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Sample records for cretaceous source rocks

  1. Cretaceous source rocks in Pakistan

    SciTech Connect

    Kari, I.B. )

    1993-02-01

    Pakistan is located at the converging boundaries of the Indian, Arabian, and Eurasian plates. Evolution of this tectonic setting has provided an array of environmental habitats for deposition of petroleum source rocks and development of structural forms. The potential Cretaceous source rocks in Central and South Indus Basin are spread over an area of about 300,000 km[sup 2]. With 2% cutoff on Total Organic Carbon, the average source rock thickness is 30-50 m, which is estimated to have generated more than 200 billion bbl of oil equivalent. To date, production of more than 30,000 bbl of oil and about 1200 million ft[sup 3] of gas per day can be directly attributed to Cretaceous source. This basin was an area of extensional tectonics during the Lower to Middle Cretaceous associated with slightly restricted circulation of the sea waters at the north-western margin of Indian Plate. Lower Cretaceous source rocks (Sembar Formation) were deposited while the basin was opening up and anoxia was prevailing. Similarly Middle to Upper Cretaceous clastics were deposited in setting favorable for preservation of organic matter. The time and depth of burial of the Cretaceous source material and optimum thermal regime have provided the requisite maturation level for generation of hydrocarbons in the basin. Central Indus basin is characterized by Cretaceous source rocks mature for gas generation. However, in South Indus Basin Cretaceous source rocks lie within the oil window in some parts and have gone past it in others.

  2. New depositional models for Cretaceous source rocks

    SciTech Connect

    Kauffman, E.G.; Villamil, T. )

    1993-02-01

    The Cretaceous marks one of the greatest periods of source rock development in geologic history, especially in coastal and epi-continental marine basins where the number, duration, and geographic extent of Corg-rich intervals exceeds that of oceanic basins. Large-scale factors regulating Cretaceous source rocks include sealevel, sedimentation rate/type, paleoclimate and marine thermal gradients, paleoceanography (circulation, stratification, chemistry, upwelling, nutrient supply), and surface water productivity. Marine dispositional settings favored as models for Corg concentration include silled and tectonically depressed basins, intersection of OMZ's with shallow continental seas, coastal upwelling, highly stratified shallow seas, and oceanic anoxic events (OAE's). All of these settings are thought to be characterized by stagnant, anoxic/highly dysoxic water masses above the sediment-water interface, and highly stressed benthic environments. This seemingly supported by fine lamination, spare bioturbation, high pyrite and Corg content of most source rocks. But high-resolution (cm-scale) sedimentologic, paleobiologic, and geochemical analyses of Jurassic-Cretaceous source rocks reveal, instead, dynamic benthic environments with active currents, episodically crowded with diverse life in event communities, and persistently characterized by longer term, low diversity resident benthic communities. These characteristics indicate rapidly fluctuating, predominantly dysoxic to oxic waters at and above the sediment-water interface for most Corg-rich black shales. A new model for source rock generation is proposed which retains the redox boundary at or near the sediment-water interface over large areas of seafloor, in part aided by extensive development of benthic microbial mats which may contribute up to 30% of the Corg to marine source rocks.

  3. Source rock potential of middle Cretaceous rocks in southwestern Montana

    SciTech Connect

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

    1996-08-01

    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 (S{sub 1}+S{sub 2}) 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% R{sub o}. Maturity is high in the Pioneer Mountains, where vitrinite reflectance averages 3.4% R{sub o}, and at Big Sky, Montana, where vitrinite reflectance averages 2.5% R{sub o}. At both localities, high R{sub o} values are due to local heat sources, such as the Pioneer batholith in the Pioneer Mountains.

  4. 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.

  5. Source rock evaluation of Cretaceous and Tertiary series in Tunisia

    SciTech Connect

    Oudin, J. )

    1988-08-01

    Tunisia represents a mature hydrocarbon province with a long exploration history. In the Sfax-Kerkennah and Gabes Gulf areas, the hydrocarbon accumulations are located in series of Cretaceous and Tertiary age. To estimate the petroleum potential of this region, an evaluation of the source rock quality of the Cretaceous and Tertiary series was undertaken. In the Sfax-Kerkennak area, most of the wells studied indicate that, in the Tertiary, Ypresian and lower Lutetian show good organic content but, taking into account the potential productivity, only the Ypresian can be considered as a potential source rock. In the Cretaceous, mainly studies in the offshore area of the Gabes Gulf, the amount of organic matter is fair and it is chiefly located in Albian and Cenomanian. The Vraconian with its quite good potential is a valuable source rock. Due to the difference in the environment of deposition for these two possible source rocks - the Ypresian with its lagoon facies being carbonate and the Vraconian shaly - variations in the type of organic matter can be noted, although both are of marine origin. The hydrocarbons generated from these source rocks reflect these variations and permit them to correlate the different crude oils found in this area with their original source beds.

  6. Controls on the distribution of Cretaceous source rocks in South America

    SciTech Connect

    Vear, A. )

    1993-02-01

    More than thirty South American basins, exhibiting a variety of structural styles, contain petroleum source rocks of Cretaceous age. However, the presence of truly [open quote]world-class[close quote] source rocks, capable of supplying multi-billion barrel oil provinces, is restricted to relatively few basins and appears to be primarily a function of large scale Cretaceous tectonic setting. In Early Cretaceous times the best source rocks were preserved in both a southern ocean and in the rift between South America and Africa. By the Late Cretaceous, these southern and eastern continental limits had become narrow passive margins. In contrast, on the northern continental margin a wide shelf to a restricted tropical sea was developing at this time. Periodic upwelling enhanced surface productivity on this shelf, which led to development of some of the world's richest source rocks. On the tectonically active western margin moderate quality source rocks were forming in a series of back-arc basins, whilst further west, in the Pacific fore-arc, organic-rich intervals were rarely deposited. This article documents what is known about each of the explored basins (including the volume and character of discovered petroleums), it investigates the geologic factors which governed the richness and quality of petroleum source rocks and it assesses how continued tectonic activity has modified or even destroyed primary source quality. Finally it predicts which of the as yet underexplored basins should contain good quality source rocks and could become prolific petroleum provinces of the future.

  7. Source rock in the lower Tertiary and Cretaceous, deep-water Gulf of Mexico

    SciTech Connect

    Wagner, B.E.; Sofer, Z.; Claxton, B.L.

    1994-12-31

    The MC-84 (King) well was drilled in the deep-water Gulf of Mexico in 1993, in Mississippi Canyon Block 84 in a water depth of 5,149 ft. This well drilled an anticlinal feature. The well penetrated an Upper Cretaceous section and crossed Middle Cretaceous Unconformity with final total depth in the Lower Cenomanian. Numerous sidewall cores were taken throughout the Lower Tertiary and Cretaceous. Six of the sidewall cores (from 14,230 to 15,170 ft subsea) are organic rich and contain Type II oil-prone kerogen (TOC values from 2.6 to 5.2% and hydrogen indices from 360 to 543 ppm). The Lower Tertiary through Lower Cenomianian section is thermally immature for oil generation, on the basis of biomarker ratios and vitrinite reflectance measurements. Organic extracts from cores in the Cretaceous section had biomarker characteristics similar to oil recovered from the Miocene in the MC-84 well. The oil was generated from a similar but more mature source rock, probably of Early Cretaceous age. Results of thermal modeling indicate that the only section thermally mature for oil generation is in the lower portion of the Lower Cretaceous, below the total depth of the well. The model also indicates that the organic-rich section equivalent to that penetrated by the MC-84 well could be mature farther to the north, where water depths are shallower, overburden thickness is greater, and heat flow is higher. Late Tertiary sediment loading in this area, primarily during the Miocene, is probably the driving mechanism for hydrocarbon generation from the Cretaceous (and possibly the Lower Tertiary) potential source rocks. This offers a favorable geological setting for capturing hydrocarbons because reservoirs and traps associated with Miocene deposition and subsequent loading-induced salt movement had formed prior to the onset of oil generation and migration.

  8. Source terrains and diagenetic imprints of Cretaceous marine rocks of the Cordillera Oriental, Colombia

    SciTech Connect

    Segall, M.P.; Allen, R.B. ); Rubiano, J.; Sarmiento, L. )

    1993-02-01

    Cretaceous marine rocks of the western Cordillera Oriental of Colombia are exposed in stratigraphic sections which reveal multiple source terrains and variable diagenetic histories that were imposed by later thrusting XRD and petrographic analyses indicate that earliest Cretaceous rocks were derived from a nearly plutonic source (Triassic-Jurassic Ibague Batholith of the Cordillera Central) which provided feldspathic lithic fragments and clay-sized illite. High smectite concentrations in the overlying Hauterivian-Barremian strata reflect contemporaneous volcanism, possibly in the Cordillera Central. This signal decreased upsection to the upper Aptian, where detrital clays (kaolinite, chlorite, feldspar, amphibole) indicate a shift to a cratonic source, probably the Guayana Shield. Cratonic detrital input continues into the Turonian-Coniacian and is accompanies by high concentrations of smectite representing another period of volcanic activity. Later tectonic activity divided the area into two regions, each with unique diagenetic signatures. Three primary clastic sources are inferred for the section east of the thrust belt, however, the mineral assemblage is masked by later diagenesis. Sediments within the thrust belt show greater variability in the relative abundance of mineral assemblages and more poorly crystallized illite than occurs to the east of the thrust section. The preservation of much of the original mineralogic components within the thrust section indicates that these sediments have experienced only limited diagenetic overprinting as a result of a relatively short burial history. These contrasting signatures have important implications for hydrocarbon maturation within Cretaceous source rocks in a structurally complex region.

  9. A plate tectonic-paleoceanographic hypothesis for Cretaceous source rocks and cherts of northern South America

    SciTech Connect

    Villamil, T.; Arango, C.

    1996-12-31

    New paleocontinental reconstructions show a northern migration of the South American Plate with respect to the paleoequator from the Jurassic to the Late Cretaceous. This movement caused the northern margin of South America to migrate from a position south to a position north of the paleoequator. Ekman transport generated net surface water movement towards the south during times when northern South America was south of the paleoequator. This situation favored downwelling and prevented Jurassic and earliest Cretaceous marine source rocks from being deposited. When northern South America was north of the paleoequator Ekman transport forced net water movement to the north favoring upwelling, paleoproductivity, and the deposition of one of the best marine source rocks known (the La Luna, Villeta, and equivalents). This plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern South America. The stratigraphic record reflects this increase in paleoproductivity through time. This can be observed in facies (non-calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts) and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages, followed by stressed foraminifer populations and finally by radiolarians. Total organic carbon and source rock quality were affected by this long term increase in paleoproductivity but also, and more markedly, by a punctuated sequence stratigraphic record dominated by low- frequency changes in relative sea level. The magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon.

  10. A plate tectonic-paleoceanographic hypothesis for Cretaceous source rocks and cherts of northern South America

    SciTech Connect

    Villamil, T.; Arango, C. )

    1996-01-01

    New paleocontinental reconstructions show a northern migration of the South American Plate with respect to the paleoequator from the Jurassic to the Late Cretaceous. This movement caused the northern margin of South America to migrate from a position south to a position north of the paleoequator. Ekman transport generated net surface water movement towards the south during times when northern South America was south of the paleoequator. This situation favored downwelling and prevented Jurassic and earliest Cretaceous marine source rocks from being deposited. When northern South America was north of the paleoequator Ekman transport forced net water movement to the north favoring upwelling, paleoproductivity, and the deposition of one of the best marine source rocks known (the La Luna, Villeta, and equivalents). This plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern South America. The stratigraphic record reflects this increase in paleoproductivity through time. This can be observed in facies (non-calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts) and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages, followed by stressed foraminifer populations and finally by radiolarians. Total organic carbon and source rock quality were affected by this long term increase in paleoproductivity but also, and more markedly, by a punctuated sequence stratigraphic record dominated by low- frequency changes in relative sea level. The magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon.

  11. Thermochronology of lower Cretaceous source rocks in the Idaho-Wyoming thrust belt

    SciTech Connect

    Burtner, R.L.; Nigrini, A.; Donelick, R.A.

    1994-10-01

    Lower Cretaceous organic-rich source rocks that are thermally mature to postmature crop out on the Absaroka, Darby, and Prospect plates in linear belts that run parallel to the trace of the thrusts in the Idaho-Wyoming portion of the Idaho-Wyoming-Utah thrust belt. Although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic-rich strata, commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt. In a companion paper, Burtner and Nigrini demonstrated that gravity-driven fluid flow in the Idaho-Wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the Early Cretaceous foreland basin eastward toward the stable platform. In this paper we demonstrate, through the application of organic maturation indicators and a new refinement of the apatite fission track technique, that this process heated Lower Cretaceous organic-rich source rocks to temperatures sufficient to generate hydrocarbons. Hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt.

  12. Source rock in the Lower Tertiary and Cretaceous, deep-water Gulf of Mexico

    SciTech Connect

    Wagner, B.E.; Sofer, Z.; Claxton, B.L.

    1994-09-01

    Amoco drilled three wells in the deep-water Gulf of Mexico in 1993. One well, in Mississippi Canyon Block 84 (W.D. 5200 ft), drilled a structural feature. The well penetrated Cretaceous section and crossed the middle Cenomanian unconformity. Six sidewall cores from 14,230-15,200 ft (subsea) contained TOC values from 2.6 to 5.2% with hydrogen indices front 360 to 543 ppm in lower Tertiary and Cretaceous shales. All six cores were thermally immature, for oil generation, based on biomarker ratios and vitrinite reflectance measurements. Organic extracts from cores in the Cretaceous had biomarker characteristics similar to oil reservoired in the Miocene. The oil was probably generated from a similar, but more mature, source rock. The high structural position of the well prevented the lower Tertiary and Upper Cretaceous section from entering the oil window at this location. There are over 2000 ft of structural relief and an additional 6000-8000 ft of Lower Cretaceous section below the level penetrated by the well. It is probable that an equivalent section off structure is in the oil window. Prior to drilling, estimates of expected thermal maturities and temperatures were made using {sub BASINMOD}, a hydrocarbon generation/expulsion modeling package. The model predicted higher well temperatures (e,g., 225{degrees}F vs. 192{degrees}F) and lower vitrinite maturity (0.44% vs. 0.64%) than encountered in the well. Vitrinite reflectance equivalents of 0.41% and 0.43% were calculated from biomarker ratios of the Cretaceous core extracts, matching the {sub BASINMOD} predicted value of 0.44%.

  13. Cretaceous source rock characterization of the Atlantic Continental margin of Morocco

    SciTech Connect

    Jabour, H. )

    1993-02-01

    Characterization of the petroleum potential for the Atlantic margin of Morocco has been based primarily on limited, antiently acquired organic geochemical data. These indicate the area of drilling behind the paleoshelf edge to be only fair in organic carbon and C15+ extract values with predominantly terrestrial kerogen types. Recently acquired geochemical data obtained from relatively recent drilling both behind and beyond the paleoshelf edge indicate 4 depositional facies containing hydrogen rich amorphous kerogen assemblages. These are: (1) Lower to Mid Jurassic inner shelf facies probably deposited in algal rich lagoon-like, (2) Lower Cretaceous non marine coaly facies probably deposited in algal rich swamplike environments, (3) Middle Cretaceous facies characterized by restrited anoxic environment with sediments rich in marine kerogen types deposited under sluggish wather circulation, (4) Upper Cretaceous to Tertiary outer-shelf to Upper slope facies probably deposited under algal-rich upwelling systems. Of these, the Cretaceous facies is the most widespread and represents the best source rock potential characteristics. Correlation of these facies to recently acquired good quality seismic packages allows for extrapolation of probable organic facies distribution throughout the continental margin. This should enhance the hydrocarbon potential of the Mesozoic and Cenozoic sediments both landward and seaward of the paleoshelf edge and thus permits refinement of strategies for hydrocarbon exploration in the area.

  14. 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.

  15. Origin of crude oil in eastern Gulf Coast: Upper Jurassic, Upper Cretaceous, and lower Tertiary source rocks

    SciTech Connect

    Sassen, R.

    1988-02-01

    Analysis of rock and crude oil samples suggests that three source rocks have given rise to most crude oil in reservoirs of the eastern Gulf Coast. Carbonate source rocks of the Jurassic Smackover Formation are characterized by algal-derived kerogen preserved in an anoxic and hypersaline environment, resulting in crude oils with distinct compositions. Migration commenced during the Cretaceous, explaining the emplacement of Smackover-derived crude oil in Jurassic and in some Cretaceous reservoirs. Upper Cretaceous clastic and carbonate source rocks are also present. Much crude oil in Upper Cretaceous reservoirs has been derived from organic-rich marine shales of the Tuscaloosa Formation. These shales are characterized by algal and higher plant kerogen, resulting in distinct crude oil compositions. Migration commenced during the Tertiary, but was mostly focused to Upper Cretaceous reservoirs. Lower Tertiary shales, including those of the Wilcox Formation, are quite organic-rich and include downdip marine facies characterized by both algal and higher plant kerogen. Crude oils in lower Tertiary reservoirs are dissimilar to crude oils from deeper and older source rocks. Migration from lower Tertiary shales commenced during the late Tertiary and charged Tertiary reservoirs. Although most crude oil in the eastern Gulf Coast has been emplaced by short-range migration, often with a strong vertical component, some long-range lateral migration (> 100 km) has occurred along lower Tertiary sands. The framework of crude oil generation and migration onshore has important implications with respect to origin of crude oil in the Gulf of Mexico.

  16. Petroleum geochemistry of oil and gas from Barbados: Implications for distribution of Cretaceous source rocks and regional petroleum prospectivity

    USGS Publications Warehouse

    Hill, R.J.; Schenk, C.J.

    2005-01-01

    Petroleum produced from the Barbados accretionary prism (at Woodbourne Field on Barbados) is interpreted as generated from Cretaceous marine shale deposited under normal salinity and dysoxic conditions rather than from a Tertiary source rock as previously proposed. Barbados oils correlate with some oils from eastern Venezuela and Trinidad that are positively correlated to extracts from Upper Cretaceous La Luna-like source rocks. Three distinct groups of Barbados oils are recognized based on thermal maturity, suggesting petroleum generation occurred at multiple levels within the Barbados accretionary prism. Biodegradation is the most significant process affecting Barbados oils resulting in increased sulfur content and decreased API gravity. Barbados gases are interpreted as thermogenic, having been co-generated with oil, and show mixing with biogenic gas is limited. Gas biodegradation occurred in two samples collected from shallow reservoirs at the Woodbourne Field. The presence of Cretaceous source rocks within the Barbados accretionary prism suggests that greater petroleum potential exists regionally, and perhaps further southeast along the passive margin of South America. Likewise, confirmation of a Cretaceous source rock indicates petroleum potential exists within the Barbados accretionary prism in reservoirs that are deeper than those from Woodbourne Field.

  17. Hydrocarbon potential of Cretaceous sediments in the Lower and Middle Benue Trough, Nigeria: Insights from new source rock facies evaluation

    NASA Astrophysics Data System (ADS)

    Akande, Samuel O.; Egenhoff, Sven O.; Obaje, Nuhu G.; Ojo, Olusola J.; Adekeye, Olabisi A.; Erdtmann, Bernd D.

    2012-02-01

    The Nigerian Benue Trough is an intracratonic rift structure which evolution is related to the Early Cretaceous opening of the South Atlantic Ocean and the Gulf of Guinea. Previous hydrocarbon potential assessments of the successions in the trough revealed a number of organic rich intervals capable of yielding significant quantities of hydrocarbons in the Cretaceous sections. Stratigraphic continuity of these intervals suggests their potentials for hydrocarbons if thermally mature and both oil and gas can be generated. The present study have expanded on some previously reported source rock data of the Cretaceous formations in the Benue Trough by detailed mapping of the stratigraphic intervals with source rock potentials on the basis of their structural setting, lithologic characteristics, and depositional environments. Further characterization of the organic matter within the Cenomanian to Coniacian on one hand and the Campanian to Maastrichtian intervals were carried out to determine the geochemical character of the organic rich zones, their maturity and effectiveness to generate and expel hydrocarbons. In the Lower Benue Trough, mature facies of the Cenomanian to Turonian Eze-Aku Formation with a predominance of Types II and III kerogen, the Turonian to Coniacian Type III dominated Awgu Formation and the Type III dominated Lower Maastrichtian sub-bituminous coals of the Mamu Formation have proven potentials as oil and gas source rocks. In the Middle Benue Basin, the preserved mature intervals of the Awgu Formation shales and coals are good gas source rocks with some oil prone units in view of the predominating Type III kerogen. Targets for hydrocarbons generated by these source rock intervals should focus on the non-emergent Cretaceous reservoirs within the pre-Santonian successions whereas, the mature equivalents of the sub-bituminous coal facies would generate and charge both Upper Cretaceous reservoirs and possibly the sub-Niger Delta successions in the sub-surface.

  18. Petroleum source rock evaluations of the Cretaceous Newark Canyon Formation in north-central Nevada

    SciTech Connect

    Mullarkey, J.C.; Wendlandt, R.F. ); Clayton, J.L.; Daws, T.A. )

    1991-03-01

    The petroleum source rock potential of the Cretaceous Newark Canyon Formation, Eureka and Elko counties, Nevada, has been determined by integrated field and subsurface sampling and mapping and by geochemical analyses. Geologic mapping was supplemented by measurement of a reference stratigraphic section and four hand-held gamma-ray traverses. Cores and cuttings from three wells provide subsurface control. Sixty-six outcrop and ten subsurface Newark Canyon samples were collected and pyrolyzed (Rock-Eval II) to determine hydrocarbon yield, total organic carbon content (TOC), and thermal maturity. Two samples were solvent extracted for gas chromatography and mass spectrometry analyses to evaluate the environment of deposition. The Newark Canyon Formation is 2055 ft thick in the Cortez Range and contains 115 ft of limestone and calcareous shale with an average TOC of 2.5 weight % of type II/III kerogen (hydrogen indices 7-424 mg hydrocarbon/g TOC). The correlative section in the Pinon Range contains {approximately}200 ft of calcareous shale averaging 8% TOC (ranging up to 23.5%) of type I/II kerogen (hydrogen indices 457-912 mg hydrocarbon/g TOC). Subsurface samples are similar to the Cortez Range samples in organic content and kerogen type. The Newark Canyon Formation is marginally mature to mature with respect to petroleum generation (average T{sub max} values = {approximately}440C). This data indicates the Newark Canyon Formation is an excellent potential source rock. Saturated hydrocarbon distributions confirm field observations that indicate deposition of the Newark Canyon's organic-rich facies in a low-energy lacustrine environment.

  19. Potential petroleum source rock deposition in the middle Cretaceous Wasia Formation, Rub'Al Khali, Saudi Arabia

    SciTech Connect

    Newell, K.D.; Hennington, R.D.

    1983-03-01

    Stratigraphic correlation and regional geochemical sampling in the Rub'Al Khali (The Empty Quarter) of Saudi Arabia indicate at least two potential petroleum source rock units occur in the middle Cretaceous Wasia Formation. These two sequences, informally named the Safaniya ''source rock'' and the lower Mishrif, are dominated by oil-prone amorphous (Type II) organic matter, in places in excess of 10 weight percent organic carbon. Both units are fine-grained pelagic lime mudstones which were probably deposited in relatively quiet anoxic waters of large intraplatform embayments or basins. The Safaniya ''source rock'' and the lower Mishrif reflect strong marine transgressions on the Arabian craton in Albian to Cenomanian and Cenomanian to Turonian time, respectively. Regressive-phase sedimentary rocks overlying these two transgressive organic-rock phases are generally poor in organic carbon despite being deposited, in part, in similar forereef open-marine depositional settings. The sealevel high-stands associated with the Safaniya ''source rock'' and the lower Mishrif are partly synchronous with two recently described ''oceanic anoxic events'' respectively occurring in late Barremian to late Albian time and late Cenomanian to early Turonian time. Although there is a credible time correlation of these organic-rock units with oceanic anoxic events, their connection to oceanic anoxic events could be strengthened if they could be traced out to the vicinity of the middle Cretaceous continental margin.

  20. Lower Tertiary and Upper Cretaceous source rocks in Louisiana and Mississippi: Implications to Gulf of Mexico crude oil

    SciTech Connect

    Sassen, R. )

    1990-06-01

    The Lower Tertiary Sparta Formation, Wilcox Group, and the Midway Group in southern Louisiana include organic-rich source facies that generate crude oil at relatively high thermal maturities. The Wilcox Group is an important source of Wilcox crude oil, and regional kerogen variations explain two crude oil subfamilies. Wilcox crude oils in downdip areas of southern Louisiana migrated short distances, but long-range lateral migration (about 150 km) best explains Wilcox crude oils far updip from mature source rocks. Crude oils in Oligocene and younger reservoirs in southern Louisiana migrated vertically from deep lower Tertiary source rocks. Some crude oils in Upper Cretaceous Tuscaloosa reservoirs were emplaced by long-range lateral migration from Tuscaloosa source rocks. Given little evidence of upper Tertiary source rocks and the overmaturity problems of Mesozoic source rocks, most crude oils in upper Tertiary and Pleistocene reservoirs of the Gulf continental shelf are best explained by vertical migration from deep lower Tertiary source rocks. Even so, it is simplistic to assume an exclusive lower Tertiary origin. Many Tertiary and Pleistocene crude oils of this study probably include an overprint of high-maturity hydrocarbons from Mesozoic sources. 12 figs., 7 tabs.

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

    SciTech Connect

    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 interval 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.

  2. 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.

  3. Cretaceous source rock sedimentation and its relation to transgressive peaks and geodynamic events for the Central Tethys

    SciTech Connect

    Flexer, A. ); Honigstein, A.; Rosenfeld, A. ); Lipson, S. ); Tarnenbaum, E. )

    1993-02-01

    The reconstruction of the Mesozoic continents shows a wide triangle-shaped Tethys (or Neotethys) between Africa and Eurasia. The Arabian Craton comprised the central part of its southern margins. The Cretaceous period started with extension, volcanism, continued by accelerated divergence during Aptian-Turonian and terminated by convergence and folding. The sea level stand, after a major fall at the commencement, is characterized by a steady stepwise rise with some minor retreats. The global oceanic anoxic events correspond to large-extent transgressions and associated with organic rich sedimentation. The accelerated building up of mid-oceanic ridges is possibly connected to a mantle plume, active around 120-80 Ma. Sea level rise and sea floor spreading is felt mainly at these times in the passive southern margins of the central Tethys. The Senonian compressive tectonic regime transforms them into active margins (destruction of oceanic crust, obduction and thrusting); sea level highstands control dysoxic sedimentation. Dysoxic sediments were observed in the Gevaram shales (Tithonian-Hauterivian). Talme Yafe marls (Late Aptian-Albian), Daliyya Formation (latest Cenomanian-Turonian) and the Mount Scopus Group (Santonian-Maastrichtian). The organic matter in the Gevaram shales is mixed marine and terrestrial (2.6% TOC) and in the Daliyya marls mostly marine (2.5% TOC). Both units have source rock possibilities and yield petroleum upon appropriate burial. The Senonian bituminous rocks (oil shales) are rich in marine organic matter (20% TOC) and are excellent source rocks in the Dead Sea area.

  4. Warm Eocene climate enhanced petroleum generation from Cretaceous source rocks: A potential climate feedback mechanism?

    NASA Astrophysics Data System (ADS)

    Kroeger, K. F.; Funnell, R. H.

    2012-02-01

    Earth surface temperatures, including in the deep sea increased by 5-10°C from the late Paleocene ca. 58 Myr ago to the Early Eocene Climatic Optimum (EECO) centered at about 51 Myr ago. A large (˜2.5‰) drop in δ13C of carbonate spans much of this interval. This suggests a long-term increase in the net flux of 13C-depleted carbon to the ocean and atmosphere that is difficult to explain by changes in surficial carbon cycling alone. We reveal a relationship between surface temperature increase and increased petroleum generation in sedimentary basins operating on 100 kyr to Myr time scales. We propose that early Eocene warming has led to a synchronization of periods of maximum petroleum generation and enhanced generation in otherwise unproductive basins through extension of the volume of source rock within the oil and gas window across hundreds of sedimentary basins globally. Modelling the thermal evolution of four sedimentary basins in the southwest Pacific predicted an up to 50% increase in petroleum generation that would have significantly increased leakage of light hydrocarbons and oil degeneration products into the atmosphere. Extrapolating our modelling results to hundreds of sedimentary basins worldwide suggests that globally increased leakage could have caused a climate feedback effect, driving or enhancing early Eocene climate warming.

  5. Lead isotope compositions of Late Cretaceous and early Tertiary igneous rocks and sulfide minerals in Arizona: Implications for the sources of plutons and metals in porphyry copper deposits

    USGS Publications Warehouse

    Bouse, R.M.; Ruiz, J.; Titley, S.R.; Tosdal, R.M.; Wooden, J.L.

    1999-01-01

    Porphyry copper deposits in Arizona are genetically associated with Late Cretaceous and early Tertiary igneous complexes that consist of older intermediate volcanic rocks and younger intermediate to felsic intrusions. The igneous complexes and their associated porphyry copper deposits were emplaced into an Early Proterozoic basement characterized by different rocks, geologic histories, and isotopic compositions. Lead isotope compositions of the Proterozoic basement rocks define, from northwest to southeast, the Mojave, central Arizona, and southeastern Arizona provinces. Porphyry copper deposits are present in each Pb isotope province. Lead isotope compositions of Late Cretaceous and early Tertiary plutons, together with those of sulfide minerals in porphyry copper deposits and of Proterozoic country rocks, place important constraints on genesis of the magmatic suites and the porphyry copper deposits themselves. The range of age-corrected Pb isotope compositions of plutons in 12 Late Cretaceous and early Tertiary igneous complexes is 206Pb/204Pb = 17.34 to 22.66, 207Pb/204Pb = 15.43 to 15.96, and 208Pb/204Pb = 37.19 to 40.33. These Pb isotope compositions and calculated model Th/U are similar to those of the Proterozoic rocks in which the plutons were emplaced, thereby indicating that Pb in the younger rocks and ore deposits was inherited from the basement rocks and their sources. No Pb isotope differences distinguish Late Cretaceous and early Tertiary igneous complexes that contain large economic porphyry copper deposits from less rich or smaller deposits that have not been considered economic for mining. Lead isotope compositions of Late Cretaceous and early Tertiary plutons and sulfide minerals from 30 metallic mineral districts, furthermore, require that the southeastern Arizona Pb province be divided into two subprovinces. The northern subprovince has generally lower 206Pb/204Pb and higher model Th/U, and the southern subprovince has higher 206Pb/204Pb and

  6. Source rock potential in Pakistan

    SciTech Connect

    Raza, H.A. )

    1991-03-01

    Pakistan contains two sedimentary basins: Indus in the east and Balochistan in the west. The Indus basin has received sediments from precambrian until Recent, albeit with breaks. It has been producing hydrocarbons since 1914 from three main producing regions, namely, the Potwar, Sulaisman, and Kirthar. In the Potwar, oil has been discovered in Cambrian, Permian, Jurassic, and Tertiary rocks. Potential source rocks are identified in Infra-Cambrian, Permian, Paleocene, and Eocene successions, but Paleocene/Eocene Patala Formation seems to be the main source of most of the oil. In the Sulaiman, gas has been found in Cretaceous and Tertiary; condensate in Cretaceous rocks. Potential source rocks are indicated in Cretaceous, Paleocene, and Eocene successions. The Sembar Formation of Early Cretaceous age appears to be the source of gas. In the Kirthar, oil and gas have been discovered in Cretaceous and gas has been discovered in paleocene and Eocene rocks. Potential source rocks are identified in Kirthar and Ghazij formations of Eocene age in the western part. However, in the easter oil- and gas-producing Badin platform area, Union Texas has recognized the Sembar Formation of Early Cretaceous age as the only source of Cretaceous oil and gas. The Balochistan basin is part of an Early Tertiary arc-trench system. The basin is inadequately explored, and there is no oil or gas discovery so far. However, potential source rocks have been identified in Eocene, Oligocene, Miocene, and Pliocene successions based on geochemical analysis of surface samples. Mud volcanoes are present.

  7. Late Cretaceous source rocks of a section in the Eastern Venezuelan Basin

    SciTech Connect

    Truskowski, I.I. )

    1993-02-01

    Micropaleontological and geochemical studies of Querecual and San Antonio formations were carried on a section (Cerro Negro) of the Serrania del Interior, in order to establish the imprint of the late Cretaceous [open quotes]Oceanic Anoxic Events[close quotes] (OAE), mentioned by numerous authors. For this purpose, the distribution patterns of microfossil assemblages, variations of organic matter content and, V/Ni ratios have been taken into account to recognize anoxic conditions. This stratigraphic section is characterized by the following: [open quotes]Anaerobic[close quotes] bottom conditions with oxigenated surface waters, indicated by the presence of a well-developed planktonic forms and virtually no benthic foraminifera. These conditions fluctuated along the section, prevailing at its base. Dysaerobic bottom conditions indicated by a low-diversity benthic foraminifera and, a well oxigenated surface waters suggested by high concentration of planktonic biota (foraminifer, radiolaria, and nannoplankton). An increase of organic matter content (TOC: 5-6%) and V/Ni ratios (3.7-4.2) are related to the [open quotes]anaerobic[close quotes] levels. Marine sediments of Brazilian continental margin display similar characteristics, which indicate that deposition of anoxic sediments was extended to the North of South America.

  8. Sedimentary environments for the massive formation of the lacustrine organic rich petroleum source rocks of late Cretaceous from Songliao Basin, China

    NASA Astrophysics Data System (ADS)

    Zhiguang, S.

    2009-12-01

    Songliao Basin is the major oil-bearing and production basin in China and containing two major sets of excellent organic matter rich source rocks developed during the two related short periods of later Cretaceous time. For a long time, these source rocks were considered unquestionably being formed under fresh or brackish lacustrine environment. However, increasing evidence and studies suggest that this may be not the case anymore, as possible marine transgression and much high salinity lacustrine environment has been suggested or implied from a number of recent studies for Songliao Basin. Here, we show our recent extensive organic geochemical studies carried out on the core samples of Nenjiang formation from a newly drilled scientific exploration well of No. 1 in Songliao Basin. The overall evidence of organic matter and biomarkers suggest that: 1) the main source rocks were likely formed under a much saline(even mesosaline) lacustrine environment, as the existence of a number high saline related biomarkers and their ratios such Pr/Ph, MTTCI, α-MTTC/δ-MTTC, α-MTTC /γ-MTTC, Gammacerane/C30hop are in favor of a mesosaline to saline environments; 2) during the major source rocks formation periods, a photic zone oxygen depletion and stratified water column was suggested by the strong occurrence of a series of aryl isoprenoids and Isorenieratane; 3) a general mild to strong reduced sedimentary environments were concluded from the consistent of a number of index. Fig 1 Correlation between MTTCI vs Pr/Ph ratios with indication of salinity fields (after SCHWARK et al., 1998)

  9. Application of sequence stratigraphy to reservoir and hydrocarbon source rock prediction in the Cretaceous carbonate platforms of Maracaibo Basin, Venezuela

    SciTech Connect

    Murat, B.; Azpiritxaga, I. )

    1993-02-01

    Prediction of reservoir and source rocks is enhanced by an understanding of the sequential organization of the sedimentary units. In the Maracaibo Basin, the carbonate Cogollo Group and the basal part of the Shaly La Luna Formation (Upper Barremian to Lower Cenomanian) have been subdivided into a hierarchy of cycles ranging from parasequences (4th and 5th order) up to Regressive-Transgressive cycles (2nd order). Sedimentation during this period on a passive platform under the influence of eustatic sea level fluctuations, led to a succession of about twenty 3rd order sequences (depending on their location on the platform) composed of Transgressive Systems Tracts (TST) and Highstand Systems Tracts (HST). Their boundaries and maximum flooding surfaces can be traced on wireline logs and on cored material. These sequences belong to three Regressive-Transgressive 2nd order cycles showing a 3-stage evolution of infill, aggradation and backstepping. Sedimentary facies vary laterally within systems tracts and vertically from one cycle to another. Most basal TST units display high energy sediments prone to porosity development, whereas the basal HST units are generally characterized by muddier sediments. The best reservoirs are at the top of HST units, with development of both early dolomite and grainy packstones with moderate reservoir quality. Maximum oil productivity occurs where matrix porosity is associated with fractures, which are always best developed within the aggrading stage. Finally, source-rock intervals coincide with the maximum flooding surfaces which limit second order cycles.

  10. Organic facies variations, source rock potential, and sea level changes in Cretaceous black shales of the Quebrada Ocal, upper Magdalena Valley, Colombia

    SciTech Connect

    Mann, U.; Stein, R.

    1997-04-01

    A 290-m-thick middle Cretaceous black shale sequence in the upper Magdalena Valley, a present-day intramontane basin located between the Central and Eastern cordilleras of Colombia, was investigated with organic-geochemical and microscopic analyses. As a result of the investigation, we were able to (1) differentiate four organic facies types, (2) estimate their source rock potential, and (3) integrated these facies into a sequence stratigraphic framework. The four organic facies types were type C, BC, B, and D. Type C contains a district terrigenous organic matter component in lowstand or highstand deposits. Organic facies type BC is characterized by an increase and a better preservation of marine organic matter. BC belongs to the lower part of the transgressive systems tract. Sediments of organic facies type B have the highest amount of marine organic matter due to excellent preservation under anoxic conditions. The absence of bioturbation and the enrichment of trace metals are further implications for deposition under anoxic conditions. Facies type B is found in the upper part of the transgressive systems tract and contains the best petroleum source rock potential. Facies B occurrence coincides with sea level highstand and correlates especially with a maximum flooding in northern South America during the Turonian. Organic facies type D is also related to highstand deposits, but shows a high rate of reworking and degradation of organic matter.

  11. Groundwater from Lower Cretaceous rocks in Kansas

    USGS Publications Warehouse

    Keene, Katherine M.; Bayne, Charles Knight

    1976-01-01

    Sandstones in Lower Cretaceous rocks contain supplies, of water that may be adequate to meet increasing present and future demands for supplemental municipal and domestic use in central and western Kansas. An estimated 70 to 80 million acre-feet (86,000 to 99,000 cubic hectometers) of water containing less than 1,000 milligrams per liter dissolved solids may be acceptable for use at the present (1976). An additional 10 to 15 million acre-feet (12,000 to 18,000 cubic hectometers) containing 1,000 to 3,000 milligrams per liter dissolved solids is estimated to be available for use in the future with appropriate desalinization. Lower Cretaceous rocks crop out from Washington County on the north to Comanche County on-the south. The rocks dip from a structural high in the southwest part of the State to structural lows in the northwest and north-central part. Depth below land surface increases generally northwestward to about 2,600 feet (790 meters); thickness of the rocks increases westward, nearly zero to about 850 feet (260 meters). The rocks consist chiefly of marine to nonmarine shale and silt- stone interbedded with coastal to deltaic sandstone. The interbedded sandstone, which composes about one-third of the rocks, consists of one or more lenses that thicken westward to about 400 feet (120 meters) in the central part of western Kansas. The yield of water to individual wells is related to areal extent, thickness, and interconnection of the sand lenses and to grain size and cementation of the sand. Large amounts of water may be pumped by wells where loosely cemented sand lenses are interconnected. Wells commonly yield adequate supplies for domestic and stock use; reported yields from municipal and irrigation wells range from about 100 to 2,000 gallons per minute (6 to 125 liters per second). Recharge to the Lower Cretaceous-rocks occurs in the area of outcrop and from hydraulically connected saturated Cenozoic rocks, especially in the southern part of the State

  12. Late Cretaceous multicolored shales and phosphatic sedimentary rocks in Egypt

    SciTech Connect

    Glenn, C.R.; Garrison, R.E.; Arthur, M.A.

    1983-03-01

    Upper Cretaceous transitional fluvial to marine variegated shale (upper Nubia Formation) and the fully marine Duwi (phosphate) Formation occur as thin, widespread, shallow-marine deposits in an east-west-trending belt spanning the lower-middle latitudes of Egypt. On a larger scale, the phosphoritic rocks in Egypt represent but a small portion of a laterally extensive Middle Eastern-North African phosphogenic province of Upper Cretaceous-Lower Tertiary age that accounts for accumulation of minable marine phosphate in excess of 70 billion tons. Phosphorites, porcelanites/cherts, organic carbon-rich shales, glauconitic sandstones, and bioclastic and fine-grained carbonate rocks variously reflect major hemipelagic and shallow-water carbonate sedimentation. Biosiliceous hemipelagic deposits, now diagenetically altered to procelanite and chert, reflect low energy depositional conditions that were periodically interrupted by high energy, possibly storm-induced currents and/or down-slope redeposition. Both dark shales and porcelanites locally contain abundant organic matter and are commonly finely laminated. Porcelanites and black shales are phosphatic, containing phosphatic grains identical, morphologically and chemically, to those found in associated phosphorites, and are probably the source from which the phosphorites were derived. The organic carbon-rich shales of the Duwi Formation appear to be quite laterally extensive and may, depending on thermal maturity, represent potential hydrocarbon source rocks in other portions of the region (e.g., Western Desert, Gulf of Suez), where they are more deeply buried.

  13. Source rock potential of upper cretaceous marine shales in the Wind River Basin, Wyoming: Chapter 8 in Petroleum systems and geologic assessment of oil and gas resources in the Wind River Basin Province, Wyoming

    USGS Publications Warehouse

    Finn, Thomas M.

    2007-01-01

    /S3 ratios indicate that it is capable of generating both oil and gas. Maps showing the distribution of kerogen types and organic richness for the lower shaly member of the Cody Shale are similar to the Mowry and show that lower shaly member of the Cody is more organic rich and more oil-prone in the eastern part of the basin. Analyses of samples of the upper sandy member of the Cody Shale indicate that it has little or no potential as a source rock. Thermal maturity mapping based on vitrinite reflectance measurements in the coal-bearing post-Cody Upper Cretaceous and Paleocene rocks shows that Upper Cretaceous marine shales in the deeper parts of the Wind River Basin are thermally mature to overmature with respect to hydrocarbon generation.

  14. Well-log signatures of alluvial-lacustrine reservoirs and source rocks, Lagoa-Feia Formations, Lower Cretaceous, Campos Basin, offshore Brazil

    SciTech Connect

    Abrahao, D.; Warme, J.E.

    1988-01-01

    The Campos basin is situated in offshore southeastern Brazil. The Lagoa Feia is the basal formation in the stratigraphic sequence of the basin, and was deposited during rifting in an evolving complex of lakes of different sizes and chemical characteristics, overlying and closely associated with rift volcanism. The stratigraphic sequence is dominated by lacustrine limestones and shales (some of them organic-rich), and volcaniclastic conglomerates deposited on alluvial fans. The sequence is capped by marine evaporites. In the Lagoa Feia Formation, complex lithologies make reservoirs and source rocks unsuitable for conventional well-log interpretation. To solve this problem, cores were studied and the observed characteristics related to log responses. The results have been extended through the entire basin for other wells where those facies were not cored. The reservoir facies in the Lagoa Feia Formation are restricted to levels of pure pelecypod shells (''coquinas''). Resistivity, sonic, neutron, density, and gamma-ray logs were used in this work to show how petrophysical properties are derived for the unconventional reservoirs existing in this formation. The same suite of logs was used to develop methods to define geochemical characteristics where source rock data are sparse in the organic-rich lacustrine shales of the Lagoa Feia Formation. These shales are the main source rocks for all the oil discovered to date in the Campos basin.

  15. The overthrusted Zaza Terrane of middle Cretaceous over the North American continental carbonate rocks of upper Jurassic-Lower Cretaceous age - relationships to oil generation

    SciTech Connect

    Echevarria Rodriguez, G.; Castro, J.A.; Amaro, S.V.

    1996-08-01

    The Zaza Terrane is part of the Caribbean plate thrust over the southern edge of the North American basinal and platform carbonate rocks of upper Jurassic-Lower Cretaceous age. Zaza Terrane are volcanic and ophiolitic rocks of Cretaceous age. The ophiolites are mostly serpentines which behave as reservoirs and seals. All Cuban oil fields are either within Zaza Terrane or basinal carbonates underneath, or not far away to the north of the thrust contacts. It appears that the overthrusting of the Zaza Terrane caused the generation of oil in the basinal carbonate source rocks underneath, due to the increase of rock thickness which lowered the oil window to a deeper position and increased the geothermal gradient. Oil generation was after thrusting, during post-orogenic. API gravity of oil is light toward the south and heavy to very heavy to the north. Source rocks to the south are probably of terrigenous origin.

  16. Two Distinct Sets of Magma Sources in Cretaceous Rocks From Magnet Cove, Prairie Creek, and Other Igneous Centers of the Arkansas Alkaline Province, USA

    NASA Astrophysics Data System (ADS)

    Duke, G. I.; Carlson, R. W.; Eby, G. N.

    2008-12-01

    Two distinct sets of magma sources from the Arkansas alkaline province (~106-89 Ma) are revealed by Sr-Nd-Pb isotopic compositions of olivine lamproites vs. other alkalic rock types, including carbonatite, ijolite, lamprophyres, tephrite, malignite, jacupirangite, phonolite, trachyte, and latite. Isotopic compositions of diamond-bearing olivine lamproites from Prairie Creek and Dare Mine Knob point to Proterozoic lithosphere as an important source, and previous Re-Os isotopic data indicate derivation from subcontinental mantle lithosphere. Both sources were probably involved in lamproite generation. Magnet Cove carbonatites and other alkalic magmas were likely derived from an asthenospheric source. Lamproite samples are isotopically quite different from other rock types in Sr-Nd-Pb isotopic space. Although three lamproite samples from Prairie Creek have a large range of SiO2 contents (40-60 wt %), initial values of ɛNd (-10 to -13), 206Pb/204Pb (16.61-16.81), 207Pb/204Pb (15.34-15.36), and 208Pb/204Pb (36.57-36.76) are low and similar. Only 87Sr/86Sr(i) displays a wide range in the Prairie Creek lamproites (0.70627-0.70829). A fourth lamproite from Dare Mine Knob has the most negative ɛNd(i) of -19. Lamproite isotope values show a significant crustal component and isotopically overlap subalkalic rhyolites from the Black Hills (SD), which assimilated Proterozoic crust. Six samples of carbonatite, ijolite, and jacupirangite from Magnet Cove and Potash Sulphur Springs exhibit the most depleted Sr-Nd isotopic signatures of all samples. For these rock types, 87Sr/86Sr(i) is 0.70352 - 0.70396, and ɛNd(i) is +3.8 - +4.3. Eight other rock types have a narrow range of ɛNd(i) (+1.9 - +3.7), but a wide range of 87Sr/86Sr(i) (0.70424 - 0.70629). These 14 samples comprise a fairly tight cluster of Pb isotopic values: 206Pb/204Pb (18.22-19.23), 207Pb/204Pb (15.54-15.62), and 208Pb/204Pb (38.38-38.94), suggesting very little crustal assimilation. They are most similar to EM-2

  17. Diagenesis and burial history of nonmarine Upper Cretaceous rocks in the central Uinta Basin, Utah

    SciTech Connect

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

    1988-01-01

    Rocks of the Upper Cretaceous nonmarine undifferentiated Tuscher and Farrer Formations yield thermogenic gas and some oil from interbedded carbonaceous shales and coal beds. They are interbedded with low-permeability sandstones and formed in a complex fluvial system in the Western Interior foreland basin. Gas-prone source rocks are within the zone of catagenesis, and active hydrocarbon generation probably began about 30 Ma, following deposition of about 9,000 ft of Tertiary sediments during basin subsidence. The similarity between past and present-day geothermal gradients (1.6/degrees/F/100 ft) in the Wilkin Ridge well suggests that heat flow through the central part of the Uinta Basin has been relatively uniform from the Late Cretaceous to the present.

  18. 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.

  19. Aquifers in Cretaceous rocks of the central Coastal Plain of North Carolina

    USGS Publications Warehouse

    Winner, M.D.; Lyke, W.L.

    1989-01-01

    Aquifers in rocks of Cretaceous age are the major source of groundwater for public supplies in the central Coastal Plain. These aquifers consist of sand, gravel, and limestone beds of the Peedee, Black Creek, and the upper and lower Cape Fear aquifers, each separated by a confining unit composed of clay and silt beds. The aquifers and confining units (1) rest upon crystalline basement rocks; (2) dip and thicken to the east-southeast; and (3) are overlain by younger aquifers and confining units in deposits of Quaternary and Tertiary age. The top of the uppermost aquifer, the Peedee, ranges from 122 ft above to 595 ft below sea level. The maximum thickness of all aquifers and confining units in Cretaceous rocks is more than 1,600 ft. Aquifers and confining units were defined and correlated for this report using 125 geophysical logs and accompanying drillers ' logs, water level data, and water quality information regarding chloride concentrations in water. This analysis allowed the construction of seven hydrogeologic cross sections that depict the continuity of all the aquifers and confining units. These cross sections also show water levels and chloride concentrations in water from various test intervals and describe where chloride concentration in water exceeds 250 mg/L within each aquifer. Detailed maps of each Cretaceous aquifer show altitude of its top, thickness, areas of selected sand percentages, transition zones from fresh to saltwater, and the thickness of the confining unit.

  20. Stratigraphic relationships of Cretaceous and early Tertiary rocks of a part of northwestern San Juan basin

    USGS Publications Warehouse

    Baltz, Elmer Harold

    1953-01-01

    The Bridge Timber Mountain area in south-central La Plata County, southwestern Colorado lies mostly in the northwestern part of the Central San Juan Basin but contains a segment of the bounding Hogback 'monocline' and Four-Corners platform. The area contains rocks of late Cretaceous through early Eocene age, as well as Pliocene, Pleistocene, and Recent terrace and pediment gravels. The Pictured Cliffs sandstone of late Montana age is the latest marine formation present. Retreat of the Cretaceous seas from the area marked the beginning of Laramide orogenic activity and the earliest stages of deformation which produced the modern San Juan Basin. The Fruitland formation and Kirtland shale were deposited in brackish water and on coastal plains left by the retreating Cretaceous sea. Beds of the Farmington sandstone member and upper shale member of the Kirtland shale show evidence of a new source of sediments to the north or northeast distinct from the southwestern source area of older Cretaceous rocks. The McDermott 'formation', composed mainly of volcanic debris, is considered to be a local lower member of the Animas formation. Beds of the upper member of the Animas formation of Cretaceous and Paleocene age are considered to extend entirely across the area and into New Mexico. Overstep of higher sandstone and shale beds of the upper member across lower conglomeratic beds shows that folding on the Hogback 'monocline' began during deposition of the upper member. Beds of the upper member of the Animas formation grade laterally southward into Paleocene beds of the Nacimiento formation, but upper Nacimiento beds overstep folded beds of the Animas formation on the Hogback 'monocline' at the north end of Bridge Timber Mountain. The San Jose formation of Paleocene and Eocene age is conformable with the Nacimiento formation except at the north end of Bridge Timber Mountain where upper San Jose beds overstep all older tilted beds down to the Fruitland formation. The heavy

  1. Depositional relations of cretaceous and Lower Tertiary Rocks, Northeastern Alaska

    SciTech Connect

    Molenaar, C.M.

    1983-07-01

    Analysis of depositional environments, new paleontologic data, and analogy with depositional patterns observed in areas to the west all indicate the need for revision of Cretaceous and lower Tertiary stratigraphy in northeastern Alaska. In the Sadlerochit Mountains area of the Arctic National Wildlife Refuge, the northernderived (Ellesmerian), late Neocomian Kemik Sandstone Member and organic-rich pebble shale member of the Kongakut Formation unconformably overlie Jurassic and Triassic rocks. The unconformity, which is of midNeocomian age, is present throughout northernmost Alaska and passes southward into a conformable shelf sequence. After pebble shale deposition, the depositional pattern is simply one of progradational basin filling from a southern (Brookian) provenance. This pattern is represented in vertical sequence initially by deep-marine basinal deposits succeeded by prodelta slope shales, and ultimately by deltaic deposits that prograded to the east or northeast in a predictable fashion over most of the area.

  2. 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.

  3. Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

    NASA Astrophysics Data System (ADS)

    Shellnutt, J. G.; Lee, T.-Y.; Torng, P.-K.; Yang, C.-C.; Lee, Y.-H.

    2016-07-01

    Silicic volcanic rocks at Hadjer el Khamis, near Lake Chad, are considered to be an extension of the Cameroon volcanic line (CVL) but their petrogenetic association is uncertain. The silicic rocks are divided into peraluminous and peralkaline groups with both rock types chemically similar to within-plate granitoids. In situ U/Pb zircon dating yielded a mean 206Pb/238U age of 74.4 ± 1.3 Ma indicating the magmas erupted ˜10 million years before the next oldest CVL rocks (i.e., ˜66 Ma). The Sr isotopes (i.e., ISr = 0.7021-0.7037) show a relatively wide range but the Nd isotopes (i.e., 143Nd/144Ndi = 0.51268-0.51271) are uniform and indicate that the rocks were derived from a moderately depleted mantle source. Thermodynamic modeling shows that the silicic rocks likely formed by fractional crystallization of a mafic parental magma but that the peraluminous rocks were affected by low temperature alteration processes. The silicic rocks are more isotopically similar to Late Cretaceous basalts identified within the Late Cretaceous basins (i.e., 143Nd/144Ndi = 0.51245-0.51285) of Chad than the uncontaminated CVL rocks (i.e., 143Nd/144Ndi = 0.51270-0.51300). The age and isotopic compositions suggest the silicic volcanic rocks of the Lake Chad region are related to Late Cretaceous extensional volcanism in the Termit basin. It is unlikely that the silicic volcanic rocks are petrogenetically related to the CVL but it is possible that magmatism was structurally controlled by suture zones that formed during the opening of the Central Atlantic Ocean and/or the Pan-African Orogeny.

  4. Cretaceous pollen in Pliocene rocks: Implications for Pliocene climate in the southwestern United States

    NASA Astrophysics Data System (ADS)

    Farley Fleming, R.

    1994-09-01

    Pliocene rocks of the Imperial and Palm Spring Formations in southern California contain reworked Cretaceous pollen that helps determine the timing of erosion of Cretaceous rocks on the Colorado Plateau. The stratigraphic distribution of reworked pollen in the Imperial and Palm Spring Formations suggests that erosion of Cretaceous rocks in the southern part of the Colorado Plateau began by 4.5 Ma. Erosion of Cretaceous rocks in the northern part of the plateau began at 3.9 Ma. This erosional history indicates that rapid and extensive erosion of the Colorado Plateau occurred during the Pliocene and supports the hypothesis that much of the Grand Canyon was cut during the Pliocene, rather than earlier in the Tertiary. Rapid erosion and transport from the Colorado Plateau require the climate in that region during the Pliocene to have been significantly wetter than it is today.

  5. Major marine source rocks and stratigraphic cycles

    SciTech Connect

    Duval, B.C.

    1995-11-01

    The identification of continental encroachment cycles and subcycles by using sequence stratigraphy can assist explorationists in locating source rocks. The continental encroachment cycles are associated with the breakup of the supercontinents and fit a smooth long-term eustatic curve. They are first order, with a duration greater than 50 m.y., and are composed of transgressive and regressive phases inducing major changes in shoreline. The limit between the transgressive and regressive phases corresponds to a major downlap surface, and major marine source rocks are often found in association with this surface, particularly in the northern hemisphere. Potential {open_quotes}secondary{close_quotes} source rock intervals can also be sought by sequence stratigraphy because each continental encroachment cycle is composed of several subcycles, and the same configuration of a regressive forestepping phase overlying a transgressive backstepping phase also creates a downlap surface that may correspond with organic-rich intervals. The stratigraphic distribution of source rocks and related reserves fits reasonably well with continental encroachment cycles and subcycles. For instance, source rocks of Silurian, Upper Jurassic, and Middle-Upper Cretaceous are associated with eustatic highs and bear witness to this relationship. The recognition and mapping of such downlap surfaces is therefore a useful step to help map source rocks. The interpretation of sequence stratigraphy from regional seismic lines, properly calibrated with geochernical data whenever possible, can be of considerable help in the process. Several examples from around the world illustrate the power of the method: off-shore of eastern Venezuela, coastal basin of Angola, western Africa, the North Sea, south Algeria, and the North Caucasian trough.

  6. Volcanological, petrographical and geochemical characteristics of Late Cretaceous volcanic rocks around Borçka-Artvin region (NE Turkey)

    NASA Astrophysics Data System (ADS)

    Baser, Rasim; Aydin, Faruk; Oguz, Simge

    2015-04-01

    This study presents volcanological, petrographical and geochemical data for late Cretaceous volcanic rocks from the Borçka-Artvin region (NE Turkey) in order to investigate their origin and magmatic evolution. Based on the previous ages and recent field studies, the late Cretaceous time in the study area is characterized by two different bimodal volcanic periods. The first bimodal period of the late Cretaceous volcanism is mainly represented by mafic rock series (basaltic-basaltic andesitic pillow lavas and hyaloclastites) in the lower part, and felsic rock series (dacitic lavas, hyaloclastites, and pyrite-bearing tuffs) in the upper part. The second bimodal period of the late Cretaceous volcanism begins with mafic rock suites (basaltic-andesitic lavas and dikes-sills) and grades upward into felsic rock suites (biotite-bearing rhyolitic lavas and hyaloclastites), which are intercalated with hyaloclastites and red pelagic limestones. All volcano-sedimentary units are covered by Late Campanian-Paleocene clayey limestones and biomicrites with lesser calciturbidites. The mafic volcanic series of the study area, which comprise basaltic and andesitic rocks, generally show amygdaloidal and aphyric to porphyritic texture with phenocrysts of calcic to sodic plagioclase and augite in a hyalopilitic matrix of plag+cpx+mag. Zircon and magnetite are sometimes observed as accessory minerals, whereas chlorite, epidote and calcite are typical alteration products. On the other hand, the felsic volcanic series consisting of dacitic and rhyolitic rocks mostly display porphyritic and glomeroporphyritic textures 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 such as zircon, apatite and magnetite are common. Typical alteration products are sericite and clay minerals. Late Cretaceous Artvin-Borçka bimodal rock series generally display a

  7. Cretaceous pollen in Pliocene rocks: implications for Pliocene climate in the southwestern United States

    USGS Publications Warehouse

    Fleming, R.F.

    1994-01-01

    Pliocene rocks of the Imperial and Palm Spring Formations in southern California contain reworked Cretaceous pollen that helps determine the timing of erosion of Cretaceous rocks on the Colorado Plateau. The stratigraphic distribution of the pollen suggests that erosion of Cretaceous rocks in the southern part of the Colorado Plateau began by 4.5 Ma, and in the northern part of the plateau at 3.9 Ma. This erosional history indicates that rapid and extensive erosion of the Colorado Plateau occurred during the Pliocene and supports the hypothesis that much of the Grand Canyon was cut during the Pliocene, rather than earlier in the Tertiary. Rapid erosion and transport from the Colorado Plateau require the climate in that region during the Pliocene to have been significantly wetter than it is today. -from Author

  8. Depositional controls, distribution, and effectiveness of world's petroleum source rocks

    SciTech Connect

    Klemme, H.D.; Ulmishek, G.F.

    1989-03-01

    Six stratigraphic intervals representing one-third of Phanerozoic time contain source rocks that have provided more than 90% of the world's discovered oil and gas reserves (in barrels of oil equivalent). The six intervals include (1) Silurian (generated 9% of the world's reserves); (2) Upper Devonian-Tournaisian (8% of reserves); (3) Pennsylvanian-Lower Permian (8% of reserves); (4) Upper Jurassic (25% of reserves); (5) middle Cretaceous (29% of reserves); and (6) Oligocene-Miocene (12.5% of reserves). This uneven distribution of source rocks in time has no immediately obvious cyclicity, nor are the intervals exactly repeatable in the commonality of factors that controlled the formation of source rocks. In this study, source rocks of the six intervals have been mapped worldwide together with oil and gas reserves generated by these rocks. Analysis of the maps shows that the main factors affecting deposition of these source rocks and their spatial distribution and effectiveness in generating hydrocarbon reserves are geologic age, global and regional tectonics, paleogeography, climate, and biologic evolution. The effect of each of the factors on geologic setting and quality of source rocks has been analyzed. Compilation of data on maturation time for these source rocks demonstrated that the majority of discovered oil and gas is very young, more than 80% of the world's oil and gas reserves have been generated since Aptian time, and nearly half of the world's hydrocarbons have been generated and trapped since the Oligocene.

  9. 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

    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)

  10. Cretaceous rocks from southwestern Montana to southwestern Minnesota, northern Rocky Mountains, and Great Plains

    USGS Publications Warehouse

    Dyman, T.S.; Cobban, W.A.; Fox, J.E.; Hammond, R.H.; Nichols, D.J.; Perry, W.J.; Porter, K.W.; Rice, D.D.; Setterholm, D.R.; Shurr, G.W.; Tysdal, R.G.; Haley, J.C.; Campen, E.B.

    1994-01-01

    In Montana, Wyoming, North and South Dakota, and Minnesota, Cretaceous strata are preserved in the asymmetric Western Interior foreland basin. More than 5,200 m (17,000 ft) of Cretaceous strata are present in southwestern Montana, less than 300 m (1,000 ft) in eastern South Dakota. The asymmetry resulted from varying rates of subsidence due to tectonic and sediment loading. The strata consist primarily of sandstone, siltstone, mudstone, and shale. Conglomerate is locally abundant along the western margin, whereas carbonate is present in most areas of the eastern shelf. Sediment was deposited in both marine and nonmarine environments as the shoreline fluctuated during major tectonic and eustatic cycles.A discussion of Cretaceous strata from southwestern to east-central Montana, the Black Hills, eastern South Dakota, and southwestern Minnesota shows regional stratigraphy and facies relations, sequence, boundaries, and biostratigraphic and radiometric correlations. The thick Cretaceous strata in southwestern Montana typify nonmarine facies of the rapidly subsiding westernmost part of the basin. These strata include more than 3,000 m (10,000 ft) of synorogenic conglomerate of the Upper Cretaceous part of the Beaverhead Group. West of the Madison Range, sequence boundaries bracket the Kootenai (Aptian and Albian), the Blackleaf (Albian and Cenomanian), and the Frontier Formations (Cenomanian and Turonian); sequence boundaries are difficult to recognize because the rocks are dominantly non-marine. Cretaceous strata in east-central Montana (about 1,371 m; 4,500 ft thick) lie at the approximate depositional axis of the basin and are mostly marine terrigenous rocks. Chert-pebble zones in these rocks reflect stratigraphic breaks that may correlate with sequence boundaries to the east and west. Cretaceous rocks of the Black Hills region consist of a predominantly marine clastic sequence averaging approximately 1,524 m (5,000 ft) thick. The Cretaceous System in eastern South

  11. Early Cretaceous bimodal volcanic rocks in the southern Lhasa terrane, south Tibet: Age, petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Ding, Lin; Liu, Zhi-Chao; Zhang, Li-Yun; Yue, Ya-Hui

    2017-01-01

    Limited geochronological and geochemical data from Early Cretaceous igneous rocks of the Gangdese Belt have resulted in a dispute regarding the subduction history of Neo-Tethyan Ocean. To approach this issue, we performed detailed in-situ zircon U-Pb and Hf isotopic, whole-rock elemental and Sr-Nd isotopic analyses on Late Mesozoic volcanic rocks exposed in the Liqiongda area, southern Lhasa terrane. These volcanic rocks are calc-alkaline series, dominated by basalts, basaltic andesites, and subordinate rhyolites, with a bimodal suite. The LA-ICPMS zircon U-Pb dating results of the basaltic andesites and rhyolites indicate that these volcanic rocks erupted during the Early Cretaceous (137-130 Ma). The basaltic rocks are high-alumina (average > 17 wt.%), enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs), showing subduction-related characteristics. They display highly positive zircon εHf(t) values (+ 10.0 to + 16.3) and whole-rock εNd(t) values (+ 5.38 to + 7.47). The silicic suite is characterized by low Al2O3 (< 15.4 wt.%), Mg# (< 40), and TiO2 (< 0.3 wt.%) abundances; enriched and variable concentrations of LILEs and REEs; and strongly negative Eu anomalies (Eu/Eu* = 0.08-0.19), as well as depleted Hf isotopic compositions (εHf(t) = + 4.9 to + 16.4) and Nd isotopic compositions (εNd(t) = + 5.26 to + 6.71). Consequently, we envision a process of basaltic magmas similar to that of MORB extracted from a source metasomatized by slab-derived components for the petrogenesis of mafic rocks, whereas the subsequent mafic magma underplating triggered partial melting of the juvenile crust to generate acidic magma. Our results confirm the presence of Early Cretaceous volcanism in the southern Lhasa terrane. Combined with the distribution of the contemporary magmatism, deformation style, and sedimentary characteristics in the Lhasa terrane, we favor the suggestion that the Neo

  12. Source rocks of the Sub-Andean basins

    SciTech Connect

    Raedeke, L.D. )

    1993-02-01

    Seven source rock systems were mapped using a consistent methodology to allow basin comparison from Trinidad to southern Chile. Silurian and Devonian systems, deposited in passive margin and intracratonic settings, have fair-good original oil/gas potential from central and northern Bolivia to southern Peru. Kerogens range from mature in the foreland to overmature in the thrust belt. Permian to Carboniferous deposition in local restricted basins formed organic-rich shales and carbonates with very good original oil/gas potential, principally in northern Bolivia and southern Peru. Late Triassic to early Jurassic marine shales and limestones, deposited in deep, narrow, basins from Ecuador to north-central maturity. Locally, in the Cuyo rift basin of northern Argentina, a Triassic lacustrine unit is a very good, mature oil source. Early Cretaceous to Jurassic marine incursions into the back-arc basins of Chile-Argentina deposited shales and limestones. Although time transgressive (younging to the south), this system is the principal source in southern back-arc basins, with best potential in Neuquen, where three intervals are stacked A late Cretaceous marine transgressive shale is the most important source in northern South America. The unit includes the La Luna and equivalents extending from Trinidad through Venezuela, Colombia, Ecuador, and into northern Peru. Elsewhere in South America upper Cretaceous marine-lacustrine rocks are a possible source in the Altiplano and Northwest basins of Bolivia and Argentina. Middle Miocene to Oligocene source system includes shallow marine, deltaic, and lacustrine sediments from Trinidad to northern Peru.

  13. Relative contribution of Precambrian metamorphic rocks and Cretaceous-Tertiary igneous rocks to Oligocene and Holocene fluvial sands and the unroofing of a magmatic arc

    SciTech Connect

    Molinaroli, E.; Basu, A. )

    1991-03-01

    Oligocene and Holocene fluvial sands were deposited in small extensional basins in a magmatic arc in southwestern Montana under relatively humid and semi-arid conditions, respectively. The source rocks are roof-pendants and thrust-slices of Precambrian metamorphic rocks (PCM) and Cretaceous-Tertiary igneous rocks (KTI) that make up the arc. The authors have surveyed 143,607 heavy mineral grains (HMGs) in polished thin sections of 55 samples collected from adjacent but discrete geomorphologic units. In the Holocene sands, of 5440 HMGs 519 are garnets and of 97,667 HMGs 395 are zircons. In the Oligocene sandstones, of 6397 HMGs 998 are garnets, and of 45,940 HMGs 331 are zircons. Garnets are absent in the igneous rocks and zircons are extremely rare in the metamorphic rocks. Garnets ar estimated to be about 100 times as abundant in the metamorphic rocks as the zircons are in the igneous rocks. Mass balance calculations show that the proportion of PCM/(PCM+KTI) ranges from 0 to 21% in Oligocene sandstones, and from 3 to 76% in Holocene sands in different local units. However, the overall PCM/(PCM+KTI) proportions in the Holocene and the Oligocene sands in southwestern Montana are 19% and 18%, respectively. This suggests that the roof pendants, thrust slices, and magmatic arc rocks have been unroofed in constant proportions since the Oligocene although locally the proportions have been different.

  14. Characterization of the source horizons within the Late Cretaceous transgressive sequence of northeast Africa

    SciTech Connect

    Robinson, V. ); Engel, M. )

    1991-03-01

    Source rocks were deposited in northeastern Africa during a major Late Cretaceous transgression. The preserved stratigraphic sequence begins with a series of fluvio-deltaic sands and progresses up into a thick marine carbonate section. These deposits represent ever increasing water depths and isolation from the continental landmass. Across northeast Africa and portions of Arabia, oil-prone source facies were deposited along the mid to outer shelf during the initial phases of this Late Cretaceous transgression. Within the source sequence itself, variations in the organic matter record the changing influences of coastal upwelling, development of anoxia, and terrigenous input. In Egypt, the transgression deposited sediments found today in the upper portion of the Nubian through Thebes formations. The source facies found within this sequence include portions of the Duwi and Dakhla formations. Both the Duwi and Dakhla record changes in salinity, depth of the water column, and oxygen concentration, which are depicted in the organic matter content, quality, and type. The variability observed in the source sequence in Egypt can be related to the Late Cretaceous source facies preserved across northeast Africa.

  15. A review of magnetic stratigraphy investigations in Cretaceous pelagic carbonate rocks

    NASA Astrophysics Data System (ADS)

    Lowrie, W.; Channell, J. E. T.; Alvarez, W.

    1980-07-01

    Pelagic carbonate rocks possess many suitable characteristics for paleomagnetic and magnetostratigraphic studies. Paleomagnetic results are summarized for seven lengthy sections of pelagic limestones and marls from Umbria and the southern Alps in Italy. Differences in apparent polar wander paths from these two regions are interpreted in terms of tectonic rotation of allochthonous Umbria. The magnetic stratigraphies of the paleontologically dated sections are independent of their tectonic differences and are combined to form a continuous record of geomagnetic polarity for the Barremian through Maastrichtian stages of the Cretaceous. All but one of the reversals in these sections are confirmed by duplication in at least one other section. Additional Cretaceous reversals have been reported in other land sections and in DSDP (Deep Sea Drilling Project) and IPOD (International Program of Ocean Drilling) cores. Some of these reversals are not defined well magnetically, and confirmation of others is clouded by imprecise paleontological dates. If real, they are probably of short duration. The confirmed reversal sequence correlates well with the Cretaceous oceanic magnetic anomaly sequence. The ages of certain key anomalies are altered: Late Cretaceous anomalies 29-34 are younger, and Early Cretaceous anomalies M0 and M1 are older than previously thought. The longer duration of the Cretaceous magnetic quiet interval of normal polarity results in a reduction of corresponding sea floor spreading rates to about 70% of earlier values, but they are still appreciably higher than during formation of the preceding M sequence anomalies.

