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Sample records for baltoscandian ordovician strata

  1. Hydraulic testing of low-permeability Silurian and Ordovician strata, Michigan Basin, southwestern Ontario

    NASA Astrophysics Data System (ADS)

    Beauheim, Richard L.; Roberts, Randall M.; Avis, John D.

    2014-02-01

    Straddle-packer hydraulic testing was performed in 31 Silurian intervals and 66 Ordovician intervals in six deep boreholes at the Bruce nuclear site, located near Tiverton, Ontario, as part of site-characterization activities for a proposed deep geologic repository (DGR) for low- and intermediate-level radioactive waste. The straddle-packer assembly incorporated a hydraulic piston to initiate in situ pulse tests within low hydraulic conductivity (<1E-10 m/s) test intervals. Pressure transient data collected during the hydraulic tests were analyzed using the well-test simulator nSIGHTS to estimate the hydraulic properties specified as fitting parameters for the tested intervals, quantify parameter uncertainty, and define parameter correlations. Horizontal hydraulic conductivities of the Silurian test intervals range from approximately 4E-14 to 4E-8 m/s. The average horizontal hydraulic conductivities of the Ordovician intervals range from 2E-16 to 2E-10 m/s. The Lower Member of the Cobourg Formation, the proposed host formation of the DGR between 660 and 688 meters below ground surface, was found to have a horizontal hydraulic conductivity of 4E-15 to 3E-14 m/s. The formation pressures inferred from the hydraulic testing, confirmed by long-term monitoring, show that the Upper Ordovician and Middle Ordovician Trenton Group are significantly underpressured relative to a density-compensated hydrostatic condition and relative to the overlying Silurian strata and underlying Black River Group and Cambrian strata. These underpressures could not persist if hydraulic conductivities were not as low as those measured.

  2. Hydraulic Testing of Silurian and Ordovician Strata at the Bruce Site

    NASA Astrophysics Data System (ADS)

    Beauheim, R. L.; Avis, J. D.; Chace, D. A.; Roberts, R. M.; Toll, N. J.

    2009-05-01

    Ontario Power Generation is proposing a Deep Geologic Repository (DGR) for the long-term management of its Low and Intermediate Level Radioactive Waste (L&ILW) within a Paleozoic-age sedimentary sequence beneath the Bruce Site near Tiverton, Ontario, Canada. The concept envisions that the DGR would be excavated at a depth of approximately 680 m within the Ordovician Cobourg Formation, a massive, dense, argillaceous limestone. A key attribute of the Bruce site is the extremely low permeabilities associated with the thick Ordovician carbonate and argillaceous bedrock formations that will host and enclose the DGR. Such rock mass permeabilities are thought sufficiently low to contribute toward or govern a diffusion-dominated transport regime. To support this concept, hydraulic testing was performed in 2008 and 2009 in two deep boreholes at the proposed repository site, DGR-3 and DGR-4. The hydraulic testing was performed using a straddle-packer tool with a 30.74-m test interval. Sequential tests were performed over the entire open lengths of the boreholes from the F Unit of the Silurian Salina Formation into the Ordovician Gull River Formation, a distance of approximately 635 m. The tests consisted primarily of pressure-pulse tests, with a few slug tests performed in several of the higher permeability Silurian units. The tests are analyzed using the nSIGHTS code, which allows the entire pressure history a test interval has experienced since it was penetrated by the drill bit to be included in the test simulation. nSIGHTS also allows the model fit to the test data to be optimized over an n-dimensional parameter space to ensure that the final solution represents a true global minimum rather than simply a local minimum. The test results show that the Ordovician-age strata above the Coboconk Formation (70+ m below the Cobourg) have average horizontal hydraulic conductivities of 1E-13 m/s or less. Coboconk and Gull River hydraulic conductivities are as high as 1E-11 m

  3. Karst development in the Tobosa basin (Ordovician-Devonian) strata in the El Paso border region of west Texas

    SciTech Connect

    Lemone, D.V. . Dept. of Geological Sciences)

