that phosphorite deposits may be lucky survivors of a series of inter-related tectonic, geochemical, sedimentological, and oceanic conditions. This paradigm shift has been facilitated by an awareness of the widespread nature of phosphogenesis-the formation of authigenic P-bearing minerals in marine sediments that contributes to phosphorite formation. This process occurs not just in continental margin sediments, but in deep sea oozes as well, and helps to clarify the driving forces behind phosphorite formation and links to marine P geochemistry. Two processes come into play to make phosphorite deposits: chemical dynamism and physical dynamism. Chemical dynamism involves the diagenetic release and subsequent concentration of P-bearing minerals particularly in horizons, controlled by a number of sedimentological and biogeochemical factors. Physical dynamism involves the reworking and sedimentary capping of P-rich sediments, which can either concentrate the relatively heavy and insoluble disseminated P-bearing minerals or provide an episodic change in sedimentology to concentrate chemically mobilized P. Both processes can result from along-margin current dynamics and/or sea level variations. Interestingly, net P accumulation rates are highest (i.e., the P removal pump is most efficient) when phosphorites are not forming. Both physical and chemical pathways involve processes not dominant in deep sea environments and in fact not often coincide in space and time even on continental margins, contributing to the rarity of high-quality phosphorite deposits and the limitation of phosphate rock reserves. This limitation is becoming critical, as the human demand for P far outstrips the geologic replacement for P and few prospects exist for new discoveries of phosphate rock. Copyright © 2011 Elsevier Ltd. All rights reserved.

Geochemical study of crude oils from the Xifeng oilfield of the Ordos basin, China

NASA Astrophysics Data System (ADS)

Duan, Y.; Wang, C. Y.; Zheng, C. Y.; Wu, B. X.; Zheng, G. D.

2008-01-01

The Xifeng oilfield is the largest newly-discovered oilfield in the Ordos basin. In order to determine the possible source, crude oils collected systematically from the oilfield and an adjacent oilfield have been examined isotopically and molecularly. The predominance of long-chain n-alkanes, high abundance of C 29 sterane, lower ratios of C 25/C 26 tricyclic terpane and C 25 tricyclic terpane/C 24 tetracyclic terpane and high C 24 tetracyclic terpane/(C 24 tetracyclic terpane + C 26 tricyclic terpanes ratio in the studied oils suggest generation from a source with mixed terrigenous and algal-bacterial organic matter. The presence of diterpenoid hydrocarbon with abietane skeletons is characteristic of the main contribution of higher land plants to the oils. The biomarker distributions in the oils show that they were formed under a weakly reducing freshwater environment. Molecular maturity parameters indicate that the crude oils are mature. The oil-source rock correlation and oil migration investigation suggest that the oils in the Xifeng oilfield originated from the source rocks of the Yanchang formation deposited in a shallow to deep freshwater lacustrine environment, especially Chang-7 source rocks. The data from the distribution of pyrrolic nitrogen compounds indicate that the charging direction of the Chang-8 crude oils is mainly from the Zhuang 12 well northeast of the oilfield toward the southwest. This direction of oil migration is consistent with that indicated by regional geological data.

Rho kinase inhibition drives megakaryocyte polyploidization and proplatelet formation through MYC and NFE2 downregulation.

PubMed

Avanzi, Mauro P; Goldberg, Francine; Davila, Jennifer; Langhi, Dante; Chiattone, Carlos; Mitchell, William Beau

2014-03-01

The processes of megakaryocyte polyploidization and demarcation membrane system (DMS) formation are crucial for platelet production, but the mechanisms controlling these processes are not fully determined. Inhibition of Rho kinase (ROCK) signalling leads to increased polyploidization in umbilical cord blood-derived megakaryocytes. To extend these findings we determined the effect of ROCK inhibition on development of the DMS and on proplatelet formation. The underlying mechanisms were explored by analysing the effect of ROCK inhibition on the expression of MYC and NFE2, which encode two transcription factors critical for megakaryocyte development. ROCK inhibition promoted DMS formation, and increased proplatelet formation and platelet release. Rho kinase inhibition also downregulated MYC and NFE2 expression in mature megakaryocytes, and this down-regulation correlated with increased proplatelet formation. Our findings suggest a model whereby ROCK inhibition drives polyploidization, DMS growth and proplatelet formation late in megakaryocyte maturation through downregulation of MYC and NFE2 expression. © 2014 John Wiley & Sons Ltd.

30 CFR 250.1601 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... means a well drilled through cap rock into the core at a salt dome for the purpose of producing brine. Cap rock means the rock formation, a body of limestone, anhydride, and/or gypsum, overlying a salt dome. Sulphur deposit means a formation of rock that contains elemental sulphur. Sulphur production...

30 CFR 250.1601 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... means a well drilled through cap rock into the core at a salt dome for the purpose of producing brine. Cap rock means the rock formation, a body of limestone, anhydride, and/or gypsum, overlying a salt dome. Sulphur deposit means a formation of rock that contains elemental sulphur. Sulphur production...

CO2-Water-Rock Wettability: Variability, Influencing Factors, and Implications for CO2 Geostorage.

PubMed

Iglauer, Stefan

2017-05-16

Carbon geosequestration (CGS) has been identified as a key technology to reduce anthropogenic greenhouse gas emissions and thus significantly mitigate climate change. In CGS, CO 2 is captured from large point-source emitters (e.g., coal fired power stations), purified, and injected deep underground into geological formations for disposal. However, the CO 2 has a lower density than the resident formation brine and thus migrates upward due to buoyancy forces. To prevent the CO 2 from leaking back to the surface, four trapping mechanisms are used: (1) structural trapping (where a tight caprock acts as a seal barrier through which the CO 2 cannot percolate), (2) residual trapping (where the CO 2 plume is split into many micrometer-sized bubbles, which are immobilized by capillary forces in the pore network of the rock), (3) dissolution trapping (where CO 2 dissolves in the formation brine and sinks deep into the reservoir due to a slight increase in brine density), and (4) mineral trapping (where the CO 2 introduced into the subsurface chemically reacts with the formation brine or reservoir rock or both to form solid precipitates). The efficiency of these trapping mechanisms and the movement of CO 2 through the rock are strongly influenced by the CO 2 -brine-rock wettability (mainly due to the small capillary-like pores in the rock which form a complex network), and it is thus of key importance to rigorously understand CO 2 -wettability. In this context, a substantial number of experiments have been conducted from which several conclusions can be drawn: of prime importance is the rock surface chemistry, and hydrophilic surfaces are water-wet while hydrophobic surfaces are CO 2 -wet. Note that CO 2 -wet surfaces dramatically reduce CO 2 storage capacities. Furthermore, increasing pressure, salinity, or dissolved ion valency increases CO 2 -wettability, while the effect of temperature is not well understood. Indeed theoretical understanding of CO 2 -wettability and the ability to quantitatively predict it are currently limited although recent advances have been made. Moreover, data for real storage rock and real injection gas (which contains impurities) is scarce and it is an open question how realistic subsurface conditions can be reproduced in laboratory experiments. In conclusion, however, it is clear that in principal CO 2 -wettability can vary drastically from completely water-wet to almost completely CO 2 -wet, and this possible variation introduces a large uncertainty into trapping capacity and containment security predictions.

Reconnaissance stratigraphic studies in the Susitna basin, Alaska, during the 2014 field season

USGS Publications Warehouse

LePain, David L.; Stanley, Richard G.; Harun, Nina T.; Helmold, Kenneth P.; Tsigonis, Rebekah

2015-01-01

The Susitna basin is a poorly-understood Cenozoic successor basin immediately north of Cook Inlet in south-central Alaska (Kirschner, 1994). The basin is bounded by the Castle Mountain fault and Cook Inlet basin on the south, the Talkeetna Mountains on the east, the Alaska Range on the north, and the Alaska–Aleutian Range on the west (fig. 2-1). The Cenozoic fill of the basin includes coal-bearing nonmarine rocks that are partly correlative with Paleogene strata in the Matanuska Valley and Paleogene and Neogene formations in Cook Inlet (Stanley and others, 2013, 2014). Mesozoic sedimentary rocks are present in widely-scattered uplifts in and around the margins of the basin; these rocks differ significantly from Mesozoic rocks in the forearc basin to the south. Mesozoic strata in the Susitna region were likely part of a remnant ocean basin that preceded the nonmarine Cenozoic basin (Trop and Ridgway, 2007). The presence of coal-bearing strata similar to units that are proven source rocks for microbial gas in Cook Inlet (Claypool and others, 1980) suggests the possibility of a similar system in the Susitna basin (Decker and others, 2012). In 2011 the Alaska Division of Geological & Geophysical Surveys (DGGS) and Alaska Division of Oil and Gas, in collaboration with the U.S. Geological Survey, initiated a study of the gas potential of the Susitna basin (Gillis and others, 2013). This report presents a preliminary summary of the results from 14 days of helicopter-supported field work completed in the basin in August 2014. The goals of this work were to continue the reconnaissance stratigraphic work begun in 2011 aimed at understanding reservoir and seal potential of Tertiary strata, characterize the gas source potential of coals, and examine Mesozoic strata for source and reservoir potential

Geochemical evaluation of part of the Cambay basin, India

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, A.; Rao, K.L.N.

1993-01-01

In Broach-Jambusar and Ahmedabad-Mehsana blocks of Cambay basin, India, the hydrocarbon generated (HCG) and hydrocarbon expelled (HCE) per unit area of four Paleogene formations were computed at 38 locations to select the best targets and thus reduce exploration risk. Fractional generation curves, which show relation between vitrinite reflectance and fraction of original generative potential converted to hydrocarbons, were constructed for study areas and used to calculate HCG through remaining generation potential (S[sub 2] of Rock-Eval) and the thickness of the sedimentary section. HCE was estimated by subtracting volatile hydrocarbon content (S[sub 1] of Rock-Eval), representing the unexpelled in-situ-generated bitumen, frommore » the computed value of HCG. HCG and HCE, which combine source rock richness, thickness, and maturity, are useful for comparative evaluation of charging capacity of source rocks. Positive and negative HCEs characterize drainage and accumulation locales, respectively. In the study areas, the major generative depressions are at Sobhasan/Linch/Wadu and Ahmedabad in the Ahmedabad-Mehsana block and the Tankari and Broach depressions in the Broach-Jambusar block. In these areas, Paleogene source rocks have generated between 3 million and 12 million MT hydrocarbon/km[sup 2]. The major known oil and gas accumulations, which are in middle to lower Eocene sandstones in vicinity of the generative depressions, overlie 2 million to 7 million MT hydrocarbon/km[sup 2] and HCG contours in both blocks and correlate well with negative HCE in the reservoir. Isopach maps of several major middle to lower Eocene reservoir sandstones in conjunction with HCG maps for Paleogene section help to delineate favorable exploration locales. 23 refs., 31 figs.« less

AR-39Ar-40 dating of basalts and rock breccias from Apollo 17 and the malvern achondrite

NASA Technical Reports Server (NTRS)

Kirsten, T.; Horn, P.

1977-01-01

The principles and the potential of the Ar-39/Ar-40 dating technique are illustrated by means of results obtained for 12 Apollo 17 rocks. Emphasis is given to methodical problems and the geological interpretation of lunar rock ages. Often it is ambigious to associate a given lunar breccia with a certain formation, or a formation with a basin. In addition, large-scale events on the Moon have not necessarily reset radiometric clocks completely. One rock fragment has a well-defined plateau age of 4.28 b.y., but the ages of two Apollo 17 breccias define an upper limit for the formation age of the Serenitatis basin at 4.05 b.y. Ages derived from five mare basalts indicate cessation of mare volcanism at Taurus-Littrow approximately 3.78 b.y. ago. Ca/Ar-37 exposure ages show that Camelot Crater was formed by an impact approximately 95 m.y. ago. After a short summary of the lunar timetable as it stands at the end of the Apollo program, we report about Ar-39/Ar-40 and rare gas studies on the Malvern meteorite. This achondrite resembles lunar highland breccias in texture as well as in rare-gas patterns. It was strongly annealed at some time between 3.4 and 3.8 b.y. ago. The results indicate that very similar processes have occurred on the Moon and on achondritic parent bodies at comparable times, leading to impact breccias with strikingly similar features, including the retention of rare-gas isotopes from various sources.

Landslides and rock fall processes in the proglacial area of the Gepatsch glacier, Tyrol, Austria - Quantitative assessment of controlling factors and process rates

NASA Astrophysics Data System (ADS)

Vehling, Lucas; Rohn, Joachim; Moser, Michael

2013-04-01

Due to the rapid deglaciation since 1850, lithological structures and topoclimatic factors, mass movements like rock fall, landslides and complex processes are important contributing factors to sediment transport and modification of the earth's surface in the steep, high mountain catchment of the Gepatsch reservoir. Contemporary geotechnical processes, mass movement deposits, their source areas, and controlling factors like material properties and relief parameters are mapped in the field, on Orthofotos and on digital elevation models. The results are presented in an Arc-Gis based geotechnical map. All mapped mass movements are stored in an Arc-Gis geodatabase and can be queried regarding properties, volume and controlling factors, so that statistical analyses can be conducted. The assessment of rock wall retreat rates is carried out by three different methods in multiple locations, which differ in altitude, exposition, lithology and deglaciation time: Firstly, rock fall processes and rates are investigated in detail on five rock fall collector nets with an overall size of 750 m2. Rock fall particles are gathered, weighed and grain size distribution is detected by sieving and measuring the diameter of the particles to distinct between rock fall processes and magnitudes. Rock wall erosion processes like joint formation and expansions are measured with high temporal resolution by electrical crack meters, together with rock- and air temperature. Secondly, in cooperation with the other working groups in the PROSA project, rock fall volumes are determined with multitemporal terrestrial laserscanning from several locations. Lately, already triggered rock falls are accounted by mapping the volume of the deposit and calculating of the bedrock source area. The deposition time span is fixed by consideration of the late Holocene lateral moraines and analysing historical aerial photographs, so that longer term rock wall retreat rates can be calculated. In order to limit homogenous bedrock sections for calculating specific rock wall retreat rates and to extrapolate the local determinated rock wall retreat rates to larger scale, bedrock areas will be divided into units of similar morphodynamic intensities which will be therefore classified by a rock mass strength (RMS) system. The RMS-System contains lithological and topoclimatic factors but also takes the measured rock wall retreat rates into account.

Lower continental crust formation through focused flow in km-scale melt conduits: The zoned ultramafic bodies of the Chilas Complex in the Kohistan island arc (NW Pakistan)

NASA Astrophysics Data System (ADS)

Jagoutz, O.; Müntener, O.; Burg, J.-P.; Ulmer, P.; Jagoutz, E.

2006-02-01

Whole-rock and Sm-Nd isotopic data of the main units of the Chilas zoned ultramafic bodies (Kohistan paleo-island arc, NW Pakistan) indicate that ultramafic rocks and gabbronorite sequences stem from a common magma. However, field observations rule out formation of both ultramafic and mafic sequences in terms of gravitational crystal settling in a large magma chamber. Contacts between ultramafic and gabbronorite sequences show emplacement of the dunitic bodies into a semi-consolidated gabbronoritic crystal-mush, which in turn has intruded and reacted with the ultramafic rocks to produce concentric zoning. Field and petrological observations indicate a replacive origin of the dunite. Bulk Mg#'s of dunitic rocks range from 0.87-0.81 indicating that the dunite-forming melt underwent substantial fractionation-differentiation and that percolative fractional crystallization probably generated the dunitic core. The REE chemistry of clinopyroxene in primitive dunite samples and the Nd isotopic composition of ultramafic rocks are in equilibrium with the surrounding gabbronorite. Accordingly, liquids that formed the dunitic rocks and later the mafic sequence derived from a similar depleted source ( ɛNd˜4.8). We propose a mechanism for the comagmatic emplacement, where km-scale ultramafic bodies represent continuous channels reaching down into the upper mantle. The melt-filled porosity in these melt channels diminishes the mean-depth-integrated density difference to the surrounding rocks. Due to buoyancy forces, melt channels raise into the overlying crustal sequence. In the light of such processes, the ultramafic bodies are interpreted as melt channels through which the Chilas gabbronorite sequence was fed. The estimated basaltic-andesitic, low Mg# (˜0.53) bulk composition of the Chilas gabbronorite sequence closely matches estimates of lower crustal compositions. Since the mafic sequence originated from a primary, high Mg# (> 0.7) basaltic arc magma, differentiation of such high Mg# magmas within km-scale isolated melt conduits may explain the "Mg#-gap" between bulk estimates of the continental crust and primary basaltic magmas, a major paradox in the andesite model of crust formation.

Sedimentary provenance of Maastrichtian oil shales, Central Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Fathy, Douaa; Wagreich, Michael; Mohamed, Ramadan S.; Zaki, Rafat

2017-04-01

Maastrichtian oil shales are distributed within the Central Eastern Desert in Egypt. In this study elemental geochemical data have been applied to investigate the probable provenance of the sedimentary detrital material of the Maastrichtian oil shale beds within the Duwi and the Dakhla formations. The Maastrichtian oil shales are characterized by the enrichment in Ca, P, Mo, Ni, Zn, U, Cr and Sr versus post-Archean Australian shales (PAAS). The chondrite-normalized patterns of the Maastrichtian oil shale samples are showing LREE enrichment, HREE depletion, slightly negative Eu anomaly, no obvious Ce anomaly and typical shale-like PAAS-normalized patterns. The total REE well correlated with Si, Al, Fe, K and Ti, suggesting that the REE of the Maastrichtian oil shales are derived from terrigenous source. Chemical weathering indices such as Chemical Index of Alteration (CIA), Chemical Proxy of Alteration (CPA) and Plagioclase Index of Alteration (PIA) indicate moderate to strong chemical weathering. We suggest that the Maastrichtian oil shale is mainly derived from first cycle rocks especially intermediate rocks without any significant inputs from recycled or mature sources. The proposed data illustrated the impact of the parent material composition on evolution of oil shale chemistry. Furthermore, the paleo-tectonic setting of the detrital source rocks for the Maastrichtian oil shale is probably related to Proterozoic continental island arcs

Petroleum surface oil seeps from Palaeoproterozoic petrified giant oilfield

NASA Astrophysics Data System (ADS)

Melezhik, V.; Fallick, A.; Filippov, M.; Lepland, A.; Rychanchik, D.; Deines, Yu.; Medvedev, P.; Romashkin, A.; Strauss, H.

2009-04-01

Evidence of petroleum generation and migration has been previously reported from rocks dating as early as 3.25 Ga. Micron-size carbonaceous streaks and bitumen micronodules were found in abundance in Archaean rocks across the Pilbara craton in Australia suggesting pervasive petroleum generation and migration. However, none of the Archaean petroleum deposits has been reported to be preserved in quantity due to destructive effects of deformation and thermal obliteration during metamorphism. During the Palaeoproterozoic, unprecedented accumulation of Corg-rich rocks worldwide, known as the 2.0 Ga Shunga Event, occurred during the early stage of progressive oxidation of terrestrial environments, and in the aftermath of the Lomagundi-Jatuli isotopic event, which based on the magnitude and duration of positive d13C was the greatest perturbation of the global carbon cycle in Earth history. C. 2.0 Ga Zaonezhskaya Formation (ZF) rocks from the Onega Basin in Russian Fennoscandia contain evidence for substantial accumulation and preservation of organic matter (up to 75 wt.-% total organic carbon) with an estimated original petroleum potential comparable to a modern supergiant oilfield. The basin contains a uniquely preserved petrified oilfield including evidence of oil traps and oil migration pathways. Here, we report the discovery of the surface expression of a migration pathway, along which petroleum was flowing from the sub-surface. This surface oil seep, the first occurrence ever reported from the Palaeoproterozoic, appears as originally bitumen clasts redeposited in Palaeoproterozoic lacustrine turbidites of the Kondopozhskaya Formation. The d13Corg of clastic pyrobitumen ranges between -35.4 and -36.0 per mill (n = 14) which is within the range of interbed- and vein-trapped fossil oil (-46 and -24 per mill), suggesting similar source. Biogenic organic matter, whose isotopic composition was modified during thermal maturation, is the likely source for the migrated hydrocarbon. Oil seeps, being a very common attribute of almost every major petroleum-producing province in the world, highlight the scale of oil generation and migration in the Onega Basin. The large d13C variability in interbed-trapped pyrobitumen and in organic matter (OM) of the ZF can be entirely explained neither by isotopic fractionation during petroleum generation nor by metamorphic processes, thus it might reflect a primary feature. The source material could have had a wide range of compositions that could have reacted in various ways to the subsequent maturation and alteration. We tentatively suggest that small-scale pyrobitumen accumulations may reflect the initial isotope heterogeneity of the source. In contrast, the seeps d13C are homogeneous, thus perhaps reflecting a large-scale migration and accumulation of composite oil produced by mixing and homogenisation of various oil sources. However, the low H/C of OM and pyrobitumens suggests that the source rock's various components with apparent diversity of original d13C have been over-matured. Although these values are compatible with being the source of the seeps, robust source-reservoir correlation cannot be made. In the evolutionary context, it is significant that the 2.0 Ga OM-rich rocks and generation of supergiant oilfields occurred in the aftermath of the Lomagundi-Jatuli isotopic event, and during the course of the early stage of oxidation of the terrestrial atmosphere. Whether enhanced biomass or change in the preservation potential caused such unprecedented OM accumulation and large-scale oil generation remains to be investigated.

Tungsten isotope evidence that mantle plumes contain no contribution from the Earth's core

NASA Astrophysics Data System (ADS)

Scherstén, Anders; Elliott, Tim; Hawkesworth, Chris; Norman, Marc

2004-01-01

Osmium isotope ratios provide important constraints on the sources of ocean-island basalts, but two very different models have been put forward to explain such data. One model interprets 187Os-enrichments in terms of a component of recycled oceanic crust within the source material. The other model infers that interaction of the mantle with the Earth's outer core produces the isotope anomalies and, as a result of coupled 186Os-187Os anomalies, put time constraints on inner-core formation. Like osmium, tungsten is a siderophile (`iron-loving') element that preferentially partitioned into the Earth's core during core formation but is also `incompatible' during mantle melting (it preferentially enters the melt phase), which makes it further depleted in the mantle. Tungsten should therefore be a sensitive tracer of core contributions in the source of mantle melts. Here we present high-precision tungsten isotope data from the same set of Hawaiian rocks used to establish the previously interpreted 186Os-187Os anomalies and on selected South African rocks, which have also been proposed to contain a core contribution. None of the samples that we have analysed have a negative tungsten isotope value, as predicted from the core-contribution model. This rules out a simple core-mantle mixing scenario and suggests that the radiogenic osmium in ocean-island basalts can better be explained by the source of such basalts containing a component of recycled crust.

Chronologic implications for slow cooling of troctolite 76535 and temporal relationships between the Mg-suite and the ferroan anorthosite suite

NASA Astrophysics Data System (ADS)

Borg, Lars E.; Connelly, James N.; Cassata, William S.; Gaffney, Amy M.; Bizzarro, Martin

2017-03-01

Ages have been obtained using the 87Rb-87Sr, 147Sm-143Nd, and 146Sm-142Nd isotopic systems for one of the most slowly cooled lunar rocks, Apollo 17 Mg-suite troctolite 76535. The 147Sm-143Nd, 146Sm-142Nd, and Rb-Sr ages derived from plagioclase, olivine, and pyroxene mineral isochrons yield concordant ages of 4307 ± 11 Ma, 4299+29/-35 Ma, and 4279 ± 52 Ma, respectively. These ages are slightly younger than the age determined on ferroan anorthosite suite (FAS) rock 60025 and are therefore consistent with the traditional magma ocean model of lunar differentiation in which the Mg-suite is intruded into the anorthositic crust. However, the Sm-Nd ages record when the rock passed below the closing temperature of the Sm-Nd system in this rock at ∼825 °C, whereas the Rb-Sr age likely records the closure temperature of ∼650 °C. A cooling rate of 3.9 °C/Ma is determined using the ages reported here and in the literature and calculated closure temperatures for the Ar-Ar, Pb-Pb, Rb-Sr, and Sm-Nd systems. This cooling rate is in good agreement with cooling rates estimated from petrographic observations. Slow cooling can lower apparent Sm-Nd crystallization ages by up to ∼80 Ma in the slowest cooled rocks like 76535, and likely accounts for some of the variation of ages reported for lunar crustal rocks. Nevertheless, slow cooling cannot account for the overlap in FAS and Mg-suite rock ages. Instead, this overlap appears to reflect the concordance of Mg-suite and FAS magmatism in the lunar crust as indicated by ages calculated for the solidus temperature of 76535 and 60025 of 4384 ± 24 Ma and 4383 ± 17, respectively. Not only are the solidus ages of 76535 and 60025 nearly concordant, but the Sm-Nd isotopic systematics suggest they are derived from reservoirs that were minimally differentiated prior to ∼4.38 Ga. Although the Sr isotopic composition of 60025 indicates its source was minimally differentiated, the Sr isotopic composition of 76535 indicates it underwent fractionation just prior to solidification of the 76535. These observations are consistent with both a magma ocean or a serial magmatism model of lunar differentiation. In either model, differentiation of lunar source regions must occur near the solidification age of thee samples. Perhaps the best estimate for the formation age of lunar source regions is the Rb-Sr model age of the 76535 source region age of 4401 ± 32 Ma. This is in good agreement with Sm-Nd model ages for the formation of ur-KREEP and suggests that differentiation of a least part of the Moon could not have occurred prior to ∼4.43 Ga.

Salinity sources of Kefar Uriya wells in the Judea Group aquifer of Israel. Part 1—conceptual hydrogeological model

NASA Astrophysics Data System (ADS)

Avisar, D.; Rosenthal, E.; Flexer, A.; Shulman, H.; Ben-Avraham, Z.; Guttman, J.

2003-01-01

In the Yarkon-Taninim groundwater basin, the karstic Judea Group aquifer contains groundwater of high quality. However, in the western wells of the Kefar Uriya area located in the foothills of the Judea Mountains, brackish groundwater was locally encountered. The salinity of this water is caused presumably by two end members designated as the 'Hazerim' and 'Lakhish' water types. The Hazerim type represents surface water percolating through a highly fractured thin chalky limestone formation overlying the Judea Group aquifer. The salinity of the water derives conjointly from several sources such as leachates from rendzina and grumosols, dissolution of caliche crusts which contain evaporites and of rock debris from the surrounding formations. This surface water percolates downwards into the aquifer through a funnel- or chimney-like mechanism. This local salinization mechanism supercedes another regional process caused by the Lakhish waters. These are essentially diluted brines originating from deep formations in the western parts of the Coastal Plain. The study results show that salinization is not caused by the thick chalky beds of the Senonian Mt Scopus Group overlying the Judea Group aquifer, as traditionally considered but prevalently by aqueous leachates from soils and rock debris. The conceptual qualitative hydrogeological model of the salinization as demonstrated in this study, is supported by a quantitative hydrological model presented in another paper in this volume.

The origin, source, and cycling of methane in deep crystalline rock biosphere.

PubMed

Kietäväinen, Riikka; Purkamo, Lotta

2015-01-01

The emerging interest in using stable bedrock formations for industrial purposes, e.g., nuclear waste disposal, has increased the need for understanding microbiological and geochemical processes in deep crystalline rock environments, including the carbon cycle. Considering the origin and evolution of life on Earth, these environments may also serve as windows to the past. Various geological, chemical, and biological processes can influence the deep carbon cycle. Conditions of CH4 formation, available substrates and time scales can be drastically different from surface environments. This paper reviews the origin, source, and cycling of methane in deep terrestrial crystalline bedrock with an emphasis on microbiology. In addition to potential formation pathways of CH4, microbial consumption of CH4 is also discussed. Recent studies on the origin of CH4 in continental bedrock environments have shown that the traditional separation of biotic and abiotic CH4 by the isotopic composition can be misleading in substrate-limited environments, such as the deep crystalline bedrock. Despite of similarities between Precambrian continental sites in Fennoscandia, South Africa and North America, where deep methane cycling has been studied, common physicochemical properties which could explain the variation in the amount of CH4 and presence or absence of CH4 cycling microbes were not found. However, based on their preferred carbon metabolism, methanogenic microbes appeared to have similar spatial distribution among the different sites.

The origin, source, and cycling of methane in deep crystalline rock biosphere

PubMed Central

Kietäväinen, Riikka; Purkamo, Lotta

2015-01-01

The emerging interest in using stable bedrock formations for industrial purposes, e.g., nuclear waste disposal, has increased the need for understanding microbiological and geochemical processes in deep crystalline rock environments, including the carbon cycle. Considering the origin and evolution of life on Earth, these environments may also serve as windows to the past. Various geological, chemical, and biological processes can influence the deep carbon cycle. Conditions of CH4 formation, available substrates and time scales can be drastically different from surface environments. This paper reviews the origin, source, and cycling of methane in deep terrestrial crystalline bedrock with an emphasis on microbiology. In addition to potential formation pathways of CH4, microbial consumption of CH4 is also discussed. Recent studies on the origin of CH4 in continental bedrock environments have shown that the traditional separation of biotic and abiotic CH4 by the isotopic composition can be misleading in substrate-limited environments, such as the deep crystalline bedrock. Despite of similarities between Precambrian continental sites in Fennoscandia, South Africa and North America, where deep methane cycling has been studied, common physicochemical properties which could explain the variation in the amount of CH4 and presence or absence of CH4 cycling microbes were not found. However, based on their preferred carbon metabolism, methanogenic microbes appeared to have similar spatial distribution among the different sites. PMID:26236303

Magma-magma interaction in the mantle beneath eastern China

NASA Astrophysics Data System (ADS)

Zeng, Gang; Chen, Li-Hui; Yu, Xun; Liu, Jian-Qiang; Xu, Xi-Sheng; Erdmann, Saskia

2017-04-01

In addition to magma-rock and rock-rock reaction, magma-magma interaction at mantle depth has recently been proposed as an alternative mechanism to produce the compositional diversity of intraplate basalts. However, up to now no compelling geochemical evidence supports this novel hypothesis. Here we present geochemistry for the Longhai basalts from Fujian Province, southeastern China, which demonstrates the interaction between two types of magma at mantle depth. At Longhai, the basalts form two groups, low-Ti basalts (TiO2/MgO < 0.25) and high-Ti basalts (TiO2/MgO > 0.25). Calculated primary compositions of the low-Ti basalts have compositions close to L + Opx + Cpx + Grt cotectic, and they also have low CaO contents (7.1-8.1 wt %), suggesting a mainly pyroxenite source. Correlations of Ti/Gd and Zr/Hf with the Sm/Yb ratios, however, record binary mixing between the pyroxenite-derived melt and a second, subordinate source-derived melt. Melts from this second source component have low Ti/Gd and high Zr/Hf and Ca/Al ratios, thus likely representing a carbonated component. The Sr, Nd, Hf, and Pb isotopic compositions of the high-Ti basalts are close to the low-Ti basalts. The Sm/Yb ratio of the high-Ti basalts, however, is markedly elevated and characterized by crossing rare earth element patterns at Ho, suggesting that they have source components comparable to the low-Ti basalts, but that they have experienced garnet and clinopyroxene fractionation. We posit that mingling of SiO2-saturated tholeiitic magma with SiO2-undersaturated alkaline magma might trigger such fractionation. Therefore, the model of magma-magma interaction and associated deep evolution of magma in the mantle is proposed to explain the formation of Longhai basalts. It may, moreover, serve as a conceptual model for the formation of tholeiitic to alkaline intraplate basalts worldwide.

New Insights into the Provenance of the Southern Junggar Basin in the Jurassic from Heavy Mineral Analysis and Sedimentary Characteristics

NASA Astrophysics Data System (ADS)

Zhou, T. Q.; Wu, C.; Zhu, W.

2017-12-01

Being a vital component of foreland basin of Central-western China, Southern Junggar Basin has observed solid evidences of oil and gas in recent years without a considerable advancement. The key reason behind this is the lack of systematic study on sedimentary provenance analysis of the Southern Junggar basin. Three parts of the Southern Junggar basin, including the western segment (Sikeshu Sag), the central segment (Qigu Fault-Fold Belt) and the eastern segment (Fukang Fault Zone), possess varied provenance systems, giving rise to difficulties for oil-gas exploration. In this study, 3468 heavy minerals data as well as the sedimentary environment analysis of 10 profiles and 7 boreholes were used to investigate the provenances of the deposits in the southern Junggar basin . Based on this research, it reveals that: Sikeshu sag initially shaped the foreland basin prototype in the Triassic and its provenance area of the sediments from the Sikeshu sag has primarily been situated in zhongguai uplift-chepaizi uplift depositional systems located in the northwestern margin of the Junggar Basin. From the early Jurassic, the key sources were likely to be late Carboniferous to early Permain post-collisional volcanic rocks from the North Tian Shan block to Centrao Tian Shan. In the Xishanyao formation, Abundant lithic metamorphic, epidote and garnet that suggests the source rocks were possibly late Carboniferous subduction-related arc volcanic rocks of the Central Tian Shan. In the Toutunhe formation, Bogda Mountains began uplifting and gradually becoming the major provenance. Moreover, the sedimentary boundaries of Junggar basin have also shifted towards the North Tian Shan again. In the late Jurassic, the conglomerates of the Kalazha formation directly overlie the fine-grained red beds of Qigu formation, which throw light on the rapid tectonic uplift of the North Tian Shan. In the eastern segment, meandering river delta and shore-lacustrine environments were fully developed in Badaowan formation indicating that the provenance of sediments mainly derived from the Kelameili Mountains. During the late Jurassic, the rapid uplift of Bogda Mountains could result into the distinct difference in heavy mineral assemblages between the eastern segment and the central segments.

Mineralogical and geochemical characterization of waste rocks from a gold mine in northeastern Thailand: application for environmental impact protection.

PubMed

Assawincharoenkij, Thitiphan; Hauzenberger, Christoph; Ettinger, Karl; Sutthirat, Chakkaphan

2018-02-01

Waste rocks from gold mining in northeastern Thailand are classified as sandstone, siltstone, gossan, skarn, skarn-sulfide, massive sulfide, diorite, and limestone/marble. Among these rocks, skarn-sulfide and massive sulfide rocks have the potential to generate acid mine drainage (AMD) because they contain significant amounts of sulfide minerals, i.e., pyrrhotite, pyrite, arsenopyrite, and chalcopyrite. Moreover, both sulfide rocks present high contents of As and Cu, which are caused by the occurrence of arsenopyrite and chalcopyrite, respectively. Another main concern is gossan contents, which are composed of goethite, hydrous ferric oxide (HFO), quartz, gypsum, and oxidized pyroxene. X-ray maps using electron probe micro-analysis (EPMA) indicate distribution of some toxic elements in Fe-oxyhydroxide minerals in the gossan waste rock. Arsenic (up to 1.37 wt.%) and copper (up to 0.60 wt.%) are found in goethite, HFO, and along the oxidized rim of pyroxene. Therefore, the gossan rock appears to be a source of As, Cu, and Mn. As a result, massive sulfide, skarn-sulfide, and gossan have the potential to cause environmental impacts, particularly AMD and toxic element contamination. Consequently, the massive sulfide and skarn-sulfide waste rocks should be protected from oxygen and water to avoid an oxidizing environment, whereas the gossan waste rocks should be protected from the formation of AMD to prevent heavy metal contamination.

Late Cretaceous volcanism in south-central New Mexico: Conglomerates of the McRae and Love Ranch Formations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapman-Fahey, J.L.; McMillan, N.J.; Mack, G.H.

Evidence to support Late Cretaceous volcanism in south central New Mexico is restricted to a small area of 75-Ma-old andesitic rocks at Copper Flats near Hillsboro, and volcanic clasts in the McRae (Late Cretaceous/Paleocene ) and Love Ranch (Paleocene/Eocene). Formations located in the Jornada del Muerto basin east and northeast of the Caballo Mountains. Major and trace element data and petrographic analysis of 5 samples from Copper Flats lavas and 40 samples of volcanic clasts from the McRae and Love Ranch conglomerates will be used to reconstruct the Cretaceous volcanic field. The McRae Formation consists of two members: the lowermore » Jose Creek and the upper Hall Lake. The lowermost Love Ranch Formation is unconformable in all places on the Hall Lake Member. Stratigraphic variations in clast composition from volcanic rocks in the lower Love Ranch Formation to Paleozoic and Precambrian clasts in the upper Love Ranch Formation reflect the progressive unroofing of the Laramide Rio Grande Uplift. Volcanic clasts in the McRae and Love Ranch Formations were derived from the west and south of the depositional basin, but the source area for McRae clasts is less well constrained. Stratigraphic, chemical, and petrographic data will be used to reconstruct the volcanic complex and more clearly define magma genesis and metasomatism associated with Laramide deformation.« less

System and method for investigating sub-surface features of a rock formation with acoustic sources generating conical broadcast signals

DOEpatents

Vu, Cung Khac; Skelt, Christopher; Nihei, Kurt; Johnson, Paul A.; Guyer, Robert; Ten Cate, James A.; Le Bas, Pierre -Yves; Larmat, Carene S.

2015-08-18

A method of interrogating a formation includes generating a conical acoustic signal, at a first frequency--a second conical acoustic signal at a second frequency each in the between approximately 500 Hz and 500 kHz such that the signals intersect in a desired intersection volume outside the borehole. The method further includes receiving, a difference signal returning to the borehole resulting from a non-linear mixing of the signals in a mixing zone within the intersection volume.

Magmatism in the Shapinggou district of the Dabie orogen, China: Implications for the formation of porphyry Mo deposits in a collisional orogenic belt

NASA Astrophysics Data System (ADS)

Ren, Zhi; Zhou, Taofa; Hollings, Pete; White, Noel C.

2018-05-01

The Shapinggou molybdenum deposit is located in the Qinling-Dabie Orogen, which hosts the world's largest molybdenum belt. The igneous rocks at Shapinggou can be divided into two stages (136-127 Ma and 118-114 Ma), the early suite of felsic (136-127 Ma, SiO2 = 58.0 to 72.9 wt%) and mafic rocks (133-128 Ma, SiO2 = 45.2 to 57.0 wt%), and a later suite comprising syenite (117 Ma, SiO2 = 64.2 to 65.0 wt%), quartz syenite porphyry (116 Ma, 62.5 to 70.0 wt%), granite porphyry (112 Ma, SiO2 = 75.5 to 77.6 wt%) and diorite porphyry (111 Ma, SiO2 = 56.6 to 59.7 wt%). The early-stage felsic rocks display high SiO2, Al2O3, Na2O, K2O, Sr, LREE contents, and Sr/Y, (La/Yb)N ratios, initial Sr isotope ratios of 0.7076 to 0.7089, but low MgO, FeOT, Y, Yb contents and negative εNd(t) values, consistent with partial melting of the lower continental crust. The early-stage mafic rocks exhibit low SiO2, high MgO, Ni and Cr contents, consistent with an upper mantle source, but trace element and isotope data suggest a role for crustal contamination. The late-stage syenite and quartz syenite porphyry show high abundances of Na2O, K2O, Al2O3, HFSEs (e.g., Th, U, Zr, Hf) and significant negative Eu anomalies. The late-stage granite porphyry displays high SiO2 contents, and depletions in Ba, Sr, Eu and Ti. The geochemical features of the late-stage intrusions are similar to A-type granites. Crystal fractionation of plagioclase, K-feldspar, biotite/ muscovite, amphibole/ garnet and Fe-Ti oxides controlled the evolution of the magma. The geochemical and isotopic data suggest that the rocks at Shapinggou were likely derived from a mixed source of lithospheric mantle, subducted continental crust of the Yangtze Block (Kongling Group) and partial melts of the Dabie Complex. Early stage rocks represent melts of the source with a lower proportion of Dabie Complex materials, whereas late stage rocks were derived from a source with a higher proportion Dabie Complex component. The geochemical and isotopic variations of the intrusions at Shapinggou were controlled by both source characteristics and fractional crystallization. Although the Shapinggou deposit is located in a continental collision orogen, the magmas formed in an intraplate extension setting, with an increase in the amount of extension from the early to late stages. As well, both stages intrusions at Shapinggou were generated by the addition of heat, due to lithospheric delamination, mantle upwelling and rapid mantle convection, related to the far-field effects of the westward subduction of the paleo-Pacific Plate beneath the Asian continent. The geochemistry and setting suggest that the formation of a giant Mo deposit does not require a Mo-rich magma source, but rather an efficient convection mechanism for the transport of volatiles and Mo in a granitic magma system. The fluids derived from the granite porphyry at Shapinggou were more oxidised than that from the barren intrusions.

Provenance and metamorphic PT conditions of Cryogenian-Ediacaran metasediments from the Kid metamorphic complex, Sinai, NE Arabian-Nubian Shield: Insights from detrital zircon geochemistry and mineral chemistry

NASA Astrophysics Data System (ADS)

El-Bialy, Mohammed Z.; Ali, Kamal A.; Abu El-Enen, Mahrous M.; Ahmed, Ahmed H.

2015-12-01

The Malhaq and Um Zariq formations occupy the northern part of the Neoproterozoic Kid metamorphic complex of SE Sinai, NE Arabian-Nubian Shield. This study presents new mineral chemistry data and LA-ICP-MS analyses of the trace element concentrations on zircons separated from metapelites from these formations. The detrital zircons of Um Zariq Formation are more enriched in ΣREE, whereas Malhaq Formation zircons are markedly HREE-enriched with strongly fractionated HREE patterns. The quite differences in the overall slope and size of the Eu and Ce anomalies between REE patterns of the two zircon suites provide a robust indication of different sources. The Ti-in-zircon thermometer has revealed that the zircons separated from Malhaq Formation were crystallized within the 916-1018 °C range, while those from Um Zariq Formation exhibit higher range of crystallization temperatures (1084-1154 °C). The detrital zircons of Malhaq Formation were derived mainly from mafic source rocks (basalt and dolerite), whereas Um Zariq Formation zircons have varied and more evolved parent rocks. Most of the investigated zircons from both formations are concluded to be unaltered magmatic that were lately crystallized from a high LREE/HREE melt. All the studied detrital zircon grains show typical trace elements features of crustal-derived zircons. All of the Um Zariq Formation and most of Malhaq Formation detrital zircons are geochemically discriminated as continental zircons. Both formation metapelites record similar, overlapping peak metamorphic temperatures (537-602 °C and 550-579 °C, respectively), and pressures (3.83-4.93 kbar and 3.69-4.07 kbar, respectively). The geothermal gradient, at the peak metamorphic conditions, was quite high (37-41 °C/km) corresponding to metamorphism at burial depth of 14-16 km. The peak regional metamorphism of Um Zariq and Malhaq formations is concluded to be generated during extensional regime and thinning of the lithosphere in an island arc setting with heat flow from the underlying arc granitoids.

GRANNY, a data bank of chemical analyses of Laramide and younger high-silica rhyolites and granites from Colorado and north-central New Mexico

USGS Publications Warehouse

Steigerwald, Celia H.; Mutschler, Felix E.; Ludington, Steve

1983-01-01

GRANNY is a data bank containing information on 507 chemically analyzed Laramide or younger high-silica rhyolites and granites from Colorado and north-central New Mexico. The data were compiled from both published and unpublished sources. The data bank is designed to aid in the recognition of igneous rocks with a high exploration potential for the discovery of molybdenum (and other lithophile element) deposits. Information on source reference, geographic location, age, mineralogic and petrologic characteristics, major constituent analyses, and trace element analyses for each sample are given. The data bank is available in two formats: 1) paper- or microfiche-hardcopy, and 2) fixed format computer readable magnetic tape.

Isotropic events observed with a borehole array in the Chelungpu fault zone, Taiwan.

PubMed

Ma, Kuo-Fong; Lin, Yen-Yu; Lee, Shiann-Jong; Mori, Jim; Brodsky, Emily E

2012-07-27

Shear failure is the dominant mode of earthquake-causing rock failure along faults. High fluid pressure can also potentially induce rock failure by opening cavities and cracks, but an active example of this process has not been directly observed in a fault zone. Using borehole array data collected along the low-stress Chelungpu fault zone, Taiwan, we observed several small seismic events (I-type events) in a fluid-rich permeable zone directly below the impermeable slip zone of the 1999 moment magnitude 7.6 Chi-Chi earthquake. Modeling of the events suggests an isotropic, nonshear source mechanism likely associated with natural hydraulic fractures. These seismic events may be associated with the formation of veins and other fluid features often observed in rocks surrounding fault zones and may be similar to artificially induced hydraulic fracturing.

Lower Cody Shale (Niobrara equivalent) in the Bighorn Basin, Wyoming and Montana: thickness, distribution, and source rock potential

USGS Publications Warehouse

Finn, Thomas M.

2014-01-01

The lower shaly member of the Cody Shale in the Bighorn Basin, Wyoming and Montana is Coniacian to Santonian in age and is equivalent to the upper part of the Carlile Shale and basal part of the Niobrara Formation in the Powder River Basin to the east. The lower Cody ranges in thickness from 700 to 1,200 feet and underlies much of the central part of the basin. It is composed of gray to black shale, calcareous shale, bentonite, and minor amounts of siltstone and sandstone. Sixty-six samples, collected from well cuttings, from the lower Cody Shale were analyzed using Rock-Eval and total organic carbon analysis to determine the source rock potential. Total organic carbon content averages 2.28 weight percent for the Carlile equivalent interval and reaches a maximum of nearly 5 weight percent. The Niobrara equivalent interval averages about 1.5 weight percent and reaches a maximum of over 3 weight percent, indicating that both intervals are good to excellent source rocks. S2 values from pyrolysis analysis also indicate that both intervals have a good to excellent source rock potential. Plots of hydrogen index versus oxygen index, hydrogen index versus Tmax, and S2/S3 ratios indicate that organic matter contains both Type II and Type III kerogen capable of generating oil and gas. Maps showing the distribution of kerogen types and organic richness for the lower shaly member of the Cody Shale show that it is more organic-rich and more oil-prone in the eastern and southeastern parts of the basin. Thermal maturity based on vitrinite reflectance (Ro) ranges from 0.60–0.80 percent Ro around the margins of the basin, increasing to greater than 2.0 percent Ro in the deepest part of the basin, indicates that the lower Cody is mature to overmature with respect to hydrocarbon generation.

Pitted rock surfaces on Mars: A mechanism of formation by transient melting of snow and ice

NASA Astrophysics Data System (ADS)

Head, James W.; Kreslavsky, Mikhail A.; Marchant, David R.