  16. Structural controls on source rock distribution and maturation in southeast Turkey

    SciTech Connect

    Reed, J.D.; Ottensman, V.V.; Cushing, G.W. ); Aytuna, S. )

    1990-05-01

    Production from the western part of the Zagros fold and thrust belt southeastern Turkey is characterized by high-sulfur (2-3%) oils from middle Cretaceous Mardin Formation. The oils are generated from two carbonate sources, one from the middle Cretaceous passive margin sequence and one deposited as a part of the Upper Cretaceous foreland basin sequence. Both sources are associated with transgressive events coincident with two recognized Cretaceous oceanic anoxic events in Cenomanian-Turonian and Coniacian-Santonian. Geochemical markers in the oils substantiate the restricted, anoxic conditions characteristic of their source rock deposition. During the Upper Cretaceous compressional event, horsts formed buttresses to advancing oceanic thrust sheets. The oceanic thrust sheets consisted of the Karadut and Kocali formations, oceanic equivalents of the Mesozoic shelf. The middle and Upper Cretaceous source facies were rapidly and deeply buried by the tectonically thickened thrust sheets adjacent to the buttresses. Thick burial by the oceanic rocks was critical for thermal maturation of the sources. Geohistory modeling shows generation occurred during the Tertiary coincidental with tectonic activity that probably allowed oil migration to occur along new or reactivated Cretaceous faults.

  17. Regional stratigraphic cross sections of Cretaceous rocks from east-central Arizona to the Oklahoma Panhandle

    USGS Publications Warehouse

    Molenaar, C.M.; Cobban, W.A.; Merewether, E.A.; Pillmore, C.L.; Wolfe, D.G.; Holbrook, J.M.

    2002-01-01

    Sedimentary rocks of Cretaceous age along Transect DD'' in eastern Arizona, northern New Mexico, southern Colorado, and western Oklahoma consist mainly of sandstone, siltstone, shale, limestone, and bentonite. They accumulated as sediments in continental, nearshore marine, and offshore marine environments on the west side of a north-trending epicontinental sea. The rocks record intermittent deposition and erosion as well as regional and local subsidence and uplift possibly beginning in Aptian time (about 121-112 Ma) and occurring in Albian through Maastrichtian time (about 112-65.4 Ma). Most of the Lower Cretaceous (Berriasian through Aptian, 142-112 Ma) in this transect is represented by a basal unconformity. The Cretaceous rocks and unconformities along the transect are depicted on the attached lithostratigraphic cross sections (sheets 1 and 2); one extending from the Mogollon Rim in eastern Arizona to Pagosa Springs in southwestern Colorado and the other from Pagosa Springs, Colorado, to Kenton in western Oklahoma. The same rocks and unconformities are also represented on the attached chronostratigraphic profile (sheet 3), which was prepared mainly from surface and subsurface data shown on the lithostratigraphic cross sections.

  18. Stratigraphy and paleontology of Mid-Cretaceous rocks in Minnesota and contiguous areas

    USGS Publications Warehouse

    Cobban, William Aubrey; Merewether, E.A.

    1983-01-01

    PART A: Molluscan fossils are locally abundant at outcrops of Upper Cretaceous rocks in eastern North and South Dakota, northeastern Nebraska, northwestern Iowa, and western and northern Minnesota. Other Cretaceous mollusks have been found in the glacial deposits in Minnesota, Iowa, and Illinois. The oldest well dated marine mollusks are of earliest late Cenomanian age and occur in northwestern Iowa. Mollusks of marginal marine and nonmarine environments in northwestern Iowa and south-central Minnesota are probably of slightly younger late Cenomanian age. The youngest mollusks treated in this report are bivalves of Santonian age found in the Niobrara Formation in eastern North and South Dakota. The collections indicate the presence or former presence of the following ammonite zones in the northeastern part of the Western Interior seaway: Santonian: Scaphites depressus-Clioscaphites choteauensis Coniacian: Scaphites uentrocosus; Scaphites preuentricosus Turonian: Scaphites coruensis; Scaphites whitfieldi; Prionocyclus hyatti; Subprionocyclus percarinatus; Collignoniceras woollgari; Watinoceras coloradoense Cenomanian: Dunueganoceras albertense; Dunueganoceras pondi PART B: Sedimentary rocks of early Late Cretaceous age occur in the eastern parts of North Dakota, South Dakota, and Nebraska, and in Minnesota and western Iowa. They are generally included in, from oldest to youngest, the Dakota Formation, Graneros Shale, Greenhorn Formation, Carlile Shale, and Niobrara Formation. However, in eastern North Dakota, they are also assigned to, in ascending order, the Belle Fourche Shale, Greenhorn Formation, Carlile Shale, and Niobrara Formation. The Graneros Shale and laterally equivalent strata in the Belle Fourche Shale grade eastward into the Coleraine Formation of northeastern Minnesota and probably into the Windrow Formation of southeastern Minnesota. Cretaceous beds locally overlie rocks of Precambrian, Paleozoic, and Jurassic ages, and they are generally overlain by

  19. Composition and provenance of placer deposits in McCourt Tongue of Rock Springs Formation (Upper Cretaceous), Rock Springs uplift area, Wyoming

    SciTech Connect

    Schneider, G.B.

    1986-08-01

    Heavy minerals from placer sandstones were studied from samples collected at five widely spaced outcrops of the McCourt Tongue on the southeastern flank of the Rock Springs uplift and on the northern flank of the Uinta Mountains. The placers were deposited along a northeast-trending, strand-plain shoreline of the Cretaceous Interior seaway. Heavy minerals from the five localities occur in very fine-grained sandstone and are composed of about 85% opaque iron and titanium minerals, including magnetite, hematite, and ilmenite. About 15% consist of nonopaque minerals, which are mostly zircon, garnet, tourmaline, and rutile with minor amounts of sphene, hornblende, and apatite. The cementing material is mostly hematite. The nonopaque suite is as much as 96% zircon grains, with 3/sup 0/ of roundness and five color varieties. The heavy minerals are from both plutonic and volcanic source areas. The plutonic minerals suggest a westerly source in Precambrian rocks of Utah and Idaho. The volcanic minerals were probably derived from areas of volcanic activity in Alberta and Montana. The composition, distribution, and provenance of the deposits help establish a framework for regressive Upper Cretaceous shorelines in the central Rocky Mountain area.

  20. New ichnological, paleobotanical and detrital zircon data from an unnamed rock unit in Yukon-Charley Rivers National Preserve (Cretaceous: Alaska): Stratigraphic implications for the region

    USGS Publications Warehouse

    Fiorillo, Anthony R.; Fanti, Federico; Hults, Chad; Hasiotis, Stephen T

    2014-01-01

    A paleontological reconnaissance survey on Cretaceous and Paleogene terrestrial units along the Yukon River drainage through much of east-central Alaska has provided new chronostratigraphic constraints, paleoclimatological data, and the first information on local biodiversity within an ancient, high-latitude ecosystem. The studied unnamed rock unit is most notable for its historic economic gold placer deposits, but our survey documents its relevance as a source rock for Mesozoic terrestrial vertebrates, invertebrates, and associated flora. Specifically, new U-Pb ages from detrital zircons combined with ichnological data are indicative of a Late Cretaceous age for at least the lower section of the studied rock unit, previously considered to be representative of nearly exclusively Paleogene deposition. Further, the results of our survey show that this sedimentary rock unit preserves the first record of dinosaurs in the vast east-central Alaska region. Lastly, paleobotanical data, when compared to correlative rock units, support previous interpretations that the Late Cretaceous continental ecosystem of Alaska was heterogeneous in nature and seasonal.

  1. SHRIMP U-Pb dating and geochemistry of the Cretaceous plutonic rocks in the Korean Peninsula: A new tectonic model of the Cretaceous Korean Peninsula

    NASA Astrophysics Data System (ADS)

    Kim, Sung Won; Kwon, Sanghoon; Park, Seung-Ik; Lee, Changyeol; Cho, Deung-Lyong; Lee, Hong-Jin; Ko, Kyoungtae; Kim, Sook Ju

    2016-10-01

    The Cretaceous tectonomagmatism of the Korean Peninsula was examined based on geochemical and geochronological data of the Cretaceous plutonic rocks, along with distribution of volcano-sedimentary nonmarine N- to NE-trending fault bounded sedimentary basins. We conducted sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages and whole-rock geochemical compositions of 21 Cretaceous plutonic rocks, together with previously published data, from the central to southern Korean Peninsula. Four age groups of plutonic rocks were identified: Group I (ca. 119-106 Ma) in the northern to central area, Group II (ca. 99-87 Ma) in the central southern area, Group III (ca. 85-82 Ma) in the central to southern area, and Group IV (ca. 76-67 Ma) in the southernmost area. These results indicate a sporadic trenchward-younging trend of the Cretaceous magmatism in the Korean Peninsula. The Group I, II, and III rocks are dominated by high-K calc-alkaline I-type rocks with rift-related A-type granitoids. In contrast, the Group IV rocks are high-K calc-alkaline I-type plutonic rocks with no A-type rocks. The geochemical signatures of the entire groups indicated LREEs (light rare earth elements) enrichments and negative Nb, Ta, and Ti anomalies, indicating normal arc magmatism. A new tectonic model of the Cretaceous Korean Peninsula was proposed based on temporal and spatial distribution of the Cretaceous plutons represented by four age groups; 1) magmatic quiescence throughout the Korean Peninsula from ca. 160 to 120 Ma, 2) intrusions of the I- and A-type granitoids in the northern and central Korean Peninsula (Group I plutonic rocks from ca. 120 to 100 Ma) resulted from the partial melting of the lower continental crust due to the rollback of the Izanagi plate expressed as the conversion from flat-lying subduction to normal subduction. The Gyeongsang nonmarine sedimentary rift basin in the Korean Peninsula and adakite magmatism preserved in the present-day Japanese Islands

  2. Upper Jurassic to Lower Cretaceous(?) synorogenic sedimentary rocks in the southern Spring Mountains, Nevada

    NASA Astrophysics Data System (ADS)

    Carr, Michael D.

    1980-08-01

    A newly recognized sequence of Upper Jurassic to Lower Cretaceous(?) terrigenous rocks in the Good-springs district, Nevada, was deposited during the emplacement of the Contact thrust plate. Two facies are recognized: (1) interbedded conglomerate and sandstone derived from Mesozoic igneous and terrigenous platform rocks and (2) interbedded carbonate and sandstone-clast conglomerate, quartz sandstone, and red shale. No igneous detritus occurs in the facies with carbonate-clast conglomerate. Carbonate clasts could only have been derived from the Paleozoic carbonate sequence, which was exposed in the area by latest Jurassic to earliest Cretaceous thrusting. The age of rocks from a volcanic unit within the synorogenic sequence was determined radiometrically to be 150 ± 10 m.y. (K-Ar on biotite). The sequence was deposited disconformably on deeply eroded rocks of the early Mesozoic platform and ultimately overridden from the west by the Contact thrust plate. Information from the sequence corroborates previously reported regional data regarding the timing and nature of the Contact-Red Springs thrust event. *Present address: U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025

  3. Hydrocarbon transfer pathways from Smackover source rocks to younger reservoir traps in the Monroe gas field, NE Louisiana

    SciTech Connect

    Zimmerman, R.K. )

    1993-09-01

    The Monroe gas field contained more than 7 tcf of gas in its virgin state. Much of the original gas reserves have been produced through wells penetrating the Upper Cretaceous Monroe Gas Rock Formation reservoir. Other secondary reservoirs in the field area are Eocene Wilcox, the Upper Cretaceous Arkadelphia, Nacatoch, Ozan, Lower Cretaceous, Hosston, Jurassic Schuler, and Smackover. As producing zones, these secondary producing zones reservoirs have contributed an insignificant amount gas to the field. The source of much of this gas appears to have been in the lower part of the Jurassic Smackover Formation. Maturation and migration of the hydrocarbons from a Smackover source into Upper Cretaceous traps was enhanced and helped by igneous activity, and wrench faults/unconformity conduits, respectively. are present in the pre-Paleocene section. Hydrocarbon transfer pathways appear to be more vertically direct in the Jurassic and Lower Cretaceous section than the complex pattern present in the Upper Cretaceous section.

  4. Hydrogeology of aquifers in Cretaceous and younger rocks in the vicinity of Onslow and southern Jones counties, North Carolina

    USGS Publications Warehouse

    Lyke, W.L.; Winner, M.D.

    1990-01-01

    Unconsolidated sediments in Onslow and Jones Counties, North Carolina overlie crystalline basement rocks and range in thickness from about 700 ft to more than 1,800 ft, thickening toward the east. This material is composed of permeable sand and limestone interlayered with relatively impermeable clay and silt beds. Sediments are divided into two groups: aquifers in Quaternary-, and Tertiary-aged rocks and aquifers in Cretaceous-aged rocks. Aquifers in the Cretaceous rocks provide most of the groundwater for public supplies and are the focus of this report. The aquifers in Cretaceous rocks are the Peedee, Black Creek, upper Cape Fear, and lower Cape Fear aquifers, which are composed of beds or groups of beds of sand and gravel. Each aquifer is overlain by a clay and silt bed, that impedes the flow of water between aquifers. The thickness of Cretaceous hydrogeologic units ranges from about 700 ft to more than 1, 300 ft. Hydrogeologic units are correlated using 60 geophysical logs and accompanying drillers ' logs along with water level and water quality data. Three hydrogeologic sections demonstrate the continuity of the aquifers and confining units, show water levels and chloride concentration in water from test intervals, and delineate where chloride concentration in water exceeds 250 mg/L within each aquifer. Maps of each aquifer in Cretaceous rocks show altitude of its top, thickness, sand percentage, and the transition from freshwater to saltwater. Maps of the confining units show thickness and sand percentage of each.

  5. Source-rock distribution model of the periadriatic region

    SciTech Connect

    Zappaterra, E. )

    1994-03-01

    The Periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic-sedimentary cycles. Tectonic evolution progressed from a Triassic-Early Jurassic (Liassic) continental rifting stage on the northern edge of the African craton, through an Early Jurassic (Middle Liassic)-Late Cretaceous/Eocene oceanic rifting stage and passive margin formation, to a final continental collision and active margin deformation stage in the Late Cretaceous/Eocene to Holocene. Extensive shallow-water carbonate platform deposits covered large parts of the Periadriatic region in the Late Triassic. Platform breakup and development of a platform-to-basin carbonate shelf morphology began in the Late Triassic and extended through the Cretaceous. On the basis of this paleogeographic evolution, the regional geology of the Periadriatic region can be expressed in terms of three main Upper Triassic-Paleogene sedimentary sequences: (A), the platform sequence; (B), the platform to basin sequence; and (C), the basin sequence. These sequences developed during the initial rifting and subsequent passive-margin formation tectonic stages. The principal Triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the Periadriatic region are associated with sequence B areas. No major hydrocarbon accumulations can be directly attributed to the Jurassic-Cretaceous epioceanic and intraplatform source rock sequences. The third episode of source bed deposition characterizes the final active margin deformation stage and is represented by Upper Tertiary organic-rich terrigenous units, mostly gas-prone. These are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the Periadriatic region. 82 refs., 11 figs., 2 tabs.

  6. Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska

    USGS Publications Warehouse

    Bundtzen, Thomas K.; Miller, Marti L.; Goldfarb, Richard J.; Miller, Lance D.

    1997-01-01

    Placer gold and precious metal-bearing lode deposits of southwestern Alaska lie within a region 550 by 350 km, herein referred to as the Kuskokwim mineral belt. This mineral belt has yielded 100,240 kg (3.22 Moz) of gold, 12, 813 kg (412,000 oz) of silver, 1,377,412 kg (39,960 flasks) of mercury, and modest amounts of antimony and tungsten derived primarily from the late Cretaceous-early Tertiary igneous complexes of four major types: (1) alkali-calcic, comagmatic volcanic-plutonic complexes and isolated plutons, (2) calc-alkaline, meta-aluminous reduced plutons, (3) peraluminous alaskite or granite-porphyry sills and dike swarms, and (4) andesite-rhyolite subaerial volcanic rocks.About 80 percent of the 77 to 52 Ma intrusive and volcanic rocks intrude or overlie the middle to Upper Cretaceous Kuskokwim Group sedimentary and volcanic rocks, as well as the Paleozoic-Mesozoic rocks of the Nixon Fork, Innoko, Goodnews, and Ruby preaccretionary terranes.The major precious metal-bearing deposit types related to Late Cretaceous-early Tertiary igneous complexes of the Kuskokwim mineral belt are subdivided as follows: (1) plutonic-hosted copper-gold polymetallic stockwork, skarn, and vein deposits, (2) peraluminous granite-porphory-hosted gold polymetallic deposits, (3) plutonic-related, boron-enriched silver-tin polymetallic breccia pipes and replacement deposits, (4) gold and silver mineralization in epithermal systems, and (5) gold polymetallic heavy mineral placer deposits. Ten deposits genetically related to Late Cretaceous-early Tertiary intrusions contain minimum, inferred reserves amounting to 162,572 kg (5.23 Moz) of gold, 201,015 kg (6.46 Moz) silver, 12,160 metric tons (t) of tin, and 28,088 t of copper.The lodes occur in veins, stockworks, breccia pipes, and replacement deposits that formed in epithermal to mesothermal temperature-pressure conditions. Fluid inclusion, isotopic age, mineral assemblage, alteration assemblage, and structural data indicate that

  7. Stratigraphic framework of Lower and Upper Cretaceous rocks in central and eastern Montana

    USGS Publications Warehouse

    Condon, Steven M.

    2000-01-01

    This study shows the lithology, thickness, distribution, and correlation of Lower and Upper Cretaceous rocks in central and eastern Montana. The described stratigraphic units range from the Aptian Kootenai Formation (oldest) to the Maastrichtian Hell Creek Formation (youngest). An included text report describes the units, and most formations or members are also represented by isopach maps. Structure contour maps of three horizons are also included. Correlations across the study area are shown on a series of cross sections. All text and illustrations are included as Adobe PDF files.

  8. Cretaceous plutonic rocks in the Donner Lake-Cisco Grove area, northern Sierra Nevada, California

    USGS Publications Warehouse

    Kulow, Matthew J.; Hanson, Richard E.; Girty, Gary H.; Girty, Melissa S.; Harwood, David S.

    1998-01-01

    The northernmost occurrences of extensive, glaciated exposures of the Sierra Nevada batholith occur in the Donner Lake-Cisco Grove area of the northern Sierra Nevada. The plutonic rocks in this area, which are termed here the Castle Valley plutonic assemblage, crop out over an area of 225 km2 and for the most part are shown as a single undifferentiated mass on previously published geological maps. In the present work, the plutonic assemblage is divided into eight separate intrusive units or lithodemes, two of which each consist of two separate plutons. Compositions are dominantly granodiorite and tonalite, but diorite and granite form small plutons in places. Spectacular examples of comb layering and orbicular texture occur in the diorites. U-Pb zircon ages have been obtained for all but one of the main units and range from ~120 to 114 Ma, indicating that the entire assemblage was emplaced in a narrow time frame in the Early Cretaceous. This is consistent with abundant field evidence that many of the individual phases were intruded penecontemporaneously. The timing of emplacement correlates with onset of major Cretaceous plutonism in the main part of the Sierra Nevada batholith farther south. The emplacement ages also are similar to isotopic ages for gold-quartz mineralization in the Sierran foothills west of the study area, suggesting a direct genetic relationship between the voluminous Early Cretaceous plutonism and hydrothermal gold mineralization.

  9. An Insight into Environment and Provenance from Geochemistry of the Early Cretaceous Sedimentary Rocks, Upper Magdalena Valley, Colombia

    NASA Astrophysics Data System (ADS)

    Duarte, J.; Roy, P. D.; Lozano-SantaCruz, R.; Lopez-Balbiaux, N.; De La Parra, F.

    2016-12-01

    The Basin of the Upper Magdalena Valley is one of the most important petroleum producing basins of Colombia and the sandstones (upper member) of the early Cretaceous Caballos Formation represents one of the well-known reservoirs of this basin. In this study, we used abundances of organic carbon, carbonate and sulfur, and concentrations of major and trace elements in all three members of the Caballos Formation in order to identify the possible provenance and infer paleo-productivity and paleo-environment during the middle Aptian-middle Albian. The sedimentary rocks (i.e., sandstone, siltstone and shale) comprises mainly of quartz, kaolinite, illite, siderite and pyrite. Calcite and dolomite are present in some samples but in scarce amounts. Both the ternary diagrams (A-CN-K and A-C-N) suggest that clastic fractions of the sedimentary rocks were sourced from a source enriched in Ca-bearing plagioclase (anorthite), similar to the andesitic-basaltic lavas of the Jurassic Saldaña Formation. However, the upper and lower members were more and homogenously altered compared to the heterogeneously altered middle member. Calculated indices of alteration (CIA and PIA) indicate extreme alterations for the lower and upper members and moderate to extreme alteration for the middle member. Different degrees of alteration of the sedimentary rocks follows the atmospheric CO2 concentrations inferred for the Aptian-Albian interval. Mineralogical and geochemical data suggest a depositional environment with pH varying between 7 and 9. Higher alteration caused mobility of Si with respect to Al and hence we observed incongruences between lithological and geochemical classifications. Different abundances of siderite and pyrite along with higher organic carbon and redox-sensible trace elements suggest in general anoxic environments of deposition. However, sedimentary rocks of the middle and upper member were deposited in a relatively more anoxic environment compared to sedimentary rocks of

  10. Reservoir, seal, and source rock distribution in Essaouira Rift Basin

    SciTech Connect

    Ait Salem, A. )

    1994-07-01

    The Essaouira onshore basin is an important hydrocarbon generating basin, which is situated in western Morocco. There are seven oil and gas-with-condensate fields; six are from Jurassic reservoirs and one from a Triassic reservoir. As a segment of the Atlantic passive continental margin, the Essaouira basin was subjected to several post-Hercynian basin deformation phases, which resulted in distribution, in space and time, of reservoir, seal, and source rock. These basin deformations are synsedimentary infilling of major half grabens with continental red buds and evaporite associated with the rifting phase, emplacement of a thick postrifting Jurassic and Cretaceous sedimentary wedge during thermal subsidence, salt movements, and structural deformations in relation to the Atlas mergence. The widely extending lower Oxfordian shales are the only Jurassic shale beds penetrated and recognized as potential and mature source rocks. However, facies analysis and mapping suggested the presence of untested source rocks in Dogger marine shales and Triassic to Liassic lacustrine shales. Rocks with adequate reservoir characteristics were encountered in Triassic/Liassic fluvial sands, upper Liassic dolomites, and upper Oxfordian sandy dolomites. The seals are provided by Liassic salt for the lower reservoirs and Middle to Upper Jurassic anhydrite for the upper reservoirs. Recent exploration studies demonstrate that many prospective structure reserves remain untested.

  11. Geochemical and Sr-Nd isotopic characteristics of Upper Cretaceous (calc-alkaline) and Miocene (alkaline) volcanic rocks: Elazığ, Eastern Taurides, Turkey

    NASA Astrophysics Data System (ADS)

    Kürüm, Sevcan; Tanyıldızı, Özge

    2017-10-01

    The massive volcanic suite of Upper Cretaceous Elazığ Magmatic Complex, and Miocene basic volcanic rocks of crop out to the southern vicinity of Elazığ. The petrographical studies indicated that the massive volcanic suite of Upper Cretaceous are of basalt, spilitic basalt, basaltic andesite, andesite, trachite, dacite/ryolithe and dolerite in composition, and the Miocene volcanic rocks are basalt in composition. According to the geochemical data, which are conformable with the petrographical ones, Upper Cretaceous volcanic rocks are of low and medium-K contaning types and calc-alkalin in general, and enriched with respect to LILE and HREE contents. They also contain low Ti, have negative Nb and Ta anomaly and low 143Nd/147Nd and high 87Sr/86Sr ratios. Geochemical and isotopic data for the massive volcanic suite point out that these volcanic rocks were originated from an upper mantle source (lithospheric) which undergone fractional crystallisation and crustal contamination and enriched by these processes and metasomatized within a subduction zone. Miocene volcanic rocks are of high-K alkaline type, alkali basalt/basanite in composition and products of intraplate volcanism. These rocks are richer in some major oxide contents such as Na2O, K2O, MgO and trace element contents such as Nb, Sr, Zr compared to the massive volcanic rocks of Upper Cretaceous, and they are also enriched with respect to their LILE and HREE contents. The remarkable decrease from LREE towards HREE in the REE/Chondrite-normalized variation diagram indicates a magmatic differentiation process. The MgO and Ni ratios of Miocene volcanic rocks are not conformable with those of primitive basalt composition. However, all the chemical and isotopic (low 87Sr/86Sr ratio and positive (+) εNd values) data indicate that the source magma of these volcanic rocks was derived from a depleted garnet free magma (astenospheric mantle) and was modified once again by the post collosional geodynamical events and

  12. West-east lithostratigraphic cross section of Cretaceous rocks from central Utah to western Kansas

    USGS Publications Warehouse

    Anna, Lawrence O.

    2012-01-01

    A west-east lithostratigraphic cross section of the Cretaceous rocks from central Utah to western Kansas was prepared as part of the former Western Interior Cretaceous (WIK) project, which was part of the Global Sedimentary Geology Program started in 1989. This transect is similar to that published by Dyman and others (1994) as a summary paper of the WIK project but extends further east and is more detailed. Stratigraphic control was provided by 32 geophysical logs and measured sections tied to ammonite and Inoceramus faunal zones. A variable datum was used, including the base of the Castlegate Sandstone for the western part of the section, and the fossil ammonite zone Baculites obtusus for the middle and eastern section. Lower Cretaceous units and the Frontier Formation and Mowry Shale are shown as undifferentiated units. Cretaceous strata along the transect range in thickness from more than 7,000 ft in the structural foredeep of the western overthrust belt in central Utah, to about 11,000 ft near the Colorado-Utah border as a result of considerable thickening of the Mesaverde Group, to less than 3,500 ft in the eastern Denver Basin, Kansas resulting in a condensed section. The basal Mancos Shale rises stepwise across the transect becoming progressively younger to the west as the Western Interior Seaway transgressed westward. The section illustrates large scale stratigraphic relations for most of the area covered by the seaway, from central Utah, Colorado, to west-central Kansas. These strata are predominantly continental and shoreline deposits near the Sevier thrust belt in Utah, prograding and regressive shorelines to the east with associated flooding surfaces, downlapping mudstones, and transgressive parasequences (shoreface) that correlate to condensed zones across the seaway in central Colorado and eastern Denver Basin.

  13. The Cretaceous-Tertiary extinction: A lethal mechanism involving anhydrite target rocks

    USGS Publications Warehouse

    Brett, R.

    1992-01-01

    The Chicxulub Crater, Yucatan, Mexico, is a leading contender as the site for the impact event that caused the Cretaceous-Tertiary (K-T) extinctions. A considerable thickness of anhydrite (CaSO4) forms part of the target rock. High temperatures resulting from impact would drive SO2 off from the anhydrite. Hundreds of billions of tonnes of sulfuric acid aerosol would thus enter the stratosphere and cause considerable cooling of the Earth's surface, decrease photosynthesis by orders of magnitude, deplete the ozone layer, and permit increased UV radiation to reach the Earth's surface. Finally, the aerosol would fall back to Earth as acid rain and devastate land and some lacustrine biota and near-surface marine creatures. The presence of anhydrite in the Chicxulub target rock may thus help explain the many extinctions observed at the K-T boundary. ?? 1992.

  14. Selected plant microfossil records of the terminal Cretaceous event in terrestrial rocks, western North America

    USGS Publications Warehouse

    Nichols, D.J.

    2007-01-01

    Terrestrial or nonmarine rocks of western North America preserve a record of major disruption and permanent alteration of plant communities precisely at the K-T boundary - in the same rocks that preserve geochemical and mineralogical evidence of the terminal Cretaceous impact event. Plant microfossil records from many localities show abrupt disappearance of pollen species (= plant extinctions) closely associated with impact ejecta deposits containing iridium and shocked quartz. Localities discussed in detail in this review are Starkville South, Clear Creek North, Old Raton Pass, and Sugarite in the Raton Basin of Colorado and New Mexico; West Bijou in the Denver Basin, Colorado; Sussex in the Powder River Basin, Wyoming; and Pyramid Butte and Mud Buttes in the Williston Basin, North Dakota. ?? 2007 Elsevier B.V. All rights reserved.

  15. Petrogenesis of the early Cretaceous volcanic rocks in the North Huaiyang tectono-magmatic unit of the Dabie Orogen, eastern China: Implications for crust-mantle interaction

    NASA Astrophysics Data System (ADS)

    Gao, Xin-Yu; Zhao, Tai-Ping; Zhao, Jun-Hong

    2016-03-01

    New elemental and isotopic data are presented for the early Cretaceous felsic to mafic volcanic rocks in the North Huaiyang tectono-magmatic unit (NHY) of the Dabie Orogen, in order to investigate their petrogenesis and provide insights into the nature of the late Mesozoic lithosphere mantle beneath the region and its tectonic relationship with neighboring blocks. LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Jingangtai Formation erupted in a quite short interval about 5 Mys during the Early Cretaceous (128-123 Ma). The rocks have wide ranges of SiO2 (48-68 wt.%) and MgO (0.6-5.6 wt.%) contents. They are enriched in large-ion-lithophile-elements (LILE) (e.g. Rb, Ba) and light rare-earth-elements (LREE), and depleted in high field strength elements (e.g. Nb, Ta and Ti) with weak negative Eu anomalies (Eu/Eu∗ = 0.71-0.94). Meanwhile, the rocks show relatively high whole-rock initial 87Sr/86Sr ratios (0.7074-0.7094), strong negative εNd(t) (-19.1 to -15.8) and zircon εHf values (-20.7 to -14.1). Such typical "continental" geochemical characteristics did not result from crustal contamination during magma ascent, but from an enriched mantle source modified by materials from the subducted Yangtze Craton during the Triassic continental collision. We propose that the petrogenesis of the large-scale contemporaneous magmatism of Dabie Orogen including felsic to mafic volcanic rocks in the NHY reflects an intensive lithospheric thinning and extension during the early Cretaceous as a tectonic response to the change of plate motion of westward subducted Pacific Plate beneath the Eurasian continent.

  16. Paleomagnetism of Cretaceous and Paleocene sedimentary rocks across the Castle Mountain Fault, south central Alaska

    NASA Astrophysics Data System (ADS)

    Stamatakos, John A.; Kodama, K. P.; Vittorio, L. F.; Pavlis, T. L.

    Paleomagnetic and rock magnetic analyses on 217 samples from 13 sites in the Paleocene Chickaloon Formation south of the Castle Mountain Fault and 111 samples from 9 sites in the coeval, but lithologically distinct, Arkose Ridge Formation north of this fault indicate that these rocks contain a pre-folding magnetization carried by fine grained (<1.0μm) single domain magnetite. Secondary magnetizations are common, possibly as the result of the presence of authigenic or hydrothermal pyrrhotite. Although characteristic magnetizations were isolated for the Chickaloon and Arkose Ridge rocks, the best results were obtained from demagnetization plane analysis which estimates the location of the paleomagnetic pole for the Chickaloon Formation at 50.5°N, 277.2°E, δm = 12.2°, δP = 7.77deg;, and a paleomagnetic pole for the Arkose Ridge Formation at 60.4°N, 138.6°E, δm = 11.6°, δp = 6.4°. These results suggest that there is no paleomagnetically discernible latitudinal offset across the Castle Mountain Fault since Paleocene time, but that both the Chickaloon and Arkose Ridge rocks, as part of the Peninsular terrane, originated approximately 1600±1200 km south of their present position with respect to North America. One possible explanation of these data is that the Peninsular terrane was accreted to North America at mid-latitudes in the Cretaceous and was subsequently translated northward by right-lateral strike-slip faulting parallel to the North American margin. Hence, the Arkose Ridge and Chickaloon results may be indicative of the cumulative right-hand displacement occurring on these faults since Paleocene time. However, a calculation using the pole to the small circle fit of the present-day curvature of the Tintina-Northern Rocky Mountain Trench and Denali fault systems, and the maximum amount of structurally estimated offset across these fault systems, indicates that motion on these faults can account for no more than half of the paleomagnetically observed

  17. 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

  18. Reverse Polarity Magnetized Melt Rocks from the Cretaceous/Tertiary Chicxulub Structure, Yucatan Peninsula, Mexico

    NASA Technical Reports Server (NTRS)

    Urrutia-Fucugauchi, J.; Marin, Luis; Sharpton, Virgil L.

    1994-01-01

    We report paleomagnetic results for core samples of the breccia and andesitic rocks recovered from the Yucatan-6 Petrolcos Mexicanos exploratory well within the Chicxulub structure (about 60 km SSW from its center), northern Yucatan, Mexico. A previous study has shown that the rocks studied contain high iridium levels and shocked breccia clasts and an Ar/Ar date of 65.2 +/- 0.4 Ma. Andesitic rocks are characterized by stable single-component magnetizations with a mean inclination of -42.6 deg +/- 2.4 deg. Breccias present a complex paleomagnetic record characterized by multivectorial magnetizations with widely different initial NRM inclinations. However, after alternating field demagnetization, well defined characteristic components with upward inclinations are defined. IRM acquisition experiments, comparison of IRM and NRM coercivity spectra and the single component magnetization of the andesitic rocks indicate the occurrence of iron-rich titanomagnetites of single or pseudo-single domain states as the dominant magnetic carriers. Mean inclinations from the andesitic rocks and most of the breccia samples give a mean inclination of about -40 deg to -45 deg, indicating a reverse polarity for the characteristic magnetization that is consistent with geomagnetic chron 29R, which spans the Cretaceous/Tertiary (K/T) boundary. The inclination is also consistent with the expected value (and corresponding paleolatitude) for the site estimated from the reference polar wander curve for North America. We suggest that the characteristic magnetizations for the andesitic and breccia rocks are the result of shock heating at the time of formation of the impact structure and that the age, polarity and pateolatitude are consistent with a time at the K/T boundary.

  19. Chemical Remagnetization of Jurassic Carbonates and a Primary Paleolatitude of Lower Cretaceous Volcaniclastic Rocks of the Tibetan Himalaya

    NASA Astrophysics Data System (ADS)

    Huang, W.; Van Hinsbergen, D. J. J.; Dekkers, M. J.; Garzanti, E.; Dupont Nivet, G.; Lippert, P. C.; Li, X.; Maffione, M.; Langereis, C. G.; Hu, X.; Guo, Z.; Kapp, P. A.

    2014-12-01

    Paleolatitudes for the Tibetan Himalaya Zone based on paleomagnetic inclinations provide kinematic constraints of the passive northern Indian margin and the extent of 'Greater India' before the India-Asia collision. Here, we present a paleomagnetic investigation of the Jurassic (carbonates) to Lower Cretaceous (volcaniclastic rocks) Wölong section of the Tibetan Himalaya in the Everest region. The carbonates yield positive fold tests, suggesting that the remanent magnetizations have a pre-folding origin. However, detailed paleomagnetic analyses, rock magnetic tests, end-member modeling of acquisition curves of isothermal remanent magnetization, and petrographic studies reveal that the magnetic carrier of the Jurassic carbonates is authigenic magnetite, whereas the dominant magnetic carrier of the Lower Cretaceous volcaniclastic rocks is detrital magnetite. We conclude that the Jurassic carbonates were remagnetized, whereas the Lower Cretaceous volcaniclastics retain a primary remanence. We hypothesize that remagnetization of the Jurassic carbonates was probably caused by the oxidation of early diagenetic pyrite to magnetite within the time interval at ~86-84 Ma during the latest Cretaceous Normal Superchron and earliest deposition of Cretaceous oceanic red beds in the Tibetan Himalaya. The remagnetization of the limestones prevents determining the size of 'Greater India' during Jurassic time. Instead, a paleolatitude of the Tibetan Himalaya of 23.8±2.1° S at ~86-84 Ma is suggested. This value is lower than the expected paleolatitude of India from apparent polar wander path (APWP). The volcaniclastic rocks with the primary remanence, however, yielded a Lower Cretaceous paleolatitude of Tibetan Himalaya of 55.5±3° S, fitting well with the APWP of India.

  20. Index to selected machine-readable geohydrologic data for Precambrian through Cretaceous rocks in Kansas

    USGS Publications Warehouse

    Spinazola, J.M.; Hansen, C.V.; Underwood, E.J.; Kenny, J.F.; Wolf, R.J.

    1987-01-01

    Machine-readable geohydrologic data for Precambrian through Cretaceous rocks in Kansas were compiled as part of the USGS Central Midwest Regional Aquifer System Analysis. The geohydrologic data include log, water quality, water level, hydraulics, and water use information. The log data consist of depths to the top of selected geologic formations determined from about 275 sites with geophysical logs and formation lithologies from about 190 sites with lithologic logs. The water quality data consist of about 10,800 analyses, of which about 1 ,200 are proprietary. The water level data consist of about 4 ,480 measured water levels and about 4,175 equivalent freshwater hydraulic heads, of which about 3,745 are proprietary. The hydraulics data consist of results from about 30 specific capacity tests and about 20 aquifer tests, and interpretations of about 285 drill stem tests (of which about 60 are proprietary) and about 75 core-sample analyses. The water use data consist of estimates of freshwater withdrawals from Precambrian through Cretaceous geohydrologic units for each of the 105 counties in Kansas. Average yearly withdrawals were estimated for each decade from 1940 to 1980. All the log and water use data and the nonproprietary parts of the water quality , water level, and hydraulics data are available on magnetic tape from the USGS office in Lawrence, Kansas. (Author 's abstract)

  1. Middle Jurassic to early Cretaceous igneous rocks along eastern North American continental margin

    SciTech Connect

    Jansa, L.F.; Pe-Piper, G.

    1988-03-01

    Late Middle Jurassic and Early Cretaceous mafic dikes, sills, flows, and local volcaniclastic sediments are intercalated within continental shelf sediments from the Baltimore Canyon Trough northward to the Grand Banks of Newfoundland. The igneous rocks on the eastern North American margin are mainly alkali basalts of intraplate affinity. The late Middle Jurassic igneous activity was of short duration, at about 140 Ma, and was restricted to Georges Bank where it led to construction of several volcanic cones. The main period of igneous activity was concentrated at about 120 Ma in the Aptian/Berremian. The activity consists of dike swarms in Baltimore Canyon, occasional dikes on the Scotian Shelf, and the growth of stratovolcanoes on the Scotian Shelf and Grand Banks. Younger dikes (approx. 95 Ma) also are present on the Grand Banks. With regard to oil exploration on the continental margin, care must be taken to properly identify igneous and volcaniclastic rocks on mechanical logs, drill cuttings, and cores. Reflection seismic profiles can be used to map the areal extent of sills, flows, and low-angle dikes, which commonly show distinctive seismic responses. However, steeply dipping dikes generally produce little, if any, seismic response. Isotopic-age determinations of igneous rocks, combined with biostratigraphic-age determinations of adjacent strata, are invaluable for stratigraphic correlation, establishing chronology of seismic sequences, and analysis of basin sedimentation and tectonic history. 9 figures, 2 tables.

  2. World petroleum systems with Jurassic source rocks

    SciTech Connect

    Klemme, H.D. )

    1993-11-08

    Fourteen petroleum systems with Upper Jurassic source rocks contain one quarter of the world's discovered oil and gas. Eleven other systems with Lower and Middle Jurassic source rocks presently have a minor but significant amount of discovered oil and gas. The purpose of this article is to review the systems geologically, describe their location in space and time on a continental scale, estimate their relative petroleum system recovery efficiencies, and outline the effect their essential elements and processes have on their petroleum plumbing.

  3. Thermal and geotectonic setting of Cretaceous volcanic rocks near Ica, Peru, in relation to Andean crustal thinning

    NASA Astrophysics Data System (ADS)

    Atherton, M. P.; Aguirre, L.

    1992-01-01

    The Cretaceous volcanic rocks of the Ica region, Peru, were deposited in the Cañete marginal basin developed on the Precambrian Arequipa Massif, which was split and thinned along southwardpropagating faults. They are compositionally bimodal, calc-alkaline, high-Al 2O 3 rocks with shoshonitic affinities and a pronounced enriched within-plate character. This contrasts markedly with the equivalent rocks of the Huarmey Basin to the north, which lie directly on mantle-derived material and are chiefly low-K, thleiitic basalts and basaltic andesites, with trace-element abundances related to subduction and/or asthenospheric components. The Ica rocks also show a characteristic very low-grade, nondeformational prehnite-pumpellyite to zeolite facies metamorphism formed under moderate thermal gradients. This contrasts strongly with the high thermal gradient of the rocks to the north, which relates to the more extensive crustal splitting and/or thinning in that direction. These metamorphic patterns, together with the lava chemistry, are important elements in modeling the thermal and geotectonic setting, which has close affinities to a model of the Icelandic rifting system. The source of the Ica rocks is thought to be old enriched mantle beneath the Precambrian Arequipa Massif, in contrast to the mantle beneath the basin to the north, which is much younger and less enriched. This change along the axis of the basin is similar to the K-h relationships suggested at subduction zones. However, the direction of subduction along this sector has been approximately E-W, and the enrichment, which is a right angles to this, relates to the history of the subcontinental mantle along the Andean margin. It is also associated with an abrupt compositional change in the Peruvian Coastal Batholith rocks of slightly younger age, marking a major segmental difference in Mesozoic magma composition along the axis of the Andes. Crustal contributions are not considered to be important, certainly not

  4. Geologic assessment of undiscovered oil and gas resources—Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups, United States Gulf of Mexico Coastal Plain and State Waters

    USGS Publications Warehouse

    Swanson, Sharon M.; Enomoto, Catherine B.; Dennen, Kristin O.; Valentine, Brett J.; Cahan, Steven M.

    2017-02-10

    In 2010, the U.S. Geological Survey (USGS) assessed Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups and their equivalent units for technically recoverable, undiscovered hydrocarbon resources underlying onshore lands and State Waters of the Gulf Coast region of the United States. This assessment was based on a geologic model that incorporates the Upper Jurassic-Cretaceous-Tertiary Composite Total Petroleum System (TPS) of the Gulf of Mexico basin; the TPS was defined previously by the USGS assessment team in the assessment of undiscovered hydrocarbon resources in Tertiary strata of the Gulf Coast region in 2007. One conventional assessment unit (AU), which extends from south Texas to the Florida panhandle, was defined: the Fredericksburg-Buda Carbonate Platform-Reef Gas and Oil AU. The assessed stratigraphic interval includes the Edwards Limestone of the Fredericksburg Group and the Georgetown and Buda Limestones of the Washita Group. The following factors were evaluated to define the AU and estimate oil and gas resources: potential source rocks, hydrocarbon migration, reservoir porosity and permeability, traps and seals, structural features, paleoenvironments (back-reef lagoon, reef, and fore-reef environments), and the potential for water washing of hydrocarbons near outcrop areas.In Texas and Louisiana, the downdip boundary of the AU was defined as a line that extends 10 miles downdip of the Lower Cretaceous shelf margin to include potential reef-talus hydrocarbon reservoirs. In Mississippi, Alabama, and the panhandle area of Florida, where the Lower Cretaceous shelf margin extends offshore, the downdip boundary was defined by the offshore boundary of State Waters. Updip boundaries of the AU were drawn based on the updip extent of carbonate rocks within the assessed interval, the presence of basin-margin fault zones, and the presence of producing wells. Other factors evaluated were the middle

  5. A detailed paleomagnetic investigation of Cretaceous igneous rocks: New contributions from Colombia and Paraguay

    NASA Astrophysics Data System (ADS)

    Kapper, Lisa; Calvo-Rathert, Manuel; Cejudo Ruiz, Ruben; Sanchez Bettucci, Leda; Irurzun, Alicia; Carrancho, Ángel; Gogichaishvili, Avto; Morales, Juan; Sinito, Ana; Mejia, Victoria; Nivia Guevara, Alvaro

    2016-04-01

    We present rock magnetic results, paleodirections and -intensities from Cretaceous samples from two locations from South America. On the one hand we report paleomagnetic results from the Western Cordillera of Colombia from 15 sites north of Cali. These volcanic rock samples were related to age determinations from close localities of 92.5 ± 1.1 Ma on average, occuring during the Cretaceous Normal Superchron (CNS). On the other hand we show results from an alkaline dike swarm in the Asunción Rift, Eastern Paraguay. Previous investigations suggest that these dikes extruded in a rather short period of 126-127 Ma, during normal and reversed polarity field configuration, right before the onset of the CNS. Rock magnetic measurements of both sites show that the main magnetic component is a low-coercivity mineral, e.g., (titanium)magnetite, with a large range of grain sizes from multi- to single domain, or mixtures of several grain sizes in a sample. For the Colombian site we obtained an average Virtual Geomagnetic Pole (VGP), whose latitude compares well with those for South and North America of Besse and Courtillot (2002) with a similar age. For the determination of the Virtual Dipole Moments (VDMs) the Thellier-Coe method did not give successful results, probably due to minerals in the range of multidomain grain size. Therefore, we applied the multispecimen protocol on ten specimens. Six successful determinations produced an average VDM of 2.3 x 10-22 Am2. This value is rather low, but in good agreement with other data from the same time period. Directional investigation of the Eastern Paraguayan dike swarm show highly clustered promising results with six out of 22 sites having an α95 ≤ 10.0° . Most of these sites show a reversed polarity; however, one intermediate polarity site has a very reliable direction as well. This and the occurrence of normal polarity sites suggest that the dikes may have not appeared at the same time but rather during the transition from

  6. Stratigraphic revision of Campanian (Upper Cretaceous) rocks in the Henry Basin, Utah

    SciTech Connect

    Eaton, J.G. )

    1990-01-01

    Upper Cretaceous strata in the Henry Basin of south-central Utah include a 1,575 ft thick sequence of marginal marine and continental rocks of Campanian age. Stratigraphic study of this sequence indicates the need for changes in nomenclature and boundary definitions. Paleontologic study of the same sequence provides a basis for improved interpretations of depositional environments and age. The Mancos Shale of the Henry Basin is here redefined to include only strata up to the top of the Blue Gate Shale Member. The overlying Muley Canyon Sandstone and Masuk member are here removed from the Mancos Shale and given separate formation status. The lower and upper boundaries of the Muley Canyon Sandstone are redefined. The lower boundary is defined at the first prominent sandstone above the Mancos Shale. The upper boundary is defined at the base of the coal deposits overlying the bioturbated sandstones. The Muley Canyon Sandstone was deposited along a wave-dominated coastline and marks the final regression of Cretaceous epeiric seas from the area in the earliest Campanian. A type section of the overlying Masuk Formation is here designated and the formation is divided into three informal members. Abundant nonmarine molluscs and vertebrates have been recovered throughout the Masuk Formation and indicate a coastal floodplain depositional environment with only minor brackish influence. The vertebrate fauna supports an early Campanian age for the formation. The overlying Tarantula Mesa Sandstone and the beds on Tarantula Mesa are entirely nonmarine in origin, and fossils recovered from the beds on Tarantula Mesa support correlation of the unit to the lower part of the Kaiparowits Formation.

  7. Shifts in Archaeal Communities Associated with Lithological and Geochemical Variations in Subsurface Cretaceous Rock

    SciTech Connect

    Takai, Ken; Mormile, Melanie R.; Mckinley, J P.; Brockman, Fred J.; Holben, William E.; Kovacik, William P.; Fredrickson, Jim K.

    2003-04-01

    Subsurface microbial community structure in relation to geochemical gradients and lithology was investigated using a combination of molecular phylogenetic and geochemical analyses. Discreet groundwater and substratum samples were obtained from depths ranging from 182 to 190 m beneath the surface at approximately 10-cm intervals using a multi-level sampler (MLS) that straddled Cretaceous shale and sandstone formations at a site in the southern San Juan Basin in New Mexico. DNA and RNA were extracted directly from quartzite sand substratum loaded into individual cells of the MLS and colonized in situ for six months. PCR-mediated T-RFLP analysis of archaeal rRNA genes (rDNA) in conjunction with partial sequencing analysis of archaeal rDNA libraries and quantitative RNA hybridization with oligonucleotide probes were used to probe community structure and function. Although total microbial populations remained relatively constant over the entire depth interval sampled, significant shifts in archaeal populations, predominantly methanogens, were observed. These shifts coincided with the geochemical transition from relatively high methane (26 mM), low sulfate (<3 mg l-1) concentrations in the region adjacent to the organic matter-rich shale to relatively low-methane (<0.5 mM), high-sulfate (48 mg l-1) conditions in the organic-poor sandstone beneath the shale. These results indicate that active, phylogenetically diverse archaeal communities were present in the subsurface Cretaceous rock environment at this site and that major archaeal clades shifted dramatically over scales of tens of centimeters, corresponding to changes in the lithology and geochemical gradients.

  8. North Slope, Alaska: Source rock distribution, richness, thermal maturity, and petroleum charge

    USGS Publications Warehouse

    Peters, K.E.; Magoon, L.B.; Bird, K.J.; Valin, Z.C.; Keller, M.A.

    2006-01-01

    Four key marine petroleum source rock units were identified, characterized, and mapped in the subsurface to better understand the origin and distribution of petroleum on the North Slope of Alaska. These marine source rocks, from oldest to youngest, include four intervals: (1) Middle-Upper Triassic Shublik Formation, (2) basal condensed section in the Jurassic-Lower Cretaceous Kingak Shale, (3) Cretaceous pebble shale unit, and (4) Cretaceous Hue Shale. Well logs for more than 60 wells and total organic carbon (TOC) and Rock-Eval pyrolysis analyses for 1183 samples in 125 well penetrations of the source rocks were used to map the present-day thickness of each source rock and the quantity (TOC), quality (hydrogen index), and thermal maturity (Tmax) of the organic matter. Based on 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 TOC (TOCo) and the original hydrogen index (HIo) prior to thermal maturation. The quantity and quality of oil-prone organic matter in Shublik Formation source rock generally exceeded that of the other units prior to thermal maturation (commonly TOCo > 4 wt.% and HIo > 600 mg hydrocarbon/g TOC), although all are likely sources for at least some petroleum on the North Slope. We used Rock-Eval and hydrous pyrolysis methods to calculate expulsion factors and petroleum charge for each of the four source rocks in the study area. Without attempting to identify the correct methods, we conclude that calculations based on Rock-Eval pyrolysis overestimate expulsion factors and petroleum charge because low pressure and rapid removal of thermally cracked products by the carrier gas retards cross-linking and pyrobitumen formation that is otherwise favored by natural burial maturation. Expulsion factors and petroleum charge based on hydrous pyrolysis may also be high

  9. Biostratigraphic correlation chart of some Upper Cretaceous rocks from the Lost Soldier area, Wyoming to west of Craig, Colorado

    USGS Publications Warehouse

    Bader, J.W.; Gill, J.R.; Cobban, W.A.; Law, B.E.

    1983-01-01

    This chart depicts the time-stratigraphic relations of some Upper Cretaceous rocks along the eastern and southeastern margins of the Greater Green River Basin, south-central Wyoming and northwestern Colorado. The purpose of this report is to release a preferred set of correlations based upon marine mollusk biostratigraphy. The senior author, with the help of B. E. Law, has acquired, synthesized, compiled, and interpreted data from various sources. These include selected published documents (see "References Cited") and unpublished reports of fossil identifications by W. A. Cobban who examined collections made by the late J. R. Gill. Numerous measured sections of Gill's were also utilized. It must be emphasized that all interpretations on this chart are based on information obtained from these sources and the senior author has yet to substantiate these correlations in the field. Not all data from the area of this study is included herein because it is either repetitive in nature or its reliability is uncertain. This uncertainty is due to the ambiguity inherent in both fossil identification and stratigraphic interpretation. Questionable unpublished material has been omitted while published data which is inconsistent with the senior author's correlations may be found in the footnotes portion of this report. The rock units are assigned to a range of ammonites that have been related to an absolute time scale. The ammonite zonation and age boundaries are adapted from Obradovich and Cobban (1975). "D" numbers are provided for each geographic locality where fossils were collected and described by personnel of the U.S. Geological Survey. These fossils may be accessed at the offices of the Survey in Lakewood, Colorado.

  10. The Late Cretaceous igneous rocks of Romania (Apuseni Mountains and Banat): the possible role of amphibole versus plagioclase deep fractionation in two different crustal terranes

    NASA Astrophysics Data System (ADS)

    Vander Auwera, Jacqueline; Berza, Tudor; Gesels, Julie; Dupont, Alain

    2016-04-01

    We provide new whole-rock major and trace elements as well as 87Sr/86Sr and 143Nd/144Nd isotopic data of a suite of samples collected in the Late Cretaceous volcanic and plutonic bodies of the Apuseni Mts. (Romania) that belong to the Banatitic Magmatic and Metallogenic Belt, also called the Apuseni-Banat-Timok-Srednogorie belt. The samples define a medium- to high-K calc-alkaline differentiation trend that can be predicted by a three-step fractional crystallization process which probably took place in upper crustal magma chambers. Published experimental data indicate that the parent magma (Mg# = 0.47) of the Apuseni Mts. trend could have been produced by the lower crustal differentiation of a primary (in equilibrium with a mantle source) magma. The Late Cretaceous magmatic rocks of the Apuseni Mts. and Banat display overlapping major and trace element trends except that Sr is slightly lower and Ga is higher in the Apuseni Mts. parent magma. This difference can be accounted for by fractionating plagioclase-bearing (Apuseni Mts.) or amphibole-bearing (Banat) cumulates during the lower crustal differentiation of the primary magma to the composition of the parent magma of both trends. This, together with results obtained on the Late Cretaceous igneous rocks from the Timok area in Eastern Serbia, further suggests variation of the water content of the primary magma along and across the belt. The Apuseni Mts. versus the Banat samples display different isotopic compositions that likely resulted from the assimilation of two distinct crustal contaminants, in agreement with their emplacement in two separate mega-units of Alpine Europe.

  11. Natural gas accumulations in low-permeability Tertiary, and Cretaceous (Campanian and Maastrichtian) rock, Uinta Basin, Utah

    SciTech Connect

    Fouch, T.D.; Wandrey, C.J.; Pitman, J.K.; Nuccio, V.F.; Schmoker, J.W.; Rice, D.D.; Johnson, R.C.; Dolton, G.L.

    1992-02-01

    This report characterizes Upper Cretaceous Campanian and Maastrichtian, and lower Tertiary gas-bearing rocks in the Uinta Basin with special emphasis on those units that contain gas in reservoirs that have been described as being tight. The report was prepared for the USDOE whose Western Tight Gas Sandstone Program cofunded much of this research in conjunction with the US Geological Survey's Evolution of Sedimentary Basins, and Onshore Oil and Gas Programs. (VC)

  12. Natural gas accumulations in low-permeability Tertiary, and Cretaceous (Campanian and Maastrichtian) rock, Uinta Basin, Utah. Final report

    SciTech Connect

    Fouch, T.D.; Wandrey, C.J.; Pitman, J.K.; Nuccio, V.F.; Schmoker, J.W.; Rice, D.D.; Johnson, R.C.; Dolton, G.L.

    1992-02-01

    This report characterizes Upper Cretaceous Campanian and Maastrichtian, and lower Tertiary gas-bearing rocks in the Uinta Basin with special emphasis on those units that contain gas in reservoirs that have been described as being tight. The report was prepared for the USDOE whose Western Tight Gas Sandstone Program cofunded much of this research in conjunction with the US Geological Survey`s Evolution of Sedimentary Basins, and Onshore Oil and Gas Programs. (VC)

  13. Source rock maturation, San Juan sag

    SciTech Connect

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

    1989-09-01

    Kinetic modeling for thermal histories was simulated for seven wells in the San Juan sag honoring measured geochemical data. Wells in the area of Del Norte field (Sec. 9, T40N, R5E), where minor production has been established from an igneous sill reservoir, show that the Mancos Shale source rocks are in the mature oil generation window as a combined result of high regional heat flow and burial by approximately 2,700 m of Oligocene volcanic rocks. Maturation was relatively recent for this area and insignificant during Laramide subsidence. In the vicinity of Gramps field (Sec. 24, T33N, R2E) on the southwest flank of the San Juan sag, these same source rocks are exposed due to erosion of the volcanic cover but appear to have undergone a similar maturation history. At the north and south margins of the sag, two wells (Champlin 34A-13, Sec. 13, T35N, R4.5E; and Champlin 24A-1, Sec. 1, T44N, R5E) were analyzed and revealed that although the regional heat flow was probably similar to other wells, the depth of burial was insufficient to cause maturation (except where intruded by thick igneous sills that caused localized maturation). The Meridian Oil 23-17 South Fork well (Sec. 17, T39N, R4E) was drilled in a deeper part of the San Juan sag, and source rocks were intruded by numerous igneous sills creating a complex maturation history that includes overmature rocks in the lowermost Mancos Shale, possible CO{sub 2} generation from the calcareous Niobrara Member of the Mancos Shale, and mature source rocks in the upper Mancos Shale.

  14. Petroleum source rock potential on Jamaica

    SciTech Connect

    Rodrigues, K.

    1983-01-10

    By means of standard geochemical techniques, geologists evaluated the hydrocarbon source rock potential of Jamaican shales and mudstones in terms of the amount, type, and maturity of the organic matter preserved in these sediments. Samples taken from outcrops and well cores revealed that shales from the Chapelton and Windsor formations may have the best potential for hydrocarbon generation.

  15. Middle Triassic source rocks in north Lombardy

    SciTech Connect

    Gnaccolini, M.; Gaetani, M.; Mattavelli, L.; Leoni, C.; Poliani, G.; Riva, A.

    1988-08-01

    Using molecular geochemistry techniques, we established that the Perledo-Verenna and Meride Formations (Middle Triassic, southern Alps) represent the source rocks of the Gaggiano and Villafortuna deep oil fields discovered 40 km northwest of Milan. To find the geological factors which control the areal extent thickness and organic matter distribution relative to these sequences, a sedimentological and geochemical study was undertaken.

  16. Mantle Source of Cretaceous Seafloor in the Nova-Canton Trough

    NASA Astrophysics Data System (ADS)

    Pyle, D. G.; Mahoney, J. J.

    2006-12-01

    The Nova-Canton Trough (NCT) is an 8-km-deep abyss that merges with the far western trace of the Clipperton Fracture Zone north-northwest of the Manihiki Plateau. Ocean crust in this region formed during Cretaceous long magnetic normal Chron 34. Larson (Geology, 25, 779) argued that the NCT is part of an aborted rift system that formed between the Ontong Java and Manihiki plume heads, and terminated plateau construction around 120 Ma via drain-off of plume mantle to the region of rifting. Taylor (EPSL, 241, 372) instead proposed the two plateaus formed as one short-lived mega-plateau that broke apart, and that the NCT is part of the post-breakup transform system that separated a series of short spreading segments. Recently, the R.V. Kilo Moana dredged four sites along the prominent north-facing escarpment of the NCT between 168° 06' W and 168° 42' W at ~1° 24' S, and retrieved basalt, diabase, gabbro, pyroxenite, peridotite, serpentinite, breccias and sedimentary rocks. The diversity of rock types recovered demonstrates that a large cross-section through Cretaceous seafloor is exposed. The MgO content of the basalt and diabase samples varies from 8.9-4.3 wt.%. Incompatible element patterns display relative depletions in alteration- resistant large-ion lithophile elements, and most samples have a distinctive hump-shaped REE pattern, with chondrite-normalized (Sm/Yb)n >1.3 and (La/Sm)n <0.75, suggesting generation by high pressure, relatively low-degree melting of a MORB-type mantle source. One sample is less light-REE- depleted, with (La/Sm)n= 0.96. Age-adjusted (to 120 Ma) Nd-Pb isotope ratios plot within the high- 206Pb/204Pb portion of the Pacific MORB field at ɛNd values between +8.2 and +7.5. In contrast, data for the Ontong Java and Manihiki plateaus fall well below the Pacific MORB field at lower 206Pb/204Pb and ɛNd < +6.6. Thus, our data provide no evidence for Ontong Java or Manihiki mantle components in the NCT source.

  17. Paleontologic and stratigraphic relations of phosphate beds in Upper Cretaceous rocks of the Cordillera Oriental, Colombia

    USGS Publications Warehouse

    Maughan, Edwin K.; Zambrano O., Francisco; Mojica G., Pedro; Abozaglo M., Jacob; Pachon P., Fernando; Duran R., Raul

    1979-01-01

    Phosphorite crops out in the Cordillera Oriental of the Colombian Andes in rocks of Late Cretaceous age as strata composed mostly of pelletal carbonate fluorapatite. One stratum of Santonian age near the base of the Galembo Member of the La Luna Formation crops out at many places in the Departments of Santander and Norte de Santander and may be of commercial grade. This stratum is more than one meter thick at several places near Lebrija and near Sardinata, farther south it is locally one meter thick or more near the base of the Guadalupe Formation in the Department of Boyaca. Other phosphorite beds are found at higher stratigraphic levels in the Galembo Member and the Guadalupe Formation, and at some places these may be commercial also. A stratigraphically lower phosphorite occurs below the Galembo Member in the Capacho Formation (Cenomanian age) in at least one area near the town of San Andres, Santander. A phosphorite or pebbly phosphate conglomerate derived from erosion of the Galembo Member forms the base of the Umir Shale and the equivalent Colon Shale at many places. Deposition of the apatite took place upon the continental shelf in marine water of presumed moderate depth between the Andean geosyncline and near-shore detrital deposits adjacent to the Guayana shield. Preliminary calculations indicate phosphorite reserves of approximately 315 million metric tons in 9 areas, determined from measurements of thickness, length of the outcrop, and by projecting the reserves to a maximum of 1,000 meters down the dip of the strata into the subsurface. Two mines were producing phosphate rock in 1969; one near Turmeque, Boyaca, and the other near Tesalia, Huila.

  18. Plesiosaur-bearing rocks from the Late Cretaceous Tahora Fm, Mangahouanga, New Zealand - a palaeoenvironmental study

    NASA Astrophysics Data System (ADS)

    Vajda, Vivi; Raine, J. Ian

    2010-05-01

    Mangahouanga Stream, Hawkes Bay, New Zealand is world-famous for its high southern latitude vertebrate fossils including plesiosaurs, mosasaurs and more rarely, dinosaurs. The fossils are preserved in the conglomeratic facies of the Maungataniwha Sandstone Member of the Tahora Formation. A palynological investigation of sediments from the boulders hosting vertebrate fossils reveals well-preserved palynological assemblages dominated by pollen and spores from land plants but also including marine dinoflagellate cysts in one sample. The palynofacies is strongly dominated by wood fragments including charcoal, and the sample taken from a boulder hosting plesiosaur vertebrae is entirely terrestrially derived, suggesting a fresh-water habitat for at least some of these plesiosaurs. The key-pollen taxa Nothofagidites senectus and Tricolpites lilliei, together with the dinocyst Isabelidinium pellucidum and the megaspore Grapnelispora evansii, strongly indicate an early Maastrichtian age for the host rock. The terrestrial palynoflora reflects a mixed vegetation dominated by podocarp conifers and angiosperms with a significant tree-fern subcanopy component. The presence of taxa with modern temperate distributions such as Nothofagus (southern beech), Proteaceae and Cyatheaceae (tree-ferns), indicates a mild-temperate climate and lack of severe winter freezing during the latest Cretaceous, providing an ecosystem which most probably made it possible for polar dinosaurs to overwinter. The paper is dedicated to Mrs Joan Wiffen who with her great persistence, enthusiasm and courage put Mangahouanga on the world map, becoming a role model for many young scientists.

  19. Analysis of compaction effects on coal fracture patterns, Upper Cretaceous Rock Springs Formation, Southwestern Wyoming

    SciTech Connect

    Laubach, S.E.; Schultz-ela, D.D.; Tyler, R. )

    1993-07-01

    Fracture styles in a coal bed of Upper Cretaceous Rock Springs Formation, Mesaverde Group, in southwestern Wyoming, shift from closely spaced opening-mode (extension) fractures to calcite-filled normal faults where cleat-forming conditions were perturbed under a lens of sandstone. Analysis of coal deformation shows that shear stress was augmented in the coal layer below the tapering edge of the sandstone lens, favoring normal fault development. Because these faults have little primary porosity and have synkinematic calcite fill, the coal bed is likely to have low permeability compared with that of coal having opening-mode fractures typical of other parts of the formation. Coalbed methane reservoirs in depositional facies where highly lenticular sandstones (height-to-length ratio of 0.3 or greater) are interbedded with coal beds may contain low-permeability zones resulting from this shift in fracture style. Such changes in fracture style could interfere with the success of well completions, compartmentalize and channelize gas and water flow, and create traps for gas accumulation. 31 refs., 13 figs.

  20. Oxidation state inherited from the magma source and implications for mineralization: Late Jurassic to Early Cretaceous granitoids, Central Lhasa subterrane, Tibet

    NASA Astrophysics Data System (ADS)

    Cao, MingJian; Qin, KeZhang; Li, GuangMing; Evans, Noreen J.; McInnes, Brent I. A.; Li, JinXiang; Zhao, JunXing

    2017-05-01

    Arc magmas are more oxidized than mid-ocean ridge basalts; however, there is continuing debate as to whether this higher oxidation state is inherited from the source magma or developed during late-stage magmatic differentiation processes. Well-constrained Late Jurassic to Early Cretaceous arc-related intermediate to felsic rocks derived from distinct magma sources provide us with a good opportunity to resolve this enigma. A series of granitoids from the western Central Lhasa subterrane were analyzed for whole-rock magnetic susceptibility, Fe2O3/FeO ratios, and trace elements in zircon. Compared to Late Jurassic samples (1.8 ± 2.0 × 10-4 emu g-1 oe-1, Fe3+/Fetotal = 0.32 ± 0.07, zircon Ce4+/Ce3+* = 15.0 ± 13.4), Early Cretaceous rocks show higher whole-rock magnetic susceptibility (5.8 ± 2.5 × 10-4 emu g-1 oe-1), Fe3+/Fetotal ratios (0.43 ± 0.04), and zircon Ce4+/Ce3+* values (23.9 ± 22.3). In addition, positive correlations among whole-rock magnetic susceptibility, Fe3+/Fetotal ratios, and zircon Ce4+/Ce3+* reveal a slight increase in oxidation state from fO2 = QFM to NNO in the Late Jurassic to fO2 = ˜NNO in the Early Cretaceous. Obvious linear correlation between oxidation indices (whole-rock magnetic susceptibility, zircon Ce4+/Ce3+*) and source signatures (zircon ɛHf(t), TDM C ages) indicates that the oxidation state was predominantly inherited from the source with only a minor contribution from magmatic differentiation. Thus, the sources for both the Late Jurassic and Early Cretaceous rocks were probably influenced by mantle wedge-derived magma, contributing to the increased fO2. Compared to ore-forming rocks at giant porphyry Cu deposits, the relatively low oxidation state (QFM to NNO) and negative ɛHf(t) (-16 to 0) of the studied granitoids implies relative infertility. However, this study demonstrates two potential fast and effective indices (fO2 and ɛHf(t)) to evaluate the fertility of granitoids for porphyry-style mineralization. In an

  1. Geochronology and geochemistry of Cretaceous Nanshanping alkaline rocks from the Zijinshan district in Fujian Province, South China: Implications for crust-mantle interaction and lithospheric extension

    NASA Astrophysics Data System (ADS)

    Li, Bin; Jiang, Shao-Yong

    2014-10-01

    In situ zircon U-Pb ages and Hf isotopic data, major and trace elements, and Sr-Nd-Pb isotopic compositions are reported for Nanshanping alkaline rocks from the Zijingshan district in southwestern Fujian Province (the Interior or Western Cathaysia Block) of South China. The Nanshanping alkaline rocks, which consist of porphyritic quartz monzonite, porphyritic syenite, and syenite, revealed a Late Cretaceous age of 100-93 Ma. All of the rocks show high SiO2, K2O + Na2O, and LREE but low CaO, Fe2O3T, MgO, and HFSE (Nb, Ta, P, and Ti) concentrations. These rocks also exhibit uniform initial 87Sr/86Sr ratios of 0.7078 to 0.7087 and εNd(t) values of -4.1 to -7.2, thus falling within the compositional field of Cretaceous basalts and mafic dikes occurring in the Cathaysia Block. Additionally, these rocks display initial Pb isotopic compositions with a 206Pb/204Pbi ratio of 18.25 to 18.45, a 207Pb/204Pbi ratio of 15.63 to 15.67, and a 208Pb/204Pbi ratio of 38.45 to 38.88. Combined with the zircon Hf isotopic compositions (εHf(t) = -11.7 to -3.2), which are different from those of the basement rocks, we suggest that Nanshanping alkaline rocks were primarily derived from a subduction-related enriched mantle source. High Rb/Sr (0.29-0.65) and Zr/Hf (37.5-49.2) but relatively low Ba/Rb (4.4-8.1) ratios suggest that the parental magmas of these rocks were most likely formed via partial melting of a phlogopite-bearing mantle source with carbonate metasomatism. The relatively high SiO2 (62.35-70.79 wt.%) and low Nb/Ta (10.0-15.3) ratios, positive correlation between SiO2 and (87Sr/86Sr)I, and negative correlation between SiO2 and εNd(t) of these rocks suggest that the crustal materials were also involved in formation of the Nanshanping alkaline rocks. Combined with geochemical and isotopic features, we infer magmatic processes similar to AFC (assimilation and fractional crystallization) involving early fractionation of clinopyroxene and olivine and subsequent fractionation of

  2. 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.

  3. Hydrogeochemical Characterization of Formation Waters in Cretaceous Rocks from Southeast Mexico

    NASA Astrophysics Data System (ADS)

    Mendez-Ortiz, B. A.; Carrillo-Chavez, A.; Tritlla, J.; Levresse, G.; Varela, M.; Clara, L.; Caballero, E.

    2007-05-01

    Formation waters were sampled from ten different producing wells in several Cretaceous oil fields in central and north Tabasco, southeast of Mexico. All of them were analyzed for mayor and trace ions, as well as for 18O and D isotopes. The salinity in the central oil fields (TSD in ppm) ranges from 221,972 ppm to 243,372 ppm. The salinities are very similar in different oil wells. These salinities are 1 to 14 times higher than the salinity found in another fields (15,299 to 16,557 ppm), and 1 to 5 times higher than other field. A northern oil field salinity is characterized also by an important heterogeneity of it salinity due to salt intrusion and interaction with non uniform structures. The major ions analysis (Na+, Ca2+, K+, Mg+, Cl+, SO42-, HCO3-) suggests water-rock interactions in all the oil fields. This is the case, particularly marked in the central fields, where the brines are enriched in Mg in a range from 10 to 274 ppm. This is due to brines/dolomites interaction, while in other oil field, the higher concentration of Mg was only of 1.17 ppm. The central oil fields present depletion on sulfate concentrations (<5.9 ppm). This could be due to precipitation of metal sulfide (thermal reduction) in the form of pyrite and marcasite. Halogens (Br, Cl) concentration indicates three different origins for the formation waters. Water from the central wells is plotted on the evaporated marine water evolution line. Water from the southern wells is located close to marine water in the halite dissolution zone, whereas water form the northern wells is plotted in the diluted waters zone. Cl and Br evolution in the central field samples shows two different groups, and clearly reveal mixing processes between marine water and highly evolved evaporated seawater. Whereas water from the northern wells is plotted in the mixing zone between seawater with low salinity water trapped in Tertiary sediments which can migrate until mixed with older formation waters. The D-O stable

  4. Factors limiting potential of evaporites as hydrocarbon source rocks

    SciTech Connect

    Katz, B.J.; Bissada, K.K.; Wood, J.W.

    1987-05-01

    It is well established that evaporite-bearing sequences account for a substantial proportion of petroleum occurrences. Examples can be cited from the Mesozoic of the Middle East, the Cretaceous of Latin America, and many others. An examination of effective source rocks within these provinces reveals that carbonate facies generate the bulk of the hydrocarbons. The higher evaporites (gypsum, anhydrate, halite, etc) seldom contribute to the resource base. Geochemical analyses of the higher evaporites reveal low organic carbon contents and imperceptible pyrolysis yields. These observations are not consistent with many of the current concepts of organic matter accumulation in evaporite environments, which suggests that hypersalinity should be especially favorable because abundant nutrient supply enhances primary productivity and elevated salt content enhances preservation efficiency. Their recent studies on oxidation of labile phytoplankton remains and relative sedimentation rates of organic and inorganic constituents in hypersaline brines suggest that three factors contribute to the observed low concentrations of hydrogen-enriched organic matter in the higher evaporites: (1) the density contrast between hypersaline brines and suspended organic matter retards the settling rate of the organic matter and prolongs its exposure to oxidative processes; (2) high concentrations of sulfates, and possibly nitrates, provide a secondary oxidizer for labile phytoplankton remains; and (3) high precipitation rates of the evaporite minerals dilute any organic matter which reaches the sediment-water interface. This paper will examine these factors in the modern and ancient record and discuss their influence on source-bed distribution through time and space.

  5. Source rock, maturity data indicate potential off Namibia

    SciTech Connect

    Bray, R.; Lawrence, S.; Swart, R.

    1998-08-10

    Namibia`s territorial waters occupy a large portion of West Africa`s continental shelf. The area to the 1,000 m isobath is comparable in size to the combined offshore areas of Gabon, Congo, Zaire, and Angola. Around half as much again lies in 1,000--2,500 m of water. The whole unlicensed part of this area will be open for bidding when the Third Licensing Round starts Oct. 1, 1998. Offshore Namibia is underexplored by drilling with only seven exploration wells drilled. Shell`s Kudu field represents a considerable gas resource with reserves of around 3 tcf and is presently the only commercial discovery.Namibia`s offshore area holds enormous exploration potential. Good quality sandstone reservoirs are likely to be distributed widely, and a number of prospective structural and stratigraphic traps have been identified. The recognition of Cretaceous marine oil-prone source rocks combined with the results of new thermal history reconstruction and maturity modeling studies are particularly significant in assessment of the oil potential. The paper discusses resource development and structures, oil source potential, maturity, and hydrocarbon generation.

  6. Magma sources during Gondwana breakup: chemistry and chronology of Cretaceous magmatism in Westland, New Zealand

    NASA Astrophysics Data System (ADS)

    van der Meer, Quinten H. A.; Waight, Tod E.; Scott, James M.

    2013-04-01

    Cretaceous-Paleogene rifting of the Eastern Gondwana margin thinned the continental crust of Zealandia and culminated in the opening of the Tasman Sea between Australia and New Zealand and the Southern Ocean, separating both from Antarctica. The Western Province of New Zealand consists of a succession of metasedimentary rocks intruded by Palaeozoic and Mesozoic granitoids that formed in an active margin setting through the Phanerozoic. Upon cessation of subduction, the earliest stages of extension (~110-100 Ma) were expressed in the formation of metamorphic core complexes, followed by emplacement of granitoid plutons, the deposition of terrestrial Pororari Group sediments in extensional half-grabens across on- and offshore Westland, and the intrusion of mafic dikes from ~90 Ma. These dikes are concentrated in the swarms of the Paparoa and Hohonu Ranges and were intruded prior to and simultaneous with volumetrically minor A-type plutonism at 82 Ma. The emplacement of mafic dikes and A-type plutonism at ~82 Ma is significant as it coincides with the age of the oldest seafloor in the Tasman Sea, therefore it represents magmatism coincident with the initiation of seafloor spreading which continued until ~53 Ma. New 40Ar-39Ar ages indicate that the intrusion of mafic dikes in basement lithologies both preceded and continued after the initial opening of the Tasman Sea, including an additional population of ages at ~70 Ma. This indicates either a prolonged period of extension-related magmatism that continued >10 Ma after initial breakup, or two discrete episodes of magmatism during Tasman Sea spreading. Volumetrically minor Cenozoic within-plate magmatism continued sporadically throughout the South Island and bears a characteristic HIMU (high time integrated U/Pb) signature. A detailed geochemistry and chronological study of Cretaceous mafic and felsic magmatism is currently in progress and aims to better understand the transition of magma sources from a long lived active

  7. PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous Tertiary continental collision

    NASA Astrophysics Data System (ADS)

    Azizi, H.; Moinevaziri, H.; Mohajjel, M.; Yagobpoor, A.

    2006-06-01

    Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic age to the northeast. The Qom formation (Oligocene-Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta-arkose, marble and quartzite. The metabasites are metamorphosed to greenschist and amphibolite facies from a basaltic and gabbroic protolith of tholeiitic and calc-alkaline rocks. Geothermobarometry based on the equivalence of minerals stability and their paragenesis in these rocks and microprobe analyses by several different methods indicate that metamorphism occurred in a temperature range between 450 and 680 °C at 5.5 and 7.5 kb pressure. Rims of minerals reveal a considerable decrease of pressure (<2 kb) and insignificant decrease of temperature. The PTt path of this metamorphism is normal. The MFG line passes above the triple junction of Al 2SiO 5 polymorphs, and the average geothermal gradient during metamorphism was from 27 to 37 °C/km, which is more concordant with the temperature regime of collision zones. We infer that crustal thickening during post-Cretaceous (possibly Eocene) collision of the Arabian plate and the Azerbaijan-Albourz block was the main factor that caused the metamorphism in the studied area.

  8. Depositional history and seismic stratigraphy of Lower Cretaceous rocks in the National Petroleum Reserve in Alaska and adjacent areas

    SciTech Connect

    Molenaar, C.M.

    1989-01-01

    Lower Cretaceous rocks, which are widespread throughout the National Petroleum Reserve in Alaska (NPRA) and adjacent areas north of the Brooks Range, make up the major part of the thick sedimentary fill of the Colville basin. Much seismic and well information obtained since 1974 has aided considerably in understanding these rocks. These data include about 20,000 km of seismic lines, covering much of the NPRA with a grid spacing of 10-20 km, and 28 exploratory wells that bring the total to more than 50 wells in and adjacent to the NPRA. The purpose of this chapter is to interpret the depositional history of Lower Cretaceous rocks in the NPRA and adjacent areas on the basis of the latest seismic and well data and well data and on information from outcrops in the southern part of the Colville basin. The basin geometry and depositional history described in earlier reports are repeated here in the context of the overall Lower Cretaceous depositional history. Well data (including paleontology) and seismic data are used almost exclusively to interpret relations in the northern foothills and coastal plain areas. Surface data and some well data are used in the southern parts of the northern foothills, and surface data are used exclusively to interpret the depositional history in the southern foothills and Brooks Range. The quality of seismic data is fair to good in most of the coastal plain, where the structure is simple. In the northern foothills, tracing seismic reflections is more difficult, especially in the shallower part of the section because of structural complications in the thrust-faulted anticlines. The quality of seismic data across the structurally complex southern foothills area is inadequate to correlate stratigraphic units of the outcrop area of the southern foothills with subsurface units to the north.

  9. Effects of sources and diagenesis on the isotopic and chemical composition of carbon and sulfur in cretaceous shales

    SciTech Connect

    Whittaker, S.G.; Kyser, T.K. )

    1990-10-01

    The Cretaceous Lea Park Formation of south-central Saskatchewan contains organic matter from marine and terrestrial sources in proportions that vary as a result of deposition during the Campanian Claggett transgressive-regressive cycle in the Western Interior seaway of North America. The relative proportions of organic matter from these sources were determined using a terrestrial index (TI) that compares n-alkanes considered to be of terrestrial origin, n-C{sub 25} to n-C{sub 29}, to those considered to be of marine origin, n-C{sub 15} to n-C{sub 22}. The C isotopic composition of Cretaceous marine organic matter is found to be near {minus}32{per thousand} while terrestrial organic matter is near {minus}24{per thousand}. The lower {delta}{sup 13}C values of marine organic matter from the Lea Park Formation, as compared with those of Recent marine organic matter, are similar to the relation observed in other Cretaceous rocks; {delta}{sup 13}C values of terrestrial organic matter, however, are similar to those of the present. Pyrite formation in the Lea Park mudstones was limited by the availability of metabolizable organic matter, with the great amount of pyrite typically associated with organic matter having the lowest TI values. {delta}{sup 34}Spy values range nearly 30{per thousand} and vary directly with the composition of associated organic matter. Variations in the supply of metabolizable organic matter were more important than differences in sedimentation rate in producing the range of {delta}{sup 34}Spy values. {Delta}{sup 34}S values vary with the composition of organic matter and become larger when associated with more metabolizable organic matter.

  10. Contrasting Protoliths of Cretaceous Metamorphic Rocks from the Luk Ulo Accretionary Wedge Complex of Central Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Kadarusman, A.; Massone, H.; Permana, H.; Munasri, A.

    2005-12-01

    Rocks of the Lok Ulo Accretionary Complex crop out over a small (<100 km2) area in the Karangsambung residency of Central Java. They are part of Cretaceous accretionary wedge complexes in Central Indonesia, which are distributed sporadically in an arc extending from southwest and central Java to southeast Kalimantan and southern Sulawesi. The Lok Ulo complex consists of various types of rocks occurring as tectonic slabs in a black-shale matrix tectonic melange. The slabs are composed of a dismembered ophiolite, sedimentary rocks, and crystalline schists and gneisses. Detailed work on all the various metamorphic rock types in the Lok Ulo complex will be the focus of the study. Our investigations already show that the metamorphic rocks have two different kinds of protoliths and differ in P-T evolution as well. The first group (called `oceanic plate protolith') consists of fine-grained metabasites with metapelitic intercalations ranging from greenschist to amphibolite facies. High-pressure rocks such as eclogite, partially containing lawsonite, jadeite-glaucophane schist and blueschist crop out in a thin zone between the low-grade schists and a serpentinite zone along Kali Muncar. They are associated with a succession of metabasalt, serpentinite, chert and red limestone as common constituents of an ophiolite. The second group (called `continental crustal protolith') consists of low to high grade medium pressure metapelites, calc-silicate rocks, and metagranites (gneisses, quartzites, marbles, felsic granulites), and minor bimodal low grade metavolcanic. These rocks are presumably associated with a monotonous sequence of metapelites from the chlorite zone up to the garnet zone exposed in the northern and eastern part of the Karangsambung area (e.g. Kali Loning). Our findings suggest that the metamorphic rocks from the Lok Ulo complex are not the simple result of subduction metamorphism along the Indo-Australian oceanic plate (margin of the Sundaland craton) in the

  11. Elemental and Sr-Nd isotopic geochemistry of Cretaceous to Early Paleogene granites and volcanic rocks in the Sikhote-Alin Orogenic Belt (Russian Far East): implications for the regional tectonic evolution

    NASA Astrophysics Data System (ADS)

    Zhao, Pan; Jahn, Bor-ming; Xu, Bei

    2017-09-01

    The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80-57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87Sr/86Sr ratios range from 0.7048 to 0.7114, and εNd(t) values vary from +1.7 to -3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The

  12. Geochemistry, geochronology, and tectonic setting of Early Cretaceous volcanic rocks in the northern segment of the Tan-Lu Fault region, northeast China

    NASA Astrophysics Data System (ADS)

    Ling, Yi-Yun; Zhang, Jin-Jiang; Liu, Kai; Ge, Mao-Hui; Wang, Meng; Wang, Jia-Min

    2017-08-01

    We present new geochemical and geochronological data for volcanic and related rocks in the regions of the Jia-Yi and Dun-Mi faults, in order to constrain the late Mesozoic tectonic evolution of the northern segment of the Tan-Lu Fault. Zircon U-Pb dating shows that rhyolite and intermediate-mafic rocks along the southern part of the Jia-Yi Fault formed at 124 and 113 Ma, respectively, whereas the volcanic rocks along the northern parts of the Jia-Yi and Dun-Mi faults formed at 100 Ma. The rhyolite has an A-type granitoid affinity, with high alkalis, low MgO, Ti, and P contents, high rare earth element (REE) contents and Ga/Al ratios, enrichments in large-ion lithophile (LILEs; e.g., Rb, Th, and U) and high-field-strength element (HFSEs; e.g., Nb, Ta, Zr, and Y), and marked negative Eu anomalies. These features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment. The basaltic rocks are enriched in light REEs and LILEs (e.g., Rb, K, Th, and U), and depleted in heavy REEs, HFSEs (e.g., Nb, Ta, Ti, and P), and Sr. These geochemical characteristics indicate that these rocks are calc-alkaline basalts that formed in an intraplate extensional tectonic setting. The dacite is a medium- to high-K, calc-alkaline, I-type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc. Therefore, the volcanic rocks along the Jia-Yi and Dun-Mi faults were formed in an extensional regime at 124-100 Ma (Early Cretaceous), and these faults were extensional strike-slip faults at this time.

  13. Geochemical modelling of the principal source rocks of the Barinas and Maracaibo basins, western Venezuela

    SciTech Connect

    Tocco, R.; Gallango, O.; Parnaud, F.

    1996-08-01

    This study presents a geochemical modelling of the principal source rocks in the western Venezuelan Basins. The area covers more than 100,000 km{sup 2}, and includes Lake Maracaibo and Barinas Basins. The geochemical modelling recognizes three source rocks: (1) A principal, K3-K4-K5 Cretaceous sequences, represented by La Luna, Capacho and Navay formations, (2) a secondary, corresponding to the T4 Oligocene sequence, represent by the Carbonera Formation, and (3) an accessory source rock, K7-K8 Paleocene sequences, represented by the carbonaceous shales and coals of the Orocue Group and Marcelina Formation. Three periods of hydrocarbon expulsion were defined for La Luna Formation (Early Eocene-Late Eocene, Middle Miocene-Early Miocene and Early Miocene-Holocene) and a principal period of hydrocarbon expulsion for Orocue Group and Carbonera Formation (Plio-Pleistocene and Middle Miocene Plio-Pleistocene). The 90% of hydrocarbons generated correspond to the principal source rock La Luna Formation, and the 10% to Tertiary source rocks (Carbonera Formation and Orocue Group). Five petroleum systems were identified: Lake Maracaibo, southwest of the Lake Maracaibo Basin, the Lara nappes, the extensive basins of eastern Zulia and the Barinas subbasin.

  14. Hydrocarbon migration and accumulation in the Upper Cretaceous Qingshankou Formation, Changling Sag, southern Songliao Basin: Insights from integrated analyses of fluid inclusion, oil source correlation and basin modelling

    NASA Astrophysics Data System (ADS)

    Dong, Tian; He, Sheng; Wang, Dexi; Hou, Yuguang

    2014-08-01

    The Upper Cretaceous Qingshankou Formation acts as both the source and reservoir sequence in the Changling Sag, situated in the southern end of the Songliao Basin, northeast China. An integrated approach involving determination of hydrocarbon charging history, oil source correlation and hydrocarbon generation dynamic modeling was used to investigate hydrocarbon migration processes and further predict the favorable targets of hydrocarbon accumulations in the Qingshankou Formation. The hydrocarbon generation and charge history was investigated using fluid inclusion analysis, in combination with stratigraphic burial and thermal modeling. The source rocks began to generate hydrocarbons at around 82 Ma and the hydrocarbon charge event occurred from approximately 78 Ma to the end of Cretaceous (65.5 Ma) when a large tectonic uplift took place. Correlation of stable carbon isotopes of oils and extracts of source rocks indicates that oil was generated mainly from the first member of Qingshankou Formation (K2qn1), suggesting that hydrocarbon may have migrated vertically. Three dimensional (3D) petroleum system modeling was used to evaluate the processes of secondary hydrocarbon migration in the Qingshankou Formation since the latest Cretaceous. During the Late Cretaceous, hydrocarbon, mainly originated from the Qianan depression, migrated laterally to adjacent structural highs. Subsequent tectonic inversion, defined as the late Yanshan Orogeny, significantly changed hydrocarbon migration patterns, probably causing redistribution of primary hydrocarbon reservoirs. In the Tertiary, the Heidimiao depression was buried much deeper than the Qianan depression and became the main source kitchen. Hydrocarbon migration was primarily controlled by fluid potential and generally migrated from relatively high potential areas to low potential areas. Structural highs and lithologic transitions are potential traps for current oil and gas exploration. Finally, several preferred hydrocarbon

  15. Provenance of late Ordovician to early Cretaceous sedimentary rocks from southern Ghana, as inferred from Nd isotopes and trace elements

    NASA Astrophysics Data System (ADS)

    Asiedu, D. K.; Hegner, E.; Rocholl, A.; Atta-Peters, D.

    2005-04-01

    Geochemical and Nd-isotopic data are reported for 24 shale and sandstone samples comprising the Upper Ordovician to Lower Cretaceous Sekondian Group, southern Ghana. The data are interpreted in terms of the provenance of these siliclastic sediments and the Paleozoic and Mesozoic geologic development of southern Ghana. The sandstones and shales generally have trace element characteristics typical of material eroded from the upper continental crust. Cr and Ni concentrations are low suggesting their derivation from dominantly felsic sources. There appear to be chemical and Nd-isotopic differences between the lower formations (i.e., Ajua Shale and Elmina Sandstone) and the uppermost formation (i.e., Essikado Sandstone) on one hand, and the upper formations (i.e., Takoradi Sandstone, Takoradi Shale, Effia Nkwanta Beds and Sekondi Sandstone) on the other. The upper formations are characterized by evolved major element compositions, high large-ion lithophile element abundances, large negative Eu-anomalies (0.58-0.73), and low ɛNd values (-10.8 to -4.1), indicating stable craton settings. On the other hand, the Ajua Shale, Elmina Sandstone, and Essikado Sandstone formations have less evolved major element compositions, lower large-ion lithophile abundances, and higher Eu-anomalies (0.69-0.88), and this may reflect an active margin setting of the source (juvenile-type Birimian felsic volcanics and/or granitoids) rather than Phanerozoic active continental settings. The upper formations have TDM model ages of 1.8-2.3 Ga indicating that the Paleoproterozoic Birimian rocks are the ultimate sources, whereas the lower formations and uppermost formation have slightly younger TDM values of 1.6-1.9 Ga suggesting of a component from the Pan-African mobile belt. These differences in model ages may, however, be related to lithology (rather than stratigraphy) where the shales (1.6-2.3 Ga; mean, 1.9 Ga) typically give older ages than the sandstones (1.6-1.9 Ga; mean 1.7 Ga).

  16. Updated paleomagnetic pole from Cretaceous plutonic rocks of the Sierra Nevada, California: Tectonic displacement of the Sierra Nevada block

    USGS Publications Warehouse

    Hillhouse, J.W.; Gromme, S.

    2011-01-01

    We report remanent magnetization measurements from 13 sites in Cretaceous plutonic rocks in the northern Sierra Nevada (38??N-39.5??N). By increasing the number of available paleomagnetic sites, the new data tighten constraints on the displacement history of the Sierra Nevada block and its pre-extensional position relative to interior North America. We collected samples in freshly exposed outcrops along four highway transects. The rocks include diorite, granodiorite, and tonalite with potassium-argon ages (hornblende) ranging from 100 Ma to 83 Ma. By combining our results with previous paleomagnetic determinations from the central and southern Sierra Nevada (excluding sites from the rotated southern tip east of the White Wolf-Kern Canyon fault system), we find a mean paleomagnetic pole of 70.5??N, 188.2??E, A95 = 2.6?? (N = 26, Fisher concentration parameter, K = 118). Thermal demagnetization indicates that the characteristic remanence is generally unblocked in a narrow range within 35 ??C of the Curie temperature of pure magnetite. Small apparent polar wander during the Cretaceous normal-polarity superchron, plus prolonged acquisition of remanence at the site level, may account for the low dispersion of virtual geomagnetic poles and relatively large K value. Tilt estimates based on overlapping sediments, stream gradients, and thermochronology of the Sierra Nevada plutons vary from 0?? to 3?? down to the southwest. Without tilt correction, the mean paleomagnetic pole for the Sierra Nevada is essentially coincident with the North American reference pole during the Cretaceous stillstand (125 Ma to 80 Ma). At 95% confidence, the apparent latitude shift is 1.1?? ?? 3.0?? (positive northward), and the apparent rotation is negligible, 0.0?? ?? 4.7??. Correcting for each degree of tilt, which is limited to 3?? on geologic evidence, increases the rotation anomaly 2.2?? counterclockwise, while the apparent latitude shift remains unchanged. ?? 2011 Geological Society of

  17. Coeval Ar-40/Ar-39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites

    NASA Technical Reports Server (NTRS)

    Swisher, Carl C., III; Grajales-Nishimura, Jose M.; Montanari, Alessandro; Margolis, Stanley V.; Claeys, Philippe; Alvarez, Walter; Renne, Paul; Cedillo-Pardo, Esteban; Maurrasse, Florentin J.-M. R.; Curtis, Garniss H.

    1992-01-01

    Ar-40/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from Ar-40/Ar-39 ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The Ar-40/Ar-39 ages, in conjunction with geochemical and petrological similarities, strengthen the suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

  18. Geochemical analysis of selected hydrocarbon samples in the Douala basin, Cameroon: Implications for an oil-prone source rock

    SciTech Connect

    Ackerman, W.C.; Boatwright, D.C. ); Burwood, R.; Mycke, B.; Van Lerberche, D. ); Bondjo, E.; Tamfu, S.; Ovono, D. )

    1993-09-01

    Several oil seeps from the onshore Douala basin in southwest Cameroon have been analyzed by GC/MS, PY/GC, and PY/GC/MS to determine the nature and quality of their source rocks. Geochemical data indicate oil-prone source rocks exist in the Upper Cretaceous to middle Tertiary passive margin sedimentary section. Paleoenvironmental indicators suggest these source rocks were deposited in paralic/deltaic to hypersaline marine settings. In conjunction with existing geological data, two geochemical models are proposed. (1) The oils were derived from a kerogen facies, which grades from a hypersaline marine environment in the Albian to a marine facies in the Cenomanian Maastrichtian. (2) The oils were derived from a hypersaline marine facies in the Albian and a second marine facies deposited during the Oligocene. Although previous work by other authors has shown the Upper Cretaceous/lower Tertiary source rocks from wells in the Logbaba gas field to be gas prone (type III), data from the present study provide evidence that at least one mature oil-prone source rock exists within this interval elsewhere in the basin.

  19. Rock Magnetic and Grain Size Variation Along A 50m Cretaceous Sedimentary Section of The Marilia Formation (bauru Basin), Brazil

    NASA Astrophysics Data System (ADS)

    Tamrat, E.; Ernesto, M.; Watanabe, J.; Saad, A. R.; Fulfaro, V. J.

    We present a detailed rock magnetic investigation of a sedimentary section from the Marilia Formation of the Bauru Basin (22.22S, 49.96W), Brasil. Sampling was con- ducted over 0.5m interval of a 50m Late Cretaceous sedimentary deposit. The deposits are consists of coarse to conglomeratic sandstones with abundant calciferous cement and nodules. A total of 81 samples from 67 sites have carried out using hysteresis loop and thermomagnetic curves in order to identify the magnetic mineral and distribution of their grain-size. Trends in rock magnetic parameters with remanent saturation be- low 300mT and moderate coercivity of remanence are consistent with a contribution of Pseudo-single domain to small Multi-domain magnetite. High temperature exper- iments of the magnetic susceptibility up to 700C indicate abundant magnetite with minor contribution of titanomaghemite. Changes in hysteresis parameters are consis- tent with changes in the relative amounts of the different magnetite size fractions. On the basis of rock magnetic investigation, a sample of the Marilia Formation appears to be a reliable recorder of the geomagnetic field during sediment deposition. Their straightforward mineralogy and minimal changes in magnetic concentration consti- tute an opportunity to examine not only rock magnetic and grain size variation, but directional changes and magnetostratigraphy data as well.

  20. Hot rock and wildfires: assessing the potential of the proximal Cretaceous-Palaeogene impact melt spherules to ignite wildfires

    NASA Astrophysics Data System (ADS)

    Hadden, Rory; Belcher, Claire M.; Scott, Sarah; Fereres, Sonia; Lautenberger, Chris; Fernandez-Pello, A. Carlos

    2010-05-01

    It is generally accepted that an extraterrestrial body collided with the Earth 65 m.y. ago and that the 200-km-wide Chicxulub Crater on the Yucatan Peninsula, Mexico, is the mark of this impact. This impact blasted melted asteroidal and target rock debris across the planet, depositing the Cretaceous-Palaeogene (K-Pg) boundary impact rock layers. Several models have suggested that the thermal radiation released by the K-Pg impact ought to have been sufficient to have ignited wildfires locally, if not globally. However, a more recent model by Goldin and Melosh (2009) suggests the thermal flux to the ground surface was a maximum of 19 kW m sq. This model is consistent with the record of wildfire indicators analysed from K-Pg boundary impact rocks, which show little evidence for wildfires associated with this event across the western interior of North America. The K-Pg impact is known to have formed thick proximal ejecta deposits consisting of large (typically 1-10mm) melt spherules up to 2000km in distance from Chicxulub crater. This zone includes areas of land that are known to have been emergent from the ocean at this time and where forests may have come into direct contact with the hot ejecta. Here we test the ability of these large super-heated melt spherules to ignite wildfires in the areas proximal to Chicxulub crater using laboratory experiments. Metal ball-bearings of a variety of sizes (4.4-19.1mm in diameter) and heated to a variety of temperatures (500-1100oC) were dropped onto cellulose and pine needle fuel beds. The former is a well-characterised "laboratory" fuel while the latter is a natural fuel relevant to wildfire spread. The temperature of the fuel beds was recorded (via thermocouples) at eight locations moving away from the spherule impact point in the cellulose fuel beds, whereas mass loss of the fuel bed was used to characterise ignition in pine needle fuel beds. Our results suggest that vegetated areas receiving impacts of spherules 4.4mm or

  1. 70 million years of coastal upwelling in California; source rocks and paleoceanography

    SciTech Connect

    Fonseca, C.

    1996-12-31

    The Late Mesozoic-Cenozoic marine sequence of California displays a unique record of coastal upwelling and productivity in the form of distinctive diatomaceous and organic-rich deposits including the upper Cretaceous-lower Paleocene Moreno Formation, the Eocene Kreyenhagen Formation and the Miocene Monterey Formation. Unique sedimentological characteristics of these ancient upwelling systems include (a) Finely laminated biosiliceous-rich shales (>30% biogenic silica content), (b) Distinctive laminae composed by monospecific diatom resting spores, (c) Good source rock quality (>300 mg HC/mg org C), and (d) High accumulation rates in mid water anoxic conditions. Detailed study of individual laminae in sediments of these formations revealed concentration of monospecific diatom resting spores and an abundance of Stephanopyxis sp. and Coscinodiscus sp. Like Recent upwelling systems, preserved laminations of monospecific resting spores reflect strong seasonal upwelling that lead to high organic matter production and enhancement of anoxia. The presence of spores in the ancient and modern upwelling systems is evidence that diatoms have adapted and successfully competed in the highly productive California Margin since the Late Cretaceous. The Moreno, the Kreyenhagen and the Monterey Formation account for a significant portion of major petroleum source beds in California and contain an important record of coastal upwelling and paleoceanographic change in the northeastern Pacific Ocean over the past 70 million years. It is suggested that potential Late Maestrichtian source rocks could have been deposited along other favorable upwelling areas of the Eastern Pacific Rim.

  2. 70 million years of coastal upwelling in California; source rocks and paleoceanography

    SciTech Connect

    Fonseca, C. )

    1996-01-01

    The Late Mesozoic-Cenozoic marine sequence of California displays a unique record of coastal upwelling and productivity in the form of distinctive diatomaceous and organic-rich deposits including the upper Cretaceous-lower Paleocene Moreno Formation, the Eocene Kreyenhagen Formation and the Miocene Monterey Formation. Unique sedimentological characteristics of these ancient upwelling systems include (a) Finely laminated biosiliceous-rich shales (>30% biogenic silica content), (b) Distinctive laminae composed by monospecific diatom resting spores, (c) Good source rock quality (>300 mg HC/mg org C), and (d) High accumulation rates in mid water anoxic conditions. Detailed study of individual laminae in sediments of these formations revealed concentration of monospecific diatom resting spores and an abundance of Stephanopyxis sp. and Coscinodiscus sp. Like Recent upwelling systems, preserved laminations of monospecific resting spores reflect strong seasonal upwelling that lead to high organic matter production and enhancement of anoxia. The presence of spores in the ancient and modern upwelling systems is evidence that diatoms have adapted and successfully competed in the highly productive California Margin since the Late Cretaceous. The Moreno, the Kreyenhagen and the Monterey Formation account for a significant portion of major petroleum source beds in California and contain an important record of coastal upwelling and paleoceanographic change in the northeastern Pacific Ocean over the past 70 million years. It is suggested that potential Late Maestrichtian source rocks could have been deposited along other favorable upwelling areas of the Eastern Pacific Rim.

  3. Sr-Nd-Hf-Pb isotope geochemistry of basaltic rocks from the Cretaceous Gyeongsang Basin, South Korea: Implications for basin formation

    NASA Astrophysics Data System (ADS)

    Choi, S.; Kwon, S.; Lee, D.

    2013-12-01

    To better understand the formative mechanism of the Cretaceous Gyeongsang Basin in South Korea, we determined the geochemical compositions of Early Cretaceous syntectonic basaltic rocks intercalated with basin sedimentary assemblages. Two distinct compositional groups appeared: tholeiitic to calc-alkaline basalts from the Yeongyang sub-basin and high-K to shoshonitic basaltic trachyandesites from the Jinju and Uiseong sub-basins. All collected samples exhibit patterns of light rare earth element enrichment and chondrite-normalized (La/Yb)N ratios ranging from 2.4 to 23.6. In a primitive-mantle-normalized spidergram, the samples show distinctive negative anomalies in Nb, Ta, and Ti and a positive anomaly in Pb. The basalts exhibit no or a weak positive U anomaly in a spidergram, but the basaltic trachyandesites show a negative U anomaly. The basalts have highly radiogenic Sr [(87Sr/86Sr)i = 0.70722-0.71145], slightly negative ɛNd, positive ɛHf [(ɛNd)i = -2.7 to 0.0; (ɛHf)i = +2.9 to +6.4], and radiogenic Pb isotopic compositions [(206Pb/204Pb)i = 18.20-19.19; (207Pb/204Pb)i = 15.60-15.77; (208Pb/204Pb)i = 38.38-39.11]. The basaltic trachyandesites are characterized by radiogenic Sr [(87Sr/86Sr)i = 0.70576-0.71119] and unradiogenic Nd, Hf, and Pb isotopic compositions [(ɛNd)i = -14.0 to -1.4; (ɛHf)i = -17.9 to +3.7; (206Pb/204Pb)i = 17.83-18.25; (207Pb/204Pb)i = 15.57-15.63; (208Pb/204Pb)i = 38.20-38.70]. The 'crust-like' signatures, such as negative Nb-Ta anomalies, elevated Sr isotopic compositions, and negative ɛNd(t) and ɛHf(t) values, of the basaltic trachyandesites resemble the geochemistry of Early Cretaceous mafic volcanic rocks from the southern portion of the eastern North China Craton. Considering the lower-crust-like low U/Pb and high Th/U ratios and the unradiogenic Pb isotopic compositions, the basaltic trachyandesites are considered to be derived from lithospheric mantle modified by interaction with melts that originated from foundered eclogite

  4. Sr-Nd-Hf-Pb isotope geochemistry of basaltic rocks from the Cretaceous Gyeongsang Basin, South Korea: Implications for basin formation

    NASA Astrophysics Data System (ADS)

    Kwon, Sun-Ki; Choi, Sung Hi; Lee, Der-Chuen

    2013-09-01

    To better understand the formative mechanism of the Cretaceous Gyeongsang Basin in South Korea, we determined the geochemical compositions of Early Cretaceous syntectonic basaltic rocks intercalated with basin sedimentary assemblages. Two distinct compositional groups appeared: tholeiitic to calc-alkaline basalts from the Yeongyang sub-basin and high-K to shoshonitic basaltic trachyandesites from the Jinju and Uiseong sub-basins. All collected samples exhibit patterns of light rare earth element enrichment and chondrite-normalized (La/Yb)N ratios ranging from 2.4 to 23.6. In a primitive-mantle-normalized spidergram, the samples show distinctive negative anomalies in Nb, Ta, and Ti and a positive anomaly in Pb. The basalts exhibit no or a weak positive U anomaly in a spidergram, but the basaltic trachyandesites show a negative U anomaly. The basalts have highly radiogenic Sr [(87Sr/86Sr)i = 0.70722-0.71145], slightly negative εNd, positive εHf [(εNd)i = -2.7 to 0.0; (εHf)i = +2.9 to +6.4], and radiogenic Pb isotopic compositions [(206Pb/204Pb)i = 18.20-19.19; (207Pb/204Pb)i = 15.60-15.77; (208Pb/204Pb)i = 38.38-39.11]. The basaltic trachyandesites are characterized by radiogenic Sr [(87Sr/86Sr)i = 0.70576-0.71119] and unradiogenic Nd, Hf, and Pb isotopic compositions [(εNd)i = -14.0 to -1.4; (εHf)i = -17.9 to +3.7; (206Pb/204Pb)i = 17.83-18.25; (207Pb/204Pb)i = 15.57-15.63; (208Pb/204Pb)i = 38.20-38.70]. The “crust-like” signatures, such as negative Nb-Ta anomalies, elevated Sr isotopic compositions, and negative εNd(t) and εHf(t) values, of the basaltic trachyandesites resemble the geochemistry of Early Cretaceous mafic volcanic rocks from the southern portion of the eastern North China Craton. Considering the lower-crust-like low U/Pb and high Th/U ratios and the unradiogenic Pb isotopic compositions, the basaltic trachyandesites are considered to be derived from lithospheric mantle modified by interaction with melts that originated from foundered

  5. Simulation of ground-water flow in aquifers in Cretaceous rocks in the central Coastal Plain, North Carolina

    USGS Publications Warehouse

    Eimers, J.L.; Lyke, W.L.; Brockman, A.R.

    1990-01-01

    The principal sources of water-supply in Cretaceous rocks in the central Coastal Plain of North Carolina are the Peedee, Black Creek, and upper Cape Fear aquifers. Ground-water withdrawals from these aquifers have increased from about 0.25 million gallons per day in 1910 to over 29 million gallons per day in 1986, causing water-level declines as much as 160 feet. The maximum rate of water-level decline in 1986 is about 11 feet per year in the Black Creek aquifer. A quasi-three dimensional ground-water flow model was constructed and calibrated for the period 1900 to 1986 to simulate past water-level declines and to estimate the effects of future pumpage. Comparisons of 1,867 observed and model-computed heads were made at 323 well sites. The average difference between computed and observed water levels is -1 foot. About 68 percent of all the differences between computed and observed water levels falls in the range from -21.0 to 21.0 feet. Simulation indicates that the 29 million gallons per day of pumpage in 1986 was supplied by (1) increased recharge (net discharge of 2 million gallons per day in 1900 changed to net recharge of 18 million gallons per day in 1986), (2) increased lateral inflow to the aquifers of about 8 million gallons per day, and (3) depletion of ground-water storage of about 1 million gallons per day. Two pumping scenarios simulated head changes through 1991 and were based on (1) constant pumpage at the 1986 rates in each aquifer, and (2) continuing increases in pumping rates from 1986 through 1991 and rates varying from 10 to 19 percent per year for the three pumped aquifers. For scenario 1, water-level declines exceeded 5 feet locally; however, water-level rises of about 1 foot occurred in two areas. For scenario 2, water-level declines ranged from 1 foot to 30 feet in some pumping centers.

  6. Implications of Late Cretaceous U-Pb zircon ages of granitic intrusions cutting ophiolitic and volcanogenic rocks for the assembly of the Tauride allochthon in SE Anatolia (Helete area, Kahramanmaraş Region, SE Turkey)

    NASA Astrophysics Data System (ADS)

    Nurlu, Nusret; Parlak, Osman; Robertson, Alastair; von Quadt, Albrecht

    2016-01-01

    An assemblage of NE-SW-trending, imbricate thrust slices (c. 26 km E-W long × 6.3 km N-S) of granitic rocks, basic-felsic volcanogenic rocks (Helete volcanics), ophiolitic rocks (Meydan ophiolite) and melange (Meydan melange) is exposed near the Tauride thrust front in SE Anatolia. The volcanogenic rocks were previously assumed to be Eocene because of associated Nummulitic limestones. However, ion probe U-Pb dating of zircons extracted from the intrusive granitic rocks yielded ages of 92.9 ± 2.2-83.1 ± 1.5 Ma (Cenomanian-Campanian). The Helete volcanic unit and the overlying Meydan ophiolitic rocks both are intruded by granitic rocks of similar age and composition. Structurally underlying ophiolite-related melange includes similar-aged, but fragmented granitic intrusions. Major, trace element and rare earth element analyses coupled with electron microprobe analysis of the granitic rocks show that they are metaluminus to peraluminus and calc-alkaline in composition. A magmatic arc setting is inferred from a combination of tectonomagmatic discrimination, ocean ridge granite-normalized multi-element patterns and biotite geochemistry. Sr-Nd-Pb isotope data further suggest that the granitoid rocks were derived from variably mixed mantle and crustal sources. Granitic rocks cutting the intrusive rocks are inferred to have crystallized at ~5-16 km depth. The volcanogenic rocks and granitic rocks originated in a supra-subduction zone setting that was widely developed throughout SE Anatolia. Initial tectonic assembly took place during the Late Cretaceous probably related to northward subduction and accretion beneath the Tauride continent (Keban and Malatya platforms). Initial tectonic assembly was followed by exhumation and then transgression by shelf-depth Nummulitic limestones during Mid-Eocene, as documented in several key outcrops. Final emplacement onto the Arabian continental margin took place during the Early Miocene.

  7. Paleomagnetism of Jurassic and Cretaceous rocks in central Patagonia: a key to constrain the timing of rotations during the breakup of southwestern Gondwana?

    NASA Astrophysics Data System (ADS)

    Geuna, Silvana E.; Somoza, Rubén; Vizán, Haroldo; Figari, Eduardo G.; Rinaldi, Carlos A.

    2000-08-01

    A paleomagnetic study in Jurassic and Cretaceous rocks from the Cañadón Asfalto basin, central Patagonia, indicates the occurrence of about 25-30° clockwise rotation in Upper Jurassic-lowermost Cretaceous rocks, whereas the overlying mid-Cretaceous rocks do not show evidence of rotation. This constrains the tectonic rotation to be related to a major regional unconformity in Patagonia, which in turn seems to be close in time with the early opening of the South Atlantic Ocean. The sense and probably the timing of this rotation are similar to those of other paleomagnetically detected rotations in different areas of southwestern Gondwana, suggesting a possible relationship between these and major tectonic processes related with fragmentation of the supercontinent. On the other hand, the mid-Cretaceous rocks in the region yield a paleopole located at Lat. 87° South, Long. 159° East, A95=3.8°. This pole position is consistent with coeval high-quality paleopoles of other plates when transferred to South American coordinates, implying it is an accurate determination of the Aptian (circa 116 Ma) geomagnetic field in South America.

  8. Preliminary hydrocarbon source rock assessment of the Paleozoic and Mesozoic formations of the western Black Sea region of Turkey

    SciTech Connect

    Harput, B.O.; Demirel, I.H.; Karayigit, A.I.; Aydin, M.; Sahintuerk, O.; Bustin, R.M.

    1999-12-01

    Source rock maturity and potential of Paleozoic and Mesozoic formations in the Eregli, Zonguldak, Bartin, Ulus, and Eflani subregions of the western Black Sea region (WBSR), have been investigated by rock-eval pyrolysis, reflected-light microscopy, and palynofacies analyses. The % Ro values of dispersed organic matter of the Paleozoic formations primarily range from 0.72 to 1.8%, but values as high as 2.6% occur locally in the Silurian Findikli Formation in the Eregli subregion. The % Ro values of Namurian-Westphalian coal seams in the K20/H well drilled in the Zonguldak subregion range from 0.87 to 1.52%, with increasing depth consistent with sedimentary depth of burial. Most Cretaceous age samples have reflectance values ranging from 0.44 to 1.6% Ro that indicates they are marginally mature to mature with respect to the oil window. Rock-eval pyrolysis demonstrates that the Paleozoic formations have limited oil-generation potential (HI values {le} 200 mg HC/g C{sub org}), but good gas potential (TOC values up to 3%). Cretaceous formations have better petroleum source rock characteristics, but they too are primarily gas prone. Variations in the source rock maturity probably reflect variable burial histories in different localities of the WBSR.

  9. Hydrocarbon potential of hydrocarbon source rocks of the New Siberian Islands, Russian Arctic

    NASA Astrophysics Data System (ADS)

    Gaedicke, Christoph; Sobolev, Peter; Franke, Dieter; Piepjohn, Karsten; Brandes, Christian; Kus, Jolanta; Scheeder, Georg

    2016-04-01

    The New Siberian Islands are bridging the Laptev Sea with the East Siberian Sea. The Laptev and East Siberian Seas cover large areas of the continental margin of northeastern Arctic Russia. The East Siberian Shelf encompassing an area of 935.000 km2 is still virtually unexplored and most of the geological models for this shelf are extrapolations of the geology of the New Siberian Islands, the Wrangel Island and the northeast Siberian landmass. Apart from few seismic reflection lines, airborne magnetic data were the primary means of deciphering the structural pattern of the East Siberian Shelf. The Laptev Shelf covers an area of about 66.000 km2 and occupies a shelf region, where the active mid-oceanic spreading ridge of the Eurasian Basin hits the slope of the continental margin. During the joint VSEGEI/BGR field expedition CASE 13 (Circum Arctic Structural Events) in summer 2011 we sampled outcrops from the New Siberian Archipelago including the De Long Islands. 102 samples were collected and the Upper Palaeozoic to Lower Cenozoic units are found to be punctuated by several organic-rich intervals. Lithology varies from continental dominated clastic sedimentary rocks with coal seams to shallow marine carbonates and deep marine black shales. Rock-Eval pyrolysis, gas chromatography/mass spectrometry and organic petrography studies were performed to estimate organic matter contents, composition, source, and thermal maturity. According to the results of our analyses, samples from several intervals may be regarded as potential petroleum source rocks. The Lower Devonian shales have the highest source rock potential of all Paleozoic units. Triassic samples have a good natural gas potential. Cretaceous and Cenozoic low-rank coals, lignites, and coal-bearing sandstones display some gas potential. The kerogen of type III (humic, gas-prone) dominates. Most of the samples (except some of Cretaceous and Paleogene age) reached the oil generation window.

  10. Mineral chemical compositions of late Cretaceous volcanic rocks in the Giresun area, NE Turkey: Implications for the crystallization conditions

    NASA Astrophysics Data System (ADS)

    Oǧuz, Simge; Aydin, Faruk; Uysal, İbrahim; Şen, Cüneyt

    2016-04-01

    This contribution contains phenocryst assemblages and mineral chemical data of late Cretaceous volcanic (LCV) rocks from the south of Görele and Tirebolu areas (Giresun, NE Turkey) in order to investigate their crystallization conditions. The LCV rocks in the study area occur in two different periods (Coniasiyen-Early Santonian and Early-Middle Campanian), which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic and rhyolitic) within each period. The basaltic and andesitic rocks in both periods generally exhibit porphyritic to hyalo-microlitic porphyritic texture, and contain phenocrysts of plagioclase and pyroxene, whereas the dacitic and rhyolitic rocks of the volcanic sequence usually show a vitrophyric texture with predominant plagioclase, K-feldspar, quartz and lesser amphibole-biotite phenocrysts. Zoned plagioclase crystals of the mafic and felsic rocks in different volcanic periods are basically different in composition. The compositions of plagioclase in the first-stage mafic rocks range from An52 to An78 whereas those of plagioclase from the first-stage felsic rocks have lower An content varying from An38 to An50. Rim to core profile for the zoned plagioclase of the first-stage mafic rocks show quite abrupt and notable compositional variations whereas that of the first-stage felsic rocks show slight compositional variation, although some of the grains may display reverse zoning. On the other hand, although no zoned plagioclase phenocryst observed in the second-stage mafic rocks, the compositions of microlitic plagioclase show wide range of compositional variation (An45-80). The compositions of zoned plagioclase in the second-stage felsic rocks are more calcic (An65-81) than those of the first-stage felsic rocks, and their rim to core profile display considerable oscillatory zoning. The compositions of pyroxenes in the first- and second-stage mafic-intermediate rocks vary over a wide range from

  11. Paleomagnetism, rock-magnetism and geochemical aspects of early Cretaceous basalts of the Paraná Magmatic Province, Misiones, Argentina

    NASA Astrophysics Data System (ADS)

    Mena, Mabel; Orgeira, María Julia; Lagorio, Silvia

    2006-10-01

    The basalts of the Posadas Formation were extruded during the huge continental volcanism that affected the Paraná Basin in the Lower Cretaceous. We have carried out a paleomagnetic and rock-magnetic study on samples collected along a basalt outcrop section in Misiones, Argentina and determined that rocks classified as tholeiitic basalts and andesi-basalts are characterized by a low to intermediate content of Ti. Paleomagnetic and rock-magnetic studies suggest that the main magnetic mineral is low-Ti titanomagnetite of superparamagnetic (SP) to single-domain (SD) sizes, and very low amounts of multi-domain (MD) particles. The stable magnetic remanence enabled us to define characteristic remanent magnetizations (ChRMs) with a maximum angular deviation (MAD) <5° in most cases; and in all the cases, a MAD <10°. The sequence has registered at least two polarity reversions, starting from a normal polarity at the base. The calculated virtual geomagnetic poles (VGPs) present an elongated distribution similar to other distributions of VGPs published for the Paraná Magmatic Province. The elongated distribution of the VGPs could be a real feature of the geomagnetic field at a time of frequent changes of polarity.

  12. An integrated petrophysical and rock physics analysis to improve reservoir characterization of Cretaceous sand intervals in Middle Indus Basin, Pakistan

    NASA Astrophysics Data System (ADS)

    Azeem, Tahir; Chun, Wang Yan; MonaLisa; Khalid, Perveiz; Xue Qing, Liu; Ehsan, Muhammad Irfan; Jawad Munawar, Muhammad; Wei, Xie

    2017-03-01

    The sand intervals of the Lower Goru Formation of the Cretaceous age, widely distributed in the Middle and Lower Indus Basin of Pakistan, are proven reservoirs. However, in the Sawan gas field of the Middle Indus Basin, these sandstone intervals are very deep and extremely heterogeneous in character, which makes it difficult to discriminate lithologies and fluid saturation. Based on petrophysical analysis and rock physics modeling, an integrated approach is adopted to discriminate between lithologies and fluid saturation in the above-mentioned sand intervals. The seismic velocities are modeled using the Xu–White clay–sand mixing rock physics model. The calibrated rock physics model shows good consistency between measured and modeled velocities. The correlation between measured and modeled P and S wave velocities is 92.76% and 84.99%, respectively. This calibrated model has been successfully used to estimate other elastic parameters, even in those wells where both shear and sonic logs were missing. These estimated elastic parameters were cross-plotted to discriminate between the lithology and fluid content in the target zone. Cross plots clearly separate the shale, shaly sand, and gas-bearing sand clusters, which was not possible through conventional petrophysical analysis. These data clusters have been exported to the corresponding well for the purpose of interpolation between wells and to analyze the lateral and vertical variations in lithology and fluid content in the reservoir zone.

  13. 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

    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.

  14. 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

    2016-05-01

    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.

  15. Stratigraphic controls on the source rock distribution, Llanos Orientales Basin, Colombia

    SciTech Connect

    Ramon, J.C.; Fajardo, A.; Rubiano, J.; Reyes, A. )

    1996-01-01

    All available rock and oil geochemistry analyses were tied to a high-resolution stratigraphic framework for more than 50 wells in the Central Llanos Orientates Basin. New Tertiary generation input is proposed. The best source rock intervals are at the base and top of the Gacheta Formation (Upper Cretaceous) and in the middle of the Barco-Cuervos (Paleocene) and Mirador (Eocene) formations. These organic-rich zones contain type II and III kerogen. TOC contents range from about 1% up to 15%. The four source rock intervals occur within marine shales near condensed sections, at the position maximum accommodation/sediment-supply (A/S) ratios. The development of conditions that allow accumulation and preservation of anomalously high fractions of organic matter might be explained by two mechanisms. Increased A/S ratio results in retention of more sediment in the coastal plain, thus reducing the tendency for siliciclastic sediment to dilute the organic matter accumulating on the shelf. Also, deeper water might restrict circulation, enhancing bottom anoxic conditions. In the more transitional and continental sequences, increased A/S ratio is associated with higher phreatic water level. A high ground water table enhances preservation of coaly intervals. The sea-level rise brings marine water into valleys and low-gradient coastal plains. The resulting embayments, marsh and swampy areas are organic-prone, contributing to the source rock potential of strata associated with high conditions and base-level rise-to-fall turnaround positions.

  16. Stratigraphic controls on the source rock distribution, Llanos Orientales Basin, Colombia

    SciTech Connect

    Ramon, J.C.; Fajardo, A.; Rubiano, J.; Reyes, A.

    1996-12-31

    All available rock and oil geochemistry analyses were tied to a high-resolution stratigraphic framework for more than 50 wells in the Central Llanos Orientates Basin. New Tertiary generation input is proposed. The best source rock intervals are at the base and top of the Gacheta Formation (Upper Cretaceous) and in the middle of the Barco-Cuervos (Paleocene) and Mirador (Eocene) formations. These organic-rich zones contain type II and III kerogen. TOC contents range from about 1% up to 15%. The four source rock intervals occur within marine shales near condensed sections, at the position maximum accommodation/sediment-supply (A/S) ratios. The development of conditions that allow accumulation and preservation of anomalously high fractions of organic matter might be explained by two mechanisms. Increased A/S ratio results in retention of more sediment in the coastal plain, thus reducing the tendency for siliciclastic sediment to dilute the organic matter accumulating on the shelf. Also, deeper water might restrict circulation, enhancing bottom anoxic conditions. In the more transitional and continental sequences, increased A/S ratio is associated with higher phreatic water level. A high ground water table enhances preservation of coaly intervals. The sea-level rise brings marine water into valleys and low-gradient coastal plains. The resulting embayments, marsh and swampy areas are organic-prone, contributing to the source rock potential of strata associated with high conditions and base-level rise-to-fall turnaround positions.

  17. Geochemistry and petrology of Late Cretaceous subvolcanic rocks (Macka-Trabzon) in the north of the eastern Black Sea region, NE-Turkey

    NASA Astrophysics Data System (ADS)

    Aydin, Faruk

    2013-04-01

    In this study, geochronological, geochemical and isotopical data for the early Campanian subvolcanic rocks (Macka-Trabzon) in the north of the eastern Blacksea region, northeastern Turkey, have initially been presented with the aim of determining its magma source and geodynamic evolution. The subvolcanic rocks cutting the subduction-related Late Cretaceous volcano-sedimantary rocks in the region are characterized by several sills and dykes with columnar structures and they consist of amphibole-rich quartz-diorite and quartz-tonalite porphyries, with some dioritic mafic microgranular enclaves. The host rocks have a microgranular porphyritic texture, and they contain 15-25% phenocryst of plagioclase and amphibole and have a matrix that is composed primarily of fine-grained quartz, orthoclase, and plagioclase. Accessory apatite, zircon and Fe-Ti oxides are present in all of the rocks. Secondary minerals such as epidote, calcite, sericite and clays are sometimes observed in the matrix or as hydothermal alteration products of some amphibole and plagioclase phenocrysts. When compared to the host rocks, the magmatic enclaves without quartz are fine-grained, and they contain higher ferromagnesian phases and lower feldspar minerals. Ar-Ar geochronology studies on the amphibole separates reveal that the porphyries have a crystallization ages of 81±0.5 Ma. All samples show a high-K calc-alkaline differentiation trend and I-type features with metaluminous character. The rocks and magmatic enclaves are characterized by enrichment of LILE and depletion of HFSE with negative Nb, Ti, Zr and P anomalies. The chondrite-normalized REE patterns are not fractionated [(La/Yb)N = 9-11] and do not display Eu anomalies (Eu/Eu* = 0.7-0.9). The porphyritic rocks and their enclaves are almost isotopically similar. Sr-Nd isotopic data for all of the samples display initial Sr = 0.7085-0.7087, epsilon Nd (81 Ma) = -6.0 to -6.9, with TDM = 1.38-1.63 Ga. The lead isotopic ratios are (206Pb/204Pb

  18. Applying Bioaugmentation to Treat DNAPL Sources in Fractured Rock

    DTIC Science & Technology

    2017-03-27

    GUIDANCE DOCUMENT Applying Bioaugmentation to Treat DNAPL Sources in Fractured Rock ESTCP Project ER-201210 MARCH 2017 Charles Schaefer, Ph.D...12-C-0062 Applying Bioaugmentation to Treat DNAPL Sources in Fractured Rock 5b. GRANT NUMBER NA 5c. PROGRAM ELEMENT NUMBER NA 6. AUTHOR(S...Approved for Public Release, Distribution is Unlimited 13. SUPPLEMENTARY NOTES None 14. ABSTRACT Management of fractured rock sites impacted by

  19. Rock avalanches caused by earthquakes: source characteristics.

    PubMed

    Keefer, D K

    1984-03-23

    Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability.

  20. Extraction of whole versus ground source rocks: Fundamental petroleum geochemical implications including oil-source rock correlation

    USGS Publications Warehouse

    Price, L.C.; Clayton, J.L.

    1992-01-01

    In petroleum geochemistry, extractable hydrocarbons (HCs) in source rocks have typically been studied by grinding the rock to a fine powder (???100 mesh) and then extracting the HCs from the rock with a solvent. This procedure carries the implicit assumption that the HCs are homogeneously distributed throughout the rock. However, sequential Soxhlet extractions of whole (unpowdered) source rocks have shown that progressive extracts from the same rock can be quite different and may not even correlate with each other. A crude oil-like material clearly has been fractionated from indigenous bitumen in these rocks, has moved to cracks and parting laminae in the rocks, is ready for expulsion from the rocks, and is thus most accessible to the first extracting solvents. This process, which we believe is largely due to HC gases and carbon dioxide generated over all maturation ranks in source rocks, carries petroleum geochemical implications of a fundamental nature for oil-source rock correlations and gives insight into primary migration mechanisms, origin of oil deposits, and use of maturity and organic-facies indices. ?? 1992.

  1. Extraction of whole versus ground source rocks: Fundamental petroleum geochemical implications including oil-source rock correlation

    SciTech Connect

    Price, L.C.; Clayton, J.L. )

    1992-03-01

    In petroleum geochemistry, extractable hydrocarbons (HCs) in source rocks have typically been studied by grinding the rock to a fine powder ({le}100 mesh) and then extracting the HCs from the rock with a solvent. This procedure carries the implicit assumption that the HCs are homogeneously distributed throughout the rock. However, sequential Soxhlet extractions of whole (unpowdered) source rocks have shown that progressive extracts from the same rock can be quite different and may not even correlate with each other. A crude oil-like material clearly has been fractionated from indigenous bitumen in these rocks, has moved to cracks and parting laminae in the rocks, is ready for expulsion from the rocks, and is thus most accessible to the first extracting solvents. This process, which the authors believe is largely due to HC gases and carbon dioxide generated over all maturation ranks in source rocks, carries petroleum geochemical implications of a fundamental nature for oil-source rock correlations and gives insight into primary migration mechanisms, origin of oil deposits, and use of maturity and organic-facies indices.

  2. Basin richness and source rock disruption - a fundamental relationship

    USGS Publications Warehouse

    Price, L.C.

    1994-01-01

    Primary petroleum migration (expulsion from source rocks) remains the least understood parameter controlling the genesis of oil deposits. It is hypothesised that source rocks must be physically disrupted before meaningful expulsion can occur. Faulting, with accompanying significant fracturing, would appear to be the optimum naturally-occurring process for physical disruption of source rocks. If these hypotheses are valid, intensity of faulting in deeply-buried HC "kitchens' containing mature source rocks should strongly correlate with increasing basin richness. This possible relationship is examined in this paper; it is found that there is a strong correlation of increasing basin richness with increasing structural intensity over and adjacent to basin depocentres. This correlation thus supports the hypothesis that physical disruption of mature source rocks is a necessary, and previously unappreciated, controlling parameter for oil expulsion. -from Author

  3. Lithofacies and palynostratigraphy of some Cretaceous and Paleocene rocks, Surghar and Salt Range coal fields, northern Pakistan

    USGS Publications Warehouse

    Warwick, Peter D.; Javed, Shahid; Mashhadi, S. Tahir A.; Shakoor, Tariq; Khan, Asrar M.; Khan, A. Latif

    1995-01-01

    The stratigraphic relation between the Cretaceous generally non-coal-bearing Lumshiwal Formation (64 to 150 m thick) and the Paleocene coal-bearing Hangu Formation (5 to 50 m thick) in the Surghar Range of north-central Pakistan is complex. Both formations contain remarkably similar lithofacies: one or two types of sandstone lithofacies; a combined lithofacies of mudstone, claystone, carbonaceous shale, and coal beds; and a rare carbonate lithofacies. An analysis of pollen data from rock samples collected from various stratigraphic positions indicates that the formations are separated by a disconformity and that the age of the Lumshiwal Formation is Early Cretaceous and the age of the Hangu is Paleocene. Previous workers had suggested that the age of the Lumshiwal is Late Cretaceous. An analysis of sedimentologic, stratigraphic, and paleontologic data indicates that both the Lumshiwal and Hangu Formations probably were deposited in shallow-marine and deltaic environments. The rocks of the Lumshiwal become more terrestrial in origin upward, whereas the rocks of the Hangu become more marine in origin upward. The contact between the two formations is associated with a laterally discontinuous lateritic paleosol (assigned to the Hangu Formation) that is commonly overlain by the economically important Makarwal coal bed. This coal bed averages 1.2 m in thickness. No other coal beds in the Surghar Range are as thick or as laterally continuous as the Makarwal coal bed. Analytical data from the Makarwal and one other Hangu coal bed indicate that Surghar Range coal beds range from high-volatile B to high-volatile C bituminous in apparent rank. Averaged, as-received results of proximate and ultimate analyses of coal samples are (1) moisture content, 5.4 percent; (2) ash yield, 12.5 percent; (3) total sulfur content, 5 percent; and (4) calorific value, 11034 Btu/lb (British thermal units per pound). Minor- and trace-element analyses indicate that these coals contain relatively

  4. Petroleum source rock potential of Mesozoic condensed section deposits in southwestern Alabama

    SciTech Connect

    Mancini, E.A; Tew, B.H.; Mink, R.M. )

    1991-03-01

    Because condensed section deposits in carbonates and siliclastics are generally fine-grained lithologies often containing relatively high concentrations of organic matter, these sediments have the potential to be petroleum source rocks if buried under conditions favorable for hydrocarbon generation. In the Mesozoic deposits of southwestern Alabama, only the Upper Jurassic Smackover carbonate mudstones of the condensed section of the LZAGC-4.1 cycle have realized their potential as hydrocarbon source rocks. These carbonate mudstones contain organic carbon concentrations of algal and amorphous kerogen of up to 1.7% and have thermal alteration indices of 2- to 3+. The Upper Cretaceous Tuscaloosa marine claystones of the condensed section of the UZAGC-2.5 cycle are rich (up to 2.9%) in herbaceous and amorphous organic matter but have not been subjected to burial conditions favorable for hydrocarbon generation. The Jurassic Pine Hill/Norphlet black shales of the condensed section of the LZAGC-3.1 cycle and the Upper Jurassic Haynesville carbonate mudstones of the condensed section of the LZAGC-4.2 cycle are low (0.1%) in organic carbon. Although condensed sections within depositional sequences should have the highest source rock potential, specific environmental, preservational, and/or burial history conditions within a particular basin will dictate whether or not the potential is realized as evidenced by the condensed sections of the Mesozoic depositional sequences in southwestern Alabama. Therefore, petroleum geologists can use sequence stratigraphy to identify potential source rocks; however, only through geochemical analyses can the quality of these potential source rocks be determined.

  5. Lagoonal deposits in the Upper Cretaceous Rock Springs Formation (Mesaverde Group), southwest Wyoming

    USGS Publications Warehouse

    Kirschbaum, M.A.

    1989-01-01

    Most paleogeographic reconstructions of the Rock Springs Formation show shorelines having lobate to arcuate deltas. These shorelines are oriented NE-SW, with the sea to the southeast. Brackish-water bodies are usually shown in interdistributary areas or associated with abandoned delta lobes, and are open to the sea. In this study, a sedimentary sequence 30-50 m thick is interpreted as interdeltaic deposits. Brackish-water deposits within the sequence are interpreted as interdeltaic lagoons rather than interdistributary bays. Three facies associations (units) are recognized in nine measured sections of the study interval. Unit A consists of interbedded sandstone, mudrock and coal which occur in both fining- and coarsening-upward sequences less than 10 m thick. Fining-upward sequences decrease in thickness and frequency upwards in unit A and are interpreted as distributary channels. Coarsening-upward sequences associated with the channels are interpreted as crevasse splays that filled lakes or interdistributary bays. In the upper part of the unit where only minor channels are present, the coarsening-upward sequences are interpreted as bay deltas. Unit B consists of fossiliferous silty shale and bioturbated sandy siltstone. A low-diversity fauna of bivalves, gastropods, ostracods and foraminifers indicates that brackish-water conditions existed. Unit B intertongues with unit A to the northwest and with unit C to the southeast, and is interpreted as lagoonal deposits. Unit C consists of crossbedded and burrowed sandstone in beds 0.5-9 m thick. Sandstones are laterally continuous in the southeast but become tabular bodies enclosed within unit B to the northwest. Laterally continuous sandstones are interpreted as shoreface deposits on the basis of multidirectional crossbeds, marine trace fossils and continuity. Tabular sandstones are interpreted as flood-tidal deltas on the basis of NW-oriented crossbeds, pinchouts to the northwest and enclosure within unit B. Scoured

  6. Zircon U-Pb dating, geochemical and Sr-Nd-Hf isotopic characteristics of the Jintonghu monzonitic rocks in western Fujian Province, South China: Implication for Cretaceous crust-mantle interactions and lithospheric extension

    NASA Astrophysics Data System (ADS)

    Li, Bin; Jiang, Shao-Yong; Lu, An-Huai; Zhao, Hai-Xiang; Yang, Tang-Li; Hou, Ming-Lan

    2016-09-01

    Comprehensive petrological, in situ zircon U-Pb dating, Ti-in-zircon temperature and Hf isotopic compositions, whole rock geochemical and Sr-Nd isotopic data are reported for the Jintonghu monzonitic intrusions in the western Fujian Province (Interior Cathaysia Block), South China. The Jintonghu monzonitic intrusions were intruded at 95-96 Ma. Their Sr-Nd-Hf isotopic compositions are similar to the coeval and nearby enriched lithospheric mantle-derived mafic and syenitic rocks, indicating that the Jintonghu monzonitic rocks were likely derived from partial melting of the enriched mantle sources. Their high Nb/Ta ratios (average 21.6) suggest that the metasomatically enriched mantle components were involved, which was attributed to the modification of slab-derived fluid and melt by the subduction of the paleo-Pacific Plate. The presence of mafic xenoliths, together with geochemical and isotopic features indicates a mafic-felsic magma mixing. Furthermore, the Jintonghu intrusions may have experienced orthopyroxene-, biotite- and plagioclase-dominated crystallization. Crust-mantle interaction can be identified as two stages, including that the Early Cretaceous mantle metasomatism and lithospheric extension resulted from the paleo-Pacific slab subduction coupled with slab rollback, and the Late Cretaceous crustal activation and enhanced extension induced by dip-angle subduction and the underplating of mantle-derived mafic magma.

  7. Burial History, Thermal Maturity, and Oil and Gas Generation History of Source Rocks in the Bighorn Basin, Wyoming and Montana

    USGS Publications Warehouse

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

    2008-01-01

    Burial history, thermal maturity, and timing of oil and gas generation were modeled for seven key source-rock units at eight well locations throughout the Bighorn Basin in Wyoming and Montana. Also modeled was the timing of cracking to gas of Phosphoria Formation-sourced oil in the Permian Park City Formation reservoirs at two well locations. Within the basin boundary, the Phosphoria is thin and only locally rich in organic carbon; it is thought that the Phosphoria oil produced from Park City and other reservoirs migrated from the Idaho-Wyoming thrust belt. Other petroleum source rocks include the Cretaceous Thermopolis Shale, Mowry Shale, Frontier Formation, Cody Shale, Mesaverde and Meeteetse Formations, and the Tertiary (Paleocene) Fort Union Formation. Locations (wells) selected for burial history reconstructions include three in the deepest parts of the Bighorn Basin (Emblem Bench, Red Point/Husky, and Sellers Draw), three at intermediate depths (Amoco BN 1, Santa Fe Tatman, and McCulloch Peak), and two at relatively shallow locations (Dobie Creek and Doctor Ditch). The thermal maturity of source rocks is greatest in the deep central part of the basin and decreases to the south, east, and north toward the basin margins. The Thermopolis and Mowry Shales are predominantly gas-prone source rocks, containing a mix of Type-III and Type-II kerogens. The Frontier, Cody, Mesaverde, Meeteetse, and Fort Union Formations are gas-prone source rocks containing Type-III kerogen. Modeling results indicate that in the deepest areas, (1) the onset of petroleum generation from Cretaceous rocks occurred from early Paleocene through early Eocene time, (2) peak petroleum generation from Cretaceous rocks occurred during Eocene time, and (3) onset of gas generation from the Fort Union Formation occurred during early Eocene time and peak generation occurred from late Eocene to early Miocene time. Only in the deepest part of the basin did the oil generated from the Thermopolis and

  8. Paleotemperatures and paleodepths of the Upper Cretaceous rocks in El Qusaima, Northeastern Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Orabi, O. H.; Zahran, E.

    2014-03-01

    The planktonic foraminiferal morphogroups and planktonic quantitative analysis as well as the lithological variations across the Coniacian to Maastrichtian sediments of El Qusaima section (Northeastern Sinai, Egypt) are studied in detail in order to detect the prevailing paleoecological conditions along these sediments. At the studied area of El Qusaima section there is a gradual cooling started at the base of Globotruncana elevata Zone (early-middle Campanian) of the lower part of the Markha Member and continued till Globotruncana aegyptiaca Zone (Late Campanian) of the upper part of the Markha Member. This trend corresponds to the onset of a global cooling that began at about 73 Ma (Late Campanian) and ended the Cretaceous greenhouse climate mode. At El Qusaima section, a gradual warming started at the base of Pseudogumbelina palpebra Zone (Late Maastrichtian) and continued till Plummerita hantkeninoides Zone (latest Maastrichtian) due to the high abundance of Plummerita hantkeninoides and Plummeritareicheli, which have been flourishing in warm waters. So this warming near the end of the Maastrichtian is a global event as shown by many authors.

  9. Paleostress analysis of the Cretaceous rocks in the eastern margin of the Dead Sea transform, Jordan

    NASA Astrophysics Data System (ADS)

    Dead Sea transform, the; Diabat, Jordan A. A.; Atallah, M.; Salih, M. R.

    2004-04-01

    This paper presents the first paleostress results from fault-slip data on Cretaceous limestone at the eastern rim of the Dead Sea transform (DST) in Jordan. Stress inversion of fault-slip data is performed using an improved right dieder method, followed by rotational optimization (Delvaux, TENSOR Program). The orientation of the principal stress axes ( σ1, σ2 and σ3) and the ratio of the principal stress differences ( R) show two main paleostress fields marking two main stress regimes, strike-slip and extensional. The first is characterized by NNW-SSE compression and ENE-WSW extension and related to Middle Miocene-Recent sinistral movement along the Dead Sea transform and the opening of the Red Sea. The second paleostress field is a WNW-ESE compression and NNE-SSW extension restricted to the northern part of the investigated area. This stress field could be associated with the development of the Syrian Arc fold belt which started during the Turonian, or it may be due to an anticlockwise rotation of the first stress field.

  10. Dolomitization of felsic volcaniclastic rocks in continental strata: A study from the Lower Cretaceous of the A'nan Sag in Er'lian Basin, China

    NASA Astrophysics Data System (ADS)

    Zhu, Shifa; Yue, Hui; Zhu, Xiaomin; Sun, Shuyang; Wei, Wei; Liu, Xin; Jia, Ye

    2017-05-01

    Dolomitization of fine-grained volcaniclastic rocks is common in the Lower Cretaceous of the A'nan Sag in the Er'lian Basin of China. Analysis of core samples shows that the organic-rich volcaniclastic rocks are mainly composed of reworked felsic volcanic materials and terrigenous clay minerals. The fine-grained volcaniclastic rocks can be divided into four types: volcaniclastic rocks without carbonatization, volcaniclastic rocks with ferroan dolomites, dolomitized and calcified volcaniclastic rocks, and calcified volcaniclastic rocks. The parent rocks of the volcaniclastic rocks have high silicon and potassium contents and low iron and magnesium contents, and are probably felsic magma of the calc-alkaline series. The average values of δ13CPDB of the carbonate minerals are about 3.13‰; the average values of δ18OPDB are about - 16.74‰. The compositions of C and O isotopes are probably influenced by bacterial methanogenesis. Iron, magnesium, and calcium are probably derived from illitization of terrigenous smectite. A model for dolomitization of felsic volcaniclastic rock is proposed, including three stages: 1) mixed sedimentation and bacterial methanogenesis (< 75 °C); 2) transformation of clay minerals (> 70 °C) and dolomitization (75 to 97 °C); and 3) dissolution. Late dissolution of authigenic carbonate minerals, creating abundant secondary pores, is significant for hydrocarbon accumulation.