2011-09-01

Pits in rocks on the surface of Mars have been observed at several locations. Similar pits are observed in rocks in the Mars-like hyperarid, hypothermal stable upland zone of the Antarctic Dry Valleys; these form by very localized chemical weathering due to transient melting of small amounts of snow on dark dolerite boulders preferentially heated above the melting point of water by sunlight. We examine the conditions under which a similar process might explain the pitted rocks seen on the surface of Mars (rock surface temperatures above the melting point; atmospheric pressure exceeding the triple point pressure of H2O; an available source of solid water to melt). We find that on Mars today each of these conditions is met locally and regionally, but that they do not occur together in such a way as to meet the stringent requirements for this process to operate. In the geological past, however, conditions favoring this process are highly likely to have been met. For example, increases in atmospheric water vapor content (due, for example, to the loss of the south perennial polar CO2 cap) could favor the deposition of snow, which if collected on rocks heated to above the melting temperature during favorable conditions (e.g., perihelion), could cause melting and the type of locally enhanced chemical weathering that can cause pits. Even when these conditions are met, however, the variation in heating of different rock facets under Martian conditions means that different parts of the rock may weather at different times, consistent with the very low weathering rates observed on Mars. Furthermore, as is the case in the stable upland zone of the Antarctic Dry Valleys, pit formation by transient melting of small amounts of snow readily occurs in the absence of subsurface active layer cryoturbation.

Tectonics of Chukchi Sea Shelf sedimentary basins and its influence on petroleum systems

NASA Astrophysics Data System (ADS)

Agasheva, Mariia; Antonina, Stoupakova; Anna, Suslova; Yury, Karpov

2016-04-01

The Chukchi Sea Shelf placed in the East Arctic offshore of Russia between East Siberian Sea Shelf and North Slope Alaska. The Chukchi margin is considered as high petroleum potential play. The major problem is absence of core material from drilling wells in Russian part of Chukchi Shelf, hence strong complex geological and geophysical analyses such as seismic stratigraphy interpretation should be provided. In addition, similarity to North Slope and Beaufort Basins (North Chukchi) and Hope Basin (South Chukchi) allow to infer the resembling sedimentary succession and petroleum systems. The Chukchi Sea Shelf include North and South Chukchi Basins, which are separated by Wrangel-Herald Arch and characterized by different opening time. The North Chukchi basin is formed as a general part of Canada Basin opened in Early Cretaceous. The South Chukchi Basin is characterized by a transtensional origin of the basin, this deformation related to motion on the Kobuk Fault [1]. Because seismic reflections follow chronostratigraphic correlations, it is possible to achieve stratigraphic interpretation. The main seismic horizons were indicated as: PU, JU, LCU, BU, mBU marking each regional unconformities. Reconstruction of main tectonic events of basin is important for building correct geological model. Since there are no drilling wells in the North and South Chukchi basins, source rocks could not be proven. Referring to the North Chukchi basin, source rocks equivalents of Lower Cretaceous Pebble Shale Formation, Lower Jurassic Kingdak shales and Upper Triassic Shublik Formation (North Slope) is possible exhibited [2]. In the South Chukchi, it is possible that Cretaceous source rocks could be mature for hydrocarbon generation. Erosions and uplifts that could effect on hydrocarbon preservation was substantially in Lower Jurassic and Early Cretaceous periods. Most of the structures may be connected with fault and stratigraphy traps. The structure formed at Wrangel-Herald Arch to North-Chukchi through similar to well-known structure in Norwegian part of Barents Sea - Loppa High. In South Chukchi basin, the seismic wave shows interesting structures akin to diaper fold. Inversion-related anticlines and stratigraphic pinch-outs traps could presence in Cretaceous-Cenozoic cross section. As a result, we gathered and analyzed source rocks and reservoir analogs and gained improved sedimentary models in Eastern Russian Shelfs (Laptev, East Siberian and Chukchi Seas). Appropriate tectonic conditions, proven by well testing source rocks in North Slope and high thickness of basins suggest a success of hydrocarbon exploration in Russian part of Chukchi Sea Shelf. [1] Verzhbitsky V. E., S. D. Sokolov, E. M. Frantzen, A. Little, M. I. Tuchkova, and L.I. Lobkovsky, 2012, The South Chukchi Sedimentary Basin (Chukchi Sea, Russian Arctic): Age, structural pattern,and hydrocarbon potential, in D. Gao, ed., Tectonics and sedimentation: Implications for petroleum systems: AAPG Memoir 100, p.267-290. [2] Peters K. E., Magoon L. B., Bird K. J., Valin Z. C., Keller M. A. North Slope, Alaska: Source rock distribution, richness, thermal maturity, and petroleum charge AAPG Bulletin, V. 90, No. 2 (February 2006), 2006, P. 261-292.

The Chuar Petroleum System, Arizona and Utah

USGS Publications Warehouse

Lillis, Paul G.

2016-01-01

The Neoproterozoic Chuar Group consists of marine mudstone, sandstone and dolomitic strata divided into the Galeros and Kwagunt Formations, and is exposed only in the eastern Grand Canyon, Arizona. Research by the U.S. Geological Survey (USGS) in the late 1980s identified strata within the group to be possible petroleum source rocks, and in particular the Walcott Member of the Kwagunt Formation. Industry interest in a Chuar oil play led to several exploratory wells drilled in the 1990s in southern Utah and northern Arizona to test the overlying Cambrian Tapeats Sandstone reservoir, and confirm the existence of the Chuar in subcrop. USGS geochemical analyses of Tapeats oil shows in two wells have been tentatively correlated to Chuar bitumen extracts. Distribution of the Chuar in the subsurface is poorly constrained with only five well penetrations, but recently published gravity/aeromagnetic interpretations provide further insight into the Chuar subcrop distribution. The Chuar petroleum system was reexamined as part of the USGS Paradox Basin resource assessment in 2011. A map was constructed to delineate the Chuar petroleum system that encompasses the projected Chuar source rock distribution and all oil shows in the Tapeats Sandstone, assuming that the Chuar is the most likely source for such oil shows. Two hypothetical plays were recognized but not assessed: (1) a conventional play with a Chuar source and Tapeats reservoir, and (2) an unconventional play with a Chuar source and reservoir. The conventional play has been discouraging because most surface structures have been tested by drilling with minimal petroleum shows, and there is some evidence that petroleum may have been flushed by CO2 from Tertiary volcanism. The unconventional play is untested and remains promising even though the subcrop distribution of source facies within the Chuar Group is largely unknown.

Petroleum geology and resources of the Dnieper-Donets Basin, Ukraine and Russia

USGS Publications Warehouse

Ulmishek, Gregory F.

2001-01-01

The Dnieper-Donets basin is almost entirely in Ukraine, and it is the principal producer of hydrocarbons in that country. A small southeastern part of the basin is in Russia. The basin is bounded by the Voronezh high of the Russian craton to the northeast and by the Ukrainian shield to the southwest. The basin is principally a Late Devonian rift that is overlain by a Carboniferous to Early Permian postrift sag. The Devonian rift structure extends northwestward into the Pripyat basin of Belarus; the two basins are separated by the Bragin-Loev uplift, which is a Devonian volcanic center. Southeastward, the Dnieper-Donets basin has a gradational boundary with the Donbas foldbelt, which is a structurally inverted and deformed part of the basin. The sedimentary succession of the basin consists of four tectono-stratigraphic sequences. The prerift platform sequence includes Middle Devonian to lower Frasnian, mainly clastic, rocks that were deposited in an extensive intracratonic basin. 1 The Upper Devonian synrift sequence probably is as thick as 4?5 kilometers. It is composed of marine carbonate, clastic, and volcanic rocks and two salt formations, of Frasnian and Famennian age, that are deformed into salt domes and plugs. The postrift sag sequence consists of Carboniferous and Lower Permian clastic marine and alluvial deltaic rocks that are as thick as 11 kilometers in the southeastern part of the basin. The Lower Permian interval includes a salt formation that is an important regional seal for oil and gas fields. The basin was affected by strong compression in Artinskian (Early Permian) time, when southeastern basin areas were uplifted and deeply eroded and the Donbas foldbelt was formed. The postrift platform sequence includes Triassic through Tertiary rocks that were deposited in a shallow platform depression that extended far beyond the Dnieper-Donets basin boundaries. A single total petroleum system encompassing the entire sedimentary succession is identified in the Dnieper-Donets basin. Discovered reserves of the system are 1.6 billion barrels of oil and 59 trillion cubic feet of gas. More than one-half of the reserves are in Lower Permian rocks below the salt seal. Most of remaining reserves are in upper Visean-Serpukhovian (Lower Carboniferous) strata. The majority of discovered fields are in salt-cored anticlines or in drapes over Devonian horst blocks; little exploration has been conducted for stratigraphic traps. Synrift Upper Devonian carbonate reservoirs are almost unexplored. Two identified source-rock intervals are the black anoxic shales and carbonates in the lower Visean and Devonian sections. However, additional source rocks possibly are present in the deep central area of the basin. The role of Carboniferous coals as a source rock for gas is uncertain; no coal-related gas has been identified by the limited geochemical studies. The source rocks are in the gas-generation window over most of the basin area; consequently gas dominates over oil in the reserves. Three assessment units were identified in the Dnieper-Donets Paleozoic total petroleum system. The assessment unit that contains all discovered reserves embraces postrift Carboniferous and younger rocks. This unit also contains the largest portion of undiscovered resources, especially gas. Stratigraphic and combination structural and stratigraphic traps probably will be the prime targets for future exploration. The second assessment unit includes poorly known synrift Devonian rocks. Carbonate reef reservoirs along the basin margins probably will contain most of the undiscovered resources. The third assessment unit is an unconventional, continuous, basin-centered gas accumulation in Carboniferous low-permeability clastic rocks. The entire extent of this accumulation is unknown, but it occupies much of the basin area. Resources of this assessment unit were not estimated quantitatively.

Black shale source rocks and oil generation in the Cambrian and Ordovician of the central Appalachian Basin, USA

USGS Publications Warehouse

Ryder, R.T.; Burruss, R.C.; Hatch, J.R.

1998-01-01

Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft3 (tcf) of gas have been produced from Cambrian and Ordovician reservoirs (carbonate and sandstone) in the Ohio part of the Appalachian basin and on adjoining arches in Ohio, Indiana, and Ontario, Canada. Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Findlay and Kankakee arches and in small fields distributed along the Knox unconformity. Based on new geochemical analyses of oils, potential source rocks, bitumen extracts, and previously published geochemical data, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician blcak shale (Utica and Antes shales) in the Appalachian basin. Moroever, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lower Silurian Clinton sands of eastern Ohio originated in the same source rocks. Oils from the Cambrian and Ordovician reservoirs have similar saturated hydrocarbon compositions, biomarker distributions, and carbon isotope signatures. Regional variations in the oils are attributed to differences in thermal maturation rather than to differences in source. Total organic carbon content, genetic potential, regional extent, and bitument extract geochemistry identify the balck shale of the Utica and Antes shales as the most plausible source of the oils. Other Cambrian and Ordovician shale and carbonate units, such as the Wells Creek formation, which rests on the Knox unconformity, and the Rome Formation and Conasauga Group in the Rome trough, are considered to be only local petroleum sources. Tmax, CAI, and pyrolysis yields from drill-hole cuttings and core indicate that the Utica Shale in eastern and central Ohio is mature with respect to oil generation. Burial, thermal, and hydrocarbon-generation history models suggest that much of the oil was generated from the Utica-Antes source in the late Paleozoic during the Alleghanian orogeny. A pervasive fracture network controlled by basement tectonics aided in the distribution of oil from the source to the trap. This fracture network permitted oil to move laterally and stratigraphically downsection through eastward-dipping, impermeable carbonate sequences to carrier zones such as the Middle Ordovician Knox unconformity, and to reservoirs such as porous dolomite in the Middle Ordovician Trenton Limestone in the Lima-Indiana field. Some of the oil and gas from the Utica-Antes source escaped vertically through a partially fractured, leaky Upper Ordovician shale seal into widespread Lower Silurian sandstone reservoirs.Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft3 (tcf) of gas have been produced from Cambrian and Ordovician reservoirs (carbonate and sandstone) in the Ohio part of the Appalachian basin and on adjoining arches in Ohio, Indiana, and Ontario, Canada. Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Findlay and Kankakee arches and in small fields distributed along the Knox unconformity. Based on new geochemical analyses of oils, potential source rocks, bitumen extracts, and previously published geochemical data, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician black shale (Utica and Antes shales) in the Appalachian basin. Moreover, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lower Silurian Clinton sands of eastern Ohio originated in these same source rocks.

Ages and origins of rocks of the Killingworth dome, south-central Connecticut: Implications for the tectonic evolution of southern New England

USGS Publications Warehouse

Aleinikoff, J.N.; Wintsch, R.P.; Tollo, R.P.; Unruh, D.M.; Fanning, C.M.; Schmitz, M.D.

2007-01-01

The Killingworth dome of south-central Connecticut occurs at the southern end of the Bronson Hill belt. It is composed of tonalitic and trondhjemitic orthogneisses (Killingworth complex) and bimodal metavolcanic rocks (Middletown complex) that display calc-alkaline affinities. Orthogneisses of the Killingworth complex (Boulder Lake gneiss, 456 ?? 6 Ma; Pond Meadow gneiss, ???460 Ma) were emplaced at about the same time as eruption and deposition of volcanic-sedimentary rocks of the Middletown complex (Middletown Formation, 449 ?? 4 Ma; Higganum gneiss, 459 ?? 4 Ma). Hidden Lake gneiss (339 ?? 3 Ma) occurs as a pluton in the core of the Killingworth dome, and, on the basis of geochemical and isotopic data, is included in the Killingworth complex. Pb and Nd isotopic data suggest that the Pond Meadow, Boulder Lake, and Hidden Lake gneisses (Killingworth complex) resulted from mixing of Neoproterozoic Gander terrane sources (high 207Pb/204Pb and intermediate ??Nd) and less radiogenic (low 207Pb/204Pb and low ??Nd) components, whereas Middletown Formation and Higganum gneiss (Middletown complex) were derived from mixtures of Gander basement and primitive (low 207Pb/204Pb and high ??Nd) sources. The less radiogenic component for the Killingworth complex is similar in isotopic composition to material from Laurentian (Grenville) crust. However, because published paleomagnetic and paleontologic data indicate that the Gander terrane is peri-Gondwanan in origin, the isotopic signature of Killingworth complex rocks probably was derived from Gander basement that contained detritus from non-Laurentian sources such as Amazonia, Baltica, or Oaxaquia. We suggest that the Killingworth complex formed above an east-dipping subduction zone on the west margin of the Gander terrane, whereas the Middletown complex formed to the east in a back-arc rift environment. Subsequent shortening, associated with the assembly of Pangea in the Carboniferous, resulted in Gander cover terranes over the Avalon terrane in the west; and in the Middletown complex over the Killingworth complex in the east. Despite similarities of emplacement age, structural setting, and geographic continuity of the Killingworth dome with Oliverian domes in central and northern New England, new and published isotopic data suggest that the Killingworth and Middletown complexes were derived from Gander crust, and are not part of the Bronson Hill arc that was derived from Laurentian crust. The trace of the Ordovician Iapetan suture (the Red Indian line) between rocks of Laurentian and Ganderian origin probably extends from Southwestern New Hampshire west of the Pelham dome of northcentral Massachusetts and is coverd by Mesozoic rocks of the Hartford basin.

Characterization of coal-derived hydrocarbons and source-rock potential of coal beds, San Juan Basin, New Mexico and Colorado, U.S.A.

USGS Publications Warehouse

Rice, D.D.; Clayton, J.L.; Pawlewicz, M.J.

1989-01-01

Coal beds are considered to be a major source of nonassociated gas in the Rocky Mountain basins of the United States. In the San Juan basin of northwestern New Mexico and southwestern Colorado, significant quantities of natural gas are being produced from coal beds of the Upper Cretaceous Fruitland Formation and from adjacent sandstone reservoirs. Analysis of gas samples from the various gas-producing intervals provided a means of determining their origin and of evaluating coal beds as source rocks. The rank of coal beds in the Fruitland Formation in the central part of the San Juan basin, where major gas production occurs, increases to the northeast and ranges from high-volatile B bituminous coal to medium-volatile bituminous coal (Rm values range from 0.70 to 1.45%). On the basis of chemical, isotopic and coal-rank data, the gases are interpreted to be thermogenic. Gases from the coal beds show little isotopic variation (??13C1 values range -43.6 to -40.5 ppt), are chemically dry (C1/C1-5 values are > 0.99), and contain significant amounts of CO2 (as much as 6%). These gases are interpreted to have resulted from devolatilization of the humic-type bituminous coal that is composed mainly of vitrinite. The primary products of this process are CH4, CO2 and H2O. The coal-generated, methane-rich gas is usually contained in the coal beds of the Fruitland Formation, and has not been expelled and has not migrated into the adjacent sandstone reservoirs. In addition, the coal-bed reservoirs produce a distinctive bicarbonate-type connate water and have higher reservoir pressures than adjacent sandstones. The combination of these factors indicates that coal beds are a closed reservoir system created by the gases, waters, and associated pressures in the micropore coal structure. In contrast, gases produced from overlying sandstones in the Fruitland Formation and underlying Pictured Cliffs Sandstone have a wider range of isotopic values (??13C1 values range from -43.5 to -38.5 ppt), are chemically wetter (C1/C1-5 values range from 0.85 to 0.95), and contain less CO2 (< 2%). These gases are interpreted to have been derived from type III kerogen dispersed in marine shales of the underlying Lewis Shale and nonmarine shales of the Fruitland Formation. In the underlying Upper Cretaceous Dakota Sandstone and Tocito Sandstone Lentil of the Mancos Shale, another gas type is produced. This gas is associated with oil at intermediate stages of thermal maturity and is isotopically lighter and chemically wetter at the intermediate stage of thermal maturity as compared with gases derived from dispersed type III kerogen and coal; this gas type is interpreted to have been generated from type II kerogen. Organic matter contained in coal beds and carbonaceous shales of the Fruitland Formation has hydrogen indexes from Rock-Eval pyrolysis between 100 and 350, and atomic H:C ratios between 0.8 and 1.2. Oxygen indexes and atomic O:C values are less than 24 and 0.3, respectively. Extractable hydrocarbon yields are as high as 7,000 ppm. These values indicate that the coal beds and carbonaceous shales have good potential for the generation of liquid hydrocarbons. Voids in the coal filled with a fluorescent material that is probably bitumen is evidence that liquid hydrocarbon generation has taken place. Preliminary oil-source rock correlations based on gas chromatography and stable carbon isotope ratios of C15+ hydrocarbons indicate that the coals and (or) carbonaceous shales in the Fruitland Formation may be the source of minor amounts of condensate produced from the coal beds at relatively low levelsof thermal maturity (Rm=0.7). ?? 1989.

Sedimentary facies analysis of the Mesozoic clastic rocks in Southern Peru (Tacna, 18°S): Towards a paleoenvironmental Redefinition and stratigraphic Reorganization

NASA Astrophysics Data System (ADS)

Alván, Aldo; Jacay, Javier; Caracciolo, Luca; Sánchez, Elvis; Trinidad, Inés

2018-07-01

The Mesozoic rocks of southern Peru comprise a Middle Jurassic to Early Cretaceous sedimentary sequence deposited during a time interval of approximately 34 Myr. In Tacna, these rocks are detrital and constitute the Yura Group (Callovian to Tithonian) and the Hualhuani Formation (Berriasian). Basing on robust interpretation of facies and petrographic analysis, we reconstruct the depositional settings of such units and provide a refined stratigraphic framework. Accordingly, nine types of sedimentary facies and six architectural elements are defined. They preserve the record of a progradational fluvial system, in which two styless regulated the dispersion of sediments: (i) a high-to moderate-sinuosity meandering setting (Yura Group), and a later (ii) incipient braided setting (Hualhuani Formation). The Yura Group (Callovian-Tithonian) represents the onset of floodplain deposits and lateral accretion of point-bar deposits sited on a semi-flat topography. Nonetheless, the progradational sequence was affected by at least two rapid marine ingressions occurred during Middle Callovian and Tithonian times. Such marine ingressions reveal the proximity of a shallow marine setting and incipient carbonate deposition. In response to increase in topographic gradient, the Hualhuani Formation (Berriasian) deposited as extensive multistory sandy channels. The mineralogy of the Mesozoic sediments suggests sediment supplies and intense recycling from a craton interior (i.e. Amazon Craton and/or plutonic sources) located eastward of the study area.

Dissolution of Olivine, Siderite, and Basalt at 80 Deg C in 0.1 M H2SO4 in a Flow Through Process: Insights into Acidic Weathering on Mars

NASA Technical Reports Server (NTRS)

Golden, D. C.; Ming, D. W.; Hausrath, E. M.; Morris, R. V.; Niles, P. B.; Achilles, C. N.; Ross, D. K.; Cooper, B. L.; Gonzalex, C. P.; Mertzman, S. A.

2012-01-01

The occurrence of jarosite, other sulfates (e.g., Mg-and Ca-sulfates), and hematite along with silicic-lastic materials in outcrops of sedimentary materials at Meridiani Planum (MP) and detection of silica rich deposits in Gusev crater, Mars, are strong indicators of local acidic aqueous processes [1,2,3,4,5]. The formation of sediments at Meridiani Planum may have involved the evaporation of fluids derived from acid weathering of Martian basalts and subsequent diagenesis [6,7]. Also, our previous work on acid weathering of basaltic materials in a closed hydro-thermal system was focused on the mineralogy of the acid weathering products including the formation of jarosite and gray hematite spherules [8,9,10]. The object of this re-search is to extend our earlier qualitative work on acidic weathering of rocks to determine acidic dissolution rates of Mars analog basaltic materials at 80 C using a flow-thru reactor. We also characterized residual phases, including poorly crystalline or amorphous phases and precipitates, that remained after the treatments of olivine, siderite, and basalt which represent likely MP source rocks. This study is a stepping stone for a future simulation of the formation of MP rocks under a range of T and P.

DBP formation of aquatic humic substances

USGS Publications Warehouse

Pomes, M.L.; Green, W.R.; Thurman, E.M.; Orem, W.H.; Lerch, H.E.

1999-01-01

Aquatic humic substances (AHSs) in water generate potentially harmful disinfection by-products (DBPs) such as haloacetic acids (HAAs) and trihalomethanes (THMs) during chlorination. AHSs from two Arkansas reservoirs were characterized to define source, identify meta-dihydroxybenzene (m-DHB) structures as probable DBP precursors, and evaluate predicted HAA and THM formation potentials. Elemental nitrogen content 0.5 ??eq/mg, ??13C values of -27???, and low yields of syringyl phenols found by cupric oxide (CuO) oxidation suggest a pine tree source for the AHSs found in the Maumelle and Winona reservoirs in Little Rock, Ark. CuO oxidation yielded fewer m-DHB structures in Maumelle AHSs than in Winona AHSs. A higher 3,5-dihydroxybenzoic acid (3,5-DHBA) content correlated with increased HAA and THM formation potential. The 3,5-DHBA concentration in Winona AHSs was similar to the range found in AHSs extracted from deciduous leaf litter, twigs, and grass leachates.

Low-maturity Kulthieth Formation coal: A possible source of polycyclic aromatic hydrocarbons in benthic sediment of the northern Gulf of Alaska

USGS Publications Warehouse

Van Kooten, G. K.; Short, J.W.; Kolak, J.J.

2002-01-01

The successful application of forensic geology to contamination studies involving natural systems requires identification of appropriate endmembers and an understanding of the geologic setting and processes affecting the systems. Studies attempting to delineate the background, or natural, source for hydrocarbon contamination in Gulf of Alaska (GOA) benthic sediments have invoked a number of potential sources, including seep oils, source rocks, and coal. Oil seeps have subsequently been questioned as significant sources of hydrocarbons present in benthic sediments of the GOA in part because the pattern of relative polycyclic aromatic hydrocarbon (PAH) abundance characteristic of benthic GOA sediments is inconsistent with patterns typical of weathered seep oils. Likewise, native coal has been dismissed in part because ratios of labile hydrocarbons to total organic carbon (e.g. PAH:TOC) for Bering River coal field (BRCF) sources are too low - i.e. the coals are over mature - to be consistent with GOA sediments. We present evidence here that native coal may have been prematurely dismissed, because BRCF coals do not adequately represent the geochemical signatures of coals elsewhere in the Kulthieth Formation. Contrary to previous thought, Kulthieth Formation coals east of the BRCF have much higher PAH: TOC ratios, and the patterns of labile hydrocarbons in these low thermal maturity coals suggest a possible genetic relationship between Kulthieth Formation coals and nearby oil seeps on the Sullivan anticline. Analyses of low-maturity Kulthieth Formation coal indicate the low maturity coal is a significant source of PAH. Source apportionment models that neglect this source will underestimate the contribution of native coals to the regional background hydrocarbon signature. ?? Published by Elsevier Science Ltd. on behalf of AEHS.

A 3-D wellbore simulator (WELLTHER-SIM) to determine the thermal diffusivity of rock-formations

NASA Astrophysics Data System (ADS)

Wong-Loya, J. A.; Santoyo, E.; Andaverde, J.

2017-06-01

Acquiring thermophysical properties of rock-formations in geothermal systems is an essential task required for the well drilling and completion. Wellbore thermal simulators require such properties for predicting the thermal behavior of a wellbore and the formation under drilling and shut-in conditions. The estimation of static formation temperatures also needs the use of these properties for the wellbore and formation materials (drilling fluids and pipes, cements, casings, and rocks). A numerical simulator (WELLTHER-SIM) has been developed for modeling the drilling fluid circulation and shut-in processes of geothermal wellbores, and for the in-situ determination of thermal diffusivities of rocks. Bottomhole temperatures logged under shut-in conditions (BHTm), and thermophysical and transport properties of drilling fluids were used as main input data. To model the thermal disturbance and recovery processes in the wellbore and rock-formation, initial drilling fluid and static formation temperatures were used as initial and boundary conditions. WELLTHER-SIM uses these temperatures together with an initial thermal diffusivity for the rock-formation to solve the governing equations of the heat transfer model. WELLTHER-SIM was programmed using the finite volume technique to solve the heat conduction equations under 3-D and transient conditions. Thermal diffusivities of rock-formations were inversely computed by using an iterative and efficient numerical simulation, where simulated thermal recovery data sets (BHTs) were statistically compared with those temperature measurements (BHTm) logged in some geothermal wellbores. The simulator was validated using a well-documented case reported in the literature, where the thermophysical properties of the rock-formation are known with accuracy. The new numerical simulator has been successfully applied to two wellbores drilled in geothermal fields of Japan and Mexico. Details of the physical conceptual model, the numerical algorithm, and the validation and application results are outlined in this work.

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

NASA Astrophysics Data System (ADS)

Hong, Tao; Xu, Xing-Wang; Gao, Jun; Peters, Stephen G.; Zhang, Di; Jielili, Reyaniguli; Xiang, Peng; Li, Hao; Wu, Chu; You, Jun; Liu, Jie; Ke, Qiang

2018-01-01

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages. The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The ore-bearing adakitic intrusions in the KPCB and the adakitic Jiamate Complex intrusions were both probably generated from the same basaltic parental magmas through fractional crystallization. In addition, characteristics of the layered, magnetite-bearing, oxidized, basaltic Jiamate Complex intrusive rocks indicate that they are likely to be the parental arc magmas for the nearby porphyry Cu deposits. This conclusion is based on new interpretations of the regional and local geology, on interpretation of new geochemical analysis, new stable isotope analysis, new geothermobarometry, and new zircon age dating as well as other techniques and interpretations.

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

USGS Publications Warehouse

Hong, Tao; Xu, Xing-Wang; Gao, Jun; Peters, Stephen; Zhang, Di; Jielili, Reyaniguli; Xiang, Peng; Li, Hao; Wu, Chu; You, Jun; Liu, Jie; Ke, Qiang

2018-01-01

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages.The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The ore-bearing adakitic intrusions in the KPCB and the adakitic Jiamate Complex intrusions were both probably generated from the same basaltic parental magmas through fractional crystallization. In addition, characteristics of the layered, magnetite-bearing, oxidized, basaltic Jiamate Complex intrusive rocks indicate that they are likely to be the parental arc magmas for the nearby porphyry Cu deposits. This conclusion is based on new interpretations of the regional and local geology, on interpretation of new geochemical analysis, new stable isotope analysis, new geothermobarometry, and new zircon age dating as well as other techniques and interpretations.

Age and tectonic setting of the Mesozoic McCoy Mountains Formation in western Arizona, USA

USGS Publications Warehouse

Spencer, J.E.; Richard, S.M.; Gehrels, G.E.; Gleason, J.D.; Dickinson, W.R.

2011-01-01

The McCoy Mountains Formation consists of Upper Jurassic to Upper Cretaceous siltstone, sandstone, and conglomerate exposed in an east-west-trending belt in southwestern Arizona and southeastern California. At least three different tectonic settings have been proposed for McCoy deposition, and multiple tectonic settings are likely over the ~80 m.y. age range of deposition. U-Pb isotopic analysis of 396 zircon sand grains from at or near the top of McCoy sections in the southern Little Harquahala, Granite Wash, New Water, and southern Plomosa Mountains, all in western Arizona, identifi ed only Jurassic or older zircons. A basaltic lava fl ow near the top of the section in the New Water Mountains yielded a U-Pb zircon date of 154.4 ?? 2.1 Ma. Geochemically similar lava fl ows and sills in the Granite Wash and southern Plomosa Mountains are inferred to be approximately the same age. We interpret these new analyses to indicate that Mesozoic clastic strata in these areas are Upper Jurassic and are broadly correlative with the lowermost McCoy Mountains Formation in the Dome Rock, McCoy, and Palen Mountains farther west. Six samples of numerous Upper Jurassic basaltic sills and lava fl ows in the McCoy Mountains Formation in the Granite Wash, New Water, and southern Plomosa Mountains yielded initial ??Nd values (at t = 150 Ma) of between +4 and +6. The geochemistry and geochronology of this igneous suite, and detrital-zircon geochronology of the sandstones, support the interpretation that the lower McCoy Mountains Formation was deposited during rifting within the western extension of the Sabinas-Chihuahua-Bisbee rift belt. Abundant 190-240 Ma zircon sand grains were derived from nearby, unidentifi ed Triassic magmatic-arc rocks in areas that were unaffected by younger Jurassic magmatism. A sandstone from the upper McCoy Mountains Formation in the Dome Rock Mountains (Arizona) yielded numerous 80-108 Ma zircon grains and almost no 190-240 Ma grains, revealing a major reorganization in sediment-dispersal pathways and/or modifi cation of source rocks that had occurred by ca. 80 Ma. ?? 2011 Geological Society of America.

Heterogeneous vesiculation of 2011 El Hierro xeno-pumice revealed by X-ray computed microtomography

NASA Astrophysics Data System (ADS)

Berg, S. E.; Troll, V. R.; Deegan, F. M.; Burchardt, S.; Krumbholz, M.; Mancini, L.; Polacci, M.; Carracedo, J. C.; Soler, V.; Arzilli, F.; Brun, F.

2016-12-01

During the first week of the 2011 El Hierro submarine eruption, abundant light-coloured pumiceous, high-silica volcanic bombs coated in dark basanite were found floating on the sea. The composition of the light-coloured frothy material (`xeno-pumice') is akin to that of sedimentary rocks from the region, but the textures resemble felsic magmatic pumice, leaving their exact mode of formation unclear. To help decipher their origin, we investigated representative El Hierro xeno-pumice samples using X-ray computed microtomography for their internal vesicle shapes, volumes, and bulk porosity, as well as for the spatial arrangement and size distributions of vesicles in three dimensions (3D). We find a wide range of vesicle morphologies, which are especially variable around small fragments of rock contained in the xeno-pumice samples. Notably, these rock fragments are almost exclusively of sedimentary origin, and we therefore interpret them as relicts an the original sedimentary ocean crust protolith(s). The irregular vesiculation textures observed probably resulted from pulsatory release of volatiles from multiple sources during xeno-pumice formation, most likely by successive release of pore water and mineral water during incremental heating and decompression of the sedimentary protoliths.

Environmental consequences of shale gas exploitation and the crucial role of rock microfracturing

NASA Astrophysics Data System (ADS)

Renard, Francois

2015-04-01

The growing exploitation of unconventional gas and oil resources has dramatically changed the international market of hydrocarbons in the past ten years. However, several environmental concerns have also been identified such as the increased microseismicity, the leakage of gas into freshwater aquifers, and the enhanced water-rock interactions inducing the release of heavy metals and other toxic elements in the produced water. In all these processes, fluids are transported into a network of fracture, ranging from nanoscale microcracks at the interface between minerals and the kerogen of the source rock, to well-developed fractures at the meter scale. Characterizing the fracture network and the mechanisms of its formation remains a crucial goal. A major difficulty when analyzing fractures from core samples drilled at depth is that some of them are produced by the coring process, while some other are produced naturally at depth by the coupling between geochemical and mechanical forces. Here, I present new results of high resolution synchrotron 3D X-ray microtomography imaging of shale samples, at different resolutions, to characterize their microfractures and their mechanisms of formation. The heterogeneities of rock microstructure are also imaged, as they create local stress concentrations where cracks may nucleate or along which they propagate. The main results are that microcracks form preferentially along kerogen-mineral interfaces and propagate along initial heterogeneities according to the local stress direction, connecting to increase the total volume of fractured rock. Their lifetime is also an important parameter because they may seal by fluid circulation, fluid-rock interactions, and precipitation of a cement. Understanding the multi-scale processes of fracture network development in shales and the coupling with fluid circulation represents a key challenge for future research directions.

The origin of high hydrocarbon groundwater in shallow Triassic aquifer in Northwest Guizhou, China.

PubMed

Liu, Shan; Qi, Shihua; Luo, Zhaohui; Liu, Fangzhi; Ding, Yang; Huang, Huanfang; Chen, Zhihua; Cheng, Shenggao

2018-02-01

Original high hydrocarbon groundwater represents a kind of groundwater in which hydrocarbon concentration exceeds 0.05 mg/L. The original high hydrocarbon will significantly reduce the environment capacity of hydrocarbon and lead environmental problems. For the past 5 years, we have carried out for a long-term monitoring of groundwater in shallow Triassic aquifer in Northwest Guizhou, China. We found the concentration of petroleum hydrocarbon was always above 0.05 mg/L. The low-level anthropogenic contamination cannot produce high hydrocarbon groundwater in the area. By using hydrocarbon potential, geochemistry and biomarker characteristic in rocks and shallow groundwater, we carried out a comprehensive study in Dalongjing (DLJ) groundwater system to determine the hydrocarbon source. We found a simplex hydrogeology setting, high-level water-rock-hydrocarbon interaction and obviously original hydrocarbon groundwater in DLJ system. The concentration of petroleum hydrocarbon in shallow aquifer was found to increase with the strong water-rock interaction. Higher hydrocarbon potential was found in the upper of Guanling formation (T 2 g 3 ) and upper of Yongningzhen formation (T 1 yn 4 ). Heavily saturated carbon was observed from shallow groundwater, which presented similar distribution to those from rocks, especially from the deeper groundwater. These results indicated that the high concentrations of original hydrocarbon in groundwater could be due to the hydrocarbon release from corrosion and extraction out of strata over time.

Oxygen and hydrogen isotopic composition of the fluid during formation of anthophyllite metaultramafic rocks in the Sysert metamorphic complex, central Urals

NASA Astrophysics Data System (ADS)

Murzin, V. V.

2014-12-01

The oxygen (δ18O) and hydrogen (δD) isotopic composition of H2O-bearing minerals was studied for the ore-bearing amphibole metaultramafic rocks, which are the products of the early regional (435 ± 44 Ma) and late local (260 ± 6 Ma) silicic metasomatose in the Sysert metamorphic complex. The gold-sulfide mineralization of the Karas'evogorskoe deposit and anthophyllite-asbestos bodies of the Tersut deposit are related to the regional and local metasomatose combined with plagiogranitization and potassium granitization, respectively. The H2O-bearing minerals of metasomatites (anthophyllite, tremolite, talc) of the Karas'evogorskoe and Tersut deposits are characterized by heavier δ18O (9.8 to 12.2 and 7.6 to 9.4‰, respectively) and lighter ·D (87 to -91 and -56 to -67‰, respectively) values. The calculated isotopic composition of the fluid in equilibrium with these minerals indicates a heterogeneous source of water for the fluids related to the formation of metasomatites and the metamorphic origin of fluids. During the regional metasomatose, this fluid was a result of equilibrium of the deep fluid with volcanosedimentary rocks enriched in the heavy oxygen isotope. At the local metasomatose, the metamorphic fluid was formed by interaction of magmatic water produced by potassium granitization with ultramafic rocks.

Chapter 2: 2003 Geologic Assessment of Undiscovered Conventional Oil and Gas Resources in the Upper Cretaceous Navarro and Taylor Groups, Western Gulf Province, Texas

USGS Publications Warehouse

Condon, S.M.; Dyman, T.S.

2006-01-01

The Upper Cretaceous Navarro and Taylor Groups in the western part of the Western Gulf Province were assessed for undiscovered oil and gas resources in 2003. The area is part of the Smackover-Austin-Eagle Ford Composite Total Petroleum System. The rocks consist of, from youngest to oldest, the Escondido and Olmos Formations of the Navarro Group and the San Miguel Formation and the Anacacho Limestone of the Taylor Group (as well as the undivided Navarro Group and Taylor Group). Some units of the underlying Austin Group, including the 'Dale Limestone' (a term of local usage that describes a subsurface unit), were also part of the assessment in some areas. Within the total petroleum system, the primary source rocks comprise laminated carbonate mudstones and marine shales of the Upper Jurassic Smackover Formation, mixed carbonate and bioclastic deposits of the Upper Cretaceous Eagle Ford Group, and shelf carbonates of the Upper Cretaceous Austin Group. Possible secondary source rocks comprise the Upper Jurassic Bossier Shale and overlying shales within the Upper Jurassic to Lower Cretaceous Cotton Valley Group, Lower Cretaceous marine rocks, and the Upper Cretaceous Taylor Group. Oil and gas were generated in the total petroleum system at different times because of variations in depth of burial, geothermal gradient, lithology, and organic-matter composition. A burial-history reconstruction, based on data from one well in the eastern part of the study area (Jasper County, Tex.), indicated that (1) the Smackover generated oil from about 117 to 103 million years ago (Ma) and generated gas from about 52 to 41 Ma and (2) the Austin and Eagle Ford Groups generated oil from about 42 to 28 Ma and generated gas from about 14 Ma to the present. From the source rocks, oil and gas migrated upsection and updip along a pervasive system of faults and fractures as well as along bedding planes and within sandstone units. Types of traps include stratigraphic pinchouts, folds, faulted folds, and combinations of these. Seals consist of interbedded shales and mudstones and diagenetic cementation. The area assessed is divided into five assessment units (AUs): (1) Travis Volcanic Mounds Oil (AU 50470201), (2) Uvalde Volcanic Mounds Gas and Oil (AU 50470202), (3) Navarro-Taylor Updip Oil and Gas (AU 50470203), (4) Navarro-Taylor Downdip Gas and Oil (AU 50470204), and (5) Navarro-Taylor Slope-Basin Gas (AU 50470205). Total estimated mean undiscovered conventional resources in the five assessment units combined are 33.22 million barrels of oil, 1,682.80 billion cubic feet of natural gas, and 34.26 million barrels of natural gas liquids.

Compositional controls on early diagenetic pathways in fine-grained sedimentary rocks: Implications for predicting unconventional reservoir attributes of mudstones

USGS Publications Warehouse

Keller, Margaret A.; Macquaker, Joe H.S.; Taylor, Kevin G.; Polya, David

2014-01-01

Diagenesis significantly impacts mudstone lithofacies. Processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks. Selected organic-carbon-rich mudstones, from the Kimmeridge Clay and Monterey Formations, have been investigated to determine how varying starting compositions influence diagenesis.The sampled Kimmeridge Clay Formation mudstones are organized into thin homogenous beds, composed mainly of siliciclastic detritus, with some constituents derived from water-column production (e.g., coccoliths, S-depleted type-II kerogen, as much as 52.6% total organic carbon [TOC]) and others from diagenesis (e.g., pyrite, carbonate, and kaolinite). The sampled Monterey Formation mudstones are organized into thin beds that exhibit pelleted wavy lamination, and are predominantly composed of production-derived components including diatoms, coccoliths, and foraminifera, in addition to type-IIS kerogen (as much as 16.5% TOC), and apatite and silica cements.During early burial of the studied Kimmeridge Clay Formation mudstones, the availability of detrital Fe(III) and reactive clay minerals caused carbonate- and silicate-buffering reactions to operate effectively and the pore waters to be Fe(II) rich. These conditions led to pyrite, iron-poor carbonates, and kaolinite cements precipitating, preserved organic carbon being S-depleted, and sweet hydrocarbons being generated. In contrast, during the diagenesis of the sampled Monterey Formation mudstones, sulfide oxidation, coupled with opal dissolution and the reduced availability of both Fe(III) and reactive siliciclastic detritus, meant that the pore waters were poorly buffered and locally acidic. These conditions resulted in local carbonate dissolution, apatite and silica cements precipitation, natural kerogen sulfurization, and sour hydrocarbons generation.Differences in mud composition at deposition significantly influence subsequent diagenesis. These differences impact their source rock attributes and mechanical properties.

Hydrothermal Alteration Products as Key to Formation of Duricrust and Rock Coatings on Mars

NASA Astrophysics Data System (ADS)

Bishop, J. L.

1999-03-01

A model is presented for the formation of duricrust and rock coatings on Mars. Hydrothermal alteration of volcanic tephra may produce a corrosive agent that attacks rock surfaces and binds dust particles to form duricrust.

Reconstruction of paleoceanographic significance in the Atlantic, Pacific, and the Indian Ocean during the Neogene based on calcareous nannofossil productivity and coccolith size distribution of Reticulofenestra - with special reference to formation of petroleum source rocks

NASA Astrophysics Data System (ADS)

Pratiwi, S. D.; Sato, T.; Ovinda, O.; Syavitri, D.

2017-12-01

We studied in detail the calcareous nannofossils assemblages from the ODP Sites of the western Pacific, Bahama Bank of Caribbean Sea, northwestern Pacific, Equatorial Pacific and the Indian Ocean to reconstruct the Cenozoic paleoceanographic evolution and correlate with the global events. The absolute abundant of coccolith (number/g) is gradually increased from NN6 throughout NN19 Zone, while the relative abundance of Discoaster is decreased in the Pacific Ocean. The size of Reticulofenestra increased five times throughout the section. However, it drastically decreased in NN8-10 (8.80 Ma), NN12-13 (5.40 Ma), NN14-NN15 (3.75 Ma), NN17/NN18 (2.52 Ma) and in NN19 Zone (0.80 Ma) in the western Pacific site. The characteristic of eutrophication condition determined by the high productivity of coccolith and the drastic decrease of the maximum size of Reticulofenestra are strongly related to the appearance of nutricline in the sea surface ocean. On the basis of the relationship between the changes of maximum sizes of Reticulofenestra and nutrient condition, these eutrophication events are clearly traceable in the western Pacific, Bahama Bank of Caribbean Sea, northwestern Pacific, Equatorial Pacific and the Indian Ocean. Two paleoceanographic events found in 8.80 Ma and 3.75 Ma are interpreted as a change to high nutrient condition resulted in the intensification of Asian Monsoon and closure of Panama Isthmus (Fig.). The upwelling of nutrient-rich oceanic waters may give rise to exceptionally high organic productivity. Organic carbon- rich facies accumulate preferentially during major intensification episodes. The timing of high productivity of coccolith during the middle to late Miocene is related and applicable to the formation of petroleum source rock and traceable to the Japan, marginal eastern North Pacific and California oil sites. This study suggests that the timing of the collapse of sea surface condition or eutrophication condition (8.00 Ma to 10.00 Ma) is correlated to the timing of formation petroleum source rocks in Circum Pacific based on calcareous nannofossils study.

Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: Occurrence of Archean oceanic plateau

NASA Astrophysics Data System (ADS)

El Atrassi, Fatima; Debaille, Vinciane; Mattielli, Nadine; Berger, Julien

2015-04-01

While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African craton in Mauritania (Amsaga area). The Amsaga Archean crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. We report the results of a combined petrologic, Sm-Nd isotopic, major element and rare earth element (REE) study of the Archean amphibolites in the West African craton. This study was conducted in order to characterize these rocks, to constrain the time of their formation and to evaluate their tectonic setting and their possible mantle source. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. They are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. These amphibolites have tholeiitic basalt composition. On a primitive mantle-normalized diagram, they display fairly flat patterns without negative anomalies for either Eu or Nb-Ta. We have shown using Sm-Nd whole rock isotopic data that these amphibolites formed at 3.3 ±0.075 Ga. They have positive ɛNdi values (+5.2 ± 1.6). These samples show isotopically juvenile features, which rule out the possibility of significant contamination of the protolith magmas by ancient continental crust. Based on these geochemical data we propose that the tholeiitic basalts were formed in an oceanic plateau tectonic setting from a mantle plume source and that they have a depleted mantle source. It is the first time that such a signature is observed in the Archean part of the West African craton, and would suggest a widespread bimodal distribution of trace elements signature in all Archean basalts.

The Talara Basin province of northwestern Peru: cretaceous-tertiary total petroleum system

USGS Publications Warehouse

Higley, Debra K.

2004-01-01

More than 1.68 billion barrels of oil (BBO) and 340 billion cubic feet of gas (BCFG) have been produced from the Cretaceous-Tertiary Total Petroleum System in the Talara Basin province, northwestern Peru. Oil and minor gas fields are concentrated in the onshore northern third of the province. Current production is primarily oil, but there is excellent potential for offshore gas resources, which is a mostly untapped resource because of the limited local market for gas and because there are few pipelines. Estimated mean recoverable resources from undiscovered fields in the basin are 1.71 billion barrels of oil (BBO), 4.79 trillion cubic feet of gas (TCFG), and 255 million barrels of natural gas liquids (NGL). Of this total resource, 15 percent has been allocated to onshore and 85 percent to offshore; volumes are 0.26 BBO and 0.72 TCFG onshore, and 1.45 BBO and 4.08 TCFG offshore. The mean estimate of numbers of undiscovered oil and gas fields is 83 and 27, respectively. Minimum size of fields that were used in this analysis is 1 million barrels of oil equivalent and (or) 6 BCFG. The Paleocene Talara forearc basin is superimposed on a larger, Mesozoic and pre-Mesozoic basin. Producing formations, ranging in age from Pennsylvanian to Oligocene, are mainly Upper Cretaceous through Oligocene sandstones of fluvial, deltaic, and nearshore to deep-marine depositional origins. The primary reservoirs and greatest potential for future development are Eocene sandstones that include turbidites of the Talara and Salinas Groups. Additional production and undiscovered resources exist within Upper Cretaceous, Paleocene, and Oligocene formations. Pennsylvanian Amotape quartzites may be productive where fractured. Trap types in this block-faulted basin are mainly structural or a combination of structure and stratigraphy. Primary reservoir seals are interbedded and overlying marine shales. Most fields produce from multiple reservoirs, and production is reported commingled. For this reason, and also because geochemical data on oils and source rocks is very limited, Tertiary and Cretaceous production is grouped into one total petroleum system. The most likely source rocks are Tertiary marine shales, but some of the Cretaceous marine shales are also probable source rocks, and these would represent separate total petroleum systems. Geochemical data on one oil sample from Pennsylvanian rock indicates that it was probably also sourced from Tertiary shales.