  11. The Bolivian source rocks: Sub Andean Zone-Madre de Dios-Chaco

    SciTech Connect

    Moretti, I.; Montemurro, G.; Aguilera, E.; Perez, M.; Martinez, E.Diaz

    1996-08-01

    A complete study of source rocks has been carried out in the Bolivian foothills and foreland (Sub Andean Zone, Chaco and Madre de Dios) in order to quantify the petroleum potential of the area. Besides the classical mid-Devonian source rocks (Tequeje Formation in the north, Limoncito Formation in the center and Los Monos Formation in the south), others are important: the Tomachi Formation (late Devonian) in the north and the Copacabana Formation (Upper Carboniferous-lower Permian) in the northern Sub Andean Zone. Both show an excellent potential with S{sub 2} over 50 mg HC/g and average values higher than 10 mg HC/g over few hundred meters. The Latest Cretaceous Flora Formation present locally a high potential but is very thin. Almost all the source rocks matured during the Neogene due to the subsidence in the Andean foreland and in the piggyback basins, and are thus involved on the current petroleum system. Silurian and Lower Paleozoic units also contain thick shale beds, but these source rocks were mature before the Jurassic in the south of the country. In the center, the Silurian is not nowadays overmature and may play an important role. The different zones are compared based on their Source Potential Index which indicates that the richest areas are the northern Sub Andean Zone and the Madre de Dios basin with SPI greater than 10 t/m{sup 2}. Since these two areas remain almost unexplored, these results allow us to be optimistic about the possibilities for future exploration.

  12. Molecular analysis of deep subsurface Cretaceous rock indicates abundant Fe(III)- and S(zero)-reducing bacteria in a sulfate-rich environment.

    PubMed

    Kovacik, William P; Takai, Ken; Mormile, Melanie R; McKinley, James P; Brockman, Fred J; Fredrickson, James K; Holben, William E

    2006-01-01

    A multilevel sampler (MLS) was emplaced in a borehole straddling anaerobic, sulfate-rich Cretaceous-era shale and sandstone rock formations approximately 200 m below ground surface at Cerro Negro, New Mexico. Sterile quartzite sand contained in chambers in the sampler allowed in situ colonization and recovery of nucleic acids for molecular analyses. Denaturing gradient gel electrophoresis and 16S rRNA gene cloning results indicated a homogeneously distributed bacterial community across the shale-sandstone interface. delta-Proteobacteria sequences were common at all depths, and were dominated by members of the Geobacteraceae family (Pelobacter, Desulphuromonas and Geobacter). Other members of this group are capable of dissimilatory Fe(III) and/or S degrees reduction, but not sulfate reduction. RNA hybridization data also suggested that Fe(III)-/S degrees -reducing bacteria were predominant. These findings are striking considering the lack of significant concentrations of these electron acceptors in this environment. The next most abundant bacterial group indicated was the sulfate reducers, including Desulfobacterium, Desulfocapsa and Desulfobulbus. Sequences related to fermenters, denitrifiers and acetogens were also recovered. The presence of a phylogenetically and functionally diverse microbial community in this deep subsurface environment likely reflects the complex nature of the primary energy and carbon sources, kerogen associated with the shale.

  13. Preliminary results on the characterization of Cretaceous and lower Tertiary low-permeability (tight) gas-bearing rocks in the Wind River Basin, Wyoming

    SciTech Connect

    Fouch, T.D.; Keefer, W.R.; Finn, T.M.

    1993-12-31

    The Wind River Basin is a structural and sedimentary basin in central Wyoming (Figure 1) that was created during the Laramide orogeny from Late Cretaceous through Eocene time. The objectives of the Wind River Basin tight gas sandstone project are to define the limits of the tight gas accumulation in the basin and to estimate in-place and recoverable gas resources. The approximate limits of the tight gas accumulation are defined from available drillhole information. Geologic parameters, which controlled the development of the accumulation, are studied in order to better understand the origins of tight gas accumulations, and to predict the limits of the accumulation in areas where little drillhole information is available. The architecture of sandstone reservoirs are studied in outcrop to predict production characteristics of similar reservoirs within the tight gas accumulation. Core and cuttings are used to determine thermal maturities, quality of source rocks, and diagenetic histories. Our work thus far has concentrated in the Wind River Indian Reservation in the western part of the basin.

  14. Molecular analysis of deep subsurface Cretaceous rock indicates abundant Fe(III)- and S°-reducing bacteria in a sulfate-rich environment

    SciTech Connect

    Kovacik, William P.; Takai, Ken; Mormile, Melanie R.; McKinley, James P.; Brockman, Fred J.; Fredrickson, Jim K.; Holben, William E.

    2006-01-01

    A multi-level sampler (MLS) was emplaced in a borehole straddling anaerobic, sulfate-rich Cretaceous-era shale and sandstone rock formations {approx}200 m below ground surface at Cerro Negro, New Mexico. Sterile quartzite sand contained in chambers in the sampler allowed in situ colonization and recovery of nucleic acids for molecular analyses. DGGE and 16S rRNA gene cloning results indicated a homogeneously distributed bacterial community across the shale/sandstone interface. ?-Proteobacteria sequences were common at all depths, and were dominated by members of the Geobacteraceae family (Pelobacter, Desulfuromonas, and Geobacter). Other members of this group are capable of dissimilatory Fe(III) and/or S0 reduction, but not sulfate reduction. RNA hybridization data also suggested that Fe(III)/S0 reducing bacteria were predominant. These findings are striking considering the lack of significant concentrations of these electron acceptors in this environment. The next most abundant bacterial group indicated was the sulfate reducers, including Desulfobacterium, Desulfocapsa and Desulfobulbus. Sequences related to fermenters, denitrifiers and acetogens were also recovered. The presence of a phylogenetically and functionally diverse microbial community in this deep subsurface environment likely reflects the complex nature of the primary energy and carbon sources, kerogen associated with the shale.

  15. Geohydrology and chemical quality of water in Middle and Upper Jurassic and Lower Cretaceous rocks, western Kansas

    USGS Publications Warehouse

    Kume, Jack

    1984-01-01

    Fresh and saline water occur in Upper Jurassic and Lower Cretaceous rocks in western Kansas. The maximum thickness of the Jurassic aquifer is about 50 feet. During 1981, water levels ranged from 255 to 1,160 feet below land surface; the static heads ranged from about 2,400 to 3,100 feet above sea level and the hydraulic gradient ranged from 16 feet per mile toward the northeast to 40 feet per mile toward the north. The water is moderately saline, very hard, a sodium sulfate or sodium chloride type, and unsuitable for drinking and irrigation. The maximum thickness of the Cheyenne aquifer is about 190 feet. During 1981, water levels ranged from 267 to 375 feet below land surface; the static heads varied from less than 2,300 to more than 3,200 feet above sea level; and the hydraulic gradient was 8 feet per mile toward the east. The water is fresh to moderately saline, soft to very hard, a sodium sulfate or sodium , bicarbonate type, and suitable to unsuitable for drinking and irrigation. The maximum thickness of the Dakota aquifer is about 150 feet. During 1982, water levels ranged from 24 to 604 feet below land surface; the static heads ranged from about 2,100 to 3,200 feet above sea level; and the hydraulic gradient was 11 feet per mile toward the east and northeast. The water is fresh to slightly saline, soft to very hard, and suitable to unsuitable for drinking and irrigation. (USGS)

  16. Configuration of the base of the Edwards-Trinity aquifer system and hydrogeology of the underlying pre-Cretaceous rocks, west-central Texas

    USGS Publications Warehouse

    Barker, Rene A.; Ardis, Ann F.

    1992-01-01

    The most permeable pre-Cretaceous rocks are in the eastern half of the study area where they compose the Hickory aquifer (in Upper Cambrian rocks), Ellenburger-San Saba aquifer (Upper Cambrian- Lower Ordovician), and Marble Falls aquifer (Lower Pennsylvanian). These aquifers are hydraulically connected to the northeastern fringe of the Edwards-Trinity aquifer system, as their up-turned margins crop out around the flanks of the breached Llano uplift. The Rustler aquifer in rocks of Late Permian age underlies parts of the Trans-Pecos region, where it yields small amounts of greatly mineralized water for industrial and agricultural purposes. The Dockum aquifer in rocks of Late Triassic age directly underlies the Edwards-Trinity aquifer system in western parts of the study area, and locally increases the saturated thickness of the ground-water-flow system by an average of about 200 feet. Despite these notable exceptions, the collective effect of the pre-Cretaceous rocks is that 01 a barrier to ground-water flow, which limits the exchange of water across the base of the Edwards-Trinity aquifer system.

  17. 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.

  18. Andesitic crustal growth via mélange partial melting: Evidence from Early Cretaceous arc dioritic/andesitic rocks in southern Qiangtang, central Tibet

    NASA Astrophysics Data System (ADS)

    Hao, Lu-Lu; Wang, Qiang; Wyman, Derek A.; Ou, Quan; Dan, Wei; Jiang, Zi-Qi; Yang, Jin-Hui; Li, Jie; Long, Xiao-Ping

    2016-05-01

    Deciphering the petrogenesis of andesitic/dioritic rocks is fundamental to understanding the formation of the continental crust. Here we present detailed petrology, geochronology, major and trace element, Sr-Nd-Hf-O isotope data for the Early Cretaceous (˜122 Ma) dioritic rocks in the Bizha area in southern Qiangtang, Tibet. The dioritic rocks are characterized by large ion lithophile elements, Pb, and light rare earth elements but depletion of high field strength elements with slightly enriched and variable ɛNd(t) values of -0.01 to -3.31 and initial 87Sr/86Sr isotopic ratios of 0.7053-0.7062. They also have variable magmatic zircon Hf-O isotope compositions (ɛHf(t) = -5.3 to +3.6 and δ18O = +7.3 to +9.5 ‰). Combined with contemporary andesitic lavas in southern Qiangtang, we suggest that the intermediate magmatic rocks in this area were most probably derived by partial melting of a subduction mélange, which is a mixture of mid-oceanic ridge basalts (MORBs), sediments, and mantle wedge peridotites, formed along the interface between the subducted slab and the overlying mantle wedge in a subduction channel before ˜124 Ma. The mélange diapir melting was triggered by the asthenospheric upwelling and hot corner flow caused by roll-back of the northward subducted Bangong-Nujiang oceanic slab during the Early Cretaceous. The Early Cretaceous intermediate magmatic rocks in southern Qiangtang have an overall continental crust-like andesitic composition. Therefore, partial melting of mélange provides an important support for the generation of andesitic magmas in continental arcs and the "andesite model" for crustal growth.

  19. Petrogenesis and geodynamic setting of Early Cretaceous felsic rocks in the Gan-Hang Belt, Southeast China: Constraints from geochronology and geochemistry of the tuffs and trachyandesitic rocks in Shengyuan volcanic Basin

    NASA Astrophysics Data System (ADS)

    Shu, Xun; Yang, Shui-Yuan; Jiang, Shao-Yong; Ye, Mao

    2017-07-01

    The Late Mesozoic geology of the Gan-Hang Belt is characterized by extensive magmatism forming a belt of volcanic-intrusive complex. The geochronology, petrogenesis, and geodynamic setting of the Late Mesozoic magmatic rocks in the Gan-Hang Belt are still controversial. The Shengyuan volcanic Basin is located in the NW region of the belt and mainly contains crystal tuff, welded tuff, and trachyandesitic rocks. We integrate geochronological and geochemical data for these tuffs and trachyandesitic rocks, to explore the origin of these rocks and improve our understanding of the Late Mesozoic magmatic and tectonic evolution of the region. Zircon U-Pb dating shows that these samples were formed in the Early Cretaceous (135-137 Ma). All the tuffs have a pronounced A2-type geochemical signature and their chemical compositions are controlled by crystal fractionation. All trachyandesitic rocks exhibit high K2O contents and were attributed to the shoshonite series; they are characterized by arc-like trace element distribution patterns, with significant enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) but depletion in high field-strength elements (HFSE). Moreover, all the tuffs and trachyandesitic rocks were characterized by negative whole rock εNd(t) and zircon εHf(t). An integrated interpretation of all these geochemical data leads to the conclusion that the Shengyuan trachyandesitic rocks were primarily derived from mantle materials and oceanic crust-derived melt. The Shengyuan tuffs were formed by the partial melting of the Proterozoic orthometamorphic and parametamorphic rocks. Our studies together with previous published data suggest that the Early Cretaceous A-type felsic rocks, with ages between 138 Ma and 122 Ma, occurred along the Gan-Hang Belt, indicating an important Late Mesozoic extensional event in the Belt. This event represents a back-arc tectonic setting due to the rollback of the Paleo-Pacific plate.

  20. Partial melting of subducted paleo-Pacific plate during the early Cretaceous: Constraint from adakitic rocks in the Shaxi porphyry Cu-Au deposit, Lower Yangtze River Belt

    NASA Astrophysics Data System (ADS)

    Deng, Jianghong; Yang, Xiaoyong; Li, Shuang; Gu, Huangling; Mastoi, Abdul Shakoor; Sun, Weidong

    2016-10-01

    A large porphyry Cu-Au deposit associated with early Cretaceous intrusive rocks has been discovered and explored in the Shaxi area, Lower Yangtze River Belt (LYRB), eastern China. We studied two types of intrusive rocks in the Shaxi area: Cu-Au mineralization related diorites and quartz-diorites (adakitic rocks), and newly found high Sr/Y ratio biotite-gabbros. They were formed almost simultaneously with crystallization ages of ca. 130 to 129 Ma, younger than the early stage shoshonitic rocks (Longmenyuan, Zhuanqiao and Shuangmiao Fm.) in the Luzong volcanic basin, 10 km south of the Shaxi area. These intrusive rocks show similar distribution patterns of trace elements (enriched in LILEs and depleted in HFSEs) and REEs (enriched in LREEs and depleted in HREEs, no Eu negative anomaly, flat HREE patterns). The diorites and quartz-diorites are adakitic rocks with calc-alkaline affinity, distinguished from other adakitic rocks in the LYRB which are high-K calc-alkaline series. The biotite-gabbros are not adakitic rocks, although they are characterized by high Sr/Y ratios.

  1. Paleoceanography and paleolimnology of petroleum source rocks

    SciTech Connect

    Pratt, L.M. )

    1990-11-01

    Sedimentary strata containing greater than 0.5 wt. % organic carbon are unusual in both modern and ancient depositional settings. Rates of primary production (photosynthesis), recycling (decompositional efficiency), and sediment accumulation (clastic dilution) are the principal factors determining organic carbon contents of sediments and sedimentary rocks. Clastic dilution is the dominant factor in all aquatic environments when sediment accumulation rates are above about 100 mg/cm{sup 2}/yr or sedimentation rates are above about 300 m/10{sup 6}/yr. Enhanced primary productivity associated with upwelling is the dominant control on burial and preservation of organic matter in modern marine environments, but benthic anoxia related to restricted circulation may be the dominant factor in many modern lakes and most ancient epicontinental seas. During transportation and sedimentation in marine and lacustrine environments, organic detritus can by oxidized to carbon dioxide or incorporated into new biomass by bacterial communities that sequentially transfer electrons from organic matter to oxygen, nitrate, iron (Fe{sup 3+}), manganese (Mn{sup 4+}), sulfate, and carbon dioxide. Zonation of early diagenetic minerals results from progressive changes in the composition of pore water and sediment as organic matter is buried to depths of about 10 m. Mineralic and stable isotopic (carbon and sulfur) compositions of diagenetic carbonates and iron sulfides reflect depth-related bacterial and redox zones. Data bearing on these processes contribute to development of comprehensive basin models because they can be used to reconstruct changes in salinity and oxygen content of bottom water.

  2. The Kingak shale of northern Alaska-regional variations in organic geochemical properties and petroleum source rock quality

    USGS Publications Warehouse

    Magoon, L.B.; Claypool, G.E.

    1984-01-01

    The Kingak Shale, a thick widespread rock unit in northern Alaska that ranges in age from Early Jurassic through Early Cretaceous, has adequate to good oil source rock potential. This lenticular-shaped rock unit is as much as 1200 m thick near the Jurassic shelf edge, where its present-day burial depth is about 5000 m. Kingak sediment, transported in a southerly direction, was deposited on the then marine continental shelf. The rock unit is predominantly dark gray Shale with some interbeds of thick sandstone and siltstone. The thermal maturity of organic matter in the Kingak Shale ranges from immature (2.0%R0) in the Colville basin toward the south. Its organic carbon and hydrogen contents are highest in the eastern part of northern Alaska south of and around the Kuparuk and Prudhoe Bay oil fields. Carbon isotope data of oils and rock extracts indicate that the Kingak Shale is a source of some North Slope oil, but is probably not the major source. ?? 1984.

  3. Thermal maturity patterns of Cretaceous and Tertiary rocks, San Juan Basin, Colorado and New Mexico

    USGS Publications Warehouse

    Law, B.E.

    1992-01-01

    Horizontal and vertical thermal maturity patterns and time-temperature modeling indicate that the high levels of thermal maturity in the northern part of the basin are due to either: 1) convective heat transfer associated with a deeply buried heat source located directly below the northern part of the basin or 2) the circulation of relatively hot fluids into the basin from a heat source north of the basin located near the San Juan Mountains. Time-temperature and kinetic modeling of nonlinear Rm profiles indicates that present-day heat flow is insufficient to account for the measured levels of thermal maturity. Furthermore, in order to match nonlinear Rm profiles, it is necessary to assign artifically high thermal-conductivity values to some of the stratigraphic units. These unrealistically high thermal conductivities are interpreted as evidence of convective heat transfer. -from Author

  4. Evolving source areas for upper Cretaceous-lower Tertiary marine to continental strata of central Colombia

    SciTech Connect

    Ressetar, R.; Segall, M.P.; Laverde, F.E.; Allen, R.B.

    1989-03-01

    Late Cretaceous marine conditions in the Upper Magdalena Valley (UMV) and the Sabana of Colombia ended with deposition of the regressive Guadalupe (Campanian-Maastrichtian) and Guaduas (Maastrichtian-Paleocene) Formations, followed by terrestrial deposition of the Gualanday Group (Eocene). X-ray diffraction, SEM, and thin-section analyses of samples from the southern UMV and the Sabana reveal compositional trends related to different depositional conditions and to evolving source terrains. The upper Guadalupe Formation of the southern UMV is mineralogically distinct from the overlying units, containing high average concentrations of illite/smectite (40%) and clay-size quartz (20%) with little discrete illite. The data indicate that after deposition of the Guadalupe Formation from a volcanic/metamorphic source, the sediment source changed or was completely cut off. Chemical weathering was enhanced during deposition of the Guaduas Formation in the UMV, but marine sedimentation, reflected in the uniform composition, continued in the Sabana. Anomalously high illite/smectite concentrations and overall variability in the Gualanday Group indicate a return to a volcanic source with deposition in an alluvial fan/fluvial environment.

  5. Geochronology, geochemistry, and deformation history of Late Jurassic-Early Cretaceous intrusive rocks in the Erguna Massif, NE China: Constraints on the late Mesozoic tectonic evolution of the Mongol-Okhotsk orogenic belt

    NASA Astrophysics Data System (ADS)

    Tang, Jie; Xu, Wen-Liang; Wang, Feng; Zhao, Shuo; Li, Yu

    2015-09-01

    This paper presents new zircon and sphene U-Pb ages, biotite and hornblende 40Ar/39Ar ages, Hf isotopic data, and geochemical data for five Mesozoic plutons in the Erguna Massif of NE China. These data are used to constrain the late Mesozoic tectonic evolution of the Mongol-Okhotsk orogenic belt. This new dating, when combined with previously published ages, indicates that the Late Jurassic-Early Cretaceous (J3-K1) intrusive rocks can be subdivided into three stages that represent periods of magmatism during the Late Jurassic ( 155 Ma), early Early Cretaceous ( 137 Ma), and late Early Cretaceous ( 123 Ma). In addition, the rocks have undergone later deformation recorded by peak ages of 137 and 123 Ma. The Late Jurassic and early Early Cretaceous intrusive rocks in the study area are dominantly syenogranites and are either A-type granites or are classified as alkaline series, suggesting that they formed in an extensional environment. The late Early Cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment, along with coeval bimodal volcanics. These data, combined with the presence of regional unconformities in the northern part of Hebei Province and western part of Liaoning Province, and the spatial distribution of coeval volcanic rocks in NE China, suggest the Late Jurassic and early Early Cretaceous magmatisms and the early Early Cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the Mongol-Okhotsk Ocean. In comparison, the late Early Cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the Mongol-Okhotsk tectonic regime or the subduction of the Paleo-Pacific Plate, or the combined influence of these two tectonic regimes.

  6. Age and petrogenesis of Na-rich felsic rocks in western Iran: Evidence for closure of the southern branch of the Neo-Tethys in the Late Cretaceous

    NASA Astrophysics Data System (ADS)

    Nouri, Fatemeh; Azizi, Hossein; Golonka, Jan; Asahara, Yoshihiro; Orihashi, Yuji; Yamamoto, Koshi; Tsuboi, Motohiro; Anma, Ryo

    2016-03-01

    Intermediate to felsic volcanic and granitic rocks with high Na2O concentrations (5.2-9.1 wt.%) are widely distributed in the Harsin area along the Zagros thrust zone in western Iran. Most of these rocks are classified as low-potassium tholeiite, display affinity with oceanic plagiogranite and contain somewhat high Na content and low concentrations of K2O, Al2O3, Rb, Sr and Ca. Thus, we prefer to apply the term Na-rich felsic rocks to this complex. U-Pb dating yielded ages of 94.6 ± 2.7 Ma (2σ) from baddeleyite and 95.0 ± 2.4 Ma (2σ) from zircon grains, indicating that the complex crystallized in the Late Cretaceous. Based on the mineral compositions, the crystallization occurred at low pressures (mostly < 2 kbar) and low temperatures (< 750 °C). High initial ratios of 143Nd/144Nd (0.51288-0.51304) and positive values of ɛNd(t) (+ 7.0 to + 11.5) are consistent with those of mid-oceanic ridge basalt (MORB). During collision of the Arabian plate and Biston-Avoraman block in the Late Cretaceous, an increasing geothermal gradient was responsible for partial melting of altered mafic rocks and for producing the Na-rich felsic rocks in the Harsin area. The presence of these types of rocks along the main Zagros fault indicates local collisions. These collisions were caused by southwestward subduction under the Arabian plate in the southern branch of the Neo-Tethys. This event was the first stage of the Zagros collision, which was followed by collision of the Arabian and Iranian plates during the Eocene through Neogene.

  7. The Cretaceous-Tertiary (K/T) impact: One or more source craters?

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian

    1992-01-01

    The Cretaceous-Tertiary (K/T) boundary is marked by signs of a worldwide catastrophe, marking the demise of more than 50 percent of all living species. Ever since Alvarez et al. found an enrichment of IR and other siderophile elements in rocks marking the K/T boundary and interpreted it as the mark of a giant asteroid (or comet) impact, scientists have tried to understand the complexities of the K/T boundary event. The impact theory received a critical boost by the discovery of shocked minerals that have so far been found only in association with impact craters. One of the problems of the K/T impact theory was, and still is, the lack of an adequate large crater that is close to the maximum abundance of shocked grains in K/T boundary sections, which was found to occur in sections in Northern America. The recent discovery of impact glasses from a K/T section in Haiti has been crucial in establishing a connection with documented impact processes. The location of the impact-glass findings and the continental nature of detritus found in all K/T sections supports at least one impact site near the North American continent. The Manson Impact Structure is the largest recognized in the United States, 35 km in diameter, and has a radiometric age indistinguishable from that of the Cretaceous-Tertiary (K/T) boundary. Although the Manson structure may be too small, it may be considered at least one element of the events that led to the catastrophic loss of life and extinction of many species at that time. A second candidate for the K/T boundary crater is the Chicxulub structure, which was first suggested to be an impact crater more than a decade ago. Only recently, geophysical studies and petrological (as well as limited chemical) analyses have indicated that this buried structure may in fact be of impact origin. At present we can conclude that the Manson crater is the only confirmed crater of K/T age, but Chicxulub is becoming a strong contender; however, detailed geochemical

  8. Variable sources for Cretaceous to recent HIMU and HIMU-like intraplate magmatism in New Zealand

    NASA Astrophysics Data System (ADS)

    van der Meer, Q. H. A.; Waight, T. E.; Scott, J. M.; Münker, C.

    2017-07-01

    Continental intraplate magmas with isotopic affinities similar to HIMU are identified worldwide. Involvement of an asthenospheric HIMU or HIMU-like source is contested because the characteristic radiogenic Pb compositions coupled with unradiogenic Sr and intermediate Nd and Hf compositions can also result from in-situ ingrowth in metasomatised lithospheric mantle. Sr-Nd-Pb-Hf isotopic compositions of late Cretaceous lamprophyre dikes from Westland, New Zealand, provide new insights into the formation of a HIMU-like alkaline intraplate magmatic province under the Zealandia continent. The oldest (102-100 Ma) calc-alkaline lamprophyres are compositionally similar to the preceding arc-magmatism (206Pb/204Pb(i) = 18.6, 207Pb/204Pb(i) = 15.62, 208Pb/204Pb(i) = 38.6, 87Sr/86Sr(i) = 0.7063-0.7074, εNd(i) = -2.1 - +0.1 and εHf(i) = -0.2 - +2.3) and are interpreted as melts originating from subduction-modified lithosphere. Alkaline dikes erupted on the inboard Gondwana margin shortly after cessation of subduction (92-84 Ma) have heterogeneous isotopic properties: 206Pb/204Pb(i) = 18.7 to 19.4, 207Pb/204Pb(i) = 15.60 to 15.65, 208Pb/204Pb(i) = 38.6 to 39.4, 87Sr/86Sr(i) = 0.7031 to 0.7068, εNd(i) = +4.5 to +8.0 and εHf(i) = +5.1 to +8.0. Melt compositions point to an amphibole-bearing spinel facies lithospheric mantle source enriched by metasomatism that introduced, amongst many elements, U + Th which lead to rapid ingrowth to HIMU-like compositions. Importantly, this HIMU-like source enrichment appears to have completely originated from the complex local subduction history. A coeval episode of alkaline magmatism (mainly 98-82 Ma) occurred outboard of Gondwana's former active margin and on the Hikurangi oceanic plateau (accreted to Zealandia in the Early Cretaceous) with compositions closer to true HIMU (206Pb/204Pb(i) ≈ 20.5, 207Pb/204Pb(i) ≈ 15.7, 208Pb/204Pb(i) ≈ 40.0, εNd(i) ≈ 4.5 and εHf(i) ≈ 4.0). In contrast to the inboard HIMU-like magmas, the

  9. Geochemical evidence for Paleozoic oil in Lower Cretaceous O Sandstone, northern Denver basin

    USGS Publications Warehouse

    Clayton, J.L.

    1989-01-01

    Organic geochemical properties of the oil produced from the Lower Cretaceous O sandstone on the eastern flank of the Denver basin indicate that this oil has been derived from a different source rock than other Cretaceous oils in the basin. O sandstone oil is characterized by low pristane/phytane ratio, high isoprenoid/n-alkane ratios, high asphaltene content, high sulfur content, and slight predominance of even-carbon numbered n-alkanes in the C25+ fraction. These features are evidence of a Paleozoic source and indicate a carbonate rock is the likely source. Preliminary source rock evaluation and correlation data suggest that calcareous black shales and marls of Middle Pennsylvanian (Desmoinesian) age are the source of the O sandstone oil. This is the first reported occurrence of oil from Paleozoic source rocks in a Cretaceous reservoir in the Denver basin. -from Author

  10. New oil source rocks cut in Greek Ionian basin

    SciTech Connect

    Karakitsios, V.; Rigakis, N.

    1996-02-12

    The Ionian zone of Northwest Greece (Epirus region) constitutes part of the most external zones of the Hellenides (Paxos zone, Ionian zone, Gavrovo Tripolitza zone). The rocks of the Ionian zone range from Triassic evaporites and associated breccias through a varied series of Jurassic through Upper Eocene carbonates and lesser cherts and shales followed by Oligocene flysch. The surface occurrences of petroleum in the Ionian zone are mainly attributed to Toarcian Lower Posidonia beds source rocks and lesser to late Callovian-Tithonian Upper Posidonia beds and to the Albian-Cenomanian Upper Siliceous zone or Vigla shales of the Vigla limestones. Oil that could not be attributed to the above source rocks is believed to have an origin from Triassic formations that contain potential source rocks in Albania and Italy. However, several samples of the shales of Triassic breccias from outcrops and drillholes were analyzed in the past, but the analytical results were not so promising since their hydrocarbon potential was low. In this article, the authors will present their analytical results of the Ioannina-1 well, where for the first time they identified some very rich source beds in the Triassic breccias formation of Northwest Greece.

  11. Subcritical water extraction of trace metals from petroleum source rock.

    PubMed

    Akinlua, Akinsehinwa; Smith, Roger M

    2010-06-15

    The extraction of trace metals from petroleum source rock by superheated water was investigated and the conditions for maximum yield were determined. The results showed that no significant extraction was attained at 100 degrees C but the extraction was enhanced at higher temperatures. The optimum temperature for superheated water extraction of the metals from petroleum source rocks was 250 degrees C. Extraction yields increased with enhanced extraction time. Exhaustive extraction time for all the trace metals determined in this study was attained at 30min. Comparison of results of leaching these trace metals by superheated water with those of acid digestion revealed that cadmium, chromium, manganese and nickel had better yields with superheated water while vanadium had better yield with acid digestion. The results showed that the temperature and kinetic rates have significant effects on superheated water extraction of metals from petroleum source rocks. The results also revealed that effective leaching of some metals from petroleum source rocks by superheated water can be achieved without any modification except for vanadium.

  12. Cretaceous mafic conglomerate near Gualala offset 350 miles by San Andreas fault from oceanic crustal source near Eagle Rest Peak, California

    USGS Publications Warehouse

    Ross, Donald C.; Wentworth, Carl M.; McKee, Edwin D.

    1973-01-01

    Upper Cretaceous mafic conglomerate and quartz-plagioclase arkose that crop out on the southwest side of the San Andreas fault near Gualala, Calif., may have been eroded from a gabbroic terrane that now lies about 350 miles to the southeast, on the opposite side of the San Andreas fault. The plagioclase arkose near Gualala contains little or no K-feldspar, and the conglomerate is characterized by quartz-bearing mafic rocks that lack K-feldspar volcanic rocks, diabase, and diorite to gabbro. Hornblendes from these clasts yield K/Ar ages of 141±4,175±7, and 186±7 m.y. The arkose and conglomerate appear to have been eroded from a chert-poor ophiolite (oceanic crust) sequence that, according to paleocurrent evidence, lay east of the present San Andreas fault. Near Eagle Rest Peak, 350 milessoutheast of Gualala, similar mafic quartz-bearing volcanic rocks, diabase, and gabbro are exposed in a small structurally isolated areathat abuts the San Andreas fault on the southwest. These rocks yield hornblende K/Ar ages of 134±4, 165±4, and 207±10 m.y. They mayalso be the source of two small fault slivers of similar mafic rocks, which yield hornblende K/Ar ages between 144 and 172 m.y. Theseslivers now lie 100 and 200 miles to the northwest along the San Andreas fault at Gold Hill and Logan.

  13. Hydrogen in rocks: an energy source for deep microbial communities

    NASA Technical Reports Server (NTRS)

    Freund, Friedemann; Dickinson, J. Thomas; Cash, Michele

    2002-01-01

    To survive in deep subsurface environments, lithotrophic microbial communities require a sustainable energy source such as hydrogen. Though H2 can be produced when water reacts with fresh mineral surfaces and oxidizes ferrous iron, this reaction is unreliable since it depends upon the exposure of fresh rock surfaces via the episodic opening of cracks and fissures. A more reliable and potentially more voluminous H2 source exists in nominally anhydrous minerals of igneous and metamorphic rocks. Our experimental results indicate that H2 molecules can be derived from small amounts of H2O dissolved in minerals in the form of hydroxyl, OH- or O3Si-OH, whenever such minerals crystallized in an H2O-laden environment. Two types of experiments were conducted. Single crystal fracture experiments indicated that hydroxyl pairs undergo an in situ redox conversion to H2 molecules plus peroxy links, O3Si/OO\\SiO3. While the peroxy links become part of the mineral structure, the H2 molecules diffused out of the freshly fractured mineral surfaces. If such a mechanism occurred in natural settings, the entire rock column would become a volume source of H2. Crushing experiments to facilitate the outdiffusion of H2 were conducted with common crustal igneous rocks such as granite, andesite, and labradorite. At least 70 nmol of H2/g diffused out of coarsely crushed andesite, equivalent at standard pressure and temperature to 5,000 cm3 of H2/m3 of rock. In the water-saturated, biologically relevant upper portion of the rock column, the diffusion of H2 out of the minerals will be buffered by H2 saturation of the intergranular water film.

  14. Hydrogen in rocks: an energy source for deep microbial communities.

    PubMed

    Freund, Friedemann; Dickinson, J Thomas; Cash, Michele

    2002-01-01

    To survive in deep subsurface environments, lithotrophic microbial communities require a sustainable energy source such as hydrogen. Though H2 can be produced when water reacts with fresh mineral surfaces and oxidizes ferrous iron, this reaction is unreliable since it depends upon the exposure of fresh rock surfaces via the episodic opening of cracks and fissures. A more reliable and potentially more voluminous H2 source exists in nominally anhydrous minerals of igneous and metamorphic rocks. Our experimental results indicate that H2 molecules can be derived from small amounts of H2O dissolved in minerals in the form of hydroxyl, OH- or O3Si-OH, whenever such minerals crystallized in an H2O-laden environment. Two types of experiments were conducted. Single crystal fracture experiments indicated that hydroxyl pairs undergo an in situ redox conversion to H2 molecules plus peroxy links, O3Si/OO\\SiO3. While the peroxy links become part of the mineral structure, the H2 molecules diffused out of the freshly fractured mineral surfaces. If such a mechanism occurred in natural settings, the entire rock column would become a volume source of H2. Crushing experiments to facilitate the outdiffusion of H2 were conducted with common crustal igneous rocks such as granite, andesite, and labradorite. At least 70 nmol of H2/g diffused out of coarsely crushed andesite, equivalent at standard pressure and temperature to 5,000 cm3 of H2/m3 of rock. In the water-saturated, biologically relevant upper portion of the rock column, the diffusion of H2 out of the minerals will be buffered by H2 saturation of the intergranular water film.

  15. Hydrogen in rocks: an energy source for deep microbial communities

    NASA Technical Reports Server (NTRS)

    Freund, Friedemann; Dickinson, J. Thomas; Cash, Michele

    2002-01-01

    To survive in deep subsurface environments, lithotrophic microbial communities require a sustainable energy source such as hydrogen. Though H2 can be produced when water reacts with fresh mineral surfaces and oxidizes ferrous iron, this reaction is unreliable since it depends upon the exposure of fresh rock surfaces via the episodic opening of cracks and fissures. A more reliable and potentially more voluminous H2 source exists in nominally anhydrous minerals of igneous and metamorphic rocks. Our experimental results indicate that H2 molecules can be derived from small amounts of H2O dissolved in minerals in the form of hydroxyl, OH- or O3Si-OH, whenever such minerals crystallized in an H2O-laden environment. Two types of experiments were conducted. Single crystal fracture experiments indicated that hydroxyl pairs undergo an in situ redox conversion to H2 molecules plus peroxy links, O3Si/OO\\SiO3. While the peroxy links become part of the mineral structure, the H2 molecules diffused out of the freshly fractured mineral surfaces. If such a mechanism occurred in natural settings, the entire rock column would become a volume source of H2. Crushing experiments to facilitate the outdiffusion of H2 were conducted with common crustal igneous rocks such as granite, andesite, and labradorite. At least 70 nmol of H2/g diffused out of coarsely crushed andesite, equivalent at standard pressure and temperature to 5,000 cm3 of H2/m3 of rock. In the water-saturated, biologically relevant upper portion of the rock column, the diffusion of H2 out of the minerals will be buffered by H2 saturation of the intergranular water film.

  16. New paleomagnetic results from Upper Cretaceous arc-type rocks from the northern and southern branches of the Neotethys ocean in Anatolia

    NASA Astrophysics Data System (ADS)

    Cengiz Cinku, Mualla; Heller, Friedrich; Ustaömer, Timur

    2017-03-01

    A paleomagnetic study of Cretaceous arc type rocks in the Central-Eastern Pontides and in the Southeastern Taurides investigates the tectonic and paleolatitudinal evolution of three volcanic belts in Anatolia, namely the Northern and Southern Volcanic Belts in the Pontides and the SE Taurides volcanic belt. The paleomagnetic data indicate that magnetizations were acquired prior to folding at most sampling localities/sites, except for those in the Erzincan area in the Eastern Pontides. The Southern Volcanic Belt was magnetized at a paleolatitude between 23.8_{-3.8}^{+4.2} °N and 20.2_{-1.2}^{+1.3} °N. Hisarlı (J Geodyn 52:114-128, 2011) reported a more northerly paleolatitude (26.6_{-4.6}^{+5.1} °N) for the Northern Volcanic Belt. The comparison of the new paleomagnetic results with previous ones in Anatolia allows to conclude that the Southern Volcanic Belt in the Central-Eastern Pontides was emplaced after the Northern Volcanic Belt as a result of slab-roll back of the Northern Neotethys ocean in the Late Cretaceous. In the Southeast Taurides, Upper Cretaceous arc-related sandstones were at a paleolatitude of 16.8_{-3.8}^{+4.2} . The Late Cretaceous paleomagnetic rotations in the Central Pontides exhibit a counterclockwise rotation of R± Δ R=-37.1° ± 5.8° (Group 1; Çankırı, Yaylaçayı Formation) while Maastrichtian arc type rocks in the Yozgat area (Group 2) show clockwise rotations R + ΔR = 33.7° ± 8.4° and R + ΔR = 29.3° ± 6.0°. In the SE Taurides counterclockwise and clockwise rotations of R± Δ R=-48.6°± 5.2° and R± Δ R=+34.1° ± 15.1° are obtained (Group 4; Elazığ Magmatic Complex). The Late Cretaceous paleomagnetic rotations in the Pontides follow a general trend in concordance with the shape of the suture zone after the collision between the Pontides and the Kırşehir block. The affect of the westwards excursion of the Anatolian plate and the associated fault bounded block rotations in Miocene are observed in the east of the

  17. Source rock potential of shallow-water evaporitic settings

    SciTech Connect

    Warren, J.K.

    1986-05-01

    In the major evaporitic environments on the world's surface today, most organic matter accumulates in shallow subaqueous to seasonally subaerially exposed, algal-mat sediments. Given the present depositional setting, this organic matter probably could not be preserved to form source rocks. However, if the authors place such evaporite deposition into a geologic context, source rocks could have formed in shallow-water settings in the past. Such settings were characterized by hydrologic conditions that allowed the retention of hypersaline, anoxic pore water to depths where the organic material was buried deep enough to generate hydrocarbons. When deep-basin, shallow-water, evaporite successions were laid down in basins such as the Mediterranean during the late Miocene, the Michigan basin during the Silurian, and in other large saline giants, conditions were right for source rocks to form within shallow-water and salt-flat evaporitic environments. The evaporites in these saline giants were deposited under conditions of relatively shallow water (< 50 m); the basin never appears to have dried out, but water levels changed quickly (approx. 10,000 years) from shallow to deep. Continual water saturation coupled with saline pore fluids prevented the inflow of fresh, oxidizing ground water into the basin center of shallow-water organic-rich evaporites. Immature hydrocarbons derived from such rocks today drip from the 5.5-m.y. old evaporites of Sicily in active salt and sulfur mines. Organic-rich sediments could also be preserved to generate hydrocarbons in rapidly subsiding rift basins. In such basins, rapid burial has prevented the entrance of fresher oxygenated waters and the associated degradation and destruction of the organic matter. The early continental rift stage generates the source rocks; the ephemeral streams, wadis, and dune fields become the reservoirs, and the subsequent evaporite stage seals the reservoir.

  18. Actualistic sandstone petrofacies: Discriminating modern and ancient source rocks

    SciTech Connect

    Ingersoll, R.V. )

    1990-08-01

    Actualistic models relating plate-tectonic setting to sedimentary basins and provenance successfully predict modal compositions of sand and sandstone at the scale of continents and ocean basins (third-order models). Second-order models may be used to identify source regions within a given tectonic setting, such as source terranes within the Rio Grande rift of New Mexico. First-order models relate the composition of modern alluvial sand directly to specific source rocks (e.g., granite). Petrographic data from locally derived sand of known provenance may be used to statistically discriminate compositions according to their source rocks, thus defining actualistic petrofacies. Ancient petrofacies may be compared to the actualistic petroficies, in order to better constrain provenance and paleotectonic reconstructions. This approach may be applied at first-, second-, or third-order scales. At first- and second-order scales, stepwise discriminant analysis reveals the Tertiary provenance history of the Rio Grande rift of north-central New Mexico by comparing Tertiary petrofacies with modern petrofacies of known provenance. Application of this technique provides needed objectivity in source-rock and paleotectonic reconstructions.

  19. Isotopic composition of salt efflorescence from the sandstone castellated rocks of the Bohemian Cretaceous Basin (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Schweigstillová, Jana; Přikryl, Richard; Novotná, Miroslava

    2009-07-01

    The origin of sulphates in sulphate-rich efflorescences on quartz sandstones with a clay matrix, exposed in rural areas of the Czech Republic is interpreted, based upon an isotopic study of S and O. Sulphates such as gypsum and/or alums exhibit δ34S ranging from +1.3 to +6.1‰ and δ18O from +5.3 to +8.8‰. The low variability of S and O isotopes indicates a common source of the sulphur and a similar mode of sulphate formation. Atmospheric sulphates with a similar isotopic signature occur in the area, due to the combustion of sulphurous coal in power plants, located a few tens of kilometres from the sampling points. The sulphates crystallize from supersaturated pore waters that represent atmospheric precipitation, rich in sulphates, having percolated through the porous sandstone system. The previously proposed model of efflorescence growth (that it is due to the oxidation of pyrite) can be excluded, due to both the rare occurrence of pyrite and also to its different isotopic signature (δ34S about -22‰). Although gypsum prevails in the central and eastern part of the studied area, the north and north-west of the Bohemian Cretaceous Basin (the most polluted region) exhibits a significant presence of alums (NH4 + or K+-NH4 +-rich). Formation of alums can be explained by the partial dissolution of clay minerals or feldspars present in the sandstone matrix. Release of alumina from these phases is facilitated by the low pH of the precipitation (pH 4-4.5) and also locally by organic acids, traces of which were found in the studied efflorescences by the use of infrared spectroscopy.

  20. Multiple sources for the origin of the early Cretaceous Xinxian granitic batholith and its tectonic implications for the western Dabie orogen, eastern China

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Xu, Zhaowen; Chen, Maohong; Yu, Yang

    2016-02-01

    This paper investigates the petrogenesis of the Xinxian granitic batholith and its tectonic implications for the Dabie orogen. Two Xinxian granites yield Early Cretaceous 238U/206Pb ages of 122.7 ± 1.3 Ma and 123.6 ± 2.2 Ma. The granites are metaluminous differentiated I-type granites, with A/NKC ranging from 0.90 to 0.96. The chondrite-normalised REE patterns display significant LREE/HREE enrichments with moderate negative Eu anomalies (Eu/Euδ = 0.30 ~ 0.85). The granites show enrichments in large-ion lithophile elements (LILEs, e.g. Rb, K, Th and U) and depletions in Sr, Ba and high field strength elements (HFSEs, e.g. Nb, Ta and Ti). Inherited zircons of different age (Neoproterozoic, one Early Proterozoic, one Archean and two Triassic inherited metamorphic zircons) are identified. The Early Cretaceous magmatic zircons contain enriched Hf isotopes with ɛ Hf ( t) values ranging from -26.9 to -18.7 (average = -22.5), more enriched than their probable alleged source, i.e. the Dabie Complex, represented by the Neoproterozoic and Triassic inherited zircons. Thus, the Archean and Early Proterozoic crustal materials may represent an enriched end member source for the parental magma of the Xinxian granites. Provenance analysis of the magmatic zircons in the North China and Yangtze blocks demonstrates that the Early Proterozoic inherited zircon in Xinxian has North China affinity. Thus, we proposed a multiple-sourced petrogenetic model for the Xinxian granitic batholith, which suggests that the batholith was formed by the remelting of a mixed crustal assemblage, including the Archean and Early Proterozoic crust of the North China Block, the Neoproterozoic crust of the Yangtze Block, as well as some Triassic collision-related ultra-high pressure (UHP) metamorphic rocks.

  1. Bulk densities and porosities of Cenozoic and Cretaceous basin-filling strata and Cretaceous and older basement rocks, Los Angeles Basin, California, determined from measurements of core samples

    USGS Publications Warehouse

    Beyer, L.A.; McCulloh, T.H.

    1998-01-01

    This report describes and provides a digital data file of selected bulk properties of subsurface rocks sampled in and around Los Angeles basin, California. Selected properties include measured dry bulk density (range 0.78 to 3.01 g/cm3), measured or estimated grain (matrix) density, calculated water saturated bulk density (range 1.47 to 3.01 g/cm3), calculated total porosity (range 0 to 69 porosity percent), geologic age, and lithology. Most of the rocks are conventional core samples taken from wells drilled by the petroleum industry. A small percentage of the core samples are from shallow borings. Rocks studied range in age from pre-Cambrian (?) to Recent and include sedimentary (98.8%), and volcanic, metamorphic and intrusive (1.2%) samples. Core samples studied were taken from measured drillhole depths that range from 35 to 20,234 ft (11 to 6,167 m). Version 1.0 of the data base (dated June 1998) contains information for 7378 samples from 234 wells, including two redrilled wells. This report/data base can be accessed on U. S. Geological Survey servers at http://geopubs.wr.usgs.gov/open-file/of98-788. Periodic additions to the on-line data base will be provided as new data is gathered.

  2. Composition, age, and petrogenesis of Late Cretaceous intrusive rocks in the central Big Belt Mountains, Broadwater and Meagher counties, Montana

    USGS Publications Warehouse

    Du Bray, E.A.; Snee, L.W.

    2002-01-01

    Cretaceous intrusions hosted by the Proterozoic Newland Formation. The northern intrusion, centered on Boulder Baldy, consists of outer, intermediate, and core zones composed of aegirine-augite quartz monzonite, hornblende quartz monzodiorite, and biotite granodiorite, respectively. The southern intrusion, north of Mount Edith, is compositionally indistinguishable from the intermediate zone of the northern intrusion.

  3. Oxygen isotope geochemistry of the silicic volcanic rocks of the Etendeka-Parana province: Source constraints

    SciTech Connect

    Harris, C.; Milner, S.C.; Armstrong, R.A. ); Whittingham, A.M. )

    1990-11-01

    Oxygen isotope ratios of pyroxene phenocrysts in the silicic volcanic rocks from the Cretaceous Etendeka-Parana flood basalt province (Namibia, South America) are believed to reflect the {delta}{sup 18}O values of the original magmas. The authors recognize a high {delta}{sup 18}O value type ({delta}{sup 18}O pyroxene {approximately} +10{per thousand}) found in the south of both regions, and a low {delta}{sup 18}O value type ({delta}{sup 18}O pyroxene {approximately} +6.5{per thousand}) found in the north. Other differences between thee two rhyolite types include higher concentrations of incompatible elements and lower initial {sup 87}Sr/{sup 86}Sr ratios in the low {delta}{sup 18}O value type. The authors suggest that the regional distribution of rhyolite types reflects differences in source composition, which can best be explained if the sources are lower crustal, Late Proterozoic mobile belt material (high {delta}{sup 18}O) and Archean lower crust (low {delta}{sup 18}O).

  4. Rock comminution as a source of hydrogen for subglacial ecosystems

    NASA Astrophysics Data System (ADS)

    Telling, J.; Boyd, E. S.; Bone, N.; Jones, E. L.; Tranter, M.; Macfarlane, J. W.; Martin, P. G.; Wadham, J. L.; Lamarche-Gagnon, G.; Skidmore, M. L.; Hamilton, T. L.; Hill, E.; Jackson, M.; Hodgson, D. A.

    2015-11-01

    Substantial parts of the beds of glaciers, ice sheets and ice caps are at the pressure melting point. The resulting water harbours diverse subglacial microbial ecosystems capable of affecting global biogeochemical cycles. Such subglacial habitats may have acted as refugia during Neoproterozoic glaciations. However, it is unclear how life in subglacial environments could be supported during glaciations lasting millions of years because energy from overridden organic carbon would become increasingly depleted. Here we investigate the potential for abiogenic H2 produced during rock comminution to provide a continual source of energy to support subglacial life. We collected a range of silicate rocks representative of subglacial environments in Greenland, Canada, Norway and Antarctica and crushed them with a sledgehammer and ball mill to varying surface areas. Under an inert atmosphere in the laboratory, we added water, and measured H2 production with time. H2 was produced at 0 °C in all silicate-water experiments, probably through the reaction of water with mineral surface silica radicals formed during rock comminution. H2 production increased with increasing temperature or decreasing silicate rock grain size. Sufficient H2 was produced to support previously measured rates of methanogenesis under a Greenland glacier. We conclude that abiogenic H2 generation from glacial bedrock comminution could have supported life and biodiversity in subglacial refugia during past extended global glaciations.

  5. Methane and carbon at equilibrium in source rocks

    PubMed Central

    2013-01-01

    Methane in source rocks may not exist exclusively as free gas. It could exist in equilibrium with carbon and higher hydrocarbons: CH4 + C < = > Hydrocarbon. Three lines of evidence support this possibility. 1) Shales ingest gas in amounts and selectivities consistent with gas-carbon equilibrium. There is a 50% increase in solid hydrocarbon mass when Fayetteville Shale is exposed to methane (450 psi) under moderate conditions (100°C): Rock-Eval S2 (mg g-1) 8.5 = > 12.5. All light hydrocarbons are ingested, but with high selectivity, consistent with competitive addition to receptor sites in a growing polymer. Mowry Shale ingests butane vigorously from argon, for example, but not from methane under the same conditions. 2) Production data for a well producing from Fayetteville Shale declines along the theoretical curve for withdrawing gas from higher hydrocarbons in equilibrium with carbon. 3) A new general gas-solid equilibrium model accounts for natural gas at thermodynamic equilibrium, and C6-C7 hydrocarbons constrained to invariant compositions. The results make a strong case for methane in equilibrium with carbon and higher hydrocarbons. If correct, the higher hydrocarbons in source rocks are gas reservoirs, raising the possibility of substantially more gas in shales than analytically apparent, and far more gas in shale deposits than currently recognized. PMID:24330266

  6. Methane and carbon at equilibrium in source rocks.

    PubMed

    Mango, Frank D

    2013-12-12

    Methane in source rocks may not exist exclusively as free gas. It could exist in equilibrium with carbon and higher hydrocarbons: CH4 + C < = > Hydrocarbon. Three lines of evidence support this possibility. 1) Shales ingest gas in amounts and selectivities consistent with gas-carbon equilibrium. There is a 50% increase in solid hydrocarbon mass when Fayetteville Shale is exposed to methane (450 psi) under moderate conditions (100°C): Rock-Eval S2 (mg g-1) 8.5 = > 12.5. All light hydrocarbons are ingested, but with high selectivity, consistent with competitive addition to receptor sites in a growing polymer. Mowry Shale ingests butane vigorously from argon, for example, but not from methane under the same conditions. 2) Production data for a well producing from Fayetteville Shale declines along the theoretical curve for withdrawing gas from higher hydrocarbons in equilibrium with carbon. 3) A new general gas-solid equilibrium model accounts for natural gas at thermodynamic equilibrium, and C6-C7 hydrocarbons constrained to invariant compositions. The results make a strong case for methane in equilibrium with carbon and higher hydrocarbons. If correct, the higher hydrocarbons in source rocks are gas reservoirs, raising the possibility of substantially more gas in shales than analytically apparent, and far more gas in shale deposits than currently recognized.

  7. Source-rock evaluation of the Dakhla Formation black shale in Gebel Duwi, Quseir area, Egypt

    NASA Astrophysics Data System (ADS)

    El Kammar, M. M.

    2015-04-01

    A relatively thick Upper Cretaceous-Lower Tertiary sedimentary succession is exposed in Gebel Duwi, Red Sea area, through an almost horizontal tunnel cutting the NE dipping strata from Quseir to Thebes formations. The black shale belonging to Dakhla Formation represents a real potential for future energy resource for Egypt. Dakhla Formation consists mainly of organic-rich calcareous shale to argillaceous limestone that can be considered as a good to excellent source rock potential. The total organic carbon (TOC) content ranges from 2.04% to 12.08%, and the Hydrogen Index (HI) values range from 382 to 1024 mg HC/g TOC. Samples of the Dakhla Formation contain mostly kerogen of types I and II that prone oil and oil-gas, indicating marine organic matter derived mainly from algae and phytoplankton organisms and proposing typical oil source kerogen. The average of the potential index (PI) value is 0.02 mg HC/g rock, which indicates the beginning of a considerable amount of oil generation from the Dakhla Formation. The Tmax values range from 427 to 435 °C. Based on the Tmax data and PI values, the studied black shale samples are immature to early mature for hydrocarbon generation in the Duwi area. The data reduction suggests four main factors covering about 91% of the total variances. The average of the calorific value (459 kcal/kg) indicates unworkable efficiency of such black shale for direct combustion use in power stations. However, selective operation of specific horizons having the highest calorific values may provide viable resources.

  8. 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

  9. Geohydrology and simulation of steady-state flow conditions in regional aquifer systems in Cretaceous and older rocks underlying Kansas, Nebraska, and parts of Arkansas, Colorado, Missouri, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming

    USGS Publications Warehouse

    Signor, D.C.; Helgesen, J.O.; Jorgensen, D.G.; Leonard, R.B.

    1997-01-01

    Three regional aquifers systems are the basis for describing the geohydrology of bedrock aquifers in the central United States. The Great Plains aquifer system, composed of Lower Cretaceous sandstone, generally contains brackish water (1,000 to 10,000 milligrams per liter dissolved solids); the Western Interior Plains aquifer system of lower Paleozoic rocks contains saline water and is laterally adjacent to the freshwater-bearing Ozark Plateaus aquifer system composed of rocks of the same age.

  10. Cretaceous crust-mantle interaction and tectonic evolution of Cathaysia Block in South China: Evidence from pulsed mafic rocks and related magmatism

    NASA Astrophysics Data System (ADS)

    Li, Bin; Jiang, Shao-Yong; Zhang, Qian; Zhao, Hai-Xiang; Zhao, Kui-Dong

    2015-10-01

    Cretaceous tectono-magmatic evolution of the Cathaysia Block in South China is important but their mechanism and geodynamics remain highly disputed. In this study we carried out a detailed geochemical study on the recently found Kuokeng mafic dikes in the western Fujian Province (the Interior Cathaysia Block) to reveal the petrogenesis and geodynamics of the Cretaceous magmatism. Kuokeng mafic dikes were emplaced in three principal episodes: ~ 129 Ma (monzogabbro), ~ 107 Ma (monzodiorite), and ~ 97 Ma (gabbro). Geochemical characteristics indicate that the monzogabbros were derived from the unmodified mantle source, while gabbros were likely derived from metasomatized mantle by subducted slab (fluids and sediments). Sr-Nd isotope compositions indicate that the parental magmas of the monzodiorites were generated by mixing of enriched, mantle-derived, mafic magmas and felsic melts produced by partial melting of crustal materials. Until the Early Cretaceous (~ 123 Ma), the dominant ancient Interior Cathaysia lithospheric mantle exhibited insignificant subduction signature, indicating the melting of asthenospheric mantle and the consequent back-arc extension, producing large-scale partial melting of the crustal materials under the forward subduction regime of the paleo-Pacific plate. The monzodiorites and gabbros appear to be associated with northwestward subduction of Pacific plate under an enhanced lithospheric extensional setting, accompanying with mantle modification, which triggered shallower subduction-related metasomatically enriched lithospheric mantle to melt partially. After ca. 110 Ma, the coastal magmatic belts formed due to a retreat and rollback of the subducting Pacific Plate underneath SE China in the continental margin arc system.

  11. Geochronological and geochemical constraints on the petrogenesis of late Cretaceous volcanic rock series from the eastern Sakarya zone, NE Anatolia-Turkey

    NASA Astrophysics Data System (ADS)

    Aydin, Faruk; Oǧuz, Simge; Şen, Cüneyt; Uysal, İbrahim; Başer, Rasim

    2016-04-01

    New SHRIMP zircon U-Pb ages and whole-rock geochemical data as well as Sr-Nd-Pb and δ18O isotopes of late Cretaceous volcanic rock series from the Giresun and Artvin areas (NE Anatolia, Turkey) in the northern part of the eastern Sakarya zone (ESZ) provide important evidence for northward subduction of the Neo-Tethyan oceanic lithosphere along the southern border of the ESZ. In particular, tectonic setting and petrogenesis of these subduction-related volcanites play a critical role in determining the nature of the lower continental crust and mantle dynamics during late Mesozoic orogenic processes in this region. The late Cretaceous time in the ESZ is represented by intensive volcanic activities that occurred in two different periods, which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic to rhyolitic) within each period. Although there is no geochronological data for the lower mafic-intermediate rock series of the first volcanic period, U-Pb zircon dating from the first cycle of felsic rocks yielded ages ranging from 88.6±1.8 to 85.0±1.3 Ma (i.e. Coniacian-Early Santonian). The first volcanic period in the region is generally overlain by reddish biomicrite-rich sedimentary rocks of Santonian-Early Campanian. U-Pb zircon dating for the second cycle of mafic-intermediate and felsic rocks yielded ages varying from 84.9±1.7 to 80.8±1.5Ma (i.e. Early to Middle Campanian). The studied volcanic rocks have mostly transitional geochemical character changing from tholeiitic to calc-alkaline with typical arc signatures. N-MORB-normalised multi-element and chondrite-normalised rare earth element (REE) patterns show that all rocks are enriched in LILEs (e.g. Rb, Ba, Th) and LREEs (e.g. La, Ce) but depleted in Nb and Ti. In particular, the felsic samples are characterised by distinct negative Eu anomalies. The samples are characterized by a wide range of Sr-Nd-Pb isotopic compositions (initial ɛNd values from -7

  12. Geochemistry of shales of the Upper Cretaceous Hayang Group, SE Korea: implications for provenance and source weathering at an active continental margin

    NASA Astrophysics Data System (ADS)

    Lee, Y. I.

    2009-04-01

    Shales of the Upper Cretaceous Hayang Group in the Yeongyang Subbasin, southeastern Korea were deposited in fluvio-lacustrine environments as the Paleo-Pacific (Izanagi) Plate obliquely subducted beneath the Asian continent. Major and trace element compositions derived from shales analyzed from the Hayang Group reveal geochemical signatures that are different from Post-Archean average Australian Shale (PAAS), but are typical of igneous rocks found in the continental-margin island arc settings. For example, most major element concentrations are depleted relative to PAAS; among them MgO and MnO depletions are most pronounced in all shales. CaO enrichment is notable in some formations due to the presence of secondary calcite as dispersed micro-calcite nodules. Sc, Y, and Th concentrations are also slightly depleted relative to PAAS while chondrite-normalized REE data for shales from the Hayang Group show moderate to large uniform LREE enrichment but variable HREE depletions. In addition, they are more fractionated than PAAS, and have significant negative Eu anomalies. Moreover, the chemical index of alteration and A-CN-K relations comply that the source area was dominated by non-steady state weathering regimes indicative of active uplift along an active continental margin. These regions were punctuated by two periods of steady-state weathering or alternatively by enhanced recycling of sediments. The latter interpretation is in accord with the timing of exposure of a cherty sequence in the source area. Mixing calculations based on REE data suggest that the average shale in the Hayang Group was derived from sources composed of Precambrian granitic gneiss, arc basaltic rocks, Triassic Yeongdeok Granite in the subbasin, and the Mino accretionary complex of SW Japan with ratios around 43.7 (31.8-73.2):26.4 (15.8-36.7) :15.4 (2.8-33.9):14.5 (0.0-33.8). However, these proportions change up sequence.

  13. Geochemistry of shales of the Upper Cretaceous Hayang Group, SE Korea: Implications for provenance and source weathering at an active continental margin

    NASA Astrophysics Data System (ADS)

    Lee, Yong Il

    2009-03-01

    Shales of the Upper Cretaceous Hayang Group in the Yeongyang Subbasin, southeastern Korea were deposited in fluvio-lacustrine environments as the Paleo-Pacific (Izanagi) Plate obliquely subducted beneath the Asian continent. Major and trace element compositions derived from shales analyzed from the Hayang Group reveal geochemical signatures that are different from Post-Archean average Australian Shale (PAAS), but are typical of igneous rocks found in the continental-margin island arc settings. For example, most major element concentrations are depleted relative to PAAS; among them MgO and MnO depletions are most pronounced in all shales. CaO enrichment is notable in some formations due to the presence of secondary calcite as dispersed micro-calcite nodules. Sc, Y, and Th concentrations are also slightly depleted relative to PAAS while chondrite-normalized REE data for shales from the Hayang Group show moderate to large uniform LREE enrichment but variable HREE depletions. In addition, they are more fractionated than PAAS, and have significant negative Eu anomalies. Moreover, the chemical index of alteration and A-CN-K relations comply that the source area was dominated by non-steady state weathering regimes indicative of active uplift along an active continental margin. These regions were punctuated by two periods of steady-state weathering or alternatively by enhanced recycling of sediments. The latter interpretation is in accord with the timing of exposure of a cherty sequence in the source area. Mixing calculations based on REE data suggest that the average shale in the Hayang Group was derived from sources composed of Precambrian granitic gneiss, arc basaltic rocks, Triassic Yeongdeok Granite in the subbasin, and the Mino accretionary complex of SW Japan with ratios around 43.7 (31.8-73.2):26.4 (15.8-36.7):15.4 (2.8-33.9):14.5 (0.0-33.8). However, these proportions change up sequence.

  14. Expelling of hydrocarbon in undercompacted oil-source rocks

    SciTech Connect

    Zhou, Guojun ); Chen, Fajing )

    1994-08-01

    The clay of source rocks below a certain depth is generally undercompacted. Historical analysis of undercompacted EK2 mudstone in the Huang Hua depression, North China basin, has shown that the peak of the undercompacted zone decreases under a certain depth, mainly due to development of a microfracture caused by abnormally high pressure. Based on the compaction history of mudstones and the hydraulic fracturing condition in this area, the depth of the microfracture developed in the EK2 undercompacted zone is calculated at 2900 m, which is also verified by fluorescence data. Geochemical evidence has also shown that many hydrocarbons are expelled under 2900 m.

  15. Potential cretaceous play in the Rharb basin of northern Morocco

    SciTech Connect

    Jobidon, G.P. )

    1993-09-01

    The autochthonous Cretaceous in the Rharb basin of northern Morocco is located underneath a cover of neogene sediments and of the Prerif nappe olistostrome, which was emplaced during the Tortonian 7 m.y. The presence of infranappe Cretaceous sediments is documented in a few onshore wells in the Rharb basin and in the adjacent Prerif Rides area, as well as in the Rif Mountains. Their presence in the deeper portion of the Rharb basin is difficult to detail because of poor seismic resolution data beneath dispersive prerif nappe. A recent study of offshore seismic data acquired by PCIAC in 1987 indicates that the infranappe interval can be more than 1500 m thick in some of the offshore Kenitra area. These sediments have seismic signatures that would correspond to Middle Cretaceous transgressions, culminating with a Turonian highstand. Their deposition systems were located on the northern and western flanks of the Meseta and were followed by a hiatus lasting until the Miocene. Regional studies of gravity and magnetic data provide and additional understanding of the Rif province, its evolution, and the possible presence of autochthonous Cretaceous sediments below the prerif nappe cover. The infranappe of Rharb basin has a good potential to develop into a major hydrocarbon play with the presence of middle Cretaceous reservoir rocks, Turonian-Cenomanian black shale source rocks, as well as the timely combination of trap formation, source rock maturation, and hydrocarbon migration.

  16. Anthropogenic sources stimulate resonance of a natural rock bridge

    NASA Astrophysics Data System (ADS)

    Moore, Jeffrey R.; Thorne, Michael S.; Koper, Keith D.; Wood, John R.; Goddard, Kyler; Burlacu, Relu; Doyle, Sarah; Stanfield, Erik; White, Benjamin

    2016-09-01

    The natural modes of vibration of bedrock landforms, as well as the sources and effects of stimulated resonance remain poorly understood. Here we show that seismic energy created by an induced earthquake and an artificial reservoir has spectral content coincident with the natural modes of vibration of a prominent rock bridge. We measured the resonant frequencies of Rainbow Bridge, Utah using data from two broadband seismometers placed on the span, and identified eight distinct vibrational modes between 1 and 6 Hz. A distant, induced earthquake produced local ground motion rich in 1 Hz energy, stimulating a 20 dB increase in measured power at the bridge's fundamental mode. Moreover, we establish that wave action on Lake Powell, an artificial reservoir, generates microseismic energy with peak power ~1 Hz, also exciting resonance of Rainbow Bridge. These anthropogenic sources represent relatively new energy input for the bridge with unknown consequences for structural fatigue.

  17. Subdivision and regional stratigraphy of the pre-Punta Gorda rocks (lowermost cretaceous-jurassic?) in South Florida

    USGS Publications Warehouse

    Applegate, A.V.; Winston, George O.; Palacas, James George

    1981-01-01

    In recent years several wells have been drilled in the South Florida Basin through carbonate and evaporite sequences to depths as much as 5,300 ft below the Punta Gorda Anhydrite. The deepest well penetrated igneous basement rocks to a total depth of 18, 670 ft. Correlation of anhydrite beds below the Punta Gorda has revealed several thick anhydrite units (200 to 400 ft) with regional persistence. The pre-Punta Gorda section is subdivided into four easily identifiable units listed in order of increasing age — Lehigh Acres (lowermost Comanchean), Pumpkin Bay (upper Coahuilan), Bone Island (lower Coahuilan), and Wood River (Jurassic?) Formations, all newly named in this report. In addition, the Lehigh Acres is divided into the West Felda Shale (base), Twelve Mile, and Able Members which are also named and defined in this report. Geochemical evidence indicates that the Lehigh Acres unit and the upper part of the Pumpkin Bay unit contain the most likely source beds for petroleum. Only two production tests have been carried out in the basin in strata below the oil-productive Sunniland Limestone. One was through casing in a Wood River dolomite zone. It reportedly produced water and some gas. The other was a drill stem test in an upper Pumpkin Bay dolomite zone which produced only water. In the Gulf Florida State Lease 826Y (Permit No. 275), a moderately porous, 350-ft-thick Pumpkin Bay dolomite zone was observed. As this well is west of the axis of the basin, better reservoir conditions presumably exist on the West Florida shelf than onshore.

  18. Early Cretaceous shelf-edge deltas of the Baltimore Canyon Trough: principal sources for sediment gravity deposits of the northern Hatteras Basin

    USGS Publications Warehouse

    Poag, C. Wylie; Swift, B. Ann; Schlee, John S.; Ball, Mahlon M.; Sheetz, Linda L.

    1990-01-01

    We present evidence that the principal sources for Early Cretaceous (Berriasian-Valanginian) gravity-flow deposits of the northern Hatteras Basin were three large shelf-edge deltas located along the outer margin of the Baltimore Canyon Trough, ∼ 100 km southeast of Cape Charles, Virginia, Ocean City, Maryland, and Long Branch, New Jersey. Sedimentary detritus from the central Appalachian highlands and the Maryland-Virginia coastal plain was transported across the Early Cretaceous continental shelf to form the Cape Charles and Ocean City deltas, whereas deposits of the Long Branch delta came chiefly from the Adirondack and New England highlands. Each delta supplied sediment gravity flows to large slope aprons and submarine-fan complexes on the Early Cretaceous continental slope and rise. The most conspicuous distributary of sediment on the Early Cretaceous continental rise extends 500 km basinward from the Ocean City delta, where its distal deposits were cored at Deep Sea Drilling Project Site 603.

  19. Late Jurassic-Early Cretaceous episodic development of the Bangong Meso-Tethyan subduction: Evidence from elemental and Sr-Nd isotopic geochemistry of arc magmatic rocks, Gaize region, central Tibet, China

    NASA Astrophysics Data System (ADS)

    Zhang, Yu-Xiu; Li, Zhi-Wu; Yang, Wen-Guang; Zhu, Li-Dong; Jin, Xin; Zhou, Xiao-Yao; Tao, Gang; Zhang, Kai-Jun

    2017-03-01

    The Bangong Meso-Tethys plays a critical role in the development of the Tethyan realm and the initial elevation of the Tibetan Plateau. However, its precise subduction polarity, and history still remain unclear. In this study, we synthesize a report for the Late Jurassic-Early Cretaceous two-phase magmatic rocks in the Gaize region at the southern margin of the Qiangtang block located in central Tibet. These rocks formed during the Late Jurassic-earliest Cretaceous (161-142 Ma) and Early Cretaceous (128-106 Ma), peaking at 146 Ma and 118 Ma, respectively. The presence of inherited zircons indicates that an Archean component exists in sediments in the shallow Qiangtang crust, and has a complex tectonomagmatic history. Geochemical and Sr-Nd isotopic data show that the two-phase magmatic rocks exhibit characteristics of arc magmatism, which are rich in large-ion incompatible elements (LIIEs), but are strongly depleted in high field strength elements (HFSEs). The Late Jurassic-earliest Cretaceous magmatic rocks mixed and mingled among mantle-derived mafic magmas, subduction-related sediments, or crustally-derived felsic melts and fluids, formed by a northward and steep subduction of the Bangong Meso-Tethys ocean crust. The magmatic gap at 142-128 Ma marks a flat subduction of the Meso-Tethys. The Early Cretaceous magmatism experienced a magma MASH (melting, assimilation, storage, and homogenization) process among mantle-derived mafic magmas, or crustally-derived felsic melts and fluids, as a result of the Meso-Tethys oceanic slab roll-back, which triggered simultaneous back-arc rifting along the southern Qiangtang block margin.

  20. Eclogite-, amphibolite- and blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and thermal evolution of the Chilean subduction interface during the Cretaceous

    NASA Astrophysics Data System (ADS)

    Hyppolito, Thais; Angiboust, Samuel; Juliani, Caetano; Glodny, Johannes; Garcia-Casco, Antonio; Calderón, Mauricio; Chopin, Christian

    2016-11-01

    Few localities in the Patagonian Andes expose remnants of the Mesozoic Chilean paleo-accretionary complex. We focus on the Diego de Almagro Island high-pressure/low-temperature (HP/LT) Complex, a pluri-kilometer thick sequence comprising metavolcanic rocks with oceanic affinities and metasedimentary rocks. In this study, the deepest segments of the Chilean subduction interface in Patagonia are characterized for the first time. Despite its apparent homogeneity, the complex is actually composed of two tectonic units with distinct ages of metamorphism and thermal evolution: the garnet amphibolite (GA) and the underlying blueschist (BS) units. The GA unit mafic rocks exhibit epidote, phengite, titanite, rutile, chloritoid and paragonite inclusions in prograde garnet I, diopside + albite intergrows replacing omphacite inclusions in garnet II, and relict omphacite (XJd45) included in edenitic-pargasitic amphiboles. Thermobarometric results show that these rocks were buried along a relatively cold prograde path (c. 11 °C/km) and reached eclogite-facies near peak pressure conditions (c. 550-600 °C, 1.6 GPa). The GA unit underwent a pervasive stage of amphibolitization during decompression at c. 1.3 GPa. Field and petrological observations, together with multi-mineral Rb-Sr dating, indicate that amphibolitization of the GA unit took place along the subduction interface at c. 120 Ma in a slightly warmer subduction regime (c. 13-14 °C/km), in agreeement with the formation of coetanoeus amphibolites at c. 35 km. The underlying BS unit (i) yields four consistent Rb-Sr deformation ages of c. 80 Ma, i.e. 40 Ma younger than the overlying rocks from the GA unit; (ii) exhibits slightly cooler peak metamorphic conditions (c. 520-550 °C, 1.6 GPa) indicating burial along a prograde path of c. 10 °C/km (iii) does not show amphibolite-facies overprint as seen in the GA unit. After a long residence time under amphibolite-facies conditions, the amphibolitized rocks of the GA unit

  1. Stratigraphic Analysis of Upper Cretaceous Rocks in the Mahajanga Basin, Northwestern Madagascar: Implications for Ancient and Modern Faunas.

    PubMed

    Rogers; Hartman; Krause

    2000-05-01

    Upper Cretaceous strata of the Mahajanga Basin, northwestern Madagascar, yield some of the most significant and exquisitely preserved vertebrate fossils known from Gondwana. The sedimentology of these strata and their stratigraphic relations have been the focus of renewed geological investigations during the course of five expeditions since 1993. We here designate stratotypes and formalize the terrestrial Maevarano Formation, with three new members (Masorobe, Anembalemba, Miadana), and the overlying marine Berivotra Formation. The Maevarano Formation accumulated on a broad, semiarid alluvial plain bounded to the southeast by crystalline highlands and to the northwest by the Mozambique Channel. The Berivotra Formation was deposited in an open marine setting that evolved from a clastic- to a carbonate-dominated shelf, resulting in deposition of the overlying Betsiboka limestone of Danian age. New stratigraphic data clearly indicate that the Maevarano Formation correlates, at least in part, with the Maastrichtian Berivotra Formation, and this in turn indicates that the most fossiliferous portions of the Maevarano Formation are Maastrichtian in age, rather than Campanian as previously reported. This revised age for the Maevarano vertebrate assemblage indicates that it is approximately contemporaneous with the vertebrate fauna recovered from the Deccan basalt volcano-sedimentary sequence of India. The comparable age of these two faunas is significant because the faunas appear to be more similar to one another than either is to those from any other major Gondwanan landmass. The revised age of the Maevarano Formation, when considered in the light of our recent fossil discoveries, further indicates that the ancestral stocks of Madagascar's overwhelmingly endemic modern vertebrate fauna arrived on the island in post-Mesozoic times. The basal stocks of the modern vertebrate fauna are conspicuously absent in the Maevarano Formation. Finally, the revised age of the Maevarano

  2. DHI evaluation by combining rock physics simulation and statistical techniques for fluid identification of Cambrian-to-Cretaceous clastic reservoirs in Pakistan

    NASA Astrophysics Data System (ADS)

    Ahmed, Nisar; Khalid, Perveiz; Shafi, Hafiz Muhammad Bilal; Connolly, Patrick

    2017-08-01

    The use of seismic direct hydrocarbon indicators is very common in exploration and reservoir development to minimise exploration risk and to optimise the location of production wells. DHIs can be enhanced using AVO methods to calculate seismic attributes that approximate relative elastic properties. In this study, we analyse the sensitivity to pore fluid changes of a range of elastic properties by combining rock physics studies and statistical techniques and determine which provide the best basis for DHIs. Gassmann fluid substitution is applied to the well log data and various elastic properties are evaluated by measuring the degree of separation that they achieve between gas sands and wet sands. The method has been applied successfully to well log data from proven reservoirs in three different siliciclastic environments of Cambrian, Jurassic, and Cretaceous ages. We have quantified the sensitivity of various elastic properties such as acoustic and extended elastic (EEI) impedances, elastic moduli (K sat and K sat-μ), lambda-mu-rho method (λρ and μρ), P-to-S-wave velocity ratio (V P/V S), and Poisson's ratio (σ) at fully gas/water saturation scenarios. The results are strongly dependent on the local geological settings and our modeling demonstrates that for Cambrian and Cretaceous reservoirs, K sat-μ, EEI, V P/V S, and σ are more sensitive to pore fluids (gas/water). For the Jurassic reservoir, the sensitivity of all elastic and seismic properties to pore fluid reduces due to high overburden pressure and the resultant low porosity. Fluid indicators are evaluated using two metrics: a fluid indicator coefficient based on a Gaussian model and an overlap coefficient which makes no assumptions about a distribution model. This study will provide a potential way to identify gas sand zones in future exploration.

  3. Whole-Rock Geochemistry and Zircon U-Pb Isotopes of the Late Cretaceous Granitoids of the Eastern Taurus (turkey): Implications for Petrogenesis and Geodynamic Setting

    NASA Astrophysics Data System (ADS)

    Beyarslan, Melahat; Lin, Yu-Chin; Chung, Sun-Lin; Feyzi Bingol, Ahmet; Yildirim, Esra

    2015-04-01

    The granitoid plutons out crop largely in the Eastern Taurus, in Turkey. New data, including a combination of field relation, U-Pb zircon geochronology and rock geochemistry on the granitoids in the Eastern Taurus of the Tethyan orogen in Turkey, come from four plutons ( Pertek, Baskil, Göksun and Şifrin). Pertek, Baskil and Göksun plutons consist mainly of diorite, quartz-diorites, tonalite, granodiorites and granites of I-type, with minor monzonite, the Şifrin pluton consists of syenogranite, syenite, monzogranite, monzonite. U-Pb zircon geochronology of four samples of diorite and granite from Pertek and Baskil plutons indicate ages of 86±2 - 79 ± 1Ma. U-Pb zircon geochronology of four samples from the Şifrin granitoid yield ages 77±1-72±1 Ma. Considering these ages, emplacement of the plutons took place during Late Cretaceous (Santonian-Campanian), from 86 to 72 Ma. Although the SiO2 of rocks forming granitoids varies in wide range ( 46.792- 74.092 wt%), they show arc and syn-collision geochemical affinity, with enrichment of LILE (K, Rb, Sr and Ba) and depletion of HFSE (Nb, Ta and Ti) and P. Geochemical data indice that the diorite, tonalite and granodiorite are low-K tholeiite, monzodiorite, monzogranite, granite and K-granite are calc-alkaline and high-K calc-alkaline and monzonite, syenomonzonite and syenite of Şifrin pluton and some samples of the Pertek pluton are shoshonitic. The Eastern Taurus granitoids would be formed by partial melting of possible juvenile arc-derived rocks during subduction of the South Branch of the Neo-Tethyan oceanic crust and subsequent arc-continent collision.

  4. Red Sea/Gulf of Aden source rock geochemical evaluation

    SciTech Connect

    Ducreux, C.; Mathurin, G.; Latreille, M. )

    1991-08-01

    The potential of hydrogen generation in the Red Sea and Gulf of Aden was studied by geochemical analyses of 2,271 samples from 23 wells drilled in 6 countries within the area. Selection of candidate source beds was primarily a function of the sedimentary column penetrated by drilling (i.e., whereas sub-Tertiary sediments are accessible in Somalia and Yemen in the Gulf of Aden, sampling below the thick Neogene evaporitic sequence in the Red Sea could not be achieved due to a general lack of penetration to such levels). Organic matter content and type, maturity levels, petroleum potential of the rock analyzed, and its capacity to have generated liquid or gaseous hydrocarbons are the basic results provided by the analyses. Geochemical well correlations within and between subbasins are presented using the two most representative parameters: total organic carbon (TOC) and Petroleum Potential (PP = S{sub 1} + S{sub 2}), expressed in kilograms of hydrocarbons per ton of rock. In general, results obtained in the two rift basins, with sampling mostly in Neogene sediments in the Red Sea and in sub-Tertiary and Tertiary sediments in the Gulf of Aden, indicate the presence of favorable sources preferentially in this sub-Tertiary succession. It is stressed that geochemical analysis results are from wells whose locations are generally on structural highs and, therefore, are not representative (especially in terms of maturation) of conditions in adjacent depressions, particularly where the difference in structural level is great. Sound simulation modeling makes possible the reconstruction regional thermal and burial history and, thus, identification of maturation kitchens.

  5. Source-rock geochemistry of the San Joaquin Basin Province, California: Chapter 11 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.; Valin, Zenon C.; Lillis, Paul G.

    2007-01-01

    Source-rock thickness and organic richness are important input parameters required for numerical modeling of the geohistory of petroleum systems. Present-day depth and thickness maps for the upper Miocene Monterey Formation, Eocene Tumey formation of Atwill (1935), Eocene Kreyenhagen Formation, and Cretaceous-Paleocene Moreno Formation source rocks in the San Joaquin Basin were determined using formation tops data from 266 wells. Rock-Eval pyrolysis and total organic carbon data (Rock-Eval/TOC) were collected for 1,505 rock samples from these source rocks in 70 wells. Averages of these data for each well penetration were used to construct contour plots of original total organic carbon (TOCo) and original hydrogen index (HIo) in the source rock prior to thermal maturation resulting from burial. Sufficient data were available to construct plots of TOCo and HIo for all source-rock units except the Tumey formation of Atwill (1935). Thick, organic-rich, oil-prone shales of the upper Miocene Monterey Formation occur in the Tejon depocenter in the southern part of the basin with somewhat less favorable occurrence in the Southern Buttonwillow depocenter to the north. Shales of the upper Miocene Monterey Formation generated most of the petroleum in the San Joaquin Basin. Thick, organic-rich, oil-prone Kreyenhagen Formation source rock occurs in the Buttonwillow depocenters, but it is thin or absent in the Tejon depocenter. Moreno Formation source rock is absent from the Tejon and Southern Buttonwillow depocenters, but thick, organic-rich, oil-prone Moreno Formation source rock occurs northwest of the Northern Buttonwillow depocenter adjacent to the southern edge of Coalinga field.

  6. Permian, Jurassic and Early Cretaceous palynofloral assemblages from subsurface sedimentary rocks in Chuperbhita Coalfield, Rajmahal Basin, India.

    PubMed

    Tripathi, A

    2001-04-01

    The results of a palynological analysis of the sedimentary sequence of Borehole RCH-151, Chuperbhita Coalfield, Rajmahal Basin, Bihar are presented here. The borehole penetrated the Rajmahal Formation (comprising two traps sandwiching an intertrappean bed), the thinly represented Dubrajpur Formation and in its lower part, the Coal Measures. The coal-bearing interval is associated with Scheuringipollenites barakarensis, Faunipollenites varius, Densipollenites indicus, Gondisporites raniganjensis and Densipollenites magnicorpus Assemblage Zones. The presence of these biostratigraphic units indicates correlation with the Barakar Formation (Early Permian) and the Barren Measures and Raniganj Formations (both Late Permian). This is the first record, in the Chuperbhita Coalfield, of Late Permian strata, which appear to represent a condensed sequence. Prior to the present study, the Permian succession was thought to have been associated entirely with the Barakar Formation. The overlying Dubrajpur Formation yielded a distinct spore-pollen assemblage (in association with the first report of dinoflagellate, Phallocysta), which is assigned to the newly identified Callialasporites turbatus palynozone of latest Early to early Middle Jurassic age. The diverse spore-pollen flora of the intertrappean bed (Rajmahal Formation) incorporates several age marker taxa, viz. Undulatisporites, Leptolepidites, Klukisporites, Ruffordiaspora, and Coptospora. The assemblages from intertrappean beds are correlated with the Ruffordiaspora australiensis palynozone of Australia. Thus the palynodating indicates Permian, latest Early to early Mid-Jurassic and Early Cretaceous age for the strata studied. This is the first record of definite Jurassic microfossils from the non-marine sequence of Rajmahal Basin, India.

  7. A plankton-residue model to explain trace-element enrichments in oil-source rocks

    SciTech Connect

    Piper, D.Z.; Isaacs, C.M. )

    1996-01-01

    Sedimentary deposits enriched in organic matter commonly have high concentrations of many trace elements. In the past, trace-element enrichment was attributed to accumulation by precipitation/adsorption reactions under conditions of bottom-water sulfate reduction, or from a seawater that itself had an unusually high concentration of trace elements. Examination of the ancient and modern sediment record shows, however, that many trace elements in these deposits accumulated within an organic fraction whose composition closely approached that of modem plankton; their accumulation further required only a moderate rate of primary productivity. Specific examples are represented by the accumulation of Cu, Cd, Mo, Ni, and Zn in the California Borderland today and by their abundance in Quaternary sediment from the Japan Sea, Cretaceous sediment from the Atlantic Ocean, the Miocene Monterey Formation, and the Permian Phosphoria Formation. Accordingly, we propose that the elevated trace-element concentration of many oil-source rocks, above that contributed by the detrital fraction, is a residue from the diagenetic degradation of marine plankton. Recent studies have shown that the burial rate (accumulation rate) of organic matter can rep- resent less than 5% of its rain rate (depositional rate) onto the sea floor and as little as 1 % of primary productivity. By contrast, several of the trace elements, once deposited on the sea floor, can be largely retained. In the Japan Sea sediment, for example, Cu: and Zn: organic-matter ratios in the marine fraction of 9 sediment alone average 10 times their ratios in plankton, suggesting a 90% loss of the organic matter that rained onto the sea floor, but Zn: Cu ratios and other trace-element: Cu ratios in this and other deposits closely approach modern plankton values.

  8. A plankton-residue model to explain trace-element enrichments in oil-source rocks

    SciTech Connect

    Piper, D.Z.; Isaacs, C.M.

    1996-12-31

    Sedimentary deposits enriched in organic matter commonly have high concentrations of many trace elements. In the past, trace-element enrichment was attributed to accumulation by precipitation/adsorption reactions under conditions of bottom-water sulfate reduction, or from a seawater that itself had an unusually high concentration of trace elements. Examination of the ancient and modern sediment record shows, however, that many trace elements in these deposits accumulated within an organic fraction whose composition closely approached that of modem plankton; their accumulation further required only a moderate rate of primary productivity. Specific examples are represented by the accumulation of Cu, Cd, Mo, Ni, and Zn in the California Borderland today and by their abundance in Quaternary sediment from the Japan Sea, Cretaceous sediment from the Atlantic Ocean, the Miocene Monterey Formation, and the Permian Phosphoria Formation. Accordingly, we propose that the elevated trace-element concentration of many oil-source rocks, above that contributed by the detrital fraction, is a residue from the diagenetic degradation of marine plankton. Recent studies have shown that the burial rate (accumulation rate) of organic matter can rep- resent less than 5% of its rain rate (depositional rate) onto the sea floor and as little as 1 % of primary productivity. By contrast, several of the trace elements, once deposited on the sea floor, can be largely retained. In the Japan Sea sediment, for example, Cu: and Zn: organic-matter ratios in the marine fraction of 9 sediment alone average 10 times their ratios in plankton, suggesting a 90% loss of the organic matter that rained onto the sea floor, but Zn: Cu ratios and other trace-element: Cu ratios in this and other deposits closely approach modern plankton values.

  9. Geochemical constraints on source region of Cretaceous/Tertiary impact glasses

    NASA Astrophysics Data System (ADS)

    Sigurdsson, H.; Bonte, Ph.; Turpin, L.; Chaussidon, M.; Metrich, N.; Steinberg, M.; Pradel, Ph.; D'Hondt, S.

    1991-10-01

    New trace elements and stable and radiogenic isotope data are presented which show that the silicic black glass spherules from the K/T boundary layer at Beloc in Haiti are derived from continental crust of andesitic composition, whereas the high-Ca glass formed by melting of evaporite-rich sediment. This is confirmed by melting experiments with evaporite and andesite at 1200-1400 C which approximately reproduce the high-Ca glass. The temperature-dependent variation of sulfur content in synthetic high-Ca glasses indicates a formation temperature of 1300 C for the Haiti glasses. The geology of the impact site inferred from the geochemistry of the Haiti glasses matches the lithologies found in the 180-km Chicxulub structure which occurs in Cretaceous evaporite deposits in Mexico. The high sulfur content of the calcic glasses suggests that the impact may have generated significant emissions of sulfur dioxide to the atmosphere, causing short-term global cooling.

  10. Subduction-related High- to Ultrahigh-Potassic Rocks of the Ankara-Erzincan Suture Belt of Turkey: a geochemical and isotopic approach to source and petrogenesis

    NASA Astrophysics Data System (ADS)

    Genc, S. Can; Gulmez, Fatma; Karacik, Zekiye; Tuysuz, Okan; Prelevic, Dejan; Roden, Michael F.; Hames, Willis E.; Zeki Billor, M.

    2014-05-01

    that the magmatic rock suites of LCVS had different crystallization history. REE melting modelings suggest a common mantle source, which contains variable amount of spinel lerzolite and garnet lerzolitic proportions. Considering the presence of some phlogopite-bearing clinopyroxenite xenolits in the lamprophyre and the leucite-bearing rocks, we propose that the LCVS ultrapotassic rocks were possibly derived from the low degree partial melting of veined SCLM. Keywords: High- to Ultrahigh-K, Isotope, Ar-Ar, Cretaceous, Turkey, Veined SCLM Lustrino, M., Wilson, M., 2007. ESR 81, 1-65. Peccerillo, A., 1995. Springer-Verlag. 365pp.

  11. 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.

  12. Characteristics of the Middle Jurassic marine source rocks and prediction of favorable source rock kitchens in the Qiangtang Basin of Tibet

    NASA Astrophysics Data System (ADS)

    Ding, Wenlong; Wan, Huan; Zhang, Yeqian; Han, Guangzhi

    2013-04-01

    We have evaluated the hydrocarbon-bearing potential of Middle Jurassic marine source rocks in the Qiangtang Basin, Tibet, through a comprehensive study of samples from a large number of surface outcrops in different structural units, and from the Qiang-D2 Well in the southern Qiangtang Depression. Data that were acquired, including the depositional environment, thickness of sedimentary units, and organic geochemistry, are used to identify the principal controlling factors and predict the location of favorable hydrocarbon kitchens. The source rocks are mainly platform limestone of the Middle Jurassic Buqu Formation. This formation comprises a suite of intra-platform sag marls, micrites, and black shales that were deposited in a deep-water and restricted depositional environment. The marls form hydrocarbon-rich source rocks with organic matter that is mainly type II and in the mature to highly mature stage. In the Dongco-Hulu Lake and Tupoco-Baitan Lake deep sags, limestone also forms a medium-level source rock. In the Qiangtang Basin, limestone is the favorable source rock kitchen and is more significant in this regard than mudstone. The results provide important constraints on evaluating the hydrocarbon potential of Jurassic marine source rocks and for locating petroleum resources in the Qiangtang Basin.

  13. Explosion Source Characteristics in Frozen and Unfrozen Rock

    DTIC Science & Technology

    2008-09-30

    can alter seismic yield. Central Alaska has abrupt lateral boundaries in discontinuous permafrost , and we detonated 3 shots in frozen, saturated rock...Central Alaska has abrupt lateral boundaries in discontinuous permafrost , Q) and we detonated 3 shots in frozen, saturated rock and 3 shots nearby in...rock. To find a possible location for the experiment, we consulted the permafrost map of Alaska (Ferrians, 1965) for regions of discontinuous permafrost

  14. Availability of petrographic thin-sections from measured sections and wells in Early- to Late-Cretaceous Nanushuk Group rocks, National Petroleum Reserve in Alaska, North Slope, Alaska

    SciTech Connect

    Bartsch-Winkler, S.

    1983-01-01

    A collection of thin sections from rocks of the Early- to Late-Cretaceous Nanushuk Group, North Slope, are available for study. The thin sections are from measured sections collected in 1977 and 1978, and from wells drilled within the boundaries of the National Petroleum Reserve in Alaska. The thin sections which are predominantly sandstones, have been stained with sodium cobaltinitrite for potassium-feldspar and with alizarin red-s for calcite. They have been injected, under vacuum, with blue plastic dye in order to examine the pore space for diagenetic and porosity characteristics. The majority of the samples from measured sections have not undergone petrographic analysis. Details of the stratigraphy and locations of many of the surface samples, and discussions of the petrographic characteristics of the sandstones comprising selected measured sections have been reported in the literature cited in this report. Requests for specimen loans should be directed to: Irvin L. Tailleur, Office of National Petroleum Reserve in Alaska, US Geological Survey, M.S. 87, 345 Middlefield Road, Menlo Park, CA 94025. 16 references, 1 figure, 1 table.

  15. Petrology and chemistry of late Cretaceous volcanic rocks from the southernmost segment of the Western Cordillera of Colombia (South America)

    NASA Astrophysics Data System (ADS)

    Spadea, P.; Espinosa, A.

    1996-03-01

    This paper presents new data on the petrology and chemistry of the igneous rocks composing the Mesozoic basement of southernmost Western Cordillera of Colombia along the Ricaurte-Altaquer section. The studied sequence includes variably metamorphosed submarine lavas, breccias, tuffs and dykes of basalt to andesite composition, and minor, shallow quartz microdiorite intrusives. A Campanian age is recorded by radiolarian faunas from chert strata capping the lavas. Two different tholeiitic suites and a younger calc-alkaline suite, represented by hornblende andesite, are distinguished. One tholeiitic suite, represented by plagioclase and pyroxene phyric lavas, evolves from basalt to basaltic andesite. It is characterized by the occurrence of diopsidic pyroxene as early crystallising phase, by depletion in high-field strength elements, particularly Nb and by relative enrichment in light REE and Th. The second tholeiitic suite, which includes aphyric or poorly phyric lavas of basalt to dacite composition, differs from the first group in having moderately low {FeO tot}/{MgO} ratio and lower P 2O 5 content for a given SiO 2, and higher {Ti}/{Zr}and{Y}/{Zr} ratios. The pyroxene chemistry of the two suites also differs. The primary geochemical characteristics of the two suites suggest a similarity with tholeiitic suites generated in island-arc environment. The hornblende andesite has mineralogical and chemical characteristics of calc-alkaline lavas erupted in an oceanic setting in an evolved island-arc. Petrologic and geochemical evidence suggests that the volcanic rocks from the Ricaurte-Altraquer section are similar to the island-arc tholeiite volcanics from the upper Macuchi Formation of northern Ecuador and can be correlated partly with this unit. Conversely, they are petrochemically dissimilar from the typical Diabase Group volcanic rocks, characterized by transitional MORB lavas, extensively present to the north in the Western Cordillera of Colombia.

  16. Tektites in Cretaceous-Tertiary boundary rocks on Haiti and their bearing on the Alvarez impact extinction hypothesis

    USGS Publications Warehouse

    Izett, G.A.

    1991-01-01

    Relic tektites are associated with a Pt-group metal abundance anomaly and shocked minerals in a thin marl bed that marks the K-T boundary on Haiti. The presence of these three impact-produced materials at the precise K-T boundary enormously strengthens the Alvarez impact extinction hypothesis. The Haitian tektites are the first datable impact products in K-T boundary rocks, and 40Ar-39Ar ages of the glass show that the K-T boundary and impact event are coeval at 64.5 ?? 0.1 Ma. -from Author

  17. A Re-examination of Shallow Paleomagnetic Inclinations From the Cretaceous Valle Group Sedimentary Rocks, Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Li, Y.; Kodama, K. P.; Smith, D. P.

    2001-05-01

    A paleomagnetic, rock magnetic, and sedimentological study was conducted in order to determine whether depositional/compactional processes have caused the shallow inclinations observed in the Valle Group sedimentary rocks. A total of 126 samples (14 sites) were collected from the middle Cenomanian section of the Valle along the northern coast of the Vizcaino Peninsula, Baja California, approximately 20 km east of Punta Eugenia at Campito. Samples were subjected to detailed thermal and alternating field (af) demagnetization, typically in 14 steps to 610° C for thermal demagnetization and ~24 steps to 130 mT for af demagnetization. NRMs were strong for marine sedimentary rocks, typically 10 mA/m. The mean of the site means for the demagnetized data was Inc=54.2° , Dec=306° , α 95=4.8° , N=12, in geographic coordinates, and Inc=20.5° , Dec=341.3° , α 95=4° , N=12 in stratigraphic coordinates. AMS fabrics have minimum axes clustered nearly perpendicular to bedding, typical of primary depositional/compactional fabrics. Some sites exhibited minimum axes clustering about 10° from the vertical and maximum axes clustered about 10° from the horizontal suggesting that currents and/or initial bedding dip affected the magnetization of these samples at deposition. Since the stratigraphy of the Valle Group dips consistently to the NE at approximately 50° , we sampled a tight slump fold at one site in order to constrain the age of magnetization. Both the AMS fabric and the characteristic remanence (ChRM) fail the fold test at the 95% confidence level. At another site, we sampled adjacent beds each approximately 5 cm thick composed of coarse, medium, or fine-grained sandstone. The directions of these beds are within 2° of each other. These results can be interpreted to indicate either a late remagnetization of the Valle group or an acquisition of the Valle's detrital remanence after slumping, but early in the rock's post-depositional history. Smith and Busby's (1993

  18. Uranium, yttrium, and rare earth elements accumulation during the Cretaceous anoxic events in carbonaceous rocks in the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Savelyeva, Olga; Philosofova, Tatyana; Bergal-Kuvikas, Olga; Savelyeva, Svetlana

    2017-04-01

    We have studied the carbonate-siliceous section of paleooceanic Albian-Cenomanian deposits on the Kamchatsky Mys peninsula (Eastern Kamchatka, Russia) [1].The section is represented by a rhythmic alternation of planktonic limestones and jaspers, accumulated in the open ocean environment. The rhythmicity can be attributed to climate variations that reflect a fluctuation of astronomical parameters (Milankovitch cycles) [2, 3].The section contains two beds enriched in organic carbon, corresponding to the two oceanic anoxic events - MCE and OAE2 [3]. The maximum content of organic matter in those beds reaches 68%. Our geochemical studies revealed an enrichment of the carbonaceous rocks in some major and trace elements including PGE, in comparison with the surrounding limestone and jasper [4].The accumulation of the ore elements in carbonaceous beds is caused by euxinic conditions during sedimentation.The content of uranium, yttrium, and rare earth elements in carbonaceous rocks is up to 60, 142 and 312 ppm respectively. Phosphate grains (bone detritus) with microinclusions of yttrium and uranium minerals were revealed in the carbonaceous rocks using the scanning electron microscope. These data prove the hypothesis of the sorbtion of U and Y by phosphate detritus from seawater. Microprobe analysis also showed an increased content of Cu, Zn, V in some pyrite framboids, which indicates that these elements are fixed in rocks by Fe-sulphide phase or organic matter under euxinic conditions. Our research may bring us closer to understanding the mechanism of syngenetic accumulation of metals in the black shales. This work was supported by the RFBR (No. 16-05-00546). [1] Palechek, T.N., Savelyev, D.P., Savelyeva, O.L. (2010) Stratigraphy and Geological Correlation 18, (1) 63-82. [2] Savelyeva, O.L. (2010). Vestnik Kraunts. Nauki o zemle 1 (15), 45-55 (in Russian). [3] Savelyev, D.P., Savelyeva, O.L., Palechek, T.N., Pokrovsky, B.G. (2012) Geophysical Research Abstracts, 14, EGU

  19. Thermal maturation and petroleum source rocks in Forest City and Salina basins, mid-continent, U. S. A

    SciTech Connect

    Newell, K.D.; Watney, W.L.; Hatch, J.R.; Xiaozhong, G.

    1986-05-01

    Shales in the Middle Ordovician Simpson Group are probably the source rocks for a geochemically distinct group of lower pristane and low phytane oils produced along the axis of the Forest City basin, a shallow cratonic Paleozoic basin. These oils, termed Ordovician-type oils, occur in some fields in the southern portion of the adjacent Salina basin. Maturation modeling by time-temperature index (TTI) calculations indicate that maturation of both basins was minimal during the early Paleozoic. The rate of maturation significantly increased during the Pennsylvanian because of rapid regional subsidence in response to the downwarping of the nearby Anadarko basin. When estimated thicknesses of eroded Pennsylvanian, Permian, and Cretaceous strata are considered, both basins remain relatively shallow, with maximum basement burial probably not exceeding 2 km. According to maturation modeling and regional structure mapping, the axes of both basins should contain Simpson rocks in the early stages of oil generation. The probability of finding commercial accumulations of Ordovician-type oil along the northwest-southeast trending axis of the Salina basin will decrease in a northwestward direction because of (1) westward thinning of the Simpson Group, and (2) lesser maturation due to lower geothermal gradients and shallower paleoburial depths. The optimum localities for finding fields of Ordovician-type oil in the southern Salina basin will be in down-plunge closures on anticlines that have drainage areas near the basin axis.

  20. Subsalt source rock maturity in the Sudanese Red Sea

    SciTech Connect

    Geiger, C. |; Pigott, J.; Forgotson, J.M. Jr.

    1995-08-01

    Thermal modeling can demonstrate that stratal salt deposits may provide a significant heat conduit and conceptually provide a basis for hypothermal fairways of hydrocarbon aspiration in regions of dominant thermal overmaturity. However, accurate evaluation of thermal maturity suppression by modeling must be geologically constrained. With respect to the Tertiary Tokar Delta of offshore Sudan, ID tectonic subsidence analysis of boreholes in the region reveals at least two major pu1ses of crustal extension and associated heating (24-20 m.a. and 5.4-2.7 m.a.). Integrating the borehole geochemical information with a Tokar Delta seismic stratigraphic interpretation allows the construction of constrained 2D thermal basin models through time using Procom BMT. The best match between the observed and modelled vitrinite reflectance values is achieved by using a two phase tectonic stretching model with pulses at 22{+-}2 m.a. and 4{+-}1.5 m.a. and incremental subcrustal stretching factors which vary between 2.65-2.75. Utilizing these parameters suggests the top of the oil window to occur within the Zeit Formation and bottom of the oil window to exist at the base of the Dungunab Salt. As only subsalt source rocks are observed, this model would tend to negate the possibility of the occurrence of liquid hydrocarbons. For the Tokar Delta the presently observed general high heat flow is so high that it leads in all cases to overcooked organics for a subsalt source. However, that hydrocarbons in the post-salt Zeit Formation of the Tokar Delta have been discovered suggests significant secondary hydrocarbon migration to have occurred within the late Miocene (15.4 - 5.4 m.a.). Potential migration pathways would be a1ong basement-induced fault conduits. If true, similar secondary migration play concepts may be applicable elsewhere in the Red Sea.

  1. The deep Cretaceous aquifer in the Aleppo and Steppe basins of Syria: assessment of the meteoric origin and geographic source of the groundwater

    NASA Astrophysics Data System (ADS)

    Stadler, S.; Geyh, M. A.; Ploethner, D.; Koeniger, P.

    2012-09-01

    A drilling project was carried out in Syria to assess the potential of the deep groundwater resources of the Cretaceous aquifer, composed of Cenomanian-Turonian limestones and dolomites. In this context, isotope (14C, 3H, δ13C, δ18O, δ2H) and hydrochemical analyses were performed on wells in and around the Aleppo and Steppe basins. The interpretation includes complementary results from published and unpublished literature. The results provide evidence that many new wells pump mixed groundwater from the Cretaceous aquifer and the overlying Paleogene aquifer. Radiocarbon measurements confirmed dominating Pleistocene groundwater in the Cretaceous aquifer and mainly Holocene groundwater in the Paleogene aquifer. Most groundwater in the Cretaceous aquifer seems to be recharged in the western limestone ridges, stretching from Jebel az Zawiyah (south of Idlep) via Jebel Samane (south of Afrin and A'zaz) to the region north of Aleppo, and in the Northern Palmyrides mountain belt. Some recharge also occurs around the basalt plateau of the Jebel al Hass, south east of Aleppo. It is concluded that the Taurus Mountains and the Euphrates River do not recharge the Cretaceous aquifer. The sources of recharge seem to be occasionally occurring intensive winter storms that approach from Siberia.

  2. Discordant paleomagnetic data for middle-Cretaceous intrusive rocks from northern Baja California: Latitude displacement, tilt, or vertical axis rotation?

    NASA Astrophysics Data System (ADS)

    BöHnel, Harald; Delgado-Argote, Luis A.; Kimbrough, David L.

    2002-10-01

    Paleomagnetic results and U/Pb zircon dating from the San Marcos dike swarm and the El Testerazo pluton in the Cretaceous Peninsular Ranges batholith of northern Baja California are used to evaluate alternative pre-Neogene paleogeographic reconstructions of the Baja California peninsula. The San Marcos dike swarm is a dense, northwest striking, regional dike swarm that is exposed over an ˜100 km long segment of the batholith and has yielded a U/Pb zircon crystallization age of 120 ± 1 Ma. Dike attitudes from the swarm suggest a regionally consistent average ˜320°E strike and ˜79°NE dip. The El Testerazo pluton is a younger tonalite intrusion that truncates the northern end of the dike swarm. All but one of 36 sites sampled in this study show remanence of normal polarity. Paleopoles for the San Marcos dike swarm and El Testerazo pluton are indistinguishable and were combined into a paleopole at 248.1°E, 86.6°N, A95 = 4.8°, which is displaced with respect to the 122 Ma reference pole for stable North America at 198.2°E, 72.3°N, A95 = 3.3°. The displacement may be described by an apparent clockwise rotation of 18° ± 6° and an apparent northward shift of 8° ± 5°. Restoring a northward shift of about 3°, related to the separation of Baja California from North America since 10 Ma, only a marginal northward displacement of 5° ± 5° is left. The clockwise rotation may be the result of crustal block rotations within the right-lateral shear systems in northern Baja California, although there is no geological evidence that supports this possibility. Alternatively, the difference between paleopole and reference pole may be due to tilting of the study area. Restoring a northeastward tilt of 11°, based on the mean dip measured for the San Marcos dike swarm in the study area, yields a paleopole at 187.6°E, 70.8°N, A95 = 5.6°, which is indistinguishable from the 122 Ma North American reference pole. The tilting hypothesis suggested previously as a

  3. Rocks.

    ERIC Educational Resources Information Center

    Lee, Alice

    This science unit is designed for limited- and non-English speaking students in a Chinese bilingual education program. The unit covers rock material, classification, characteristics of types of rocks, and rock cycles. It is written in Chinese and simple English. At the end of the unit there is a list of main terms in both English and Chinese, and…

  4. Rock Magnetic Cyclostratigraphy of the Mid-Cretaceous Greenhorn Limestone, South-Central Colorado---Influence of Orbitally Induced Climate Variability for Chornostratigraphy

    NASA Astrophysics Data System (ADS)

    Sellers, T.; Geissman, J. W.; Jackson, J.

    2015-12-01

    We are testing the hypothesis that depositional processes of the mid-Cretaceous Greenhorn Limestone were influenced by orbitally-driven climate variations using rock magnetic data. Correlation of the data, including anhysteretic remanent magnetization (ARM), magnetic susceptibility, isothermal remanent magnetization in different DC fields to saturation, and hysteresis properties, from three continuously exposed sections of the full Greenhorn Limestone provides detailed spatial distribution for the depositional processes and magnetic mineral climate encoding. The Greenhorn Limestone includes the Lincoln Limestone, Hartland Shale, and the Bridge Creek Limestone members and consists of calcareous shales and limestones representing near maximum depths in the Cretaceous interior seaway. The sections, each about 30 m thick, extend from the upper Graneros Shale, through the Greenhorn Formation, to the lower Carlisle Shale, with samples collected at a two to five cm interval and are located at Badito, CO; north of Redwing, CO; and at the Global boundary Stratotype Section and Point (GSSP) at Lake Pueblo, CO. Our over 1000 samples were hand crushed to granule size pieces and packed into 7cc IODP boxes. Bulk magnetic susceptibility, anhysteretic remanent magnetization (ARM) intensity at different peak AF levels, and isothermal remanent magnetization (IRM) intensity record variations in magnetic mineral concentration and are proxies to determine orbital scale cycles and precise stratigraphic correlation between sections. ARM intensities in a peak field of 100 mT at both sites range between 1.2 x 10-3 and 1.3 x 10-4 A/m and better define periodic variation within the Greenhorn Limestone displaying differences in ferromagnetic mineral content of detrital origin. Magnetic susceptibility, which ranges from 3.5 x 10-2 to 2.86 x 10-3, also shows periodic variation with a strong correlation among the three sections. Saturation IRM at 100 mT ranges from 3.2 x 10-1 to 1.1x 10-2 A

  5. Partial melting of the mélange for the growth of andesitic crust indicated by the Early Cretaceous arc dioritic/andesitic rocks in southern Qiangtang, central Tibet

    NASA Astrophysics Data System (ADS)

    Hao, LuLu; Wang, Qiang; Wyman, Derek; Ou, Quan; Dan, Wei; Jiang, ZiQi; Yang, JinHui; Long, XiaoPing; Li, Jie

    2016-04-01

    Deciphering the petrogenesis of andesitic/dioritic rocks is fundamental to understanding the formation of the continental crust. Here we present the detailed petrology, geochronology, major and trace element, Sr-Nd-Hf-O isotope data for the Early Cretaceous (ca. 122 Ma) dioritic rocks in the Bizha area in southern Qiangtang, Tibet. The dioritic rocks are characterized by large ion lithophile elements, Pb and light rare earth elements but depletion of high field strength elements with slightly enriched and variable ɛNd(t) values of -0.01 to -3.31 and initial 87Sr/86Sr isotopic ratios of 0.7053 to 0.7062. They also have variable magmatic zircon Hf-O isotope compositions (ɛHf(t) = -5.3 to +3.6 and δ18O = 7.3 to 9.5 ‰). Combined with contemporary andesitic lavas in southern Qiangtang, we suggest that the intermediate magmatic rocks in this area were most probably derived by partial melting of the mélange, which is a mixture of the middle oceanic ridge basalts (MORBs), sediments and mantle wedge peridotites, formed along the interface between the subducted slab and the overlying mantle wedge in a subduction channel before ~ 124 Ma. The mélange diapir melting was triggered by the asthenospheric upwelling and hot corner flow caused by roll-back of the northward subducted Bangong-Nujiang oceanic slab during the Early Cretaceous. The Early Cretaceous intermediate magmatic rocks in southern Qiangtang have an overall continental crust-like andesitic composition. Therefore, partial melting of the mélange provides an important support for the generation of andesitic magmas in continental arcs and the "andesite model" for crustal growth.

  6. Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration

    NASA Astrophysics Data System (ADS)

    Wei, Chun-Sheng; Zhao, Zi-Fu

    2017-01-01

    Since water is only composed of oxygen and hydrogen, δ18O and δ2H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (-65 ± 1o vs. -20 ± 2°) the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ18O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss.

  7. Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration

    PubMed Central

    Wei, Chun-Sheng; Zhao, Zi-Fu

    2017-01-01

    Since water is only composed of oxygen and hydrogen, δ18O and δ2H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (−65 ± 1o vs. −20 ± 2°); the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ18O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss. PMID:28091552

  8. Dual sources of water overprinting on the low zircon δ(18)O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration.

    PubMed

    Wei, Chun-Sheng; Zhao, Zi-Fu

    2017-01-16

    Since water is only composed of oxygen and hydrogen, δ(18)O and δ(2)H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (-65 ± 1(o) vs. -20 ± 2°); the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ(18)O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss.

  9. Geochemistry of Lower Cretaceous limestones of the Alisitos Formation, Baja California, México: Implications for REE source and paleo-redox conditions

    NASA Astrophysics Data System (ADS)

    Madhavaraju, J.; Löser, Hannes; Lee, Yong Il; Santacruz, R. Lozano; Pi-Puig, T.

    2016-03-01

    Measurement of the major and trace elements were carried out on the Lower Cretaceous limestones interbedded in the volcano-sedimentary Alisitos Formation, northwestern México to understand the source of rare earth elements (REEs) and paleo-redox conditions. The five limestone beds (from the base up, Unit 5 to Unit 9) of the Alisitos Formation show large variations in SiO2 content (0.9-27.9%). A low concentration of CaO is observed in Unit 6 and Unit 8, and high content of CaO is observed in Unit 5, Unit 7 and Unit 9. The limestones are depleted in many trace elements with respect to Post-Archaean Australian Shale (PAAS), whereas Sr shows slight enrichment when compared to PAAS. The concentrations of ΣREE are higher in Unit 6 and Unit 8 (37.4 ± 7.5; 46.6 ± 19.4; respectively) than Unit5, Unit7, and Unit 9 (9.1 ± 3.2; 11.3 ± 9.4; 4.2 ± 2.5; respectively). The limestones of the Alisitos Formation show a non-seawater-like REE + Y pattern with positive Eu anomalies relative to PAAS (0.95-2.47). Variations in ΣREE, Al2O3, Zr, Sc, REE + Y patterns, and Y/Ho ratios are influenced mainly by the amount of terrigenous materials. The variations in the Eu/Eu*, La/Sc and La/Co suggest that the terrigenous materials included in the lower four limestone beds (from Unit 5, Unit 6, Unit 7 and Unit 8) were likely contributed by intermediate to felsic rocks whereas terrigenous materials from Unit 9 were derived from mafic to intermediate source rocks. The slightly negative to slightly positive Ce anomalies in the studied limestones resulted from variations in the bottom water oxygenation. This was also corroborated by V/Cr and Ni/Co ratios suggesting that the depositional environments experienced large fluctuations in oxygenation conditions ranging from oxic to anoxic conditions during the deposition of limestones of the Alisitos Formation.

  10. Modified method for estimating petroleum source-rock potential using wireline logs, with application to the Kingak Shale, Alaska North Slope

    USGS Publications Warehouse

    Rouse, William A.; Houseknecht, David W.

    2016-02-11

    In 2012, the U.S. Geological Survey completed an assessment of undiscovered, technically recoverable oil and gas resources in three source rocks of the Alaska North Slope, including the lower part of the Jurassic to Lower Cretaceous Kingak Shale. In order to identify organic shale potential in the absence of a robust geochemical dataset from the lower Kingak Shale, we introduce two quantitative parameters, $\\Delta DT_\\bar{x}$ and $\\Delta DT_z$, estimated from wireline logs from exploration wells and based in part on the commonly used delta-log resistivity ($\\Delta \\text{ }log\\text{ }R$) technique. Calculation of $\\Delta DT_\\bar{x}$ and $\\Delta DT_z$ is intended to produce objective parameters that may be proportional to the quality and volume, respectively, of potential source rocks penetrated by a well and can be used as mapping parameters to convey the spatial distribution of source-rock potential. Both the $\\Delta DT_\\bar{x}$ and $\\Delta DT_z$ mapping parameters show increased source-rock potential from north to south across the North Slope, with the largest values at the toe of clinoforms in the lower Kingak Shale. Because thermal maturity is not considered in the calculation of $\\Delta DT_\\bar{x}$ or $\\Delta DT_z$, total organic carbon values for individual wells cannot be calculated on the basis of $\\Delta DT_\\bar{x}$ or $\\Delta DT_z$ alone. Therefore, the $\\Delta DT_\\bar{x}$ and $\\Delta DT_z$ mapping parameters should be viewed as first-step reconnaissance tools for identifying source-rock potential.

  11. Geochemistry and geochronology from Cretaceous magmatic and sedimentary rocks at 6°35‧ N, western flank of the Central cordillera (Colombian Andes): Magmatic record of arc growth and collision

    NASA Astrophysics Data System (ADS)

    Jaramillo, J. S.; Cardona, A.; León, S.; Valencia, V.; Vinasco, C.

    2017-07-01

    The spatio-temporal, compositional and deformational record of magmatic arcs are sensible markers of the long-term evolution of convergent margins including collisional events. In this contribution, field relations, U-Pb LA-ICP-MS zircon geochronology from magmatic and sedimentary rocks, and whole-rock geochemistry from volcanic and plutonic rocks are used to reconstruct the Cretaceous arc growth and collision in the awakening of the Northern Andean orogeny in northwestern Colombia. The Quebradagrande Complex that includes a sequence of volcanic rocks intercalated with quartz-rich sediments is a tholeiitic arc characterized by an enrichment in LREE and Nb-Ti anomalies that document crustal thickening in an arc system that was already active by ca. 93 Ma. This arc was built associated with thin continental and newly formed oceanic crust, as suggested by the presence of Triassic and older detrital zircons in the associated sandstones. This fringing arc subsequently experienced deformation and a major switch to and enriched calc-alkaline high-k plutonism between 70 and 73 Ma. The deformation record and changes in composition are related to an opposite double-vergence Molucca-sea type arc-arc collision that ended with the accretion to the continental margin of an allochthonous island arc built on an oceanic plateau associated with the Caribbean plate. The new time-framework suggest that the Late Cretaceous to Paleocene collisional tectonics include various stages before the switching to a subduction-dominated regime in most of the Cenozoic.

  12. Cretaceous may hold promise in Majunga basin, Madagascar

    SciTech Connect

    Lalaharisaina, J.V. ); Ferrand, N.J. )

    1994-08-01

    Recent drilling in the Majunga basin of northwestern Madagascar revealed unexpected light oil shows in excellent quality reservoir sands of Mid-Cretaceous age. Regional reconstructions show the development of a prograding clastic shelf from the Aptian until the Mid-Turonian that extended laterally from the northwest costs of Madagascar into Northwest India and Southeast Pakistan. Six untested play concepts have been identified in Cretaceous reservoirs of the Majunga basin. These plays offer multiple objectives in the depth range of 800--2,500 m within a well defined area. Further untested plays exist for Tertiary and Dogger objectives. The paper describes the geologic setting, exploration history the Cretaceous reservoirs, source rocks, and other potential plays. Political changes in Madagascar the last four years have led to an open door policy for foreign investment. Favorable terms are on offer for investment in the petroleum sector, and high potential exists for development on this island continent.

  13. Acid rock drainage and rock weathering in Antarctica: important sources for iron cycling in the Southern Ocean.

    PubMed

    Dold, B; Gonzalez-Toril, E; Aguilera, A; Lopez-Pamo, E; Cisternas, M E; Bucchi, F; Amils, R

    2013-06-18

    Here we describe biogeochemical processes that lead to the generation of acid rock drainage (ARD) and rock weathering on the Antarctic landmass and describe why they are important sources of iron into the Antarctic Ocean. During three expeditions, 2009-2011, we examined three sites on the South Shetland Islands in Antarctica. Two of them displayed intensive sulfide mineralization and generated acidic (pH 3.2-4.5), iron-rich drainage waters (up to 1.78 mM Fe), which infiltrated as groundwater (as Fe(2+)) and as superficial runoff (as Fe(3+)) into the sea, the latter with the formation of schwertmannite in the sea-ice. The formation of ARD in the Antarctic was catalyzed by acid mine drainage microorganisms found in cold climates, including Acidithiobacillus ferrivorans and Thiobacillus plumbophilus. The dissolved iron (DFe) flux from rock weathering (nonmineralized control site) was calculated to be 0.45 × 10(9) g DFe yr(-1) for the nowadays 5468 km of ice-free Antarctic rock coastline which is of the same order of magnitude as glacial or aeolian input to the Southern Ocean. Additionally, the two ARD sites alone liberate 0.026 and 0.057 × 10(9) g DFe yr(-1) as point sources to the sea. The increased iron input correlates with increased phytoplankton production close to the source. This might even be enhanced in the future by a global warming scenario, and could be a process counterbalancing global warming.

  14. Petrogenesis of Cretaceous shoshonitic rocks in the northern Wuyi Mountains, South China: A result of the roll-back of a flat-slab?

    NASA Astrophysics Data System (ADS)

    Li, Wu-Xian; Li, Xian-Hua; Wang, Xuan-Ce; Yang, Dong-Sheng

    2017-09-01

    Potassic magmatism is commonly linked to post-/late-orogenic environments, such as foundering or convection thinning of continental lithosphere. Their petrogenesis is crucial for constraining the chemical and physical properties of the remnant sub-continental lithospheric mantle. Here we report new SHRIMP zircon U-Pb ages, whole rock geochemical results and Sr-Nd and zircon Hf isotope data from four potassic plutons (the Da'an, Yingcheng, Zixi and Honggong plutons) in the northern Wuyi Mountains, South China. SHRIMP U-Pb zircon analyses indicate that these potassic rocks formed at 139-126 Ma. They are characterized by high SiO2 (56-73%) and K2O (3.8-6.7%), with a K2O/Na2O ratio of 2.18-2.04, plotting within the field of high-SiO2 shoshonites. Their ISr and εNd(t) values vary from 0.7077 to 0.7162 and - 5.66 to - 10.52, respectively. The initial zircon εHf(t) values range from 2.3 to - 13.1, corresponding to TDM modal ages between 707 and 1330 Ma. These geochemical and isotope characteristics indicate that these shoshonites derived from a subduction-modified ancient subcontinental lithospheric mantle, and then underwent significantly fractional crystallization of K-feldspar, plagioclase, and accessory minerals, such as apatite and Fe-Ti oxides during magma ascent. We interpret that asthenospheric mantle upwelling (caused by eastward roll-back of a flat-slab?) triggered partial melting of the metasomatized lithospheric mantle to result in the Early Cretaceous shoshonitic magmatism in the northern Wuyi Mountains. An integration of our new results with compiled data from the interior of the South China Block reveals that the arc-like geochemical signature is confined to the Wuyi Mountains region, but becomes little or even invisible toward inland in South China. This implies that the far-field effects of the early Mesozoic subduction only reached the Wuyi Mountains, ca. 500 km away from the trench, consistent with flat or shallow subduction models.

  15. Source Rock (shales) Pore Space Transformation during Hydrocarbon Generation

    NASA Astrophysics Data System (ADS)

    Giliazetdinova, D. R.; Korost, D. V.; Sudin, V. V.

    2015-12-01

    The main objective of this investigations is to study the factors controlling changes in rock structure during catagenetic transformation of organic matter. Hydrocarbon generation and primary migration can be controlled by numerous parameters; the most important are temperature, pressure, hydrocarbon composition, and organic matter type and content. Several experimental studies focused on the influence of these main parameters. However few dedicated works investigated how the primary structure characteristic and organic matter content affects the pore space transformation of rocks. For this purpose we simulated the primary migration processes in laboratory conditions (pyrolises and CT scanning) in order to observe the dynamics of pore space transformation. Our experiments demonstrate that after each stage of heating the rocks change their original morphology with the formation of new pores and conduits connecting the primary voids. The samples with relatively low content in organic matter revealed fewer changes in pore space morphology, in contrast to rocks rich in organic content. Our results also highlight that the newly formed pore structures are directly related with the original structure of the unaltered rocks and the primary connectivity of the organics. Most of the structural changes were observed during the sequential heating between 260 - 430 ° C; within this interval also occur the most intense reactions for hydrocarbons formation.

  16. Subsurface stratigraphic cross sections of cretaceous and lower tertiary rocks in the Wind River Basin, central Wyoming: Chapter 9 in Petroleum systems and geologic assessment of oil and gas resources in the Wind River Basin Province, Wyoming

    USGS Publications Warehouse

    Finn, Thomas M.

    2007-01-01

    The stratigraphic cross sections presented in this report were constructed as part of a project conducted by the U.S. Geological Survey to characterize and evaluate the undiscovered oil and gas resources of the Wind River Basin (WRB) in central Wyoming. The primary purpose of the cross sections is to show the stratigraphic framework and facies relations of Cretaceous and lower Tertiary rocks in this large, intermontane structural and sedimentary basin, which formed in the Rocky Mountain foreland during the Laramide orogeny (Late Cretaceous through early Eocene time). The WRB is nearly 200 miles (mi) long, 70 mi wide, and encompasses about 7,400 square miles (mi2) (fig. 1). The basin is structurally bounded by the Owl Creek and Bighorn Mountains on the north, the Casper arch on the east, the Granite Mountains on the south, and the Wind River Range on the west.

  17. Petroleum source rocks of the Junggar, Tarim, and Turpan basins, northwest China

    SciTech Connect

    Graham, S.A.; Brassell, S.; Carroll, A.R.; McKnight, C.L.; Chu, J.; Hendrix, M.S. ); Xiao, X. ); Demaison, G. ); Liang, Y. )

    1990-05-01

    The sedimentary basins of Xinjiang Uygur Autonomous Region, China, are poorly explored for petroleum. Volumetric adequacy of petroleum source rocks is a critical exploration risk in these basins, particularly because source rock data are limited. However, recent studies provide new source rock data and permit speculative assessment of source rock potential of Xinjiang basins. The Junggar basin, best explored of Xinjiang basins and containing a giant oil field, is underlain over much of its extent by an Upper Permian lacustrine oil-shale sequence that is known for its organic richness and oil source quality. Depending on position in the basin, the Permian section ranges from immature to overmature and is inferred to be the principal source of oil in the basin. Upper Triassic-Middle Jurassic coal measures, including lacustrine rocks, constitute a secondary source rock sequence in the Junggar basin. The smaller intermontane Turpan basin contains a very similar Upper Triassic-Middle Jurassic sequence, which, where sufficiently deeply buried, probably comprises the only significant oil source sequence in the basin. The vast Tarim basin offers the greatest potential variety of petroleum source rocks of all Xinjiang basins, but remains the least well documented. From limited, but geologically planned and focused sampling, Cambrian, Carboniferous, and Permian strata are considered unlikely to be major oil source contributors in the dominantly shallow-marine Paleozoic section of the northern Tarim basin. Only Ordovician black shales appear to have significant oil source potential, and a lower Paleozoic source is confirmed for some Tarim oils by gas chromatography-mass spectrometry analysis. The Upper Triassic-Middle Jurassic sequence of northern Tarim basin, similar to that of the Junggar and Turpan basins in comprising a section rich in coal and lacustrine shale, constitutes another, potentially significant oil source.

  18. Prediction of source rock characteristics based on terpane biomarkers in crude oils: a multivariate statistical approach

    SciTech Connect

    Zumberge, J.E.

    1987-06-01

    The distributions of eight tricyclic and eight pentacyclic terpanes were determined for 216 crude oils located worldwide with subsequent simultaneous RQ-mode factor analysis and stepwise discriminate analysis for the purpose of predicting source rock features or depositional environments. Five categories of source rock beds are evident: nearshore marine; deeper-water marine; lacustrine; phosphatic-rich source beds; and Ordovician age source rocks. The first two factors of the RQ-mode factor analysis describe 45 percent of the variation in the data set; the tricyclic terpanes appear to be twice as significant as pentacyclic terpanes in determining the variation among samples. Lacustrine oils are characterized by greater relative abundances of C/sub 21/ diterpane and gammacerane; nearshore marine sources by C/sub 19/ and C/sub 20/ diterpanes and oleanane; deeper-water marine facies by C/sub 24/ and C/sub 25/ tricyclic and C/sub 31/ plus C/sub 32/ extended hopanes; and Ordovician age oils by C/sub 27/ and C/sub 29/ pentacyclic terpanes. Although thermal maturity trends can be observed in factor space, the trends to do necessarily obscure the source rock interpretations. Also, since bacterial degradation of crude oils rarely affects tricyclic terpanes, biodegraded oils can be used in predicting source rock features. The precision to which source rock depositional environments are determined might be increased with the addition of other biomarker and stable isotope data using multivariate statistical techniques.

  19. Laser microprobe analysis of trace element composition in quartz silt for source rock determination

    SciTech Connect

    Gerber, D. . Dept. of Geology); Kennedy, S.K. . Dept. of Geology RJ Lee Group, Monroeville, PA )

    1992-01-01

    Provenance and source rock determination is one of the major problems that sedimentologists address. Undulatory extinction and polycrystallinity have been used to extract provenance information from sand-size quartz, but these are less informative with silt-size quartz. It is known that quartz contains trace elements which might be related to source rock. The purpose of this study was first to determine if the laser microprobe can detect trace elements in natural quartz, and second to determine if the quartz released from different crystalline source rocks have sufficiently different trace element composition to differentiate them. Ten silt samples from 5 source rocks (Pedlar Formation, Lovingston Fm. granitic gneiss, Lovingston Fm. mylonitic gneiss, an unnamed Precambrian layered granulite gneiss, and cataclastic rocks) of the Greenfield and Sherando Quadrangles of Virginia. Forty quartz grains for each sample were analyzed. The laser microprobe was able to detect Na, Mg, Al, K, Ca, Ti, Mn and Fe. Al and Fe were the most commonly observed trace element. The trace element content within quartz from each individual source was not uniform; one or more trace elements were detected in some grains while none were detected in others. In addition, there was overlap in the trace element distribution among the sources and quartz cannot be uniquely assigned to a source rock based on trace element composition. However, quartz from the Pedlar Fm. contains Al less frequently and quartz from the cataclastics and the layered granulite gneiss contains Fe more frequently than does quartz from the other sources. These results put some constraints on source rock interpretation and the analysis of more dissimilar rocks may show greater differences.

  20. 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

  1. Maps showing thermal maturity of Upper Cretaceous marine shales in the Wind River Basin, Wyoming

    USGS Publications Warehouse

    Finn, Thomas M.; Pawlewicz, Mark J.

    2013-01-01

    The Wind River Basin is a large Laramide (Late Cretaceous through Eocene) structural and sedimentary basin that encompasses about 7,400 square miles in central Wyoming. The basin is bounded by the Washakie Range, Owl Creek, and southern Bighorn Mountains on the north, the Casper arch on the east and northeast, the Granite Mountains on the south, and the Wind River Range on the west. Important conventional and unconventional oil and gas resources have been discovered and produced from reservoirs ranging in age from Mississippian through Tertiary. It has been suggested that various Upper Cretaceous marine shales are the principal hydrocarbon source rocks for many of these accumulations. Numerous source rock studies of various Upper Cretaceous marine shales throughout the Rocky Mountain region have led to the conclusion that these rocks have generated, or are capable of generating, oil and (or) gas. With recent advances and success in horizontal drilling and multistage fracture stimulation there has been an increase in exploration and completion of wells in these marine shales in other Rocky Mountain Laramide basins that were traditionally thought of only as hydrocarbon source rocks. Important parameters that control hydrocarbon production from shales include: reservoir thickness, amount and type of organic matter, and thermal maturity. The purpose of this report is to present maps and a structural cross section showing levels of thermal maturity, based on vitrinite reflectance (Ro), for Upper Cretaceous marine shales in the Wind River Basin.

  2. Petroleum potentialities of central Tunisia as deduced from identification and characterization of oil source rocks

    SciTech Connect

    Saidi, M.; Acheche, M.H.; Inoubli, H. ); Belayouni, H. )

    1991-08-01

    Many potential oil source rocks occur within the Tunisian stratigraphic column, including Silurian-Devonian shales, Albian and upper Albian-Vraconian carbonates, Cenomanian-Turonian black shales and lower Eocene carbonates. This focuses on the inventory of potential oil source rocks in central Tunisia ranging from middle Jurassic to Turonian. The emphasis is on determining their genetic potential and whether they could have generated oil and gas. Geochemical data obtained from the analysis of at least 2,147 samples show this region to be of significant interest as a petroleum prospective area. The main source rocks identified are Toarcian shales, upper Albian-Vraconian carbonates and Cenomanian-Turonian black shales. They contain predominantly type 2 organic matter (oil and gas prone) and are at the low maturity limit of the oil window. The occurrence of those source rocks close to numerous potential reservoir facies supports the conclusion that central Tunisia is a very interesting area for petroleum exploration.

  3. Geochemistry of the Jurassic and Upper Cretaceous shales from the Molango Region, Hidalgo, eastern Mexico: Implications for source-area weathering, provenance, and tectonic setting

    NASA Astrophysics Data System (ADS)

    Armstrong-Altrin, John S.; Nagarajan, Ramasamy; Madhavaraju, Jayagopal; Rosalez-Hoz, Leticia; Lee, Yong Il; Balaram, Vysetti; Cruz-Martínez, Adriana; Avila-Ramírez, Gladis

    2013-04-01

    This study focuses on the Jurassic (Huayacocotla and Pimienta Formations) and Upper Cretaceous (Méndez Formation) shales from the Molango Region, Hidalgo, Mexico. In this article, we discuss the mineralogy, major, and trace element geochemistry of the Mesozoic shales of Mexico. The goal of this study is to constrain the provenance of the shales, which belong to two different periods of the Mesozoic Era and to understand the weathering conditions and tectonic environments of the source region.

  4. 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. 

  5. Strontium isotopic evidence for an enriched source for post-subduction volcanic rocks, Dominican Republic

    SciTech Connect

    Wertz, W.K.; Perfit, M.R.; Shuster, R.D.

    1985-01-01

    Later Cenozoic volcanic rocks from the eastern Las Cuevas region (ELCR), Dominican Republic are dominantly shoshonitic and are associated with a series of east-west trending faults. The ELCR rocks are highly enriched in Sr, Ba, and light REE, but contain relatively low amounts of Rb and HFS ions. Several basalts appear to be unfractionated and have Mg-numbers of >75. These transitional to alkalic volcanic rocks are atypical of Caribbean igneous rocks and are more similar to alkaline centers associated with late-stage, island arc volcanism in other regions. Elevated /sup 87/Sr//sup 86/Sr ratios (0.7041-0.7048) are high in comparison to most other igneous rocks from the Caribbean region and indicate that they were derived from a source relatively enriched in LIL and REE in comparison to the sources which gave rise to the majority of Caribbean igneous rocks. /sup 87/Sr//sup 86/Sr values increase linearly with increasing Sr contents, suggesting mixing of sources with relatively low Sr contents and depleted /sup 87/Sr//sup 86/Sr with material that is highly enriched in Sr and with /sup 87/Sr//sup 86/Sr values around 0.706. This enriched component may be a fluid derived from melting/dehydrating subducted oceanic crust and sediment which metasomatically veined the sub-arc mantle. Small degrees of partial melting (<7%) of this source may be responsible for the unusual and enriched chemical composition of the ELCR volcanic rocks.

  6. Soils, slopes and source rocks: Application of a soil chemistry model to nutrient delivery to rift lakes

    NASA Astrophysics Data System (ADS)

    Harris, Nicholas B.; Tucker, Gregory E.

    2015-06-01

    The topographic evolution of rift basins may be critical to the deposition of lacustrine source rocks such as the organic-rich Lower Cretaceous shales of the South Atlantic margin. Soils have been proposed as a key link between topography and source rock deposition by providing nutrients for the algae growth in rift lakes. Decreasing topographic relief from active rift to late rift has several effects on soils: soils become thicker and finer, erosion of dead surface and soil organic matter decreases, and the fractionation of precipitation between runoff and infiltration may favor increased infiltration. This hypothesis is tested by application of CENTURY, a complex box model that simulates transfer of nutrients within soil pools. The model is first applied to a rainforest soil, with several parameters individually varied. Infiltration experiments show that the concentrations of C, N and P in groundwater decrease rapidly as infiltration decreases, whether due to increased slope or to decreased precipitation. Increased erosion of surface plant litter and topsoil results in substantially decreased nutrient concentrations in groundwater. Increased sand content in soil causes an increase in nutrient concentration. We integrate these variables in analyzing topographic swathes from the Rio Grande Rift, comparing the southern part of the rift, where topography is relatively old and reduced, to the northern rift. C and P concentrations in groundwater increase as slope gradient decreases, resulting in substantially larger C and P concentrations in groundwater in the southern rift than the northern rift. Nitrogen concentrations in groundwater depends on whether infiltration varies as a function of slope gradient; in experiments where the fraction of infiltrated precipitation decreased with increasing slope, N concentrations was also substantially higher in the southern rift; but in experiments where that fraction was held constant, N concentrations was lower in the southern

  7. Extensional tectonic influence on lower and upper cretaceous stratigraphy and reservoirs, southern Powder River basin, Wyoming

    SciTech Connect

    Mitchell, G.C.; Rogers, M.H.

    1993-04-01

    The southern Powder River basin has been influenced significantly by an extensional system affecting Lower Cretaceous, Upper Cretaceous and Tertiary units. The system is composed of small throw, nearly vertical normal faults which are identified in the Cretaceous marine shales and that we believe are basement derived. Resultant fractures were present at erosional/depositional surfaces, both marine and nonmarine, that, in part, controlled erosion and subsequent deposition of Lower and Upper Cretaceous rocks. The normal faults also affected coal deposition in the Tertiary, now exposed at the surface. The erosion and resultant deposition formed extensive stratigraphic traps in Cretaceous units in both conventional and unconventional reservoirs. These reservoirs are interbedded with mature source rocks that have generated and expelled large amounts of hydrocarbons. Resulting overpressuring in the Fall River through the Niobrara formations has kept fractures open and has preserved primary porosity in the reservoirs. The normal faults offset thin sandstone reservoirs forming permeability barriers. Associated fractures may have provided vertical pathways for organic acids that assisted development of secondary porosity in Upper Cretaceous sandstones. These normal...faults and fractures provide significant potential for the use of horizontal drilling techniques to evaluate fractured, overpressured conventional and unconventional reservoirs.

  8. Major element variation and possible source materials of apollo 12 crystalline rocks.

    PubMed

    Kushiro, I; Haramura, H

    1971-03-26

    Nine different crystalline rocks of the Apollo 12 samples have been analyzed with conventional chemical rock analysis methods. Five of the rocks have normative quartz, whereas the others have normative olivine and hypersthene. The rocks show a wide range in the ratio of iron to magnesium, and their compositions fall on relatively smooth curves in the oxide variation diagram. It is suggested that these rocks, with one exception, represent different parts of a differentiated magmatic body, in which magmatic differentiation by crystallization and settling of olivine was most effective. The source material of the original magma may be peridotite with or without minor amounts of plagioclase or spinel or garnet, with the presence or absence of these minerals dependent on the depth of magma generation.

  9. 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.

  10. Source rock study of Smackover Formation from east Texas to Florida

    SciTech Connect

    Sassen, R.; Moore, C.H.

    1987-05-01

    Analyses of core and crude oil samples indicate that the laminated lime mudstone facies of the lower Smackover Formation is a significant source rock across the trend. The source facies was deposited in an anoxic and hypersaline environment that permitted preservation of algal kerogen. Moreover, source potential also occurs in undifferentiated Gilmer-Smackover rocks of east Texas deposited in a carbonate slope environment. Thermal maturity is the key factor that controls the generation of crude oil by the carbonate source facies and the eventual destruction of hydrocarbons in upper Smackover and Norphlet reservoirs. Once the regional thermal maturity framework is understood, it is possible to construct a source rock model that explains the distribution of crude oil, gas condensate, and methane across the trend. Calculated thermal maturity histories provide insight to the timing of hydrocarbon generation and migration and to the timing of hydrocarbon destruction and sulfate reduction in deep reservoirs. Basic geochemical strategies for exploration are suggested. One strategy is to focus exploration effort on traps formed prior to the time of crude oil migration that were nearest to effective source rocks. Another strategy is to avoid drilling reservoir rocks that are thermally overmature for preservation of hydrocarbons.

  11. Sr-Nd-Hf isotopes of the intrusive rocks in the Cretaceous Xigaze ophiolite, southern Tibet: Constraints on its formation setting

    NASA Astrophysics Data System (ADS)

    Zhang, Liang-Liang; Liu, Chuan-Zhou; Wu, Fu-Yuan; Zhang, Chang; Ji, Wei-Qiang; Wang, Jian-Gang

    2016-08-01

    The Cretaceous Xigaze ophiolite is best exposed at the central part of the Yarlung-Zangbo Suture Zone, Tibet Plateau. It consists of a thick section of mantle peridotites, but a relatively thin mafic sequence. This study presents geochronological and geochemical data for intrusive dykes (both mafic and felsic) and basalts to revisit the formation setting of the Xigaze ophiolite. The rodingites are characterized by high CaO and low Na2O contents relative to mafic dykes and show big variations in trace element compositions. Both gabbros and diabases have similar geochemical compositions, with MgO contents of 6.42-11.48 wt% and Mg# of 0.56-0.71. They display REE patterns similar to N-MORB and are variably enriched in large ion lithophile elements. Basalts have fractionated compositions and display LREE-depleted patterns very similar to N-MORB. They do not show obvious enrichment in LILE and depletion in high-field-strength elements, but a negative Nb anomaly is present. The studied plagiogranites have compositions of trondhjemite to tonalite, with high Na2O and low K2O contents. They have low TiO2 contents less than 1 wt%, consistent with melts formed by anatexis of gabbros rather than by differentiation of basalts. Zircons from seven samples, including three rodingites, three plagiogranites, and one gabbro, have been dated and yielded U-Pb ages of 124.6 ~ 130.5 Ma, indicating the Xigaze ophiolite was formed during the Early Cretaceous. They have mantle-like δ18O values of + 4.92 ~ + 5.26‰ and very positive εHf(t) values of + 16 ~ + 13.3. Ages of the rodingites and less altered gabbros indicate that serpentinization was occurred at ~ 125 Ma. Occurrence of both gabbroic and diabase dykes within the serpentinites suggests that the mantle lithosphere of the Xigaze ophiolite was rapidly exhumed. Both mafic and felsic dykes have slightly more radiogenic 87Sr/86Sr ratios relative to MORB, but depleted Hf-Nd isotpe compositions. They have a limited range of ε

  12. Melt source and evolution of I-type granitoids in the SE Tibetan Plateau: Late Cretaceous magmatism and mineralization driven by collision-induced transtensional tectonics

    NASA Astrophysics Data System (ADS)

    Yang, Li-Qiang; Deng, Jun; Dilek, Yildirim; Meng, Jian-Yin; Gao, Xue; Santosh, M.; Wang, Da; Yan, Han

    2016-02-01

    We report new whole-rock geochemical and Sr-Nd-Pb isotope and zircon U-Pb age and Hf isotope data of the Hongshan intrusive suite in the Triassic Yidun Terrane, eastern Tibet. These data allow us to explore the possible causative links between the magmatism and the coeval Cu-Mo mineralization in the region. The Hongshan intrusive rocks have SiO2 of 65.06-73.60 wt.%, K2O of 3.17-6.41 wt.%, and P2O5 of 0.11-0.39 wt.%, enriched in Rb, Th, and U, and depleted in Ba, Sr, P, Ti, Nb, and Eu. These rocks are of high-K calc-alkaline to shoshonite series, showing geochemical signatures of metaluminous to slightly peraluminous I-type granite. Magmatic zircons separated from four samples yielded weighted mean 206Pb/238U ages of 79 ± 0.7 Ma, 78 ± 0.5 Ma, 77 ± 0.8 Ma, and 76 ± 0.8 Ma. Low MgO (0.42-1.47 wt%), low HREE and Y, varying εHf(t) (- 9.5 to - 2.2), and negative εNd(t) (- 7.7 to - 5.8) suggest that magmas of the late Cretaceous Hongshan plutons were most likely generated by partial melting and mixing of ~ 20% juvenile lower crust-derived melts, represented by the ca. 215 Ma basaltic andesite from the southern Yidun Terrane, with ancient basement-derived melts represented by the Baoshan S-type granitic melts from the Zhongza Block. We consider that partial melting processes are capable of removing chalcophile elements (such as Cu) and leaving siderophile metals (such as Mo) as residue in the lower crust of the Yidun Terrane, consequently inducing porphyry Cu-Mo mineralization. This consideration enables us to propose that the Triassic subduction-modified, copper-rich lithosphere was crucial for the giant copper mineralization that occurred in the Yidun Terrane during the late Cretaceous. Lithospheric-scale, transtensional faulting, developed as a result of collision-induced escape tectonics in SE Tibet, triggered asthenospheric upwelling, which in turn caused intra-plate extension and magmatism during the late Cretaceous, forming the Hongshan and coeval I

  13. Importance of hydrous pyrolysis studies in properly identifying source rocks of the Unita basin

    SciTech Connect

    Ruble, T.E.; Lewan, M.D.; Philp, R.P.