Constraining the Dynamic Rupture Properties with Moment Tensor Derived Vp/Vs Ratios.

NASA Astrophysics Data System (ADS)

Smith-Boughner, L.; Baig, A. M.; Urbancic, T.; Viegas, G. F.

2014-12-01

The goal of hydraulic fracturing is to increase the permeability of rocks to extract hydrocarbons from "tight" formations. This process stimulates fluid-driven fractures which induce microseismic events. Successfully treating the formations, stimulating large volumes of the reservoir, depends on targeting parts of the formation with more "brittleness", a property which is frequently characterized from the mechanical properties of the rock. Typically, these properties are constrained using well-logs, vertical seismic profiles and 3-D seismic surveys. Such tools provide a static view of the reservoir on very large or very small scales. While lithology controls the average rock strength within a unit, the content (gas or fluid filled), the shape of the pore space and the concentration of micro-fractures alters the mechanical properties of the reservoir. Seismic moment tensor inversion of the events generated during these stimulations reveals that they are significantly non-double-couple, and are described by a tensile angle and a Poisson's ratio (or, equivalently, ratio of shear to compressional velocities, Vp/Vs) of the rock-fracture system. Following Vavryčuk (2011), the mechanical properties of the reservoir (i.e. Vp/Vs ratio) are estimated as the hydraulic fracture progresses from an extensive catalog of microseismic events spanning magnitudes of -1.5 to 0.8 in the Horn-River Basin, Canada. Studying several fracture stages in the reservoir reveals temporal and spatial variations in the rock strength within a unit as hydraulic fracturing proceeds. Initially, the estimated values of Vp/Vs are quite close to those determined from 3-D seismic surveys. As the stage progresses, previously fractured regions have lower Vp/Vs values. At the onset of maximum treating pressure, regions have anomalously high Vp/Vs values, which could reflect short-term local concentrations of high pore pressures or other interactions of the treatment with the formation. The relationship between source parameters and variations in Vp/Vs are also examined. This technique has the potential to provide a unique and dynamic view of variations in the reservoir both spatially and temporally.

Petroleum Systems of the Nigerian Sector of Chad Basin: Insights from Field and Subsurface Data

NASA Astrophysics Data System (ADS)

Suleiman, A. A.; Nwaobi, G. O.; Bomai, A.; Dauda, R.; Bako, M. D.; Ali, M. S.; Moses, S. D.

2017-12-01

A.A. Suleiman, A. Bomai, R. Dauda, O.G. NwaobiNigerian National Petroleum CorporationAbstract:Formation of the West and Central African Rift systems (WCARS) reflects intra-plate deformation linked to the Early to Late Cretaceous opening of South Atlantic Ocean. From an economic point of view, the USGS (2010) estimated Chad Basin, which is part of WCARS rift system to contain, up to 2.32 BBO and 14.62 TCF. However, there has been no exploration success in the Nigerian sector of the Chad Basin principally because of a poor understanding of the basin tectono-stratigraphic evolution and petroleum system development. In this study, we use 3D seismic, geochemical and field data to construct a tectono-stratigraphic framework of the Nigerian sector of Chad Basin; within this framework we then investigate the basins petroleum system development. Our analysis suggests two key plays exist in the basin, Lower and Upper Cretaceous plays. Pre-Bima lacustrine shale and the Gongila Formation constitute the prospective source rocks for the Lower Cretaceous play, whereas the Fika Shale may provide the source, for the Upper Cretaceous play. Source rock hydrocarbon modeling indicates possible oil and gas generation and expulsion from the lacustrine shales and Fika Shale in Cretaceous and Tertiary times respectively. Bima Sandstone and weathered basement represent prospective reservoirs for the Lower Cretaceous play and intra-Fika sandstone beds for the Upper Cretaceous play. We identify a range of trapping mechanisms such as inversion-related anticlines. Shales of the Gongila Formation provide the top sealing for the Lower Cretaceous play. Our field observations have proved presence of the key elements of the petroleum system in the Nigerian Sector of the Chad Basin. It has also demonstrated presence of igneous intrusions in the stratigraphy of the basin that we found to influence the hydrocarbon potential of the basin through source rock thermal maturity and degradation. Our study indicates that Nigerian sector of the Chad Basin is affected by igneous activity and basin inversion both of which impact its petroleum system development. Therefore, a detailed study of the tectono-stratigraphic framework of a rift basin is crucial to investigate the development of its petroleum system and hydrocarbon prospectivity.

Provenance Analysis of Upper Cretaceous - Paleogene Sandstones in the Foreland Basin System of the Tansen Unit, Central Nepal

NASA Astrophysics Data System (ADS)

Neupane, B.; Ju, Y.; Allen, C.

2016-12-01

The continental deposits foreland basin of Central Nepal, Amile Formation, Bhainskati Formation and Dumri Formation (Tansen unit) are the key region for provenance analysis, preserved almost complete sedimentation history of tectonic collision of Indian and Asian plates. Samples from two field traverses are examined petrographically and through zircon U-Pb dating, one traverse through the Tansen Group, and another through its potential source rocks, the Higher and Tethys Himalaya. The Tansen Group ages are well known through fossil assemblages. We examine sandstone-bearing units of the Tansen Group, the upper 3 of 5 Formations. The optical petrography data and resulting classify Tansen sediments as "recycled orogenic" and "Quartzose recycled", indicating that Indian cratonal sediments as the likely source of sediments for the Amile Formations, and the Tethyan Himalaya as the source for the Bhainskati Formation, and both the Tethys and Higher Himalaya as the major sources for the Dumri Formation. The Cretaceous to Paleocene pre-collisional Amile Formation is dominated by a broad 1830 Ma age peak with neither Paleozoic nor Neoproterozic zircons, but hosts a significant proportion (23%) of syndepositional Cretaceous zircons (121 to 105 Ma) indicative of nearby Cretaceous volcanism at that time. Therefore, the rare volcanic fragments in detritus of Amile Formation were derived from the Rajmahal Volcanic Province defining the middle to late Cretaceous depositional age. The other Formations of the Tansen Group are more similar to Tethys units than to Higher Himalaya. Further, the 23+/-1 Ma zircons in two of the crystalline Higher Himalaya units suggest that they could not have been exposed until at or after this time.

Modeling deformation processes of salt caverns for gas storage due to fluctuating operation pressures

NASA Astrophysics Data System (ADS)

Böttcher, N.; Nagel, T.; Goerke, U.; Khaledi, K.; Lins, Y.; König, D.; Schanz, T.; Köhn, D.; Attia, S.; Rabbel, W.; Bauer, S.; Kolditz, O.

2013-12-01

In the course of the Energy Transition in Germany, the focus of the country's energy sources is shifting from fossil to renewable and sustainable energy carriers. Since renewable energy sources, such as wind and solar power, are subjected to annual, seasonal, and diurnal fluctuations, the development and extension of energy storage capacities is a priority in German R&D programs. Common methods of energy storage are the utilization of subsurface caverns as a reservoir for natural or artificial fuel gases, such as hydrogen, methane, or the storage of compressed air. The construction of caverns in salt rock is inexpensive in comparison to solid rock formations due to the possibility of solution mining. Another advantage of evaporite as a host material is the self-healing capacity of salt rock. Gas caverns are capable of short-term energy storage (hours to days), so the operating pressures inside the caverns are fluctuating periodically with a high number of cycles. This work investigates the influence of fluctuating operation pressures on the stability of the host rock of gas storage caverns utilizing numerical models. Therefore, we developed a coupled Thermo-Hydro-Mechanical (THM) model based on the finite element method utilizing the open-source software platform OpenGeoSys. Our simulations include the thermodynamic behaviour of the gas during the loading/ unloading of the cavern. This provides information on the transient pressure and temperature distribution on the cavern boundary to calculate the deformation of its geometry. Non-linear material models are used for the mechanical analysis, which describe the creep and self-healing behavior of the salt rock under fluctuating loading pressures. In order to identify the necessary material parameters, we perform experimental studies on the mechanical behaviour of salt rock under varying pressure and temperature conditions. Based on the numerical results, we further derive concepts for monitoring THM quantities in the vicinity of the cavern. These programs will allow detecting changes of the host rock properties during the construction and operation of the storage facility. The developed model will be used by public authorities for land use planning issues.

Evolution of silicic magma in the upper crust: the mid-Tertiary Latir volcanic field and its cogenetic granitic batholith, northern New Mexico, USA

USGS Publications Warehouse

Lipman, P.W.

1988-01-01

Structural and topographic relief along the eastern margin of the Rio Grande rift, northern New Mexico, provides a remarkable cross-section through the 26-Ma Questa caldera and cogenetic volcanic and plutonic rocks of the Latir field. Exposed levels increase in depth from mid-Tertiary depositional surfaces in northern parts of the igneous complex to plutonic rocks originally at 3-5 km depths in the S. Erosional remnants of an ash-flow sheet of weakly peralkaline rhyolite (Amalia Tuff) and andesitic to dactitic precursor lavas, disrupted by rift-related faults, are preserved as far as 45 km beyond their sources at the Questa caldera. Broadly comagmatic 26 Ma batholithic granitic rocks, exposed over an area of 20 by 35 km, range from mesozonal granodiorite to epizonal porphyritic granite and aplite; shallower and more silicic phases are mostly within the caldera. Compositionally and texturally distinct granites defined resurgent intrusions within the caldera and discontinuous ring dikes along its margins: a batholithic mass of granodiorite extends 20 km S of the caldera and locally grades vertically to granite below its flat-lying roof. A negative Bouguer gravity anomaly (15-20 mgal), which encloses exposed granitic rocks and coincides with boundaries of the Questa caldera, defined boundaries of the shallow batholith, emplaced low in the volcanic sequence and in underlying Precambrian rocks. Paleomagnetic pole positions indicate that successively crystallised granitic plutons cooled through Curie temperatures during the time of caldera formation, initial regional extension, and rotational tilting of the volcanic rocks. Isotopic ages for most intrusions are indistinguishable from the volcanic rocks. These relations indicate that the batholithic complex broadly represents the source magma for the volcanic rocks, into which the Questa caldera collapsed, and that the magma was largely liquid during regional tectonic disruption. -from Author

The Potential Role of Formate for Synthesis and Life in Serpentinization Systems

NASA Astrophysics Data System (ADS)

Lang, S. Q.; Frueh-Green, G. L.; Bernasconi, S. M.; Brazelton, W. J.; McGonigle, J. M.

2016-12-01

The high hydrogen concentrations produced during water-rock serpentinization reactions provide abundant thermodynamic energy that can drive the synthesis of organic compounds both biotically and abiotically. We investigated the synthesis of abiotic carbon and the metabolic pathways of the microbial inhabitants of the high energy but low diversity serpentinite-hosted Lost City Hydrothermal Field. High concentrations of the organic acid formate can be attributed to two sources. In some locations formate lacks detectable 14C, demonstrating it was formed abiotically from mantle-derived CO2. In other locations there is an additional modern contribution to the formate pool, potentially indicating active cycling with modern seawater dissolved inorganic carbon by microorganisms. The presence of this carbon source is likely critical for the survival of the subsurface microbial communities that inhabit alkaline serpentinization environments, where inorganic carbon is severely limited. Archaeal lipids produced by the Lost City Methanosarcinales (LCMS) also largely lack 14C, requiring their carbon source to be similarly 14C-free. Metagenomic evidence suggests that the LCMS could use formate for methanogenesis and, altogether, the data suggests that these organisms cannot rely on inorganic carbon as their carbon source and substrate for methanogenesis. Considering the lack of dissolved inorganic carbon in this system, the ability to utilize formate may have been a key evolutionary adaptation for survival in serpentinite-hosted environments. In the Lost City system, the LCMS apparently rely upon an abiotically produced organic carbon source, which may enable the Lost City microbial ecosystem to survive in the absence of photosynthesis or its byproducts.

A CO2-Silica Geothermometer for Low Temperature Geothermal Resource Assessment, with Application to Resources in the Safford Basin, Arizona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Witcher, James C.; Stone, Claudia

1983-11-01

Geothermics is the study of the earth's heat energy, it's affect on subsurface temperature distribution, it's physical and chemical sources, and it's role in dynamic geologic processes. The term, geothermometry, is applied to the determination of equilibrium temperatures of natural chemical systems, including rock, mineral, and liquid phases. An assemblage of minerals or a chemical system whose phase composition is a function of temperature and pressure can be used as a geothermometer. Thus a geothermometer is useful to determine the formation temperature of rock or the last equilibrium temperature of a flowing aqueous solution such as ground water and hydrothermalmore » fluids.« less

Structural controls and evolution of gold-, silver-, and REE-bearing copper-cobalt ore deposits, Blackbird district, east-central Idaho: Epigenetic origins

USGS Publications Warehouse

Lund, K.; Tysdal, Russell G.; Evans, Karl V.; Kunk, Michael J.; Pillers, Renee M.

2011-01-01

Textural data at all scales indicate that the host sites for veins and the tectonic evolution of both host rocks and mineral deposits were kinematically linked to Late Cretaceous regional thrust faulting. Heat, fluids, and conduits for generation and circulation of fluids were part of the regional crustal thickening. The faulting also juxtaposed metaevaporite layers in the Mesoproterozoic Yellowjacket Formation over Blackbird district host rocks. We conclude that this facilitated chemical exchange between juxtaposed units resulting in leaching of critical elements (Cl, K, B, Na) from metaevaporites to produce brines, scavenging of metals (Co, Cu, etc) from rocks in the region, and, finally, concentrating metals in the lower-plate ramp structures. Although the ultimate source of the metals remains undetermined, the present Cu-Co ± Au (± Ag ± Ni ± REE) Blackbird ore deposits formed during Late Cretaceous compressional deformation.

Vestiges of the proto-Caribbean seaway: Origin of the San Souci Volcanic Group, Trinidad

NASA Astrophysics Data System (ADS)

Neill, Iain; Kerr, Andrew C.; Chamberlain, Kevin R.; Schmitt, Axel K.; Urbani, Franco; Hastie, Alan R.; Pindell, James L.; Barry, Tiffany L.; Millar, Ian L.

2014-06-01

Outcrops of volcanic-hypabyssal rocks in Trinidad document the opening of the proto-Caribbean seaway during Jurassic-Cretaceous break-up of the Americas. The San Souci Group on the northern coast of Trinidad comprises the San Souci Volcanic Formation (SSVF) and passive margin sediments of the ~ 130-125 Ma Toco Formation. The Group was trapped at the leading edge of the Pacific-derived Caribbean Plate during the Cretaceous-Palaeogene, colliding with the para-autochthonous margin of Trinidad during the Oligocene-Miocene. In-situ U-Pb ion probe dating of micro-zircons from a mafic volcanic breccia reveal the SSVF crystallised at 135.0 ± 7.3 Ma. The age of the SSVF is within error of the age of the Toco Formation. Assuming a conformable contact, geodynamic models indicate a likely origin for the SSVF on the passive margin close to the northern tip of South America. Immobile element and Nd-Hf radiogenic isotope signatures of the mafic rocks indicate the SSVF was formed by ≪10% partial melting of a heterogeneous spinel peridotite source with no subduction or continental lithospheric mantle component. Felsic breccias within the SSVF are more enriched in incompatible elements, with isotope signatures that are less radiogenic than the mafic rocks of the SSVF. The felsic rocks may be derived from re-melting of mafic crust. Although geochemical comparisons are drawn here with proto-Caribbean igneous outcrops in Venezuela and elsewhere in the Caribbean more work is needed to elucidate the development of the proto-Caribbean seaway and its rifted margins. In particular, ion probe dating of micro-zircons may yield valuable insights into magmatism and metamorphism in the Caribbean, and in altered basaltic terranes more generally.

Effects of fluid-rock interactions on faulting within active fault zones - evidence from fault rock samples retrieved from international drilling projects

NASA Astrophysics Data System (ADS)

Janssen, C.; Wirth, R.; Kienast, M.; Yabe, Y.; Sulem, J.; Dresen, G. H.

2015-12-01

Chemical and mechanical effects of fluids influence the fault mechanical behavior. We analyzed fresh fault rocks from several scientific drilling projects to study the effects of fluids on fault strength. For example, in drill core samples on a rupture plane of an Mw 2.2 earthquake in a deep gold mine in South Africa the main shock occurred on a preexisting plane of weakness that was formed by fluid-rock interaction (magnesiohornblende was intensively altered to chlinochlore). The plane acted as conduit for hydrothermal fluids at some time in the past. The chemical influence of fluids on mineralogical alteration and geomechanical processes in fault core samples from SAFOD (San Andreas Fault Observatory at Depth) is visible in pronounced dissolution-precipitation processes (stylolites, solution seams) as well as in the formation of new phases. Detrital quartz and feldspar grains are partially dissolved and replaced by authigenic illite-smectite (I-S) mixed-layer clay minerals. Transmission Electron Microscopy (TEM) imaging of these grains reveals that the alteration processes and healing were initiated within pores and small intra-grain fissures. Newly formed phyllosilicates growing into open pore spaces likely reduced the fluid permeability. The mechanical influence of fluids is indicated by TEM observations, which document open pores that formed in-situ in the gouge material during or after deformation. Pores were possibly filled with formation water and/or hydrothermal fluids suggesting elevated fluid pressure preventing pore collapse. Fluid-driven healing of fractures in samples from SAFOD and the DGLab Gulf of Corinth project is visible in cementation. Cathodoluminescence microscopy (CL) reveals different generations of calcite veins. Differences in CL-colors suggest repeated infiltration of fluids with different chemical composition from varying sources (formation and meteoric water).

Metallogeny of the midcontinent rift system of North America

USGS Publications Warehouse

Nicholson, S.W.; Cannon, W.F.; Schulz, K.J.

1992-01-01

The 1.1 Ga Midcontinent rift system of North America is one of the world's major continental rifts and hosts a variety of mineral deposits. The rocks and mineral deposits of this 2000 km long rift are exposed only in the Lake Superior region. In the Lake Superior region, the rift cuts across Precambrian basement terranes ranging in age from ??? 1850 Ma to more than 3500 Ma. Where exposed, the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks. Beneath the center of Lake Superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection profiles. This region hosts two major classes of mineral deposits, magmatic and hydrothermal. All important mineral production in this region has come from hydrothermal deposits. Rift-related hydrothermal deposits include four main types: (1) native copper deposits in basalts and interflow sediments; (2) sediment-hosted copper sulfide and native copper; (3) copper sulfide veins and lodes hosted by rift-related volcanic and sedimentary rocks; and (4) polymetallic (five-element) veins in the surrounding Archean country rocks. The scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals. Where hydrothermal sulfides occur (i.e., shale-hosted copper sulfides), the source of sulfur was local sedimentary rocks. Magmatic deposits have locally supported exploration and minor production, but most are subeconomic presently. These deposits occur in intrusions exposed near the margins of the rift and include CuNiPGE and TiFe (V) in the Duluth Complex, U-REE-Nb in small carbonatites, and breccia pipes resulting from local hydrothermal activity around small felsic intrusions. Mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization. Most of the sulfide deposits in intrusions, however, contain sulfur derived from country rocks; the interaction between magma and country rocks was important in generation of the magmatic CuNi sulfide deposits. A mantle plume origin has been proposed for the formation of the Midcontinent rift. More than 1 million km3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift, providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines. These brines were heated by a steep geothermal gradient that resulted from the melting and underplating of magma derived from the plume. Hydrothermal deposits were emplaced for at least 30-40 m.y. after rift magmatism and extension ceased. This time lag may reflect either the time required to heat deeply buried rocks and fluids within the rift, or may be due to the timing of post-rift compression that may have provided the driving mechanism for expulsion of hydrothermal fluids from deep portions of the rift. ?? 1992.

Deep-water lithofacies and conodont faunas of the Lisburne Group, western Brooks Range, Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1992

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Anita G.; Schmidt, Jeanine M.

1993-01-01

Deep-water lithofacies of the Lisburne Group occur in thrust sheets in the western part of the foreland fold and thrust belt of the Brooks Range and represent at least three discrete units. The Kuna Formation (Brooks Range allochthon) consists mostly of spiculitic mudstone and lesser shale; subordinate carbonate layers are chiefly diagenetic dolomite. Predominantly shale sections of the Kuna that contain few sponge spicules occur in the western part of the study area. The Akmalik Chert (Picnic Creek allochthon) is mostly radiolarian-spiculitic chert; rare limy beds are calcitized radiolarite. The Rim Butte unit (Ipnavik River allochthon) consists chiefly of calcareous turbidites, derived from both shallow- and deep-water sources, interbedded with spiculitic mudstone. Much of the material in the turbidites came from a contemporaneous carbonate platform and margin, but some fossils and lithic clasts were eroded from older, already lithified carbonate-platform rocks. All three units appear to be roughly coeval and are chiefly Osagean (late Early Mississippian) in age in the study area.Shallow-water lithofacies of the Lisburne Group exposed in the Howard Pass area (Brooks Range allochthon) are mostly of Meramecian (early Late Mississippian) age. Thus, these carbonate-platform rocks were not the source of the calcareous turbidites in the Rim Butte unit. Rim Butte turbidites could have been derived from older platform carbonate rocks such as those of the Utukok Formation (Kelly River allochthon) exposed mainly to the west of the Howard Pass quadrangle.

The influence of spreading rate, basement composition, fluid chemistry and chimney morphology on the formation of gold-rich SMS deposits at slow and ultraslow mid-ocean ridges

NASA Astrophysics Data System (ADS)

Knight, Robert D.; Roberts, Stephen; Webber, Alexander P.

2018-01-01

Seafloor massive sulphide (SMS) deposits are variably enriched in precious metals including gold. However, the processes invoked to explain the formation of auriferous deposits do not typically apply to mid-ocean ridge settings. Here, we show a statistically significant, negative correlation between the average gold concentration of SMS deposits with spreading rate, at non-sedimented mid-ocean ridges. Deposits located at slow spreading ridges (20-40 mm/a) have average gold concentrations of between 850 and 1600 ppb; however, with increasing spreading rate (up to 140 mm/a), gold concentrations gradually decrease to between 50 and 150 ppb. This correlation of gold content with spreading rate may be controlled by the degree and duration of fluid-rock interaction, which is a function of the heat flux, crustal structure (faulting) and the permeability of the source rocks. Deposits at ultraslow ridges, including ultramafic-hosted deposits, are particularly enriched in gold. This is attributed to the higher permeability of the ultramafic source rocks achieved by serpentinisation and the inherent porosity of serpentine minerals, combined with relatively high gold concentrations in peridotite compared with mid-ocean ridge basalt. Variations in fluid chemistry, such as reducing conditions and the potential for increased sulphur availability at ultramafic-hosted sites, may also contribute to the high concentrations observed. Beehive chimneys, which offer more favourable conditions for gold precipitation, may be more prevalent at ultramafic-hosted sites due to diffuse low-velocity venting compared with more focussed venting at basalt-hosted sites.

Re-Os geochronology and Os isotope fingerprinting of petroleum sourced from a Type I lacustrine kerogen: Insights from the natural Green River petroleum system in the Uinta Basin and hydrous pyrolysis experiments

NASA Astrophysics Data System (ADS)

Cumming, Vivien M.; Selby, David; Lillis, Paul G.; Lewan, Michael D.

2014-08-01

Rhenium-osmium (Re-Os) geochronology of marine petroleum systems has allowed the determination of the depositional age of source rocks as well as the timing of petroleum generation. In addition, Os isotopes have been applied as a fingerprinting tool to correlate oil to its source unit. To date, only classic marine petroleum systems have been studied. Here we present Re-Os geochronology and Os isotope fingerprinting of different petroleum phases (oils, tar sands and gilsonite) derived from the lacustrine Green River petroleum system in the Uinta Basin, USA. In addition we use an experimental approach, hydrous pyrolysis experiments, to compare to the Re-Os data of naturally generated petroleum in order to further understand the mechanisms of Re and Os transfer to petroleum. The Re-Os geochronology of petroleum from the lacustrine Green River petroleum system (19 ± 14 Ma - all petroleum phases) broadly agrees with previous petroleum generation basin models (∼25 Ma) suggesting that Re-Os geochronology of variable petroleum phases derived from lacustrine Type I kerogen has similar systematics to Type II kerogen (e.g., Selby and Creaser, 2005a,b; Finlay et al., 2010). However, the large uncertainties (over 100% in some cases) produced for the petroleum Re-Os geochronology are a result of multiple generation events occurring through a ∼3000-m thick source unit that creates a mixture of initial Os isotope compositions in the produced petroleum phases. The 187Os/188Os values for the petroleum and source rocks at the time of oil generation vary from 1.4 to 1.9, with the mode at ∼1.6. Oil-to-source correlation using Os isotopes is consistent with previous correlation studies in the Green River petroleum system, and illustrates the potential utility of Os isotopes to characterize the spatial variations within a petroleum system. Hydrous pyrolysis experiments on the Green River Formation source rocks show that Re and Os transfer are mimicking the natural system. This transfer from source to bitumen to oil does not affect source rock Re-Os systematics or Os isotopic compositions. This confirms that Os isotope compositions are transferred intact from source to petroleum during petroleum generation and can be used as a powerful correlation tool. These experiments further confirm that Re-Os systematics in source rocks are not adversely affected by petroleum maturation. Overall this study illustrates that the Re-Os petroleum geochronometer and Os isotope fingerprinting tools can be used on a wide range of petroleum types sourced from variable kerogen types.

Re-Os geochronology and Os isotope fingerprinting of petroleum sourced from a Type I lacustrine kerogen: insights from the natural Green River petroleum system in the Uinta Basin and hydrous pyrolysis experiments

USGS Publications Warehouse

Cumming, Vivien M.; Selby, David; Lillis, Paul G.; Lewan, Michael D.

2014-01-01

Rhenium–osmium (Re–Os) geochronology of marine petroleum systems has allowed the determination of the depositional age of source rocks as well as the timing of petroleum generation. In addition, Os isotopes have been applied as a fingerprinting tool to correlate oil to its source unit. To date, only classic marine petroleum systems have been studied. Here we present Re–Os geochronology and Os isotope fingerprinting of different petroleum phases (oils, tar sands and gilsonite) derived from the lacustrine Green River petroleum system in the Uinta Basin, USA. In addition we use an experimental approach, hydrous pyrolysis experiments, to compare to the Re–Os data of naturally generated petroleum in order to further understand the mechanisms of Re and Os transfer to petroleum. The Re–Os geochronology of petroleum from the lacustrine Green River petroleum system (19 ± 14 Ma – all petroleum phases) broadly agrees with previous petroleum generation basin models (∼25 Ma) suggesting that Re–Os geochronology of variable petroleum phases derived from lacustrine Type I kerogen has similar systematics to Type II kerogen (e.g., Selby and Creaser, 2005a, Selby and Creaser, 2005b and Finlay et al., 2010). However, the large uncertainties (over 100% in some cases) produced for the petroleum Re–Os geochronology are a result of multiple generation events occurring through a ∼3000-m thick source unit that creates a mixture of initial Os isotope compositions in the produced petroleum phases. The 187Os/188Os values for the petroleum and source rocks at the time of oil generation vary from 1.4 to 1.9, with the mode at ∼1.6. Oil-to-source correlation using Os isotopes is consistent with previous correlation studies in the Green River petroleum system, and illustrates the potential utility of Os isotopes to characterize the spatial variations within a petroleum system. Hydrous pyrolysis experiments on the Green River Formation source rocks show that Re and Os transfer are mimicking the natural system. This transfer from source to bitumen to oil does not affect source rock Re–Os systematics or Os isotopic compositions. This confirms that Os isotope compositions are transferred intact from source to petroleum during petroleum generation and can be used as a powerful correlation tool. These experiments further confirm that Re–Os systematics in source rocks are not adversely affected by petroleum maturation. Overall this study illustrates that the Re–Os petroleum geochronometer and Os isotope fingerprinting tools can be used on a wide range of petroleum types sourced from variable kerogen types.

Contrasting sources of Late Paleozoic rhyolite magma in the Polish Lowlands: evidence from U-Pb ages and Hf and O isotope composition in zircon

NASA Astrophysics Data System (ADS)

Słodczyk, Elżbieta; Pietranik, Anna; Glynn, Sarah; Wiedenbeck, Michael; Breitkreuz, Christoph; Dhuime, Bruno

2018-02-01

The Polish Lowlands, located southwest of the Teisseyre-Tornquist Zone, within Trans-European Suture Zone, were affected by bimodal, but dominantly rhyolitic, magmatism during the Late Paleozoic. Thanks to the inherited zircon they contain, these rhyolitic rocks provide a direct source of information about the pre-Permian rocks underlying the Polish Lowland. This paper presents zircon U-Pb geochronology and Hf and O isotopic results from five drill core samples representing four rhyolites and one granite. Based on the ratio of inherited vs. autocrystic zircon, the rhyolites can be divided into two groups: northern rhyolites, where autocrystic zircon is more abundant and southern rhyolites, where inherited zircon dominates. We suggest that the magma sources and the processes responsible for generating high silica magmas differ between the northern and southern rhyolites. Isotopically distinct sources were available during formation of northern rhyolites, as the Hf and O isotopes in magmatic zircon differ between the two analysed localities of northern rhyolites. A mixing between magmas formed from Baltica-derived mudstone-siltstone sediments and Avalonian basement or mantle can explain the diversity between the zircon compositions from the northern localities Daszewo and Wysoka Kamieńska. Conversely, the southern rhyolites from our two localities contain zircon with similar compositions, and these units can be further correlated with results from the North East German Basin, suggesting uniform source rocks over this larger region. Based on the ages of inherited zircon and the isotopic composition of magmatic ones, we suggest that the dominant source of the southern rhyolites is Variscan foreland sediments mixed with Baltica/Avalonia-derived sediments.

Geologic Assessment of Undiscovered Gas Resources of the Eastern Oregon and Washington Province

USGS Publications Warehouse

U.S. Geological Survey Eastern Oregon and Washington Province Assessment Team, (compiler)

2008-01-01

The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geology-based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States, focusing on the distribution, quantity, and availability of oil and natural gas resources. The USGS has completed an assessment of the undiscovered oil and gas potential of the Eastern Oregon and Washington Province of Oregon and Washington (USGS Province 5005). The province is a priority Energy Policy and Conservation Act (EPCA) province for the National Assessment because of its potential for oil and gas resources. The assessment of this province is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (stratigraphy, sedimentology, petrophysical properties), and hydrocarbon traps (trap formation and timing). In the Eastern Oregon and Washington Province, the USGS used this geologic framework to define one total petroleum system and two assessment units within the total petroleum system, and quantitatively estimated the undiscovered gas resources within each assessment unit.

Petrology and isotopic geochemistry of the Archaean basement lithologies near Gardiner, Montana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guy, R.E.; Sinha, A.K.

1985-01-01

In an attempt to recognize potential source rocks for some of the rhyolites of the Yellowstone Rhyolite Plateau, four major exposures of Precambrian rocks have been analyzed for major and trace elements and isotopic composition. The terrain is characterized by granitic gneisses with subordinant mica schist, quartzite, amphibolite, and two-mica granite. The gneiss units from the northern (Yankee Jim Canyon) and eastern (Lamar Canyon) outcrops are characterized by k-feldspar augen in a gneissic groundmass of two-feldspar--quartz--mica--epidote. The feldspar compositions are Or/sub 95/ and An/sub 5-15/ indicating metamorphic re-equilibration. Mafic phases are iron-rich with Fe:Mg of 1.0 in epidote, 0.7 inmore » pyroxene, and 0.5 in biotite. Sr isotopic analyses yield present day values of 0.7201-0.7519 for Lamar Canyon, 0.7157-0.7385 for Yankee Jam Canyon, and 0.7200-0.7679 for mica schist from the western and northern outcrops. Rb-Sr whole-rock data indicate a complicated isotopic history with ages ranging from 2800 to 3600 my. The 2800 my ages are consistent with ages for the Tobacco Root and Ruby Mountains to the NW (James and Hedge, 1980) and the Beartooth Range to the NE (Nunes and Tilton, 1971) while the 3600 my age may be related to the formation of the protolith. The rhyolites of the northern Yellowstone Rhyolite Plateau (Sr/sub I/=0.7100) cannot be derived from the exposed Archaean rocks based on Sr isotopic and whole-rock chemistry, and must be derived from lithologies not exposed in the area. This study shows that care must be taken when using surface lithologies to model potential sources materials for volcanic rocks in an associated terrain.« less

Three-dimensional seismic tomography from P wave and S wave microearthquake travel times and rock physics characterization of the Campi Flegrei Caldera

NASA Astrophysics Data System (ADS)

Vanorio, T.; Virieux, J.; Capuano, P.; Russo, G.

2005-03-01

The Campi Flegrei (CF) Caldera experiences dramatic ground deformations unsurpassed anywhere in the world. The source responsible for this phenomenon is still debated. With the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes, a multidisciplinary approach dealing with three-dimensional delay time tomography and rock physics characterization has been followed. Selected seismic data were modeled by using a tomographic method based on an accurate finite difference travel time computation which simultaneously inverts P wave and S wave first-arrival times for both velocity model parameters and hypocenter locations. The retrieved P wave and S wave velocity images as well as the deduced Vp/Vs images were interpreted by using experimental measurements of rock physical properties on CF samples to take into account steam/water phase transition mechanisms affecting P wave and S wave velocities. Also, modeling of petrophysical properties for site-relevant rocks constrains the role of overpressured fluids on velocity. A flat and low Vp/Vs anomaly lies at 4 km depth under the city of Pozzuoli. Earthquakes are located at the top of this anomaly. This anomaly implies the presence of fractured overpressured gas-bearing formations and excludes the presence of melted rocks. At shallow depth, a high Vp/Vs anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase. Finally, maps of the Vp*Vs product show a high Vp*Vs horseshoe-shaped anomaly located at 2 km depth. It is consistent with gravity data and well data and might constitute the on-land remainder of the caldera rim, detected below sea level by tomography using active source seismic data.

Petrogenetic and geodynamic origin of the Neoarchean Doré Lake Complex, Abitibi subprovince, Superior Province, Canada

NASA Astrophysics Data System (ADS)

Polat, Ali; Frei, Robert; Longstaffe, Fred J.; Woods, Ryan

2018-04-01

The Neoarchean (ca. 2728 Ma) anorthosite-bearing Doré Lake Complex in the northeastern Abitibi subprovince, Quebec, was emplaced into an association of intra-oceanic tholeiitic basalts and gabbros known as the Obatogamau Formation. The Obatogamau Formation constitutes the lower part of the Roy Group, which is composed of two cycles of tholeiitic-to-calc-alkaline volcanic and volcaniclastic rocks, siliciclastic and chemical sedimentary rocks, and layered mafic-to-ultramafic sills. In this study, we report major and trace element results, and Nd, Sr, Pb and O isotope data for anorthosites, leucogabbros, gabbros and mafic dykes from the Doré Lake Complex and spatially associated basalts and gabbros of the Obatogamau Formation to assess their petrogenetic origin and geodynamic setting. Field and petrographic observations indicate that the Doré Lake Complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions, resulting in widespread epidotization (20-40%) and chloritization (10-40%) of many rock types. Plagioclase recrystallized mainly to anorthite and albite endmembers, erasing intermediate compositions. Metamorphic alteration also led to the mobilization of many elements (e.g., LILE and transition metals) and to significant disturbance of the Rb-Sr and U-Pb isotope systems, resulting in 1935 ± 150 and 3326 ± 270 Ma errorchron ages, respectively. The Sm-Nd isotope system was less disturbed, yielding an errorchron age of 2624 ± 160 Ma. On many binary major and trace element diagrams, the least altered anorthosites and leucogabbros, and the gabbros and mafic dykes of the Doré Lake Complex plot in separate fields, signifying the presence of two distinct magma types in the complex. The gabbros and mafic dykes in the Doré Lake Complex share the geochemical characteristics of tholeiitic basalts and gabbros in the Obatogamau Formation, suggesting a possible genetic link between the two rock associations. Initial ɛNd (+2.6 to +5.0) and δ18O (+6.1 to +7.9‰) values for the Doré Lake Complex and gabbros of the Obatogamau Formation (ɛNd = +2.8 to +4.0; δ18O = +7.3 to 8.0‰) are consistent with depleted mantle sources. All rock types in the Doré Lake Complex and the Roy Group share the trace element characteristics of modern arc magmas, suggesting a suprasubduction zone setting for these two lithological associations. On the basis of regional geology and geochemical data, we suggest that the Doré Lake Complex and the Obatogamau Formation represent a dismembered fragment of a suture zone, like many Phanerozoic ophiolites, resulting from closure of a back-arc basin between 2703 and 2690 Ma.

Fluctuations in fluvial style in the Wasatch Formation, Piceance Basin, Colorado: Climatic, tectonic, or sediment driven

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nadon, G.C.; Lorenz, J.C.; Lafrenier, L.

1996-01-01

The Molina Member of the Wasatch Formation is a primary objective for light gas sandstone production. The G-Sandstone unit of the Molina produces an average of 200 MCFGPD. The chert-rich sandstones and conglomerates of the Molina Member, which are exposed in two subparallel belts on the western and eastern sides of the basin, are strikingly different from the remainder of the Wasatch formation. The underlying Atwell Gulch Member and overlying Shire Member are composed of floodplain mudstones with well developed paleosols and rare, lenticular channel sandstones. Both units are interpreted as anastomosed fluvial deposits. The Molina Member, which varies frommore » 32-118 m thick and in places contains clasts >0.2 m, is more difficult to interpret. Different portions of individual sections contain significant proportions of parallel laminated sandstones up to 5 m thick and several hundred meters wide. These parallel laminated sandstones are most common to the north along the western outcrop bell. They are interbedded with sandstones and conglomerates that are typical of a braided fluvial deposit. The contact between the two fluvial styles is sharp but conformable. The Molina Member therefore represents a perturbation in fluvial style from suspended-load to bedload and back to suspended-load over a restricted time interval. This may be the product of a change in climate, i.e., a change in rainfall amount or timing in the source area, source rock, e.g., the unroofing of a Jurassic eolian sandstone, or an increase in the depositional slope due to uplift. The return to a mud-dominated depositional system in the Shire Member argues for either climatic or source-rock variations as the primary control of the fluvial style.« less

Fluctuations in fluvial style in the Wasatch Formation, Piceance Basin, Colorado: Climatic, tectonic, or sediment driven?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nadon, G.C.; Lorenz, J.C.; Lafrenier, L.

1996-12-31

The Molina Member of the Wasatch Formation is a primary objective for light gas sandstone production. The G-Sandstone unit of the Molina produces an average of 200 MCFGPD. The chert-rich sandstones and conglomerates of the Molina Member, which are exposed in two subparallel belts on the western and eastern sides of the basin, are strikingly different from the remainder of the Wasatch formation. The underlying Atwell Gulch Member and overlying Shire Member are composed of floodplain mudstones with well developed paleosols and rare, lenticular channel sandstones. Both units are interpreted as anastomosed fluvial deposits. The Molina Member, which varies frommore » 32-118 m thick and in places contains clasts >0.2 m, is more difficult to interpret. Different portions of individual sections contain significant proportions of parallel laminated sandstones up to 5 m thick and several hundred meters wide. These parallel laminated sandstones are most common to the north along the western outcrop bell. They are interbedded with sandstones and conglomerates that are typical of a braided fluvial deposit. The contact between the two fluvial styles is sharp but conformable. The Molina Member therefore represents a perturbation in fluvial style from suspended-load to bedload and back to suspended-load over a restricted time interval. This may be the product of a change in climate, i.e., a change in rainfall amount or timing in the source area, source rock, e.g., the unroofing of a Jurassic eolian sandstone, or an increase in the depositional slope due to uplift. The return to a mud-dominated depositional system in the Shire Member argues for either climatic or source-rock variations as the primary control of the fluvial style.« less

Detrital and volcanic zircon U-Pb ages from southern Mendoza (Argentina): An insight on the source regions in the northern part of the Neuquén Basin

NASA Astrophysics Data System (ADS)

Naipauer, Maximiliano; Tapia, Felipe; Mescua, José; Farías, Marcelo; Pimentel, Marcio M.; Ramos, Victor A.

2015-12-01

The infill of the Neuquén Basin recorded the Meso-Cenozoic geological and tectonic evolution of the southern Central Andes being an excellent site to investigate how the pattern of detrital zircon ages varies trough time. In this work we analyze the U-Pb (LA-MC-ICP-MS) zircon ages from sedimentary and volcanic rocks related to synrift and retroarc stages of the northern part of the Neuquén Basin. These data define the crystallization age of the synrift volcanism at 223 ± 2 Ma (Cerro Negro Andesite) and the maximum depositional age of the original synrift sediments at ca. 204 Ma (El Freno Formation). Two different pulses of rifting could be recognized according to the absolute ages, the oldest developed during the Norian and the younger during the Rhaetian-Sinemurian. The source regions of the El Freno Formation show that the Choiyoi magmatic province was the main source rock of sediment supply. An important amount of detrital zircons with Triassic ages was identified and interpreted as a source area related to the synrift magmatism. The maximum depositional age calculated for the Tordillo Formation in the Atuel-La Valenciana depocenter is at ca. 149 Ma; as well as in other places of the Neuquén Basin, the U-Pb ages calculated in the Late Jurassic Tordillo Formation do not agree with the absolute age of the Kimmeridgian-Tithonian boundary (ca. 152 Ma). The main source region of sediment in the Tordillo Formation was the Andean magmatic arc. Basement regions were also present with age peaks at the Carboniferous, Neoproterozoic, and Mesoproterozoic; these regions were probably located to the east in the San Rafael Block. The pattern of zircon ages summarized for the Late Jurassic Tordillo and Lagunillas formations were interpreted as a record of the magmatic activity during the Triassic and Jurassic in the southern Central Andes. A waning of the magmatism is inferred to have happened during the Triassic. The evident lack of ages observed around ca. 200 Ma suggests cessation of the synrift magmatism. The later increase in magmatic activity during the Early Jurassic is attributed to the onset of Andean subduction, with maximum peaks at ca. 191 and 179 Ma. The trough at ca. 165 Ma and the later increase in the Late Jurassic could be explained by changes in the relative convergence rate in the Andean subduction regime, or by the shift to a more mafic composition of the magmatism with minor zircon fertility.

The Jurassic section along McElmo Canyon in southwestern Colorado

USGS Publications Warehouse

O'Sullivan, Robert B.

1997-01-01

In McElmo Canyon, Jurassic rocks are 1500-1600 ft thick. Lower Jurassic rocks of the Glen Canyon Group include (in ascending order) Wingate Sandstone, Kayenta Formation and Navajo Sandstone. Middle Jurassic rocks are represented by the San Rafael Group, which includes the Entrada Sandstone and overlying Wanakah Formation. Upper Jurassic rocks comprise the Junction Creek Sandstone overlain by the Morrison Formation. The Burro Canyon Formation, generally considered to be Lower Cretaceous, may be Late Jurassic in the McElmo Canyon area and is discussed with the Jurassic. The Upper Triassic Chinle Formation in the subsurface underlies, and the Upper Cretaceous Dakota Sandstone overlies, the Jurassic section. An unconformity is present at the base of the Glen Canyon Group (J-0), at the base of the San Rafael Group (J-2), and at the base of the Junction Creek Sandstone (J-5). Another unconformity of Cretaceous age is at the base of the Dakota Sandstone. Most of the Jurassic rocks consist of fluviatile, lacustrine and eolian deposits. The basal part of the Entrada Sandstone and the Wanakah Formation may be of marginal marine origin.

Fan-structure wave as a source of earthquake instability

NASA Astrophysics Data System (ADS)

Tarasov, Boris

2015-04-01

Today frictional shear resistance along pre-existing faults is considered to be the lower limit on rock shear strength at confined compression corresponding to the seismogenic layer. This determines the lithospheric strength and the primary earthquake mechanism associated with frictional stick-slip instability on pre-existing faults. This paper introduces a recently identified shear rupture mechanism providing a paradoxical feature of hard rocks - the possibility of shear rupture propagation through the highly confined intact rock mass at shear stress levels significantly less than frictional strength. In the new mechanism the rock failure, associated with consecutive creation of small slabs (known as 'domino-blocks') from the intact rock in the rupture tip, is driven by a fan-shaped domino structure representing the rupture head. The fan-head combines such unique features as: extremely low shear resistance (below the frictional strength), self-sustaining stress intensification in the rupture tip (providing easy formation of new domino-blocks), and self-unbalancing conditions in the fan-head (making the failure process inevitably spontaneous and violent). An important feature of the fan-mechanism is the fact that for the initial formation of the fan-structure an enhanced local shear stress is required, however, after completion of the fan-structure it can propagate as a dynamic wave through intact rock mass at shear stresses below the frictional strength. Paradoxically low shear strength of pristine rocks provided by the fan-mechanism determines the lower limit of the lithospheric strength and favours the generation of new faults in pristine rocks in preference to frictional stick-slip instability along pre-existing faults. The new approach reveals an alternative role of pre-existing faults in earthquake activity: they represent local stress concentrates in pristine rock adjoining the fault where special conditions for the fan-mechanism nucleation are created, while further dynamic propagation of the new fault (earthquake) occurs at low field stresses even below the frictional strength. However, the proximity of the pre-existing discontinuities to the area of instability caused by the fan mechanism creates the illusion of stick-slip instability on the pre-existing faults, thus concealing the real situation.

Petroleum geology and resources of the North Caspian Basin, Kazakhstan and Russia

USGS Publications Warehouse

Ulmishek, Gregory F.

2001-01-01

The North Caspian basin is a petroleum-rich but lightly explored basin located in Kazakhstan and Russia. It occupies the shallow northern portion of the Caspian Sea and a large plain to the north of the sea between the Volga and Ural Rivers and farther east to the Mugodzhary Highland, which is the southern continuation of the Ural foldbelt. The basin is bounded by the Paleozoic carbonate platform of the Volga-Ural province to the north and west and by the Ural, South Emba, and Karpinsky Hercynian foldbelts to the east and south. The basin was originated by pre-Late Devonian rifting and subsequent spreading that opened the oceanic crust, but the precise time of these tectonic events is not known. The sedimentary succession of the basin is more than 20 km thick in the central areas. The drilled Upper Devonian to Tertiary part of this succession includes a prominent thick Kungurian (uppermost Lower Permian) salt formation that separates strata into the subsalt and suprasalt sequences and played an important role in the formation of oil and gas fields. Shallow-shelf carbonate formations that contain various reefs and alternate with clastic wedges compose the subsalt sequence on the 1 basin margins. Basinward, these rocks grade into deep-water anoxic black shales and turbidites. The Kungurian salt formation is strongly deformed into domes and intervening depressions. The most active halokinesis occurred during Late Permian?Triassic time, but growth of salt domes continued later and some of them are exposed on the present-day surface. The suprasalt sequence is mostly composed of clastic rocks that are several kilometers thick in depressions between salt domes. A single total petroleum system is defined in the North Caspian basin. Discovered reserves are about 19.7 billion barrels of oil and natural gas liquids and 157 trillion cubic feet of gas. Much of the reserves are concentrated in the supergiant Tengiz, Karachaganak, and Astrakhan fields. A recent new oil discovery on the Kashagan structure offshore in the Caspian Sea is probably also of the supergiant status. Major oil and gas reserves are located in carbonate reservoirs in reefs and structural traps of the subsalt sequence. Substantially smaller reserves are located in numerous fields in the suprasalt sequence. These suprasalt fields are largely in shallow Jurassic and Cretaceous clastic reservoirs in salt dome-related traps. Petroleum source rocks are poorly identified by geochemical methods. However, geologic data indicate that the principal source rocks are Upper Devonian to Lower Permian deep-water black-shale facies stratigraphically correlative to shallow-shelf carbonate platforms on the basin margins. The main stage of hydrocarbon generation was probably in Late Permian and Triassic time, during deposition of thick orogenic clastics. Generated hydrocarbons migrated laterally into adjacent subsalt reservoirs and vertically, through depressions between Kungurian salt domes where the salt is thin or absent, into suprasalt clastic reservoirs. Six assessment units have been identified in the North Caspian basin. Four of them include Paleozoic subsalt rocks of the basin margins, and a fifth unit, which encompasses the entire total petroleum system area, includes the suprasalt sequence. All five of these assessment units are underexplored and have significant potential for new discoveries. Most undiscovered petroleum resources are expected in Paleozoic subsalt carbonate rocks. The assessment unit in subsalt rocks with the greatest undiscovered potential occupies the south basin margin. Petroleum potential of suprasalt rocks is lower; however, discoveries of many small to medium size fields are expected. The sixth identified assessment unit embraces subsalt rocks of the central basin areas. The top of subsalt rocks in these areas occurs at depths ranging from 7 to 10 kilometers and has not been reached by wells. Undiscovered resources of this unit did not rec

Petrology and sedimentology of the Horlick Formation (Lower Devonian), Ohio Range, Transantarctic Mountains

USGS Publications Warehouse

McCartan, Lucy; Bradshaw, Margaret A.

1987-01-01

The Horlick Formation of Early Devonian age is as thick as 50 m and consists of subhorizontal, interbedded subarkosic sandstone and chloritic shale and mudstone. The Horlick overlies an erosion surface cut into Ordovician granitic rocks and is, in turn, overlain by Carboniferous and Permian glacial and periglacial deposits. Textures, sedimentary structures, and ubiquitous marine body fossils and animal traces suggest that the Horlick was deposited on a shallow shelf having moderate wave energy and a moderate tidal range. The source terrane probably lay to the north, and longshore transport was toward the west.

The geology and mechanics of formation of the Fort Rock Dome, Yavapai County, Arizona

USGS Publications Warehouse

Fuis, Gary S.

1996-01-01

The Fort Rock Dome, a craterlike structure in northern Arizona, is the erosional product of a circular domal uplift associated with a Precambrian shear zone exposed within the crater and with Tertiary volcanism. A section of Precambrian to Quaternary rocks is described, and two Tertiary units, the Crater Pasture Formation and the Fort Rock Creek Rhyodacite, are named. A mathematical model of the doming process is developed that is consistent with the history of the Fort Rock Dome.

Evidence for Seismogenic Hydrogen Gas, a Potential Microbial Energy Source on Earth and Mars

NASA Astrophysics Data System (ADS)

McMahon, Sean; Parnell, John; Blamey, Nigel J. F.

2016-09-01

The oxidation of molecular hydrogen (H2) is thought to be a major source of metabolic energy for life in the deep subsurface on Earth, and it could likewise support any extant biosphere on Mars, where stable habitable environments are probably limited to the subsurface. Faulting and fracturing may stimulate the supply of H2 from several sources. We report the H2 content of fluids present in terrestrial rocks formed by brittle fracturing on fault planes (pseudotachylites and cataclasites), along with protolith control samples. The fluids are dominated by water and include H2 at abundances sufficient to support hydrogenotrophic microorganisms, with strong H2 enrichments in the pseudotachylites compared to the controls. Weaker and less consistent H2 enrichments are observed in the cataclasites, which represent less intense seismic friction than the pseudotachylites. The enrichments agree quantitatively with previous experimental measurements of frictionally driven H2 formation during rock fracturing. We find that conservative estimates of current martian global seismicity predict episodic H2 generation by Marsquakes in quantities useful to hydrogenotrophs over a range of scales and recurrence times. On both Earth and Mars, secondary release of H2 may also accompany the breakdown of ancient fault rocks, which are particularly abundant in the pervasively fractured martian crust. This study strengthens the case for the astrobiological investigation of ancient martian fracture systems.

The search for a source rock for the giant Tar Sand triangle accumulation, southeastern Utah

USGS Publications Warehouse

Huntoon, J.E.; Hansley, P.L.; Naeser, N.D.

1999-01-01

A large proportion (about 36%) of the world's oil resource is contained in accumulations of heavy oil or tar. In these large deposits of degraded oil, the oil in place represents only a fraction of what was present at the time of accumulation. In many of these deposits, the source of the oil is unknown, and the oil is thought to have migrated over long distances to the reservoirs. The Tar Sand triangle in southeastern Utah contains the largest tar sand accumulation in the United States, with 6.3 billion bbl of heavy oil estimated to be in place. The deposit is thought to have originally contained 13-16 billion bbl prior to the biodegradation, water washing, and erosion that have taken place since the middle - late Tertiary. The source of the oil is unknown. The tar is primarily contained within the Lower Permian White Rim Sandstone, but extends into permeable parts of overlying and underlying beds. Oil is interpreted to have migrated into the White Rim sometime during the Tertiary when the formation was at a depth of approximately 3500 m. This conclusion is based on integration of fluid inclusion analysis, time-temperature reconstruction, and apatite fission-track modeling for the White Rim Sandstone. Homogenization temperatures cluster around 85-90??C for primary fluid inclusions in authigenic, nonferroan dolomite in the White Rim. The fluid inclusions are associated with fluorescent oil-bearing inclusions, indicating that dolomite precipitation was coeval with oil migration. Burial reconstruction suggests that the White Rim Sandstone reached its maximum burial depth from 60 to 24 Ma, and that maximum burial was followed by unroofing from 24 to 0 Ma. Time-temperature modeling indicates that the formation experienced temperatures of 85-90??C from about 35 to 40 Ma during maximum burial. Maximum formation temperatures of about 105-110??C were reached at about 24 Ma, just prior to unroofing. Thermal modeling is used to examine the history of potential source rocks for the White Rim oil. The most attractive potential sources for White Rim oil include beds within one or more of the following formations: the Proterozoic Chuar Group, which is present in the subsurface southwest of the Tar Sand triangle; the Mississippian Delle Phosphatic Member of the Deseret Limestone and equivalent formations, the Permian Kaibab Limestone, the Sinbad Limestone Member of the Triassic Moenkopi Formation, and the Jurassic Arapien Shale, Twin Creek Limestone, and Carmel Formation, which are present west of the Tar Sand triangle; the Pennsylvanian Paradox Formation in the Paradox basin east of the Tar Sand triangle; and the Permian Park City Formation northwest of the Tar Sand triangle. Each formation has a high total organic carbon content and is distributed over a wide enough geographic area to have provided a huge volume of oil. Source beds in all of the formations reached thermal maturity at times prior to or during the time that migration into the White Rim is interpreted to have occurred. Based on all available data, the most likely source for the Tar Sand triangle appears to be the Mississippian Delle Phosphatic Member of the Deseret Limestone. Secondary migration out of the Delle is interpreted to have occurred during the Cretaceous, during Sevier thrusting. Subsequent tertiary migration into the Tar Sand triangle reservoir is interpreted to have occurred later, during middle Tertiary Laramide deformation.

New petrofacies in upper Cretaceous section of southern California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colburn, I.P.; Oliver, D.

1986-04-01

A distinctive sandstone-conglomerate petrofacies is recognized throughout the Late Cretaceous (Maestrichtian-late Campanian) Chatsworth Formation in the Simi Hills. It is named the Woolsey Canyon petrofacies after the district where it was first recognized. The petrofacies is also recognized in the Late Cretaceous (late Campanian and possibly early Maestrichtian) Tuna Canyon Formation of the central Santa Monica Mountains. The conglomerates in the petrofacies are composed predominantly of angular pebble-size clasts of argillite, quartz-rich rocks (orthoquartzarenite, metaorthoquartzarenite, mice quartz schist) and leucocratic plutoniate (granite-granodiorite). The conglomerate texture and composition are mirrored in the sandstone. The uniformly angular character of the conglomerate clastsmore » and the survival of argillite clasts indicate that the detritus underwent no more than 5 mi of subaerial transport before it entered the deep marine realm. Foraminifers collected from mudstones interbedded with the conglomerates indicate upper bathyal water depth at the site of deposition. A source terrane of low to moderate relief is indicated by the absence of cobbles and boulders. Bed forms, sedimentary structures, and textural features indicate the detritus moved north from its source terrane to be deposited by turbidity currents, debris flows, and grain flows on the Chatsworth Submarine Fan. The detritus of the Woolsey Canyon petrofacies was derived from basement rocks, now largely buried beneath the Los Angeles basin, that were being eroded during the formation of the Cretaceous Los Angeles erosion surface. The detritus came from the Los Angeles arch of that surface.« less

Chemical evolution of Himalayan leucogranites based on an O, U-Pb and Hf study of zircon

NASA Astrophysics Data System (ADS)

Hopkinson, Thomas N.; Warren, Clare J.; Harris, Nigel B. W.; Hammond, Samantha J.; Parrish, Randall R.

2015-04-01

Crustal melting is a characteristic process at convergent plate margins, where crustal rocks are heated and deformed. Miocene leucogranite sheets and plutons are found intruded into the high-grade metasedimentary core (the Greater Himalayan Sequence, GHS) across the Himalayan orogen. Previously-published Himalayan whole-rock data suggest that these leucogranites formed from a purely meta-sedimentary source, isotopically similar to those into which they now intrude. Bulk rock analyses carry inherent uncertainties, however: they may hide contributions from different contributing sources, and post-crystallization processes such as fluid interaction may significantly alter the original chemistry. In contrast, zircon is more able to retain precise information of the contributing sources of the melt from which it crystallises whilst its resistant nature is impervious to post-magmatic processes. This multi-isotope study of Oligocene-Miocene leucogranite zircons from the Bhutan Himalaya, seeks to differentiate between various geochemical processes that contribute to granite formation. Hf and O isotopes are used to detect discrete changes in melt source while U-Pb isotopes provide the timing of zircon crystallisation. Our data show that zircon rims of Himalayan age yield Hf-O signatures that lie within the previously reported whole-rock GHS field, confirming the absence of a discernible mantle contribution to the leucogranite source. Importantly, we document a decrease in the minimum ɛHf values during Himalayan orogenesis through time, correlating to a change in Hf model age from 1.4 Ga to 2.4 Ga. Nd model ages for the older Lesser Himalayan metasediments (LHS) that underthrust the GHS are significantly older than those for the GHS (2.4-2.9 Ga compared with 1.4-2.2 Ga), and as such even minor contributions of LHS material incorporated into a melt would significantly increase the resulting Hf model age. Hence our leucogranite data suggest either a change of source within the GHS over time, or an increasing contribution from older Lesser Himalayan (LHS) material in the melt. This is the first time that an evolutionary trend in the chemistry of Himalayan crustal melts has been recognized. Thus these new data show that, at least in the Himalaya, accessory phase geochemistry can provide more detailed insight into tectonic processes than bulk rock geochemistry.

MX Siting Investigation. Geotechnical Evaluation. Detailed Aggregate Resources Study. Pahroc Study Area, Nevada.

DTIC Science & Technology

1981-06-05

source is a fairly limited outcrop of calcareous sandstone classified as dolomite rock (Do). Class RBIb Sources: Pour basin-fill sources within the study...Paleozoic rocks consist of limestone, dolomite , and quartzite with interbedded sandstone and shale. These units are generally exposed along the northern...categories simplify discussion and presentation without altering the conclusions of the study. 2.2.1 Rock Units Dolomite rocks (Do) and carbonate rocks

Conceptual models of the formation of acid-rock drainage at road cuts in Tennessee

USGS Publications Warehouse

Bradley, Michael W.; Worland, Scott; Byl, Tom

2015-01-01

Pyrite and other minerals containing sulfur and trace metals occur in several rock formations throughout Middle and East Tennessee. Pyrite (FeS2) weathers in the presence of oxygen and water to form iron hydroxides and sulfuric acid. The weathering and interaction of the acid on the rocks and other minerals at road cuts can result in drainage with low pH (< 4) and high concentrations of trace metals. Acid-rock drainage can cause environmental problems and damage transportation infrastructure. The formation and remediation of acid-drainage from roads cuts has not been researched as thoroughly as acid-mine drainage. The U.S Geological Survey, in cooperation with the Tennessee Department of Transportation, is conducting an investigation to better understand the geologic, hydrologic, and biogeochemical factors that control acid formation at road cuts. Road cuts with the potential for acid-rock drainage were identifed and evaluated in Middle and East Tennessee. The pyrite-bearing formations evaluated were the Chattanooga Shale (Devonian black shale), the Fentress Formation (coal-bearing), and the Precambrian Anakeesta Formation and similar Precambrian rocks. Conceptual models of the formation and transport of acid-rock drainage (ARD) from road cuts were developed based on the results of a literature review, site reconnaissance, and the initial rock and water sampling. The formation of ARD requires a combination of hydrologic, geochemical, and microbial interactions which affect drainage from the site, acidity of the water, and trace metal concentrations. The basic modes of ARD formation from road cuts are; 1 - seeps and springs from pyrite-bearing formations and 2 - runoff over the face of a road cut in a pyrite-bearing formation. Depending on site conditions at road cuts, the basic modes of ARD formation can be altered and the additional modes of ARD formation are; 3 - runoff over and through piles of pyrite-bearing material, either from construction or breakdown material weathered from shale, and 4 - the deposition of secondary-sulfate minerals can store trace metals and, during rainfall, result in increased acidity and higher concentrations of trace metals in storm runoff. Understanding the factors that control ARD formation and transport are key to addressing the problems associated with the movement of ARD from the road cuts to the environment. The investigation will provide the Tennessee Department of Transportation with a regional characterization of ARD and provide insights into the geochemical and biochemical attributes for the control and remediation of ARD from road cuts.

Peruvian Arid Coast and Agriculture, South America

NASA Technical Reports Server (NTRS)

1991-01-01

The coast of Peru, between the Pacific Ocean and the Andes Mountains is very arid (16.5S, 72.5W). For several thousand years, water from numerous small streams has been used for traditional flood and canal irrigation agriculture. However, during the past decade innovative techniques have tapped new water sources for increased agricultural production. Ground water in the porous sedimentary rock formations has been tapped for well irrigation agriculture.

Petroleum Source Rock Maturation Data Constrain Predictions of Natural Hydrocarbon Seepage into the Atmosphere

NASA Astrophysics Data System (ADS)

Mansfield, M. L.

2013-12-01

Natural seepage of methane from the lithosphere to the atmosphere occurs in regions with large natural gas deposits. According to some authors, it accounts for roughly 5% of the global methane budget. I explore a new approach to estimate methane fluxes based on the maturation of kerogen, which is the hydrocarbon polymer present in petroleum source rocks, and whose pyrolysis leads to the formation of oil and natural gas. The temporal change in the atomic H/C ratio of kerogen lets us estimate the total carbon mass released by it in the form of oil and natural gas. Then the time interval of active kerogen pyrolysis lets us estimate the average annual formation rate of oil and natural gas in any given petroleum system. Obviously, this is an upper bound to the average annual rate at which natural gas seeps into the atmosphere. After adjusting for bio-oxidation of natural gas, I conclude that the average annual seepage rate in the Uinta Basin of eastern Utah is not greater than (3100 × 900) tonne/y. This is (0.5 × 0.15)% of the total flux of methane into the atmosphere over the Basin, as measured during aircraft flights. I speculate about the difference between the regional 0.5% and the global 5% estimates.

Geology of the Cupsuptic quadrangle, Maine

USGS Publications Warehouse

Harwood, David S.

1966-01-01

The Cupsuptic quadrangle, in west-central Maine, lies in a relatively narrow belt of pre-Silurian rocks extending from the Connecticut River valley across northern New Hampshire to north-central Maine. The Albee Formation, composed of green, purple, and black phyllite with interbedded-quartzite, is exposed in the core of a regional anticlinorium overlain to the southeast by greenstone of the Oquossoc Formation which in turn is overlain by black slate of the Kamankeag Formation. In the northern part of the quadrangle the Albee Formation is overlain by black slate, feldspathic graywacke, and minor greenstone of the Dixville Formation. The Kamankeag Formation is dated as 1-ate Middle Ordovician by graptolites (zone 12) found near the base of the unit. The Dixville Formation is correlated with the Kamankeag Formation and Oquossoc Formation and is considered to be Middle Ordovician. The Albee Formation is considered to be Middle to Lower Ordovician from correlations with similar rocks in northeastern and southwestern Vermont. The Oquossoc and Kamankeag Formations are correlated with the Amonoosuc and Partridge Formations of northern New Hampshire. The pre-Silurian rocks are unconformably overlain by unnamed rocks of Silurian age in the southeast, west-central, and northwest ninths of the quadrangle. The basal Silurian units are boulder to cobble polymict conglomerate and quartz-pebble conglomerate of late Lower Silurian (Upper Llandovery) age. The overlying rocks are either well-bedded slate and quartzite, silty limestone, or arenaceous limestone. Thearenaceous limestone contains Upper Silurian (Lower Ludlow) brachiopods. The stratified rocks have been intruded by three stocks of biotite-muscovite quartz monzonite, a large body of metadiorite and associated serpentinite, smaller bodies of gabbro, granodiorite, and intrusive felsite, as well as numerous diabase and quartz monzonite dikes. The metadiorite and serpentinite, and possibly the gabbro and granodiorite are Late Ordovician in age. The quartz monzonite is considered to be Late Devonian. Five tectonic events are inferred from the structural features in the area. The earliest was a period of folding producing tightly-appressed, northeast-trending folds in the rocks of pre-Silurian age. In the second stage the folded pre-Silurian rocks were uplifted, eroded, and truncated to produce a major unconformity between the Middle Ordovician and Lower Silurian rocks. These events constitute the Taconic orogeny. The third tectonic event was a period of folding, probably of Middle Devonian age, that warped the unconformity and overlying rocks into open, gently-plunging, east-trending folds. This period of folding undoubtedly changed the attitude of the early folds in the pre-Silurian units but it did not produce any recognizable, cross-cutting planar features in the older rocks. The fourth tectonic event was a period of igneous intrusion that locally deformed the northeast-trending folds in the pre-Silurian rocks into a macroscopic drag fold plunging at 80 degrees in a direction S.10?w. A north-trending, subvertical slip cleavage was produced locally during this period of Late Devonian (?) deformation. A period of faulting, possibly of Triassic age, dislocated some of the earlier features. The rocks are in the chlorite zone of regional metamorphism, but have been contact metamorphosed to sillimanite-bearing hornfels adjacent to the quartz monzonite stocks. The chemical changes in chlorite, biotite, garnet, cordierite, and muscovite in the chlorite, biotite, andalusite, and sillimanite zones have been-studied by optical and x-ray methods and by partial chemical analyses. The progressive changes in mineral assemblages have been graphically portrayed on quaternary diagrams and ternary projections.

delta 15N and non-carbonate delta 13C values for two petroleum source rock reference materials and a marine sediment reference material

USGS Publications Warehouse

Dennen, Kristin O.; Johnson, Craig A.; Otter, Marshall L.; Silva, Steven R.; Wandless, Gregory A.

2006-01-01

Samples of United States Geological Survey (USGS) Certified Reference Materials USGS Devonian Ohio Shale (SDO-1), and USGS Eocene Green River Shale (SGR-1), and National Research Council Canada (NRCC) Certified Marine Sediment Reference Material (PACS-2), were sent for analysis to four separate analytical laboratories as blind controls for organic rich sedimentary rock samples being analyzed from the Red Dog mine area in Alaska. The samples were analyzed for stable isotopes of carbon (delta13Cncc) and nitrogen (delta15N), percent non-carbonate carbon (Wt % Cncc) and percent nitrogen (Wt % N). SDO-1, collected from the Huron Member of the Ohio Shale, near Morehead, Kentucky, and SGR-1, collected from the Mahogany zone of the Green River Formation are petroleum source rocks used as reference materials for chemical analyses of sedimentary rocks. PACS-2 is modern marine sediment collected from the Esquimalt, British Columbia harbor. The results presented in this study are, with the exceptions noted below, the first published for these reference materials. There are published information values for the elemental concentrations of 'organic' carbon (Wt % Corg measured range is 8.98 - 10.4) and nitrogen (Wt % Ntot 0.347 with SD 0.043) only for SDO-1. The suggested values presented here should be considered 'information values' as defined by the NRCC Institute for National Measurement Reference Materials and should be useful for the analysis of 13C, 15N, C and N in organic material in sedimentary rocks.

Alaskan North Slope petroleum systems

USGS Publications Warehouse

Magoon, L.B.; Lillis, P.G.; Bird, K.J.; Lampe, C.; Peters, K.E.

2003-01-01

Six North Slope petroleum systems are identified, described, and mapped using oil-to-oil and oil-to-source rock correlations, pods of active source rock, and overburden rock packages. To map these systems, we assumed that: a) petroleum source rocks contain 3.2 wt. % organic carbon (TOC); b) immature oil-prone source rocks have hydrogen indices (HI) >300 (mg HC/gm TOC); c) the top and bottom of the petroleum (oil plus gas) window occur at vitrinite reflectance values of 0.6 and 1.0% Ro, respectively; and d) most hydrocarbons are expelled within the petroleum window. The six petroleum systems we have identified and mapped are: a) a southern system involving the Kuna-Lisburne source rock unit that was active during the Late Jurassic and Early Cretaceous; b) two western systems involving source rock in the Kingak-Blankenship, and GRZ-lower Torok source rock units that were active during the Albian; and c) three eastern systems involving the Shublik-Otuk, Hue Shale and Canning source rock units that were active during the Cenozoic. The GRZ-lower Torok in the west is correlative with the Hue Shale to the east. Four overburden rock packages controlled the time of expulsion and gross geometry of migration paths: a) a southern package of Early Cretaceous and older rocks structurally-thickened by early Brooks Range thrusting; b) a western package of Early Cretaceous rocks that filled the western part of the foreland basin; c) an eastern package of Late Cretaceous and Paleogene rocks that filled the eastern part of the foreland basin; and d) an offshore deltaic package of Neogene rocks deposited by the Colville, Canning, and Mackenzie rivers. This petroleum system poster is part of a series of Northern Alaska posters on modeling. The poster in this session by Saltus and Bird present gridded maps for the greater Northern Alaskan onshore and offshore that are used in the 3D modeling poster by Lampe and others. Posters on source rock units are by Keller and Bird as well as Peters and others. Sandstone and shale compaction properties used in sedimentary basin modeling are covered in a poster by Rowan and others. The results of this modeling exercise will be used in our next Northern Alaska oil and gas resource assessment.

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam Onboard Curiosity

USGS Publications Warehouse

Le Deit, Laetitia; Mangold, Nicolas; Forni, Olivier; Cousin, Agnes; Lasue, Jeremie; Schröder, Susanne; Wiens, Roger C.; Sumner, Dawn Y.; Fabre, Cecile; Stack, Katherine M.; Anderson, Ryan; Blaney, Diana L.; Clegg, Samuel M.; Dromart, Gilles; Fisk, Martin; Gasnault, Olivier; Grotzinger, John P.; Gupta, Sanjeev; Lanza, Nina; Le Mouélic, Stephane; Maurice, Sylvestre; McLennan, Scott M.; Meslin, Pierre-Yves; Nachon, Marion; Newsom, Horton E.; Payre, Valerie; Rapin, William; Rice, Melissa; Sautter, Violaine; Treiman, Alan H.

2016-01-01

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. From ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.

Geology of the Lake Mary quadrangle, Iron County, Michigan

USGS Publications Warehouse

Bayley, Richard W.

1959-01-01

The Lake Mary quadrangle is in eastern Iron County, in the west part of the Upper Peninsula of Michigan. The quadrangle is underlain by Lower and Middle Precambrian rocks, formerly designated Archean and Algonkian rocks, and is extensively covered by Pleistocene glacial deposits. A few Upper Precambrian (Keweenawan) diabase dikes and two remnants of sandstone and dolomite of early Paleozoic age are also found in the area. The major structural feature is the Holmes Lake anticline, the axis of which strikes northwest through the northeast part of the quadrangle. Most of the quadrangle, therefore, is underlain by rock of the west limb of the anticline. To the northwest along the fold axis, the Holmes Lake anticline is separated from the Amasa oval by a saddle of transverse folds in the vicinity of Michigamme Mountain in the Kiernan quadrangle. The Lower Precambrian rocks are represented by the Dickinson group and by porphyritic red granite whose relation to the Dickinson group is uncertain, but which may be older. The rocks of the Dickinson group are chiefly green to black metavolcanic schist and red felsite, some of the latter metarhyolite. The dark schist is commonly magnetic. The Dickinson group underlies the core area of the Holmes Lake anticline, which is flanked by steeply dipping Middle Precambrian formations of the Animikie series. A major unconformity separates the Lower Precambrian rocks from the overlying Middle Precambrian rocks. In ascending order the formations of the Middle Precambrian are the Randville dolomite, the Hemlock formation, which includes the Mansfield iron-bearing slate member, and the Michigamme slate. An unconformity occurs between the Hemlock formation and Michigamme slate. The post-Hemlock unconformity is thought to be represented in the Lake Mary quadrangle by the absence of iron-formation of the Amasa formation, which is known to lie between the Hemlock and the Michigamme to the northwest of the Lake Mary quadrangle in the Crystal Falls quadrangle. Post-Hemlock erosion may account also for the absence of iron-formation of the Fence River formation on the east limb of the Holmes Lake anticline within the Lake Mary quadrangle. The Randville dolomite is not exposed and is known only from diamond drilling in the northeast part of the area where it occurs in the east and west limbs of the Holmes Lake anticline. The formation has a maximum thickness of about 2,100 feet; this includes a lower arkosic phase, some of which is quartz pebble conglomerate, a medial dolomitic phase, and an upper slate phase. The triad is gradational. Included within the formation are a few beds of chloritic schist thought to be of volcanic origin. An unconformity between the Randville and the succeeding Hemlock is not indicated in the quadrangle, but is probably present. The Hemlock formation is best exposed in the northwest and south-central parts of the area. The apparent thickness of the formation is 10,000- 17,000 feet. It is composed mainly of mafic metavolcanic rocks and intercalated slate and iron-formation. In the north part of the quadrangle the volcanic rocks are greenstone, which includes altered basaltic flow rocks, volcanic breccia, tuff, and slate. Pillow structures are common in the metabasalt. It is not certain if any Hemlock rocks are present in the east limb of the Holmes Lake anticline. In the south part of the quadrangle, the rocks of the Hemlock are chiefly chlorite and hornblende schist and hornfels. Pyroxene hornfels is sparingly present. At least two sedimentary slate belts are included in the Hemlock formation. One of these, the Mansfield iron-bearing slate member, includes in its upper part an altered chert-siderite iron-formation 30 to over 150 feet thick from which iron ore has been mined at the Mansfield location. The position of the iron-bearing rocks has been determined magnetically, and past explorations for iron ore are discussed. Though probably; unconformable, the contact between the Hemlock and the Michigamme formations appears conformable. The Michigamme slate consists of at least 4,000 feet of interbedded mica schist and granulite, the altered equivalents of the slate and graywacke characteristic of the Michigamme in adjacent areas. The Michigamme rocks are best exposed in the south part of the quadrangle in the vicinity of Peavy Pond. Two periods of regional metamorphism have resulted in the alteration of almost all of the rocks of the quadrangle. The Lower Precambrian rocks underwent at least one period of metamorphism, uplift, and erosion before the deposition of the Randville dolomite. After the deposition of the Michigamme slate, a post-Middle Precambrian period of regional metamorphism occurred with attending deformation and igneous intrusion. The grade of metamorphism rises toward the south in the area. The rocks in the northern two-thirds of the quadrangle are representative of greenschist facies of regional metamorphism, whereas the rocks in the southern onethird of the quadrangle are representative of the albite-epidote-amphibolite, the amphibolite, and the pyroxene hornfels facies, the metamorphic node centering about the intrusive Peavy Pond complex in the Peavy Pond area. The Precambrian sedimentary and volcanic rocks are cut by intrusive igneous rocks of different types and several different ages. Gabbroic sills and dikes invaded the Hemlock rocks at some time after the Hemlock was deposited and before the post-Middle Precambrian orogeny and metamorphism. Some contact metamorphism attended the intrusion of the major sills. One of the sills, the West Kiernan sill, is well differentiated. A syntectonic igneous body, composed of gabbro and minor ultramafic parts and fringed with intermediate and felsic differentiates and hybrids, the Peavy; Pond complex, was intruded into the Hemlock and Michigamme formations during the post-Middle Precambrian orogeny. The complex is situated in the Peavy Pond area at the crest of the regional metamorphic node. Contact-altered sedimentary and volcanic rocks margin the complex. The effects of regional metamorphism have been superposed on the contact metamorphic rocks peripheral to the complex and on the igneous rocks of the complex as well. The mafic augite-bearing rocks of the complex emplaced early in the orogeny were deformed by granulation at the peak of the deformation and subsequently metamorphosed to hornblende rocks. Some of the intermediate and felsic rocks of the complex were foliated by the deformation, while the more fluid, felsic parts of the complex were intruded under orogenic stress and crystallized after the peak of deformation. The deformation culminated in major faulting during which the formations were dislocated, and some of the granite of the complex was extremely brecciated. A few diabase dikes, probably of Keweenawan age, have intruded the deformed and altered Animikie rocks. The only known metallic resource is iron ore. The Mansfield mine produced 1¥2 million tons of high-grade iron ore between the years 1890 and 1913. Sporadic exploration since 1913 has failed to reveal other ore deposits of economic importance.

The Classification Ability with Naked Eyes According to the Understanding Level about Rocks of Pre-service Science Teachers

NASA Astrophysics Data System (ADS)

Seong, Cho Kyu; Ho, Chung Duk; Pyo, Hong Deok; Kyeong Jin, Park

2016-04-01

This study aimed to investigate the classification ability with naked eyes according to the understanding level about rocks of pre-service science teachers. We developed a questionnaire concerning misconception about minerals and rocks. The participant were 132 pre-service science teachers. Data were analyzed using Rasch model. Participants were divided into a master group and a novice group according to their understanding level. Seventeen rocks samples (6 igneous, 5 sedimentary, and 6 metamorphic rocks) were presented to pre-service science teachers to examine their classification ability, and they classified the rocks according to the criteria we provided. The study revealed three major findings. First, the pre-service science teachers mainly classified rocks according to textures, color, and grain size. Second, while they relatively easily classified igneous rocks, participants were confused when distinguishing sedimentary and metamorphic rocks from one another by using the same classification criteria. On the other hand, the understanding level of rocks has shown a statistically significant correlation with the classification ability in terms of the formation mechanism of rocks, whereas there was no statically significant relationship found with determination of correct name of rocks. However, this study found that there was a statistically significant relationship between the classification ability with regard the formation mechanism of rocks and the determination of correct name of rocks Keywords : Pre-service science teacher, Understanding level, Rock classification ability, Formation mechanism, Criterion of classification

Pliocene granodioritic knoll with continental crust affinities discovered in the intra-oceanic Izu-Bonin-Mariana Arc: Syntectonic granitic crust formation during back-arc rifting

NASA Astrophysics Data System (ADS)

Tani, Kenichiro; Dunkley, Daniel J.; Chang, Qing; Nichols, Alexander R. L.; Shukuno, Hiroshi; Hirahara, Yuka; Ishizuka, Osamu; Arima, Makoto; Tatsumi, Yoshiyuki

2015-08-01

A widely held hypothesis is that modern continental crust of an intermediate (i.e. andesitic) bulk composition forms at intra-oceanic arcs through subduction zone magmatism. However, there is a critical paradox in this hypothesis: to date, the dominant granitic rocks discovered in these arcs are tonalite, rocks that are significantly depleted in incompatible (i.e. magma-preferred) elements and do not geochemically and petrographically represent those of the continents. Here we describe the discovery of a submarine knoll, the Daisan-West Sumisu Knoll, situated in the rear-arc region of the intra-oceanic Izu-Bonin-Mariana Arc. Remotely-operated vehicle surveys reveal that this knoll is made up entirely of a 2.6 million year old porphyritic to equigranular granodiorite intrusion with a geochemical signature typical of continental crust. We present a model of granodiorite magma formation that involves partial remelting of enriched mafic rear-arc crust during the initial phase of back-arc rifting, which is supported by the preservation of relic cores inherited from initial rear-arc source rocks within magmatic zircon crystals. The strong extensional tectonic regime at the time of intrusion may have allowed the granodioritic magma to be emplaced at an extremely shallow level, with later erosion of sediment and volcanic covers exposing the internal plutonic body. These findings suggest that rear-arc regions could be the potential sites of continental crust formation in intra-oceanic convergent margins.

Sudbury Breccia and suevite as glacial indicators transported 800 km to Kentland Astrobleme, Indiana

NASA Technical Reports Server (NTRS)

Mchone, John F.; Dietz, Robert S.; Peredery, Walter V.

1992-01-01

A glacial erratic whose place of origin is known by direct comparison with bedrock is known as an indicator. In 1971, while visiting the known astrobleme at Kentland, Indiana, Peredery recognized and sampled in the overlying glacial drift deposits a distinctive boulder of Sudbury suevite (black member, Onaping Formation) that normally occurs within the Sudbury Basin as an impact fall-back or wash-in deposit. The rock was sampled (but later mislaid) from a farmer's cairn next to a cleared field. Informal reports of this discovery prompted the other authors to recently reconnoiter the Kentland locality in an attempt to relocate the original boulder. Several breccia blocks were sampled but laboratory examination proved most of these probably to be diamictites from the Precambrian Gowganda Formation, which outcrops extensively in the southern Ontario. However, one sample was confirmed as typical Sudbury Breccia, which outcrops in the country rock surrounding the Sudbury Basin. Thus two glacial indicators were transported by Pleistocene continental glaciers about 820 km over a tightly proscribed path and, curiously, from one astrobleme to another. Brecciated boulders in the Illinois/Indiana till plain are usually ascribed to the Gowganda or Mississagi formations in Ontario. But impact-generated rocks need not be confused. The carbonaceous matrix of the suevite, for example, was sufficiently distinctive to assign it to the upper portion of the black Onaping. The unique and restricted source area of these indicators provide an accurate and reliable control for estimating Pleistocene ice movement.

Shale hydrocarbon reservoirs: some influences of tectonics and paleogeography during deposition: Chapter 2

USGS Publications Warehouse

Eoff, Jennifer D

2014-01-01

Fundamental to any of the processes that acted during deposition, however, was active tectonism. Basin type can often distinguish self-sourced shale plays from other types of hydrocarbon source rocks. The deposition of North American self-sourced shale was associated with the assembly and subsequent fragmentation of Pangea. Flooded foreland basins along collisional margins were the predominant depositional settings during the Paleozoic, whereas deposition in semirestricted basins was responsible along the rifted passive margin of the U.S. Gulf Coast during the Mesozoic. Tectonism during deposition of self-sourced shale, such as the Upper Jurassic Haynesville Formation, confined (re)cycling of organic materials to relatively closed systems, which promoted uncommonly thick accumulations of organic matter.

Early episodes of high-pressure core formation preserved in plume mantle

NASA Astrophysics Data System (ADS)

Jackson, Colin R. M.; Bennett, Neil R.; Du, Zhixue; Cottrell, Elizabeth; Fei, Yingwei

2018-01-01

The decay of short-lived iodine (I) and plutonium (Pu) results in xenon (Xe) isotopic anomalies in the mantle that record Earth’s earliest stages of formation. Xe isotopic anomalies have been linked to degassing during accretion, but degassing alone cannot account for the co-occurrence of Xe and tungsten (W) isotopic heterogeneity in plume-derived basalts and their long-term preservation in the mantle. Here we describe measurements of I partitioning between liquid Fe alloys and liquid silicates at high pressure and temperature and propose that Xe isotopic anomalies found in modern plume rocks (that is, rocks with elevated 3He/4He ratios) result from I/Pu fractionations during early, high-pressure episodes of core formation. Our measurements demonstrate that I becomes progressively more siderophile as pressure increases, so that portions of mantle that experienced high-pressure core formation will have large I/Pu depletions not related to volatility. These portions of mantle could be the source of Xe and W anomalies observed in modern plume-derived basalts. Portions of mantle involved in early high-pressure core formation would also be rich in FeO, and hence denser than ambient mantle. This would aid the long-term preservation of these mantle portions, and potentially points to their modern manifestation within seismically slow, deep mantle reservoirs with high 3He/4He ratios.

Formation and tectonic evolution of the Cretaceous Jurassic Muslim Bagh ophiolitic complex, Pakistan: Implications for the composite tectonic setting of ophiolites

NASA Astrophysics Data System (ADS)

Khan, Mehrab; Kerr, Andrew C.; Mahmood, Khalid

2007-10-01

The Muslim Bagh ophiolitic complex Balochistan, Pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the Indian and Eurasian plates. These ophiolites were obducted onto the Indian continental margin around the Late Cretaceous, prior to the main collision between the Indian and Eurasian plates. The upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes. Each pluton has a transitional dunite-rich zone at its base, and new geochemical data suggest a similar mantle source region for both the plutons and dykes. In contrast, the lower nappe consists of pillow basalts, deep-marine sediments and a mélange of ophiolitic rocks. The rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid-ocean ridge. The basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the Indian plate. The two nappes of the Muslim Bagh ophiolitic complex are thus distinctively different in terms of their age, lithology and tectonic setting. The recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved.

Mars Exploration Rover APXS Results from Matijevic Hill

NASA Technical Reports Server (NTRS)

Cohen, B. A.; Clark, B. C.; Gellert, R.; Klingelhoefer, G.; Ming, D. W.; Mittlefehldt, D. W.; Morris, R. V.; Schrader, C. M.; Schroeder, C.; Yen, A. S.;

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity: Potassic Sedimentary Rocks, Gale Crater

DOE PAGES

Le Deit, L.; Mangold, N.; Forni, O.; ...

2016-05-13

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. Furthermore, from ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K 2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations then reveals that the mean K 2Omore » abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.« less

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity: Potassic Sedimentary Rocks, Gale Crater

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Deit, L.; Mangold, N.; Forni, O.

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. Furthermore, from ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K 2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations then reveals that the mean K 2Omore » abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.« less

Rock glacier outflows may adversely affect lakes: lessons from the past and present of two neighboring water bodies in a crystalline-rock watershed.

PubMed

Ilyashuk, Boris P; Ilyashuk, Elena A; Psenner, Roland; Tessadri, Richard; Koinig, Karin A

2014-06-03

Despite the fact that rock glaciers are one of the most common geomorphological expressions of mountain permafrost, the impacts of their solute fluxes on lakes still remain largely obscure. We examined water and sediment chemistry, and biota of two neighboring water bodies with and without a rock glacier in their catchments in the European Alps. Paleolimnological techniques were applied to track long-term temporal trends in the ecotoxicological state of the water bodies and to establish their baseline conditions. We show that the active rock glacier in the mineralized catchment of Lake Rasass (RAS) represents a potent source of acid rock drainage that results in enormous concentrations of metals in water, sediment, and biota of RAS. The incidence of morphological abnormalities in the RAS population of Pseudodiamesa nivosa, a chironomid midge, is as high as that recorded in chironomid populations inhabiting sites heavily contaminated by trace metals of anthropogenic origin. The incidence of morphological deformities in P. nivosa of ∼70% persisted in RAS during the last 2.5 millennia and was ∼40% in the early Holocene. The formation of RAS at the toe of the rock glacier most probably began at the onset of acidic drainage in the freshly deglaciated area. The present adverse conditions are not unprecedented in the lake's history and cannot be associated exclusively with enhanced thawing of the rock glacier in recent years.

Numerical Simulations of Thermo-Mechanical Processes during Thermal Spallation Drilling for Geothermal Reservoirs

NASA Astrophysics Data System (ADS)

Vogler, D.; Walsh, S. D. C.; Rudolf von Rohr, P.; Saar, M. O.

2017-12-01

Drilling expenses constitute a significant share of the upfront capital costs and thereby the associated risks of geothermal energy production. This is especially true for deep boreholes, as drilling costs per meter increase significantly with depth. Thermal spallation drilling is a relatively new drilling technique, particularly suited to the hard crystalline (e.g., basement) rocks in which many deep geothermal resources are located. The method uses a hot jet-flame to rapidly heat the rock surface, which leads to large temperature gradients in the rock. These temperature gradients cause localized thermal stresses that, in combination with the in situ stress field, lead to the formation and ejection of spalls. These spalls are then transported out of the borehole with the drilling mud. Thermal spallation not only in principle enables much faster rates of penetration than traditional rotary drilling, but is also contact-less, which significantly reduces the long tripping times associated with conventional rotary head drilling. We present numerical simulations investigating the influence of rock heterogeneities on the thermal spallation process. Special emphasis is put on different mineral compositions, stress regimes, and heat sources.

The role of magmas in the formation of hydrothermal ore deposits

USGS Publications Warehouse

Hedenquist, Jeffrey W.; Lowenstern, Jacob B.

1994-01-01

Magmatic fluids, both vapour and hypersaline liquid, are a primary source of many components in hydrothermal ore deposits formed in volcanic arcs. These components, including metals and their ligands, become concentrated in magmas in various ways from various sources, including subducted oceanic crust. Leaching of rocks also contributes components to the hydrothermal fluid—a process enhanced where acid magmatic vapours are absorbed by deeply circulating meteoric waters. Advances in understanding the hydrothermal systems that formed these ore deposits have come from the study of their active equivalents, represented at the surface by hot springs and volcanic fumaroles.

Zircon-pyrochlore ores of Proterozoic Gremyakha-Vyrmes polyphase massif, Kola Peninsula: source and evolution

NASA Astrophysics Data System (ADS)

Sorokhtina, Natalia; Belyatsky, Boris; Antonov, Anton; Kononkova, Natalia; Lepekhina, Elena; Kogarko, Lia

2017-04-01

The alkaline-ultrabasic Gremyakha-Vyrmes massif occurs within the Central Kola terrane in the northern part of the Fennoscandian Shield and consists of diverse rock complexes: basic-ultrabasic rocks, foidolites, alkaline metasomatic rocks and carbonatites, alkaline granites and granosyenites. Nb-Zr ore deposit is confined to alkaline metasomatic rocks developed over foidolites. The metasomatites are represented by albitites and aegirinites occur as submeridionally orientated zones extending up to 6-8 km and several hundred meters thickness. They are mainly composed of albite and aegirine, but amphibole, annite, microcline, fluorapatite, titanite, ilmenite, pyrochlore group minerals, zircon are present [Sorokhtina et al., 2016]. Carbonatites are developed sporadically and accessory zircon but not the pyrochlore is observed only in contact zones with albitites and aegerinites. In metasomatites, zircon and pyrochlore are main rare metal minerals, which are formed at the latest stages of crystallization. Ca-dominant fluorcalcio- and hydroxycalciopyrochlores are the most abundant, whereas U-dominant pyrochlore, oxyuranobetafite, zero-valent-dominant (Ba, Sr-dominant) pyrochlore, hydro- or kenopyrochlore are rare. The pyrochlore-group minerals form heterogeneous metacrystals containing inclusions of host rock minerals, calcite, ilmenite, zircon, sulfides, and graphite. While pyrochlore is replaced by Si-rich "pyrochlore" (SiO2 is up to 18 wt.%.), cation-deficient hydrated pyrochlore, Fe-Si-Nb, U-Si-Nb, and Al-Si-Nb phases along fracture zones and margins. The early generation zircon is represented by large heterogeneous metacrystals filled with inclusions of various host rock minerals, calcite, ilmenite, thorite, thorianite and sulfides, while the late zircons are empty of inclusions. Zircons are nearly stoichiometric in composition; but intermediate zones are enriched in Pb, Y and Th, and overgrowths are enriched Hf only. According to CL and ion-microprobe analysis zircon has polygenetic nature: some relics inherited from foidolite crystallized at about 800°C, whereas the newly formed - at 600°C [Watson et al., 2006]. The time interval of the magmatic massif formation may be estimated as long as 80-100 Ma only. The basic-ultrabasic rocks and foidolites were intruded consistently at 1982 ± 6 Ma and 1894±12 according to SHRIMP-II U-Pb zircon dating, but the whole-rock Sm-Nd isotope dating has resulted in 1879±99 Ma and reflects the impact of alkaline granite intrusion (1871±9 Ma). The late differentiates from alkaline magma crystallization were the main source of rare metals for zircon-pyrochlore ores of alkaline metasomatites. The metasomatic rocks (aegirinites, albitites) and carbonatites were formed as late as 1910 ± 15 Ma (SHRIMP-II U-Pb zircon, titanite, pyrochlore). While some pyrochlore grains from metasomatites are showed that U-Pb age of ore formation is 1766 ± 24 and 1764 ± 19 respectively. That can be attributed to additional source of rare metals connected with fluids formed during regional metamorphism 1750 m.y. ago [Glebovitskii et al., 2014]. The last probable source of rare-metal material and ore-deposit evolution stage (recrystallization) is established by individual pyrochlore grain Sm-Nd and U-Pb systems and evidences tectono-thermal activity at the Paleozoic plume magmatism, which was followed by structural and chemical mineral changes. The research was done within the framework of the scientific program of Russian Academy of Sciences and state contract K41.2014.014 with Sevzapnedra. References: Watson E. B., Wark D. A., Thomas J. B. Crystallization thermometers for zircon and rutile // Contrib. Mineral. Petrol. 2006. 151, 413-433. Glebovitskii V.A., Bushmin S.A., Belyatsky B.V., Bogomolov E.S., Borozdin A.P., Savva E.V., Lebedeva Y.M. Rb-Sr age of metasomatism and ore formation in the low-temperature shear zones of the Fenno-Karelian craton, Baltic Shield // Petrology. 2014. 22(2). 184-204. Sorokhtina N.V., Kogarko L.N., Shpachenko A.K., Senin V. G. Composition and Conditions of Crystallization of zircon from the rare-metal ores of the Gremyakha-Vyrmes massif, Kola Peninsula // Geochemistry International. 2016. 54 (12). 1035-1048.