    1995-12-01

    The Uinta Basin in northeastern Utah historically has received considerable attention from petroleum geochemists; as a classic model of hydrocarbon generation from lacustrine source rocks. Previous work has focused primarily on the organic-rich Type-I algal kerogen contained in the Mahogany zone of the upper Green River Formation. Although recently published geochemical data suggest Mahogany zone source rocks are too immature to have generated the basin`s hydrocarbon reserves, this unit has been used as an analog for open lacustrine source rocks inferred to be buried more deeply. A series of hydrous pyrolysis experiments were conducted to examine this hypothesis. Source rocks included both the Mahogany zone and the basal Green River {open_quotes}black shale facies{close_quotes}. Compositional differences in the expelled pyrolysates suggest only the {open_quotes}black shale facies{close_quotes} is the source of the waxy crude oils produced in the Uinta Basin. Kinetic parameters derived from these experiments support such an interpretation and offer new insights for modeling hydrocarbon generation. These parameters have also been compared to previously reported values and those determined by Rock-Eval analysis.

  14. [The evaluation of hydrocarbon potential generation for source rocks by near-infrared diffuse reflection spectra].

    PubMed

    Zhang, Yu-Jia; Xu, Xiao-Xuan; Song, Ning; Wu, Zhong-Chen; Zhou, Xiang; Chen, Jin; Cao, Xue-Wei; Wang, Bin

    2011-04-01

    Near-infrared (NIR) and mid-infrared (MIR) diffuse reflection spectra were compared and evaluated for hydrocarbon potential generation of source rocks. Near-infrared diffuse reflectance often exhibits significant differences in the spectra due to the non-homogeneous distribution of the particles, so the signal-to-noise ratio of NIR is much lower than MIR It is too difficult to get accurate results by NIR without using a strong spectral preprocessing method to remove systematic noise such as base-line variation and multiplicative scatter effects. In the present paper, orthogonal signal correction (OSC) and an improved algorithm of it, i.e. direct orthogonal signal correction (DOSC), are used as different methods to preprocess both the NIR and MIR spectra of the hydrocarbon source rocks. Another algorithm, wavelet multi-scale direct orthogonal signal correction (WMDOSC), which is a combination of discrete wavelet transform (DWT) and DOSC, is also used as a preprocessing method. Then, the calibration model of hydrocarbon source rocks before and after pretreatment was established by interval partial least square (iPLS). The experimental results show that WMDOSC is more successfully applied to preprocess the NIR spectra data of the hydrocarbon source rocks than other two algorithms, and NIR performed as good as MIR in the analysis of hydrocarbon potential generation of source rocks with WMDOSC-iPLS pretreatment calibration model.

  15. Palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin, northern South China Sea.

    PubMed

    Li, Wenhao; Zhang, Zhihuan; Wang, Weiming; Lu, Shuangfang; Li, Youchuan; Fu, Ning

    2014-01-01

    The main factors of the developmental environment of marine source rocks in continental margin basins have their specificality. This realization, in return, has led to the recognition that the developmental environment and pattern of marine source rocks, especially for the source rocks in continental margin basins, are still controversial or poorly understood. Through the analysis of the trace elements and maceral data, the developmental environment of Miocene marine source rocks in the Qiongdongnan Basin is reconstructed, and the developmental patterns of the Miocene marine source rocks are established. This paper attempts to reveal the hydrocarbon potential of the Miocene marine source rocks in different environment and speculate the quality of source rocks in bathyal region of the continental slope without exploratory well. Our results highlight the palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin of the northern South China Sea and speculate the hydrocarbon potential of the source rocks in the bathyal region. This study provides a window for better understanding the main factors influencing the marine source rocks in the continental margin basins, including productivity, preservation conditions, and the input of terrestrial organic matter.

  16. Palaeoenvironment and Its Control on the Formation of Miocene Marine Source Rocks in the Qiongdongnan Basin, Northern South China Sea

    PubMed Central

    Li, Wenhao; Zhang, Zhihuan; Wang, Weiming; Lu, Shuangfang; Li, Youchuan; Fu, Ning

    2014-01-01

    The main factors of the developmental environment of marine source rocks in continental margin basins have their specificality. This realization, in return, has led to the recognition that the developmental environment and pattern of marine source rocks, especially for the source rocks in continental margin basins, are still controversial or poorly understood. Through the analysis of the trace elements and maceral data, the developmental environment of Miocene marine source rocks in the Qiongdongnan Basin is reconstructed, and the developmental patterns of the Miocene marine source rocks are established. This paper attempts to reveal the hydrocarbon potential of the Miocene marine source rocks in different environment and speculate the quality of source rocks in bathyal region of the continental slope without exploratory well. Our results highlight the palaeoenvironment and its control on the formation of Miocene marine source rocks in the Qiongdongnan Basin of the northern South China Sea and speculate the hydrocarbon potential of the source rocks in the bathyal region. This study provides a window for better understanding the main factors influencing the marine source rocks in the continental margin basins, including productivity, preservation conditions, and the input of terrestrial organic matter. PMID:25401132

  17. From Source to Sink: Exhumation of the North America Cordillera Revealed by Multi-dating of Detrital Minerals from Upper Jurassic-Upper Cretaceous Sevier Foreland Basin

    NASA Astrophysics Data System (ADS)

    Painter, C. S.; Carrapa, B.; DeCelles, P. G.; Gehrels, G. E.; Thomson, S. N.

    2013-12-01

    We sampled twenty-two Late Jurassic to Late Cretaceous syn-orogenic conglomerate clasts in proximal units in the Sevier fold-thrust belt and their distal sandstone equivalents up to 300 km east of the thrust front, in Utah, Colorado, Wyoming, and South Dakota. To better constrain depositional ages, these samples were analyzed using detrital zircon U-Pb (DZ U-Pb) geochronology. To identify a thermochronometer that measures source exhumation in the North America Cordillera, both zircon (U-Th)/He and apatite fission track (AFT) thermochronology was utilized, on both the conglomerate cobbles and sandstone (detrital) samples. Eleven samples were analyzed with zircon (U-Th)/He; however, discordant ages in the conglomerate cobble samples suggest that this system was not fully reset and never experienced T> ~180 °C in the source stratigraphy during the Sevier orogeny. Eleven other samples are analyzed using apatite fission track thermochronology (AFT); AFT ages are generally similar or older than depositional ages indicating that the detrital ages record source exhumation signals, and that exhumation depth corresponds to T>~120 °C. In order to test whether or not the youngest cooling AFT age population represents a source exhumation signal or a co-magmatic signal we here performed double dating of the detrital AFT samples using apatite U-Pb thermochronology. Maximum depositional ages using DZ U-Pb match existing age controls on basin stratigraphy. Our study shows that AFT is an effective thermochronometer to detect source exhumation for Cretaceous foreland stratigraphy in the western U.S.A. Lag-times (i.e. the difference between the source exhumation age and depositional age) are ~0 to 5 Myr with relatively steady-state to slightly increasing exhumation rates suggesting orogenic growth at this time. The very short lag times also indicate limited to no storage time between source and sink. The AFT lag time of the Early Cretaceous Kelvin Formation is ~5 Myr and represents

  18. Masirah Graben, Oman: A hidden Cretaceous rift basin

    SciTech Connect

    Beauchamp, W.H.; Ries, A.C.; Coward, M.P.

    1995-06-01

    Reflection seismic data, well data, geochemical data, and surface geology suggest that a Cretaceous rift basin exists beneath the thrusted allochthonous sedimentary sequence of the Masirah graben, Oman. The Masirah graben is located east of the Huqf uplift, parallel to the southern coast of Oman. The eastern side of the northeast-trending Huqf anticlinorium is bounded by an extensional fault system that is downthrown to the southeast, forming the western edge of the Masirah graben. This graben is limited to the east by a large wedge of sea floor sediments and oceanic crust, that is stacked as imbricate thrusts. These sediments/ophiolites were obducted onto the southern margin of the Arabian plate during the collision of the Indian/Afghan plates at the end of the Cretaceous. Most of the Masirah graben is covered by an allochthonous sedimentary sequence, which is complexly folded and deformed above a detachment. This complexly deformed sequence contrasts sharply with what is believed to be a rift sequence below the ophiolites. The sedimentary sequence in the Masirah graben was stable until further rifting of the Arabian Sea/Gulf of Aden in the late Tertiary, resulting in reactivation of earlier rift-associated faults. Wells drilled in the Masirah graben in the south penetrated reservoir quality rocks in the Lower Cretaceous Natih and Shuaiba carbonates. Analyses of oil extracted from Infracambrian sedimentary rocks penetrated by these wells suggest an origin from a Mesozoic source rock.

  19. Source rock potential analysis using rock physics approach and 2D seismic data inversion: case study of Great Australian Bight

    NASA Astrophysics Data System (ADS)

    Shulakova, V.

    2015-12-01

    The quantity of total organic carbon (TOC) and its type determine the ability of source rocks to generate hydrocarbons. Thus, the quantification of TOC content is an essential part of any reservoir characterisation project. Traditionally TOC is estimated from geochemical analysis of core samples. In this case the results are limited spatially by a well location as well as vertically by a number of tested samples. At the same time TOC vertical variability might be very high, changing every 1-3 m. The several methods have been deployed to estimate TOC from well-log data which provides continuous vertical profile estimations. The basin wide information might be provided by the utilization of seismic surveys. The methodology of mapping source rocks based on seismic data has been lately reported to be successful for the thick source rocks (>20 m) with relatively high TOC values up to 3-4% (Løseth et al., 2011). We employ the described approach and demonstrate our findings for a case study from Ceduna Basin (Great Australian Bight, Australia). The reported TOC values estimated from the cores go up to only 1.3%. The organic matter is contained in thin layers of claystones interlayered with sandstones. The workflow included TOC estimation from the well-log data and then seismic data inversion performed in JasonTM software. The inverted acoustic impedance decreases nonlinearly with increasing TOC content. The obtained results comprises 2D section of TOC distribution. The calculated TOC values are in a good agreement with the results of laboratory measurements. The results of this study show that TOC can be successfully estimated from seismic data inversion even in the case of low organic matter values. Further work has to be done to understand whether this approach works for different types of organic matter and stages of its maturation. Løseth H., Wensaas L., Gading M., Duffaut K., Springer M. 2001. Can hydrocarbon source rocks be identified on seismic data? Geology 39/12.

  20. 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.

  1. A review of the paleomagnetic data from Cretaceous to lower Tertiary rocks from Vietnam, Indochina and South China, and their implications for Cenozoic tectonism in Vietnam and adjacent areas

    NASA Astrophysics Data System (ADS)

    Cung, Thu'ọ'ng Chí; Geissman, John W.

    2013-09-01

    Available paleomagnetic data from rock formations of Cretaceous age from Vietnam, Indochina and South China are compiled and reviewed in the context of their tectonic importance in a common reference frame with respect to Eurasia's coeval paleopoles. Key factors that play an important role in determining the reliability of a paleomagnetic result for utilization in tectonic studies have been taken into consideration and include the absence of evidence of remagnetization, which is a feature common to many rocks in this region. Overall, the Cretaceous paleomagnetic data from the South China Block show that the present geographic position of the South China Block has been relatively stable with respect to Eurasia since the mid-Cretaceous and that the paleomagnetically detected motion of a coherent lithospheric block must be based on the representative data obtained from different specific localities across the block in order to separate more localized, smaller scale deformation from true lithosphere scale motion (translation and/or rotation) of a tectonic block. Cretaceous to early Tertiary paleomagnetic data from the Indochina-Shan Thai Block reveal complex patterns of intra-plate deformation in response to the India-Eurasia collision. Paleomagnetically detected motions from the margins of tectonic blocks are interpreted to mainly reflect displacement of upper crustal blocks due to folding and faulting processes. Rigid, lithosphere scale block rotation is not necessarily supported by the paleomagnetic data. The paleomagnetic results from areas east and south of the Red River fault system suggest that this major transcurrent fault system has had a complicated slip history through much of the Cenozoic and that it does not demarcate completely non-rotated and significantly rotated parts of the crust in this area. However, most paleomagnetic results from areas east and south of the Red River fault system at the latitude of Yunnan Province are consistent with a very modest

  2. Factors affecting the pore space transformation during hydrocarbon generation in source rock (shales): laboratory experiment

    NASA Astrophysics Data System (ADS)

    Giliazetdinova, D. R.; Korost, D. V.

    2014-12-01

    Oil and gas generation is a set of processes which taking place in the interior, the processes can't be observable in nature. In the process of dumping the source rock, organic matter is transformed into a complex of high-molecular compounds - precursors of oil and gas (kerogen). Entering of a source column for specific thermobaric conditions, triggers the formation of low molecular weight hydrocarbon compounds. Generation of sufficient quantities of hydrocarbons leads to the primary fluid migration within the source rock. For the experiment were selected mainly siliceous-carbonate composition rocks from Domanic horizon South-Tatar arch. The main aim of experiment was heating the rocks in the pyrolyzer to temperatures which correspond katagenes stages. For monitoring changes in the morphology of the pore space X-ray microtomography method was used. As a result, when was made a study of the composition of mineral and organic content of the rocks, as well as textural and structural features, have been identified that the majority of the rock samples within the selected collection are identical. However, characteristics such as organic content and texture of rocks are different. Thus, the experiment was divided into two parts: 1) the study of the influence of organic matter content on the morphology of the rock in the process of thermal effects; 2) study the effect of texture on the primary migration processes for the same values of organic matter. Also, an additional experiment was conducted to study the dynamics of changes in the structure of the pore space. At each stage of the experiment morphology of altered rocks characterized by the formation of new pores and channels connecting the primary voids. However, it was noted that the samples with a relatively low content of the organic matter had less changes in pore space morphology, in contrast to rocks with a high organic content. At the second stage of the research also revealed that the conversion of the pore

  3. New petrofacies in upper Cretaceous section of southern California

    SciTech Connect

    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 clasts 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.

  4. Neocomian source and reservoir rocks in the western Brooks Range and Arctic Slope, Alaska

    SciTech Connect

    Mull, C.G.; Reifenstuhl, R.R.; Harris, E.E.; Crowder, R.K.

    1995-04-01

    Detailed (1:63,360) mapping of the Tingmerkpuk sandstone and associated rocks in the Misheguk Mountain and DeLong Mountains guadrangles of the western Brooks Range thrust belt documents potential hydrocarbon source and reservoir rocks in the northern foothills of the western Delong Mountains and adjacent Colville basin of northwest Alaska. Neocomian (?) to Albian micaceous shale, litharenite, and graywacke that overlies the Tingmerkpuk represents the onset of deposition of orogenic sediments derived from the Brooks Range to the south, and the merging of northern and southern sediment sources in the Colville basin. Both the proximal and distal Tingmerkpuk facies contain clay shale interbeds and overlie the Upper Jurassic to Neocomian Kingak Shale. Preliminary geochemical data show that in the thrust belt, these shales are thermally overmature (Ro 1.4-1.6), but are good source rocks with total organic content (TOC) that ranges from 1.2 to 1.8 percent. Shale in the overlying Brookian rocks is also thermally overmature (Ro 1.2-1.5 percent), but contains up to 1.8 percent TOC from a dominantly terrigenous source, and has generated gas. In outcrops at Surprise Creek, in the foothills north of the thrust belt, the Kingak (1.9 percent TOC) and underlying Triassic Shublik Formation (4.6 percent TOC) are excellent oil source rocks with thermal maturity close to peak oil generation stage (Ro0.75-0.9 percent). These rocks have lower thermal maturity values than expected for their stratigraphic position within the deeper parts of the Colville basin and indicate anomalous burial and uplift history in parts of the basin. Preliminary apatite fission-track (AFTA) data from the thrust belt indicate a stage of rapid uplift and cooling at about 53.61 Ma.

  5. Ordovician petroleum source rocks and aspects of hydrocarbon generation in Canadian portion of Williston basin

    SciTech Connect

    Osadetz, K.G.; Snowdon, L.R.

    1988-07-01

    Accumulation of rich petroleum source rocks - starved bituminous mudrocks in both the Winnipeg Formation (Middle Ordovician) and Bighorn Group (Upper Ordovician) - is controlled by cyclical deepening events with a frequency of approximately 2 m.y. Tectonics control both this frequency and the location of starved subbasins of source rock accumulation. Deepening cycles initiated starvation of offshore portions of the inner detrital and medial carbonate facies belts. Persistence of starved offshore settings was aided by marginal onlap and strandline migration in the inner detrital facies belt, and by low carbonate productivity in the medial carbonate facies belt. Low carbonate productivity was accompanied by high rates of planktonic productivity. Periodic anoxia, as a consequence of high rates of planktonic organic productivity accompanying wind-driven equatorial upwellings, is the preferred mechanism for suppressing carbonate productivity within the epeiric sea. The planktonic, although problematic, form Gloecapsamorpha prisca Zalesskey 1917 is the main contributing organism to source rock alginites. A long-ranging alga (Cambrian to Silurian), it forms kukersites in Middle and Upper Ordovician rocks of the Williston basin as a consequence of environmental controls - starvation and periodic anoxia. Source rocks composed of this organic matter type generate oils of distinctive composition at relatively high levels of thermal maturity (transformation ratio = 10% at 0.78% R/sub o/). In the Canadian portion of the Williston basin, such levels of thermal maturity occur at present depths greater than 2950 m within a region of geothermal gradient anomalies associated with the Nesson anticline. Approximately 193 million bbl (30.7 x 10/sup 6/ m/sup 3/) of oil has been expelled into secondary migration pathways from thermally mature source rocks in the Canadian portion of the basin.

  6. Assessment of hydrocarbon source rock potential of Polish bituminous coals and carbonaceous shales

    USGS Publications Warehouse

    Kotarba, M.J.; Clayton, J.L.; Rice, D.D.; Wagner, M.

    2002-01-01

    We analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity (vitrinite reflectance 0.59% to 4.28%) from the Upper Carboniferous coal-bearing strata of the Upper Silesian, Lower Silesian, and Lublin basins, Poland, to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons. We evaluated source rock potential based on Rock-Eval pyrolysis yield, elemental composition (atomic H/C and O/C), and solvent extraction yields of bitumen. An attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors. A few carbonaceous shale samples contain sufficient generation potential (pyrolysis assay and elemental composition) to be considered potential source rocks, although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective Type III source rocks. Most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion (primary migration) to occur. In view of these findings, it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil. Inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks, it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential, but could not be clearly delimited with the number of samples analysed in our study. Because of their high heteroatomic content and high amount of asphaltenes, the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content. Published by Elsevier Science B.V.

  7. Mineralogy and petrology of the Cretaceous- Tertiary boundary clay bed and adjacent clay-rich rocks, Raton Basin, New Mexico and Colorado.

    USGS Publications Warehouse

    Pollastro, R.M.; Pillmore, C.L.

    1987-01-01

    The K-T boundary occurs at the top of a kaolinitic claystone layer, commonly referred to as the 'boundary clay layer', in an interval of coal and carbonaceous shale. The boundary is defined by the disappearance of certain fossil-pollen taxa. The boundary clay layer also contains shocked quartz grains and abundance anomalies of iridium, chromium, and other elements. Each of these characteristics support the hypothesis of an asteroid impact at the end of the Cretaceous. -from Authors

  8. 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.

  9. 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.

  10. Maps showing thermal maturity of Upper Cretaceous marine shales in the Bighorn Basin, Wyoming and Montana

    USGS Publications Warehouse

    Finn, Thomas M.; Pawlewicz, Mark J.

    2014-01-01

    The Bighorn Basin is one of many structural and sedimentary basins that formed in the Rocky Mountain foreland during the Laramide orogeny, a period of crustal instability and compressional tectonics that began in latest Cretaceous time and ended in the Eocene. The basin is nearly 180 mi long, 100 mi wide, and encompasses about 10,400 mi2 in north-central Wyoming and south-central Montana. The basin is bounded on the northeast by the Pryor Mountains, on the east by the Bighorn Mountains, and on the south by the Owl Creek Mountains). The north boundary includes a zone of faulting and folding referred to as the Nye-Bowler lineament. The northwest and west margins are formed by the Beartooth Mountains and Absaroka Range, respectively. Important conventional oil and gas resources have been discovered and produced from reservoirs ranging in age from Cambrian through Tertiary. In addition, a potential unconventional basin-centered gas accumulation may be present in Cretaceous reservoirs in the deeper parts of the basin. It has been suggested by numerous authors that various Cretaceous marine shales are the principal source rock for these accumulations. Numerous studies of various Upper Cretaceous marine shales in the Rocky Mountain region have led to the general conclusion that these rocks have generated or are capable of generating oil and (or) gas. In recent years, advances in horizontal drilling and multistage fracture stimulation have resulted in increased exploration and completion of wells in Cretaceous marine shales in other Rocky Mountain Laramide basins that were previously thought of only as hydrocarbon source rocks. Important parameters controlling hydrocarbon production from these shale reservoirs include: reservoir thickness, amount and type of organic matter, and thermal maturity. The purpose of this report is to present maps and a cross section showing levels of thermal maturity, based on vitrinite reflectance (Ro), for selected Upper Cretaceous marine

  11. Restoration of Circum-Arctic Upper Jurassic source rock paleolatitude based on crude oil geochemistry

    USGS Publications Warehouse

    Peters, K.E.; Ramos, L.S.; Zumberge, J.E.; Valin, Z.C.; Scotese, C.R.

    2008-01-01

    Tectonic geochemical paleolatitude (TGP) models were developed to predict the paleolatitude of petroleum source rock from the geochemical composition of crude oil. The results validate studies designed to reconstruct ancient source rock depositional environments using oil chemistry and tectonic reconstruction of paleogeography from coordinates of the present day collection site. TGP models can also be used to corroborate tectonic paleolatitude in cases where the predicted paleogeography conflicts with the depositional setting predicted by the oil chemistry, or to predict paleolatitude when the present day collection locality is far removed from the source rock, as might occur due to long distance subsurface migration or transport of tarballs by ocean currents. Biomarker and stable carbon isotope ratios were measured for 496 crude oil samples inferred to originate from Upper Jurassic source rock in West Siberia, the North Sea and offshore Labrador. First, a unique, multi-tiered chemometric (multivariate statistics) decision tree was used to classify these samples into seven oil families and infer the type of organic matter, lithology and depositional environment of each organofacies of source rock [Peters, K.E., Ramos, L.S., Zumberge, J.E., Valin, Z.C., Scotese, C.R., Gautier, D.L., 2007. Circum-Arctic petroleum systems identified using decision-tree chemometrics. American Association of Petroleum Geologists Bulletin 91, 877-913]. Second, present day geographic locations for each sample were used to restore the tectonic paleolatitude of the source rock during Late Jurassic time (???150 Ma). Third, partial least squares regression (PLSR) was used to construct linear TGP models that relate tectonic and geochemical paleolatitude, where the latter is based on 19 source-related biomarker and isotope ratios for each oil family. The TGP models were calibrated using 70% of the samples in each family and the remaining 30% of samples were used for model validation. Positive

  12. Hydrocarbon Source Rocks in the Deep River and Dan River Triassic Basins, North Carolina

    USGS Publications Warehouse

    Reid, Jeffrey C.; Milici, Robert C.

    2008-01-01

    This report presents an interpretation of the hydrocarbon source rock potential of the Triassic sedimentary rocks of the Deep River and Dan River basins, North Carolina, based on previously unpublished organic geochemistry data. The organic geochemical data, 87 samples from 28 drill holes, are from the Sanford sub-basin (Cumnock Formation) of the Deep River basin, and from the Dan River basin (Cow Branch Formation). The available organic geochemical data are biased, however, because many of the samples collected for analyses by industry were from drill holes that contained intrusive diabase dikes, sills, and sheets of early Mesozoic age. These intrusive rocks heated and metamorphosed the surrounding sediments and organic matter in the black shale and coal bed source rocks and, thus, masked the source rock potential that they would have had in an unaltered state. In places, heat from the intrusives generated over-mature vitrinite reflectance (%Ro) profiles and metamorphosed the coals to semi-anthracite, anthracite, and coke. The maximum burial depth of these coal beds is unknown, and depth of burial may also have contributed to elevated thermal maturation profiles. The organic geochemistry data show that potential source rocks exist in the Sanford sub-basin and Dan River basin and that the sediments are gas prone rather than oil prone, although both types of hydrocarbons were generated. Total organic carbon (TOC) data for 56 of the samples are greater than the conservative 1.4% TOC threshold necessary for hydrocarbon expulsion. Both the Cow Branch Formation (Dan River basin) and the Cumnock Formation (Deep River basin, Sanford sub-basin) contain potential source rocks for oil, but they are more likely to have yielded natural gas. The organic material in these formations was derived primarily from terrestrial Type III woody (coaly) material and secondarily from lacustrine Type I (algal) material. Both the thermal alteration index (TAI) and vitrinite reflectance data

  13. Middle Ordovician Kanosh Formation: Remaining source rock potential

    SciTech Connect

    McDowell, R.R. )

    1988-10-01

    The Kanosh Formation is an early Middle Ordovician, mixed clastic an carbonate sequence exposed in Basin and Range uplifts throughout the eastern Great Basin. The initiation of Kanosh deposition corresponds to shelf-wide change from shallow-water carbonate to relatively deeper, fine-grained siliciclastic sedimentation. Thickest accumulations of the Kanosh Formation lie within a northeast-southwest elongate, intrashelf basin that may represent a re-activated, Middle Cambrian, tectonic basin. Total organic carbon content (TOC) of the Kanosh ranges from 0.02 to 5.66% (mean 0.33%). Equivalent vitrinite reflectances (R{sub o}) for the unit indicate pervasive over-maturation with respect to oil throughout most of the eastern Great Basin; however, much of this area has remaining potential for gas and gas condensate. An east-west trending corridor in southwestern Utah and southeastern Nevada had R{sub o} valves ranging from I to 2, suggesting that gas and some oil could be preserved in this trend. This corridor also approximately corresponds to the areas of highest TOCs and thickest continuous shale; consequently, it is the most favorable petroleum source area.

  14. Assessment of potential oil and gas resources in source rocks of the Alaska North Slope, 2012

    USGS Publications Warehouse

    Houseknecht, David W.; Rouse, William A.; Garrity, Christopher P.; Whidden, Katherine J.; Dumoulin, Julie A.; Schenk, Christopher J.; Charpentier, Ronald R.; Cook, Troy A.; Gaswirth, Stephanie B.; Kirschbaum, Mark A.; Pollastro, Richard M.

    2012-01-01

    The U.S. Geological Survey estimated potential, technically recoverable oil and gas resources for source rocks of the Alaska North Slope. Estimates (95-percent to 5-percent probability) range from zero to 2 billion barrels of oil and from zero to nearly 80 trillion cubic feet of gas.

  15. Source-rock evaluation of outcrop samples from Vanuatu (Malakula, Espiritu Santo, Maewo, and Pentecost)

    USGS Publications Warehouse

    Buchbinder, Binyamin; Halley, Robert B.

    1988-01-01

    The samples collected for the present study represent only a portion of the sedimentary column in the various sedimentary basins of Vanuatu.  The characterize only the outer margins of the sedimentary basins and do not necessarily reflect the source-rock potential of the deeper (offshore) parts of the basins.

  16. Sedimentology and origin of source rocks in the Tertiary Niger delta

    SciTech Connect

    Bustin, R.M.

    1988-08-01

    Organic matter in Tertiary strata of the Niger delta is mainly a mixture of types II and III, has a high pristane/phytane ratio (> 1.0), and is composed of the macerals vitrinite and minor liptinite. The main palynofacies are structured woody material, cuticles, pollen, spores, and opaque and minor amorphous organic matter. The distribution and abundance of the organic matter reflects the age and sedimentology of the strata. There is a progressive decline in mean total organic carbon (TOC) content from upper Eocene (2.2% TOC) to Pliocene strata (0.90% TOC) and an associated general decrease in hydrogen index (HI) and pristane/phytane ratio. The decrease in TOC and HI in younger strata mainly reflects increased dilution of a nearly constant supply of terrestrial organic matter associated with the generally higher sedimentation rates of younger strata. The low pristane/phytane ratio of younger strata may reflect less oxidizing depositional conditions. No rich source rocks occur in the Niger delta and, as conventionally measured, the strata have little or no oil generating potential. The poor quality of the source rocks has been compensated for by their greater volume and excellent migration routes. The Niger delta type of source rock - although an end member in terms of general source rock composition - appears to be relatively typical of Tertiary deltas.

  17. Late Cretaceous Turbidite Reservoirs Along the Equatorial West African Margin: An Industry Perspective on Source-to-Sink Relationships

    NASA Astrophysics Data System (ADS)

    Wilson, Jonathan; Kohlmann, Fabian; Nicoll, Graeme

    2017-04-01

    The source-to-sink mindset provides an important framework for the exploration geologist. It enables an integrated understanding of hinterland and basin, and can lead to subsurface risk mitigation, particularly with respect to predicting reservoir location and quality. Despite the numerous benefits associated with source-to-sink analysis, such studies are time-consuming to generate, encompassing a large array of disciplines and data, and are not routinely performed within the hydrocarbon industry. The discovery of several significant hydrocarbon fields along the equatorial West African margin has been followed by a series of expensive failures throughout the last decade associated with reservoir quality/presence. This paper discusses a case study focused on the equatorial West African margin, demonstrating how three well-known but effective approaches can be integrated to reconstruct source-to-sink relationships in an ancient sedimentary system, helping de-risk exploration efforts. The first step is to characterize the hinterland. To do this, detailed information was collected for two separate but interlinked datasets—mineral deposits and hard rock geochronology. Combined, these two datasets allow an understanding of the timing and nature of an areas tectonic evolution to be easily developed. The data can be used alongside stratigraphic data and geodynamic information from a plate tectonic model to reconstruct topography and bathymetry of the earth at different episodes of geological time. Paleo digital elevation models (PDEMs) give a first-order approximation of hinterland topography and therefore allow possible sediment source areas to be identified and potential sediment transport pathways to be visualized by means of the digital reconstruction of paleo-drainage networks and their attendant watersheds. This integrated global dataset of hinterland geochronology provides useful "source" information complemented by "sink" information contained within a detrital

  18. Cretaceous to Eocene passive margin sedimentation in Northeastern Venezuela

    SciTech Connect

    Erikson, J.P. )

    1993-02-01

    Twenty two palinspastic paleogeographic maps are presented for the Cretaceous to Eocene strata of the Serrania del Interior of northeastern Venezuela. The mapped lithologies, environmental conditions, and evolving depositional systems record [approximately]90 m.y. of dominantly marine sedimentation on the only observable Mesozoic passive margin in the Western Hemisphere. The depositional systems of the passive margin are heterogeneous at lateral (i.e., along-margin) length scales greater than [approximately]40 km. The primary lateral heterogeneity is caused by a major Lower Cretaceous deltaic system that emanated southwest of the Serrania del Interior. All important intervals, such as the laterally variable Aptian-Albian El Cantil platform limestone and the hydrocarbon source rocks of the Upper Cretaceous Querecual and San Antonio formations, are related to probable causal mechanisms and environmental conditions. Stratigraphic events have been interpreted as of either local or regional extent; based on a combination of outcrop sedimentologic analyses and regional depositional systems interpretation. The 3-dimensional distribution of depositional systems and systems tracts reveals 4-6 regional sequence boundaries separated by 4-20 m.y. Subsidence analyses support the facies interpretation of a passive margin by showing continuous, thermally dominated subsidence during the Cretaceous to Eocene interval. Subsidence and accumulation rates increased and facies changed significantly in the Oligocene, indicating the end of passive margin sedimentation and the initiation of foredeep subsidence and accumulation associated with overthrusting the eastward-advancing Caribbean Plate.

  19. Thermal maturity trends from rock-eval and vitrinite reflectance analysis on potential source rocks in eastern Nevada

    SciTech Connect

    Barker, C.E.; Peterson, J.A.; Poole, F.G. )

    1991-06-01

    Organic geochemical and petrographic analyses of potential source rock samples taken from 30 drill holes penetrating Cenozoic basins of the Basin and Range province in eastern Nevada indicate two distinct trends in thermal maturity, as expressed by vitrinite reflectance equivalent (VRE). VRE is any coal rank or other thermal maturity parameter converted to its equivalent in vitrinite reflectance units using correlation charts. One trend is an increase with depth from about 2% VRE at 500 ft to 5% VRE at 12,000 ft, which is supermature with respect to oil generation. The other trend consists of mature rocks that have a nearly uniform VRE of about 0.7% ({plus minus}0.2%) from the near surface to a depth of 12,000 ft. Both the lower and the higher range geothermal gradients measured across the area, about 0.4 to 2.5F/100 ft (8 to 45C/km), correspond with the mature and supermature trends, respectively. The authors attribute these trends to two major thermal environments common within these Cenozoic basins. The supermature trend results from high geothermal gradients found near igneous intrusions, faulted contacts of uplifted metamorphic core complexes, or other heat sources. The mature trend characterized by near-zero VRE gradients results from groundwater recharge which produces cool temperatures at depth and low geothermal gradients. These generalizations should be applied with caution to any specific area because they are based on a composite VRE depth curve and, in some localities, may not represent realistic interpretation. However, VRE profiles within individual drill holes within the region generally follow one of these trends.

  20. Assessment of Mesozoic-Kainozoic climate impact on oil-source rock potential (West Siberia)

    NASA Astrophysics Data System (ADS)

    Iskorkina, A. A.; Isaev, V. I.; Terre, D. A.

    2015-11-01

    Based on paleotemperature modeling, the evaluation of the effect of Neo-Pleistocene permafrost rock thickness on geothermal regime of the Bazhenov deposits has been performed. It has been stated that permafrost about 300 m in thickness must be considered for appropriate reconstruction of geothermal history of source rocks in the south-east areas of West Siberia. This condition is relevant to a consistent consideration of oil-generation phase history and can prevent underestimation (to 25%) of hydrocarbon-in-place resources.

  1. A rich Middle Triassic source rock in the Barents Sea Area

    SciTech Connect

    Bjoroy, M.; Hall, P.B.

    1983-05-01

    The scope of the work presented in this paper is an evaluation of the petroleum potential of the source rock which shows most promise for the Barents Sea Area. The evaluation is based on analysis of a large number of samples from a Middle Triassic black shale deposit on the various islands of the Svalbard Archipelago. This investigation has shown that the shale is an oil-prone source rock. Analysis of samples taken from areas in the Barents Sea, indicates that this shale sequence has similar potential as a source rock throughout the area south of Svalbard. Integration of this data with the available geophysical and geological data allows the authors to propose that the rich, oilprone Middle Triassic shale sequence also has a widespread distribution throughout the Norwegian Arctic. The results of the geochemical analysis undertaken on Mesozoic deposits of Svalbard and from subsea outcrops in the Barents Sea area is presented. In addition the significant geological data for the region are included. The geochemical data includes; total organic carbon content, Rock-Eval pyrolysis values, vitrinite reflectance and kerogen analysis in transmitted light. In addition some data on the amount and composition of extractable organic matter in the Triassic shales are mentioned.

  2. Cretaceous shallow drilling, US Western Interior: Core research

    SciTech Connect

    Arthur, M.A.

    1993-02-17

    This project is a continuing multidisciplinary study of middle to Upper Cretaceous marine carbonate and clastic rocks in the Utah-Colorado-Kansas corridor of the old Cretaceous seaway that extended from the Gulf Coast to the Arctic during maximum Cretaceous transgressions. It is collaborative between in the US Geological Survey (W.E. Dean, P.I.) and University researchers led by The Pennsylvania State University(M.A. Arthur, P.I.) and funded by DOE and the USGS, in part. Research focusses on the Greenhom, Niobrara and lower Pierre Shale units and their equivalents, combining biostratigraphic/paleoecologic studies, inorganic, organic and stable isotopic geochemical studies, mineralogical investigations and high-resolution geophysical logging. This research requires unweathered samples and continuous smooth exposures'' in the form of cores from at least 4 relatively shallow reference holes (i.e. < 1000m) in transect from east to west across the basin. The major initial effort was recovery in Year 1 of the project of continuous cores from each site in the transect. This drilling provided samples and logs of strata ranging from pelagic sequences that contain organic-carbon-rich marine source rocks to nearshore coal-bearing units. This transect also will provide information on the extent of thermal maturation and migration of hydrocarbons in organic-carbon-rich strata along a burial gradient.

  3. 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

  4. Volga-Ural basin, U. S. S. R. : Rich petroleum systems with a single source rock

    SciTech Connect

    Ulmishek, G.F. )

    1991-03-01

    The Volga-Ural basin has produced about 40 billion barrels of oil and still produces a billion barrels annually. The productive Middle Devonian-Lower Permian sequence is composed of various carbonate rocks (including reefs) with clastic intervals in the Middle Devonian-lower Frasnian, middle-upper Visean, and Middle Carboniferous. A single source-rock unit, the Frasnian Domanik Formation, 30-60 m thick, is responsible for productivity of the entire sedimentary section. The three clastic intervals and underlying carbonate strata contain the bulk of the hydrocarbon reserves. Widespread upward and downward vertical migration in this structurally simple basin is explained by imperfect regional seals. Imperfection of the seals has also resulted in a predominance of oil over gas. The best seal is the overpressured Domanik Formation itself; it separates the sedimentary section into two petroleum systems: one in underlying Middle Devonian-lower Frasnian clastics and the other in overlying clastic and carbonate rocks.

  5. Geochemistry and source waters of rock glacier outflow, Colorado Front Range

    USGS Publications Warehouse

    Williams, M.W.; Knauf, M.; Caine, N.; Liu, F.; Verplanck, P.L.

    2006-01-01

    We characterize the seasonal variation in the geochemical and isotopic content of the outflow of the Green Lake 5 rock glacier (RG5), located in the Green Lakes Valley of the Colorado Front Range, USA. Between June and August, the geochemical content of rock glacier outflow does not appear to differ substantially from that of other surface waters in the Green Lakes Valley. Thus, for this alpine ecosystem at this time of year there does not appear to be large differences in water quality among rock glacier outflow, glacier and blockslope discharge, and discharge from small alpine catchments. However, in September concentrations of Mg2+ in the outflow of the rock glacier increased to more than 900 ??eq L-1 compared to values of less than 40 ??eq L-1 at all the other sites, concentrations of Ca2+ were greater than 4,000 ??eq L-1 compared to maximum values of less than 200 ??eq L-1 at all other sites, and concentrations of SO42- reached 7,000 ??eq L-1, compared to maximum concentrations below 120 ??eq L-1 at the other sites. Inverse geochemical modelling suggests that dissolution of pyrite, epidote, chlorite and minor calcite as well as the precipitation of silica and goethite best explain these elevated concentrations of solutes in the outflow of the rock glacier. Three component hydrograph separation using end-member mixing analysis shows that melted snow comprised an average of 30% of RG5 outflow, soil water 32%, and base flow 38%. Snow was the dominant source water in June, soil water was the dominant water source in July, and base flow was the dominant source in September. Enrichment of ?? 18O from - 10??? in the outflow of the rock glacier compared to -20??? in snow and enrichment of deuterium excess from +17.5??? in rock glacier outflow compared to +11??? in snow, suggests that melt of internal ice that had undergone multiple melt/freeze episodes was the dominant source of base flow. Copyright ?? 2005 John Wiley & Sons, Ltd.

  6. Pore-space alteration in source rock (shales) during hydrocarbons generation: laboratory experiment

    NASA Astrophysics Data System (ADS)

    Giliazetdinova, D. R.; Korost, D. V.; Nadezhkin, D. V.

    2013-12-01

    Hydrocarbons (HC) are generated from solid organic matter (kerogen) due to thermocatalytic reactions. The rate of such reactions shows direct correlation with temperature and depends on the depth of source rock burial. Burial of sedimentary rock is also inevitably accompanied by its structural alteration owing to compaction, dehydration and re-crystallization. Processes of HC generation, primary migration and structural changes are inaccessible for direct observation in nature, but they can be studied in laboratory experiments. Experiment was carried out with a clayey-carbonate rock sample of the Domanik Horizon taken from boreholes drilled in the northeastern part of the south Tatar arch. The rock chosen fits the very essential requirements - high organic matter content and its low metamorphic grade. Our work aimed at laboratory modeling of HC generation in an undisturbed rock sample by its heating in nitrogen atmosphere based on a specified temperature regime and monitoring alterations in the pore space structure. Observations were carried out with a SkyScan-1172 X-ray microtomography scanner (resulting scan resolution of 1 μm). A cylinder, 44 mm in diameter, was prepared from the rock sample for the pyrolitic and microtomographic analyses. Scanning procedures were carried out in 5 runs. Temperature interval for each run had to match the most important stage of HC generation in the source rock, namely: (1) original structure; (2) 100-300°C - discharge of free and adsorbed HC and water; (3) 300-400°C - initial stage of HC formation owing to high-temperature pyrolysis of the solid organic matter and discharge of the chemically bound water; (4) 400-470°C - temperature interval fitting the most intense stage of HC formation; (5) 470-510°C - final stage of HC formation. Maximum sample heating in the experiment was determined as temperature of the onset of active decomposition of carbonates, i.e., in essence, irreversible metamorphism of the rock. Additional

  7. A Procedure to Determine the Optimal Sensor Positions for Locating AE Sources in Rock Samples

    NASA Astrophysics Data System (ADS)

    Duca, S.; Occhiena, C.; Sambuelli, L.

    2015-03-01

    Within a research work aimed to better understand frost weathering mechanisms of rocks, laboratory tests have been designed to specifically assess a theoretical model of crack propagation due to ice segregation process in water-saturated and thermally microcracked cubic samples of Arolla gneiss. As the formation and growth of microcracks during freezing tests on rock material is accompanied by a sudden release of stored elastic energy, the propagation of elastic waves can be detected, at the laboratory scale, by acoustic emission (AE) sensors. The AE receiver array geometry is a sensitive factor influencing source location errors, for it can greatly amplify the effect of small measurement errors. Despite the large literature on the AE source location, little attention, to our knowledge, has been paid to the description of the experimental design phase. As a consequence, the criteria for sensor positioning are often not declared and not related to location accuracy. In the present paper, a tool for the identification of the optimal sensor position on a cubic shape rock specimen is presented. The optimal receiver configuration is chosen by studying the condition numbers of each of the kernel matrices, used for inverting the arrival time and finding the source location, and obtained for properly selected combinations between sensors and sources positions.

  8. Recognition of an infracambrian source rock based on biomarkers in the Baghewala-1 oil, India

    SciTech Connect

    Peters, K.E.; Clark, M.E.; Lee, C.Y.

    1995-10-01

    Heavy, sulfur-rich oil produced from the Infra-cambrian (540-640 Ma) Jodhpur Formation in the Baghewala-1 well represents a new exploration play in the Bikaner-Nagaur basin in India and the punjab basin in Pakistan. The Baghewala-1 oil is nonbiodegraded, and thermal-maturation-dependent biomarker ratios indicate generation from the source rock within the early oil window. Age-diagnostic and source-dependent biomarkers indicate that the oil originated from algal and bacterial organic matter with no higher plant input in an Infracambrian, carbonate-rich source rock deposited under anoxic marine conditions. These characteristics support a local origin of the Baghewala-1 oil from organic-rich laminated dolomites in the Infracambrian Bilara Formation. Significant amounts of petroleum could originate from equivalents of the proposed Bilara source rock in the Punjab basin, Pakistan, where the Precambrian to lower Paleozoic section is thicker and more deeply buried than in India. Deeper burial of the source rock in the Punjab basin than in the Bikaner-Nagaur basin could generate more mature equivalents of the Baghewala-1 oil. The Baghewala-1 oil is geochemically similar to another heavy oil from the Infracambrian Salt Range Series in the nearby Karampur-1 well in Pakistan and to oils derived from carbonate-evaporite facies of the Infracambrian Huqf Group about 2000 km (1243 mi) to the southwest in the Eastern Flank province of southern Oman. These findings are consistent with published evidence that subsiding rift basins in northwest India, Pakistan, and southern Oman were in close proximity during the Infracambrian along the Middle Eastern edge of Gondwanaland.

  9. Paralavas in the Cretaceous Paraná volcanic province, Brazil - A genetic interpretation of the volcanic rocks containing phenocrysts and glass.

    PubMed

    Baggio, Sérgio B; Hartmann, Léo A; Bello, Rosa M S

    2016-01-01

    The occurrences of glassy rocks containing long and curved phenocrysts in the Paraná volcanic province, South America, are here interpreted as paralavas. The large number of thin (0.1-0.5 m) dikes and sills of glassy volcanic rocks with hopper, hollow or curved, large crystals of clinopyroxene (up to 10 cm), plagioclase (up to 1 cm), magnetite and apatite are contained in the core of thick (>70 m) pahoehoe flows. They are strongly concentrated in the state of Paraná, coincident with the presence of the large number of dikes in the Ponta Grossa arch. These rocks were previously defined as pegmatites, although other names have also been used. A paralava is here interpreted as the product of melting of basaltic rocks following varied, successive processes of sill emplacement in high-kerogen bituminous shale and ascent of the resultant methane. As the gas reached the lower portion of the most recent lava flow of the volcanic pile, the methane reacted with the silicate and oxide minerals of the host volcanic rock (1,000 ºC) and thus elevated the local temperature to 1,600 ºC. The affected area of host rock remelted (possibly 75 wt.%) and injected buoyantly the central and upper portion of the core. This methane-related mechanism explains the evidence found in the paralavas from this volcanic province, one of the largest in the continents.

  10. Effects of Host-rock Fracturing on Elastic-deformation Source Models of Volcano Deflation.

    PubMed

    Holohan, Eoghan P; Sudhaus, Henriette; Walter, Thomas R; Schöpfer, Martin P J; Walsh, John J

    2017-09-08

    Volcanoes commonly inflate or deflate during episodes of unrest or eruption. Continuum mechanics models that assume linear elastic deformation of the Earth's crust are routinely used to invert the observed ground motions. The source(s) of deformation in such models are generally interpreted in terms of magma bodies or pathways, and thus form a basis for hazard assessment and mitigation. Using discontinuum mechanics models, we show how host-rock fracturing (i.e. non-elastic deformation) during drainage of a magma body can progressively change the shape and depth of an elastic-deformation source. We argue that this effect explains the marked spatio-temporal changes in source model attributes inferred for the March-April 2007 eruption of Piton de la Fournaise volcano, La Reunion. We find that pronounced deflation-related host-rock fracturing can: (1) yield inclined source model geometries for a horizontal magma body; (2) cause significant upward migration of an elastic-deformation source, leading to underestimation of the true magma body depth and potentially to a misinterpretation of ascending magma; and (3) at least partly explain underestimation by elastic-deformation sources of changes in sub-surface magma volume.

  11. Geochemical evidence for a Cretaceous oil sand (Bima oil sand) in the Chad Basin, Nigeria

    NASA Astrophysics Data System (ADS)

    Bata, Timothy; Parnell, John; Samaila, Nuhu K.; Abubakar, M. B.; Maigari, A. S.

    2015-11-01

    Paleogeographic studies have shown that Earth was covered with more water during the Cretaceous than it is today, as the global sea level was significantly higher. The Cretaceous witnessed one of the greatest marine transgressions in Earth's history, represented by widespread deposition of sands directly on underlying basement. These sand bodies hold much of the world's heavy oil. Here, we present for the first time, geochemical evidence of a Cretaceous oil sand (Bima oil sand) in the Chad Basin, Nigeria. Bima oil sand is similar to other Cretaceous oil sands, predominantly occurring at shallow depths on basin flanks and generally lacking a seal cover, making the oil susceptible to biodegradation. The bulk properties and distribution of molecular features in oils from the Bima oil sand suggest that they are biodegraded. Sterane maturity parameters and the trisnorhopane thermal indicator for the oils suggest thermal maturities consistent with oils generated as conventional light oils, which later degraded into heavy oils. These oils also show no evidence of 25-norhopane, strongly suggesting that biodegradation occurred at shallow depths, consistent with the shallow depth of occurrence of the Bima Formation at the study locality. Low diasterane/sterane ratios and C29H/C30H ratios greater than 1 suggest a carbonate source rock for the studied oil. The Sterane distribution further suggests that the oils were sourced from marine carbonate rocks. The C32 homohopane isomerization ratios for the Bima oil sand are 0.59-0.60, implying that the source rock has surpassed the main oil generation phase, consistent with burial depths of the Fika and Gongila Formations, which are both possible petroleum source rocks in the basin.

  12. 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

  13. Organic geochemistry and hydrocarbon potential contrasts among lithologically different source rocks in the Qingxi Sag, Jiuquan Basin, Northwest China

    NASA Astrophysics Data System (ADS)

    Zhang, Weiwei; Huang, Zhilong; Gao, Gang; Yin, Yue; Li, Tianjun

    2017-04-01

    Jiuquan Basin, located in the eastern part of Hexi Corridor, is a medium- to small-sized superimposed basin in northwest China. Situated in the southwest of the basin is the Qingxi sag, in which the development of large sets of argillaceous dolomite dominate (lithological assemblage named as LSA) and dolomitic mudstone (LSB), partially being mudstone. From electronical and seismic profile features, the Lower Cretaceous can be divided into the Chijinpu Formation, Xiagou Formation, and Zhonggou Formation in the Qingxi Sag. Moreover, the Xiagou Formation can be divided into four members, represented as K1g0, K1g1, K1g2, and K1g3. The given lithological assemblages and occurrence of particular mineralogical combinations indicate that it is the product of hydrothermal deposition. Lithologically, the argillaceous dolomite and dolomitic mudstone are diametrically different in both mineral contents and types. The integration of field outcrop observation and sampling with laboratory analyses, including solvent extract, Rock-Eval (S1, S2, and Tmax), organic petrography (lithological identification, cement, grain, mineral, and maceral observation), and laboratory modeling of hydrocarbon generation, show that both LSA and LSB contains good hydrocarbon potentials but rather different mineralogical compositions. The concurrence of LSA and LSB indicates the alternate interaction between the hydrothermal deposition and normal lacustrine deposits. The LSA mainly contains Type I kerogen and much lower Pr/Ph ratio, indicating parental material sourced from lacustrine algae and bacteria and much stronger reduction depostional environment. However, the LSB mainly contains Type III kerogen, containing parental material mainly sourced from terrestrial higher plant. And in the mudstone, there is almost no Type I kerogen, indicating no substantial input of lacustrine phytoplankton. The LSA contains TOC value of 1.2-3.2% (wt), averaging 2.1% (wt); while the LSB contains 0.8-2.4% (wt) with

  14. The Lower Cretaceous Chinkeh Formation: A frontier-type play in the Liard basin of western Canada

    SciTech Connect

    Leckie, D.A. ); Potocki, D.J. ); Visser, K. )

    1991-08-01

    The Lower Cretaceous Liard basin in western Canada covers an area of 9,500 km{sup 2} (3,668 mi{sup 2}) but is relatively unexplored despite its size. The present-day expression of the basin, which formed during the latest Cretaceous to early Tertiary, trends north-south and is delineated by the outcrop of the coarse-clastic Upper Cretaceous Dunvegan Formation. The lowermost Cretaceous unit, herein named the Chinkeh Formation, is up to 32 m (105 ft) thick and unconformably overlies older Paleozoic strata. The Chinkeh Formation contains four major lithotypes: (1) conglomeratic breccia interpreted as debris-flow or talus deposits, (2) interbedded coal, carbonaceous as nonmarine valley fill or channel deposits, (3) conglomeratic lag related to marine deposits, (3) conglomeratic lag related to marine transgression, and (4) upward-coarsening sandstone interpreted as abandoned shoreline deposits. Cretaceous strata in the Liard basin have gave petroleum source-rock and reservoir potential, and hydrocarbons may be present in sandstone of the Chinkeh Formation. Potential play types include stratigraphic traps formed by incised-valley deposits and shallow-marine sandstone pinching out laterally into marine shales of the Garbutt Formation. A potential structural play may occur along the Bovie fault zone where reservoirs may abut against a shale seal on the eastern side of the fault. Potential source rocks include the lowermost Garbutt Formation and underlying Triassic Toad Garbutt formations. The Chinkeh Formation sandstone has porosity values of 8-18%.

  15. Characterizing the hypersiliceous rocks of Belgium used in (pre-)history: a case study on sourcing sedimentary quartzites

    NASA Astrophysics Data System (ADS)

    Veldeman, Isis; Baele, Jean-Marc; Goemaere, Eric; Deceukelaire, Marleen; Dusar, Michiel; De Doncker, H. W. J. A.

    2012-08-01

    Tracking raw material back to its extraction source is a crucial step for archaeologists when trying to deduce migration patterns and trade contacts in (pre-)history. Regarding stone artefacts, the main rock types encountered in the archaeological record of Belgium are hypersiliceous rocks. This is a newly introduced category of rock types comprising those rocks made of at least 90% silica. These are strongly silicified quartz sands or sedimentary quartzites, siliceous rocks of chemical and biochemical origin (e.g. flint), very pure metamorphic quartzites and siliceous volcanic rocks (e.g. obsidian). To be able to distinguish between different extraction sources, ongoing research was started to locate possible extraction sources of hypersiliceous rocks and to characterize rocks collected from these sources. Characterization of these hypersiliceous rocks is executed with the aid of optical polarizing microscopy, optical cold cathodoluminescence and scanning-electron microscopy combined with energy-dispersive x-ray spectrometry and with back-scatter electron imaging. In this paper, we focus on various sedimentary quartzites of Paleogene stratigraphical level.

  16. Organic facies and systems tracts: Implications for source rock preservation and prediction

    SciTech Connect

    Kosters, E.C.; Vanderzwaan, F.J.; Gijsbert, J. )

    1993-09-01

    Sequence stratigraphy is concerned with making predictions about reservoirs ahead of the drill, however, little attention has been paid to the configuration of organic-rich facies of source rock quality. We suggest that preservation of source rock type facies in clastic systems is mutually exclusive and time successive. The main database is a collection of cores and other samples through the Holocene Rhone delta. The early Holocene Transgressive Systems Tract (TST) contains five levels of channelization. The most significant peat bed is located immediately landward of the shoreline of maximum transgression (SMT). The Highstand Systems Tract (HST) consists of two parasequences, containing mostly laterally continuous strandplain complexes without peat. In addition to sufficient accommodation space, an important control on formation of fresh-water peats and organic-rich shelf muds is availability of river-induced nutrients. Peat quality, however, is best without riverine clastics. In a delta plain, a balance between these two controls may be reached when river-fed nutrients are trapped there indirectly. The potential for such a condition arises in a TST setting. On the shelf, eutrophication of marine habitats is also controlled by river-fed nutrients, but excess river clastics are detrimental to marine source rock quality. A balance between these two controls may be reached in HST settings where fine-grained riverine clastics are forced onto the shelf rather than in the delta plain. In this case, nutrient supply to the shelf results in large quantities of marine biomass. This biomass becomes sufficiently concentrated due to moderate fine-grained riverine sedimentation which guarantees burial and preservation. Thus, varying river-water and nutrient supply in TST and HST settings seems to control large-scale preservation patterns of both continental and marine organics. This hypothesis suggests further potential for using sequence stratigraphy for source rock occurrence.

  17. The source rock of the Nyasa Rift Basin and oil shows of Tanzania

    NASA Astrophysics Data System (ADS)

    Kagya, M.; Ntomola, S. J.; Mpanju, F.

    Several organic geochemical analyses have been carried out in the Nyasa Rift Basin. The main objective was to assess the hydrocarbon potential of this southern part of the East African Rift Valley. Much interest has been shown in the carbonaceous shales and the coals of the Karroo Formation of Carboniferous/ Permian age, locally known as K 2. They are characterized by coal measures alternating with bituminous/ carbonaceous shales, mudstones and occasional sandstone. The cores and outcrop samples from the Ilima Colliery, Mwalesi and Ivogo Ridge were studied. The screening analysis showed the samples of both the coal and carbonaceous shales to be fair to good source rocks. the visual kerogen compositions, together with HI values, suggest kerogen type III or mixed up type III/II. The thermal maturity data as shown by T max, vitrinite reflectance, spore color fluorescence, and thermal alternation index, indicate an early mature to mature oil source rock. The oil shows, as observed in the Tundaua (Pemba) and Msimbati seeps and the bituminous sands of the Wingayongo and Msimbati areas, indicate the presence of oil-generating source rocks.

  18. Brazilian continental cretaceous

    NASA Astrophysics Data System (ADS)

    Petri, Setembrino; Campanha, Vilma A.

    1981-04-01

    Cretaceous deposits in Brazil are very well developed, chiefly in continental facies and in thick sequences. Sedimentation occurred essentially in rift-valleys inland and along the coast. Three different sequences can be distinguished: (1) a lower clastic non-marine section, (2) a middle evaporitic section, (3) an upper marine section with non-marine regressive lithosomes. Continental deposits have been laid down chiefly between the latest Jurassic and Albian. The lower lithostratigraphic unit is represented by red shales with occasional evaporites and fresh-water limestones, dated by ostracods. A series of thick sandstone lithosomes accumulated in the inland rift-valleys. In the coastal basins these sequences are often incompletely preserved. Uplift in the beginning of the Aptian produced a widespread unconformity. In many of the inland rift-valleys sedimentation ceased at that time. A later transgression penetrated far into northeastern Brazil, but shortly after continental sedimentation continued, with the deposition of fluvial sandstones which once covered large areas of the country and which have been preserved in many places. The continental Cretaceous sediments have been laid down in fluvial and lacustrine environments, under warm climatic conditions which were dry from time to time. The fossil record is fairly rich, including besides plants and invertebrates, also reptiles and fishes. As faulting tectonism was rather strong, chiefly during the beginning of the Cretaceous, intercalations of igneous rocks are frequent in some places. Irregular uplift and erosion caused sediments belonging to the remainder of this period to be preserved only in tectonic basins scattered across the country.

  19. Hydrocarbon potential evaluation of the source rocks from the Abu Gabra Formation in the Sufyan Sag, Muglad Basin, Sudan

    NASA Astrophysics Data System (ADS)

    Qiao, Jinqi; Liu, Luofu; An, Fuli; Xiao, Fei; Wang, Ying; Wu, Kangjun; Zhao, Yuanyuan

    2016-06-01

    The Sufyan Sag is one of the low-exploration areas in the Muglad Basin (Sudan), and hydrocarbon potential evaluation of source rocks is the basis for its further exploration. The Abu Gabra Formation consisting of three members (AG3, AG2 and AG1 from bottom to top) was thought to be the main source rock formation, but detailed studies on its petroleum geology and geochemical characteristics are still insufficient. Through systematic analysis on distribution, organic matter abundance, organic matter type, organic matter maturity and characteristics of hydrocarbon generation and expulsion of the source rocks from the Abu Gabra Formation, the main source rock members were determined and the petroleum resource extent was estimated in the study area. The results show that dark mudstones are the thickest in the AG2 member while the thinnest in the AG1 member, and the thickness of the AG3 dark mudstone is not small either. The AG3 member have developed good-excellent source rock mainly with Type I kerogen. In the Southern Sub-sag, the AG3 source rock began to generate hydrocarbons in the middle period of Bentiu. In the early period of Darfur, it reached the hydrocarbon generation and expulsion peak. It is in late mature stage currently. The AG2 member developed good-excellent source rock mainly with Types II1 and I kerogen, and has lower organic matter abundance than the AG3 member. In the Southern Sub-sag, the AG2 source rock began to generate hydrocarbons in the late period of Bentiu. In the late period of Darfur, it reached the peak of hydrocarbon generation and its expulsion. It is in middle mature stage currently. The AG1 member developed fair-good source rock mainly with Types II and III kerogen. Throughout the geological evolution history, the AG1 source rock has no effective hydrocarbon generation or expulsion processes. Combined with basin modeling results, we have concluded that the AG3 and AG2 members are the main source rock layers and the Southern Sub-sag is

  20. A quasi-linear structure of the southern margin of Eurasia prior to the India-Asia collision: First paleomagnetic constraints from Upper Cretaceous volcanic rocks near the western syntaxis of Tibet

    NASA Astrophysics Data System (ADS)

    Yi, Zhiyu; Huang, Baochun; Yang, Liekun; Tang, Xiangde; Yan, Yonggang; Qiao, Qingqing; Zhao, Jie; Chen, Liwei

    2015-07-01

    We report the first combined geochronologic and paleomagnetic study of volcanic rocks from the Shiquanhe and Yare Basins at the westernmost Lhasa Terrane, which aims to provide an accurate constraint on the shape and paleoposition of the southern margin of Asia prior to the India-Asia collision. Three new 40Ar/39Ar ages of 92.5 ± 2.9 Ma, 92.4 ± 0.9 Ma, and 79.6 ± 0.7 Ma determined by fresh matrix or feldspar from lava flows suggest a Late Cretaceous age for the investigated units. Characteristic remanent magnetizations have been successfully isolated from 38 sites which pass positive fold and/or reversal, conglomerate tests and are hence interpreted as primary in origin. The two paleopoles obtained from Yare and Shiquanhe yield consistent paleolatitudes of 13.6°N ± 9.6°N and 14.2°N ± 2.7°N, respectively (for a reference site of 31.5°N, 80°E), indicating that the southern margin of Asia near the western syntaxis was located far south during the Late Cretaceous time. A reconstruction of the Lhasa Terrane in the frame of Eurasia with paleomagnetic data obtained from its western and eastern parts indicates that the southern margin of Eurasia probably had a quasi-linear orientation prior to the collision formerly trending approximately 315°E. This is compatible with the shape of the Neo-Tethys slab observed from seismic tomographic studies. Our findings provide a solid basis for evaluating Cenozoic crustal shortening in the Asian interior and the size of Greater India near the western syntaxis.

  1. Sources of clastic material of Cretaceous-Paleogene deposits in the southwestern part of the Amur-Zeya Basin: results of dating U-Pb detrital zircons

    NASA Astrophysics Data System (ADS)

    Sorokin, A. P.; Sorokin, A. A.

    2017-06-01

    The results of our study indicate that at the Late Cretaceous-Paleogene boundary in the southeastern part of the Amur-Zeya Basin, the sedimentation conditions changed drastically, namely, the change of provenance areas of debris. In the Maastrichtian, the clastic material was mainly transported from the Bureya-Jiamusi Superterrane and the volcanic-plutonic belts of Khingan-Okhotsk and East Sikhote-Alin located to the east: sedimentation occurred simultaneously with magmatic activity. During the Danian Stage, the major source of debris to the southern part of the basin was located to the south of the young mountain system of the Lesser Khingan (the uplifted part of the basement of the Songliao Block).

  2. 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).

  3. Cretaceous polar climates

    SciTech Connect

    Ziegler, A.M.; Horrell, M.A.; Lottes, A.L.; Gierlowski, T.C.

    1988-01-01

    The Cretaceous, like most Phanerozooic periods, was characterized by ice-free poles. Some still argue that the glacier and sea ice were there, and that the tillites, etc, have been eroded or remain undiscovered. However, diverse floras, dense forests, coal-forming cypress swamps, and dinosaurs, crocodilians, and lungfish are known from areas that were certainly at 75/sup 0/-80/sup 0/ north and south paleolatitude in the Cretaceous, implying that the coastal basins did not experience hard freezes. No deep marine connections to the North Pole existed in the Cretaceous, so oceanic polar heat transport can be discounted. However, the five north-south trending epeiric or rift-related seaways that connected or nearly connected the Tethys to the Arctic would have dampened the seasonal temperature cycle, bringing maritime climates deep into the North American and Eurasian continents and, more importantly, would have served as an energy source and channel for winter storms, much as the Gulf Stream does today. Cyclones have a natural tendency to move poleward, because of the increase in the Coriolis Paramteter, and they transport both sensible and latent heat. The coastal regions of the relatively warm polar ocean in the Cretaceous would have received continuous precipitation during the winter because cyclones would be entering from as many as five directions. Coastal rainfall would also have been abundant in the summer but for a different reason; the land-sea temperature profile would reverse, with the warm land surface drawing in moisture, while clear ice-free conditions over the ocean would allow for solar warming.

  4. Cretaceous polar climates

    SciTech Connect

    Ziegler, A.M.; Horrell, M.A.; Lottes, A.L.; Gierlowski, T.C.

    1988-02-01

    The Cretaceous, like most Phanerozoic periods, was characterized by ice-free poles. Some still argue that the glaciers and sea ice were there, and that the tillites, etc, have been eroded or remain undiscovered. However, diverse floras, dense forests, and coal-forming cypress swamps, and dinosaurs, crocodilians, and lungfish are known from areas that were certainly at 75/degree/-80/degree/ north and south paleolatitude in the Cretaceous, implying that the coastal basins did not experience hard freezes. No deep marine connections to the North Pole existed in the Cretaceous, so oceanic polar heat transport can be discounted. However, the five north-south trending epeiric or rift-related seaways that connected or nearly connected the Tethys to the Arctic would have dampened the seasonal temperature cycle, bring maritime climates deep into the North American and Eurasian continents and, more importantly, would have served as an energy source and channel for winter storms, much as the Gulf Stream does today. Cyclones have a natural tendency to move poleward, because of the increase in the Coriolis Parameter, and they transport both sensible and latent heat. The coastal regions of the relatively warm polar ocean in the Cretaceous would have received continuous precipitation during the winter because cyclones would be entering from as many as five directions. Coastal rainfall would also have been abundant in the summer but for a different reason; the land-sea temperature profile would reverse, with the warm land surface drawing in moisture, while clear ice-free conditions over the ocean would allow for solar warming.

  5. Cathodoluminescence of shocked quartz at the Cretaceous-Tertiary boundary

    NASA Astrophysics Data System (ADS)

    Owen, Michael R.; Anders, Mark H.

    Empirical studies have documented an association between rock type and the cathodoluminescence color of constituent quartz grains. Quartz from extrusive igneous sources luminesces uniform pale blue. Quartz from intrusive igneous and high-grade metamorphic rocks generally luminesces darker purple-blue, whereas quartz recrystallized under low-grade metamorphic conditions luminesces reddish-brown. Quartz grains in most sandstones luminesce a heterogeneous mixture of these colors because the grains were derived from a variety of ultimate source rocks. If shocked quartz found at the Cretaceous-Tertiary (K-T) boundary is volcanic in origin, its cathodoluminescence should be predominantly pale blue. Alternatively, quartz grains derived from bolide impact upon, and ejection of, mixed igneous, metamorphic, and sedimentary rocks should luminesce a variety of colors. Grain mounts of sand collected at the K-T boundary horizon from the Clear Creek North site in the Raton Basin, Colorado were examined. Shocked quartz luminesced a variety of colors and very few grains luminesced the pale blue color that is typical of volcanic quartz. It was concluded that the shocked quartz was derived from a petrologically diverse source region without substantial volcanic contribution. Most shocked grains apparently were derived from low-grade metamorphic rocks, with a slightly smaller contribution from high-grade metamorphic and intrusive igneous rocks. Rare quartz grains with brown-luminescing rims reflect a minor addition from detrital sedimentary sources. The apparent relative abundances of intrusive (and rare extrusive) igneous, metamorphic, and sedimentary ultimate source rocks suggested by CL colors of shock-deformed quartz at the K-T boundary is consistent with a crustal/supracrustal origin for the grains.

  6. Cathodoluminescence of shocked quartz at the Cretaceous-Tertiary boundary

    NASA Technical Reports Server (NTRS)

    Owen, Michael R.; Anders, Mark H.

    1988-01-01

    Empirical studies have documented an association between rock type and the cathodoluminescence color of constituent quartz grains. Quartz from extrusive igneous sources luminesces uniform pale blue. Quartz from intrusive igneous and high-grade metamorphic rocks generally luminesces darker purple-blue, whereas quartz recrystallized under low-grade metamorphic conditions luminesces reddish-brown. Quartz grains in most sandstones luminesce a heterogeneous mixture of these colors because the grains were derived from a variety of ultimate source rocks. If shocked quartz found at the Cretaceous-Tertiary (K-T) boundary is volcanic in origin, its cathodoluminescence should be predominantly pale blue. Alternatively, quartz grains derived from bolide impact upon, and ejection of, mixed igneous, metamorphic, and sedimentary rocks should luminesce a variety of colors. Grain mounts of sand collected at the K-T boundary horizon from the Clear Creek North site in the Raton Basin, Colorado were examined. Shocked quartz luminesced a variety of colors and very few grains luminesced the pale blue color that is typical of volcanic quartz. It was concluded that the shocked quartz was derived from a petrologically diverse source region without substantial volcanic contribution. Most shocked grains apparently were derived from low-grade metamorphic rocks, with a slightly smaller contribution from high-grade metamorphic and intrusive igneous rocks. Rare quartz grains with brown-luminescing rims reflect a minor addition from detrital sedimentary sources. The apparent relative abundances of intrusive (and rare extrusive) igneous, metamorphic, and sedimentary ultimate source rocks suggested by CL colors of shock-deformed quartz at the K-T boundary is consistent with a crustal/supracrustal origin for the grains.