Genetic and grade and tonnage models for sandstone-hosted roll-type uranium deposits, Texas Coastal Plain, USA

USGS Publications Warehouse

Hall, Susan M.; Mihalasky, Mark J.; Tureck, Kathleen; Hammarstrom, Jane M.; Hannon, Mark

2017-01-01

The coincidence of a number of geologic and climatic factors combined to create conditions favorable for the development of mineable concentrations of uranium hosted by Eocene through Pliocene sandstones in the Texas Coastal Plain. Here 254 uranium occurrences, including 169 deposits, 73 prospects, 6 showings and 4 anomalies, have been identified. About 80 million pounds of U3O8 have been produced and about 60 million pounds of identified producible U3O8 remain in place. The development of economic roll-type uranium deposits requires a source, large-scale transport of uranium in groundwater, and deposition in reducing zones within a sedimentary sequence. The weight of the evidence supports a source from thick sequences of volcanic ash and volcaniclastic sediment derived mostly from the Trans-Pecos volcanic field and Sierra Madre Occidental that lie west of the region. The thickest accumulations of source material were deposited and preserved south and west of the San Marcos arch in the Catahoula Formation. By the early Oligocene, a formerly uniformly subtropical climate along the Gulf Coast transitioned to a zoned climate in which the southwestern portion of Texas Coastal Plain was dry, and the eastern portion humid. The more arid climate in the southwestern area supported weathering of volcanic ash source rocks during pedogenesis and early diagenesis, concentration of uranium in groundwater and movement through host sediments. During the middle Tertiary Era, abundant clastic sediments were deposited in thick sequences by bed-load dominated fluvial systems in long-lived channel complexes that provided transmissive conduits favoring transport of uranium-rich groundwater. Groundwater transported uranium through permeable sandstones that were hydrologically connected with source rocks, commonly across formation boundaries driven by isostatic loading and eustatic sea level changes. Uranium roll fronts formed as a result of the interaction of uranium-rich groundwater with either (1) organic-rich debris adjacent to large long-lived fluvial channels and barrier–bar sequences or (2) extrinsic reductants entrained in formation water or discrete gas that migrated into host units via faults and along the flanks of salt domes and shale diapirs. The southwestern portion of the region, the Rio Grande embayment, contains all the necessary factors required for roll-type uranium deposits. However, the eastern portion of the region, the Houston embayment, is challenged by a humid environment and a lack of source rock and transmissive units, which may combine to preclude the deposition of economic deposits. A grade and tonnage model for the Texas Coastal Plain shows that the Texas deposits represent a lower tonnage subset of roll-type deposits that occur around the world, and required aggregation of production centers into deposits based on geologic interpretation for the purpose of conducting a quantitative mineral resource assessment.

Geochemical evaluation of Niger Delta sedimentary organic rocks: a new insight

NASA Astrophysics Data System (ADS)

Akinlua, Akinsehinwa; Torto, Nelson

2011-09-01

A geochemical evaluation of Niger Delta organic matter was carried out using supercritical fluid extraction (SFE) sample preparation procedure. Comparison of geochemical significance of gas chromatographic data of rock extracts of SFE with those of Soxhlet extraction method from previous studies was made in order to establish the usefulness of SFE in geochemical exploration. The assessment of geochemical character of the rock samples from the comparison and interpretation of other geochemical parameters were used to give more insights into understanding the source rocks characteristics of onshore and shelf portions of the Niger Delta Basin. The results of the gas chromatographic (GC) analysis of the rock extracts across the lithostratigraphic units show that Pr/Ph, Pr/nC17, Pr/nC18, CPI and odd/even preference ranged from 0.07 to 12.39, 0.04 to 6.66, 0.05 to 13.80, 0.12 to 8.4 and 0.06 to 8.12, respectively. The Rock-Eval pyrolysis data and geochemical ratios and parameters calculated from the GC data showed that most of the samples are mature and have strong terrestrial provenance while a few samples have strong marine provenance. The few marine source rocks are located in the deeper depth horizon. Pr/Ph and standard geochemical plots indicate that most of samples were derived from organic matter deposited in less reducing conditions, i.e. more of oxidizing conditions while a few samples have predominantly influence of reducing conditions. The results of trace metal analysis of older samples from Agbada Formation also indicate marine and mixed organic matter input deposited in less reducing conditions. The results obtained in this study are comparable with those obtained from previous studies when Soxhlet extraction method was used and also indicated the presence of more than one petroleum systems in the Niger Delta.

Water, air, Earth and cosmic radiation.

PubMed

Bassez, Marie-Paule

2015-06-01

In the context of the origin of life, rocks are considered mainly for catalysis and adsorption-desorption processes. Here it is shown how some rocks evolve in energy and might induce synthesis of molecules of biological interest. Radioactive rocks are a source of thermal energy and water radiolysis producing molecular hydrogen, H2. Mafic and ultramafic rocks evolve in water and dissolved carbon dioxide releasing thermal energy and H2. Peridotites and basalts contain ferromagnesian minerals which transform through exothermic reactions with the generation of heat. These reactions might be triggered by any heating process such as radioactive decay, hydrothermal and subduction zones or post-shock of meteorite impacts. H2 might then be generated from endothermic hydrolyses of the ferromagnesian minerals olivine and pyroxene. In both cases of mafic and radioactive rocks, production of CO might occur through high temperature hydrogenation of CO2. CO, instead of CO2, was proven to be necessary in experiments synthesizing biological-type macromolecules with a gaseous mixture of CO, N2 and H2O. In the geological context, N2 is present in the environment, and the activation source might arise from cosmic radiation and/or radionuclides. Ferromagnesian and radioactive rocks might consequently be a starting point of an hydrothermal chemical evolution towards the abiotic formation of biological molecules. The two usually separate worlds of rocks and life are shown to be connected through molecular and thermodynamic chemical evolution. This concept has been proposed earlier by the author (Bassez J Phys: Condens Matter 15:L353-L361, 2003, 2008a, 2008b; Bassez Orig Life Evol Biosph 39(3-4):223-225, 2009; Bassez et al. 2011; Bassez et al. Orig Life Evol Biosph 42(4):307-316, 2012, Bassez 2013) without thermodynamic details. This concept leads to signatures of prebiotic chemistry such as radionuclides and also iron and magnesium carbonates associated with serpentine and/or talc, which were discussed at the 2014 European Astrobiology Network Association conference on Signatures of Life.

Sedimentology of the Simmler and Vaqueros formations in the Caliente Range-Carrizo Plain area, California

USGS Publications Warehouse

Bartow, J. Alan

1974-01-01

The Simmler and Vaqueros Formations in the Caliente Range-Carrizo Plain area make up a large part of the thick Tertiary sedimentary sequence that was .deposited in a basin which lay along the southwest side of the present-day San Andreas fault. The evolution of this basin during Oligocene and early Miocene time and the relationship of its sedimentary record to the tectonic history is an important chapter in the Tertiary history of California. The Simmler Formation, of provincial Oligocene to early Miocene age, unconformably overlies basement rocks and an Upper Cretaceous-lower Tertiary marine sequence. It consists of a sandstone facies, which is mostly a variegated sequence of sandstone and mudstone occurring in fining-upward cycles, and a conglomerate facies, which occurs around the southwest and southeast margins of the basin. The conformably overlying Vaqueros Formation, of provincial early to middle Miocene age, is subdivided from base upward ,into the Quail Canyon Sandstone, Soda Lake Shale, and Painted Rock Sandstone Members. The Vaqueros intertongues eastward, southeastward, and northward with the continental Caliente Formation and is conformably overlain by the Monterey Shale. In the Caliente Range, northeast of major thrust faults, the Vaqueros may reach a thickness of 8,700 feet (2,650 m). Around the margin of the basin, the formation is much thinner--locally only 200 feet (60 m) thick--and is generally undivided. The Quail Canyon Sandstone Member is composed of cross-bedded or planar-stratified sandstone. The Soda Lake Shale Member consists mostly of siltstone and platy shale with a few thin sandstone interbeds. The Painted Rock Sandstone Member, the thickest and coarsest member, consists mostly of large lenticular bodies of thick-bedded coarse-grained sandstone and thinner units of siltstone. Petrology and paleocurrent studies indicate that, in a given subarea, the Simmler and Vaqueros Formations were derived from the same source terrane and that the sediments were usually transported in the same general direction. Crystalline basement terranes to the north and south were the primary sources, but the Upper Cretaceous-lower Tertiary marine sequence made substantial contributions along the southwest side of the basin. The sandstone facies of the Simmler Formation is interpreted as an alluvial plain depositional complex formed by through-flowing low-sinuosity streams, and the conglomerate facies is interpreted as alluvial fan deposits. The Vaqueros Formation in the Caliente Range forms a transgressive-regressive sequence. The Quail Canyon Sandstone and lowermost Soda Lake Shale Members represent the transgressive phase, are interpreted as beach-nearshore and offshore deposits, and are locally the marine equivalents of the upper part of the Simmler conglomerate facies. The remainder of the Soda Lake Shale Member and the Painted Rock Sandstone Member represent the regressive phase and are interpreted as a complex of deltaic and shelf-slope deposits that prograded over basinal shales and turbidites. The reconstructed basin history began in the Oligocene with alluvial plain sedimentation in an area of relatively low relief. This was interrupted in the early Miocene (ca. 25 m.y. B.P.) by the beginning of a period of crustal extension, probably related to the first interaction of the Pacific and North American plates, resulting in the formation of a rapidly subsiding marine basin. This crustal extension was followed by a period of north-south compression in the Pliocene and Pleistocene, which caused the thick accumulation of sediments in the basin to be folded and thrust over the thinner basin-margin section. The Red Hills-Chimineas-Russell fault trend, along which Cretaceous granitic and Precambrian(?) gneissic rocks had been juxtaposed in Cretaceous time, was reactivated in the Pliocene, when 8 to 9 miles (13-14.5 km) of additional right-lateral slip occurred, The pattern of north-south thrusting and rig

Barite-polymetallic mineralization of Zmeinogorsk ore district and some genetic aspects of its formation

NASA Astrophysics Data System (ADS)

Bestemianova, K. V.; Grinev, O. M.

2017-12-01

Zmeinogorsky ore district is located in the northwest part of Ore Altai megatrough, which has long-lasting history of its development and complicated geological structure. Within the ore district, which is the northwest part of the devonian Zmeinogorsk-Bystrushinsky trough, ore mineralization is associated with the system of northwest border faults and cross branch faults. There were four main stages and five phases of minerogenesis. The first stage is the stage of oregenesis beginning and quartz-chlorite-sericite wall-rock alteration rocks formation. Ore deposition and intense tectonics took place during the second stage. The third stage is the most longstanding and productive ore formation stage. There are five distinct minerogenesis phases within this stage. The fourth stage expressed in erosion development and supergene alteration of already formed ore bodies with oxidation zone formation. Main ore minerals are pyrite, chalcopyrite, sphalerite and galena. Minor minerals are tetrahedrite, bornite, tennantite and chalcocite. Precious metals minerals are acanthite, gold, electrum, gold and silver amalgams. Barren minerals are barite, quartz, calcite, gypsum. According to obtained data average isotopic composition of third stage sulphides is: pyrite -0,2‰, chalcopyrite 0‰, galena +0,5‰, sphalerite -1,2‰ for the first complex; chalcopyrite -1,9‰, galena -3,4‰, sphalerite -2,3‰, tetrahedrite -3,7‰ for the second complex; tennantite -12,8‰, bornite -8,9‰ for the third complex. Sulfur isotopic compoisiton variations indicate source inhomogeneity. Thus, there was dominant source change from mantle one in the beginning to crustal one in the end. Main oregenesis stages took place in the range of temperatures between 170 and 210°С and in the mineral-forming solutions salinity range between 3 and 10 wt % NaCl equiv.

The formation of technic soil in a revegetated uranium ore waste rock pile (Limousin, France)

NASA Astrophysics Data System (ADS)

Boekhout, Flora; Gérard, Martine; Kanzari, Aisha; Calas, Georges; Descostes, Michael

2014-05-01

Mining took place in France between 1945 and 2001 during which time ~210 different sites were exploited and/or explored. A total of 76 Kt of uranium was produced, 52 Mt of ore was extracted, but also 200 Mt of waste rocks was produced, the majority of which, with uranium levels corresponding to the natural environment. So far, the processes of arenisation and technic soil formation in waste rock piles are not well understood but have important implications for understanding the environmental impact and long-term speciation of uranium. Understanding weathering processes in waste rock piles is essential to determine their environmental impact. The main objectives of this work are to assess 1) the micromorphological features and neo-formed U-bearing phases related to weathering and 2) the processes behind arenisation of the rock pile. The site that was chosen is the Vieilles Sagnes waste rock pile in Fanay (Massif Central France) that represents more or less hydrothermally altered granitic rocks that have been exposed to weathering since the construction of the waste rock pile approximately 50 years ago. Two trenches were excavated to investigate the vertical differentiation of the rock pile. This site serves as a key location for studying weathering processes of waste rock piles, as it has not been reworked after initial construction and has therefore preserved information on the original mineralogy of the waste rock pile enabling us to access post emplacement weathering processes. The site is currently overgrown by moss, meter high ferns and small trees. At present day the rock pile material can be described as hydrothermally altered rocks and rock fragments within a fine-grained silty clay matrix exposed to surface conditions and weathering. A sandy "paleo" technic soil underlies the waste rock pile and functions as a natural liner by adsorption of uranium on clay minerals. Post-mining weathering of rock-pile material is superimposed on pre-mining hydrothermal and possible supergene alteration. Clay minerals present are kaolinite, smectite and chlorite. The formation of these minerals is however ambiguous, and can form during both hydrothermal as weathering processes, calling for a detailed micromorphological study. Micromorphological investigations on undisturbed samples by microscopic and ultramicroscopic techniques allow us to interpretate the processes behind the formation of technic soil in the matrix of the waste rock pile, as well as the rate and chronology of mineral formation and arenisation related to weathering (formation of protosoil and saprolitisation). By studying the formation of weathering aureaoles in between the different granitic blocks, we quantify the anthropogenic influence on weathering of this rock pile and their impacts on local ecosystem by comparing our site with natural occuring outcrops of granites currently subjected to weathering. Electron microscope imaging and microgeochemical mapping permits us to make detailed micromorphological observations linking nanoscale processes to petrolographical macroscopic features and field observations. Different petrographic and electronic images of the mineral paragenesis in the micromass associated to their microgeochemical characteristics will be presented. Also, the impact of previous hydrothermal alteration will be highlighted.

Geology of the Windsor quadrangle, Massachusetts

USGS Publications Warehouse

Norton, Stephen A.

1967-01-01

The Windsor quadrangle lies on the boundary between the eugeosynclinal and miogeosynclinal rocks of the Appalachian geosyncline on the western flank of the metamorphic high in western New England. Precambrian rocks crop out in a north-trending belt in the central part of the quadrangle. They have been classified into 2 formations. The Stamford Granite Gneiss crops out in the eastern half of the Precambrian terrane. It is a microcline-quartz-biotite augen gneiss. Stratified Precambrian rocks (the Hinsdale Gneiss) crop out entirely the west of the Stamford Granite Gneiss. They are predominantly highly metamorphosed felsic gneisses and .quartzites with minor calc-silicate rock, amphibolite, and graphitic gneiss. Eugeosynclinal rocks (the Hoosac Formation and the Rowe Schist), .ranging in age from Lower Cambrian to Lower Ordovician, crop out in a north-trending belt east of the Precambrian terrane. They are composed predominantly of albite schist and muscovite-chlorite schist with minor garnet schist, quartz-muscovite-calcite schist, felsic granulite and gneiss, quartzite, greenschist, and carbonaceous phyllite and schist. West of the Precambrian rocks, the Hoosac Formation is overlain by a miogeosynclinal sequence (the Dalton Formation, Cheshire Quartzite, Kitchen Brook Dolomite, Clarendon Springs Dolomite, Shelburne Marble, and the Bascom Formation) ranging in age from Lower Cambrian to Lower Ordovician. These rocks are unconformably overlain by the Berkshire Schist of Middle Ordovician age that is composed of carbonaceous schist, phyllite, and quartzite. The relationships in the zone of transition between the miogeosynclinal and eugeosynclinal rocks are unknown because the rocks of this zone are no longer present. The contact between the eugeosynclinal Hoosac Formation and the Dalton Format ion is conformable and deposition. The dominant structure is a large recumbent, northwest-facing anticline (the Hoosac nappe) with a Precambrian co re. The miogeosynclinal rocks are inverted in the northwestern part of the quadrangle and upright in the southwestern part of the quadrangle. A later generation of open, post-metamorphic folds has folded the recumbent folds in the miogeosynclinal rocks. The eugeosynclinal rocks show 3 phases of folding. The earliest folds are isoclinal, have steep plunges, were synmetamorphic, and have a strong axial plane schistosity. Two post-metamorphic generations of folds are more open and have axial plane cleavage. The development of the Hoosac nappe and the isoclinal folds was accompanied by regional metamorphism of the garnet zone. The pressure exceeded the pressure for the triple point of the Al2SiO 5 polymorphs. The composition of the paragonite coexisting with muscovite suggests a period of retrograde metamorphism for the Paleozoic rocks as well as the Cambrian rocks that were originally of higher grade (sillimanite? ). Later events include high-angle faulting (Triassic?), erosion, and Pleistocene glaciation.

Geochemistry of Eagle Ford group source rocks and oils from the first shot field area, Texas

USGS Publications Warehouse

Edman, Janell D.; Pitman, Janet K.; Hammes, Ursula

2010-01-01

Total organic carbon, Rock-Eval pyrolysis, and vitrinite reflectance analyses performed on Eagle Ford Group core and cuttings samples from the First Shot field area, Texas demonstrate these samples have sufficient quantity, quality, and maturity of organic matter to have generated oil. Furthermore, gas chromatography and biomarker analyses performed on Eagle Ford Group oils and source rock extracts as well as weight percent sulfur analyses on the oils indicate the source rock facies for most of the oils are fairly similar. Specifically, these source rock facies vary in lithology from shales to marls, contain elevated levels of sulfur, and were deposited in a marine environment under anoxic conditions. It is these First Shot Eagle Ford source facies that have generated the oils in the First Shot Field. However, in contrast to the generally similar source rock facies and organic matter, maturity varies from early oil window to late oil window in the study area, and these maturity variations have a pronounced effect on both the source rock and oil characteristics. Finally, most of the oils appear to have been generated locally and have not experienced long distance migration. 

Descartes Mountains and Cayley Plains - Composition and provenance

NASA Technical Reports Server (NTRS)

Drake, M. J.; Taylor, G. J.; Goles, G. G.

1974-01-01

Trace element compositions of petrographically characterized 2-4 mm lithic fragments from Apollo 16 soil samples are used to calculate initial REE concentrations in liquids in equilibrium with lunar anorthosites and to discuss the provenance of the Cayley Formation. Lithic fragments may be subdivided into four groups: (1) ANT rocks, (2) K- and SiO2-rich mesostasis-bearing rocks, (3) poikiloblastic rocks, and (4) (spinel) troctolites. Model liquids in equilibrium with essentially monominerallic anorthosites have initial REE concentrations 5-8 times those of chondrites. The REE contents of K- and SiO2-rich mesostasis-bearing rocks and poikiloblastic rocks are dominated by the mesostasis phases. ANT rocks appear to be more abundant in the Descartes Mountains, while poikiloblastic rocks appear to be more abundant in the Cayley Plains. Poikiloblastic rocks have intermediate to high LIL-element concentrations yet the low gamma-ray activity of Mare Orientale implies low LIL-element concentrations. Consequently, it is unlikely that the Cayley Formation is Orientale ejecta. A local origin as ejecta from smaller impacts is a more plausible model for the deposition of the Cayley Formation.

Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.; Hays, William H.

2003-01-01

The geologic map of the Nelson quadrangle, scale 1:24,000, was prepared as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Nelson area, rocks ranging in age from Middle Proterozoic through Cretaceous are exposed on three major thrust plates in which rocks have been telescoped eastward. Rocks within the thrust plates are folded and broken by thrust faults of smaller displacement than the major bounding thrust faults. Middle and Late Tertiary sedimentary and volcaniclastic rocks unconformably overlie the pre-Tertiary rocks. A major normal fault displaces rocks of the western half of the quadrangle down on the west with respect to strata of the eastern part. Alluvial and terrace gravels and local landslide deposits are present in valley bottoms and on canyon walls in the deeply dissected terrain. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part, strata of the Middle Cambrian Flathead Sandstone, Wolsey Shale, and Meagher Limestone, the Middle and Upper Cambrian Pilgrim Formation and Park Shale undivided, the Devonian Maywood, Jefferson, and lower part of the Three Forks Formation, and Lower and Upper Mississippian rocks assigned to the upper part of the Three Forks Formation and the overlying Lodgepole and Mission Canyon Limestones are complexly folded and faulted. These deformed strata are overlain structurally in the east-central part of the quadrangle by a succession of strata including the Middle Proterozoic Greyson Formation and the Paleozoic succession from the Flathead Sandstone upward through the Lodgepole Limestone. In the east-central area, the Flathead Sandstone rests unconformably on the middle part of the Greyson Formation. The north edge, northwest quarter, and south half of the quadrangle are underlain by a succession of rocks that includes not only strata equivalent to those of the remainder of the quadrangle, but also the Middle Proterozoic Newland, Greyson, and Spokane Formations, Pennsylvanian and Upper Mississippian Amsden Formation and Big Snowy Group undivided, the Permian and Pennsylvanian Phosphoria and Quadrant Formations undivided, the Jurassic Ellis Group and Lower Cretaceous Kootenai Formation. Hornblende diorite sills and irregular bodies of probable Late Cretaceous age intrude Middle Proterozoic, Cambrian and Devonian strata. No equivalent intrusive rocks are present in structurally underlying successions of strata. In this main part of the quadrangle, the Flathead Sandstone cuts unconformably downward from south to north across the Spokane Formation into the upper middle part of the Greyson Formation. Tertiary (Miocene?) strata including sandstone, pebble and cobble conglomerate, and vitric crystal tuff underlie, but are poorly exposed, in the southeastern part of the quadrangle where they are overlain by late Tertiary and Quaternary gravel. The structural complexity of the quadrangle decreases from northeast to southwest across the quadrangle. At the lowest structural level (Avalanche Butte thrust plate) exposed in the canyon of Beaver Creek, lower and middle Paleozoic rocks are folded in northwest-trending east-inclined disharmonic anticlines and synclines that are overlain by recumbently folded and thrust faulted Devonian and Mississippian rocks. The Mississippian strata are imbricated adjacent to the recumbent folds. In the east-central part of the quadrangle, a structurally overlying thrust plate, likely equivalent to the Hogback Mountain thrust plate of the Hogback Mountain quadrangle adjacent to the east (Reynolds, 20xx), juxtaposes recumbently folded Middle Proterozoic and unconformably overlying lower Paleozoic rocks on the complexly folded and faulted rocks of the Avalanche Butte thrust plate. The highest structural plate, bounded below

Assessment of unconvential (tight) gas resources in Upper Cook Inlet Basin, South-central Alaska

USGS Publications Warehouse

Schenk, Christopher J.; Nelson, Philip H.; Klett, Timothy R.; Le, Phuong A.; Anderson, Christopher P.; Schenk, Christopher J.

2015-01-01

A geologic model was developed for the assessment of potential Mesozoic tight-gas resources in the deep, central part of upper Cook Inlet Basin, south-central Alaska. The basic premise of the geologic model is that organic-bearing marine shales of the Middle Jurassic Tuxedni Group achieved adequate thermal maturity for oil and gas generation in the central part of the basin largely due to several kilometers of Paleogene and Neogene burial. In this model, hydrocarbons generated in Tuxedni source rocks resulted in overpressure, causing fracturing and local migration of oil and possibly gas into low-permeability sandstone and siltstone reservoirs in the Jurassic Tuxedni Group and Chinitna and Naknek Formations. Oil that was generated either remained in the source rock and subsequently was cracked to gas which then migrated into low-permeability reservoirs, or oil initially migrated into adjacent low-permeability reservoirs, where it subsequently cracked to gas as adequate thermal maturation was reached in the central part of the basin. Geologic uncertainty exists on the (1) presence of adequate marine source rocks, (2) degree and timing of thermal maturation, generation, and expulsion, (3) migration of hydrocarbons into low-permeability reservoirs, and (4) preservation of this petroleum system. Given these uncertainties and using known U.S. tight gas reservoirs as geologic and production analogs, a mean volume of 0.64 trillion cubic feet of gas was assessed in the basin-center tight-gas system that is postulated to exist in Mesozoic rocks of the upper Cook Inlet Basin. This assessment of Mesozoic basin-center tight gas does not include potential gas accumulations in Cenozoic low-permeability reservoirs.

Insight into subdecimeter fracturing processes during hydraulic fracture experiment in Äspö hard rock laboratory, Sweden

NASA Astrophysics Data System (ADS)

Kwiatek, Grzegorz; Martínez-Garzón, Patricia; Plenkers, Katrin; Leonhardt, Maria; Zang, Arno; Dresen, Georg; Bohnhoff, Marco

2017-04-01

We analyze the nano- and picoseismicity recorded during a hydraulic fracturing in-situ experiment performed in Äspö Hard Rock Laboratory, Sweden. The fracturing experiment included six fracture stages driven by three different water injection schemes (continuous, progressive and pulse pressurization) and was performed inside a 28 m long, horizontal borehole located at 410 m depth. The fracturing process was monitored with two different seismic networks covering a wide frequency band between 0.01 Hz and 100000 Hz and included broadband seismometers, geophones, high-frequency accelerometers and acoustic emission sensors. The combined seismic network allowed for detection and detailed analysis of seismicity with moment magnitudes MW<-4 (source sizes approx. on cm scale) that occurred solely during the hydraulic fracturing and refracturing stages. We relocated the seismicity catalog using the double-difference technique and calculated the source parameters (seismic moment, source size, stress drop, focal mechanism and seismic moment tensors). The physical characteristics of induced seismicity are compared to the stimulation parameters and to the formation parameters of the site. The seismic activity varies significantly depending on stimulation strategy with conventional, continuous stimulation being the most seismogenic. We find a systematic spatio-temporal migration of microseismic events (propagation away and towards wellbore injection interval) and temporal transitions in source mechanisms (opening - shearing - collapse) both being controlled by changes in fluid injection pressure. The derived focal mechanism parameters are in accordance with the local stress field orientation, and signify the reactivation of pre-existing rock flaws. The seismicity follows statistical and source scaling relations observed at different scales elsewhere, however, at an extremely low level of seismic efficiency.

Alteration of fault rocks by CO2-bearing fluids with implications for sequestration

NASA Astrophysics Data System (ADS)

Luetkemeyer, P. B.; Kirschner, D. L.; Solum, J. G.; Naruk, S.

2011-12-01

Carbonates and sulfates commonly occur as primary (diagenetic) pore cements and secondary fluid-mobilized veins within fault zones. Stable isotope analyses of calcite, formation fluid, and fault zone fluids can help elucidate the carbon sources and the extent of fluid-rock interaction within a particular reservoir. Introduction of CO2 bearing fluids into a reservoir/fault system can profoundly affect the overall fluid chemistry of the reservoir/fault system and may lead to the enhancement or degradation of porosity within the fault zone. The extent of precipitation and/or dissolution of minerals within a fault zone can ultimately influence the sealing properties of a fault. The Colorado Plateau contains a number of large carbon dioxide reservoirs some of which leak and some of which do not. Several normal faults within the Paradox Basin (SE Utah) dissect the Green River anticline giving rise to a series of footwall reservoirs with fault-dependent columns. Numerous CO2-charged springs and geysers are associated with these faults. This study seeks to identify regional sources and subsurface migration of CO2 to these reservoirs and the effect(s) faults have on trap performance. Data provided in this study include mineralogical, elemental, and stable isotope data for fault rocks, host rocks, and carbonate veins that come from two localities along one fault that locally sealed CO2. This fault is just tens of meters away from another normal fault that has leaked CO2-charged waters to the land surface for thousands of years. These analyses have been used to determine the source of carbon isotopes from sedimentary derived carbon and deeply sourced CO2. XRF and XRD data taken from several transects across the normal faults are consistent with mechanical mixing and fluid-assisted mass transfer processes within the fault zone. δ13C range from -6% to +10% (PDB); δ18O values range from +15% to +24% (VSMOW). Geochemical modeling software is used to model the alteration productions of fault rocks from fluids of various chemistries coming from several different reservoirs within an active CO2-charged fault system. These results are compared to data obtained in the field.

Experiments on the role of water in petroleum formation

NASA Astrophysics Data System (ADS)

Lewan, M. D.

1997-09-01

Pyrolysis experiments were conducted on immature petroleum source rocks under various conditions to evaluate the role of water in petroleum formation. At temperatures less than 330°C for 72 h, the thermal decomposition of kerogen to bitumen was not significantly affected by the presence or absence of liquid water in contact with heated gravel-sized source rock. However, at 330 and 350°C for 72 h, the thermal decomposition of generated bitumen was significantly affected by the presence or absence of liquid water. Carbon-carbon bond cross linking resulting in the formation of an insoluble bitumen (i.e., pyrobitumen) is the dominant reaction pathway in the absence of liquid water. Conversely, thermal cracking of carbon-carbon bonds resulting in the generation of saturate-enriched oil, which is similar to natural crude oils, is the dominant reaction pathway in the presence of liquid water. This difference in reaction pathways is explained by the availability of an exogenous source of hydrogen, which reduces the rate of thermal decomposition, promotes thermal cracking, and inhibits carbon-carbon bond cross linking. The distribution of generated n-alkanes is characteristic of a free radical mechanism, with a broad carbon-number distribution (i.e., C 5 to C 35) and only minor branched alkanes from known biological precursors (i.e., pristane and phytane). The generation of excess oxygen in the form of CO 2 in hydrous experiments and the high degree of hydrocarbon deuteration in a D 2O experiment indicate that water dissolved in the bitumen is an exogenous source of hydrogen. The lack of an effect on product composition and yield with an increase in H + activity by five orders of magnitude in a hydrous experiment indicates that an ionic mechanism for water interactions with thermally decomposing bitumen is not likely. Several mechanistically simple and thermodynamically favorable reactions that are consistent with the available experimental data are envisaged for the generation of exogenous hydrogen and excess oxygen as CO 2. One reaction series involves water oxidizing existing carbonyl groups to form hydrogen and car☐yl groups, with the latter forming CO 2 by decar☐ylation with increasing thermal stress. Another reaction series involves either hydrogen or oxygen in dissolved water molecules directly interacting with unpaired electrons to form a hydrogen-terminated free-radical site or an oxygenated functional group, respectively. The latter is expected to be susceptible to oxidation by other dissolved water molecules to generate additional hydrogen and CO 2. In addition to water acting as an exogenous source of hydrogen, it is also essential to the generation of an expelled saturate-enriched oil that is similar to natural crude oil. This role of water is demonstrated by the lack of an expelled oil in an experiment where a liquid Ga sbnd In alloy is substituted for liquid water. Experiments conducted with high salinity water and high water/rock ratios indicate that selective aqueous solubility of hydrocarbons is not responsible for the expelled oil generated in hydrous pyrolysis experiments. Similarly, a hydrous pyrolysis experiment conducted with isolated kerogen indicates that expelled oil in hydrous pyrolysis is not the result of preferential sorption of polar organic components by the mineral matrix of a source rock. It is envisaged that dissolved water in the bitumen network of a source rock causes an immiscible saturate-enriched oil to become immiscible with the thermally decomposing polar-enriched bitumen. The overall geochemical implication of these results is that it is essential to consider the role of water in experimental studies designed to understand natural rates of petroleum generation, expulsion mechanisms of primary migration, thermal stability of crude oil, reaction kinetics of biomarker transformations, and thermal maturity indicators in sedimentary basins.

Experiments on the role of water in petroleum formation

USGS Publications Warehouse

Lewan, M.D.

1997-01-01

Pyrolysis experiments were conducted on immature petroleum source rocks under various conditions to evaluate the role of water in petroleum formation. At temperatures less than 330??C for 72 h, the thermal decomposition of kerogen to bitumen was not significantly affected by the presence or absence of liquid water in contact with heated gravel-sized source rock. However, at 330 and 350??C for 72 h, the thermal decomposition of generated bitumen was significantly affected by the presence or absence of liquid water. Carbon-carbon bond cross linking resulting in the formation of an insoluble bitumen (i.e., pyrobitumen) is the dominant reaction pathway in the absence of liquid water. Conversely, thermal cracking of carbon-carbon bonds resulting in the generation of saturate-enriched oil, which is similar to natural crude oils, is the dominant reaction pathway in the presence of liquid water. This difference in reaction pathways is explained by the availability of an exogenous source of hydrogen, which reduces the rate of thermal decomposition, promotes thermal cracking, and inhibits carbon-carbon bond cross linking. The distribution of generated n-alkanes is characteristic of a free radical mechanism, with a broad carbon-number distribution (i.e., C5 to C35) and only minor branched alkanes from known biological precursors (i.e., pristane and phytane). The generation of excess oxygen in the form of CO2 in hydrous experiments and the high degree of hydrocarbon deuteration in a D2O experiment indicate that water dissolved in the bitumen is an exogenous source of hydrogen. The lack of an effect on product composition and yield with an increase in H+ activity by five orders of magnitude in a hydrous experiment indicates that an ionic mechanism for water interactions with thermally decomposing bitumen is not likely. Several mechanistically simple and thermodynamically favorable reactions that are consistent with the available experimental data are envisaged for the generation of exogenous hydrogen and excess oxygen as CO2. One reaction series involves water oxidizing existing carbonyl groups to form hydrogen and carboxyl groups, with the latter forming CO2 by decarboxylation with increasing thermal stress. Another reaction series involves either hydrogen or oxygen in dissolved water molecules directly interacting with unpaired electrons to form a hydrogen-terminated free-radical site or an oxygenated functional group, respectively. The latter is expected to be susceptible to oxidation by other dissolved water molecules to generate additional hydrogen and CO2. In addition to water acting as an exogenous source of hydrogen, it is also essential to the generation of an expelled saturate-enriched oil that is similar to natural crude oil. This role of water is demonstrated by the lack of an expelled oil in an experiment where a liquid Ga-In alloy is substituted for liquid water. Experiments conducted with high salinity water and high water/rock ratios indicate that selective aqueous solubility of hydrocarbons is not responsible for the expelled oil generated in hydrous pyrolysis experiments. Similarly, a hydrous pyrolysis experiment conducted with isolated kerogen indicates that expelled oil in hydrous pyrolysis is not the result of preferential sorption of polar organic components by the mineral matrix of a source rock. It is envisaged that dissolved water in the bitumen network of a source rock causes an immiscible saturate-enriched oil to become immiscible with the thermally decomposing polar-enriched bitumen. The overall geochemical implication of these results is that it is essential to consider the role of water in experimental studies designed to understand natural rates of petroleum generation, expulsion mechanisms of primary migration, thermal stability of crude oil, reaction kinetics of biomarker transformations, and thermal maturity indicators in sedimentary basins. Copyright ?? 1997 Elsevier Science Ltd.

Hydrogeology of the carbonate rocks of the Lebanon Valley, Pennsylvania

USGS Publications Warehouse

Meisler, Harold

1963-01-01

The Lebanon Valley, which is part of the Great Valley in southeastern Pennsylvania, is underlain by carbonate rocks in the southern part and by shale in the northern part. The carbonate rocks consist of alternating beds of limestone and dolomite of Cambrian and Ordovician age. Although the beds generally dip to the south, progressively younger beds crop out to the north, because the rocks are overturned. The stratigraphic units, from oldest to youngest, are: the Buffalo Springs Formation, Snitz Creek, Schaefferstown, Millbach, and Richland Formations of the Conococheague Group; the Stonehenge, Rickenbach, Epler, and Ontelaunee Formations of the Beekmantown Group; and the Annville, Myerstown, and Hershey Limestones.

Acid Sulfate Weathering on Mars: Results from the Mars Exploration Rover Mission

NASA Technical Reports Server (NTRS)

Ming, Douglas W.; Morris, R. V.; Golden, D. C.

2006-01-01

Sulfur has played a major role in the formation and alteration of outcrops, rocks, and soils at the Mars Exploration Rover landing sites on Meridiani Planum and in Gusev crater. Jarosite, hematite, and evaporite sulfates (e.g., Mg and Ca sulfates) occur along with siliciclastic sediments in outcrops at Meridiani Planum. The occurrence of jarosite is a strong indicator for an acid sulfate weathering environment at Meridiani Planum. Some outcrops and rocks in the Columbia Hills in Gusev crater appear to be extensively altered as suggested by their relative softness as compared to crater floor basalts, high Fe(3+)/FeT, iron mineralogy dominated by nanophase Fe(3+) oxides, hematite and/or goethite, corundum-normative mineralogies, and the presence of Mg- and Casulfates. One scenario for aqueous alteration of these rocks and outcrops is that vapors and/or fluids rich in SO2 (volcanic source) and water interacted with rocks that were basaltic in bulk composition. Ferric-, Mg-, and Ca-sulfates, phosphates, and amorphous Si occur in several high albedo soils disturbed by the rover's wheels in the Columbia Hills. The mineralogy of these materials suggests the movement of liquid water within the host material and the subsequent evaporation of solutions rich in Fe, Mg, Ca, S, P, and Si. The presence of ferric sulfates suggests that these phases precipitated from highly oxidized, low-pH solutions. Several hypotheses that invoke acid sulfate weathering environments have been suggested for the aqueous formation of sulfate-bearing phases on the surface of Mars including (1) the oxidative weathering of ultramafic igneous rocks containing sulfides; (2) sulfuric acid weathering of basaltic materials by solutions enriched by volcanic gases (e.g., SO2); and (3) acid fog (i.e., vapors rich in H2SO4) weathering of basaltic or basaltic-derived materials.

SHRIMP U-Pb evidence for a Late Silurian age of metasedimentary rocks in the Merrimack and Putnam-Nashoba terranes, eastern New England

USGS Publications Warehouse

Wintsch, R.P.; Aleinikoff, J.N.; Walsh, G.J.; Bothner, Wallace A.; Hussey, A.M.; Fanning, C.M.

2007-01-01

U-Pb ages of detrital, metamorphic, and magmatic zircon and metamorphic monazite and titanite provide evidence for the ages of deposition and metamorphism of metasedimentary rocks from the Merrimack and Putnam-Nashoba terranes of eastern New England. Rocks from these terranes are interpreted here as having been deposited in the middle Paleozoic above Neoproterozoic basement of the Gander terrane and juxtaposed by Late Paleozoic thrusting in thin, fault-bounded slices. The correlative Hebron and Berwick formations (Merrimack terrane) and Tatnic Hill Formation (Putnam-Nashoba terrane), contain detrital zircons with Mesoproterozoic, Ordovician, and Silurian age populations. On the basis of the age of the youngest detrital zircon population (???425 Ma), the Hebron, Berwick and Tatnic Hill formations are no older than Late Silurian (Wenlockian). The minimum deposition ages of the Hebron and Berwick are constrained by ages of cross-cutting plutons (414 ?? 3 and 418 ?? 2 Ma, respectively). The Tatnic Hill Formation must be older than the oldest metamorphic monazite and zircon (???407 Ma). Thus, all three of these units were deposited between ???425 and 418 Ma, probably in the Ludlovian. Age populations of detrital zircons suggest Laurentian and Ordovician arc provenance to the west. High grade metamorphism of the Tatnic Hill Formation soon after deposition probably requires that sedimentation and burial occurred in a fore-arc environment, whereas time-equivalent calcareous sediments of the Hebron and Berwick formations probably originated in a back-arc setting. In contrast to age data from the Berwick Formation, the Kittery Formation contains primarily Mesoproterozoic detrital zircons; only 2 younger grains were identified. The absence of a significant Ordovician population, in addition to paleocurrent directions from the east and structural data indicating thrusting, suggest that the Kittery was derived from peri-Gondwanan sources and deposited in the Fredericton Sea. Thus, the Kittery should not be considered part of the Laurentian-derived Merrimack terrane; it more likely correlates with the early Silurian Fredericton terrane of northeastern New England and Maritime Canada.

Detailed north-south cross section showing environments of deposition, organic richness, and thermal maturities of lower Tertiary rocks in the Uinta Basin, Utah

USGS Publications Warehouse

Johnson, Ronald C.

2014-01-01

The Uinta Basin of northeast Utah has produced large amounts of hydrocarbons from lower Tertiary strata since the 1960s. Recent advances in drilling technologies, in particular the development of efficient methods to drill and hydraulically fracture horizontal wells, has spurred renewed interest in producing hydrocarbons from unconventional low-permeability dolomite and shale reservoirs in the lacustrine, Eocene Green River Formation. The Eocene Green River Formation was deposited in Lake Uinta, a long-lived saline lake that occupied the Uinta Basin, the Piceance Basin to the east, and the intervening Douglas Creek arch. The focus of recent drilling activity has been the informal Uteland Butte member of the Green River Formation and to a much lesser extent the overlying R-0 oil shale zone of the Green River Formation. Initial production rates ranging from 500 to 1,500 barrels of oil equivalent per day have been reported from the Uteland Butte member from horizontal well logs that are as long as 4,000 feet (ft);. The cross section presented here extends northward from outcrop on the southern margin of the basin into the basin’s deep trough, located just south of the Uinta Mountains, and transects the area where this unconventional oil play is developing. The Monument Butte field, which is one of the fields located along this line of section, has produced hydrocarbons from conventional sandstone reservoirs in the lower part of the Green River Formation and underlying Wasatch Formation since 1981. A major fluvial-deltaic system entered Lake Uinta from the south, and this new line of section is ideal for studying the effect of the sediments delivered by this drainage on hydrocarbon reservoirs in the Green River Formation. The cross section also transects the Greater Altamont-Bluebell field in the deepest part of the basin, where hydrocarbons have been produced from fractured, highly overpressured marginal lacustrine and fluvial reservoirs in the Green River, Wasatch, and North Horn Formations since 1970. Datum for the cross section is sea level so that hydrocarbon source rocks and reservoir rocks could be integrated into the structural framework of the basin.

Petroleum geology and resources of the West Siberian Basin, Russia

USGS Publications Warehouse

Ulmishek, Gregory F.

2003-01-01

The West Siberian basin is the largest petroleum basin in the world covering an area of about 2.2 million km2. The basin occupies a swampy plain between the Ural Mountains and the Yenisey River. On the north, the basin extends offshore into the southern Kara Sea. On the west, north, and east, the basin is surrounded by the Ural, Yenisey Ridge, and Turukhan-Igarka foldbelts that experienced major deformations during the Hercynian tectonic event and the Novaya Zemlya foldbelt that was deformed in early Cimmerian (Triassic) time. On the south, the folded Caledonian structures of the Central Kazakhstan and Altay-Sayan regions dip northward beneath the basin?s sedimentary cover. The basin is a relatively undeformed Mesozoic sag that overlies the Hercynian accreted terrane and the Early Triassic rift system. The basement is composed of foldbelts that were deformed in Late Carboniferous?Permian time during collision of the Siberian and Kazakhstan continents with the Russian craton. The basement also includes several microcontinental blocks with a relatively undeformed Paleozoic sedimentary sequence. The sedimentary succession of the basin is composed of Middle Triassic through Tertiary clastic rocks. The lower part of this succession is present only in the northern part of the basin; southward, progressively younger strata onlap the basement, so that in the southern areas the basement is overlain by Toarcian and younger rocks. The important stage in tectono-stratigraphic development of the basin was formation of a deep-water sea in Volgian?early Berriasian time. The sea covered more than one million km2 in the central basin area. Highly organic-rich siliceous shales of the Bazhenov Formation were deposited during this time in anoxic conditions on the sea bottom. Rocks of this formation have generated more than 80 percent of West Siberian oil reserves and probably a substantial part of its gas reserves. The deep-water basin was filled by prograding clastic clinoforms during Neocomian time. The clastic material was transported by a system of rivers dominantly from the eastern provenance. Sandstones within the Neocomian clinoforms contain the principal oil reservoirs. The thick continental Aptian?Cenomanian Pokur Formation above the Neocomian sequence contains giant gas reserves in the northern part of the basin. Three total petroleum systems are identified in the West Siberian basin. Volumes of discovered hydrocarbons in these systems are 144 billion barrels of oil and more than 1,300 trillion cubic feet of gas. The assessed mean undiscovered resources are 55.2 billion barrels of oil, 642.9 trillion cubic feet of gas, and 20.5 billion barrels of natural gas liquids. The largest known oil reserves are in the Bazhenov-Neocomian total petroleum system that includes Upper Jurassic and younger rocks of the central and southern parts of the basin. Oil reservoirs are mainly in Neocomian and Upper Jurassic clastic strata. Source rocks are organic-rich siliceous shales of the Bazhenov Formation. Most discovered reserves are in structural traps, but stratigraphic traps in the Neocomian clinoform sequence are pro-ductive and are expected to contain much of the undiscovered resources. Two assessment units are identified in this total petroleum system. The first assessment unit includes all conventional reservoirs in the stratigraphic interval from the Upper Jurassic to the Cenomanian. The second unit includes unconventional (or continuous), self-sourced, fractured reservoirs in the Bazhenov Formation. This unit was not assessed quantitatively. The Togur-Tyumen total petroleum system covers the same geographic area as the Bazhenov-Neocomian system, but it includes older, Lower?Middle Jurassic strata and weathered rocks at the top of the pre-Jurassic sequence. A Callovian regional shale seal of the Abalak and lower Vasyugan Formations separates the two systems. The Togur-Tyumen system is oil-prone; gas reserves are insignificant. The principal o

Total petroleum systems of the Illizi Province, Algeria and Libya; Tanezzuft-Illizi

USGS Publications Warehouse

Klett, T.R.