  7. Uranium-Lead Zircon Ages and Sr, Nd, and Pb Isotope Geochemistry of Selected Plutonic Rocks from Western Idaho

    USGS Publications Warehouse

    Unruh, Daniel M.; Lund, Karen; Kuntz, Mel A.; Snee, Lawrence W.

    2008-01-01

    Across the Salmon River suture in western Idaho, where allochthonous Permian to Cretaceous oceanic rocks are juxtaposed against Proterozoic North American rocks, a wide variety of plutonic rocks are exposed. Available data indicate much variation in composition, source, and structural state of these plutons. The plutonic rocks were long described as the western border zone of the Cretaceous Idaho batholith but limited pre-existing age data indicate more complicated origins. Because the affinity and age of the plutonic rocks cannot be reliably determined from field relations, TIMS U-Pb dating in conjunction with Sr, Nd, and Pb isotopic studies of selected plutons across the suture in western Idaho were undertaken. The data indicate three general groups of plutons including (1) those that intruded the island arc terranes during the Triassic and Jurassic, those that intruded near the western edge of oceanic rocks along the suture in the Early Cretaceous, and the plutons of the Idaho batholith that intruded Proterozoic North American rocks in the Late Cretaceous. Plutons that intruded Proterozoic North American rocks commonly include xenocrystic zircons and in several cases, ages could not be determined. The least radiogenic Sr and most radiogenic Nd are found among the Blue Mountains superterrane island arc samples. Suture-zone plutons have isotopic characteristics that span the range between Idaho batholith and island arc samples but mostly follow island arc signatures. Plutons of the Idaho batholith have the most radiogenic initial Pb and Sr ratios and the least radiogenic Nd of the samples analyzed.

  8. Late Cretaceous intraplate silicic volcanism in the Lake Chad region: incipient continental rift volcanism vs. Cameroon Line volcanism

    NASA Astrophysics Data System (ADS)

    Shellnutt, G.; Lee, T. Y.; Torng, P. K.; Yang, C. C.

    2015-12-01

    The crustal evolution of west-central Africa during the Cretaceous was directly related to plate motion associated with the opening of the central Atlantic Ocean. Late Cretaceous (~66 Ma) to recent magmatism related to the Cameroon Line stretches from Northern Cameroon (i.e. Golda Zuelva) to the Gulf of Guinea (i.e. Pagalu) and is considered to be due to mantle-crust interaction. The volcanic rocks at Hadjer el Khamis, west-central Chad, are considered to be amongst the oldest volcanic rocks of the Cameroon Line but their relationship is uncertain because they erupted during a period of a regional extension associated with the opening of the Late Cretaceous (~75 Ma) Termit basin. The silicic volcanic rocks can be divided into a peraluminous group and a peralkaline group with both rock types having similar chemical characteristics as within-plate granitoids. In situ U/Pb zircon dating yielded a mean 206Pb/238U age of 74.4 ± 1.3 Ma and indicates the rocks erupted ~10 million years before the next oldest eruption attributed to the Cameroon Line. The Sr isotopes (i.e. ISr = 0.7050 to 0.7143) show a wide range but the Nd isotopes (i.e. 143Nd/144Ndi = 0.51268 to 0.51271) are more uniform and indicate that the rocks were derived from a moderately depleted mantle source. Major and trace elemental modeling show that the silicic rocks likely formed by shallow fractionation of a mafic parental magma where the peraluminous rocks experienced crustal contamination and the peralkaline rocks did not. The silicic rocks are more isotopically similar to Late Cretaceous basalts in the Doba and Bongor basins (i.e. ISr = 0.7040 to 0.7060; 143Nd/144Ndi = 0.51267 to 0.51277) of southern Chad than to rocks of the Cameroon Line (i.e. ISr = 0.7026 to 0.7038; 143Nd/144Ndi = 0.51270 to 0.51300). Given the age and isotopic compositions, it is likely that the silicic volcanic rocks of the Lake Chad area are related to Late Cretaceous extensional tectonics rather than to Cameroon Line magmatism.

  9. Occurrences of Chert in Jurassic-Cretaceous Calciturbidites (SW Turkey)

    NASA Astrophysics Data System (ADS)

    Gül, Murat

    2015-10-01

    The Lycian Nappes, containing ophiolite and sedimentary rocks sequences, crop out in the southwest Turkey. The Tavas Nappe is a part of the Lycian Nappes. It includes the Lower Jurassic-Upper Cretaceous calciturbidites. Chert occurrences were observed in the lower part of this calciturbidite. These cherts can be classified on the basis of length, internal structure and host rock. Chert bands are 3.20-35.0min length and 7.0-35.0 cm thick. Chert lenses are 5.0-175.0 cm in length and 1.0-33.0 cm thick. According to its internal structure, granular chert (bladedlarge equitant quartz minerals replaced the big calcite mineral of fossil shell) and porcelanious chert (microcrystalline silica replaced micrite) have been separated. Cherts are generally associated with calcarenite-calcirudite, the others with calcilutite. Micritic calcite patches of cherts point out an uncompleted silicification. The source of silica was dominantly quartz-rich, older, basal rocks and to a lesser extent radiolarians. The coarse-grained calciturbidites act as a way for silica transportation. Some calcite veins (formed during transportation and emplacement of nappes) cut both calciturbidites and cherts. Thus, chert occurrences evolved before emplacement of nappes (the latest Cretaceous-Late Miocene period) during the epigenetic phase.

  10. Hydrocarbon shows and petroleum source rocks in sediments as old as 1.7 billion years

    NASA Astrophysics Data System (ADS)

    Jackson, M. J.; Powell, T. G.; Summons, R. E.; Sweet, I. P.

    1986-08-01

    The discovery of indigenous live oil in 1.4-Gyr-old rocks in the McArthur Basin of northern Australia is reported. Previously reported occurrences of indigenous Precambrian oil are less than 1 Gyr old. Potential petroleum source rocks in the McArthur Basin range in age from 1.4-1.7 Gyr and were deposited in marine and lacustrine environments. In parts of the basin they have been buried sufficiently deeply to have generated hydrocarbons. They span the period corresponding to the appearance of eukaryotic organisms, and because of their low degree of thermal alteration, they provide a valuable resource for the study of primitive biota through their hydrocarbon biomarkers. The hydrocarbon composition of the oil is consistent with a derivation from organic matter of prokaryotic origin. These results show that exploration of previously ignored mid-Proterozoic sediments may lead to the discovery of new reserves of oil.

  11. Source characteristics of long runout rock avalanches triggered by the 2008 Wenchuan earthquake, China

    NASA Astrophysics Data System (ADS)

    Qi, Shengwen; Xu, Qiang; Zhang, Bing; Zhou, Yuande; Lan, Hengxing; Li, Lihui

    2011-03-01

    The May 12, 2008 Wenchuan, China Earthquake which measured M w = 8.3 according to Chinese Earthquake Administration - CEA ( M w = 7.9 according to the USGS) directly triggered many landslides, which caused about 20,000 deaths, a quarter of the total. Rock avalanches were among the most destructive landslides triggered by this seismic event, and have killed more people than any other type of landslide in this earthquake. The Donghekou rock avalanche, one example of a catastrophic avalanche triggered by the Wenchuan earthquake, occurred in Qingchuan and buried one primary school and 184 houses, resulting in more than 780 deaths, and in addition, caused the formation of two landslide dams, which formed barrier lakes. Combining aerial images (resolution of 0.5 m) with field investigations, this paper lists some parameters of 66 cases in one table, and details source characteristics of six typical cases. It has been found that most of the long runout rock avalanches have source areas with high relief and steep inclination, causing the debris in the travel courses to accelerate. There was also a large amount of saturated Holocene-age loose deposits formed by a river or gully that existed in the travel courses. Comparison studies indicate that saturated Holocene loose deposits in the travel courses could be the most important factor for the causes of the long runout characteristic of the rock avalanches especially when they traveled over gentle or even flat ground surfaces. Furthermore, the relationships among the relief slope gradient, runout and covered area are investigated, and a threshold line for predicting the maximum horizontal runout distance under certain change in elevation is presented.

  12. Calcium isotope analytical technique for mafic rocks and its applications on constraining the source of Cenozoic ultra-potassic rocks in the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Zhang, Z.; Xu, J.

    2013-12-01

    Ca isotope analytical technique for mafic rocks has been recently developed and set up at our lab. About mg level of a mafic rock sample was digested, and then a sub portion of the solution contains about 100ug Ca was spiked with a 42Ca-43Ca double spike and went through the column chemistry. Generally the Ca recovery is almost 100% and the procedure blank is about 50-150ng. Finally, about 5-10ug of the collected Ca cut was measured on our Triton TIMS. The precision of the data was around 0.1 per mil and the data we collected for standards are consistent with those reported by previous studies. There are two groups of Cenozoic ultra-potassic rocks that are widespread in Tibetan Plateau: a northern group in Songpan-Ganzi and Qiangtang Terranes and a southern group in Lhasa Terrane. Previous petrology evidence, such as a relative enrichment in large ion lithophile element (LILE); negative Ta,Nb and Ti anomalies and high LREE/HREE ratio, support that those rocks are both derived from sub-continental lithospheric mantle (SCLM). However, differences between these two groups of rocks do exist: the southern group has higher K2O, Rb, Zr, Th, contents and a higher Rb/Ba, coupled with lower Al2O3, CaO, Na2O, Sr; the southern 87Sr/86Sr ratios are higher while the 143Nd/144Nd ratios are lower, etc. These suggest that the rocks could be derived from different mantle sources or produced by different geological processes. Ca isotope is chosen in this study to better understand the source of the ultra-potassic rocks because Ca isotope has been a great tracer of different geological reservoirs and the isotopic compositions of Ca may represent different genesic processes. We propose that the ultra-potassic rocks in the Tibet should have significant 40Ca enrichments due to the decay from 40K to 40Ca, therefore the variation of Ca isotopic compositions among these ultra-potassic rocks could be obvious. We believe that based on our calcium data together with earlier Sr, Nd, Pb data

  13. Correlation of oils and source rock characteristics using biological markers, Cuyama Basin, California

    SciTech Connect

    Lillis, P.G.

    1988-03-01

    Biological marker data obtained from gas chromatography and gas chromatography/mass spectrometry were used to correlate the oils in the Cuyama basin and to characterize the potential source facies. Biological markers provide a wealth of information about petroleum and source rocks, including information on paleoecology, depositional environment, and thermal maturity. Pristane/phytane ratios and sterane and hopanoid distributions indicate the source facies was deposited in a restricted marine basin and the organic matter was derived primarily from marine phytoplankton with a significant contribution from land plants and bacteria. Previous studies have documented that the Miocene Monterey Formation is a major source rock for oils in several California basins. However, clear differences exist between the composition of Cuyama basin oils and typical Monterey oils. Cuyama basin oils have lower sulfur contents (< 0.5 wt. %), higher pristane/phytane ratios (1.7-1.9), and no 28,30-bisnorhopane, in comparison to Monterey oils, which have higher sulfur contents (1-6 wt %), lower pristane/phytane ratios (< 1), and significant amounts of 28,30-bisnorhopane. The low sulfur content of the Cuyama basin oils is probably due to precipitation of microbially reduced sulfur with iron from terrigenous clay input, this preventing sulfur incorporation into the kerogen. The higher clay content in the source facies is also indicated by higher diasterane content. Petroleum geochemistry studies indicate that the Cuyama basin oils share a common source. The source facies appears to be an atypical Monterey Formation deposited in an inboard basin, with significant terrigenous organic and clay mineral debris contributing to the autochthonous biogenous sediments.

  14. Rock Valley Source Physics Experiment Preparation: Earthquake Relocation and Attenuation Structure Characterization

    NASA Astrophysics Data System (ADS)

    Pyle, M. L.; Walter, W. R.; Myers, S.; Pasyanos, M. E.; Smith, K. D.

    2012-12-01

    The science of nuclear test monitoring relies on seismic methods to distinguish explosion from earthquakes sources. Unfortunately, the physics behind how an explosion generates seismic waves, particularly shear waves, remains incompletely understood. The Source Physics Experiments (SPE) are an ongoing series of chemical explosions designed to address this problem and advance explosion monitoring physics and associated simulation codes. The current series of explosions are located in the Climax Stock granite on the Nevada National Security Site (NNSS). A future candidate for the SPEs would allow us to make a direct comparison of earthquake and explosion sources by detonating an explosion at a well constrained earthquake hypocenter and recording the resulting signals from each source at common receivers. This possibility arises from an area of unusually shallow seismicity in the Rock Valley area of the southern NNSS. While most tectonic earthquakes occur at depths greater than 5 km, a sequence of unusually shallow earthquakes with depths of 1-2 km occurred in Rock Valley in May of 1993. The main shock had a magnitude of approximately 3.7 and 11 more events in the sequence had magnitudes over 2. The shallow depths of these events were well constrained by temporary stations deployed at the time by the University of Nevada-Reno (UNR). As part of a feasibility study for a future Rock Valley SPE, LLNL, UNR and NSTec are working to re-instrument and improve our understanding of the Rock Valley region. Rock Valley is a complex set of left oblique-slip segmented fault blocks; it is a regular source region for small magnitude shallow earthquakes. A dense seismic network was operated in the southern NNSS through the Yucca Mountain project (1992-2010). Although much of the older network has been removed, six new Rock Valley telemetered seismic stations located at both original 1993 sites and additional sites, have been installed and operating since early 2011. In order to

  15. Cretaceous rift related magmatism in central-western South America

    NASA Astrophysics Data System (ADS)

    Viramonte, J. G.; Kay, S. M.; Becchio, R.; Escayola, M.; Novitski, I.

    1999-03-01

    The Cretaceous-Paleocene Andean basin system of central-western South America, comprises northwestern Argentina and southwestern Bolivia. It is situated between 62°-68°W and 18°-27°S, but extends westward to northern Chile and northward to Bolivia and Peru. These basins have been interpreted as an aborted foreland rift. In a general sense, it may be possible to relate this rift to the opening of the South Atlantic Ocean, however it was directly associated, in a backarc position, with the subduction of the Nazca Plate below the South American Plate. Three main magmatic episodes were recognized: the pre-rift stage (130-120 Ma) which is characterized by an early phase of anorogenic plutonism, with subalkaline and alkaline granitic intrusives; the syn-rift volcanic episode which started with a mainly alkaline volcanic activity (110-100) in which alkaline rocks prevail; a second more voluminous volcanic episode (80-75 Ma) which is characterized by an alkaline suite represented by basanites and tephriphonolites; and the last volcanic episode (65-60 Ma) which consists of lamproitic sills and basic K rich lava flows. Petrography, chemistry and chronology of the Cretaceous plutonic bodies indicate anorogenic pre-rift related A-type granite complexes closely related to the further evolution of the Cretaceous rift basin. The petrology and geochemistry of the Cretaceous volcanic rocks show strong alkaline affinities and suggest a similar rift-related origin. The geochemical and isotopic characteristics of the alkaline basalts suggest that they originated through low degrees of partial melting of a depleted mantle subcontinental lithosphere which was previously enriched by processes such as the introduction of veins rich in amphibole, high Ti phlogopite, and apatite. Cretaceous plutonic and volcanic rocks from central-southwestern South America are related to an intracontinental rift environment and although their ages are correlative with those of the Paraná volcanic

  16. Sensitivity of the close-in seismic source function to rock properties. (Condensed version)

    SciTech Connect

    App, F.N.

    1993-11-01

    This paper presents a condensed version of a full report of the same title by App, 1993, which details work in progress on the systematic investigation of parameters affecting remote identification of underground nuclear tests. The objective of this investigation is to determine and evaluate how rock properties near the source of an explosion influence the close-in seismic source function. In this study, the overshoot and steady state value of the reduced displacement potential (RDP) and the corner frequency and rolloff of the reduced velocity potential (RVP) spectra are properties of the source function used to measure effect. A series of one-dimensional calculations are made with the computational mesh divided into six phenomenological regions.

  17. The study on thermal evolution modeling of source rocks In Neopaleozoic of Hangjinqi Region in Ordos Basin

    NASA Astrophysics Data System (ADS)

    Zhao, G.

    2016-12-01

    As the one of the gas exploration key region in Ordos Basin, the challenge in Hangjinqi Region is that the understanding of the thermal evolution of source rocks is still limited. Taking the measured Ro values which reflected the characteristics of thermal evolution degree of source rocks as calibration, the thermal evolution history of source rocks of Taiyuan Formation and Member1 ,2 of Shanxi Formation In Neopaleozoic age was modeled through erosion thickness restoration, selection of ancient terrestrial heat flow, using more than 70 well logging data of different strata lithology, and establishing the corresponding geological modeling. The results show that the time when Ro values reached 0.65% meaning that the source rocks entered the threshold of hydrocarbon generation was mid-late stage of Late Triassic period in Nanzhao, shilijiahan, Azhen and Gaoraozhao areas of western and southern Hangjinqi. The time of Ro reaching 0.65% in Gongkahan Shiguhao areas in northern of Hangjinqi was early Jurassic. On the plane, the hydrocarbon source rock thermal evolution degree was characterized by the trend of gradually decreasing of Ro values from southwest to northeast. The Maximum Ro values in Xinzhao, southern part of Shilijiahan are 1.43% and 1.46% respectively, reaching over-mature stage of evolution. however, the Ro values in Shiguhao and Azhen located in the northern and eastern part of Hangjinqi are between 0.85%~1.0%, showing that the source rocks are still in the early stage of peak period of hydrocarbon generation.

  18. 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

  19. Clay mineralogy of the malmian source rock of the Vienna Basin: Effects on shale gas exploration?

    NASA Astrophysics Data System (ADS)

    Schicker, Andrea; Gier, Susanne; Herzog, Ulrich

    2010-05-01

    In an unique opportunity the diagenetic changes of clay minerals of a marlstone formation with only minor differences in provenance and depositional environment was studied from shallow (1400 m) to very deep (8550 m) burial. The clay mineralogy of 46 core samples from ten wells was quantified with X-ray diffraction in applying the mineral intensity factor (MIF)-method of Moore and Reynolds (1997). The clay fraction of the marlstone contains a prominent illite/smectite (I/S) mixed-layer mineral (20 to 70 wt%), illite (20 to 70 wt%), chlorite (0.5 to 12 wt%) and kaolinite (2 to 17 wt%). The amounts of I/S and kaolinite decrease with depth, whereas illite and chlorite increase. A gradual transformation of smectite to illite through mixed-layer I/S intermediates is recognized. With increasing depth the illite content in I/S intermediates increases from 25% to 90% in parallel the ordering of the mixed layer I/S changes from R0 (25% illite in I/S) to R1 (60-80% illite in I/S) to R3 (90% illite in I/S). R3 ordering prevails at depths greater than 4000 m and implies that the effect of the expandable mineral smectite is negligible. This paper covers a part of a shale gas feasibility study on the main Vienna Basin hydrocarbon source rock (Mikulov Formation, a Malmian marlstone) recently performed by OMV. Shale gas production usually is enabled by pumping fluids (mainly water) into a gas-mature source rock in order to generate fracture permeability. Expandable clays within the source rock can dramatically reduce stimulation effectiveness and gas production. Moore and Reynolds (1997) X-ray diffraction and the identification and analysis of clay minerals. Oxford University Press, New York, 378 p.

  20. Possible New Well-Logging Tool Using Positron Annihilation Spectroscopy to Detect TOC in Source Rocks

    NASA Astrophysics Data System (ADS)

    Patterson, Casey; Quarles, C. A.; Breyer, J. A.

    2001-10-01

    Possible New Well-Logging Tool Using Positron Annihilation Spectroscopy to Detect Total Organic Carbon (TOC) in Source Rocks PATTERSON, C., Department of Geology, Department of Physics, Texas Christian University, QUARLES, C.A., Department of Physics, Texas Christian University, Fort Worth, Texas, BREYER, J.A., Department of Geology, Texas Christian University, Fort, Worth, Texas. The positron produces two gamma rays upon annihilation with an electron. Depending on the momentum of the electron, the two resulting photons are shifted from the initial electron rest mass energy by the Doppler effect. We measure the distribution of gamma ray energies produced by annihilation on a petroleum source rock core. Core from the Mitchell Energy well T.P. Sims 2 of the Barnett Shale located in Wise County, Texas, is under study. Apparatus for the experiment consists of an Ortec Ge detector. The source used for the experiment is Ge68, which undergoes beta decay and produces the positrons that penetrate the core. It is placed on the middle of the core and covered with a small, annealed NiCu plate to prevent unnecessary background from the positrons annihilating with electrons other than in the core. Distance between the source and the detector is fixed at 6.75 inches. Measurements were made in specific locations at 2 inch increments for approximately an hour and a half where the predetermined Total Organic Carbon (TOC) values were made. Future studies involve an overall correlation of the core between experimental readings and TOC, including corrections for changes in grain size and lithology. Additional research has shown no distinct correlation between grain size and distribution of energies across the targeted spectrum. Additional corrections should be made for the decay in activity of the source. Future research also includes the determination for optimum time and distance for the source from the core. A long-term goal for the experiment is to develop an effective down

  1. Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block

    NASA Astrophysics Data System (ADS)

    Xu, Wenjing; Xu, Xisheng; Zeng, Gang

    2017-08-01

    Several recent studies have documented that the silicic rocks (SiO2 > 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of ;hidden; large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of 22,000 km2. In contrast, exposures of mafic rocks total only 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial 87Sr/86Sr = 0.7041-0.7102; εNd(t) = - 8.4 to + 1.8; weighted mean zircon εHf(t) = - 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59-13.1 and 3.5-20.9, respectively), and variable Th/La ratios (0.11-0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (<- 4) and Sm/Nd ratios (< 0.255), while the majority of the low-MgO mafic rocks (MgO < 10 wt.%) have higher εNd(t) values (>- 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial 87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.

  2. Geochemistry and argon thermochronology of the Variscan Sila Batholith, southern Italy: source rocks and magma evolution

    USGS Publications Warehouse

    Ayuso, R.A.; Messina, A.; de Vivo, B.; Russo, S.; Woodruff, L.G.; Sutter, J.F.; Belkin, H.E.

    1994-01-01

    The Sila batholith is the largest granitic massif in the Calabria-Peloritan Arc of southern Italy, consisting of syn to post-tectonic, calc-alkaline and metaluminous tonalite to granodiorite, and post-tectonic, peraluminous and strongly peraluminous, two-mica??cordierite??Al silicate granodiorite to leucomonzogranite. Mineral 40Ar/39Ar thermochronologic analyses document Variscan emplacement and cooling of the intrusives (293-289 Ma). SiO2 content in the granitic rocks ranges from ???57 to 77 wt%; cumulate gabbro enclaves have SiO2 as low as 42%. Variations in absolute abundances and ratios involving Hf, Ta, Th, Rb, and the REE, among others, identify genetically linked groups of granitic rocks in the batholith: (1) syn-tectonic biotite??amphibole-bearing tonalites to granodiorites, (2) post-tectonic two-mica??Al-silicate-bearing granodiorites to leucomonzogranites, and (3) post-tectonic biotite??hornblende tonalites to granodiorites. Chondrite-normalized REE patterns display variable values of Ce/Yb (up to ???300) and generally small negative Eu anomalies. Degree of REE fractionation depends on whether the intrusives are syn- or post-tectonic, and on their mineralogy. High and variable values of Rb/Y (0.40-4.5), Th/Sm (0.1-3.6), Th/Ta (0-70), Ba/Nb (1-150), and Ba/Ta (???50-2100), as well as low values of Nb/U (???2-28) and La/Th (???1-10) are consistent with a predominant and heterogeneous crustal contribution to the batholith. Whole rock ??18O ranges from ???+8.2 to +11.7???; the mafic cumulate enclaves have the lowest ??18O values and the two-mica granites have the highest values. ??18O values for biotite??honblende tonalitic and granodioritic rocks (9.1 to 10.8???) overlap the values of the mafic enclaves and two-mica granodiorites and leucogranites (10.7 to 11.7???). The initial Pb isotopic range of the granitic rocks (206Pb/204Pb ???18.17-18.45, 207Pb/204Pb ???15.58-15.77, 208Pb/204Pb ???38.20-38.76) also indicates the predominance of a crustal source

  3. 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

  4. Cretaceous ongonites (topaz-bearing albite-rich microleucogranites) from Ongon Khairkhan, Central Mongolia: Products of extreme magmatic fractionation and pervasive metasomatic fluid: rock interaction

    NASA Astrophysics Data System (ADS)

    Dostal, Jaroslav; Kontak, Daniel J.; Gerel, Ochir; Gregory Shellnutt, J.; Fayek, Mostafa

    2015-11-01

    Ongonites were defined at their type locality at Ongon Khairkhan, central Mongolia, as pristine magmatic topaz-bearing albite-quartz-keratophyres with up to 4 wt. % F and containing phenocrysts of albite, K-feldspar, quartz and rare mica and topaz hosted in a groundmass composed of the same minerals. However, detailed petrographic and SEM-EDS studies indicate that these rocks underwent considerable subsolidus exchange with deuteric fluids, as evidenced by the presence of albitic plagioclase (Ab~ 100) and end-member orthoclase (Or~ 100), secondary Li-Fe-rich mica (zinnwaldite) enriched in rare metals (Sn, W, Ta, Nb), pitted feldspars containing fluid inclusions, and disseminated fluorite. The ~ 120 Ma old dyke rocks, emplaced at a high structural level in the crust, are strongly peraluminous leucogranites characterized by high Al and alkalis that are also enriched in Rb, Cs, Ga and Ta, depleted in Mg, Ca, Zr, Ba, Sr and Eu, and have anomalous K/Rb, Rb/Sr, Zr/Hf and Nb/Ta ratios compared to the average continental crust. However, the suite has Nd isotopic ratios (ɛNd(120) ~- 1) similar to those of contemporaneous A-type granites of the Mongolian-Transbaikalian igneous province of the Central Asian Orogenic Belt. The inferred primary δ18O (~+ 6 to + 7‰) and Pb isotopic values are consistent with a granitic parent magma and interaction with orthomagmatic fluids. The ongonites and constituent minerals record (1) an extensive and protracted crystal fractionation history, in part due to the presence of volatiles (particularly F) which depressed the solidus temperature of the felsic rocks and extended its duration of crystallization and (2) subsolidus exchange with fluids which includes late flux of heated meteoric water as indicated by modified whole rock δ18O values (+ 0.5 to +2.7‰). The interaction of the ongonites with internally derived orthomagmatic fluids is considered to result in enrichment and/or redistribution of several incompatible elements, but not to

  5. Oils and source rocks from the Anadarko Basin: Final report, March 1, 1985-March 15, 1995

    SciTech Connect

    Philp, R. P.

    1996-11-01

    The research project investigated various geochemical aspects of oils, suspected source rocks, and tar sands collected from the Anadarko Basin, Oklahoma. The information has been used, in general, to investigate possible sources for the oils in the basin, to study mechanisms of oil generation and migration, and characterization of depositional environments. The major thrust of the recent work involved characterization of potential source formations in the Basin in addition to the Woodford shale. The formations evaluated included the Morrow, Springer, Viola, Arbuckle, Oil Creek, and Sylvan shales. A good distribution of these samples was obtained from throughout the basin and were evaluated in terms of source potential and thermal maturity based on geochemical characteristics. The data were incorporated into a basin modelling program aimed at predicting the quantities of oil that could, potentially, have been generated from each formation. The study of crude oils was extended from our earlier work to cover a much wider area of the basin to determine the distribution of genetically-related oils, and whether or not they were derived from single or multiple sources, as well as attempting to correlate them with their suspected source formations. Recent studies in our laboratory also demonstrated the presence of high molecular weight components(C{sub 4}-C{sub 80}) in oils and waxes from drill pipes of various wells in the region. Results from such a study will have possible ramifications for enhanced oil recovery and reservoir engineering studies.

  6. Geochronological, geochemical, and Sr-Nd-Hf isotopic characteristics of Cretaceous monzonitic plutons in western Zhejiang Province, Southeast China: New insights into the petrogenesis of intermediate rocks

    NASA Astrophysics Data System (ADS)

    Liu, Liang; Qiu, Jian-Sheng; Zhao, Jiao-Long; Yang, Ze-Li

    2014-05-01

    We present comprehensive petrological, geochemical, and Sr-Nd-Hf isotopic data for the Matou and Dalai plutons in western Zhejiang Province, Southeast China, with the aim of constraining the petrogenesis of monzonites and to offer new insights into the deep processes of interaction between crustal- and mantle-derived magmas beneath SE China. The Matou pluton comprises quartz monzonite, whereas the Dalai pluton consists of quartz monzodiorite. Zircon U-Pb ages obtained by laser ablation-inductively coupled plasma-mass spectrometry show that both plutons were emplaced at 99-101 Ma. Rocks of both plutons are intermediate to silicic, metaluminous to weakly peraluminous, subalkaline, and K-rich in composition. Samples of the plutons are enriched in large ion lithophile (e.g., Rb, K, and Pb) and light rare earth elements, depleted in high-field strength elements (e.g., Nb, Ta, and Ti), and have small negative or no Eu anomalies. In addition, the rocks have high Mg# values (up to 53.9), high zircon ɛHf(t) values (up to - 1.4), and low Nb/U and Ta/U ratios. Geochemical evidence suggests that both depleted asthenospheric and metasomatically enriched mantle components were involved in the formation of these monzonitic rocks. The presence of inherited zircons with Palaeoproterozoic ages and zircons with unusually low ɛHf(t) values (- 12.9) in the Matou quartz monzonites indicates that ancient crustal materials were also involved in their petrogenesis. In combination with the presence of abundant mafic microgranular enclaves (MMEs) with spheroidal to ellipsoidal-ovoidal shapes and xenocrysts within the more diffused enclaves, and the results of trace element modelling, we suggest that the Matou quartz monzonites were generated by mixing between mantle-derived mafic magmas and crustally derived silicic magmas. The Dalai pluton is relatively homogeneous and contains fewer MMEs than the Matou pluton. Zircons from the Dalai pluton show no inherited components, indicating that

  7. Petroleum source rock potential and thermal maturity, Palo Duro Basin, Texas

    SciTech Connect

    Dutton, S.P.

    1980-01-01

    Samples collected from 20 geographically widespread wells in the sparsely drilled Palo Duro Basin were analyzed for total organic carbon content (TOC). Highest values of TOC, up to 6.9%, occur in Upper Permian San Andres dolomite in the southern part of the basin. Pennsylvanian and Lower Permian (Wolfcampian) basinal shales contain up to 2.4% TOC and are fair to very good source rocks. Kerogen color and vitrinite reflectance, which indicate maximum paleotemperatures, were analyzed in all samples containing greater than 0.5% TOC. Pennsylvanian and Wolfcampian kerogen is yellow orange to orange, an indication that temperatures were sufficiently high to begin to generate hydrocarbons from lipid-rich organic material. Palo Duro Basin samples have a broad range of vitrinite reflectance values, but populations with the lowest reflectance probably indicate the true temperatures that were reached in the basin. Average reflectance in representative Pennsylvanian vitrinite is 0.52%; in Wolfcampian samples the average reflectance is 0.48%. These values are consistent with kerogen color and suggest that basinal source rocks may have begun to generate hydrocarbons.

  8. Cretaceous tectonism and volcanism in the eastern Scotian Basin, offshore Nova Scotia

    NASA Astrophysics Data System (ADS)

    Bowman, Sarah

    Early Cretaceous tectonism and volcanism is widespread in the eastern Mesozoic-Cenozoic Scotian Basin. The precise stratigraphic position of volcanic rocks within wells has been re-evaluated and the volcanological character of the rocks refined by study of cuttings and well logs. Hauterivian-Barremian volcanic rocks on the SW Grand Banks and Aptian-Albian volcanic rocks in the Orpheus Graben and SE Scotian Shelf are likely the result of Strombolian type eruptions. The timing of regional unconformities appears to mark the onset of different components of the volcanic system. The distribution of volcanism is related to the complex opening history of Europe from North America. Widespread volcanic activity indicates a regional and long-lived magma source, which resulted in elevated regional heat flow. Effects of this heat flow are seen in sediments within the Sable sub-basin, but was insufficient to significantly influence the petroleum system.

  9. Identification of aryl isoprenoids in source rocks and crude oils: Biological markers for the green sulphur bacteria

    NASA Astrophysics Data System (ADS)

    Summons, R. E.; Powell, T. G.

    1987-03-01

    A series of C 13 to C 31 aryl isoprenoids (1-alkyl,2,3,6-trimethylbenzenes) have been identified in reef-hosted oils and their source rocks from the Middle and Upper Silurian of the Michigan Basin and Middle Devonian of the Alberta Basin, Canada. Their structure has been confirmed by unambiguous synthesis of the C 14 member of the series. Their structure and isotopic composition indicate that they are derived from isorenieratene from the Chlorobiaceae family of sulphur bacteria. These results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns. The distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment. In conjunction with the aryl isoprenoids, they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation. This reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils.

  10. Was Late Cretaceous Magmatism in the Northern Rocky Mountains Really Arc-Related?

    NASA Astrophysics Data System (ADS)

    Farmer, G.

    2011-12-01

    Calc-alkaline, Cretaceous magmatism affected much of the northern Rocky Mountain region in the western U.S. and is generally interpreted as continental arc magmatism despite the fact that it occurred as far east into the continental interior as the Late Cretaceous (75 Ma to 78 Ma) Sliderock Mountain volcanoplutonic complex in south-central Montana. Magmatism may have migrated so far inboard as a response to shallowing of the dip angle of underthrust oceanic lithosphere, but the exact sources, tectonic setting and trigger mechanisms for the Late Cretaceous igneous activity remain unclear. In this study, new trace element and Nd and Sr isotopic data, combined with existing age and major element data (duBray et al., 1998, USGS Prof. Paper 1602), from the most mafic lavas present at the Sliderock Mountain Volcano were used to further define the source regions of the Late Cretaceous magmatism. The most mafic lava flows are high K (~2-3 wt. % K2O), low Ti (< 1 wt. % TiO2), low Ni (< 20 ppm) basaltic andesites. Major element oxide contents for these rocks are only weakly correlated with increasing wt. % SiO2 on conventional Harker diagrams. All of the rocks are characterized by high LILE/HFSE ratios and high Pb contents (17-20 ppm), as expected for arc-related magmatism. The rocks also have high (La/Yb)N (7-20) but show decreasing (Dy/Yb)N with increasing wt.% SiO2, suggesting a cryptic role for amphibole fractionation during evolution of their parental magmas. Initial ɛNd values range from -19 to -29 but do not covary with rock bulk composition and as a result are unlikely to represent the result of interaction with local Archean continental crust. Initial 87Sr/86Sr, in contrast, vary over a restricted range from 0.7045 to 0.7065. The lowest 87Sr/86Sr correspond to samples with the highest Sr/Y (120-190). The low ɛNd values for the basaltic andesites suggest that if these volcanic rocks were ultimately derived from ultramafic mantle sources, melting must have occurred

  11. 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

  12. 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.

  13. Preliminary investigation of oil and source rock organic geochemistry from selected Tertiary basins of Thailand

    NASA Astrophysics Data System (ADS)

    Lawwongngam, Kulwadee; Philp, R. P.

    Selected samples of crude oils and extracts from source rocks obtained from six Thailand Tertiary basins of the central plain and of the Gulf of Thailand regions were examined for geochemical properties and molecular compositions. Analyses were performed using GC, CGCMS and carbon isotope mass spectrometry. Though these results should be viewed as preliminary, the results are significant in terms of a regional understanding of the petroleum geochemistry of Thailand. Results from bulk geochemical properties and biomarker assemblages characterize derivatives of organic sources deposited in lacustrine environments. The organic matter is mainly derived from algae with varying amounts of higher plant material. However, an observed variation in the pristane/phytane ratios among the samples may imply differences in depositional oxicity. On the other hand, basinal differences in sedimentation rates, or in the oxygen concentration of the varying waters and/or sediment pore-waters resulted in spatial heterogeneities in the quantity and degree of preservation of the organic matter. In addition, a degree of physical separation between these paleo-lacustrine environments is indicated by differences in paleosalinity, e.g. the hypersaline biomarker, gammacerane, which is restricted to samples from the offshore Gulf of Thailand basins. Maturity parameters for these Tertiary oils and source rock extracts were determined using biomarker analyses of T s/T m, 22S/22S + 22R C 31 hopane, C 30 moretane/hopane, 20R/20S + 20R C 29 sterane, and aromatic compounds. Though the samples demonstrate an overall relatively low level of maturity as specified by the biomarker index, a degree of individual basinal variability is also distinguishable. The observed differences in the maturity values indicate regional heterogeneity among the basin thermal histories, suggesting differences in geothermal gradients and/or in the basin subsidence rates.

  14. 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

  15. Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador

    NASA Astrophysics Data System (ADS)

    Hughes, Richard A.; Pilatasig, Luis F.

    2002-02-01

    New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.

  16. Geochemistry of Lower Cretaceous strata of northern Priverkhoyansk Foreland Basin (NE SIBERIA): implications for provenance

    NASA Astrophysics Data System (ADS)

    Vasiliev, Dmitry; Ershova, Victoria; Ivensen, Galina; Prokopiev, Andrei

    2014-05-01

    The study area is located in the lower reaches of the Lena R., in between Chekurovka and Chucha Capes. The Lower Cretaceous clastic rocks of the northern part of the Priverkhoyansk foreland basin adjacent to the front of the Verkhoyansk fold-and-thrust belt have been studied. The Lower Cretaceous sections are composed of marine and fluvial terrigenous rocks. Marine deposits are represented by alternating sandstones and siltstones, while continental ones by alternating thick sandstones units (up to 400 m) and shale units with subordinate sandstones beds. The thickness of studied strata varies from 800-1900 m. The whole-rock geochemical analyses were done for 121 samples The geochemical study show: 1) uniform, persistent chemical composition close to that of acid igneous rocks; 2) low TiO2 content; 3) low MgO and FeO* values; 4) prevalence of FeO over Fe2O3 ; 5) high alkalies content with prevailing Na2O; 6) positive correlation between TiO2 and FeO* contents and negative correlation between Na2 O+K2 O and FeO* values. The data point to the same source of sediments both for marine and fluvial deposits with prevailing felsic rocks in provenance area. This research was supported by RFBR grants 14-05-31298, 13-05-00700, 13-05-00943 research grant of Saint Petersburg State University and Grant of President of Russia for Young Scientist MK-2902.2013.5.

  17. Single-crystal {sup 40}Ar/{sup 39}Ar ages for rocks in the lower part of the frontier formation (Upper Cretaceous), Southwest Wyoming

    SciTech Connect

    M`Gonigle, J.W.; Holmes, C.W.; Dalrymple, G.B.

    1995-04-01

    Five tuff beds in a 150 m (490 ft) thick section within the nonmarine Chalk Creek Member of the Frontier Formation and one bentonite bed within the Allen Hollow Shale Member of the Frontier Formation were sampled for {sup 40}Ar/{sup 39}Ar dating at localities south of Kemmerer, Wyoming. The study area extends from Cumberland Gap northward for 15 km (9.3 mi) past Blason Gap, and includes units 5-43 and unit 91 of the reference section measured by Cobban and Reeside in 1952. The age of the tuff beds ranges from 96.6 {plus_minus} 0.3 to 93.6 {plus_minus} 0.3 Ma and confirms the inferred Cenomanian age of much of the Chalk Creek Member. Previously, the member`s age had been based solely on its stratigraphic position between the Albian-to-lower Cenomanian marine rocks for the Aspen Shale and the lower Turonian marine shales in the middle of the Frontier Formation. The age of biotite crystals from the bentonite in the Allen Hollow Member, 92.1 {plus_minus} 0.2 Ma, confirms the paleontologic Turonian age of the member.

  18. Paleoenvironments of the Jurassic and Cretaceous Oceans: Selected Highlights

    NASA Astrophysics Data System (ADS)

    Ogg, J. G.

    2007-12-01

    There are many themes contributing to the sedimentation history of the Mesozoic oceans. This overview briefly examines the roles of the carbonate compensation depth (CCD) and the associated levels of atmospheric carbon dioxide, of the evolution of marine calcareous microplankton, of major transgressive and regressive trends, and of super-plume eruptions. Initiation of Atlantic seafloor spreading in the Middle Jurassic coincided with an elevated carbonate compensation depth (CCD) in the Pacific-Tethys mega-ocean. Organic-rich sediments that would become the oil wealth of regions from Saudi Arabia to the North Sea were deposited during a continued rise in CCD during the Oxfordian-early Kimmeridgian, which suggests a possible increase in carbon dioxide release by oceanic volcanic activity. Deep-sea deposits in near-equatorial settings are dominated by siliceous shales or cherts, which reflect the productivity of siliceous microfossils in the tropical surface waters. The end-Jurassic explosion in productivity by calcareous microplankton contributed to the lowering of the CCD and onset of the chalk ("creta") deposits that characterize the Tithonian and lower Cretaceous in all ocean basins. During the mid-Cretaceous, the eruption of enormous Pacific igneous provinces (Ontong Java Plateau and coeval edifices) increased carbon dioxide levels. The resulting rise in CCD terminated chalk deposition in the deep sea. The excess carbon was progressively removed in widespread black-shale deposits in the Atlantic basins and other regions - another major episode of oil source rock. A major long-term transgression during middle and late Cretaceous was accompanied by extensive chalk deposition on continental shelves and seaways while the oceanic CCD remained elevated. Pacific guyots document major oscillations (sequences) of global sea level superimposed on this broad highstand. The Cretaceous closed with a progressive sea-level regression and lowering of the CCD that again enabled

  19. Mid-Cretaceous Hawaiian tholeiites preserved in Kamchatka

    NASA Astrophysics Data System (ADS)

    Portnyagin, Maxim; Savelyev, Dmitry; Hoernle, Kaj; Hauff, Folkmar; Garbe-Schönberg, Dieter

    2008-11-01

    We report geochemical data on a peculiar group of Albian-Cenomanian(120-93 Ma) basalts preserved in ophiolites on the KamchatskyMys peninsula (Kamchatka, Russia) that share trace element andisotopic compositions with enriched tholeiites from the Detroitand Meiji Seamounts in the Hawaiian-Emperor Seamount chain.Melt inclusions in chromium spinel from these rocks, representativeof melt composition unaffected by post-magmatic alteration,exhibit Hawaiian-type [Th/Ba]n (0.25-0.77; i.e., distinctivelylow compared to the majority of oceanic island basalts and mid-oceanicridge basalts). Low 208Pb*/206Pb* of ~0.93 in rocks and high[Nb/La]n = 1.1-4.6 in melt inclusions suggest the presenceof a distinctive "Kea"-type component in their source.We propose that the ophiolitic basalts represent older (Earlyto middle Cretaceous) products of the Hawaiian hotspot (olderthan preserved on the northwest Pacific seafloor) that wereaccreted to the forearc of Kamchatka. The presence of similarcompositional components in modern and Cretaceous Hawaiian hotspotlavas suggests a persistent yet heterogeneous composition ofthe mantle plume, which may have sampled ≥15% of the core-mantleboundary layer over the past ~100 m.y.

  20. Geochemical relationships of petroleum in Mesozoic reservoirs to carbonate source rocks of Jurassic Smackover Formation, southwestern Alabama

    SciTech Connect

    Claypool, G.E.; Mancini, E.A.

    1989-07-01

    Algal carbonate mudstones of the Jurassic Smackover Formation are the main source rocks for oil and condensate in Mesozoic reservoir rocks in southwestern Alabama. This interpretation is based on geochemical analyses of oils, condensates, and organic matter in selected samples of shale (Norphlet Formation, Haynesville Formation, Trinity Group, Tuscaloosa Group) and carbonate (Smackover Formation) rocks. Potential and probable oil source rocks are present in the Tuscaloosa Group and Smackover Formation, respectively. Extractable organic matter from Smackover carbonates has molecular and isotopic similarities to Jurassic oil. Although the Jurassic oils and condensates in southwestern Alabama have genetic similarities, they show significant compositional variations due to differences in thermal maturity and organic facies/lithofacies. Organic facies reflect different depositional conditions for source rocks in the various basins. The Mississippi Interior Salt basin was characterized by more continuous marine to hypersaline conditions, whereas the Manila and Conecuh embayments periodically had lower salnity and greater input of clastic debris and terrestrial organic matter. Petroleum and organic matter in Jurassic rocks of southwestern Alabama show a range of thermal transformations. The gas content of hydrocarbons in reservoirs increases with increasing depth and temperature. In some reservoirs where the temperature is above 266/degrees/F(130/degrees/C), gas-condensate is enriched in isotopically heavy sulfur, apparently derived from thermochemical reduction of Jurassic evaporite sulfate. This process also resulted in increase H/sub 2/S and CO in the gas, and depletion of saturated hydrocarbons in the condensate liquids.

  1. Water Sources for Cyanobacteria Below Desert Rocks in the Negev Desert Determined by Conductivity

    NASA Technical Reports Server (NTRS)

    McKay, Christopher P.

    2016-01-01

    We present year round meteorological and conductivity measurements of colonized hypolithic rocks in the Arava Valley, Negev Desert, Israel. The data indicate that while dew is common in the Negev it is not an important source of moisture for hypolithic organisms at this site. The dominance of cyanobacteria in the hypolithic community are consistent with predictions that cyanobacteria are confined to habitats supplied by rain. To monitor the presence of liquid water under the small Negev rocks we developed and tested a simple field conductivity system based on two wires placed about 0.5 cm apart. Based on 21 replicates recorded for one year in the Negev we conclude that in natural rains (0.25 mm to 6 mm) the variability between sensor readings is between 20 and 60% decreasing with increasing rain amount. We conclude that the simple small electrical conductivity system described here can be used effectively to monitor liquid water levels in lithic habitats. However, the natural variability of these sensors indicates that several replicates should be deployed. The results and method presented have use in arid desert reclamation programs.

  2. The Talara Basin province of northwestern Peru: cretaceous-tertiary total petroleum system

    USGS Publications Warehouse

    Higley, Debra K.

    2004-01-01

    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.

  3. Late Jurassic--Early Cretaceous cooling for Late Proterozoic through Early Devonian crystalline rocks from the Bronson Hill anticlinorium, MA--VT: Evidence from apatite fission track analysis

    SciTech Connect

    Roden, M.K. . Dept. of Earth and Environmental Science)

    1993-03-01

    Ten samples of crystalline rocks from the Bronson Hill anticlinorium in north central Massachusetts--south central Vermont yield Mesozoic apatite fission track cooling ages ranging from 98 [+-] 8 to 158 [+-] 24 Ma. Compositionally, the samples include a quartz-phyric rhyolite from the Ammonoosuc Volcanics, a pegmatite from the Kempfield Anticline, a gabbro from the Prescott Intrusive Complex, the Dry Hill and Fourmile Gneisses from the Pelham Dome, Swanzey Gneiss from the Keene Dome, Pauchaug Gneiss from the Warwick Dome, and the Monson Gneiss. Published U-Pb zircon analyses for the same samples yield ages of 613 [+-] 3 Ma for the Dry Hill Gneiss; 454--442 [+-] 3 Ma for the Swanzey, Pauchaug, Monson and Fourmile Gneisses; 453 [+-] 2 Ma for the Ammonoosuc Volcanics; and 407 [+-] 3/[minus]2 Ma for the Prescott Intrusive Complex gabbro (Tucker and Robinson, 1990). Apatite fission track ages are all reset and increase in apparent age eastward from the edge of the Deerfield-Hartford Basin, consistent with published apatite fission track ages from Jurassic sedimentary units within the Deerfield and Northern Hartford Basins. Mean track lengths ranged from 13.4 to 14.4 [mu]m with moderately large standard deviations. These track length distributions suggest relatively slow cooling through the track annealing range of 70--90 C and are consistent with track length distributions for sedimentary samples within the Deerfield and Northern Hartford Basins. The trend of increasing apatite fission track apparent age eastward from the basin margin suggests several interpretations: (1) differential uplift; (2) deeper burial in the basin and adjacent areas; (3) higher heat flow along the basin margin. Zircon fission track analyses are in progress to constrain maximum burial depths and should help differentiate between these models.

  4. DRIFT spectroscopic study of diagenetic organic-clay interactions in argillaceous source rocks.

    PubMed

    Li, Yingli; Cai, Jingong; Song, Guoqi; Ji, Junfeng

    2015-09-05

    Thermo diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to study the diagenetic organic-clay interactions in argillaceous source rocks from the Dongying Depression, Bohai Bay Basin, China. The results indicated that aliphatic organic matter (OM) represented the most prominent organic functional groups in the spectra, with two CH2 stretching vibrations at approximately 2926 cm(-1) and 2852 cm(-1). The peak areas of these vibrations correlated well with the amount of total organic carbon (TOC), indicating that the OM evolution may be represented by the variation in CH2 with depth. Infrared spectra obtained from samples that were heated to 105 °C, 250 °C and 550 °C suggest that the aliphatic OM consists of two fractions: combined OM and free OM. The former was more stable between 250 °C and 550 °C. This phenomenon was correlated with the H2O stretching vibration near 3300 cm(-1), indicating that this OM was bonded to the clay via H2O bridges. The location of the broad H2O stretching band gradually shifted with depth from 3298 cm(-1) to a higher wavenumber of 3305 cm(-1), whereas the corresponding bending band shifted rapidly from 1640 cm(-1) to 1605 cm(-1), indicating a weakening of the hydrogen bond and a decrease in the combined OM fraction. The correlation between the diagenetic smectite illitization and the decrease in the amount of combined OM leads to the conclusion that the smectite illitization may be a driving force for the OM desorption. This study demonstrates the usefulness of the thermo-DRIFT approach for exploring diagenetic OM-clay interactions in argillaceous source rocks. Copyright © 2015 Elsevier B.V. All rights reserved.

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

    SciTech Connect

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

    1997-07-01

    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 southwest 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 (S{sub 1} + S{sub 2} = 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.

  6. Qualitative and quantitative analysis of Dibenzofuran, Alkyldibenzofurans, and Benzo[b]naphthofurans in crude oils and source rock extracts

    USGS Publications Warehouse

    Meijun Li,; Ellis, Geoffrey S.

    2015-01-01

    Dibenzofuran (DBF), its alkylated homologues, and benzo[b]naphthofurans (BNFs) are common oxygen-heterocyclic aromatic compounds in crude oils and source rock extracts. A series of positional isomers of alkyldibenzofuran and benzo[b]naphthofuran were identified in mass chromatograms by comparison with internal standards and standard retention indices. The response factors of dibenzofuran in relation to internal standards were obtained by gas chromatography-mass spectrometry analyses of a set of mixed solutions with different concentration ratios. Perdeuterated dibenzofuran and dibenzothiophene are optimal internal standards for quantitative analyses of furan compounds in crude oils and source rock extracts. The average concentration of the total DBFs in oils derived from siliciclastic lacustrine rock extracts from the Beibuwan Basin, South China Sea, was 518 μg/g, which is about 5 times that observed in the oils from carbonate source rocks in the Tarim Basin, Northwest China. The BNFs occur ubiquitously in source rock extracts and related oils of various origins. The results of this work suggest that the relative abundance of benzo[b]naphthofuran isomers, that is, the benzo[b]naphtho[2,1-d]furan/{benzo[b]naphtho[2,1-d]furan + benzo[b]naphtho[1,2-d]furan} ratio, may be a potential molecular geochemical parameter to indicate oil migration pathways and distances.

  7. The thermal maturation degree of organic matter from source rocks revealed by wells logs including examples from Murzuk Basin, Libya

    SciTech Connect

    Negoita, V.; Gheorghe, A.

    1995-08-01

    The customary technique used to know the organic matter quantity per rock volume it as well as the organic matter maturation stage is based on geochemical analyses accomplished on a preselected number of samples and cuttings drawn from boreholes during the drilling period. But the same objectives can be approached without any extra cost using the continuous measurements of well logs recorded in each well from the ground surface to the total depth. During the diagenetic stage, the identification of potential source rocks out of which no hydrocarbon have been generated may be carried out using a well logging suite including Gamma Ray Spectrometry, the Compensated Neutron/Litho Density combination and a Dual Induction/Sonic Log. During the catagenetic stage the onset of oil generation brings some important changes in the organic matter structure as well as in the fluid distribution throughout the pore space of source rocks. The replacement of electric conductive water by electric non-conductive hydrocarbons, together with water and oil being expelled from source rocks represent a process of different intensities dependent of time/temperature geohistory and kerogen type. The different generation and expulsion scenarios of hydrocarbons taking place during the catagenetic and metagenetic stages of source rocks are very well revealed by Induction and Laterolog investigations. Several crossplots relating vitrinite reflectance, total organic carbon and log-derived physical parameters are illustrated and discussed. The field applications are coming from Murzuk Basin, where Rompetrol of Libya is operating.

  8. Evidence of a deep mantle source for Eoarchean ultramafic rocks of Nulliak

    NASA Astrophysics Data System (ADS)

    Morino, P.; Caro, G.; Reisberg, L. C.

    2016-12-01

    The coupled 146,147Sm-142,143Nd system provides a powerful tool for constraining the timing of the earliest events in Earth history. The Nulliak assemblage of the Saglek Block of Labrador includes remarkably well-preserved ultramafic rocks that are ideally suited for the application of this tool. We obtained a 147Sm-143Nd isochron yielding a 3.78±0.09 Ga age for these rocks. The positive initial ɛ143Nd value of the isochron (1.5±0.2), coupled with the consistent positive µ142Nd anomaly (8.6±2 ppm) of these samples, allowed calculation of a model differentiation age for the Nulliak mantle source of 4.40±0.05 Ga (assuming a BSE with chondritic Sm/Nd and ɛ142Nd=0). This age is consistent with two model ages obtained from coupled 142-143Nd systematics applied to Eoarchean metasediments [1] and amphibolites [2] of the Isua Supracrustal Belt of Greenland. More surprisingly, it is also consistent with the mantle differentiation age calculated for the 2.7 Ga Theo's flow (Abitibi) [3], inviting discussion of the mechanism for creating positive ɛ142Nd in the early mantle. While Nd isotope systematics provide important information about the timing of early events in the silicate Earth, taken alone, they do not constrain the dominant differentiation process. For this reason, we have decided to couple our Nd isotopic study of the Nulliak samples with Hf isotopic analyses. In fact, crustal extraction is expected to yield positive correlations between Nd and Hf isotopes, as seen in modern basalts, while fractional crystallization of a basal magma ocean (BMO) should yield negative correlations. Our preliminary ɛ176Hfi results are coherent with the latter hypothesis, yielding values consistent with the extents of BMO perovskite fractionation constrained by modeling of the Nulliak Sm-Nd data. More generally we aim to establish the first coherent Hf-143Nd-144Nd isotope dataset on Nulliak ultramafic rocks, in order to better understand the processes that shaped their mantle

  9. Detrital sources and water mass circulation in the tropical North Atlantic during the Late Cretaceous to Paleogene

    NASA Astrophysics Data System (ADS)

    Martin, E. E.; Pugh, E.; Kamenov, G. D.; MacLeod, K. G.

    2014-12-01

    Seawater Nd isotopes from fossil fish teeth in Campanian to Paleogene calcareous claystone on Demerara Rise in the tropical North Atlantic record a change from epsilon Nd values of -17 to -11 during the late Maastrichtian. This shift has been identified in three different Ocean Drilling Program (ODP) sites that span from 600 to 1500 m paleodepths (ODP sites 1259, 1260 and 1261) and has been interpreted as a transition from a warm saline intermediate water mass formed on the South American margin, referred to as Demerara Bottom Water, to a source from the North Atlantic. A study of corresponding detrital Sr, Nd and Pb isotopes was undertaken to confirm the isotopic values derived from fish teeth record water mass compositions rather than diagenesis or boundary exchange. Several leaching procedures designed to remove Fe-Mn oxide coatings and the seawater signature they carry from the detrital fractions were tested. Sr isotopic data indicate a 0.02 M hydroxylamine hydrochloride (HH) leach was ineffective at removing the Fe-Mn oxides whereas a 1.0 M HH leach produced detrital Sr isotopic values that were consistent for all three sites and plotted farther from the seawater value. Detrital isotopic results can be divided into three intervals: 1) 73 - 66 Ma, when DBW is present, 2) 66 - 61 Ma, during the transition to North Atlantic sources, and 3) <61 Ma, when North Atlantic sources appear to dominate. During interval 1, detrital Nd isotopes increase gradually, while Sr and Pb isotopic ratios are relatively constant. Leading into interval 2, detrital Nd isotopes are fairly constant while there is a stepwise increase in Sr and Pb isotopes. Leading into interval 3, there is a large increase in Nd and decrease in Sr isotopes and a slight decrease in Pb isotopes. The subtle differences in the timing of changes in fish teeth and detrital Nd isotopes suggest the seawater signal is responding to changes in water mass rather than changes in sediment composition (boundary

  10. Early cretaceous platform-margin configuration and evolution in the central Oman mountains, Arabian peninsula

    SciTech Connect

    Pratt, B.R. ); Smewing, J.D. )

    1993-02-01

    The Hajar Supergroup (Middle Permian-Lower Cretaceous) of northeastern Oman records rifting and development of a passive margin along the edge of the Arabian platform facing Neo-Tethys. The Jurassic and Lower Cretaceous part, comprising the Sahtan, Kahmah, and Wasia groups, was deposited during the maximum extent of the broad epicontinental sea landward of this margin. These limestone units reach a total of 1500 m in thickness and correlate with the hydrocarbon reservoirs of the Arabian Peninsula. The trace of the Jurassic and Cretaceous margin in northeastern Oman followed a zigzag series of rift segments, resulting in promontories and reentrants that changed in position through time in response to the configuration and differential motion of underlying rift blocks. Synsedimentary normal faulting occurred locally in the Middle Jurassic, whereas in the Late Jurassic, the margin was eroded from variable uplift of up to 300 m before subsiding to below storm wave base. This uplift may have been caused by compression from oceanic crust that obducted along the southeastern side of the platform. The Lower Cretaceous succession in the central Oman Mountains and adjacent subsurface began with regional drowning around the Jurassic-Cretaceous boundary. The succession in the east (Saih Hatat) records a single regressive sequence, ending in the progradation of the shallow-water carbonate platform by the Cenomanian. However, the succession in the west (Jebel Akhdar and interior) is dominated by shallow-water carbonate facies, but punctuated by a second regional drowning in the late Aptian. A third, Late Cretaceous drowning terminated deposition of the Wasia Group in the Turonian and was caused by convergence of oceanic crust and foreland basic formation. The record of tectonic behavior of carbonate platforms has important implications for the development of hydrocarbon source rocks and porosity. 68 refs., 11 figs., 1 tab.

  11. Sources of Mesoproterozoic igneous rocks and formation time of the continental crust of the Kokchetav Massif (Northern Kazakhstan)

    NASA Astrophysics Data System (ADS)

    Tretyakov, A. A.; Kovach, V. P.; Degtyarev, K. E.; Shatagin, K. N.

    2016-12-01

    Within the Kokchetav massif (Northern Kazakhstan), Mesoproterozoic granites and acid volcanics are widespread: these are the youngest Precambrian igneous rocks forming basement of the region. The Nd isotopic characteristics (ɛNd( t)-4.4 ÷-9.6, t Nd(DM) 2.1-2.6 Ga) obtained for these rocks indicate that the source of their melts was the Early Precambrian continental crust. Thus, the continental crust of the Kokchetav Massif had basically been formed by the beginning of the Mesoproterozoic and during the Late Precambrian: later it became a source for the granitoid melts.

  12. Growing Pebbles and Conceptual Prisms - Understanding the Source of Student Misconceptions about Rock Formation.

    ERIC Educational Resources Information Center

    Kusnick, Judi

    2002-01-01

    Analyzes narrative essays--stories of rock formation--written by pre-service elementary school teachers. Reports startling misconceptions among preservice teachers on pebbles that grow, human involvement in rock formation, and sedimentary rocks forming as puddles as dry up, even though these students had completed a college level course on Earth…

  13. Growing Pebbles and Conceptual Prisms - Understanding the Source of Student Misconceptions about Rock Formation.

    ERIC Educational Resources Information Center

    Kusnick, Judi

    2002-01-01

    Analyzes narrative essays--stories of rock formation--written by pre-service elementary school teachers. Reports startling misconceptions among preservice teachers on pebbles that grow, human involvement in rock formation, and sedimentary rocks forming as puddles as dry up, even though these students had completed a college level course on Earth…

  14. Nanoscale Compositional Relations in Lunar Rock Patina: Deciphering Sources for Patina Components on an Apollo 17 Station 6 Boulder

    NASA Technical Reports Server (NTRS)

    Christoffersen, R.; Noble, S. K.; Keller, L. P.

    2014-01-01

    Space weathering on the Moon and other airless bodies modifies the surfaces of regolith grains as well as the space-exposed surfaces of larger rocks and boulders. As space weathering witness plates, rocks and boulders are distinguished from regolith grains based on their ability to persist as physically intact substrates over longer time scales before being disaggregated by impact processes. Because lunar surfaces, including exposed rocks, quickly develop an optically thick layer of patina, it is important to understand the compositional relationship between patinas and their underlying rock substrates, particularly to support remote-sensing of rocky lunar terrains. Based on analytical TEM techniques, supported by focused ion beam (FIB) cross-sectioning, we have begun to systematize the multi-layer microstructural complexity of patinas on rock samples with a range of space exposure histories. Our on-going work has particularly focused on lunar rock 76015, both because it has a long (approx. 22 my) exposure history, and because its surface was exposed to patina development approximately 1 m off the regolith surface on a boulder in the Apollo 17 Station 6 boulder field. Potential sources for the 76015 patina therefore include impact-melted and vaporized material derived from the local rock substrate, as well as from the mix of large boulders and regolith in the Station 6 area. While similar, there are differences in the mineralogy and chemistry of the rocks and regolith at Station 6. We were interested to see if these, or other sources, could be distinguished in the average composition, as well as the compositional nanostratigraphy of the 76015 patina. To date we have acquired a total of 9 TEM FIB cross-sections from the 76015 patina, giving us reasonable confidence of being able to arrive at an integrated average for the patina major element composition based on analytical TEM methods.

  15. Assessing the Evidence for Extensive Wildfires at the Cretaceous-Tertiary Boundary

    NASA Astrophysics Data System (ADS)

    Belcher, C. M.; Collinson, M. E.; Finch, P.; Scott, A. C.

    2004-12-01

    Models of the Cretaceous-Tertiary impact at Chicxulub have suggested that the thermal radiation released by the impact would have been sufficient to ignite extensive wildfires. Eight non-marine K-T sequences stretching from New Mexico to Saskatchewan have been studied in order to test this hypothesis. A multi-proxy approach has been devised by identifying and using key palaeo wildfire proxies (charcoal, soot and polyaromatic hydrocarbons (PAH's)) in combination to assess the extent of biomass burning as part of the K-T events. Soot and PAH's cannot be used to indicate fire location, as soot and PAH's from one large fire could be spread globally. The morphology of the soot and nature of the PAH's present can be used to determine their source, allowing identification of those created by biomass burning versus those from coal, gas and hydrocarbons in the K-T rocks. In contrast to soot and PAH's charcoal is a product uniquely produced by the combustion of vegetation. Charcoal in non-marine rocks provides an excellent tool to record the distribution of wildfires and therefore assess the extent of any thermal radiation associated with the impact at Chicxulub. Quantitative data from three different measures of charcoal abundance (in situ in polished blocks of rock and macro- and microscopic charcoal particles released from sieving of demineralised sediment) reveal that the K-T boundary rocks across the Western Interior of North America contain significantly less charcoal than is typical of the Cretaceous background of this area. The Cretaceous sedimentary rocks contain between 4 and 9 times (according to the measure used) more charcoal particles than the K-T sedimentary rocks. Taphonomic factors do not explain this difference. Furthermore non-charred plant remains are also abundant in the K-T rock layers. Re-assessment of the record of soot and PAH's reported in the K-T rocks suggests that the morphology of the soot and the signature of the PAH's is more consistent with

  16. Geological history of the Cretaceous ophiolitic complexes of northwestern South America (Colombian Andes)

    NASA Astrophysics Data System (ADS)

    Bourgois, Jacques; Toussaint, Jean-François; Gonzalez, Humberto; Azema, Jacques; Calle, Bernardo; Desmet, Alain; Murcia, Luis A.; Acevedo, Alvaro P.; Parra, Eduardo; Tournon, Jean

    1987-12-01

    The Western Cordillera of Colombia was formed by intense alpine-type nappe-forming folding and thrusting. The Cretaceous (80-120 Ma B.P.) tholeiitic material of the Western Cordilleran nappes has been obducted onto the Paleozoic and Precambrian polymetamorphic micaschists and gneiss of the Central Cordillera. Near Yarumal, the Antioquia batholith (60-80 Ma B.P.) intrudes both obducted Cretaceous oceanic material and the polymetamorphic basement rock of the Central Cordillera. Therefore, nappe emplacement and obduction onto the Central Cordillera occurred during Late Senonian to Early Paleocene. The nappes travelled from northwest to southeast so that the highest unit, the Rio Calima nappe therefore has the most northwestern source, whereas the lowest units originated from a more southeastward direction. Sedimentological analysis of the volcanoclastic and sandy turbidite material from each unit suggests a marginal marine environment. During Cretaceous times the opening of this marginal sea, from now on called the "Colombia marginal basin", probably originated by detachment of a block from the South American continent related to the Farallon-South America plate convergence. In the Popayan area (southern Colombia), the Central Cordilleran basement exhibits glaucophane schist facies metamorphism. This high pressure low temperature metamorphism is of Early Cretaceous (125 Ma B.P.) age and is related to an undated metaophiolitic complex. The ophiolitic material originating from the Western Cordilleran is thrust over both the blueschist belt and the metaophiolitic complex. These data suggest that the "Occidente Colombiano" suffered at least two phases of ophiolitic obduction during Mesozoic time.

  17. Regional hydrocarbon generation, migration, and accumulation pattern of Cretaceous strata, Powder River Basin

    SciTech Connect

    Meissner, F.F.

    1985-05-01

    A cell of abnormally high fluid pressure in the deep part of the Powder River basin is centered in an area where oil-generation-prone source rocks in the Skull Creek (oldest), Mowry, and Niobrara (youngest) formations are presently at their maximum hydrocarbon-volume generation rate. The overpressures are believed to be caused by the high conversion rate of solid kerogen in the source rocks to an increased volume of potentially expellable fluid hydrocarbons. In this area, hydrocarbons appear to be the principal mobile fluid species present in reservoirs within or proximal to the actively generating source rocks. Maximum generation pressures within the source rocks have caused vertical expulsion through a pressure-induced microfracture system and have charged the first available underlying and/or overlying sandstone carrier-reservoir bed. Hydrocarbons generated in the Skull Creek have been expelled downward into the Dakota Sandstone and upward into the Muddy Sandstone. Hydrocarbons generated in the Mowry have been expelled downward into the Muddy or upward into lower Frontier sandstones. Hydrocarbons generated in the Niobrara have been expelled downward into upper Frontier sandstones or upward into the first available overlying sandstone in the Upper Cretaceous. The first chargeable sandstone overlying the Niobrara, in ascending order, may be the (1) Shannon, (2) Sussex, (3) Parkman, (4) Teapot, or (5) Tekla, depending on the east limit of each sandstone with respect to vertical fracture migration through the Cody Shale from the underlying area of mature overpressured Niobrara source rocks.

  18. Chapter 4: The Cretaceous-Lower Tertiary Composite Total Petroleum System, Wind River Basin, Wyoming

    USGS Publications Warehouse

    Johnson, R.C.; Finn, Thomas M.; Kirschbaum, Mark A.; Roberts, Stephen B.; Roberts, Laura N.R.; Cook, Troy; Taylor, David J.

    2007-01-01

    The Cretaceous-Lower Tertiary Composite Total Petroleum System (TPS) of the Wind River Basin Province includes all strata from the base of the Lower Cretaceous Cloverly Formation to the base of the Waltman Shale Member of the Paleocene age Fort Union Formation and, where the Waltman is absent, includes strata as young as the Eocene Wind River Formation. Locally, Cretaceous-sourced gas migrated into strata as old as the Mississippian Madison Limestone, and in these areas the TPS extends stratigraphically downward to include these reservoirs. The extensive vertical migration of gases in highly fractured areas of the Wind River Basin led to the commingling of gases from several Upper Cretaceous and lower Tertiary sources, thus only two petroleum systems are recognized in these rocks, the Cretaceous-Lower Tertiary Composite TPS, the subject of this report, and the Waltman Shale TPS described by Roberts and others (Chapter 5, this CD-ROM). The Cretaceous-lower Tertiary Composite TPS was subdivided into (1) seven continuous gas assessment units (AU): (a) Frontier-Muddy Continuous Gas AU, (b) Cody Sandstone Continuous Gas AU, (c) Mesaverde--Meeteetse Sandstone Gas AU, (d) Lance-Fort Union Sandstone Gas AU, (e) Mesaverde Coalbed Gas AU, (f) Meeteetse Coalbed Gas AU, and (g) Fort Union Coalbed Gas AU; (2) one continuous oil assessement unit--- Cody Fractured Shale Continuous Oil AU; and (3) one conventional assessment Unit--- Cretaceous-Tertiary Conventional Oil and Gas AU. Estimates of undiscovered resources having the potential for additions to reserves were made for all but the Cody Fractured Shale Continuous Oil AU, which is considered hypothetical and was not quantitively assessed. The mean estimate of the total oil is 41.99 million barrels, mean estimate of gas is 2.39 trillion cubic feet, and mean estimate of natural gas liquids is 20.55 million barrels. For gas, 480.66 billion cubic feet (BCFG) is estimated for the Frontier-Muddy Continuous Gas AU, 115.34 BCFG for

  19. Petroleum evaluation of Ordovician black shale source rocks in northern Appalachian basin

    SciTech Connect

    Wallace, L.G.; Roen, J.B.

    1988-08-01

    A preliminary appraisal of the Ordovician black shale source beds in the northern part of the Appalachian basin shows that the sequence is composed of the Upper Ordovician Utica Shale and its correlatives. The shales range in thickness from less than 200 ft in the west to more than 600 ft in the east along the Allegheny Front. Structure contours indicate that the shales plunge from 2,000 ft below sea level in central Ohio and to about 12,000 ft below sea level in central and northeastern Pennsylvania. Geochemical analyses of 175 samples indicate that the sequence has an average total organic carbon content (TOC) of 1.34%. Conodont alteration indices (CAI) and production indices indicate that the stages of maturation range from diagenetic in the less deeply buried western part of the basin, which probably produced mostly oil, to catagenetic in the more deeply buried eastern part of the basin, which probably produced mostly gas. Potential for continued hydrocarbon generation is poor in the east and fair to moderate in the western part of the basin. If the authors assume that these rocks have produced hydrocarbons, the hydrocarbons have since migrated. Using an average TOC of 1%, an organic carbon to hydrocarbon conversion factor of 10%, and a volume of rock within the oil and gas generation range as defined by CAI values of 1.5-4, the Ordovician shale could have generated 165 billion bbl of oil or equivalent. If only 1% of the 165 billion bbl was trapped after migration, then 1.65 billion bbl of oil or equivalent would be available for discovery.