2000-01-01

Undiscovered conventional oil and gas resources were assessed within a total petroleum system of the Illizi Province (2056) as part of the U.S. Geological Survey World Petroleum Assessment 2000. The Illizi Province is in eastern Algeria and a small portion of western Libya. The province and its total petroleum system coincide with the Illizi Basin. Although several total petroleum systems may exist within the Illizi Province, only one “composite” total petroleum system is identified. This total petroleum system comprises a single assessment unit. The main source rocks are the Silurian Tanezzuft Formation (or lateral equivalents) and Middle to Upper Devonian mudstone. The total petroleum system was named after the oldest major source rock and the basin in which it resides. The estimated means of the undiscovered conventional petroleum volumes in the Tanezzuft-Illizi Total Petroleum System are 2,814 million barrels of oil (MMBO), 27,785 billion cubic feet of gas (BCFG), and 873 million barrels of natural gas liquids (MMBNGL).

WEST AND EAST PALISADES ROADLESS AREAS, IDAHO AND WYOMING.

USGS Publications Warehouse

Oriel, Steven S.; Benham, John R.

1984-01-01

Studies of the West and East Palisades Roadless Areas, which lie within the Idaho-Wyoming thrust belt, document structures, reservoir formations, source beds, and thermal maturities comparable to those in producing oil and gas field farther south in the belt. Therefore, the areas are highly favorable for the occurrence of oil and gas. Phosphate beds of appropriate grade within the roadless areas are thinner and less accessible than those being mined from higher thrust sheets to the southwest; however, they contain 98 million tons of inferred phosphate rock resources in areas of substantiated phosphate resource potential. Sparsely distributed thin coal seams occur in the roadless areas. Although moderately pure limestone is present, it is available from other sources closer to markets. Geochemical anomalies from stream-sediment and rock samples for silver, copper, molydenum, and lead occur in the roadless areas but they offer little promise for the occurrence of metallic mineral resources. A possible geothermal resource is unproven, despite thermal phenomena at nearby sites.

Petroleum geology and resources of the Amu-Darya basin, Turkmenistan, Uzbekistan, Afghanistan, and Iran

USGS Publications Warehouse

Ulmishek, Gregory F.

2004-01-01

The Amu-Darya basin is a highly productive petroleum province in Turkmenistan and Uzbekistan (former Soviet Union), extending southwestward into Iran and southeastward into Afghanistan. The basin underlies deserts and semideserts north of the high ridges of the Kopet-Dag and Bande-Turkestan Mountains. On the northwest, the basin boundary crosses the crest of the Karakum regional structural high, and on the north the basin is bounded by the shallow basement of the Kyzylkum high. On the east, the Amu-Darya basin is separated by the buried southeast spur of the Gissar Range from the Afghan-Tajik basin, which is deformed into a series of north-south-trending synclinoria and anticlinoria. The separation of the two basins occurred during the Neogene Alpine orogeny; earlier, they were parts of a single sedimentary province. The basement of the Amu-Darya basin is a Hercynian accreted terrane composed of deformed and commonly metamorphosed Paleozoic rocks. These rocks are overlain by rift grabens filled with Upper Permian-Triassic rocks that are strongly compacted and diagenetically altered. This taphrogenic sequence, also considered to be a part of the economic basement, is overlain by thick Lower to Middle Jurassic, largely continental, coal-bearing rocks. The overlying Callovian-Oxfordian rocks are primarily carbonates. A deep-water basin surrounded by shallow shelves with reefs along their margins was formed during this time and reached its maximum topographic expression in the late Oxfordian. In Kimmeridgian-Tithonian time, the basin was filled with thick evaporites of the Gaurdak Formation. The Cretaceous-Paleogene sequence is composed chiefly of marine clastic rocks with carbonate intervals prominent in the Valanginian, Barremian, Maastrichtian, and Paleocene stratigraphic units. In Neogene time, the Alpine orogeny on the basin periphery resulted in deposition of continental clastics, initiation of new and rejuvenation of old faults, and formation of most structural traps. A single total petroleum system is identified in the Amu-Darya basin. The system is primarily gas prone. Discovered gas reserves are listed by Petroconsultants (1996) at about 230 trillion cubic feet, but recent discoveries and recent reserve estimates in older fields should increase this number by 40 to 50 trillion cubic feet. Reserves of liquid hydrocarbons (oil and condensate) are comparatively small, less than 2 billion barrels. Most of the gas reserves are concentrated in two stratigraphic intervals, Upper Jurassic carbonates and Neocomian clastics, each of which contains about one-half of the reserves. Reserves of other stratigraphic units?from Middle Jurassic to Paleogene in age?are relatively small. Source rocks for the gas are the Lower to Middle Jurassic clastics and coal and Oxfordian basinal black shales in the east-central part of the basin. The latter is probably responsible for the oil legs and much of the condensate in gas pools. Throughout most of the basin both source-rock units are presently in the gas-window zone. Traps are structural, paleogeomorphic, and stratigraphic, as well as a combination of these types. The giant Dauletabad field is in a combination trap with an essential hydrodynamic component. Four assessment units were identified in the total petroleum system. One unit in the northeastern, northern, and northwestern marginal areas of the basin and another in the southern marginal area are characterized by wide vertical distribution of hydrocarbon pools in Middle Jurassic to Paleocene rocks and the absence of the salt of the Gaurdak Formation. The other two assessment units are stratigraphically stacked; they occupy the central area of the basin and are separated by the regional undeformed salt seal of the Gaurdak Formation. The largest part of undiscovered hydrocarbon resources of the Amu-Darya basin is expected in older of these assessment units. The mean value of total assessed resources of the Amu-Darya basin is estimated

Tectonics, basin analysis and organic geochemical attributes of Permian through Mesozoic deposits and their derivative oils of the Turpan-Hami basin, northwestern China

NASA Astrophysics Data System (ADS)

Greene, Todd Jeremy

The Turpan-Hami basin is a major physiographic and geologic feature of northwest China, yet considerable uncertainty exists as to the timing of its inception, its late Paleozoic and Mesozoic tectonic history, and the relationship of its petroleum systems to those of the nearby Junggar basin. Mesozoic sedimentary fades, regional unconformities, sediment dispersal patterns, and sediment compositions within the Turpan-Hami and southern Junggar basins suggest that these basins were initially separated between Early Triassic and Early Jurassic time. Prior to separation, Upper Permian profundal lacustrine and fan-delta fades and Triassic coarse-grained braided-fluvial/alluvial fades were deposited across a contiguous Junggar-Turpan-Hami basin. Permian through Triassic fades were derived mainly from the Tian Shan to the south as indicated by northward-directed paleocurrent directions and geochemical provenance of granitoid cobbles. Lower through Middle Jurassic strata begin to reflect ponded coal-forming, lake-plain environments within the Turpan-Hami basin. A sharp change in sedimentary-lithic-rich Lower Jurassic sandstone followed by a return to lithic volcanic-rich Middle Jurassic sandstone points to the initial uplift and unroofing of the largely andesitic Bogda Shan range, which first shed its sedimentary cover as it emerged to become the partition between the Turpan-Hami and southern Junggar basins. In Turpan-Hami, source rock age is one of three major statistically significant discriminators of effective source rocks in the basin. A newly developed biomarker parameter appears to track conifer evolution and can distinguish Permian rocks and their correlative oils from Jurassic coals and mudrocks, and their derivative oils. Source fades is a second key control on petroleum occurrence and character. By erecting rock-to-oil correlation models, the biomarker parameters separate oil families into end-member groups: Group 1 oils---Lower/Middle Jurassic peatland/swamp fades, Group 2 oils---Lower/Middle Jurassic marginal lacustrine fades, and Group 3 oils---Upper Permian lacusbine fades. Burial history exercises a third major control on petroleum in the Turpan-Hami basin. While relatively uninterrupted deep burial in the Tabei Depression exhausted Upper Permian source rocks and brought Lower/Middle Jurassic rocks well into the oil generative window, Late Jurassic uplift in the Tainan Depression eroded much of the Lower/Middle Jurassic section and preserved Upper Permian sourced oils as biodegraded, relict, heavy oils.* *This dissertation includes a CD that is multimedia (contains text and other applications that are not available in a printed format). The CD requires the following applications: Adobe Acrobat, UNIX.

Assessment of undiscovered oil and gas resources of the Devonian Marcellus Shale of the Appalachian Basin Province

USGS Publications Warehouse

Coleman, James L.; Milici, Robert C.; Cook, Troy A.; Charpentier, Ronald R.; Kirshbaum, Mark; Klett, Timothy R.; Pollastro, Richard M.; Schenk, Christopher J.

2011-01-01

Using a geology-based assessment methodology, the U.S. Geological Survey (USGS) estimated a mean undiscovered natural gas resource of 84,198 billion cubic feet and a mean undiscovered natural gas liquids resource of 3,379 million barrels in the Devonian Marcellus Shale within the Appalachian Basin Province. All this resource occurs in continuous accumulations. In 2011, the USGS completed an assessment of the undiscovered oil and gas potential of the Devonian Marcellus Shale within the Appalachian Basin Province of the eastern United States. The Appalachian Basin Province includes parts of Alabama, Georgia, Kentucky, Maryland, New York, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. The assessment of the Marcellus Shale is based on the geologic elements of this formation's total petroleum system (TPS) as recognized in the characteristics of the TPS as a petroleum source rock (source rock richness, thermal maturation, petroleum generation, and migration) as well as a reservoir rock (stratigraphic position and content and petrophysical properties). Together, these components confirm the Marcellus Shale as a continuous petroleum accumulation. Using the geologic framework, the USGS defined one TPS and three assessment units (AUs) within this TPS and quantitatively estimated the undiscovered oil and gas resources within the three AUs. For the purposes of this assessment, the Marcellus Shale is considered to be that Middle Devonian interval that consists primarily of shale and lesser amounts of bentonite, limestone, and siltstone occurring between the underlying Middle Devonian Onondaga Limestone (or its stratigraphic equivalents, the Needmore Shale and Huntersville Chert) and the overlying Middle Devonian Mahantango Formation (or its stratigraphic equivalents, the upper Millboro Shale and middle Hamilton Group).

The origin of the 1.73-1.70 Ga anorogenic Ulkan volcano-plutonic complex, Siberian platform, Russia: inferences from geochronological, geochemical and Nd-Sr-Pb isotopic data

USGS Publications Warehouse

Larin, A.M.; Amelin, Yu. V.; Neymark, L.A.; Krymsky, R. Sh

1997-01-01

The Ulkan volcano-plutonic complex, a part of a 750 km Bilyakchian-Ulkan anorogenic belt, is located in the eastern part of the Archean-Paleoproterozoic Aldan shield. The tectonic position and geochemistry indicate that the Ulkan Complex is a typical A-type or intraplate magmatic association. The felsic volcanics of the Uian Group and granitoids of the North Uchur Massif, the major igneous components of the Ulkan Complex, have U-Pb zircon and monazite ages between 1721±1 Ma and 1703±18 Ma. Together with the spatially associated 1736±6 Ma Dzhugdzhur anorthosite massif, the Ulkan Complex forms a typical Proterozoic anorthosite-granite-volcanic association with the minimum duration of formation of 12 m.y. Initial εNd values between 0 and 1.1, similar for the Uian felsic volcanics, early granitoid phases of the North Uchur Massif and high-grade metamorphic basement rocks, indicate, along with geochemical data, that the crustal source of the Ulkan parental magmas may be similar to the basement rocks. The higher εNd(T) values of -0.3 to +1.9 in the later North Uchur granitoids and associated ore-bearing metasomatites, and relatively low time-integrated Rb/Sr, U/Pb, and Th/U estimated for their sources, may demonstrate involvement of variable amounts of a depleted mantle-derived component in the generation of later phases of the North Uchur Massif. The preferred model of formation of magmas parental to the Ulkan Complex involves thermal interaction of an uprising mantle diapir with Paleoproterozoic lower crust, which was accompanied by chemical interaction between a fluid derived from the diapir, with the lower crustal rocks.

Geological Assessment of Cores from the Great Bay National Wildlife Refuge, New Hampshire

USGS Publications Warehouse

Foley, Nora K.; Ayuso, Robert A.; Ayotte, Joseph D.; Montgomery, Denise L.; Robinson, Gilpin R.

2007-01-01

Geological sources of metals (especially arsenic and zinc) in aquifer bedrock were evaluated for their potential to contribute elevated values of metals to ground and surface waters in and around Rockingham County, New Hampshire. Ayotte and others (1999, 2003) had proposed that arsenic concentrations in ground water flowing through bedrock aquifers in eastern New England were elevated as a result of interaction with rocks. Specifically in southeastern New Hampshire, Montgomery and others (2003) established that nearly one-fifth of private bedrock wells had arsenic concentrations that exceed the U.S. Environmental Protection Agency (EPA) maximum contamination level for public water supplies. Two wells drilled in coastal New Hampshire were sited to intersect metasedimentary and metavolcanic rocks in the Great Bay National Wildlife Refuge. Bulk chemistry, mineralogy, and mineral chemistry data were obtained on representative samples of cores extracted from the two boreholes in the Kittery and Eliot Formations. The results of this study have established that the primary geologic source of arsenic in ground waters sampled from the two well sites was iron-sulfide minerals, predominantly arsenic-bearing pyrite and lesser amounts of base-metal-sulfide and sulfosalt minerals that contain appreciable arsenic, including arsenopyrite, tetrahedrite, and cobaltite. Secondary minerals containing arsenic are apparently limited to iron-oxyhydroxide minerals. The geologic source of zinc was sphalerite, typically cadmium-bearing, which occurs with pyrite in core samples. Zinc also occurred as a secondary mineral in carbonate form. Oxidation of sulfides leading to the liberation of acid, iron, arsenic, zinc, and other metals was most prevalent in open fractures and vuggy zones in core intervals containing zones of high transmissivity in the two units. The presence of significant calcite and lesser amounts of other acid-neutralizing carbonate and silicate minerals, acting as a natural buffer to reduce acidity, forced precipitation of iron-oxyhydroxide minerals and the removal of trace elements, including arsenic and lead, from ground waters in the refuge. Zinc may have remained in solution to a greater extent because of complexing with carbonate and its solubility in near-neutral ground and surface waters. The regional link between anomalously high arsenic contents in ground water and a bedrock source as established by Ayotte and others (1999, 2003) and Montgomery and others (2003) was confirmed by the presence of some arsenic-bearing minerals in rocks of the Kittery and Eliot Formations. The relatively low amounts of arsenic and metals in wells in the Great Bay National Wildlife Refuge as reported by Ayotte and others (U.S. Geological Survey Water Resources Data, 2005) were likely controlled by local geochemical environments in partially filled fractures, fissures, and permeable zones within the bedrock formations. Carbonate and silicate gangue minerals that line fractures, fissures, and permeable zones likely limited the movement of arsenic from bedrock to ground water. Sources other than the two geologic formations might have been required to account for anomalously high arsenic contents measured in private bedrock aquifer wells of Rockingham County.

Mesozoic non-marine petroleum source rocks determined by palynomorphs in the Tarim Basin, Xinjiang, northwestern China

USGS Publications Warehouse

Jiang, D.-X.; Wang, Y.-D.; Robbins, E.I.; Wei, J.; Tian, N.

2008-01-01

The Tarim Basin in Northwest China hosts petroleum reservoirs of Cambrian, Ordovician, Carboniferous, Triassic, Jurassic, Cretaceous and Tertiary ages. The sedimentary thickness in the basin reaches about 15 km and with an area of 560000 km2, the basin is expected to contain giant oil and gas fields. It is therefore important to determine the ages and depositional environments of the petroleum source rocks. For prospective evaluation and exploration of petroleum, palynological investigations were carried out on 38 crude oil samples collected from 22 petroleum reservoirs in the Tarim Basin and on additionally 56 potential source rock samples from the same basin. In total, 173 species of spores and pollen referred to 80 genera, and 27 species of algae and fungi referred to 16 genera were identified from the non-marine Mesozoic sources. By correlating the palynormorph assemblages in the crude oil samples with those in the potential source rocks, the Triassic and Jurassic petroleum source rocks were identified. Furthermore, the palynofloras in the petroleum provide evidence for interpretation of the depositional environments of the petroleum source rocks. The affinity of the miospores indicates that the petroleum source rocks were formed in swamps in brackish to lacustrine depositional environments under warm and humid climatic conditions. The palynomorphs in the crude oils provide further information about passage and route of petroleum migration, which is significant for interpreting petroleum migration mechanisms. Additionally, the thermal alternation index (TAI) based on miospores indicates that the Triassic and Jurassic deposits in the Tarim Basin are mature petroleum source rocks. ?? Cambridge University Press 2008.

Origin of the ca. 50 Ma Linzizong shoshonitic volcanic rocks in the eastern Gangdese arc, southern Tibet

NASA Astrophysics Data System (ADS)

Liu, An-Lin; Wang, Qing; Zhu, Di-Cheng; Zhao, Zhi-Dan; Liu, Sheng-Ao; Wang, Rui; Dai, Jin-Gen; Zheng, Yuan-Chuan; Zhang, Liang-Liang

2018-04-01

The origin of the Eocene shoshonitic rocks within the upper part of the extensive Linzizong volcanic succession (i.e., the Pana Formation) in the Gangdese arc, southern Tibet remains unclear, inhibiting the detailed investigations on the crust-mantle interaction and mantle dynamics that operate the generation of the coeval magmatic flare-up in the arc. We report mineral composition, zircon U-Pb age and zircon Hf isotope, whole-rock element and Sr-Nd-Hf isotope data for the Pana Formation volcanic rocks from Pangduo, eastern Gangdese arc in southern Tibet. The Pana volcanic rocks from Pangduo include basalts, basaltic andesites, and dacites. SIMS and LA-ICPMS zircon U-Pb dating indicates that the Pangduo dacites were erupted at 50 ± 1 Ma, representing the volcanic equivalent of the coeval Gangdese Batholith that define a magmatic flare-up at 51 ± 1 Ma. The Pangduo volcanic rocks are exclusively shoshonitic, differing from typical subduction-related calc-alkaline volcanic rocks. The basalts have positive whole-rock ƐNd(t) (+1.7) and ƐHf(t) (+3.8) with high Zr abundances (121-169 ppm) and Zr/Y ratios (4.3-5.2), most likely derived from the partial melting of an enriched garnet-bearing lithospheric mantle that was metasomatized by subduction-related components with input from asthenosphere. Compared to the basalts, similar trace elemental patterns and decreased whole-rock ƐNd(t) (-3.5 to -3.3) and ƐHf(t) (-2.5 to -1.6) of the basaltic andesites can be attributed to the input of the ancient basement-derived material of the central Lhasa subterrane into the basaltic magmas. The coherent whole-rock Sr-Nd-Hf isotopic compositions ((87Sr/86Sr)i = 0.7064-0.7069, ƐNd(t) = -6.0 to -5.2, ƐHf(t) = -5.6 to -5.0) and varying zircon ƐHf(t) (-6.0 to +4.1) of the dacites can be interpreted by the partial melting of a hybrid lower crust source (juvenile and ancient lower crust) with incorporation of basement-derived components. Calculations of zircon-Ti temperature and whole-rock zircon saturation temperature of the dacites, and clinopyroxene crystallization temperature of the basalts suggest that the Pangduo volcanic rocks are most likely derived from the high-temperature melting of the lithosphere (including lithospheric mantle and overlying continental crust) as a result of the slab breakoff of the Neo-Tethyan oceanic lithosphere.

Granitoids of different geodynamic settings of Baikal region (Russia) their geochemical evolution and origin

NASA Astrophysics Data System (ADS)

Antipin, Viktor; Sheptyakova, Natalia

2016-04-01

In the southern folded framing of the Siberian craton the granitoid magmatism of different ages involves batholiths, small low-depth intrusions and intrusion-dyke belts with diverse mineral and geochemical characteristics of rocks. Granitoid formation could be related to the Early Paleozoic collision stage and intra-plate magmatism of the Late Paleozoic age of the geologic development of Baikal area. The Early Paleozoic granitoids of Khamar-Daban Ridge and Olkhon region revealed their closeness in age and composition. They were referred to syncollision S-type formations derived from gneiss-schistose substratum of metamorphic sequences. The magmatic rocks were classified into various geochemical types comprising formations of normal Na-alkalinity (migmatites and plagiogranites), calc-alkaline and subalkaline (K-Na granitoids, granosyenites and quartz syenites) series. It is significant, that plagiomigmatites and plagiogranites in all elements repeat the shape of the chart of normalized contents marked for trend of K-Na granitoids, but at considerably lower level of concentrations of all elements. This general pattern of element distribution might indicate similar anatectic origin of both granitoid types, but from crustal substrata distinguished by composition and geochemical features. Comparative geochemical analysis pointed out that the source of melts of the Early Paleozoic granitoids of the Olkhon (505-477 Ma) and Khamar-Daban (516-490 Ma) complexes of the Baikal region could be the crustal substratum, which is obviously the criterion for their formation in the collisional geodynamic setting. Using the Late Paleozoic subalkaline magmatism proceeding at the Khamar-Daban Range (Khonzurtay pluton, 331 Ma) as an example, it was found that the formation of monzodiorite-syenite-leucogranite series was considerably contributed by the processes of hybridism and assimilation through mixing of the upper mantle basaltoid magma derived melts of granitic composition. The involvement of the deep source is indicated by low Rb/Sr ratios and 87Sr/86Sr ratio (0.70592±0.00021) in rocks (Kazimirovskiy, 2006). The intra-plate biotite granites and leucogranites are represented by rare-metal geochemical type of rocks (311-321 Ma). Geochemical evolution promoted an increase of F, Li, Rb, Cs, Sn, Be, Ta, and Pb and a decrease of Ba, Sr, Zn, Zr, Th, and U contents in rare-metal granites, that reflects their formation from deeply differentiated residual magma. The substance of the lower crust could have the composition of biotite-bearing granulites rich in lithophyle rare elements. It is noteworthy, that the composition and isotope-geochemical features of the supposed magma-forming substratum correspond to the characteristics of the ancient Precambrian continental crust of the Southern Baikal region. These conclusions agree with the results of preceding studies of rare-metal granites in the other regions of Central Asia (Kovalenko et al, 1999). Research has been supported by RNF grant № 15-17-10010.

Mineral and energy resources of the BLM Roswell Resource Area, east-central New Mexico

USGS Publications Warehouse

Bartsch-Winkler, Susan B.

1992-01-01

The sedimentary formations of the Roswell Resource Area have significant mineral and energy resources. Some of the pre-Pennsylvanian sequences in the Northwestern Shelf of the Permian Basin are oil and gas reservoirs, and Pennsylvanian rocks in Tucumcari basin are reservoirs of oil and gas as well as source rocks for oil and gas in Triassic rocks. Pre-Permian rocks also contain minor deposits of uranium and vanadium, limestone, and associated gases. Hydrocarbon reservoirs in Permian rocks include associated gases such as carbon dioxide, helium, and nitrogen. Permian rocks are mineralized adjacent to the Lincoln County porphyry belt, and include deposits of copper, uranium, manganese, iron, polymetallic veins, and Mississippi-valley-type (MVT) lead-zinc. Industrial minerals in Permian rocks include fluorite, barite, potash, halite, polyhalite, gypsum, anhydrite, sulfur, limestone, dolomite, brine deposits (iodine and bromine), aggregate (sand), and dimension stone. Doubly terminated quartz crystals, called "Pecos diamonds" and collected as mineral specimens, occur in Permian rocks along the Pecos River. Mesozoic sedimentary rocks are hosts for copper, uranium, and small quantities of gold-silver-tellurium veins, as well as significant deposits of oil and gas, COa, asphalt, coal, and dimension stone. Mesozoic rocks contain limited amounts of limestone, gypsum, petrified wood, dinosaur remains, and clays. Tertiary rocks host ore deposits commonly associated with intrusive rocks, including platinum group elements, iron skarns, manganese, uranium and vanadium, molybdenum, polymetallic vein deposits, gold-silver- tellurium veins, and thorium-rare earth veins. Museum-quality quartz crystals in Lincoln County were formed in association with intrusive rocks in the Lincoln County porphyry belt. Industrial minerals in Tertiary rocks include fluorite, vein- and bedded-barite, caliche, limestone, and aggregate. Tertiary and Quaternary sediments host important placer deposits of gold and titanium, and minor silver, uranium occurrences, as well as important industrial commodities, including caliche, limestone and dolomite, and aggregate (sand). Quaternary basalt contains sub-ore-grade uranium, scoria, and clay deposits.

Mineral and energy resources of the Roswell Resource Area, East-Central New Mexico

USGS Publications Warehouse

Bartsch-Winkler, Susan B.; Donatich, Alessandro J.

1995-01-01

The sedimentary formations of the Roswell Resource Area have significant mineral and energy resources. Some of the pre-Pennsylvanian sequences in the Northwestern Shelf of the Permian Basin are oil and gas reservoirs, and Pennsylvanian rocks in Tucumcari Basin are reservoirs of oil and gas as well as source rocks for oil and gas in Triassic rocks. Pre-Permian rocks also contain minor deposits of uranium and vanadium, limestone, and gases. Hydrocarbon reservoirs in Permian rocks include associated gases such as carbon dioxide, helium, and nitrogen. Permian rocks are mineralized adjacent to the Lincoln County porphyry belt, and include deposits of copper, uranium, manganese, iron, polymetallic veins, and Mississippi-Valley-type lead-zinc. Industrial minerals in Permian rocks include fluorite, barite, potash, halite, polyhalite, gypsum, anhydrite, sulfur, limestone, dolomite, brine deposits (iodine and bromine), aggregate (sand), and dimension stone. Doubly terminated quartz crystals, called 'Pecos diamonds' and collected as mineral specimens, occur in Permian rocks along the Pecos River. Mesozoic sedimentary rocks are hosts for copper, uranium, and small quantities of gold-silver-tellurium veins, as well as significant deposits of oil and gas, carbon dioxide, asphalt, coal, and dimension stone. Mesozoic rocks contain limited amounts of limestone, gypsum, petrified wood, and clay. Tertiary rocks host ore deposits commonly associated with intrusive rocks, including platinum-group elements, iron skarns, manganese, uranium and vanadium, molybdenum, polymetallic vein deposits, gold-silver-tellurium veins, and thorium-rare-earth veins. Museum-quality quartz crystals are associated with Tertiary intrusive rocks. Industrial minerals in Tertiary rocks include fluorite, vein- and bedded-barite, caliche, limestone, and aggregate. Tertiary and Quaternary sediments host important placer deposits of gold and titanium, and occurrences of silver and uranium. Important industrial commodities include caliche, limestone and dolomite, and aggregate. Quaternary basalt contains sub-ore-grade uranium, scoria, and clay deposits.

D/H isotope ratios of kerogen, bitumen, oil, and water in hydrous pyrolysis of source rocks containing kerogen types I, II, IIS, and III

USGS Publications Warehouse

Schimmelmann, A.; Lewan, M.D.; Wintsch, R.P.

1999-01-01

Immature source rock chips containing different types of kerogen (I, II, IIS, III) were artificially matured in isotopically distinct waters by hydrous pyrolysis and by pyrolysis in supercritical water. Converging isotopic trends of inorganic (water) and organic (kerogen, bitumen, oil) hydrogen with increasing time and temperature document that water-derived hydrogen is added to or exchanged with organic hydrogen, or both, during chemical reactions that take place during thermal maturation. Isotopic mass-balance calculations show that, depending on temperature (310-381??C), time (12-144 h), and source rock type, between ca. 45 and 79% of carbon-bound hydrogen in kerogen is derived from water. Estimates for bitumen and oil range slightly lower, with oil-hydrogen being least affected by water-derived hydrogen. Comparative hydrous pyrolyses of immature source rocks at 330??C for 72 h show that hydrogen in kerogen, bitumen, and expelled oil/wax ranks from most to least isotopically influenced by water-derived hydrogen in the order IIS > II ~ III > I. Pyrolysis of source rock containing type II kerogen in supercritical water at 381 ??C for 12 h yields isotopic results that are similar to those from hydrous pyrolysis at 350??C for 72 h, or 330??C for 144 h. Bulk hydrogen in kerogen contains several percent of isotopically labile hydrogen that exchanges fast and reversibly with hydrogen in water vapor at 115??C. The isotopic equilibration of labile hydrogen in kerogen with isotopic standard water vapors significantly reduces the analytical uncertainty of D/H ratios when compared with simple D/H determination of bulk hydrogen in kerogen. If extrapolation of our results from hydrous pyrolysis is permitted to natural thermal maturation at lower temperatures, we suggest that organic D/H ratios of fossil fuels in contact with formation waters are typically altered during chemical reactions, but that D/H ratios of generated hydrocarbons are subsequently little or not affected by exchange with water hydrogen at typical reservoir conditions over geologic time. It will be difficult to utilize D/H ratios of thermally mature bulk or fractions of organic matter to quantitatively reconstruct isotopic aspects of paleoclimate and paleoenvironment. Hope resides in compound-specific D/H ratios of thermally stable, extractable biomarkers ('molecular fossils') that are less susceptible to hydrogen exchange with water-derived hydrogen.

Reproducing early Martian atmospheric carbon dioxide partial pressure by modeling the formation of Mg-Fe-Ca carbonate identified in the Comanche rock outcrops on Mars

NASA Astrophysics Data System (ADS)

Berk, Wolfgang; Fu, Yunjiao; Ilger, Jan-Michael

2012-10-01

The well defined composition of the Comanche rock's carbonate (Magnesite0.62Siderite0.25Calcite0.11Rhodochrosite0.02) and its host rock's composition, dominated by Mg-rich olivine, enable us to reproduce the atmospheric CO2partial pressure that may have triggered the formation of these carbonates. Hydrogeochemical one-dimensional transport modeling reveals that similar aqueous rock alteration conditions (including CO2partial pressure) may have led to the formation of Mg-Fe-Ca carbonate identified in the Comanche rock outcrops (Gusev Crater) and also in the ultramafic rocks exposed in the Nili Fossae region. Hydrogeochemical conditions enabling the formation of Mg-rich solid solution carbonate result from equilibrium species distributions involving (1) ultramafic rocks (ca. 32 wt% olivine; Fo0.72Fa0.28), (2) pure water, and (3) CO2partial pressures of ca. 0.5 to 2.0 bar at water-to-rock ratios of ca. 500 molH2O mol-1rock and ca. 5°C (278 K). Our modeled carbonate composition (Magnesite0.64Siderite0.28Calcite0.08) matches the measured composition of carbonates preserved in the Comanche rocks. Considerably different carbonate compositions are achieved at (1) higher temperature (85°C), (2) water-to-rock ratios considerably higher and lower than 500 mol mol-1 and (3) CO2partial pressures differing from 1.0 bar in the model set up. The Comanche rocks, hosting the carbonate, may have been subjected to long-lasting (>104 to 105 years) aqueous alteration processes triggered by atmospheric CO2partial pressures of ca. 1.0 bar at low temperature. Their outcrop may represent a fragment of the upper layers of an altered olivine-rich rock column, which is characterized by newly formed Mg-Fe-Ca solid solution carbonate, and phyllosilicate-rich alteration assemblages within deeper (unexposed) units.

Geochemical characteristics and reservoir continuity of Silurian Acacus in Ghadames Basin, Southern Tunisia

NASA Astrophysics Data System (ADS)

Mahmoudi, S.; Mohamed, A. Belhaj; Saidi, M.; Rezgui, F.

2017-11-01

The present work is dealing with the study of lateral and vertical continuity of the multi-layers Acacus reservoir (Ghadames Basin-Southern Tunisia) using the distribution of hydrocarbon fraction. For this purpose, oil-oil and source rock-oil correlations as well as the composition of the light fractions and a number of saturate and aromatic biomarkers parameters, including C35/C34 hopanes and DBT/P, have been investigated. Based on the ratios of light fraction and their fingerprints, the Acacus reservoir from Well1 and Well2 have found to be laterally non-connected although the hydrocarbons they contain have the same source rock. Moreover, the two oil samples from two different Acacus reservoir layers crossed by Well3-A3 and A9, display a similar hydrocarbons distribution, suggesting vertical reservoir continuity. On the other hand, the biomarker distributions of the oils samples and source rocks assess a Silurian ;Hot shale; that is the source rock feeding the Acacus reservoir. The biomarker distribution is characterized by high tricyclic terpanes contents compared to hopanes for the Silurian source rock and the two crude oils. This result is also confirmed by the dendrogram that precludes the Devonian source rocks as a source rock in the study area.

Compositional Variation of Tourmaline from the Paleoproterozoic Bhukia Gold Prospect of Aravalli Supergroup, Western India: Implications for the Provenance and Gold Metallogeny

NASA Astrophysics Data System (ADS)

Mukherjee, R.; Venkatesh, A. S.; Fareeduddin, F.

2016-12-01

Bhukia is a unique gold prospect in terms of its host lithologies such as albitite and carbonates with respect to greenstone hosted Archean gold deposits from India. Tourmaline occurs along with apatite, magnetite, graphite, chalcopyrite and gold-sulfide association in Bhukia gold prospect preserve geochemical record of changing physico-chemical conditions during its growth. Tourmalinization is one of the distinct hydrothermal alterations present in the study area. Chemical composition of two varieties of tourmalines presents as significant amounts within albitite and carbonate rocks from Bhukia gold prospect. EPMA analysis of two varieties of tourmalines viz. 1) rounded to sub-rounded, euhedral, green colored tourmalines and 2) elongated, zoned, brown colored tourmalines unlocks their chemical compositions as well as variations from core to rim. In some albitite litho-units, tourmaline occurs as major constituents (>15%), present as layers, termed as tourmalinites. Al-Fe-Mg and Na/ (Na+Ca) vs Fe/ (Fe+Mg) suggests that tourmalines from the Bhukia gold prospect are Mg-rich dravite to Fe-rich schrol in composition. Tourmalines present within the albitite rocks show variations in iron and sodium content from core to rim whereas similarity exist from core to rim in case of carbonate rocks. Presence of albite confirms the role of Na-rich fluids during the formation of tourmalines. Tourmalines present in Bhukia gold prospect is mainly influenced by boron influx and the source may be boron bearing hydrothermal fluid or boron bearing minerals. Dewatering of original un-metamorphosed rock during progressive metamorphism may remove boron from the metasedimentary rocks. Due to the mobile nature of boron, it dispersed and mixed with hydrothermal fluids and alumina that is required for the formation of the tourmaline might have been leached from metasedimentary rocks present in Bhukia gold prospect. Presence of hydrothermal alterations such as tourmalinization and albitization along with Au-Cu-graphite-magnetite association suggest this deposit to be an IOCG (Iron oxide copper gold) type.

National Assessment of Oil and Gas Project: Petroleum systems and assessment of undiscovered oil and gas in the Denver Basin Province, Colorado, Kansas, Nebraska, South Dakota, and Wyoming - USGS Province 39

USGS Publications Warehouse

Higley, Debra K.

2007-01-01

The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The USGS recently completed an assessment of undiscovered oil and gas resources of the Denver Basin Province (USGS Province 39), Colorado, Kansas, Nebraska, South Dakota, and Wyoming. Petroleum is produced in the province from sandstone, shale, and limestone reservoirs that range from Pennsylvanian to Upper Cretaceous in age. This assessment is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). The USGS used this geologic framework to define seven total petroleum systems and twelve assessment units. Nine of these assessment units were quantitatively assessed for undiscovered oil and gas resources. Gas was not assessed for two coal bed methane assessment units due to lack of information and limited potential; oil resources were not assessed for the Fractured Pierre Shale Assessment Unit due to its mature development status.

Emplacement dynamics and hydrothermal alteration of the Atengo ignimbrite, southern Sierra Madre Occidental, northwestern Mexico

NASA Astrophysics Data System (ADS)

Agarwal, Amar; Alva-Valdivia, L. M.; Rivas-Sánchez, M. L.; Herrero-Bervera, E.; Urrutia-Fucugauchi, J.; Espejel-García, V.

2017-12-01

The Sierra Madre Occidental is a thick continental arc related to the subduction of the Farallon plate beneath North America resulting in a very intense and widespread Cretaceous to Cenozoic magmatic and tectonic activity. The 28 My old Atengo ignimbrite outcrops in the southern Sierra Madre Occidental, northwestern Mexico. From 12 sites that belong to various pyroclastic and lava flows emplaced during two pulses in the Oligocene (ca. 32-28 Ma) and Early Miocene (ca. 24-20 Ma), 97 rock specimens were drilled. The mineralogical and rock magnetic properties of the Atengo ignimbrite are compared with the surrounding volcanic rocks to identify the eruption mechanism, and with the El Castillo Ignimbrite, Veracruz, Mexico, to understand the depositional conditions. The comparisons reveal that the Atengo ignimbrite erupted from a single source, but less violently than the El Castillo ignimbrite, and cooled rapidly, inhibiting the formation of subhedral grains. The source of the Atengo Ignimbrite was a Plinian-type eruption, and the characteristic mineralogical and textural properties of each flow are related to different stages of the Plinian-type eruption. Further more, hydrothermal fluids were active during the last stages of volcanism, and caused moderate to intense alteration, especially in the ignimbrites, where high permeability aided the movement of hydrothermal fluids.

Mars Rock Formation Poses Mystery-2

NASA Technical Reports Server (NTRS)

2004-01-01

This sharp, close-up image taken by the microscopic imager on the Mars Exploration Rover Opportunity's instrument deployment device, or 'arm,' shows a rock target dubbed 'Robert E,' located on the rock outcrop at Meridiani Planum, Mars. Scientists are studying the spherule, or small sphere, in the center of the image that appears to be protruding from the rock formation. This image measures 3 centimeters (1.2 inches) across and was taken on the 15th day of Opportunity's journey (Feb. 8, 2004).

Relationship of oil seep in Kudat Peninsula with surrounding rocks based on geochemical analysis

NASA Astrophysics Data System (ADS)

Izzati Azman, Nurul; Nur Fathiyah Jamaludin, Siti

2017-10-01

This study aims to investigate the relation of oil seepage at Sikuati area with the structural and petroleum system of Kudat Peninsula. The abundance of highly carbonaceous rocks with presence of lamination in the Sikuati Member outcrop at Kudat Peninsula may give an idea on the presence of oil seepage in this area. A detailed geochemical analysis of source rock sample and oil seepage from Sikuati area was carried out for their characterization and correlation. Hydrocarbon propectivity of Sikuati Member source rock is poor to good with Total Organic Carbon (TOC) value of 0.11% to 1.48%. and also categorized as immature to early mature oil window with Vitrinite Reflectance (VRo) value of 0.43% to 0.50 %Ro. Based on biomarker distribution, from Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS) analysis, source rock sample shows Pr/Ph, CPI and WI of 2.22 to 2.68, 2.17 to 2.19 and 2.46 to 2.74 respectively indicates the source rock is immature and coming from terrestrial environment. The source rock might be rich in carbonaceous material organic matter resulting from planktonic/bacterial activity which occurs at fluvial to fluvio-deltaic environment. Overall, the source rock from outcrop level of Kudat Peninsula is moderately prolific in term of prospectivity and maturity. However, as go far deeper beneath the surface, we can expect more activity of mature source rock that generate and expulse hydrocarbon from the subsurface then migrating through deep-seated fault beneath the Sikuati area.

Mapping lacustrine syn-rift reservoir distribution using spectral attributes: A case study of the Pematang Brownshale Central Sumatra Basin

NASA Astrophysics Data System (ADS)

Haris, A.; Yustiawan, R.; Riyanto, A.; Ramadian, R.

2017-07-01

Pematang Brownshale is the lake sediment, which is proven as the main source rock in Malacca Strait Area. So far Brownshale is only considered as source rock, but the well data show intercalated sand layers encountered within the Pematang Brownshale, where several downhole tests proved this series as a potential hydrocarbon reservoir. Pematang formation is a syn-rift sequent deposited in Malacca Strait following the opening of central Sumatra basin during a late cretaceous to early Oligocene, which is proven as potential source rock and reservoir. The aim of the study is to identify the distribution of sandstone reservoir in Pematang Brownshale using spectral attributes. These works were carried out by integrating log data analysis and frequency maps extracted from spectral attributes Continuous Wavelet Transform (CWT). All these data are used to delineate reservoir distribution in Pematang Brownshale. Based on CWT analysis the anomalies are only visible on the frequency of I5 and I0 Hz maps, which are categorized as low frequencies. Low-frequency shadow anomaly is commonly used as an indication of the presence of hydrocarbons. The distribution of these anomalies is covering an area of approximately 3840.66 acres or equal to I554.25 sq. km, where the low-frequency pattern is interpreted as a deltaic lacustrine feature. By considering the Pematang Brown Shale of Malacca Strait area as a potential reservoir, it would open new play to another basin that has similar characteristics.

The crazy hollow formation (Eocene) of central Utah

USGS Publications Warehouse

Weiss, M.P.; Warner, K.N.

2001-01-01

The Late Eocene Crazy Hollow Formation is a fluviatile and lacustrine unit that was deposited locally in the southwest arm of Lake Uinta during and after the last stages of the lake the deposited the Green River Formation. Most exposures of the Crazy Hollow are located in Sanpete and Sevier Counties. The unit is characterized by a large variety of rock types, rapid facies changes within fairly short distances, and different lithofacies in the several areas where outcrops of the remnants of the formation are concentrated. Mudstone is dominant, volumetrically, but siltstone, shale, sandstone, conglomerate and several varieties of limestone are also present. The fine-grained rocks are mostly highly colored, especially in shades of yellow, orange and red. Sand grains, pebbles and small cobbles of well-rounded black chert are widespread, and "salt-and-pepper sandstone" is the conspicuous characteristic of the Crazy Hollow. The salt-and-pepper sandstone consists of grains of black chert, white chert, quartz and minor feldspar. The limestone beds and lenses are paludal and lacustrine in origin; some are fossiliferous, and contain the same fauna found in the Green River Formation. With trivial exceptions, the Crazy Hollow Formation lies on the upper, limestone member of the Green River Formation, and the beds of the two units are always accordant in attitude. The nature of the contact differs locally: at some sites there is gradation from the Green River to the Crazy Hollow; at others, rocks typical of the two units intertongue; elsewhere there is a disconformity between the two. A variety of bedrock units overlie the Crazy Hollow at different sites. In the southeasternmost districts it is overlain by the late Eocene formation of Aurora; in western Sevier County it is overlain by the Miocene-Pliocene Sevier River Formation; in northernmost Sanpete County it is overlain by the Oligocene volcanics of the Moroni Formation. At many sites bordering Sanpete and Sevier Valleys the Crazy Hollow beds dip beneath Quaternary sediments that fill the two valleys. The Crazy Hollow Formation ranges from 0 to 1,307 feet (0-398 m) thick in the region, but is usually much thinner than the maximum value. At most outcrops it is only a few scores of feet (12-50 m) thick. Its age is middle Eocene, for it is only a little younger than the underlying Green River Formation. The unit developed by the washing of detritus into the basin of the southwest arm of Lake Uinta from the various source rocks in the highlands surrounding the basin. The limestone beds and lenses formed in ponds and small lakes that developed in the basin from time to time during and following the draining and evaporation of Lake Uinta. The qualities of the Crazy Hollow Formation are described in detail for 10 different areas of outcrops in the Sanpete and Sevier Valleys and vicinity.

Water and rock geochemistry, geologic cross sections, geochemical modeling, and groundwater flow modeling for identifying the source of groundwater to Montezuma Well, a natural spring in central Arizona

USGS Publications Warehouse

Johnson, Raymond H.; DeWitt, Ed; Wirt, Laurie; Arnold, L. Rick; Horton, John D.

2011-01-01

The National Park Service (NPS) seeks additional information to better understand the source(s) of groundwater and associated groundwater flow paths to Montezuma Well in Montezuma Castle National Monument, central Arizona. The source of water to Montezuma Well, a flowing sinkhole in a desert setting, is poorly understood. Water emerges from the middle limestone facies of the lacustrine Verde Formation, but the precise origin of the water and its travel path are largely unknown. Some have proposed artesian flow to Montezuma Well through the Supai Formation, which is exposed along the eastern margin of the Verde Valley and underlies the Verde Formation. The groundwater recharge zone likely lies above the floor of the Verde Valley somewhere to the north or east of Montezuma Well, where precipitation is more abundant. Additional data from groundwater, surface water, and bedrock geology are required for Montezuma Well and the surrounding region to test the current conceptual ideas, to provide new details on the groundwater flow in the area, and to assist in future management decisions. The results of this research will provide information for long-term water resource management and the protection of water rights.

Metabasalts as sources of metals in orogenic gold deposits

NASA Astrophysics Data System (ADS)

Pitcairn, Iain K.; Craw, Dave; Teagle, Damon A. H.

2015-03-01

Although metabasaltic rocks have been suggested to be important source rocks for orogenic gold deposits, the mobility of Au and related elements (As, Sb, Se, and Hg) from these rocks during alteration and metamorphism is poorly constrained. We investigate the effects of increasing metamorphic grade on the concentrations of Au and related elements in a suite of metabasaltic rocks from the Otago and Alpine Schists, New Zealand. The metabasaltic rocks in the Otago and Alpine Schists are of MORB and WPB affinity and are interpreted to be fragments accreted from subducting oceanic crust. Gold concentrations are systematically lower in the higher metamorphic grade rocks. Average Au concentrations vary little between sub-greenschist (0.9 ± 0.5 ppb) and upper greenschist facies (1.0 ± 0.5 ppb), but decrease significantly in amphibolite facies samples (0.21 ± 0.07 ppb). The amount of Au depleted from metabasaltic rocks during metamorphism is on a similar scale to that removed from metasedimentary rocks in Otago. Arsenic concentrations increase with metamorphic grade with the metabasaltic rocks acting as a sink rather than a source of this element. The concentrations of Sb and Hg decrease between sub-greenschist and amphibolite facies but concentration in amphibolite facies rocks are similar to those in unaltered MORB protoliths and therefore unaltered oceanic crust cannot be a net source of Sb and Hg in a metamorphic environment. The concentrations of Au, As, Sb, and Hg in oceanic basalts that have become integrated into the metamorphic environment may be heavily influenced by the degree of seafloor alteration that occurred prior to metamorphism. We suggest that metasedimentary rocks are much more suitable source rocks for fluids and metals in orogenic gold deposits than metabasaltic rocks as they show mobility during metamorphism of all elements commonly enriched in this style of deposit.