  20. Sources of Paleozoic granitic rocks and isotopic heterogeneity of the continental crust of the Aktau-Dzhungar microcontinent, Central Kazakhstan

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.; Shatagin, K. N.; Tret'yakov, A. A.

    2016-10-01

    Several generations of Paleozoic granitic rocks are studied with Sm-Nd isotopic methods in the northwestern part of the Aktau-Dzhungar microcontinent of Central Kazakhstan (Atasu-Mointy divide). The initial Nd isotopic composition of the granitic rocks varies in a relatively narrow range from-0.1 to-3.5ɛ; the Nd model ages are also similar (1.11-1.46 Ga). These results indicate that the crustal source of all the Paleozoic granitic rocks of the region had similar composition and, probably, age. It is shown that the t Nd(DM) values of the Paleozoic granites reflect different proportions between ancient and juvenile material in the crustal source.

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

    SciTech Connect

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

    1996-08-01

    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 the 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.

  2. Isotope geochemistry of mercury in source rocks, mineral deposits and spring deposits of the California Coast Ranges, USA

    USGS Publications Warehouse

    Smith, C.N.; Kesler, S.E.; Blum, J.D.; Rytuba, J.J.

    2008-01-01

    We present here the first study of the isotopic composition of mercury in rocks, ore deposits, and active spring deposits from the California Coast Ranges, a part of Earth's crust with unusually extensive evidence of mercury mobility and enrichment. The Franciscan Complex and Great Valley Sequence, which form the bedrock in the California Coast Ranges, are intruded and overlain by Tertiary volcanic rocks including the Clear Lake Volcanic Sequence. These rocks contain two types of mercury deposits, hot-spring deposits that form at shallow depths (< 300??m) and silica-carbonate deposits that extend to depths of 1000??m. Active springs and geothermal areas continue to precipitate Hg and Au and are modern analogues to the fossil hydrothermal systems preserved in the ore deposits. The Franciscan Complex and Great Valley Sequence contain clastic sedimentary rocks with higher concentrations of mercury than volcanic rocks of the Clear Lake Volcanic Field. Mean mercury isotopic compositions (??202Hg) for all three rock units are similar, although the range of values in Franciscan Complex rocks is greater than in either Great Valley or Clear Lake rocks. Hot spring and silica-carbonate mercury deposits have similar average mercury isotopic compositions that are indistinguishable from averages for the three rock units, although ??202Hg values for the mercury deposits have a greater variance than the country rocks. Precipitates from spring and geothermal waters in the area have similarly large variance and a mean ??202Hg value that is significantly lower than the ore deposits and rocks. These observations indicate that there is little or no isotopic fractionation (< ?? 0.5???) during release of mercury from its source rocks into hydrothermal solutions. Isotopic fractionation does appear to take place during transport and concentration of mercury in deposits, however, especially in their uppermost parts. Boiling of hydrothermal fluids, separation of a mercury-bearing CO2 vapor

  3. Cretaceous shallow drilling, US Western Interior: Core research. Technical progress report

    SciTech Connect

    Arthur, M.A.

    1993-02-17

    This project is a continuing multidisciplinary study of middle to Upper Cretaceous marine carbonate and clastic rocks in the Utah-Colorado-Kansas corridor of the old Cretaceous seaway that extended from the Gulf Coast to the Arctic during maximum Cretaceous transgressions. It is collaborative between in the US Geological Survey (W.E. Dean, P.I.) and University researchers led by The Pennsylvania State University(M.A. Arthur, P.I.) and funded by DOE and the USGS, in part. Research focusses on the Greenhom, Niobrara and lower Pierre Shale units and their equivalents, combining biostratigraphic/paleoecologic studies, inorganic, organic and stable isotopic geochemical studies, mineralogical investigations and high-resolution geophysical logging. This research requires unweathered samples and continuous smooth ``exposures`` in the form of cores from at least 4 relatively shallow reference holes (i.e. < 1000m) in transect from east to west across the basin. The major initial effort was recovery in Year 1 of the project of continuous cores from each site in the transect. This drilling provided samples and logs of strata ranging from pelagic sequences that contain organic-carbon-rich marine source rocks to nearshore coal-bearing units. This transect also will provide information on the extent of thermal maturation and migration of hydrocarbons in organic-carbon-rich strata along a burial gradient.

  4. A total petroleum system of the Browse Basin, Australia; Late Jurassic, Early Cretaceous-Mesozoic

    USGS Publications Warehouse

    Bishop, M.G.

    1999-01-01

    The Browse Basin Province 3913, offshore northern Australia, contains one important petroleum system, Late Jurassic, Early Cretaceous-Mesozoic. It is comprised of Late Jurassic through Early Cretaceous source rocks deposited in restricted marine environments and various Mesozoic reservoir rocks deposited in deep-water fan to fluvial settings. Jurassic age intraformational shales and claystones and Cretaceous regional claystones seal the reservoirs. Since 1967, when exploration began in this 105,000 km2 area, fewer than 40 wells have been drilled and only one recent oil discovery is considered potentially commercial. Prior to the most recent oil discovery, on the eastern side of the basin, a giant gas field was discovered in 1971, under a modern reef on the west side of the basin. Several additional oil and gas discoveries and shows were made elsewhere. A portion of the Vulcan sub-basin lies within Province 3913 where a small field, confirmed in 1987, produced 18.8 million barrels of oil (MMBO) up to 1995 and has since been shut in.

  5. On the location of microseismic sources in instable rock slope areas: heterogeneous vs. homogenous 3D velocity models

    NASA Astrophysics Data System (ADS)

    Coviello, Velio; Manconi, Andrea; Occhiena, Cristina; Arattano, Massimo; Scavia, Claudio

    2013-04-01

    Rock-falls are one of the most common and hazardous phenomena occurring in mountainous areas. The formation of cracks in rocks is often accompanied by a sudden release of energy, which propagates in form of elastic waves and can be detected by a suitable transducer array. Therefore, geophones are among the most effective monitoring devices to investigate eventual precursors of rock-fall phenomena. However, the identification of an efficient procedure to forecast rock-fall occurrence in space and time is still an open challenge. In this study, we aim at developing an efficient procedure to locate microseismic sources relevant to cracking mechanisms, and thus gather indications on eventual precursors of rock-fall phenomena. Common seismic location tools usually implement homogeneous or multilayered velocity models but, in case of high slope gradients and heavily fractured rock masses, these simplifications may lead to errors on the correct estimation of the source location. Thus, we analyzed how the consideration of 3D material properties on the propagation medium may influence the location. In the framework of the Alcotra 2007-2013 Project MASSA (Medium And Small Size rock-fall hazard Assessment), a monitoring system composed by 8 triaxial geophones was installed in 2010 at the J.A. Carrel hut (3829 m a.s.l., Matterhorn, NW Italian Alps) and during the first year of operation the network recorded more than 600 natural events that exceeded a fixed threshold [1]. Despite the harsh environmental conditions of the study area, eighteen points distributed as uniformly as possible in space were selected for hammering. The artificial source dataset of known coordinates was used to constrain a 3D heterogeneous velocity model through a Simultaneous Iterative Reconstructive Technique. In order to mitigate the intrinsic uncertainties of the inversion procedure, bootstrapping was performed to extend the dataset and a statistical analysis was issued to improve the model

  6. Oxygen isotope constraints on the origin of impact glasses from the cretaceous-tertiary boundary

    SciTech Connect

    Blum, J.D.; Chamberlain, C.P. )

    1992-08-21

    Laser-extraction oxygen isotope and major element analyses of individual glass spherules from Haitian Cretaceous-Tertiary boundary sediments demonstrate that the glasses fall on a mixing line between an isotopically heavy ({delta}{sup 18}O = 14 per mil) high-calcium composition and an isotopically light ({delta}{sup 18}O = 6 per mil) high-silicon composition. This trend can be explained by melting of heterogeneous source rocks during the impact of an asteroid (or comet) {approximately}65 million years ago. The data indicate that the glasses are a mixture of carbonate and silicate rocks and exclude derivation of the glasses either by volcanic processes or as mixtures of sulfate-high evaporate and silicate rocks.

  7. Melt production, redistribution and accumulation in mid-crustal source rocks, with implications for crustal-scale melt transfer

    NASA Astrophysics Data System (ADS)

    Diener, Johann F. A.; White, Richard W.; Hudson, Timothy J. M.

    2014-07-01

    Ascent of granitic melt initiates under suprasolidus conditions in the mid- to lower crust before continuing through subsolidus rocks to higher crustal levels. Whereas migration of melt in suprasolidus rocks can occur in pervasive net-like structures and involve relatively small melt volumes, ascent through the subsolidus crust requires more focused, dyke-like structures and larger volumes to prevent freezing. Migmatites in the Aus granulite terrain, southern Namibia, preserve evidence that large-scale melt redistribution and accumulation occurred in the near-source region under suprasolidus conditions. Melt that was mainly produced in metapelitic rocks utilised pervasive small-scale leucosome networks to migrate to areas surrounding pre-tectonic granite sheets. These areas are dominated by metapsammitic rocks, and abundant and voluminous leucogranite sheets attest to melt accumulation and residence occurring over a protracted period while the area was undergoing anatexis. However, the leucogranites have an anhydrous mineralogy and the surrounding rocks only preserve evidence for limited, high-temperature retrogression, consistent with substantial melt loss from the accumulation structures. We speculate that melt batches leaving the accumulation sites are likely to have been large, allowing for substantially more efficient ascent through subsolidus crust. Our results suggest that a degree of near-source melt accumulation is likely to occur during the early stages of meltmigration, and that this can significantly enhance the effectiveness of subsequent melt ascent.

  8. Petroleum source rock richness, type and maturity for four rock units on the Alaskan North Slope: are they sources for the two oil types

    SciTech Connect

    Magoon, L.B.; Claypool, G.E.

    1983-01-01

    A comprehensive petroleum geochemical study assessed the petroleum resources on the Alaskan North Slope. The collection and interpretation of geochemical data not only from exploratory wells drilled in the National Petroleum Reserve in Alaska (NPRA) but also from wells drilled to the east in the Prudhoe Bay area and from rocks exposed in the Arctic National Wildlife Refuge and in the Brooks Range from Cape Lisburne to the United States/Canadian border were studied. More than 17 different kinds of rock analyses, eight different oil analyses, and three gas analyses are being used to evaluate rock (outcrop samples, core, drill cuttings), oil (seeps, drill stem test, oil-stained core, producing well), and gas (drill stem test, producing well) samples on the North Slope. To date, the more than 60,000 analyses completed on these samples were placed into a computer-based file for storage and retrieval in tabular, graphical, or map form numerous graphical software programs were written to facilitate interpretation.

  9. Natural arsenic in Triassic rocks: A source of drinking-water contamination in Bavaria, Germany

    NASA Astrophysics Data System (ADS)

    Heinrichs, Gerold; Udluft, Peter

    The aquifer system of the Upper Triassic Keuper Sandstone, an important source of drinking water in northern Bavaria, is affected by elevated arsenic concentrations. Within the study area of 8000km2, no evidence exists for any artificial source of arsenic. Data from about 500 deep water wells show that in approximately 160 wells arsenic concentrations are 10-150μg/L. The regional distribution of arsenic in the groundwater shows that elevated arsenic concentrations are probably related to specific lithofacies of the aquifers that contain more sediments of terrestrial origin. Geochemical measurements on samples from four selected well cores show that arsenic has accumulated in the rocks. This indigenous arsenic is the source of arsenic in the groundwater of certain facies of the middle unit of the Keuper Sandstone. Résumé Le système aquifère des grès du Keuper, ressource en eau potable importante du nord de la Bavière, est marqué par des concentrations en arsenic élevées. Dans la région étudiée, qui s'étend sur 8000km2, il n'existe aucun indice d'une source artificielle d'arsenic. Les données provenant d'environ 500 puits profonds montrent que dans environ 160 puits les concentrations en arsenic sont comprises entre 10-150μg/L. La distribution régionale de l'arsenic dans les eaux souterraines montre que les concentrations élevées en arsenic sont probablement associées à des lithofaciès spécifiques qui contiennent plus de sédiments d'origine continentale. Des analyses géochimiques sur des échantillons provenant des carottes de quatre puits sélectionnés montrent que l'arsenic s'est accumulé dans ces roches. L'arsenic autochtone est la source de l'arsenic dans les eaux souterraines de certains faciès de l'unité médiane des grès du Keuper.

  10. Mineralogy of Apollo 15415 ?genesis rock' - Source of anorthosite on moon.

    NASA Technical Reports Server (NTRS)

    Steele, I. M.; Smith, J. V.

    1971-01-01

    Results of electron microprobe analyses of plagioclase points and pyroxene grains of Apollo 15415 ?genesis rock.' It is pointed out that no evidence of cumulate textures has yet appeared to support suggestions of extensive crystal-liquid differentiation producing an anorthositic crust or a lunar crust composed of a mixture of plagioclase-rich rock, basalts and minor ultramafic material, which require that plagioclase crystals float in a basaltic liquid. The plagioclase in 15415 does not show cumulate texture either. It is noted that it remains to be seen whether rock 15415 is correctly named the ?genesis rock.'

  11. 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.

  12. Early Cretaceous arc volcanic suite in Cebu Island, Central Philippines and its implications on paleo-Pacific plate subduction: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deng, Jianghong; Yang, Xiaoyong; Zhang, Zhao-Feng; Santosh, M.

    2015-08-01

    The Philippine island arc system is a collage of amalgamated terranes of oceanic, continental and island arc affinities. Here we investigate a volcanic suite in Cebu Island of central Philippines, including basalt, diabase dike, basaltic pyroclastic rock and porphyritic andesite. LA-ICP-MS U-Pb geochronology of zircon grains from the porphyritic andesite and pyroclastic rock yielded ages of 126 ± 3 Ma and 119 ± 2 Ma, respectively, indicating an Early Cretaceous age. The age distribution of the detrital zircons from river sand in the area displays a peak at ca. 118 Ma, close to the age of the pyroclastic rock. The early Cretaceous volcanic rocks in the central Philippines were previously regarded as parts of ophiolite complexes by most investigators, whereas the Cebu volcanics are distinct from these, and display calc-alkaline affinity and island arc setting, characterized by high LREE/HREE ratios and low HFSE contents. These features are similar to the Early Cretaceous arc basalts in the Amami Plateau and east Halmahera in the northernmost and southernmost West Philippine Basin respectively. Zircon Hf isotopes of the pyroclastic rocks show depleted nature similar to those of the Amami Plateau basalts, implying the subducted Pacific-type MORB as probable source. Zircon Hf isotopes of the porphyritic andesite show slight enrichment relative to that of the pyroclastic rocks and MORB, indicating subducted sediments as a minor end-member in the source. The Hf isotopic compositions of the volcanic rocks are also reflected in the detrital zircons from the river sands. We propose that the volcanic rocks of Cebu Island were derived from partial melting of sub-arc mantle wedge which was metasomatized by dehydration of subducted oceanic crust together with minor pelagic sediments. Within the tectonic environment of Southeast Asia during Early Cretaceous, the volcanic rocks in Cebu Island can be correlated to the subduction of paleo-Pacific plate. The Early Cretaceous

  13. Magmatismes tholéiitique et alcalin des demi-grabens crétacés de Mayo Oulo Léré et de Babouri Figuil (Nord du Cameroun Sud du Tchad) en domaine d'extension continentaleTholeiitic and alkaline magmatisms of the Early-Cretaceous half-grabens of Mayo Oulo Léré and Babouri Figuil (Northern Cameroon Southern Chad) in extensional structural settings

    NASA Astrophysics Data System (ADS)

    Ngounouno, Ismaı̈la; Déruelle, Bernard; Guiraud, René; Vicat, Jean-Paul

    2001-08-01

    Two major dykes of basalts, microgabbros, olivine dolerites (continental tholeiites), and of camptonites and benmoreites (alkaline rocks) are respectively exposed in the Mayo Oulo-Léré and Babouri-Figuil Early Cretaceous half-grabens (Northern Cameroon-Southern Chad). The tholeiites were probably derived from an asthenospheric source in connection with a lithospheric thinning occurring between Santonian and Eocene times. In contrast, the alkaline rocks may be derived from a deeper metasomatized mantle source.

  14. Rocks of the Thirtynine Mile volcanic field as possible sources of uranium for epigenetic deposits in central Colorado, USA.

    USGS Publications Warehouse

    Dickinson, K.A.

    1987-01-01

    The most likely volcanic source rock for uranium in epigenetic deposits of the Tallahassee Creek uranium district and nearby areas is the Wall Mountain Tuff. The widespread occurrence of the Tuff, its high apparent original uranium content, approx 11 ppm, and its apparent loss of uranium from devitrification and other alteration suggest its role in providing that element. An estimate of the original Th/U ratio is based on the present thorium and uranium contents of the basal vitrophyre of the Tuff from Castle Rock Gulch, Hecla Junction and other areas.-from Author

  15. 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

  16. 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.

  17. 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.

  18. Monterey source rock facies and petroleum formation - a synthesis of results of the cooperative Monterey organic geochemistry study

    SciTech Connect

    Rullkoetter, J.; Isaacs, C.M.

    1996-12-31

    Based on the analysis of two carefully selected coastal outcrop series of Monterey rocks and a suite of eleven crude oils from the onshore and offshore Santa Maria and Santa Barbara-Ventura basins, an interlaboratory effort was undertaken (i) to characterize organic-matter-rich sections of the source rock geochemically in terms of changes in depositional environment and (ii) to assess the effect of these variations on crude oil composition. Despite intra - and interbasinal variations in organic carbon enrichment and hydrogen richness, the organic matter appears to be largely derived from a common planktonic source. Differences in organic matter quality are primarily attributed to different extents of early diagenetic alteration, most probably by sulfate-reducing bacteria in the pore water, while differences in organic matter enrichment are suggested to essentially indicate varying levels of dilution and dissolution of biogenic mineral matter. Prolific source rock horizons with hydrogen-rich organic matter were found at the Lions Head section, whereas the Naples Beach section in general represents more highly microbially altered organic matter with lower hydrogen contents according to Rock-Eval pyrolysis. Although petroleum generation in many cases occurred at low levels of thermal stress, distinct molecular indicators suggest a significant range of maturity values among the oils investigated. Maturation behavior is clearly related to sulfur content. Maturity evolution of South Elwood oils differing from those of other oils may be organofacies related but possibly also related to local heating rate anomalies.

  19. Monterey source rock facies and petroleum formation - a synthesis of results of the cooperative Monterey organic geochemistry study

    SciTech Connect

    Rullkoetter, J. ); Isaacs, C.M. )

    1996-01-01

    Based on the analysis of two carefully selected coastal outcrop series of Monterey rocks and a suite of eleven crude oils from the onshore and offshore Santa Maria and Santa Barbara-Ventura basins, an interlaboratory effort was undertaken (i) to characterize organic-matter-rich sections of the source rock geochemically in terms of changes in depositional environment and (ii) to assess the effect of these variations on crude oil composition. Despite intra - and interbasinal variations in organic carbon enrichment and hydrogen richness, the organic matter appears to be largely derived from a common planktonic source. Differences in organic matter quality are primarily attributed to different extents of early diagenetic alteration, most probably by sulfate-reducing bacteria in the pore water, while differences in organic matter enrichment are suggested to essentially indicate varying levels of dilution and dissolution of biogenic mineral matter. Prolific source rock horizons with hydrogen-rich organic matter were found at the Lions Head section, whereas the Naples Beach section in general represents more highly microbially altered organic matter with lower hydrogen contents according to Rock-Eval pyrolysis. Although petroleum generation in many cases occurred at low levels of thermal stress, distinct molecular indicators suggest a significant range of maturity values among the oils investigated. Maturation behavior is clearly related to sulfur content. Maturity evolution of South Elwood oils differing from those of other oils may be organofacies related but possibly also related to local heating rate anomalies.

  20. REDBACK: an Open-Source Highly Scalable Simulation Tool for Rock Mechanics with Dissipative Feedbacks

    NASA Astrophysics Data System (ADS)

    Poulet, T.; Veveakis, M.; Paesold, M.; Regenauer-Lieb, K.

    2014-12-01

    Multiphysics modelling has become an indispensable tool for geoscientists to simulate the complex behaviours observed in their various fields of study where multiple processes are involved, including thermal, hydraulic, mechanical and chemical (THMC) laws. This modelling activity involves simulations that are computationally expensive and its soaring uptake is tightly linked to the increasing availability of supercomputing power and easy access to powerful nonlinear solvers such as PETSc (http://www.mcs.anl.gov/petsc/). The Multiphysics Object-Oriented Simulation Environment (MOOSE) is a finite-element, multiphysics framework (http://mooseframework.org) that can harness such computational power and allow scientists to develop easily some tightly-coupled fully implicit multiphysics simulations that run automatically in parallel on large clusters. This open-source framework provides a powerful tool to collaborate on numerical modelling activities and we are contributing to its development with REDBACK (https://github.com/pou036/redback), a module for Rock mEchanics with Dissipative feedBACKs. REDBACK builds on the tensor mechanics finite strain implementation available in MOOSE to provide a THMC simulator where the energetic formulation highlights the importance of all dissipative terms in the coupled system of equations. We show first applications of fully coupled dehydration reactions triggering episodic fluid transfer through shear zones (Alevizos et al, 2014). The dimensionless approach used allows focusing on the critical underlying variables which are driving the resulting behaviours observed and this tool is specifically designed to study material instabilities underpinning geological features like faulting, folding, boudinage, shearing, fracturing, etc. REDBACK provides a collaborative and educational tool which captures the physical and mathematical understanding of such material instabilities and provides an easy way to apply this knowledge to realistic

  1. Petrogenetic modeling of a potential uranium source rock, Granite Mountains, Wyoming

    USGS Publications Warehouse

    Stuckless, J.S.; Miesch, A.T.

    1981-01-01

    Previous studies of the granite of Lankin Dome have led to the conclusion that this granite was a source for the sandstone-type uranium deposits in the basins that surround the Granite Mountains, Wyo. Q-mode factor analysis of 29 samples of this granite shows that five bulk compositions are required to explain the observed variances of 33 constituents in these samples. Models presented in this paper show that the origin of the granite can be accounted for by the mixing of a starting liquid with two ranges of solid compositions such that all five compositions are granitic. There are several features of the granite of Lankin Dome that suggest derivation by partial melting and, because the proposed source region was inhomogeneous, that more than one of the five end members may have been a liquid. Data for the granite are compatible with derivation from rocks similar to those of the metamorphic complex that the granite intrudes. Evidence for crustal derivation by partial melting includes a strongly peraluminous nature, extremely high differentiation indices, high contents of incompatible elements, generally large negative Eu anomalies, and high initial lead and strontium isotopic ratios. If the granite of Lankin Dome originated by partial melting of a heterogeneous metamorphic complex, the initial magma could reasonably have been composed of a range of granitic liquids. Five variables were not well accounted for by a five-end-member model. Water, CO 2 , and U0 2 contents and the oxidation state of iron are all subject to variations caused by near-surface processes. The Q-mode factor analysis suggests that these four variables have a distribution determined by postmagmatic processes. The reason for failure of Cs0 2 to vary systematically with the other 33 variables is not known. Other granites that have lost large amounts of uranium possibly can be identified by Q-mode factor analysis.

  2. Origin of continental arc andesites: The composition of source rocks is the key

    NASA Astrophysics Data System (ADS)

    Chen, Long; Zhao, Zi-Fu

    2017-09-01

    The generation of continental arc andesites is generally attributed to subduction of oceanic slabs beneath continental margins, but the origin of crustal components in andesites and the petrogenetic processes of andesites remain widely debated. Common hypotheses include differentiation and crustal contamination of the mantle-derived basaltic magmas, subducted oceanic igneous rock melting and subsequent melt-peridotite interaction, relamination and melting of the subducted sediment, and partial melting of the hydrous mantle wedge peridotite. Because the relatively enriched signature of radiogenic isotope composition is generally comparable between andesites and their emplaced continental crust, the crustal contamination at the crust-mantle transition zone is often envisaged in the hypotheses for andesite petrogenesis. However, these hypotheses are not compatible with quantitative constraints from the mass balance of major elements, trace elements and their pertinent radiogenic isotopes in andesites. On the other hand, source mixing is another possible mechanism for incorporation of crustal components into the mantle source of andesitic magmas. This is realized by reaction of the mantle wedge peridotite with hydrous felsic melts that derived from partial melting of the subducted oceanic crust. Based on compilation and analysis of the geochemical data for basaltic and andesitic volcanics from the Middle and Lower Yangtze Valley, a SARSH (subduction, anataxis, reaction, storage and heating) model is advocated for andesite petrogenesis above oceanic subduction zones. According to this model, the sediment weathered from the overlying continental margin was subducted with the oceanic slab, and it then underwent dehydration and melting at subarc depths. This gives rise to the hydrous felsic melts for crustal metasomatism of the mantle wedge, generating the mantle source that is mafic in lithochemistry and enriched in trace elements and their pertinent radiogenic isotopes

  3. Thermal and petroleum-generation history of the Mississippian Eleana Formation and Tertiary source rocks, Yucca Mountain Area, Southern Nye County, Nevada

    SciTech Connect

    Barker, C.E.

    1995-06-01

    A geochemical and geologic assessment of petroleum potential in the Yucca Mountain area indicates little remaining potential for significant oil and gas generation in the Mississippian Eleana Formation or related Paleozoic rocks, and good but a really restricted potential in Tertiary rocks in Area 8 of the Nevada Test Site. Mesozoic source rocks are not present in the Yucca Mountain area. The Tertiary source rocks in Area 8 of the Nevada Test Site are typically carbon-rich, and where hydrogen-rich, they are good oil-prone source rocks that are immature to marginally mature with respect to oil and gas generation. A geologically similar occurrence of hydrothermally altered Tertiary source rocks at north Bare Mountain retains little hydrocarbon generation capacity. The implication is that hydrocarbons were generated during hydrothermal alteration and have since migrated out of the source rocks or alive been lost during exhumation. A reconstructed thermal history of the Yucca Mountain area, based on the Eleana Formation, indicates petroleum was generated in the Late Paleozoic and possibly Early Mesozoic and that the oil was lost or metamorphosed to pyrobitumen during later heating, probably related to igneous activity. The Tertiary rocks are still capable of generating oil and gas, but little potential exists for a major hydrocarbon discovery due to the restricted occurrence of good source rocks and their marginal thermal maturity when situated away from intrusions.

  4. Fractured-rock aquifers, understanding an increasingly important source of water

    USGS Publications Warehouse

    Shapiro, Allen M.

    2002-01-01

    Ground water is one of the Nation?s most important natural resources. It provides drinking water to communities, supports industry and agriculture, and sustains streams and wetlands. A long record of contributions exists in understanding ground-water movement in sand and gravel aquifers; historically, these aquifers were easily accessible and the first to be investigated. With increased demand for water, communities are looking to fractured-rock aquifers, where water moves through fractures in the rock. Frac-tures, however, may not always convey or store large quantities of water. Understanding ground-water flow through fractured-rock aquifers is an area of ground-water research that will have increasing importance to our Nation over the coming years. Many areas of the United States rely on fractured-rock aquifers for water supply. In addition, areas experiencing population growth in the Northeast, Southeast, and mountainous regions of the West are likely to rely heavily on water supplies from fractured-rock aquifers. Finding water for thirsty communities, however, is not the only societal issue requiring an understanding of ground-water flow in fractured rock. Land-use practices affect water quality in fractured-rock aquifers, particularly where ground water flows rapidly through fractures. Fractured rock aquifers also are viewed as potential repositories for radioactive and other types of waste, where it is desirable for the ground water to be inaccessible or move at a very slow rate.

  5. Source rock potential and organic matter characterization of the Messinian evaporitic sequence on Zakynthos Island, Ionian Sea

    NASA Astrophysics Data System (ADS)

    Karakitsios, Vasileios; Kafousia, Nefeli; Agiadi, Konstantina; Kontakiotis, George; de Rafelis, Marc

    2017-04-01

    In this study, we investigate the hydrocarbon potential as well as the type and thermal maturity of the organic matter in the evaporitic sequence of Kalamaki and Agios Sostis sections (Zakynthos Island, Greece). Detailed sampling of the two sections was followed by analyses for the total organic carbon (TOC) content and the petroleum potential. In Kalamaki, the TOC values range is 0.03-1.31 wt%, 0.15-1.31 wt% in the pre-evaporitic sediments and 0.03-0.95 wt% in the evaporitic sequence, partially indicating fair to good hydrocarbon potential. Overall, our samples are classified principally as non-source rocks. The total of free and pyrolizable hydrocarbons range from 0.03 to 3.41 mg HC/g rock, corresponding to little or no source rock potential. The hydrocarbon index (HI)-TOC cross-plot suggests that the studied samples represent diverse source types ranging from gas-prone to oil-prone. This plot reveals that the most promising rock units are in the evaporitic sequence of Kalamaki. Nevertheless, the HI values of the samples range from 12.46 to 271.14 mg HC/g TOC, whereas the ratio of pyrolizable to free hydrocarbons ranges from 0.02 to 9.12. Therefore, the type of organic material in the studied sediments is classified as gas prone, with the exception of one sample that is classified as gas and oil prone. Based on the HI-oxygen index (OI) plot, most of the samples are type III kerogen derived from terrestrial plant debris deposited in oxidized environments capable of producing gas. A few samples only from the evaporitic sequence are type II (oil prone), and a few from the pre- and the evaporitic sequence are type IV. The cross-plot of free hydrocarbons against TOC indicates indigenous hydrocarbon production for all sediments. Furthermore, based on the production index (PI) and Tmax values, most samples from Kalamaki are immature. However, several samples from the evaporitic sequence have reached the mature oil stage. In addition, these organic-rich evaporitic

  6. U-Th-Pb in petroleum by LA-ICP-MS: Source rocks-crude oils comparison.

    NASA Astrophysics Data System (ADS)

    Gourlan, Alexandra T.; Ricard, Estelle; Prinzhofer, Alain; Christophe, Pecheyran; Donard, Olivier X. C.

    2010-05-01

    The U, Th elemental and Pb isotopic ratios in petroleum source rocks have been determined for the first time and compared with crude oils from different regions in the World using a femtosecond laser ablation (high ablation rates) coupled to an ICP-MS and direct analysis of digested samples on ICP-MS. The advantage of femtosecond compared to nanosecond laser ablation is that it drastically reduces thermal effects, minimizes isotope and elemental fractionation and matrix effects during chemical analysis of solid samples. Fs-Laser Ablation coupled to an ICP-MS is therefore a potentially valuable tool for the determination of trace metals in crude oils as well as in solid samples such as source rocks. The principal problems encountered arise from the lack of isotopic lead standards in organic matrixes and the heterogeneity of source rocks which contain sulphides with high natural U and Th concentrations. Therefore, to determine exactly the U, Th and Pb contents in source rocks, two analytical techniques have to be compared. In one, the use of the laser ablation allows us to analyze in-situ small parts of the organic materials and to determine the proportions of two end members: pure kerogene and pure sulphides. In the other, the use of the conventional dissolution of the same pellets involves total consumption of the sample and gives an average value of the isotopic lead ratios and U, Th and Pb concentrations of the bulk sample. For the two cases a "sample-standard bracketing" procedure was applied using NIST 612 glass standard for ablation and NIST 981 in aqueous solution for the mineralization. Due to the lack of organic matrix standards, the fs-LA-ICP-MS technique produces only qualitative trace element (U, Th and Pb) and isotopic analysis of source rocks. Our results obtained on both crude oils and associated source rocks have shown that Th, U, Pb systematics determined using the two analytical methods (mineralization of kerogen directly analyzed on ICP-MS or MC

  7. Organic geochemistry and petrology of oil source rocks, Carpathian Overthrust region, southeastern Poland - Implications for petroleum generation

    USGS Publications Warehouse

    Kruge, M.A.; Mastalerz, Maria; Solecki, A.; Stankiewicz, B.A.

    1996-01-01

    The organic mailer rich Oligocene Menilite black shales and mudstones are widely distributed in the Carpathian Overthrust region of southeastern Poland and have excellent hydrocarbon generation potential, according to TOC, Rock-Eval, and petrographic data. Extractable organic matter was characterized by an equable distribution of steranes by carbon number, by varying amounts of 28,30-dinor-hopane, 18??(H)-oleanane and by a distinctive group of C24 ring-A degraded triterpanes. The Menilite samples ranged in maturity from pre-generative to mid-oil window levels, with the most mature in the southeastern portion of the study area. Carpathian petroleum samples from Campanian Oligocene sandstone reservoirs were similar in biomarker composition to the Menilite rock extracts. Similarities in aliphatic and aromatic hydrocarbon distributions between petroleum asphaltene and source rock pyrolyzates provided further evidence genetically linking Menilite kerogens with Carpathian oils.

  8. 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.

  9. Evidence from the lamarck granodiorite for rapid late cretaceous crust formation in California

    USGS Publications Warehouse

    Coleman, D.S.; Frost, T.P.; Glazner, A.F.

    1992-01-01

    Strontium and neodymium isotopic data for rocks from the voluminous 90-million-year-old Lamarck intrusive suite in the Sierra Nevada batholith, California, show little variation across a compositional range from gabbro to granite. Data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source. Recognition of local involvement of enriched mantle during generation of the Sierran batholith modifies estimates of crustal growth rates in the United States. These data indicate that parts of the Sierra Nevada batholith may consist almost entirely of juvenile crust added during Cretaceous magmatism.

  10. Evidence from the lamarck granodiorite for rapid late cretaceous crust formation in california.

    PubMed

    Coleman, D S; Glazner, A F; Frost, T P

    1992-12-18

    Strontium and neodymium isotopic data for rocks from the voluminous 90-million-year-old Lamarck intrusive suite in the Sierra Nevada batholith, California, show little variation across a compositional range from gabbro to granite. Data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source. Recognition of local involvement of enriched mantle during generation of the Sierran batholith modifies estimates of crustal growth rates in the United States. These data indicate that parts of the Sierra Nevada batholith may consist almost entirely of juvenile crust added during Cretaceous magmatism.

  11. Lead isotopes tracing the life cycle of a catchment: From source rock via weathering to human impact

    NASA Astrophysics Data System (ADS)

    Negrel, P. J.; Petelet-Giraud, E.; Guerrot, C.; Millot, R.

    2015-12-01

    Chemical weathering of rocks involves consumption of CO2, a greenhouse gas with a strong influence on climate. Among rocks exposed to weathering, basalt plays a major role in the carbon cycle as it is more easily weathered than other crystalline silicate rocks. This means that basalt weathering acts as a major atmospheric CO2 sink. The present study investigated the lead isotopes in rock, soil and sediment for constraining the life cycle of a catchment, covering source rocks, erosion processes and products, and anthropogenic activities. For this, we investigated the Allanche river drainage basin in the Massif Central, the largest volcanic areas in France, that offers opportunities for selected geochemical studies since it drains a single type of virtually unpolluted volcanic rock, with agricultural activity increasing downstream. Soil and sediment are derived exclusively from basalt weathering, and their chemistry, coupled to isotope tracing, should shed light on the behavior of chemical species during weathering from parental bedrock. Bedrock samples of the basin, compared to regional bedrock of the volcanic province, resulted from a complex history and multiple mantle reservoir sources and mixing. Regarding soils and sediments, comparison of Pb and Zr normalized to mobile K shows a linear evolution of weathering processes, whereby lead enrichment from atmospheric deposition is the other major contributor. Lead-isotope ratios showed that most of the lead budget in sediment and soil results from bedrock weathering with an influence of past mining and mineral processing of ores in the Massif Central, and deposition of lead-rich particles from gasoline combustion, but no lead input from agricultural activity. A classic box model was used to investigate the dynamics of sediment transfer at the catchment scale, the lead behavior in the continuum bedrock-soil-sediment and the historical evolution of anthropogenic aerosol emissions.

  12. Comment on "207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the Central Anatolian crust, Turkey" - Boztug, D., Tichomirowa, M. & Bombach, K., 2007, JAES 31, 71-86

    NASA Astrophysics Data System (ADS)

    Göncüoglu, M. Cemal

    A continent-oceanic island arc collision model was proposed as a new geodynamic scenario for the evolution of the Cretaceous Central Anatolian granitoids in the Central Anatolian crystalline complex (CACC) by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust, Turkey. Journal of Asian Earth Sciences 31, 71-86]. The key aspects of this model include an intra-oceanic subduction in the Neotethyan Izmir-Ankara Ocean, formation of an island arc and its subsequent collision with the northern margin of the Tauride-Anatolide Platform. The identical scenario was initially proposed by Göncüoglu et al. (1992) [Göncüoglu, M.C., Erler, A., Toprak, V., Yalınız, K., Olgun, E., Rojay, B., 1992. Geology of the western Central Anatolian Massif, Part II: Central Areas. TPAO Report No: 3155, 76 p] . Moreover, the weighted mean values of the reported 207Pb-206Pb single-zircon evaporation ages by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb-206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust: Turkey. Journal of Asian Earth Sciences 31, 71-86] from A-type granitoids in the CACC seem to be miscalculated and contrast with the field data.

  13. Paleocene-Eocene potential source rocks in the Avengco Basin, Tibet: Organic geochemical characteristics and their implication for the paleoenvironment

    NASA Astrophysics Data System (ADS)

    Han, Zhongpeng; Xu, Ming; Li, Yalin; Wei, Yushuai; Wang, Chengshan

    2014-10-01

    The Avengco Basin is located in the western part of the Tibetan Plateau and is similar to the Nima Basin in the central part of the plateau and the Lunpola Basin in the eastern part in terms of sedimentary characteristics and tectonic settings, which are well known to provide a good source rock potential. However, the organic geochemical characteristics of the Paleocene-Eocene potential source rocks in the Avengco Basin have been under debate. Thirty-four marl and mudstone outcrop samples of the Niubao Formation in the Avengco Basin were collected and subjected to the following analyses: total organic carbon (TOC), Rock-Eval pyrolysis, stable carbon isotopes of kerogen, gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Here, we present the results indicating the organic matter of the upper Niubao Formation is mainly composed of Type II kerogen with a mixed source, which is dominated by algae. However, the lower Niubao Formation has the less oil-prone Type II-III kerogen, and the sources of the organic matter are mainly terrestrial plants with less plankton. In addition, the samples are thermally immature to marginally mature. The Niubao Formation was deposited in an anoxic-oxic environment which was brackish with an imperceptible stratified water column. The upper Niubao Formation has a medium to good hydrocarbon-generating potential. However, the lower Niubao Formation has a zero to poor hydrocarbon-generating potential.

  14. Cretaceous shallow drilling, U.S. Western Interior: Core research. Final technical report

    SciTech Connect

    Arthur, M.A.

    1998-07-08

    The primary objective of the project is to construct a subsurface transect of Cretaceous strata that were deposited in the Kansas-Colorado-Utah corridor, going from marine sequences that contain organic-carbon-rich hydrocarbon source rocks in Kansas and eastern Colorado to nearshore coal-bearing units in western Colorado and Utah. The drilling transect will provide continuous, unweathered samples for inorganic, organic, and isotopic geochemical studies and mineralogical investigations to determine the characteristics of hydrocarbon source rocks. This transect also will provide information on the extent of thermal maturation and migration of hydrocarbons in organic-carbon-rich strata along a burial gradient. In addition, the eastern Colorado hole will provide characteristics of an important fractured reservoir (the Pierre Shale) in the Florence oil field, the oldest continuously producing field in the United States (>100 years; 600 wells; >14 Mbbls).

  15. Petroleum source rock evaluation of the Sebahat and Ganduman Formations, Dent Peninsula, Eastern Sabah, Malaysia

    NASA Astrophysics Data System (ADS)

    Mustapha, Khairul Azlan; Abdullah, Wan Hasiah

    2013-10-01

    The Sebahat (Middle Miocene to Early Pliocene) and Ganduman (Early Pliocene to Late Pliocene) Formations comprise part of the Dent Group. The onshore Sebahat and Ganduman Formations form part of the sedimentary sequence within the Sandakan sub-basin which continues offshore in the southern portion of the Sulu Sea off Eastern Sabah. The Ganduman Formation lies conformably on the Sebahat Formation. The shaly Sebahat Formation represents a distal holomarine facies while the sandy Ganduman Formation represents the proximal unit of a fluvial-deltaic system. Based on organic geochemical and petrological analyses, both formations posses very variable TOC content in the range of 0.7-48 wt% for Sebahat Formation and 1-57 wt% for Ganduman Formation. Both formations are dominated by Type III kerogen, and are thus considered to be gas-prone based on HI vs. Tmax plots. Although the HI-Tmax diagram indicates a Type III kerogen, petrographic observations indicate a significant amount of oil-prone liptinite macerals. Petrographically, it was observed that significant amounts (1-17% by volume) of liptinite macerals are present in the Ganduman Formation with lesser amounts in the Sebahat Formation. Both formations are thermally immature with vitrinite reflectance values in the range of 0.20-0.35%Ro for Ganduman Formation and 0.25-0.44%Ro for Sebahat Formation. Although these onshore sediments are thermally immature for petroleum generation, the stratigraphic equivalent of these sediments offshore are known to have been buried to deeper depth and could therefore act as potential source rocks for gas with minor amounts of oil.

  16. Structurally dependent source rock maturity and kerogen facies, Estancia Basin, New Mexico

    SciTech Connect

    Broadhead, R.F.

    1995-06-01

    The Estancia basin of central New Mexico is an asymmetric, north-south trending structural depression that originated during the Pennsylvanian. The present-day basin covers 1,600 mi{sup 2} (4,100 km{sup 2}). It is bounded on the east by the late Paleozoic Pedernal uplift, on the west by the Tertiary-age Manzano and Los Pinos Mountains, on the north by the Espanola basin, and on the south by Chupadera Mesa. Depth to Precambrian basement ranges from 9,000 ft (2,700 m) in a narrow graben in the eastern part of the basin to less than 1,500 ft (460 m) on a shelf to the west. Basin fill consists primarily of Pennsylvanian and Wolfcampian sandstones and shales in the graben and sandstones, shales, and marine limestones on the shelf Mature to marginally mature dark-gray to black Pennsylvanian shales are probable source rocks. Thermal Alteration Index ranges from 2.0 to 3.2. Shales become thermally mature with depth in the eastern graben. On the western shelf, shales become mature to the west as a result of increased heating from the Rio Grande rift. Total organic carbon exceeds 0.5% in many shales, sufficient for hydrocarbon generation. Kerogen types are mixed algal, herbaceous, and woody, indicating that gas, or possibly gas mixed with oil, was generated. Kerogens in shales of the eastern graben are entirely continental, gas-prone types. In limestones and shales of the western shelf, kerogens have a mixed marine and continental provenance, indicating that both oil and gas may have been generated on thermally mature parts of the shelf.

  17. [DWT-iPLS applied in the infrared diffuse reflection spectrum of hydrocarbon source rocks].

    PubMed

    Song, Ning; Xu, Xiao-xuan; Wu, Zhong-chen; Zhang, Cun-zhou; Wang, Bin

    2008-08-01

    Infrared spectroscopy is useful to monitor the quality of products on-line, or to quality multivariate properties simultaneously. The IR spectrometer satisfies the requirements of users who want to have quantitative product information in real-time because the instrument provides the information promptly and easily. However, Samples that are measured using diffuse reflectance often exhibit significant differences in the spectra due to the non-homogeneous distribution of the particles. In fact, multiple spectral measurements of the same sample can look completely different. In many cases, the scattering can be an overpowering contributor to the spectrum, sometimes accounting for most of the variance in the data. Although the degree of scattering is dependent on the wavelength of the light that is used and the particle size and refractive index of the sample, the scattering is not uniform throughout the spectrum. Typically, this appears as a baseline shift, tilt and sometimes curvature, where the degree of influence is more pronounced at the longer-wavelength end of the spectrum. The diffuse reflection spectrum is unsatisfactory and the calibration may provide unsatisfactory prediction results. So we must use some methods to remove the effects of the scattering for multivariate calibration of IR spectral signals. Discrete wavelet transform (DWT) is a good method to remove the effects of the scattering for multivariate calibration of IR spectral signals. By using DWT on individual signals as a preprocessing method in regression modeling on IR spectra, good compression is achieved with almost no loss of information, the low-frequency varying background and the high-frequency noise be removed simultaneously. In this report, we use the iPLS method to establish the calibration models of hydrocarbon source rocks. iPLS is a new regression method and the authors can get better results by using DTW- iPLS.

  18. Geochemical and detrital mode evidence for two sources of Early Proterozoic sedimentary rocks from the Tonto Basin Supergroup, central Arizona

    NASA Astrophysics Data System (ADS)

    Condie, Kent C.; Noll, Phillip D.; Conway, Clay M.

    1992-04-01

    The Tonto Basin Supergroup includes up to 6.5 km of Early Proterozoic sedimentary and volcanic rocks that were deposited in a relatively short period of time at about 1.7 Ga in central Arizona. Moderate correlations of rare earth elements (REE) and Ti with Al 2O 3 and REE distributions in detrital sediments of this supergroup suggest that these elements are contained chiefly in clay-mica and/or zircon fractions. REE distributions, including negative Eu anomalies in most Tonto Basin sediments, are similar to those in Phanerozoic shales. Weak to moderate correlations of Fe, Sc, Ni, and Co to Al 2O 3 also suggest a clay-mica control of these elements. Detrital modes and geochemical characteristics of sediments indicate two dominant sources for sedimentary rocks of the Tonto Basin Supergroup: a granitoid source and a volcanic source. The granitoid source was important during deposition of the upper part of the succession (the Mazatzal Group) as shown by increases in K 2O, Al 2O 3, and Th in pelites with stratigraphic height, and increases in Zr and Hf and decreases in Eu/Eu ∗, Cr, and Ni in in pelites of the Maverick Shale. Sediment provenance characteristics and paleocurrent indicators are consistent with deposition of the supergroup in a continental-margin back-arc basin. The granitoid sediment source appears to have been the North American craton on the north, and the volcanic source a more local source from an arc on the south.

  19. Geochemical and detrital mode evidence for two sources of Early Proterozoic sedimentary rocks from the Tonto Basin Supergroup, central Arizona

    USGS Publications Warehouse

    Condie, K.C.; Noll, P.D.; Conway, C.M.

    1992-01-01

    The Tonto Basin Supergroup includes up to 6.5 km of Early Proterozoic sedimentary and volcanic rocks that were deposited in a relatively short period of time at about 1.7 Ga in central Arizona. Moderate correlations of rare earth elements (REE) and Ti with Al2O3 and REE distributions in detrital sediments of this supergroup suggest that these elements are contained chiefly in clay-mica and/or zircon fractions. REE distributions, including negative Eu anomalies in most Tonto Basin sediments, are similar to those in Phanerozoic shales. Weak to moderate correlations of Fe, Sc, Ni, and Co to Al2O3 also suggest a clay-mica control of these elements. Detrital modes and geochemical characteristics of sediments indicate two dominant sources for sedimentary rocks of the Tonto Basin Supergroup: a granitoid source and a volcanic source. The granitoid source was important during deposition of the upper part of the succession (the Mazatzal Group) as shown by increases in K2O, Al2O3, and Th in pelites with stratigraphic height, and increases in Zr and Hf and decreases in Eu/Eu*, Cr, and Ni in in pelites of the Maverick Shale. Sediment provenance characteristics and paleocurrent indicators are consistent with deposition of the supergroup in a continental-margin back-arc basin. The granitoid sediment source appears to have been the North American craton on the north, and the volcanic source a more local source from an arc on the south. ?? 1992.

  20. Methane-derived authigenic carbonates of mid-Cretaceous age in southern Tibet: Types of carbonate concretions, carbon sources, and formation processes

    NASA Astrophysics Data System (ADS)

    Liang, Huimin; Chen, Xi; Wang, Chengshan; Zhao, Dekun; Weissert, Helmut

    2016-01-01

    Methane-derived authigenic carbonates with distinctive structures and morphologies have been documented worldwide, but they are rarely found from ancient strata in the Eastern Tethys Ocean. The methane-derived authigenic carbonates found in southern Tibet are developed in calcareous or silty shales of mid-Cretaceous age in the Xigaze forearc basin and in the Tethyan Himalaya tectonic zone. The morphology, mineralogy, elemental geochemistry and composition of carbon and oxygen isotopes of these carbonates are studied in detail. The carbonates have nodular, tubular, and tabular morphologies. They are primarily composed of carbonate cement that binds and partly replaces host sediment grains; host siliciclastic sediments are composed mainly of quartz and plagioclase feldspar; a few foraminifers; and framboidal or subhedral to euhedral pyrite. Carbonate cements dominantly are micritic calcite, with minor contribution of dolomite. Nodular concretions are characterized by depleted δ13C values, commonly ranging from -30‰ to -5‰. The δ13C values show a gradual decrease from the periphery to the center, and the CaO, SiO2, Fe2O3, Al2O3, K2O, and TiO2 contents generally show a gradual change. These features indicate that the nodular concretions grew from an early-formed center toward the periphery, and that the carbon source of the nodular concretions was derived from a mixture of methane, methanogenic CO2, and seawater-dissolved inorganic carbon. The tubular concretions are characterized by δ13C values of -8.85‰ to -3.47‰ in the Shangba Section, and -27.37‰ to -23.85‰ in the upper Gamba Section. Unlike the nodular concretions, the tubular concretions show central conduits, which are possible pathways of methane-rich fluids, suggesting that the cementation of tubular concretions begins at the periphery and proceeds inward. Moreover, the tubular concretions show morphological similarity with the methane-derived carbonate chimneys, pipes and slabs reported in

  1. Source rocks, thermal history and oil in the Carson Sink and Buena Vista Valley, west central Nevada

    SciTech Connect

    Barker, C.E.

    1995-06-01

    Rock-Eval, gas chromatography, mass spectrometry, and thermal history reconstruction data from six wells suggest that Tertiary rocks in the Carson Sink and Buena Vista Valley areas are marginally mature to overmature with respect to hydrocarbon generation and have locally expelled oil. The lacustrine Tertiary calcareous mudstones and marls in these wells have a total organic carbon (TOC) range from 0.1 to 3 wt.-%, with modes at about 0.5 to 0.7, 1.5, and 2 to 3 wt-% TOC. However, in the Standard Amoco Carson Sink 1 well, some of these samples have up to 3 wt-% less TOC than reported by Hastings (1979) and these are thought to represent drill cutting samples that have been depleted in more TOC rich rock chips. Even if the TOC data are biased, these TOC-depleted samples are still oil-prone rocks, with hydrogen indices commonly above 400 mg hydrocarbon/g C, and some samples with TOC in the 2-3 wt.-% range. Analysis of an oil show at Kyle Hot Springs in Buena Vista Valley revealed a wax-rich, low sulfur oil probably from a carbonate-rich, hypersaline lacustrine source rock. This oil could be generated from strata similar to those analyzed above. Other Tertiary source rocks in the two valleys consist of lenses of humic coals that appear to be gas prone. Shows of biogenic(?) gas from shallow wells in Tertiary to Holocene lacustrine strata are common in the Carson Sink. Mesozoic rocks locally may have remaining hydrocarbon generation potential in the Stillwater Range which lie along the eastern margin of the Carson Sink. Published conodont alteration index data shows that the Paleozoic rocks are overmature. Reconstructed thermal histories of the Carson Sink and Buena Vista Valley areas, indicate petroleum is presently being generated. Mechanisms for petroleum generation are rapid burial (140 m/m.y.) in a high geothermal gradient (45 to 110{degrees}C/km), and hydrothermal and contact metamorphism.

  2. A Multi-technique Approach for Provenance Studies of Mesozoic Clastic Rocks in the Barents Sea

    NASA Astrophysics Data System (ADS)

    Matthews, N. E.; Zimmermann, U.; Støle, L.; Ruud, C.; Mostafa, E.; Andò, S.; Borromeo, L.; Magnaghi, M.; Lapen, T. J.

    2015-12-01

    Sediments of Mesozoic age deposited in the Arctic Hammerfest and Tromsø basins (southern Barents Sea) are the focus of a comprehensive provenance study which forms part of ongoing work by the LoCrA consortium (Lower Cretaceous Basin Studies in the Arctic). Jurassic (Stø, Fuglen, Hekkingen) and Cretaceous (Knurr, Kolje, Kolmule) formations were sampled from seven wells. Analytical methods include petrography, whole-rock geochemistry, heavy mineral (HM) analysis and U-Pb on detrital zircons. HM concentration is <1%, with an ultrastable HM assemblage of zircon, rutile, tourmaline, spinel, apatite, garnet, chloritoid and common authigenic heavy minerals and opaques. Cretaceous sedimentary rocks show geochemical variations that reflect an unrecycled Upper Continental Crust signature, whereas Jurassic detritus tends to show more evidence of recycling with a relatively low input of mafic material. Kolmule Formation whole-rock geochemistry indicates sediment recycling from a major Sc-depleted but intermediate to mafic source and hence suggests input of rift detritus from the syn-depositional opening of the Atlantic Ocean. U-Pb ages for detrital zircons for Cretaceous sandstones show age groups of 200-500 Ma, 1200-1800 Ma, and 2100-2800 Ma, indicating potential source regions in the Urals/Novaya Zemlya, the Caledonides, Grenvillian/Sveconorwegian, and Palaeoproterozoic and Archean sources. Provenance data via geochemistry and HM analysis indicate different sources in the same formation basin-wide, with a significant change in provenance and sediment composition from Jurassic to Cretaceous and between the Knurr and Kolmule formations. These differences in composition need to be compared to detailed single grain studies and may only be explained in terms of basin dynamics, or even on a smaller scale, in terms of facies distributions. If so, this case study raises concerns about the use of single samples for provenance models on a larger scale.

  3. Paleoenvironments, organic petrology and Rock-Eval studies on source rock facies of the Lower Maastrichtian Patti Formation, southern Bida Basin, Nigeria

    NASA Astrophysics Data System (ADS)

    Akande, S. O.; Ojo, O. J.; Erdtmann, B. D.; Hetenyi, M.

    2005-06-01

    The southern Bida Basin in central Nigeria forms a part of the larger Bida or Middle Niger Basin, which is contiguous with the south east trending (petroliferous) Anambra Basin. These basins were major depocenters for Campanian-Maastrichtian sediments in southern and central Nigeria prior to the build up of the Tertiary Niger delta. The successions in the southern Bida Basin consist of the basal Lokoja Formation, overlain by the Patti Formation and capped by the Agbaja Formation. The Lokoja Formation is a sequence of matrix supported conglomerates and sandstones overlying the Pre-Cambrian to Lower Paleozoic basement. Depositional environments are predominantly within fluvial systems of a continental setting. The Patti Formation consists of dark grey carbonaceous shales; mudstone and siltstones representing flood plains to shallow marine deposits with likely organic rich intervals. The overlying Agbaja Formation is made up of ferruginised oolitic and kaolinitic mudstone of a marginal marine environment. Twenty samples of shales of the Patti Formation were studied by incident light microscopy and geochemical analysis to determine the maceral components, geochemical type and potential yield of the pyrolysate. Maceral analysis indicate a large abundance of vitrinite (50-85%; mean = 66%); moderate abundance of liptinites (10-33%; mean = 18%) and lesser amounts of inertinite (9-40%; mean = 16%). Total organic carbon (TOC) values vary from 0.17 to 3.8 wt.% (mean = 2.1 wt.%) with most samples having greater than 2 wt.% TOC. Three of the samples yield greater than 2 kg (HC)/ton of rock suggesting a fair source rock potential. Most of the samples are thermally immature to marginally mature with vitrinite reflectance ranging from 0.4 to 0.6% Rom and Tmax values of 407-426 °C. Given the prevalence of the humic Type III kerogen, maturity and hydrocarbon potential yields, we conclude that the Patti Formation source rock facies have moderate to fair potential for gaseous

  4. 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

  5. Evolution of organo-clay composites with respect to thermal maturity in type II organic-rich source rocks

    NASA Astrophysics Data System (ADS)

    Berthonneau, Jeremie; Grauby, Olivier; Abuhaikal, Muhannad; Pellenq, Roland J.-M.; Ulm, Franz J.; Van Damme, Henri

    2016-12-01

    Among the proposed pathways of sequestration and progressive transformation of organic matter (OM) during burial, the sorptive protection mechanism explains the strong relationship between total organic carbon (TOC) and mineral surface area (MSA) noted in numerous black shales around the globe. The complete mechanistic framework of preservation and evolution of OM in organo-mineral complexes remains, however, an enigma. On one hand, smectite layers composing the clay fraction are known to have a major influence on available surface area. OM maturation occurs, on the other hand, concurrently with the smectite illitization that provokes the closure of the interlayer spaces. The potential of smectite layers in the sequestration and preservation of organic molecules and the fate of these molecules with respect to the smectite illitization were therefore addressed. Here, the mineralogy of three organic-rich source rocks of various maturities was characterized in regards with the geochemistry of their OM. A thorough examination of the clay minerals present in the clay matrices provided evidences of mixed layer minerals containing smectite and illite layers with an increasing illite component with respect to maturity. The comprehensive interpretation of the X-ray diffractograms and analytical electron microscopy results suggested the presence of organic molecules in the inter-particulate and possibly the interlayer spaces of the smectite-rich components in immature source rocks. This eventuality was further supported by the presence of intercalated clay-organic nanocomposites observed by transmitted electron microscopy coupled with energy dispersive spectroscopy. Textural observations also showed that the increased illite content found in the overmature sample led to the reorganization of the OM and the clay particles into nano-scale aggregates. These results clarify the geochemical mechanism beyond the reported relationship between TOC and MSA and allow generalizing it

  6. Crustal Seismic Anisotropy Produced by Rock Fabric Terranes in the Taiwan Central Range Deformational Orogen: Integrative Study Combining Rock Physics, Structural Geology, and Passive/Active-Source Seismology

    NASA Astrophysics Data System (ADS)

    Okaya, D. A.; Ross, Z.; Christensen, N. I.; Wu, F. T.; Byrne, T. B.

    2014-12-01

    The island of Taiwan is currently under construction due to the collision of the northwestern corner of the Philippine Sea plate and the embedded Luzon island arc with the larger continental Eurasian plate. This collision is responsible for the current growth of the Central Range that dominates the eastern half of the island. An international collaboration involving several USA and Taiwan universities and academic institutions was formed to study how the orogen evolves through time and to understand the role of a colliding island arc in mountain building. The project, Taiwan Integrated Geodynamics Research (TAIGER), was funded by NSF-Continental Dynamics and Taiwan National Science Council. The Central Range grows at one of the most rapid rates of uplift in the world, exposing metamorphic rocks that were once at least 10 km deep. The range offers unique opportunities for studies of crustal seismic anisotropy for two major reasons: (1) its geological makeup is conducive for producing crustal seismic anisotropy; that is, the rocks are highly foliated; and (2) a seismological data volume of significant breadth offers extensive coverage of sources and recording stations throughout the region. We carried out a crustal shear wave splitting study by data mining 3300 local earthquakes collected in the TAIGER 2009 sea-land experiment. We used an automated P and S wave arrival time picking method (Ross and Ben-Zion, 2014) applied to over 100,000 event-station pairs. These data were analyzed for shear-wave splitting using the MFAST automated package (Savage et al., 2010), producing 3300 quality shear wave split measurements. The splitting results were then station-averaged. The results show NNE to NE orientation trends that are consistent with regional cleavage strikes. Average crustal shear wave split time is 0.244 sec. These measurements are consistent with rock physics measurements of Central Range slate and metamorphic acoustic velocities. The splits exhibit orientations

  7. Geochemical evidence for mudstone as the possible major oil source rock in the Jurassic Turpan Basin, Northwest China

    USGS Publications Warehouse

    Chen, J.; Qin, Yelun; Huff, B.G.; Wang, D.; Han, D.; Huang, D.

    2001-01-01

    Geologists and geochemists have debated whether hydrocarbons from Jurassic coal measures are derived from the mudstones or the coals themselves. This paper identifies mudstones as the possible major source rock of hydrocarbons in the Jurassic basins in Northwest China. The Turpan Basin is used as a representative model. Mudstones in the Middle-Lower Jurassic are very well developed in the basin and have an average genetic potential from 2 to 4 mg/g. The vitrinite reflectance of the source rocks ranges from 0.6 to 1.3%, exhibiting sufficient thermal maturity to generate oil and gas. Biomarkers in crude oils from the basin are similar to those in mudstones from the coal-bearing strata, with a low tricyclic terpane (cheilanthane) content, a relatively high content of low carbon number (less than C22) tricyclic terpanes and a low content of high carbon number tricyclic terpanes, relatively high ratios of Ts/Tm, and C29 Ts/17?? (H)-C29 norhopane, and low ratios of Tm/17?? (H)-C30 hopane and 17?? (H)-C31 homohopane/17?? (H)-C30 hopane. These characteristics and the distribution of steranes and terpanes in the crude oil and mudstone differ significantly from those of the Jurassic coals and carbonaceous shales of the basin, indicating mudstone is possibly the major source rock of the oils in the Turpan Basin. ?? 2001 Elsevier Science Ltd. All rights reserved.

  8. Magma sources and mixing for the Coastal Batholith in southern Peru: insights from new elemental and isotopic data and from comparison with California batholithic rocks

    NASA Astrophysics Data System (ADS)

    Clausen, B. L.; Martinez, A. M.; Gonzalez, L. U.; Poma, O.; Paterson, S. R.; Ianno, A.

    2013-12-01

    Seventy granitoid samples recently collected from the Arequipa segment of the Cretaceous Coastal Batholith near Ica, Peru are made up of a combination of diorites, tonalites, monzonites, and granodiorites previously divided into super-units from west to east as: Linga, Pampahuasi, Tiabaya, and Incahuasi. A few associated earlier gabbros are also included. Elemental and isotopic data and petrographic analyses from these new samples along with previous data from the same area provides a data set of about one hundred samples. They yield new insights into across-arc geochemical variation, when compared with data from California batholithic rocks in the Sierra Nevada Mountains and in the Peninsular and Transverse Ranges and Mojave Desert. >>Of the 26 new Rb-Sr isotope data points from Peru: nineteen lie on previous isochrons for the four super-units that yield ages of 80-100 Ma; six lie above the isochrons, two of which match a Pampahuasi data cluster previously interpreted as due to magma mixing; one Linga data point lies below the isochrons as part of a 140 Ma apparent isochron previously interpreted as due to mixing. >>Based on principal component analysis (PCA) of data from California and Peru, the data can be summarized in terms of four factors related to: (1) extent of differentiation and/or mixing using a MgO Harker diagram, (2) relative contributions of mantle and lower crustal input using the Nb/Yb ratio and Nd-Sr and Pb isotope plots, (3) magma source depth using Sr/Y and Gd/Yb ratios, and (4) calc-alkalinity using a K2O Harker diagram and a Rb-Sr bivariate plot. Two other plots of Al2O3 content and TiO2/Fe2O3 ratios assess alumina saturation and ilmenite/magnetite variation. >>Comparison with the two thousand California data points is impractical individually and requires a grouping of the samples, so that only mean and standard deviation of California data groups are plotted. The baseline for comparing the PCA factors [least crustal contamination, shallowest

  9. [Near Infrared Spectroscopy of the Cretaceous Red Beds in Inner Mongolia Dongshengmiao].

    PubMed

    Liao, Yi-peng; Cao, Jian-jin; Wu, Zheng-quan; Luo, Song-ying; Wang, Zheng-yang

    2015-09-01

    Take the cores and surface weathered soil from the Cretaceous red beds in the western of Dongshengmiao mine of Inner Mongolia and analysis with near-infrared spectroscopy. The result shows that near-infrared spectroscopy can identify mineral quickly through the characteristic absorption peaks of each group. The Cretaceous red beds in the western of Dongshengmiao mine is argillaceous cementation, it is mainly composed of quartz, feldspar, montmorillonite, illite, chlorite, muscovite etc, the mineral composition is mainly affected by the upstream source area. The clay mineral like montmorillonite water swelling and uneven drying shrinkage expands the original crack and creates new cracks, reduces its strength, which is the mainly reason of its disintegration. According to the composition of clay mineral, we speculate its weathering process is mainly physical weathering, the climate during the weathering is cold and dry. The results can not only improve the geological feature of the mining area, but also show that the near-infrared spectroscopy technology can analyze the mineral composition of soil and rock effectively on the basis of Mineral spectroscopy, which demonstrates the feasibility of the near-infrared spectroscopy can analyze minerals in soil and rock quickly, that shows the feasibility in geology study, provides new ideas for the future research of soil and rock.

  10. 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.

  11. Pre-earthquake signals - Part I: Deviatoric stresses turn rocks into a source of electric currents

    NASA Astrophysics Data System (ADS)

    Freund, F. T.

    2007-09-01

    Earthquakes are feared because they often strike so suddenly. Yet, there are innumerable reports of pre-earthquake signals. Widespread disagreement exists in the geoscience community how these signals can be generated in the Earth's crust and whether they are early warning signs, related to the build-up of tectonic stresses before major seismic events. Progress in understanding and eventually using these signals has been slow because the underlying physical process or processes are basically not understood. This has changed with the discovery that, when igneous or high-grade metamorphic rocks are subjected to deviatoric stress, dormant electronic charge carriers are activated: electrons and defect electrons. The activation increases the number density of mobile charge carriers in the rocks and, hence, their electric conductivity. The defect electrons are associated with the oxygen anion sublattice and are known as positive holes or pholes for short. The boundary between stressed and unstressed rock acts a potential barrier that lets pholes pass but blocks electrons. Therefore, like electrons and ions in an electrochemical battery, the stress-activated electrons and pholes in the "rock battery" have to flow out in different directions. When the circuit is closed, the battery currents can flow. The discovery of such stress-activated currents in crustal rocks has far-reaching implications for understanding pre-earthquake signals.

  12. 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.

  13. Source implications for the different geochemical features of recent basaltic rocks from the northernmost part of the Cappadocian region, Turkey

    NASA Astrophysics Data System (ADS)

    Kurkcuoglu, Biltan; Yurur, Tekin

    2017-04-01

    Extensive magmatic activities developed since middle-Miocene, in the Cappadocian Region of Central Anatolia in Turkey. The nature and the sources of the magmatism were well-constrained by previous studies. Even though the sources of Strato-volcanoes and monogenetic vents were briefly explained, extremely young basalts (1.22 - 0.094 Ka) situated in northernmost part of Cappadocian Region and erupted between the two extentional faults, are not deeply investigated. Karaburna and Gülşehir lavas (1.22, 0.094 Ka, respectively, Dogan, 2011) are considered as a part of the Central Anatolian Volcanic Province, with extremely young ages, generated either at the final or after the final stage of the Cappadocian systems. These lavas have similar LIL and HFS elements patterns with each other, however, Karaburna samples are more enriched in HFS elements. These basalts also display approximately similar trends in LIL elements ( except Rb) and reflect HFS depletion relative to the OIB signature, moreover, HFS are more enriched compared to the Hasandag basaltic rocks, all these features suggesting, basaltic rocks are originated from the modified mantle source. Karaburna and Gülşehir basalts have low Nb/La (0.45-0.5 ; 0.35-0.42), Nb/Y( 0.33-.39; 0.27-0.44 Nb/Th (2.75-4.6; 1.26-1.68) and high Ba/Nb (22-32; 38-43) ratios suggesting the contributions from the crustal sources, moreoever, Gülşehir basaltic rocks differ from the Karaburna lavas with relatively low Nb/U ( 4.5-6.4) and high Ba/La ( 14.67-17.20) Th/La (0.22-0.27), whereas Karaburna samples are represented by low Ba/La (10.04-14.90) and Th/La (0.09-0.16) ratios, these geochemical features reveal that these differences are originated either from the different degrees of crustal involvement or change in the nature of the source in a short time interval. Of all the most recent basaltic products generated in central Anatolia are alkaline in nature, besides, the trace element content, multi-element patterns and HFS/LIL and

  14. 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.

  15. Oxygen isotopes as tracers of tektite source rocks: An example from the Ivory Coast tektites and Lake Bosumtwi Crater

    NASA Technical Reports Server (NTRS)

    Blum, Joel D.; Koeberl, Christian; Chamberlain, C. Page

    1993-01-01

    Oxygen isotope studies of tektites and impact glasses provide an important tool to help in identifying the target lithologies for terrestrial impacts, including the K-T boundary impact. However, such studies may be complicated by modification of the original oxygen isotope values of some source rocks during the tektite formation process either by vapor fractionation or incorporation of meteoric water. To further investigate the relationship between the oxygen isotopic composition of tektites and their source rocks, Ivory Coast tektites and samples of impact glasses and bedrock lithologies from the Bosumtwi Crater in Ghana--which is widely believed to be the source crater for the Ivory Coast tektites--were studied. Our preliminary results suggest that the phyllites and metagraywackes from the Bosumtwi Crater were the predominant source materials for the impact glasses and tektites and that no significant oxygen isotope modification (less than 1 percent delta(O-18)) took place during impact melting. This contrasts with previous studies of moldavites and Australasian tektites and their sedimentary source materials which suggests a 4 to 5 percent lowering of delta(O-18) due to meteoric water incorporation during impact melting.

  16. Oxygen isotopes as tracers of tektite source rocks: An example from the Ivory Coast tektites and Lake Bosumtwi Crater

    NASA Technical Reports Server (NTRS)

    Blum, Joel D.; Koeberl, Christian; Chamberlain, C. Page

    1993-01-01

    Oxygen isotope studies of tektites and impact glasses provide an important tool to help in identifying the target lithologies for terrestrial impacts, including the K-T boundary impact. However, such studies may be complicated by modification of the original oxygen isotope values of some source rocks during the tektite formation process either by vapor fractionation or incorporation of meteoric water. To further investigate the relationship between the oxygen isotopic composition of tektites and their source rocks, Ivory Coast tektites and samples of impact glasses and bedrock lithologies from the Bosumtwi Crater in Ghana--which is widely believed to be the source crater for the Ivory Coast tektites--were studied. Our preliminary results suggest that the phyllites and metagraywackes from the Bosumtwi Crater were the predominant source materials for the impact glasses and tektites and that no significant oxygen isotope modification (less than 1 percent delta(O-18)) took place during impact melting. This contrasts with previous studies of moldavites and Australasian tektites and their sedimentary source materials which suggests a 4 to 5 percent lowering of delta(O-18) due to meteoric water incorporation during impact melting.

  17. Rockfall source characterization at high rock walls in complex geological settings by photogrammetry, structural analysis and DFN techniques