Geogenic Groundwater Contamination: A Case Study Of Canakkale - Western Turkey

NASA Astrophysics Data System (ADS)

Deniz, Ozan; Çalık, Ayten

2016-04-01

Study area is located NW of Turkey. Total area of the drainage basin is 465 square kilometers and mostly covered by volcanic rocks. Majority of these rocks have highly altered and lost their primary properties because of alteration processes. Especially argillic alteration is common. Tectonic movements and cooling fractures were created suitable circulation environment of groundwater in the rocks (secondary porosity). Alteration affects the composition of groundwater and some rock elements pass into groundwater during the movement of water in the cavities of rocks. High concentration of natural contaminants related to water-rock interaction in spring water has been studied in this research. Field measurements such as pH, electrical conductivity, temperature, oxidation-reduction potential and salinity carried out in 500 water points (spring, drilling, well and stream). 150 water samples taken from the water points and 50 rock samples taken from the source of springs has been investigated in point of major anion-cations, heavy metals and trace elements. Some components in the water such as pH (3.5-9.1), specific electrical conductivity (84-6400 microS/cm), aluminum (27-44902 ppb), iron (10-8048 ppb), manganese (0.13-8740 ppb), nickel (0.2-627 ppb), lead (0.1-42.5 ppb) and sulphate (10 to 1940 ppm) extremely high or low in the springs sourced from especially highly altered Miocene aged volcanic rocks. Some measured parameters highly above according to European Communities Drinking Water Regulations (2007) and TS266 (2015-Intended for Human Consumption Water Regulations of Turkey) drinking water standards. The most common element which is found in the groundwater is aluminum that is higher than to the drinking water standards (200 microg/L). The highest levels of the Al values measured in acidic waters with very low pH (3.4) emerging from altered volcanic rocks because of acid mine drainage in Obakoy district, north of the study area. The abundance of this element in some water sources is believed to be closely associated with the alteration of feldspar minerals in the andesite and basalts of the Middle Eocene Sahinli Formation. Various studies related to topic show that consumption of these water containing high aluminum, iron, manganese, nickel and lead for drinking purposes cause serious health problems (Alzheimer's, Parkinson's, physical and mental development disorders in children, various cancers, stomach - intestinal disorders and skin diseases). This situation limits the usable groundwater potential and causes potable water scarcity in the region. Consequently, while using of these groundwater resources in the region, taking several precautions are necessary and doing new water resource explorations are recommended. This study is supported by The Turkish Scientific and Technical Research Institute (Project number: 113Y577). Keywords: Geogenic groundwater contamination, Water-Rock Interaction, Canakkale

Effect of Hydrothermal Alteration on Rock Properties in Active Geothermal Setting

NASA Astrophysics Data System (ADS)

Mikisek, P.; Bignall, G.; Sepulveda, F.; Sass, I.

2012-04-01

Hydrothermal alteration records the physical-chemical changes of rock and mineral phases caused by the interaction of hot fluids and wall rock, which can impact effective permeability, porosity, thermal parameters, rock strength and other rock properties. In this project, an experimental approach has been used to investigate the effects of hydrothermal alteration on rock properties. A rock property database of contrastingly altered rock types and intensities has been established. The database details horizontal and vertical permeability, porosity, density, thermal conductivity and thermal heat capacity for ~300 drill core samples from wells THM12, THM13, THM14, THM17, THM18, THM22 and TH18 in the Wairakei-Tauhara geothermal system (New Zealand), which has been compared with observed hydrothermal alteration type, rank and intensity obtained from XRD analysis and optical microscopy. Samples were selected from clay-altered tuff and intercalated siltstones of the Huka Falls Formation, which acts as a cap rock at Wairakei-Tauhara, and tuffaceous sandstones of the Waiora Formation, which is a primary reservoir-hosting unit for lateral and vertical fluid flows in the geothermal system. The Huka Falls Formation exhibits argillic-type alteration of varying intensity, while underlying Waiora Formations exhibits argillic- and propylithic-type alteration. We plan to use a tempered triaxial test cell at hydrothermal temperatures (up to 200°C) and pressures typical of geothermal conditions, to simulate hot (thermal) fluid percolation through the rock matrix of an inferred "reservoir". Compressibility data will be obtained under a range of operating (simulation reservoir) conditions, in a series of multiple week to month-long experiments that will monitor change in permeability and rock strength accompanying advancing hydrothermal alteration intensity caused by the hot brine interacting with the rock matrix. We suggest, our work will provide new baseline information concerning fluid-rock interaction processes in geothermal reservoirs, and their effects on rock properties, that will aid improved understanding of the evolution of high-temperature geothermal systems, provide constraints to parameterization of reservoir models and assist future well planning and design through prediction of rock properties in the context of drilling strategies.

Biological Communities in Desert Varnish and Potential Implications for Varnish Formation Mechanisms

NASA Astrophysics Data System (ADS)

Lang-Yona, Naama; Maier, Stefanie; Macholdt, Dorothea; Rodriguez-Caballero, Emilio; Müller-Germann, Isabell; Yordanova, Petya; Jochum, Klaus-Peter; Andreae, Meinrat O.; Pöschl, Ulrich; Weber, Bettina; Fröhlich-Nowoisky, Janine

2017-04-01

Desert varnishes are thin, orange to black coatings found on rocks in arid and semi-arid environments on Earth. The formation mechanisms of rock varnish are still under debate and the involvement of microorganisms in this process remains unclear. In this work we aimed to identify the microbial community occurring in rock varnish to potentially gain insights into the varnish formation mechanism. For this purpose, rocks coated with desert varnish were collected from the Anza-Borrego Desert, California, USA, as well as soils from underneath the rocks. DNA from both varnish coatings and soil samples was extracted and subsequently used for metagenomic analysis, as well as for q-PCR analyses for specific species quantification. The element composition of the varnish coatings was analyzed and compared to the soil samples. Rock varnish shows similar depleted elements, compared to soil, but Mn and Pb are 50-60 times enriched compared to the soil samples, and about 100 times enriched compared to the upper continental crust. Our genomic analyses suggest unique populations and different protein functional groups occurring in the varnish compared to soil samples. We discuss these differences and try to shed light on the mechanism of Mn oxyhydroxide production in desert varnish formation.

Ancient graphite in the Eoarchean quartz-pyroxene rocks from Akilia in southern West Greenland II: Isotopic and chemical compositions and comparison with Paleoproterozoic banded iron formations

NASA Astrophysics Data System (ADS)

Papineau, Dominic; De Gregorio, Bradley T.; Stroud, Rhonda M.; Steele, Andrew; Pecoits, Ernesto; Konhauser, Kurt; Wang, Jianhua; Fogel, Marilyn L.

2010-10-01

We present detailed petrographic surveys of apatite grains in association with carbonaceous material (CM) in two banded iron formations (BIFs) from the Paleoproterozoic of Uruguay and Michigan for comparison with similar mineral associations in the highly debated Akilia Quartz-pyroxene (Qp) rock. Petrographic and Raman spectroscopic surveys of these Paleoproterozoic BIFs show that apatite grains typically occur in bands parallel to bedding and are more often associated with CM when concentrations of organic matter are high. Carbonaceous material in the Vichadero BIF from Uruguay is generally well-crystallized graphite and occurs in concentrations around 0.01 wt% with an average δ 13C gra value of -28.6 ± 4.4‰ (1 σ). In this BIF, only about 5% of apatite grains are associated with graphite. In comparison, CM in the Bijiki BIF from Michigan is also graphitic, but occurs in concentrations around 2.4 wt% with δ 13C gra values around -24.0 ± 0.3‰ (1 σ). In the Bijiki BIF, more than 78% of apatite grains are associated with CM. Given the geologic context and high levels of CM in the Bijiki BIF, the significantly higher proportion of apatite grains associated with CM in this rock is interpreted to represent diagenetically altered biomass and shows that such diagenetic mineral associations can survive metamorphism up to the amphibolite facies. Isotope compositions of CM in muffled acidified whole-rock powders from the Akilia Qp rock have average δ 13C gra values of -17.5 ± 2.5‰ (1 σ), while δ 13C carb values in whole-rock powders average -4.0 ± 1.0‰ (1 σ). Carbon isotope compositions of graphite associated with apatite and other minerals in the Akilia Qp rock were also measured with the NanoSIMS to have similar ranges of δ 13C gra values averaging -13.8 ± 5.6‰ (1 σ). The NanoSIMS was also used to semi-quantitatively map the distributions of H, N, O, P, and S in graphite from the Akilia Qp rock, and relative abundances were found to be similar for graphite associated with apatite or with hornblende, calcite, and sulfides. These analyses revealed generally lower abundances of trace elements in the Akilia graphite compared to graphite associated with apatite from Paleoproterozoic BIFs. Graphite associated with hornblende, calcite, and sulfides in the Akilia Qp rock was fluid-deposited at high-temperature from carbon-bearing fluids, and since this graphite has similar ranges of δ 13C gra values and of trace elements compared to graphite associated with apatite, we conclude that the Akilia graphite in different mineral associations formed from the same source(s) of CM. Collectively our results do not exclude a biogenic origin of the carbon in the Akilia graphite, but because some observations can not exclude graphitization of abiogenic carbon from CO 2- and CH 4-bearing mantle fluids, there remain ambiguities with respect to the exact origin of carbon in this ancient metasedimentary rock. Accordingly, there may have been several generations of graphite formation along with possibly varying mixtures of CO 2- and CH 4-bearing fluids that may have resulted in large ranges of δ 13C gra values. The possibility of fluid-deposited graphite associated with apatite should be a focus of future investigations as this may prove to be an alternative pathway of graphitization from phosphate-bearing fluids. Correlated micro-analytical approaches tested on terrestrial rocks in this work provide insights into the origin of carbon in ancient graphite and will pave the way for the search for life on other ancient planetary surfaces.

Fossil Microorganisms and Formation of Early Precambrian Weathering Profiles

NASA Technical Reports Server (NTRS)

Rozanov, A. Yu; Astafieva, M. M.; Vrevsky, A. B.; Alfimova, N. A.; Matrenichev, V. A.; Hoover, R. B.

2009-01-01

Weathering crusts are the only reliable evidences of the existence of continental conditions. Often they are the only source of information about exogenous processes and subsequently about conditions under which the development of the biosphere occurred. A complex of diverse fossil microorganisms was discovered as a result of Scanning Electron Microscope investigations. The chemical composition of the discovered fossils is identical to that of the host rocks and is represented by Si, Al, Fe, Ca and Mg. Probably, the microorganisms fixed in rocks played the role of catalyst. The decomposition of minerals comprising the rocks and their transformation into clayey (argillaceous) minerals, most likely occurred under the influence of microorganisms. And may be unique weathering crusts of Early Precambrian were formed due to interaction between specific composition of microorganism assemblage and conditions of hypergene transformations. So it is possible to speak about colonization of land by microbes already at that time and about existence of single raw from weathering crusts (Primitive soils) to real soils.

FT-Raman spectroscopic study of calcium-rich and magnesium-rich carbonate minerals.

PubMed

Edwards, Howell G M; Villar, Susana E Jorge; Jehlicka, Jan; Munshi, Tasnim

2005-08-01

Calcium and magnesium carbonates are important minerals found in sedimentary environments. Although sandstones are the most common rock colonized by endolith organisms, the production of calcium and magnesium carbonates is important in survival strategies of organisms and as a source for the removal of oxalate ions. Extremophile organisms in some situations may convert or destroy carbonates of calcium and magnesium, which gives important information about the conditions under which these organisms can survive. The identification on the surface of Mars of 'White Rock' formations, in Juventae Chasma or Sabaea Terra, as possibly carbonate rocks makes the study of these minerals a prerequisite of remote Martian exploration. Here, we show the protocol for the identification by Raman spectroscopy of different calcium and magnesium carbonates and we present a database of relevance in the search for life, extinct or extant, on Mars; this will be useful for the assessment of data obtained from remote, miniaturized Raman spectrometers now proposed for Mars exploration.

Geology of Devils Tower National Monument, Wyoming

USGS Publications Warehouse

Robinson, Charles Sherwood

1956-01-01

Devils Tower is a steep-sided mass of igneous rock that rises above the surrounding hills and the valley of the Belle Fourche River in Crook County, Wyo. It is composed of a crystalline rock, classified as phonolite porphyry, that when fresh is gray but which weathers to green or brown. Vertical joints divide the rock mass into polygonal columns that extend from just above the base to the top of the Tower. The hills in the vicinity and at the base of the Tower are composed of red, yellow, green, or gray sedimentary rocks that consist of sandstone, shale, or gypsum. These rocks, in aggregate about 400 feet thick, include, from oldest to youngest, the upper part of the Spearfish formation, of Triassic age, the Gypsum Spring formation, of Middle Jurassic age, and the Sundance formation, of Late Jurassic age. The Sundance formation consists of the Stockade Beaver shale member, the Hulett sandstone member, the Lak member, and the Redwater shale member. The formations have been only slightly deformed by faulting and folding. Within 2,000 to 3.000 feet of the Tower, the strata for the most part dip at 3 deg - 5 deg towards the Tower. Beyond this distance, they dip at 2 deg - 5 deg from the Tower. The Tower is believed to have been formed by the intrusion of magma into the sedimentary rocks, and the shape of the igneous mass formed by the cooled magma is believed to have been essentially the same as the Tower today. Devils Tower owes its impressiveness to its resistance to erosion as compared with the surrounding sedimentary rocks, and to the contrast of the somber color of the igneous column to the brightly colored bands of sedimentary rocks.

Geology and ground-water resources of Rock County, Wisconsin

USGS Publications Warehouse

LeRoux, E.F.

1964-01-01

Rock County is in south-central Wisconsin adjacent to the Illinois State line. The county has an area of about 723 square miles and had a population of about 113,000 in 1957 ; it is one of the leading agricultural and industrial counties in the State. The total annual precipitation averages about 32 inches, and the mean annual temperature is about 48 ? F. Land-surface altitudes are generally between 800 and 00 feet, but range from 731 feet, where the Rock River flows into Illinois, to above 1,080 feet, at several places in the northwestern part of the county. The northern part of Rock County consists of the hills and kettles of a terminal moraine which slopes southward to a flat, undissected outwash plain. The southeastern part of the county is an area of gentle slopes, whereas the southwestern part consists of steep-sided valleys and ridges. Rock County is within the drainage basin of the Rock River, which flows southward through the center of the county. The western and southwestern parts of ,the county are drained by the Sugar River und Coon Creek, both of which flow into the Pecatonica River in Illinois and thence into the Rock River. The southeastern part of the county is drained by Turtle Creek, which also flows into Illinois before joining the Rock River. Nearly all the lakes and ponds are in the northern one-third of the county, the area of most recent glaciation. The aquifers in Rock County are of sedimentary origin and include deeply buried sandstones, shales, and dolomites of the Upper Cambrian series. This series overlies crystalline rocks of Precambrian age and supplies water to all the cities and villages in the county. The St. Peter sandstone of Ordovician age underlies all Rock County except where the formation has been removed by erosion in the Rock and Sugar River valleys, and perhaps in Coon Creek valley. The St. Peter sandstone is the principal source of water for domestic, stock, and small industrial wells in the western half of the county. This sandstone also yields some water to uncased wells that tap the deeper rocks of the Upper Cambrian series. East of the Rock River the Platteville, Decorah, and Galena formations undifferentiated, or Platteville-Galena unit, is the principal source of water for domestic and stock wells. Unconsolidated deposits of glacial origin cover most of Rock County and supply water to many small wells. In the outwash deposits along the Rock River, wells of extremely high capacity have been developed for industrial and municipal use. The most significant feature of the bedrock surface in Rock County is the ancestral Rock River valley, which has been filled with glacial outwash to a depth of at least 396 feet below the present land surface. East of the buried valley the bedrock has a fiat, relatively undissected surface. West of the valley the bedrock surface is rugged and greatly dissected. Ground water in Rock County occurs under both water-table and artesian conditions; however, because of the interconnection and close relation of all ground water in the county, the entire system is considered to be a single groundwater body whose surface may be represented by one piezometric map. Recharge occurs locally, throughout the county. Nearly all recharge is derived directly from precipitation that percolates downward to become a part of the groundwater body. Natural movement of water in the consolidated water-bearing units is generally toward the buried Rock and Sugar River valleys. Movement of water in the sandstones of Cambrian age was calculated to be about 44 million gallons a day toward the Rock River. Discharge from wells in Rock County in 1957 was about 23 million gallons a day. Nearly 90 percent of this water was drawn from the area along the Rock River. Drilled wells, most of which were drilled by the cable-tool method, range in diameter from 3 to 26 inches, and in depth from 46 to 1,225 feet. Driven wells in alluvium and glacial drift are usually 1? to 2? in

Modelling of the petroleum formation in the Mahakam sediments (Indonesia): Organic geochemical controls of the results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brosse, E.; Burris, J.; Ouidin, J.L.

1990-06-01

Since the Miocene, the delta of the Mahakam River has accumulated thousands of meters of sediments in the eastern part of the Kutei Basin (Kalimantan, Indonesia). Source-rock candidates are the coals of the deltaic plain and several types of shales, mainly the delta front/prodelta area. Organic matter basically derives from higher plants, but each source facies presents important intrinsic variations of petroleum potential. These variations are overprinted by subsequent maturation trends. Geochemical and petrographical data are integrated on the general framework provided by a new synthetic interpretation of the sedimentary sequences, relying upon the concepts of seismic stratigraphy. From coremore » samples at a given level of maturation, the variations of several organic parameters are discussed in relation to the depositional paleoenvironment and to the possible precursors. 1D and 2D numerical routines are used to reconstruct the maturation history of source rocks. These tools are based upon a kinetic modeling of kerogen cracking. Model outputs are compared with observed maturation trends. The understanding of the initial organic facies distribution provides precise constraints in the selection of a homogenous samples set for this comparison purpose.« less

Detrital zircon ages in Korean mid-Paleozoic meta-sandstones (Imjingang Belt and Taean Formation): Constraints on tectonic and depositional setting, source regions and possible affinity with Chinese terranes

NASA Astrophysics Data System (ADS)

Han, Seokyoung; de Jong, Koen; Yi, Keewook

2017-08-01

Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Th-Pb isotopic data of detrital zircons from mature, quartz-rich meta-sandstones are used to constrain possible tectonic affinities and source regions of the rhythmically layered and graded-bedded series in the Yeoncheon Complex (Imjingang Belt) and the correlative Taean Formation. These metamorphic marine turbidite sequences presently occur along the Paleoproterozoic (1.93-1.83 Ga) Gyeonggi Massif, central Korea's main high-grade metamorphic gneiss terrane. Yet, detrital zircons yielded highly similar multimodal age spectra with peaks that do not match the age repartition in these basement rocks, as late (1.9-1.8 Ga) and earliest (∼ 2.5 Ga) Paleoproterozoic detrital modes are subordinate but, in contrast, Paleozoic (440-425 Ma) and Neoproterozoic (980-920 Ma) spikes are prominent, yet the basement essentially lacks lithologies with such ages. The youngest concordant zircon ages in each sample are: 378, 394 and 423 Ma. The maturity of the meta-sandstones and the general roundness of zircons of magmatic signature, irrespective of their age, suggest that sediments underwent considerable transport from source to sink, and possibly important weathering and recycling, which may have filtered out irradiation-weakened metamorphic zircon grains. In combination with these isotopic data, presence of a low-angle ductile fault contact between the Yeoncheon Complex and the Taean Formation and the underlying mylonitized Precambrian basement implies that they are in tectonic contact and do not have a stratigraphic relationship, as often assumed. Consequently, in all likelihood, both meta-sedimentary formations: (1) are at least of early Late Devonian age, (2) received much of their detritus from distant (reworked) Silurian-Devonian and Early Neoproterozoic magmatic sources, not present in the Gyeonggi Massif, (3) and not from Paleoproterozoic crystalline rocks of this massif, or other Korean Precambrian basement terranes, and (4) should be viewed as independent tectonic units that had sources not exposed in Korea. A thorough literature review reveals that the Yeoncheon Complex and the Taean Formation were potentially sourced from the Liuling, Nanwan and Foziling groups in the Qinling-Dabie Belt, which all show very similar detrital zircon age spectra. These immature middle-late Devonian sandstones were deposited in a pro-foreland basin formed as a result of the aborted subduction of the South Qinling Terrane below the North Qinling Terrane, which was uplifted and eroded during post-collision isostatic rebound. The submarine fans where the mature distal turbiditic Yeoncheon and Taean sandstones were deposited may have constituted the eastern terminal part of a routing system originating in the uplifted and eroded middle Paleozoic Qinling Belt and adjacent part of the foreland basin.

Coupled Mechanical and Thermal Modeling of Frictional Melt Injection to Constrain Physical Conditions of the Earthquake Source Region

NASA Astrophysics Data System (ADS)

Sawyer, W.; Resor, P. G.

2016-12-01

Pseudotachylyte, a fault rock formed through coseismic frictional melting, provides an important record of coseismic mechanics. In particular, injection veins formed at a high angle to the fault surface have been used to estimate rupture directivity, velocity, pulse length, stress and strength drop, as well as slip weakening distance and wall rock stiffness. These studies, however, have generally treated injection vein formation as a purely elastic process and have assumed that processes of melt generation, transport, and solidification have little influence on the final vein geometry. Using a modified analytical approximation of injection vein formation based on a dike intrusion model we find that the timescales of quenching and flow propagation are similar for a composite set of injection veins compiled from the Asbestos Mountain Fault, USA (Rowe et al., 2012), Gole Larghe Fault Zone, Italy (Griffith et al., 2012) and the Fort Foster Brittle Zone. This indicates a complex, dynamic process whose behavior is not fully captured by the current approach. To assess the applicability of the simplifying assumptions of the dike model when applied to injection veins we employ a finite-element time-dependent model of injection vein formation. This model couples elastic deformation of the wall rock with the fluid dynamics and heat transfer of the frictional melt. The final geometry of many injection veins is unaffected by the inclusion of these processes. However, some injection veins are found to be flow limited, with a final geometry reflecting cooling of the vein before it reaches an elastic equilibrium with the wall rock. In these cases, numerical results are significantly different from the dike model, and two basic assumptions of the dike model, self-similar growth and a uniform pressure gradient, are shown to be false. Additionally, we apply the finite-element model to provide two new constraints on the Fort Foster coseismic environment: a lower limit on the initial melt temperature of 1400 *C, and either significant coseismic wall rock softening or high transient tensile stress.

Petrophysical rock properties of the Bazhenov Formation of the South-Eastern part of Kaymysovsky Vault (Tomsk Region)

NASA Astrophysics Data System (ADS)

Gorshkov, A. M.; Kudryashova, L. K.; Lee-Van-Khe, O. S.

2016-09-01

The article presents the results of studying petrophysical rock properties of the Bazhenov Formation of the South-Eastern part of Kaymysovsky Vault with the Gas Research Institute (GRI) method. The authors have constructed dependence charts for bulk and grain density, open porosity and matrix permeability vs. depth. The results of studying petrophysical properties with the GRI method and core description have allowed dividing the entire section into three intervals each of which characterized by different conditions of Bazhenov Formation rock formation. The authors have determined a correlation between the compensated neutron log and the rock density vs. depth chart on the basis of complex well logging and petrophysical section analysis. They have determined a promising interval for producing hydrocarbons from the Bazhenov Formation in the well under study. Besides, they have determined the typical behavior of compensated neutron logs and SP logs on well logs for this interval. These studies will allow re-interpreting available well logs in order to determine the most promising interval to be involved in Bazhenov Formation development in Tomsk Region.

An Archaeological Survey of Certain Lands Adjacent to the Galisteo Dam, New Mexico.

DTIC Science & Technology

1976-03-12

of the basal- tic rock. A good candidate for the source of the cherts and petrified wood is the Cretaceous(?)- Oligocene Galisteo Formation, which is...5,500- -57- The character of the site suggests that it functioned as a farmstead, and its north exposure is additionally suggestive of primary warm ...agricultural activities. The north-exposed, south-protected locations of the more important sites would seem to indicate warm -weather occu- pation in the main

Refinement of Regional Distance Seismic Moment Tensor and Uncertainty Analysis for Source-Type Identification

DTIC Science & Technology

2014-09-02

release; distribution is unlimited. rock zone which provides a pathway for formation fluids, natural gas and crude oil from deeper strata that are... southeast Louisiana (Figure 21). It is a part of the Gulf Coast salt basin which exhibits many salt structures formed by upward flow of sedimentary salt...primarily, evaporites) on account of low density of salt and overburden pressures caused by younger sedimentary deposits (Beckman and Williamson, 1990

Overview of the potential and identified petroleum source rocks of the Appalachian basin, eastern United States: Chapter G.13 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Coleman, James L.; Ryder, Robert T.; Milici, Robert C.; Brown, Stephen; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

The Appalachian basin is the oldest and longest producing commercially viable petroleum-producing basin in the United States. Source rocks for reservoirs within the basin are located throughout the entire stratigraphic succession and extend geographically over much of the foreland basin and fold-and-thrust belt that make up the Appalachian basin. Major source rock intervals occur in Ordovician, Devonian, and Pennsylvanian strata with minor source rock intervals present in Cambrian, Silurian, and Mississippian strata.

Pore Effect on the Occurrence and Formation of Gas Hydrate in Permafrost of Qilian Mountain, Qinghai-Tibet Plateau, China

NASA Astrophysics Data System (ADS)

Gao, H.; Lu, H.; Lu, Z.

2014-12-01

Gas hydrates were found in the permafrost of Qilian Mountain, Qinghai- Tibet Plateau, China in 2008. It has been found that gas hydrates occur in Jurassic sedimentary rocks, and the hydrated gases are mainly thermogenic. Different from the gas hydrates existing in loose sands in Mallik, Mackenzie Delta, Canada and North Slope, Alaska, USA, the gas hydrates in Qilian Mountain occurred in hard rocks. For understanding the occurrence and formation mechanism of gas hydrate in hard rcok, extensive experimental investigations have been conducted to study the pore features and hydrate formation in the rocks recovered from the hydrate layers in Qilian Mountain. The structures of sedimentary rock were observed by high-resolution X-ray CT, and pore size distribution of a rock specimen was measured with the mercury-injection method. Methane hydrate was synthesized in water-saturated rocks, and the saturations of hydrate in sedimentary rocks of various types were estimated from the amount of gas released from certain volume of rock. X-ray CT observation revealed that fractures were developed in the rocks associated with faults, while those away from faults were generally with massive structure. The mercury-injection analysis of pore features found that the porosities of the hydrate-existing rocks were generally less than 3%, and the pore sizes were generally smaller than 100 nm. The synthesizing experiments found that the saturation of methane hydrate were generally lower than 6% of pore space in rocks, but up to 16% when fractures developed. The low hydrate saturation in Qilian sedimentary rocks has been found mainly due to the small pore size of rock. The low hydrate saturation in the rocks might be the reason for the failure of regional seismic and logging detections of gas hydrates in Qilian Mountain.

Geological mapping and analysis in determining resource recitivity limestone rocks in the village of Mersip and surrounding areas, district Limun, Sorolangun Regency, Jambi Province

NASA Astrophysics Data System (ADS)

Dona, Obie Mario; Ibrahim, Eddy; Susilo, Budhi Kuswan

2017-11-01

The research objective is to describe potential, to analyze the quality and quantity of limestone, and to know the limit distribution of rocks based on the value of resistivity, the pattern of distribution of rocks by drilling, the influence mineral growing on rock against resistivity values, the model deposition of limestone based on the value resistivity of rock and drilling, and the comparison between the interpretation resistivity values based on petrographic studies by drilling. Geologic Formations study area consists of assays consisting of altered sandstone, phyllite, slate, siltstone, grewake, and inset limestone. Local quartz sandstone, schist, genealogy, which is Member of Mersip Stylists Formation, consists of limestone that formed in shallow seas. Stylists Formation consists of slate, shale, siltstone and sandstone. This research methodology is quantitative using experimental observation by survey. This type of research methodology by its nature is descriptive analysis.

Sylhet-Kopili/Barail-Tipam Composite Total Petroleum System, Assam Geologic Province, India

USGS Publications Warehouse

Wandrey, Craig J.

2004-01-01

The Sylhet-Kopili/Barail-Tipam Composite total petroleum system (TPS) (803401) is located in the Assam Province in northeasternmost India and includes the Assam Shelf south of the Brahmaputra River. The area is primarily a southeast-dipping shelf overthrust by the Naga Hills on the southeast and the Himalaya Mountain range to the north. The rocks that compose this TPS are those of the Sylhet-Kopili/Barail-Tipam composite petroleum system. These rocks are those of the Eocene-Oligocene Jaintia Group Sylhet and Kopili Formations, the Oligocene Barail Group, the Oligocene-Miocene Surma and Tipam Groups. These groups include platform carbonates, shallow marine shales and sandstones, and the sandstones, siltstones, shales, and coals of deltaic and lagoonal facies. Source rocks include the Sylhet and Kopili Formation shales, Barail Group coals and shales, and in the south the Surma Group shales. Total organic content is generally low, averaging from 0.5 to 1.8 percent; it is as high as 9 percent in the Barail Coal Shales. Maturities are generally low, from Ro 0.45 to 0.7 percent where sampled. Maturity increases to the southeast near the Naga thrust fault and can be expected to be higher in the subthrust. Generation began in early Pliocene. Migration is primarily updip to the northwest (< 5 to 15 kilometers) along the northeast-trending slope of the Assam Shelf, and vertical migration occurs through reactivated basement-rooted faults associated with the plate collisions. Reservoir rocks are carbonates of the Sylhet Formation, interbedded sandstones of the Kopili Formation and sandstones of the Barail, Surma, and Tipam Groups. Permeability ranges from less than 8 mD (millidarcies) to as high as 800 mD in the Tipam Group. Porosity ranges from less than 7 percent to 30 percent. Traps are primarily anticlines and faulted anticlines with a few subtle stratigraphic traps. There is also a likelihood of anticlinal traps in the subthrust. Seals include interbedded Oligocene and Miocene shales and clays, and the thick clays of the Pliocene Gurjan Group.

Average composition of the tonalite-trondhjemite-granodiorite association: Possibilities of application

NASA Astrophysics Data System (ADS)

Chekulaev, V. P.; Glebovitsky, V. A.

2017-01-01

The possibilities of using the average compositions of tonalite-trondhjemite-granodiorite association rocks (TTG), which make up a significant part of the Archaean continental crust, have been examined. The results of the TTG average compositions obtained by other researchers and the authors' data of the average compositions of TTG from the Baltic and Ukrainian shields and the entire Archaean crust are given. It is shown that the average compositions of the Archaean TTG of continental large crustal fragments (cratons or provinces) practically do not bear any information on their sources or conditions of their formation. The possibility of obtaining of such information by means of analysis of the average compositions of TTG, composing smaller fragments of the crust, exemplified by rocks of the Karelian subprovinces of the Baltic Shield has been demonstrated.

Magnetic susceptibilities measured on rocks of the upper Cook Inlet, Alaska

USGS Publications Warehouse

Alstatt, A.A.; Saltus, R.W.; Bruhn, R.L.; Haeussler, Peter J.

2002-01-01

We have measured magnetic susceptibility in the field on most of the geologic rock formations exposed in the upper Cook Inlet near Anchorage and Kenai, Alaska. Measured susceptibilities range from less than our detection limit of 0.01 x 10-3 (SI) to greater than 100 x 10-3 (SI). As expected, mafic igneous rocks have the highest susceptibilities and some sedimentary rocks the lowest. Rocks of the Tertiary Sterling Formation yielded some moderate to high susceptibility values. Although we do not have detailed information on the magnetic mineralogy of the rocks measured here, the higher susceptibilities are sufficient to explain the magnitudes of some short-wavelength aeromagnetic anomalies observed on recent surveys of the upper Cook Inlet.

Dust input in the formation of rock varnish from the Dry Valleys (Antarctica)

NASA Astrophysics Data System (ADS)

Zerboni, A.; Guglielmin, M.

2017-12-01

Rock varnish is a glossy, yellowish to dark brown coating that covers geomorphically stable, aerially exposed rock surfaces and landforms in warm and cold arid lands. In warm deserts, rock varnish consists of clay minerals, Mn-Fe oxides/hydroxides, and Si+alkalis dust; it occasionally containis sulphates, phosphates, and organic remains. In Antarctica, rock varnish developed on a variety of bedrocks and has been described being mostly formed of Si, Al, Fe, and sulphates, suggesting a double process in its formation, including biomineralization alternated to dust accretion. We investigated rock coatings developed on sandstones outcropping in the Dry Valleys of Antarctica and most of the samples highlithed an extremely complex varnish structure, alternating tihn layer of different chemical compostion. Optical microscope evidenced the occurrence of highly birefringent minerals, occasionally thinly laminated and consisitng of Si and Al-rich minerals (clays). These are interlayered by few micron-thick dark lenses and continous layers. The latter are well evident under the scanning electron microscope and chemical analysis confirmed that they consist of different kinds of sulphates; jarosite is the most represented species, but gypsum crystals were also found. Fe-rich hypocoatings and intergranula crusts were also detected, sometimes preserving the shape of the hyphae they have replaced. Moreover, small weathering pits on sandstone surface display the occurrence of an amorphous, dark Mn/Fe-rich rock varnish. The formation of rock varnish in the Dry Valleys is a complex process, which required the accretion of airborne dust of variable composition and subsequent recrystallization of some constituent, possibly promoted by microorganisms. In particualr, the formation of sulphates seems to preserve the memory of S-rich dust produced by volcanic eruptions. On the contrary, the formation of Mn-rich varnish should be in relation with the occurrence of higher environmental humidity within weathering pits. Rock varnish in the Dry Valleys represents a potential tool to reconstruct past water availability and changes in the aeolian fallout.

Diamond formation due to a pH drop during fluid–rock interactions

DOE PAGES

Sverjensky, Dimitri A.; Huang, Fang

2015-11-03

Diamond formation has typically been attributed to redox reactions during precipitation from fluids or magmas. Either the oxidation of methane or the reduction of carbon dioxide has been suggested, based on simplistic models of deep fluids consisting of mixtures of dissolved neutral gas molecules without consideration of aqueous ions. The role of pH changes associated with water–silicate rock interactions during diamond formation is unknown. Here we show that diamonds could form due to a drop in pH during water–rock interactions. We use a recent theoretical model of deep fluids that includes ions, to show that fluid can react irreversibly withmore » eclogite at 900 °C and 5.0 GPa, generating diamond and secondary minerals due to a decrease in pH at almost constant oxygen fugacity. Overall, our results constitute a new quantitative theory of diamond formation as a consequence of the reaction of deep fluids with the rock types that they encounter during migration. Diamond can form in the deep Earth during water–rock interactions without changes in oxidation state.« less

Diamond formation due to a pH drop during fluid–rock interactions

PubMed Central

Sverjensky, Dimitri A.; Huang, Fang

2015-01-01

Diamond formation has typically been attributed to redox reactions during precipitation from fluids or magmas. Either the oxidation of methane or the reduction of carbon dioxide has been suggested, based on simplistic models of deep fluids consisting of mixtures of dissolved neutral gas molecules without consideration of aqueous ions. The role of pH changes associated with water–silicate rock interactions during diamond formation is unknown. Here we show that diamonds could form due to a drop in pH during water–rock interactions. We use a recent theoretical model of deep fluids that includes ions, to show that fluid can react irreversibly with eclogite at 900 °C and 5.0 GPa, generating diamond and secondary minerals due to a decrease in pH at almost constant oxygen fugacity. Overall, our results constitute a new quantitative theory of diamond formation as a consequence of the reaction of deep fluids with the rock types that they encounter during migration. Diamond can form in the deep Earth during water–rock interactions without changes in oxidation state. PMID:26529259

Natural Offshore Oil Seepage and Related Tarball Accumulation on the California Coastline - Santa Barbara Channel and the Southern Santa Maria Basin: Source Identification and Inventory

USGS Publications Warehouse

Lorenson, T.D.; Hostettler, Frances D.; Rosenbauer, Robert J.; Peters, Kenneth E.; Dougherty, Jennifer A.; Kvenvolden, Keith A.; Gutmacher, Christina E.; Wong, Florence L.; Normark, William R.

2009-01-01

Oil spillage from natural sources is very common in the waters of southern California. Active oil extraction and shipping is occurring concurrently within the region and it is of great interest to resource managers to be able to distinguish between natural seepage and anthropogenic oil spillage. The major goal of this study was to establish the geologic setting, sources, and ultimate dispersal of natural oil seeps in the offshore southern Santa Maria Basin and Santa Barbara Basins. Our surveys focused on likely areas of hydrocarbon seepage that are known to occur between Point Arguello and Ventura, California. Our approach was to 1) document the locations and geochemically fingerprint natural seep oils or tar; 2) geochemically fingerprint coastal tar residues and potential tar sources in this region, both onshore and offshore; 3) establish chemical correlations between offshore active seeps and coastal residues thus linking seep sources to oil residues; 4) measure the rate of natural seepage of individual seeps and attempt to assess regional natural oil and gas seepage rates; and 5) interpret the petroleum system history for the natural seeps. To document the location of sub-sea oil seeps, we first looked into previous studies within and near our survey area. We measured the concentration of methane gas in the water column in areas of reported seepage and found numerous gas plumes and measured high concentrations of methane in the water column. The result of this work showed that the seeps were widely distributed between Point Conception east to the vicinity of Coal Oil Point, and that they by in large occur within the 3-mile limit of California State waters. Subsequent cruises used sidescan and high resolution seismic to map the seafloor, from just south of Point Arguello, east to near Gaviota, California. The results of the methane survey guided the exploration of the area west of Point Conception east to Gaviota using a combination of seismic instruments. The seafloor was mapped by sidescan sonar, and numerous lines of high -resolution seismic surveys were conducted over areas of interest. Biomarker and stable carbon isotope ratios were used to infer the age, lithology, organic matter input, and depositional environment of the source rocks for 388 samples of produced crude oil, seep oil, and tarballs mainly from coastal California. These samples were used to construct a chemometric fingerprint (multivariate statistics) decision tree to classify 288 additional samples, including tarballs of unknown origin collected from Monterey and San Mateo County beaches after a storm in early 2007. A subset of 9 of 23 active offshore platform oils and one inactive platform oil representing a few oil reservoirs from the western Santa Barbara Channel were used in this analysis, and thus this model is not comprehensive and the findings are not conclusive. The platform oils included in this study are from west to east: Irene, Hildago, Harvest, Hermosa, Heritage, Harmony, Hondo, Holly, Platform A, and Hilda (now removed). The results identify three 'tribes' of 13C-rich oil samples inferred to originate from thermally mature equivalents of the clayey-siliceous, carbonaceous marl, and lower calcareous-siliceous members of the Monterey Formation. Tribe 1 contains four oil families having geochemical traits of clay-rich marine shale source rock deposited under suboxic conditions with substantial higher-plant input. Tribe 2 contains four oil families with intermediate traits, except for abundant 28,30-bisnorhopane, indicating suboxic to anoxic marine marl source rock with hemipelagic input. Tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher-plant input. Tribes 1 and 2 occur mainly south of Point Conception in paleogeographic settings where deep burial of the Monterey Formation source rock favored generation from all thre

Si-Metasomatism During Serpentinization of Jurassic Ultramafic Sea-floor: a Comparative Study

NASA Astrophysics Data System (ADS)

Vogel, M.; Frueh-Green, G. L.; Boschi, C.; Schwarzenbach, E. M.

2014-12-01

The Bracco-Levanto ophiolitic complex (northwestern Italy) represents one of the largest and better-exposed ophiolitic successions in the Northern Apennines. It is considered to be a fragment of heterogeneous Jurassic lithosphere that records tectono-magmatic and alteration histories similar to those documented along the Mid-Atlantic Ridge (MAR), such as at the 15°20'N area and the Atlantis Massif at 30°N. Structural and petrological studies on these rocks provide constraints on metamorphic/deformation processes during formation and hydrothermal alteration of the Jurassic oceanic lithosphere. We present a petrological and geochemical study of serpentinization processes and fluid-rock interaction in the Bracco-Levanto ophiolitic complex and compare these to published data from modern oceanic hydrothermal systems, such as the Lost City hydrothermal field hosted in serpentinites on the Atlantis Massif. Major element and mineral compositional data allow us to distinguish a multiphase history of alteration characterized by: (1) widespread Si-metasomatism during progressive serpentinization, and (2) multiple phases of veining and carbonate precipitation associated with circulation of seawater in the shallow ultramafic-dominated portions of the Jurassic seafloor, resulting in the formation of ophicalcites. In detail, regional variations in Si, Mg and Al content are observed in zones of ophicalcite formation, indicating metasomatic reactions and Si-Al transport during long-lived fluid-rock interaction and channelling of hydrothermal fluids. Rare earth element and isotopic analysis indicate that the Si-rich fluids are derived from alteration of pyroxenes to talc and tremolite in ultramafic rocks at depth. Comparison with serpentinites from the Atlantis Massif and 15°20'N indicates a similar degree of Si-enrichment in the modern seafloor and suggests that Si-metasomatism may be a fundamental process associated with serpentinization at slow-spreading ridge environments. However, in contrast to metasomatic processes at the MAR, we find no geochemical evidence for a gabbroic source of the fluids, and thus, processes leading to Si-rich fluids can be variable in these environments.

Regional stratigraphic framework of the Lisburne Group of ANWR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watts, K.F.; Carlson, R.C.; Harris, A.G.

1995-05-01

The Carboniferous Lisburne Group, a major carbonate platform succession, is widely exposed in the Brooks Range and forms an extensive hydrocarbon target in the subsurface of the North Slope of Alaska. Gradationally beneath carbonates of the Lisburne Group, terrigenous sediments of the Mississippian Endicott Group (conglomerate and sandstone of the Kekiktuk Formation overlain by the Kayak Shale) were derived from local and northern (Ellesmerian) source areas. Locally, at the Endicott-Lisburne transition, sandy limestones of the Itkilyariak Formation record another phase of siliciclastic influx that lies above and/or is a lateral equivalent of the Kayak Shale and Lisburne Group in areasmore » adjacent to paleotopographic highs. This siliciclastic to carbonate transition represents a major transgressive succession that onlaps northward over the sub-Mississippian unconformity, a regional angular unconformity and sequence boundary in northern Alaska. The age and nature of onlap depend upon the paleotopography of the underlying sub-Mississippian rocks and regional passive margin subsidence. The Lisburne Group is a thick succession of carbonate rocks subdivided into the Alapah Limestone and overlying Wahoo Limestone, both having informal members.« less

Experimental and Numerical Investigations on Colloid-facilitated Plutonium Reactive Transport in Fractured Tuffaceous Rocks

NASA Astrophysics Data System (ADS)

Dai, Z.; Wolfsberg, A. V.; Zhu, L.; Reimus, P. W.

2017-12-01

Colloids have the potential to enhance mobility of strongly sorbing radionuclide contaminants in fractured rocks at underground nuclear test sites. This study presents an experimental and numerical investigation of colloid-facilitated plutonium reactive transport in fractured porous media for identifying plutonium sorption/filtration processes. The transport parameters for dispersion, diffusion, sorption, and filtration are estimated with inverse modeling for minimizing the least squares objective function of multicomponent concentration data from multiple transport experiments with the Shuffled Complex Evolution Metropolis (SCEM). Capitalizing on an unplanned experimental artifact that led to colloid formation and migration, we adopt a stepwise strategy to first interpret the data from each experiment separately and then to incorporate multiple experiments simultaneously to identify a suite of plutonium-colloid transport processes. Nonequilibrium or kinetic attachment and detachment of plutonium-colloid in fractures was clearly demonstrated and captured in the inverted modeling parameters along with estimates of the source plutonium fraction that formed plutonium-colloids. The results from this study provide valuable insights for understanding the transport mechanisms and environmental impacts of plutonium in fractured formations and groundwater aquifers.

Aquifers of the Denver Basin, Colorado

USGS Publications Warehouse

Topper, R.

2004-01-01

Development of the Denver Basin for water supply has been ongoing since the late 1800s. The Denver Basin aquifer system consists of the water-yielding strata of Tertiary and Cretaceous sedimentary rocks within four overlying formations. The four statutory aquifers contained in these formations are named the Dawson, Denver, Arapahoe, and Laramie-Fox Hills. For water rights administrative purposes, the outcrop/subcrop of the Laramie-Fox Hills aquifer defines the margins of the Basin. Initial estimates of the total recoverable groundwater reserves in storage, under this 6700-mi2 area, were 295 million acre-ft. Recent geologic evidence indicates that the aquifers are very heterogeneous and their composition varies significantly with distance from the source area of the sediments. As a result, available recoverable reserves may be one-third less than previously estimated. There is no legal protection for pressure levels in the aquifer, and water managers are becoming increasingly concerned about the rapid water level declines (30 ft/yr). Approximately 33,700 wells of record have been completed in the sedimentary rock aquifers of the Denver Basin for municipal, industrial, agricultural, and domestic uses.

Hydrogeochemical Investigation of Recharge Pathways to Intermediate and Regional Groundwater in Canon de Valle and Technical Area 16, Los Alamos National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brady, Brendan W.

In aquifers consisting of fractured or porous igneous rocks, as well as conglomerate and sandstone products of volcanic formations, silicate minerals actively dissolve and precipitate (Eby, 2004; Eriksson, 1985; Drever, 1982). Dissolution of hydrated volcanic glass is also known to influence the character of groundwater to which it is exposed (White et al., 1980). Hydrochemical evolution, within saturated zones of volcanic formations, is modeled here as a means to resolve the sources feeding a perched groundwater zone. By observation of solute mass balances in groundwater, together with rock chemistry, this study characterizes the chemical weathering processes active along recharge pathwaysmore » in a mountain front system. Inverse mass balance modeling, which accounts for mass fluxes between solid phases and solution, is used to contrive sets of quantitative reactions that explain chemical variability of water between sampling points. Model results are used, together with chloride mass balance estimation, to evaluate subsurface mixing scenarios generated by further modeling. Final model simulations estimate contributions of mountain block and local recharge to various contaminated zones.« less

Geology of the Harpers Ferry Quadrangle, Virginia, Maryland, and West Virginia

USGS Publications Warehouse

Southworth, Scott; Brezinski, David K.

1996-01-01

The Harpers Ferry quadrangle covers a portion of the northeast-plunging Blue Ridge-South Mountain anticlinorium, a west-verging allochthonous fold complex of the late Paleozoic Alleghanian orogeny. The core of the anticlinorium consists of high-grade paragneisses and granitic gneisses that are related to the Grenville orogeny. These rocks are intruded by Late Proterozoic metadiabase and metarhyolite dikes and are unconformably overlain by Late Proterozoic metasedimentary rocks of the Swift Run Formation and metavolcanic rocks of the Catoctin Formation, which accumulated during continental rifting of Laurentia (native North America) that resulted in the opening of the Iapetus Ocean. Lower Cambrian metasedimentary rocks of the Loudoun, Weverton, Harpers, and Antietam Formations and carbonate rocks of the Tomstown Formation were deposited in the rift-to-drift transition as the early Paleozoic passive continental margin evolved. The Short Hill fault is an early Paleozoic normal fault that was contractionally reactivated as a thrust fault and folded in the late Paleozoic. The Keedysville detachment is a folded thrust fault at the contact of the Antietam and Tomstown Formations. Late Paleozoic shear zones and thrust faults are common. These rocks were deformed and metamorphosed to greenschist-facies during the formation of the anticlinorium. The Alleghanian deformation was accompanied by a main fold phase and a regional penetrative axial plane cleavage, which was followed by a minor fold phase with crenulation cleavage. Early Jurassic diabase dikes transected the anticlinorium during Mesozoic continental rifting that resulted in the opening of the Atlantic Ocean. Cenozoic deposits that overlie the bedrock include bedrock landslides, terraces, colluvium, and alluvium.

Combined Rock Magnetic and Dielectric studies applied to stratigraphic and archeological problems in Venezuela

NASA Astrophysics Data System (ADS)

Costanzo-Alvarez, V.; Aldana, M.; Suarez, N.

2007-05-01

In the last few years the paleomagnetism research group, at the Universidad Simon Bolivar in Caracas (Venezuela), has undertaken combined studies of rock magnetism (e.g. natural magnetic remanence, magnetic susceptibility, hysteresis parameters etc.) and dielectric properties (maximum current depolarization temperatures and average activation energies) in Cretaceous and Paleogene sedimentary sequences from eastern and western Venezuela. Our main goal has been to find new ways of defining physical markers, in fossil- poor sedimentary rocks, for stratigraphic correlations. Magneto/dielectric characterizations of these rocks have proved also useful identifying lithological discontinuities and paleoenvironmental changes. More recently these two-fold technique have been extended to archeological materials (potsherds) from a series of Venezuelan islands, in order to track down clay sources and find out about different stages of pottery craftsmanship. Magneto/Dielectric characterization of archeological potsherds seems to allow the tracing of their provenance from various mainland prehistoric settlements of distinct Venezuelan amerindian groups. In this paper we present a comprehensive review of this research applied to a contact between two sedimentary formations in eastern Venezuela (Cretaceous Chimana/Querecual) and a number of pottery samples with diverse stylistic features excavated in a single archeological site from Los Roques islands.

Magmatism, metasomatism, tectonism, and mineralization in the Humboldt Range, Pershing County, Nevada

USGS Publications Warehouse

Vikre, Peter

2014-01-01

Introduction The Humboldt Range, Pershing County, Nevada, predominantly consists of Mesozoic igneous and sedimentary rocks that were modified several times by magmatism, metasomatism, and tectonism, and contain a variety of metallic (Ag, Au, Pb, Zn, Sb, W, Hg) and non-metallic (dumortierite, pinite, fluorite) mineral deposits (Knopf, 1924; Kerr and Jenney, 1935; Kerr, 1938; Cameron, 1939; Campbell, 1939; Kerr, 1940; Page et al., 1940; Johnson, 1977; Vikre, 1978; 1981; Crosby, 2012). Early Triassic Koipato Group volcanic rocks, which are widely exposed in the range, have been altered to quartz, muscovite (sericite), chlorite, pyrite, and other minerals during emplacement of Mesozoic intrusions and by crustal thickening. Most hydrothermal alteration of volcanic rocks and formation of mineral deposits involved externally derived water and other volatiles, although some volcanic strata were apparently altered by pore or dehydration water. Cospatial hydrothermal mineral assemblages and associations, produced by events widely spaced in time, are difficult to separate because of common mineralogy (quartz, sericite, and pyrite), partial to complete recrystallization, thermally compromised Ar geochronology, and lack of comprehensive investigations of volatile sources and deformational fabric. Distinguishing between metasomatic and metamorphic processes that affected rocks in the Humboldt Range is not straightforward.

Method and system for generating a beam of acoustic energy from a borehole, and applications thereof

DOEpatents

Johnson, Paul A [Santa Fe, NM; Ten Cate, James A [Los Alamos, NM; Guyer, Robert [Reno, NV; Le Bas, Pierre-Yves [Los Alamos, NM; Vu, Cung [Houston, TX; Nihei, Kurt [Oakland, CA; Schmitt, Denis P [Katy, TX; Skelt, Christopher [Houston, TX

2012-02-14

A compact array of transducers is employed as a downhole instrument for acoustic investigation of the surrounding rock formation. The array is operable to generate simultaneously a first acoustic beam signal at a first frequency and a second acoustic beam signal at a second frequency different than the first frequency. These two signals can be oriented through an azimuthal rotation of the array and an inclination rotation using control of the relative phases of the signals from the transmitter elements or electromechanical linkage. Due to the non-linearity of the formation, the first and the second acoustic beam signal mix into the rock formation where they combine into a collimated third signal that propagates in the formation along the same direction than the first and second signals and has a frequency equal to the difference of the first and the second acoustic signals. The third signal is received either within the same borehole, after reflection, or another borehole, after transmission, and analyzed to determine information about rock formation. Recording of the third signal generated along several azimuthal and inclination directions also provides 3D images of the formation, information about 3D distribution of rock formation and fluid properties and an indication of the dynamic acoustic non-linearity of the formation.

Removing the effects of metamorphism from the Neoproterozoic carbon isotope record: a case study on Islay, western Scotland

NASA Astrophysics Data System (ADS)

Skelton, Alasdair

2016-04-01

The Port Askaig Formation on Islay, western Scotland is the first discovered tillite (glacial sediment) of Neoproterozoic age. This formation is sandwiched between carbonate rocks which preserve an extreme negative carbon isotope excursion. This so called "Islay anomaly" has been correlated with other such anomalies worldwide and together with the tillites has been cited as evidence of major (worldwide) glaciation events. During subsequent mountain building, this carbonate-tillite- carbonate sequence has been folded, producing a major en-echelon anticlinal fold system. Folding was accompanied by metamorphism at greenschist facies conditions which was, in turn, accompanied by metamorphic fluid flow. Mapping of the δ18O and δ13C values of these carbonate rocks reveals that metamorphic fluids were channelled through the axial region of the anticlinal fold. The metamorphic fluid was found to have a highly negative δ13C value, which was found to be in equilibrium with metamorphosed graphitic mudstones beneath the carbonate-tillite-carbonate sequence. Devolatilisation of these mudstones is therefore a likely source of this metamorphic fluid. Removal of the effects of metamorphic fluid flow on δ13C values recorded by metamorphosed carbonate rocks on Islay allows us to re-evaluate the isotopic evidence used to reconstruct Neoproterozoic climate. We are able to show that extreme negative δ13C values can partly be attributed to metamorphic fluid flow.

Petrogenesis of volcanic rocks that host the world-class Agsbnd Pb Navidad District, North Patagonian Massif: Comparison with the Jurassic Chon Aike Volcanic Province of Patagonia, Argentina

NASA Astrophysics Data System (ADS)

Bouhier, Verónica E.; Franchini, Marta B.; Caffe, Pablo J.; Maydagán, Laura; Rapela, Carlos W.; Paolini, Marcelo

2017-05-01

We present the first study of the volcanic rocks of the Cañadón Asfalto Formation that host the Navidad world-class Ag + Pb epithermal district located in the North Patagonian Massif, Patagonia, Argentina. These volcanic and sedimentary rocks were deposited in a lacustrine environment during an extensional tectonic regime associated with the breakup of Gondwana and represent the mafic to intermediate counterparts of the mainly silicic Jurassic Chon Aike Volcanic Province. Lava flows surrounded by autobrecciated carapace were extruded in subaerial conditions, whereas hyaloclastite and peperite facies suggest contemporaneous subaqueous volcanism and sedimentation. LA-ICPMS Usbnd Pb ages of zircon crystals from the volcanic units yielded Middle Jurassic ages of 173.9 ± 1.9 Ma and 170.8 ± 3 Ma. In the Navidad district, volcanic rocks of the Cañadón Asfalto Formation show arc-like signatures including high-K basaltic-andesite to high-K dacite compositions, Rb, Ba and Th enrichment relative to the less mobile HFS elements (Nb, Ta), enrichment in light rare earth elements (LREE), Ysbnd Ti depletion, and high Zr contents. These characteristics could be explained by assimilation of crustal rocks in the Jurassic magmas, which is also supported by the presence of zircon xenocrysts with Permian and Middle-Upper Triassic ages (281.3 Ma, 246.5, 218.1, and 201.3 Ma) and quartz xenocrysts recognized in these volcanic units. Furthermore, Sr and Nd isotope compositions suggest a contribution of crustal components in these Middle Jurassic magmas. High-K basaltic andesite has initial 87Sr/86Sr ratios of 0.70416-0.70658 and ξNd(t) values of -5.3 and -4. High-K dacite and andesite have initial 87Sr/86Sr compositions of 0.70584-0.70601 and ξNd(t) values of -4,1 and -3,2. The range of Pb isotope values (206Pb/204Pb = 18.28-18.37, 207Pb/204Pb = 15.61-15.62, and 208Pb/204Pb = 38.26-38.43) of Navidad volcanic rocks and ore minerals suggest mixing Pb sources with contributions of mantle and crust. 206Pb/204Pb isotopic ratios of Jurassic volcanic rocks of the Chon Aike Volcanic Province and sulfides of associated epithermal deposits increase with time from the volcanic event V1 (188-178 Ma) to volcanic events V2 (172-162 Ma) and V3 (157-153 Ma), reflecting variations in the radiogenic Pb source as volcanism was migrating towards the Proto Pacific margin of Gondwana.

Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

USGS Publications Warehouse

Cady, Wallace Martin; Albee, Arden Leroy; Chidester, A.H.

1963-01-01

The upper Missisquoi Valley and vicinity as described in this report covers an area of about 250 square miles at the headwaters of the Missisquoi River in north-central Vermont. About 90 percent of the area is forested and the remainder is chiefly farm land. The topography reflects the geologic structure and varied resistance of the bedrock to erosion. Most of the area is on the east limb of the Green Mountain anticlinorium, which is the principal structural feature of Vermont. The bedrock is predominantly sedimentary and volcanic rock that has been regionally metamorphosed. It was intruded before metamorphism by mafic and ultramafic igneous rocks, and after metamorphism by felsic and mafic igneous rocks. The metamorphosed sedimentary and volcanic rocks range in age from Cambrian(?) to Middle Silurian, the intrusive igneous rocks from probably Late Ordovician to probably late Permian. Metamorphism and principal folding in the region occurred in Middle Devonian time. The metamorphosed sedimentary and volcanic rocks make up a section at least 25,000 feet thick and can be divided into nine formations. The Hazens Notch formation of Cambrian(?) and Early Cambrian age is characterized by carbonaceous schist. It is succeeded in western parts of the area by the Jay Peak formation of Early Cambrian age, which is chiefly a schist that is distinguished by the general absence of carbonaceous zones; in central parts of the area the Hazens Notch formation is followed by the Belvidere Mountain amphibolite, probably the youngest of the formations of Early Cambrian age. The Ottauquechee formation, composed of carbonaceous phyllite and quartzite, and phyllitic graywacke, is of Middle Cambrian age. The Stowe formation of Late Cambrian(?) and Early(?) Ordovician age overlies the Ottauquechee and is predominantly noncarbonaceous schist, though it also contains greenstone and carbonaceous schist and phyllite. The Umbrella Hill formation of Middle Ordovician age is characteristically a conglomerate in which the mineral chloritoid is common. The overlying Moretown formation, also of Middle Ordovician age, contains granulite and slate, also greenstone and amphibolite of the Coburn Hill volcanic member. The Shaw Mountain formation, made up of conglomerate, phyllite, and limestone, is the oldest Silurian unit. The Shaw Mountain formation is succeeded by the Northfield slate of Middle Silurian age. The igneous rocks of the region include various ultramafic plutonic rocks, such as dunite, peridotite, and serpentinite, probably of Late Ordovician age; sills and nearly concordant dikes of metagabbro of Late Ordovician age; biotite granite plutons or Middle or Late Devonian age, most notably on Eltey Mountain; and hypabyssallamprophyre, probably of late Permian age. Metamorphic zoning is shown by the distribution of rocks of the epidote-amphibolite facies and the greenschist facies in and near the Green Mountains, and near Coburn Hill and Eltey Mountain. Metasomatism related to regional metamorphism has produced porphyroblasts and quartz segregations in the sedimentary and volcanic rocks, and steatitization and carbonatization of serpentinite. Contact metamorphism has formed rocks of the epidote-amphibolite facies near granite plutons, and probably calc-silicate rock at the contacts of ultramafic plutons. The axial anticline of the Green Mountain anticlinorium and other anticlines and synclines to the east are the major longitudinal structural features of the area. These structures are complicated by transverse folds, particularly a syncline in the vicinity of Tillotson Peak. Early minor cross folds that are best developed in the Hazens Notch formation are believed to be genetically related to the transverse folds. The axial planes of the cross folds are folded about the axes of the later longitudinal folds of the Green Mountain anticlinorium. The longitudinal and transverse fold systems probably formed in the same episode of defor

Geologic framework of pre-Cretaceous rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico

USGS Publications Warehouse

Condon, Steven M.

1992-01-01

This report is a discussion and summary of Jurassic and older rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico, and is based on analysis of geophysical logs and observations of outcrops. The Reservation, which is located in the northern San Juan Basin, has been the site of deposition of sediments for much of the Phanerozoic. Geologic times represented on the Reservation are the Precambrian, Cambrian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary. Rocks of Ordovician and Silurian age have not been reported in this region. Thicknesses of pre-Cretaceous sedimentary rocks range from about 750 feet (229 meters) on the Archuleta arch, east of the Reservation, to more than 8,300 feet (2,530 meters) just northwest of the Reservation. About 5,500 feet (1,676 meters) of pre-Cretaceous sedimentary rocks occur in the central part of the Reservation, near Ignacio. At Ignacio the top of the Jurassic lies at a depth of 7,600 feet (2,316 meters) below the surface, which is composed of Tertiary rocks. As much as 2,500 feet (762 meters) of Tertiary rocks occur in the area. More than 10,000 feet (3,048 meters) of Cretaceous and younger rocks, and 15,600 feet (4,755 meters) of all Phanerozoic sedimentary rocks occur in the vicinity of the Reservation. In the early Paleozoic the area that includes the Southern Ute Reservation was on the stable western shelf of the craton. During this time sediments that compose the following shallow-marine clastic and carbonate rocks were deposited: the Upper Cambrian Ignacio Quartzite (0-150 feet; 0-46 meters), Upper Devonian Elbert Formation (50-200 feet; 15-61 meters), Upper Devonian Ouray Limestone (10-75 feet; 3-23 meters), and Mississippian Leadville Limestone (0-250 feet; 0-76 meters). Mixed carbonate and clastic deposition, which was punctuated by a unique episode of deposition of evaporite sediments, continued through the Pennsylvanian after a significant episode of erosion at the end of the Mississippian. Pennsylvanian rocks on the Reservation are the Molas Formation (20-100 feet; 6-30 meters) and Hermosa Group (400-2,800 feet; 122-853 meters), which consists of the Pinkerton Trail Formation (40-120 feet; 12-36 meters), Paradox Formation and equivalent rocks (200-1,800 feet; 61-549 meters), and Honaker Trail Formation (200-1,300 feet; 61-396 meters). A unit that is transitional between the Pennsylvanian and Permian is the Rico Formation, which is about 200 feet (61 meters) thick across most of the Reservation area. The close of the Paleozoic Era was marked by a great influx of arkosic clastic sediments from uplifted highlands to the north of the Reservation area during the Permian. Near the paleomountain front the Cutler Formation (presently as thick as 8,000 feet; 2,438 meters) formed as a result of deposition of arkosic sediments; however, the original thickness of the Cutler is unknown due to an unconformity at its top. In the area of the Reservation the Cutler has group status and has been divided into several formations: the Halgaito Formation (350-800 feet; 107-244 meters), Cedar Mesa Sandstone and equivalent rocks (150-350 feet; 46-107 meters), Organ Rock Formation (500-900 feet; 152-274 meters), and De Chelly Sandstone (0-100 feet; 0-30 meters). The sediments of these formations were deposited in a variety of environments, including eolian, mud-flat, and fluvial systems. Following an episode of erosion in the Early and Middle(?) Triassic, deposition in the area of the Southern Ute Reservation continued during the Mesozoic. Sediments of the Upper Triassic Dolores and correlative Chinle Formations were deposited in fluvial, lacustrine, and minor eolian environments. On the Reservation the Dolores is 500-1,200 feet (152-366 meters) thick. Lower Jurassic eolian and fluvial deposits may have been present in much of the Reservation area but have been removed

Formation of an Anti-Core–Shell Structure in Layered Oxide Cathodes for Li-Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hanlei; Omenya, Fredrick; Whittingham, M. Stanley

The layered → rock-salt phase transformation in the layered dioxide cathodes for Li-ion batteries is believed to result in a “core-shell” structure of the primary particles, in which the core region maintains as the layered phase while the surface region undergoes the phase transformation to the rock-salt phase. Using transmission electron microscopy, here we demonstrate the formation of an “anti-core-shell” structure in cycled primary particles with a formula of LiNi0.80Co0.15Al0.05O2, in which the surface and subsurface regions remain as the layered structure while the rock-salt phase forms as domains in the bulk with a thin layer of the spinel phasemore » between the rock-salt core and the skin of the layered phase. Formation of this anti-core-shell structure is attributed to the oxygen loss at the surface that drives the migration of oxygen from the bulk to the surface, thereby resulting in localized areas of significantly reduced oxygen levels in the bulk of the particle, which subsequently undergoes the phase transformation to the rock-salt domains. The formation of the anti-core-shell rock-salt domains is responsible for the reduced capacity, discharge voltage and ionic conductivity in cycled cathode.« less

A reconnaissance for uranium in carbonaceous rocks in southwestern Colorado and parts of New Mexico

USGS Publications Warehouse

Baltz, Elmer H.

1955-01-01

Coal and carbonaceous shale of the Dakota formation of Cretaceous age were examined for radioactivity in the Colorado Plateau of southwestern Colorado and northwestern New l1exico during the summer of 1953. Older and younger sedimentary rocks and some igneous rocks also were examined, but in less detail, Weak radioactivity was detected at many places but no new deposits of apparent economic importance were discovered. The highest radioactivity of carbonaceous rocks was detected in black shale, siltstone, and sandstone of the Paradox member of the Hermosa formation of Pennsylvanian age. A sample collected from this member at the Bald Eagle prospect in Gypsum Valley, San Higuel County, Colo. contains 0.10. percent uranium. Carbonaceous rocks were investigated at several localities on the Las Vegas Plateau and the Canadian Escarpment in Harding and San Miguel Counties, northeastern New Mexico. Carbonaceous sandstone and siltstone in the middle sandstone member of the Chinle formation of Triassic age contain uranium at a prospect of the Hunt Oil Company southwest of Sabinoso in northeastern San Miguel County, N. Mex. A channel sample across 3.2 feet of mineralized rocks at this locality contains 0.22 percent uranium. Weak radioactivity was detected at two localities in carbonaceous shale of the Dakota and Purgatoire formations of Cretaceous age.

Biological marker distribution in coexisting kerogen, bitumen and asphaltenes in Monterey Formation diatomite, California

NASA Technical Reports Server (NTRS)

Tannenbaum, E.; Ruth, E.; Huizinga, B. J.; Kaplan, I. R.

1986-01-01

Organic-rich (18.2%) Monterey Formation diatomite from California was studied. The organic matter consist of 94% bitumen and 6% kerogen. Biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter. While 17 alpha(H), 18 alpha(H), 21 alpha(H)-28,30-bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes, it was not detected in the pyrolysates of the kerogen. A C40-isoprenoid with "head to head" linkage, however, was present in pyrolysates of both kerogen and asphaltenes, but not in the bitumen from the diatomite. The maturation level of the bitumen, based on the extent of isomerization of steranes and hopanes, was that of a mature oil, whereas the pyrolysate from the kerogen showed a considerably lower maturation level. These relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock. We consider the possibility, however, that some of the 28,30-bisnorhopane-rich Monterey Formation oils have not been generated through thermal degradation of kerogen, but have been expelled from the source rock at an early stage of diagenesis.

Early Precambrian crustal evolution of south India

NASA Technical Reports Server (NTRS)

Srinivasan, R.

1986-01-01

The Early Precambrian sequence in Karnataka, South India provides evidences for a distinct trend of evolution which differs from trends exhibited in many other Early Precambrian regions of the world. The supracrustal rock associations preserved in greenstone belts and as inclusions in gneisses and granulites suggest the evolution of the terrain from a stable to a mobile regime. The stable regime is represented by (1) layered ultramafic-mafic complexes, (2) orthoquartzite-basalt-rhyodacite-iron formation, and (30 ortho-quartzite-carbonate-Mn-Fe formation. The mobile regime, which can be shown on sedimentological grounds to have succeeded the stable regime, witnessed the accumulation of a greywacke-pillow basalt-dacite-rhyolite-iron formation association. Detrital sediments of the stable zone accumulated dominantly in fluvial environment and the associated volcanics are ubaerial. The volcanics of the stable regime are tholeiites derived from a zirconium and LREE-enriched sources. The greywackes of the mobile regime are turbidities, and the volcanic rocks possess continental margin (island-arc or back-arc) affinity; they show a LREE depleted to slightly LREE-enriched pattern. The evolution from a stable to a mobile regime is in contrast to the trend seen in most other regions of the world, where an early dominantly volcanic association of a mobile regime gives way upward in the sequence to sediments characteristic of a stable regime.

Petrology of the Northern Anabar alkaline-ultramafic rocks (the Siberian Craton, Russia) and the role of metasomatized lithospheric mantle in their genesis

NASA Astrophysics Data System (ADS)

Kargin, Alexey; Golubeva, Yulia; Demonterova, Elena

2017-04-01

The southeastern margin of the Anabar shield (the Siberian Craton) in Mesozoic was characterized by intense alkaline-ultramafic (include diamondiferous kimberlite) magmatism. This zone is located within the Archean-Proterozoic Hapchan terrane and includes several fields of alkaline-ultramafic rocks that formed during three main episodes (Zaytsev and Smelov, 2010; Sun et al., 2014): Late Triassic (235-205 Ma), Middle-Late Jurassic (171-149 Ma), Cretaceous (105 Ma). Following the revised classification scheme of Tappe et al. (2005), the alkaline-ultramafic rocks of the Anabar region were identified, correspondingly, as 1) Late Triassic aillikites, damtjernites, and orangeites; 2) Middle-Late Jurassic silicocarbonatites and 3) Cretaceous carbonatites. According to mineralogical, geochemical and isotopic (Sm-Nd, Rb-Sr) data on the alkaline-ultramafic rocks of the Anabar region, the following scheme of the mantle source evolution is suggested: 1). Ascent of the asthenospheric (or plume) material to the base of the lithospheric mantle containing numerous carbonate- and phlogopite-rich veins in Late Triassic led to the generation of orangeite and aillikite magmas; 2). Evolution of aillikite magmas during their ascent and interaction with the surrounding lithospheric mantle (e.g. mantle-rock assimilation and/or melt differentiation) resulted in the accumulation of Mg-Si components in alkaline-ultramafic magmas and was accompanied by a change in liquidus minerals (from apatite-carbonate to olivine and Ca-silicate). Exsolution of carbonate-rich fluid at this stage was responsible for the formation of damtjernite magmas. 3). The tectonothermal activation within the Anabar region in Jurassic was marked by the generation of silicocarbonatitic magmas. Their geochemical composition suggests decreasing abundance of phlogopite-rich veins in the lithospheric mantle source. 4). In Cretaceous, the alkaline-ultramafic magmatism shifted into the central part of the Hapchan terrane where produced several carbonatite pipes and dykes. Their geochemical composition indicates the predominance of the carbonate component in the source region and a decrease of the thickness of the lithospheric mantle. This study was supported by Russian Science Foundation №16-17-10068. Tappe S., Foley S.F., Jenner G.A. et al. 2006. Genesis of Ultramafic Lamprophyres and Carbonatites at Aillik Bay, Labrador: a Consequence of Incipient Lithospheric Thinning beneath the North Atlantic Craton // J. Petrology. V. 47 (7). P. 1261-1315. Sun J., Liu C.Z., Tappe S. et al. 2014. Repeated kimberlite magmatism beneath Yakutia and its relationship to Siberian flood volcanism: Insights from in situ U-Pb and Sr-Nd perovskite isotope analysis // Earth Planet. Sci. Lett. V. 404. P. 283-295. Zaytsev A.I., Smelov A.P., 2010. Isotope Geochronology of Kimberlite Formation Rocks from Yakutian Province // Publication of the Institute of Diamonds Geology, Siberian branch of the Russian Academy of Sciences, Yakutsk (107 pp. (in Russian)).

Some Aspects of Evolution of Microbial Rock-Formation in the Earth's History

NASA Astrophysics Data System (ADS)

Kuznetsov, V. G.

2018-01-01

Under a relatively constant system and morphology of microbiota, sedimentary rocks produced by microbial organisms (microbiolites) evolved intensively during the geological history of the Earth. The parameters that changed were the composition, extraction form, and formation environments.

Hydrocarbon potential of Central Monagas, Eastern Venezuela Basin, Venezuela

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barrios, F.; Daza, J.; Iusco, G.

1996-08-01

The Central Monagas area is part of the foreland sub-basin located on the southern flank of the Eastern Venezuela Basin. The sedimentary column of the Central Monagas is at least 7500 in thick and consists of Mesozoic (Cretaceous) and Cenozoic rocks. Interpretations of 60 regional seismic sections have been integrated with data from 12 existing wells, which cover an area of 1200 km{sup 2}. From these interpretations, basin-wide structure and interval isopach maps were constructed in order to aid the depiction of the basin architecture and tectonic history. The sub-basin developed on the southern flank of the Eastern Venezuela Basinmore » is tightly linked to its evolution from a Mesozoic extensional regime into a Cenozoic compressional and strike-slip stage. The basin formed in the Middle Mesozoic by crustal extension of a rifting process. Regional northward tilting of the slab continued during the Late Cretaceous. Finally, the transpression of the Caribbean Plate during the Oligocene-Neogene induced the overprint of compressional deformation associated with the deposition of a foredeep wedge. Geochemical source rock analysis gave an average of 1.2 TOC, and R{sub o} of 0.66 indicating a mature, marine source. The modeling of the hydrocarbon generative history of the basin indicates that the oil migration started in the Middle Miocene, after the trap was formed. Analysis and mapping of reservoir rocks and seal rocks defined the effective area limits of these critical factors. The main play in the area is the extension of the Lower Oficina Formation which is the proven petroleum target in the Eastern Venezuela Basin.« less

Petrogenesis of the ∼500 Ma Fushui mafic intrusion and Early Paleozoic tectonic evolution of the Northern Qinling Belt, Central China

NASA Astrophysics Data System (ADS)

Shi, Yu; Pei, Xiaoli; Castillo, Paterno R.; Liu, Xijun; Ding, Haihong; Guo, Zhichao

2017-06-01

The Fushui mafic intrusion in the Qinling orogenic belt (QOB) is composed of meta-gabbro, meta-gabbro-diorite, diorite, and syenite. Most of these rocks are metamorphosed under the upper greenschist facies to lower amphibolite facies metamorphism. Zircon separates from eight samples have LA-ICP-MS U-Pb ages of 497-501 Ma which are taken to be the emplacement age of magmas that formed the Fushui intrusion. Most of the zircon grains exhibit negative εHf values, correspond to TDM2 model ages of late Paleoproterozoic-early Mesoproterozoic or Neoproterozoic and suggest that the mafic rocks were most probably derived from mafic melts produced by partial melting of a previously metasomatized lithospheric mantle. The intrusion is not extensively contaminated by crustal materials and most chemical compositions of rocks are not modified during the greenschist to amphibolite-facies metamorhism. Rocks from the intrusion have primitive mantle-normalized trace element patterns with significant enrichment in light-REE and large ion lithophile elements (LILE) and depletion in high field-strength elements (HFSE). On the basis of the trace element contents, the Fushui intrusion was derived from parental magmas generated by <10% partial melting of both phlogopite-lherzolite and garnet-lherzolite mantle sources. These sources are best interpreted to be in a subduction-related arc environment and have been modified by fluids released from a subducting slab. The formation of the Fushui intrusion was related to the subduction of the Paleotethyan Shangdan oceanic lithosphere at ∼500 Ma.

Environmentally Friendly, Rheoreversible, Hydraulic-fracturing Fluids for Enhanced Geothermal Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Hongbo; Kabilan, Senthil; Stephens, Sean A.

Cost-effective creation of high-permeability reservoirs inside deep crystalline bedrock is the primary challenge for the feasibility of enhanced geothermal systems (EGS). Current reservoir stimulation entails adverse environmental impacts and substantial economic costs due to the utilization of large volumes of water “doped” with chemicals including rheology modifiers, scale and corrosion inhibitors, biocides, friction reducers among others where, typically, little or no information of composition and toxicity is disclosed. An environmentally benign, CO2-activated, rheoreversible fracturing fluid has recently been developed that significantly enhances rock permeability at effective stress significantly lower than current technology. We evaluate the potential of this novel fracturingmore » fluid for application on geothermal sites under different chemical and geomechanical conditions, by performing laboratory-scale fracturing experiments with different rock sources under different confining pressures, temperatures, and pH environments. The results demonstrate that CO2-reactive aqueous solutions of environmentally amenable Polyallylamine (PAA) represent a highly versatile fracturing fluid technology. This fracturing fluid creates/propagates fracture networks through highly impermeable crystalline rock at significantly lower effective stress as compared to control experiments where no PAA was present, and permeability enhancement was significantly increased for PAA compared to conventional hydraulic fracturing controls. This was evident in all experiments, including variable rock source/type, operation pressure and temperature (over the entire range for EGS applications), as well as over a wide range of formation-water pH values. This versatile novel fracturing fluid technology represents a great alternative to industrially available fracturing fluids for cost-effective and competitive geothermal energy production.« less

Mineralogy of Mudstone at Gale Crater, Mars: Evidence for Dynamic Lacustrine Environments

NASA Technical Reports Server (NTRS)

Rampe, E. B.; Ming, D. W.; Grotzinger, J. P.; Morris, R. V.; Blake, D. F.; Vaniman, D. T.; Bristow, T. F.; Yen, A. S.; Chipera, S. J.; Morrison, S. M.;

Source of boron in the Palokas gold deposit, northern Finland: evidence from boron isotopes and major element composition of tourmaline

NASA Astrophysics Data System (ADS)

Ranta, Jukka-Pekka; Hanski, Eero; Cook, Nick; Lahaye, Yann

2017-06-01

The recently discovered Palokas gold deposit is part of the larger Rompas-Rajapalot gold-mineralized system located in the Paleoproterozoic Peräpohja Belt, northern Finland. Tourmaline is an important gangue mineral in the Palokas gold mineralization. It occurs as tourmalinite veins and as tourmaline crystals in sulfide-rich metasomatized gold-bearing rocks. In order to understand the origin of tourmaline in the gold-mineralized rocks, we have investigated the major element chemistry and boron isotope composition of tourmaline from three areas: (1) the Palokas gold mineralization, (2) a pegmatitic tourmaline granite, and (3) the evaporitic Petäjäskoski Formation. Based on textural evidence, tourmaline in gold mineralization is divided into two different types. Type 1 is located within the host rock and is cut by rock-forming anthophyllite crystals. Type 2 occurs in late veins and/or breccia zones consisting of approximately 80% tourmaline and 20% sulfides, commonly adjacent to quartz veins. All the studied tourmaline samples belong to the alkali-group tourmaline and can be classified as dravite and schorl. The δ11B values of the three localities lie in the same range, from 0 to -4‰. Tourmaline from the Au mineralization and from the Petäjäskoski Formation has similar compositional trends. Mg is the major substituent for Al; inferred low Fe3+/Fe2+ ratios and Na values (<0.8 atoms per formula unit (apfu)) of all tourmaline samples suggest that they precipitated from reduced, low-salinity fluids. Based on the similar chemical and boron isotope composition and the Re-Os age of molybdenite related to the tourmaline-sulfide-quartz veins, we propose that the tourmaline-forming process is a result of a single magmatic-hydrothermal event related to the extensive granite magmatism at around 1.79-1.77 Ga. Tourmaline was crystallized throughout the hydrothermal process, which resulted in the paragenetic variation between type 1 and type 2. The close association of tourmaline and gold suggests that the gold precipitated from the same boron-rich source as tourmaline.

Rock.XML - Towards a library of rock physics models

NASA Astrophysics Data System (ADS)

Jensen, Erling Hugo; Hauge, Ragnar; Ulvmoen, Marit; Johansen, Tor Arne; Drottning, Åsmund

2016-08-01

Rock physics modelling provides tools for correlating physical properties of rocks and their constituents to the geophysical observations we measure on a larger scale. Many different theoretical and empirical models exist, to cover the range of different types of rocks. However, upon reviewing these, we see that they are all built around a few main concepts. Based on this observation, we propose a format for digitally storing the specifications for rock physics models which we have named Rock.XML. It does not only contain data about the various constituents, but also the theories and how they are used to combine these building blocks to make a representative model for a particular rock. The format is based on the Extensible Markup Language XML, making it flexible enough to handle complex models as well as scalable towards extending it with new theories and models. This technology has great advantages as far as documenting and exchanging models in an unambiguous way between people and between software. Rock.XML can become a platform for creating a library of rock physics models; making them more accessible to everyone.

Sedimentary environment and diagenesis of the Lower Cretaceous Chaswood Formation, southeastern Canada: The origin of kaolin-rich mudstones

NASA Astrophysics Data System (ADS)

Pe-Piper, Georgia; Dolansky, Lila; Piper, David J. W.

2005-07-01

The Lower Cretaceous fluvial sandstone-mudstone succession of the Chaswood Formation is the proximal equivalent of offshore deltaic rocks of the Scotian Basin that are reservoirs for producing gas fields. This study interprets the mineralogical consequences of Cretaceous weathering and early diagenesis in a 130-m core from the Chaswood Formation in order to better understand detrital and diagenetic minerals in equivalent rocks offshore. Mineralogy was determined by X-ray diffraction, electron microprobe analysis and scanning electron microscopy. The rocks can be divided into five facies associations: light gray mudstone, dark gray mudstone, silty mudstone and muddy sandstone, sorted sandstone and conglomerate, and paleosols. Facies transitions in coarser facies are related to deposition in and near fluvial channels. In the mudstones, they indicate an evolutionary progression from the dark gray mudstone facies association (swamps and floodplain soils) to mottled paleosols (well-drained oxisols and ultisols following syntectonic uplift). Facies transitions and regional distribution indicate that the light gray mudstone facies association formed from early diagenetic oxidation and alteration of the dark gray mudstone facies association, probably by meteoric water. Principal minerals in mudstones are illite/muscovite, kaolinite, vermiculite and quartz. Illite/muscovite is of detrital origin, but variations in abundance show that it has altered to kaolinite in the light gray mudstone facies association and in oxisols. Vermiculite developed from the weathering of biotite and is present in ultisols. The earliest phase of sandstone cementation in reducing conditions in swamps and ponds produced siderite nodules and framboidal pyrite, which were corroded and oxidized during subsequent development of paleosols. Kaolinite is an early cement, coating quartz grains and as well-crystallized, pore-filling booklets that was probably synchronous with the formation of the light gray mudstone facies association. Later illite and barite cement indicate a source of abundant K and Ba from formation water. This late diagenesis of sandstone took place when the Chaswood Formation was in continuity with the main Scotian Basin, prior to Oligocene uplift of the eastern Scotian Shelf. Findings of this study are applicable to other mid-latitude Cretaceous weathering and early diagenetic environments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

Greenland's Mineral Resources Administration (MRA) plans a series of licensing rounds off western Greenland. Meanwhile, the MRA has declared the Jameson Land basin of east central Greenland as open acreage. Greenland Geological Survey (GGU), Copenhagen, has prepared a report on the geographical conditions, logistics, exploration history, and geological development of Jameson Land. The article emphasizes source and reservoir rocks, conceptual play types with six seismic examples, and thermal history with basin modeling. It also includes two interpreted regional seismic lines, a geological and an aeromagnetic map, depth structure, and isopach maps of selected formations.

NAVAIR Portable Source Initiative (NPSI) Standard for Material Properties Reference Database (MPRD) V2.2

DTIC Science & Technology

2012-09-26

format; however, the collective identity and structure of the object are lost. In contrast, XML preserves the structure of the object by using custom...2.1.1 Classes  ROCK  SOIL  MINERAL  VEGETATION  COATING  LIQUID  METAL  CONSTRUCTION  PLASTIC  WOOD  GLASS  FABRIC...2.1.2 Subclasses Subclasses are created using relevant taxonomy from the authority in a particular class. Some examples of subclasses nomenclature in

Rhenium-osmium isotopes and highly siderophile elements in ultramafic rocks from the Eoarchean Saglek Block, northern Labrador, Canada: implications for Archean mantle evolution

NASA Astrophysics Data System (ADS)

Ishikawa, Akira; Suzuki, Katsuhiko; Collerson, Kenneth D.; Liu, Jingao; Pearson, D. Graham; Komiya, Tsuyoshi

2017-11-01

We determined highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) concentrations and 187Os/188Os ratios for ultramafic rocks distributed over the Eoarchean gneiss complex of the Saglek-Hebron area in northern Labrador, Canada in order to constrain to what extent variations in HSE abundances are recorded in Early Archean mantle that have well-resolved 182W isotope anomalies relative to the present-day mantle (∼+11 ppm: Liu et al., 2016). The samples analysed here have been previously classified into two suites: mantle-derived peridotites occurring as tectonically-emplaced slivers of lithospheric mantle, and metakomatiites comprising mostly pyroxenitic layers in supracrustal units dominated by amphibolites. Although previous Sm-Nd and Pb-Pb isotope studies provided whole-rock isochrons indicative of ∼3.8 Ga protolith formation for both suites, our whole-rock Re-Os isotope data on a similar set of samples yield considerably younger errorchrons with ages of 3612 ± 130 Ma (MSWD = 40) and 3096 ± 170 Ma (MSWD = 10.2) for the metakomatiite and lithospheric mantle suites, respectively. The respective initial 187Os/188Os = 0.10200 ± 18 for metakomatiites and 0.1041 ± 18 for lithospheric mantle rocks are within the range of chondrites. Re-depletion Os model ages for unradiogenic samples from the two suites are consistent with the respective Re-Os errorchrons (metakomatiite TRD = 3.4-3.6 Ga; lithospheric mantle TRD = 2.8-3.3 Ga). These observations suggest that the two ultramafic suites are not coeval. However, the estimated mantle sources for the two ultramafics suites are similar in terms of their broadly chondritic evolution of 187Os/188Os and their relative HSE patterns. In detail, both mantle sources show a small excess of Ru/Ir similar to that in modern primitive mantle, but a ∼20% deficit in absolute HSE abundances relative to that in modern primitive mantle (metakomatiite 74 ± 18% of PUM; lithospheric mantle 82 ± 10% of PUM), consistent with the ∼3.8 Ga Isua mantle source and Neoarchean komatiite sources around the world (∼70-86% of PUM). This demonstrates that the lower HSE abundances are not unique to the sources of komatiites, but rather might be a ubiquitous feature of Archean convecting mantle. This tentatively suggests that chondritic late accretion components boosted the convecting mantle HSE inventory after core separation in the Hadean, and that the Eoarchean to Neoarchean convecting mantle was depleted in its HSE content relative to that of today. Further investigation of Archean mantle-derived rocks is required to explore this hypothesis.

Major, trace element and isotope geochemistry (Sr-Nd-Pb) of interplinian magmas from Mt. Somma-Vesuvius (Southern Italy)

USGS Publications Warehouse

Somma, R.; Ayuso, R.A.; de Vivo, B.; Rolandi, G.

2001-01-01

Major, trace element and isotopic (Sr, Nd, Pb) data are reported for representative samples of interplinian (Protohistoric, Ancient Historic and Medieval Formations) activity of Mt. Somma-Vesuvius volcano during the last 3500 years. Tephra and lavas exhibit significant major, trace element and isotopic variations. Integration of these data with those obtained by previous studies on the older Somma suites and on the latest activity, allows to better trace a complete petrological and geochemical evolution of the Mt. Somma-Vesuvius magmatism. Three main groups of rocks are recognized. A first group is older than 12.000 yrs, and includes effusive-explosive activity of Mt. Somma. The second group (8000-2700 yrs B.P.) includes the products emitted by the Ottaviano (8000 yrs. B.P.) and Avellino (3550 yrs B.P.) plinian eruptions and the interplinian activity associated with the Protohistoric Formation. Ancient Historic Formation (79-472 A.D.), Medieval Formation (472-1139 A.D.) and Recent interplinian activity (1631-1944 A.D.) belong to the third group of activity (79-1944 A.D.). The three groups of rocks display distinct positive trends of alkalis vs. silica, which become increasingly steeper with age. In the first group there is an increase in silica and alkalis with time, whereas an opposite tendency is observed in the two younger groups. Systematic variations are also evident among the incompatible (Pb, Zr, Hf, Ta, Th, U, Nb, Rb, Cs, Ba) and compatible elements (Sr, Co, Cr). REE document variable degrees of fractionation, with recent activity displaying higher La/Yb ratios than Medieval and Ancient Historic products with the same degree of evolution. N-MORB normalized multi-element diagrams for interplinian rocks show enrichment in Rb, Th, Nb, Zr and Sm (> *10 N-MORB). Sr isotope ratios are variable, with Protohistoric rocks displaying 87Sr/86Sr= 0.70711-0.70810, Ancient Historic 87Sr/86Sr=0.70665-0.70729, and Medieval 87Sr/86Sr=0.70685-0.70803. Neodymium isotopic compositions in the interplinian rocks show a tendency to become slightly more radiogenic with age, from the Protohistoric (143Nd/144Nd=0.51240-0.51247) to Ancient Historic (143Nd/144Nd=0.51245-0.51251). Medieval interplinian activity (143Nd/144Nd: 0.51250-0.51241) lacks meaningful internal trends. All the interplinian rocks have virtually homogeneous compositions of 207Pb/204Pb and 208Pb/204Pb in acid-leached residues (207Pb/204Pb ???15.633 to 15.687, 208Pb/204Pb ???38.947 to 39.181). Values of 206Pb/204Pb are very distinctive, however, and discriminate among the three interplinian cycles of activity (Protohistoric: 18.929-18.971, Ancient Historic: 19.018-19.088, Medieval: 18.964-19.053). Compositional trends of major, trace element and isotopic compositions clearly demonstrate strong temporal variations of the magma types feeding the Somma-Vesuvius activity. These different trends are unlikely to be related only to low pressure evolutionary processes, and reveal variations of parental melt composition. Geochemical data suggest a three component mixing scheme for the interplinian activity. These involve HIMU-type and DMM-type mantle and Calabrian-type lower crust. Interaction between these components has taken place in the source; however, additional quantitative constraints must be acquired in order to better discriminate between magma characteristics inherited from the sources and those acquired during shallow level evolution.

Formation of Ocean Sedimentary Rocks as Active Planets and Life-Like Systems

NASA Astrophysics Data System (ADS)

Miura, Y.

2017-10-01

Wet shocked rocks are discarded globally and enriched elements in ocean-sedimentary rocks, which is strong indicator of ocean water of other planets. Ocean-sedimentary rocks are strong indicator of water planets and possible exo-life on planet Mars.

Rheological stratification of the Hormuz Salt Formation in Iran - microstructural study of the dirty and pure rock salts from the Kuh-e-Namak (Dashti) salt diapir

NASA Astrophysics Data System (ADS)

Závada, Prokop; Desbois, Guillaume; Urai, Janos; Schulmann, Karel; Rahmati, Mahmoud; Lexa, Ondrej; Wollenberg, Uwe

2014-05-01

Significant viscosity contrasts displayed in flow structures of a mountain namakier (Kuh-e-Namak - Dashti), between 'weak' terrestrial debris bearing rock salt types and 'strong' pure rock salt types are questioned for deformation mechanisms using detailed quantitative microstructural study including crystallographic preferred orientation (CPO) mapping of halite grains. While the solid impurity rich ("dirty") rock salts contain disaggregated siltstone and dolomite interlayers, "clean" salts (debris free) reveal microscopic hematite and remnants of abundant fluid inclusions in non-recrystallized cores of porphyroclasts. Although flow in both, the recrystallized dirty and clean salt types is accommodated by combined mechanisms of pressure-solution creep (PS), grain boundary sliding (GBS) and dislocation creep accommodated grain boundary migration (GBM), their viscosity contrasts are explained by significantly slower rates of intergranular diffusion and piling up of dislocations at hematite inclusions in clean salt types. Porphyroclasts of clean salts deform by semi-brittle and plastic mechanisms with intra-crystalline damage being induced also by fluid inclusions that explode in the crystals at high fluid pressures. Boudins of clean salt types with coarse grained and original sedimentary microstructure suggest that clean rock salts are associated with dislocation creep dominated power law flow in the source layer and the diapiric stem. Rheological contrasts between both rock salt classes apply in general for the variegated and terrestrial debris rich ("dirty") Lower Hormuz and the "clean" rock salt forming the Upper Hormuz, respectively, and suggest that large strain rate gradients likely exist along horizons of mobilized salt types of different composition and microstructure.