    1993-02-01

    Karst development within the Tobosa basin strata in the El Paso border region is best displayed during two time intervals: Middle Ordovician (27 Ma) developed on the Lower Ordovician El Paso Group and Middle Silurian to Middle Devonian (40 Ma) karst developed on the Lower-Middle Fusselman Formation. These major exposure intervals are recognized in regional outcrops as well as in the subsurface of the Permian Basin where they form major reservoirs. Minor local karsting is noted also within and upon the Upper Ordovician (Montoya Group) and within the shoaling upward members of overlying the Fusselman Formation. Middle Ordovician karsting with major cavern development extends down into McKellingon Canyon Formation approximately 1,000 feet below the top of the Lower Ordovician El Paso Group. The McKellingon is overlain by the cavern roof-forming early diagenetic dolomites, lower Scenic Drive Formation which in turn is overlain by the locally karsted upper Scenic Drive and Florida Mountains formations. Collapse of the overlying Montoya Group into El Paso Group rocks is observed. The Fusselman Formation rests disconformably on the Montoya Group. It is a massive, vuggy, fine- to coarsely-crystalline, whitish dolomite. Extensive karsting has developed on the top of the Fusselman. The middle Devonian Canutillo Formation with a basal flooding deposit overlies this karst surface. Minor karsting following fracture systems extends from the major karst of the El Paso Group up into the major karst in the Fusselman. The karst seems to be following and developing along the same linear fracture systems. If so, it is not unreasonable to interpret these fracture systems as being inherited from the earlier Precambrian structures underlying them.

  4. Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata

    NASA Astrophysics Data System (ADS)

    Present, Theodore M.; Paris, Guillaume; Burke, Andrea; Fischer, Woodward W.; Adkins, Jess F.

    2015-12-01

    Carbonate Associated Sulfate (CAS) is trace sulfate incorporated into carbonate minerals during their precipitation. Its sulfur isotopic composition is often assumed to track that of seawater sulfate and inform global carbon and oxygen budgets through Earth's history. However, many CAS sulfur isotope records based on bulk-rock samples are noisy. To determine the source of bulk-rock CAS variability, we extracted CAS from different internal sedimentary components micro-drilled from well-preserved Late Ordovician and early Silurian-age limestones from Anticosti Island, Quebec, Canada. Mixtures of these components, whose sulfur isotopic compositions vary by nearly 25‰, can explain the bulk-rock CAS range. Large isotopic variability of sedimentary micrite CAS (34S-depleted from seawater by up to 15‰) is consistent with pore fluid sulfide oxidation during early diagenesis. Specimens recrystallized during burial diagenesis have CAS 34S-enriched by up to 9‰ from Hirnantian seawater, consistent with microbial sulfate reduction in a confined aquifer. In contrast to the other variable components, brachiopods with well-preserved secondary-layer fibrous calcite-a phase independently known to be the best-preserved sedimentary component in these strata-have a more homogeneous isotopic composition. These specimens indicate that seawater sulfate remained close to about 25‰ (V-CDT) through Hirnantian (end-Ordovician) events, including glaciation, mass extinction, carbon isotope excursion, and pyrite-sulfur isotope excursion. The textural relationships between our samples and their CAS isotope ratios highlight the role of diagenetic biogeochemical processes in setting the isotopic composition of CAS.

  5. Strata-bound, silver-bearing iron, lead, and zinc sulfide deposits in Silurian and Ordovician rocks of allochthonous terranes, Nevada and northern Mexico

    USGS Publications Warehouse

    Ketner, Keith Brindley

    1983-01-01

    Allochthonous terranes in northern Nevada contain strata-bound sulfide deposits at two horizons in Silurian and Ordovician siliceous sedimentary rocks. The most intensively mineralized horizon and most extensive deposit is at the base of the Silurian. Another less extensive deposit is in the lower Middle Ordovician. Spectrographic analyses of gossan from the basal Silurian horizon indicate anomalously high values of lead and zinc; and in about 40 percent of the samples, silver values are anomalously high. Suhsurface samples contain the primary minerals pyrite, galena, and sphalerite. The basal Silurian deposits are in thick-bedded chert that is overlain by micaceous siltstone. They are underlain by a thick-bedded black chert unit of Late Ordovician age. The basal Silurian gossan has been identified also in southwestern Nevada and in northern Mexico in stratigraphic sequences very similar to that of northern Nevada.

  6. Successful Integration of Seismic Reflection Data for Evaluating the Sequestration Potential of the Cambrian and Ordovician Strata of the Illinois Basin, USA

    NASA Astrophysics Data System (ADS)

    Leetaru, H. E.; Couëslan, M.; Brown, A. L.; Finley, R. J.

    2011-12-01

    The Cambro-Ordovician strata form the most important carbon sink available for the sequestration of CO2 in the heavily industrialized Midwest of the United States. In the Illinois Basin, the three most significant suitable for sequestration are the Cambrian Mt. Simon Sandstone, the Cambrian carbonate intervals in the Knox Group, and the Ordovician St. Peter Sandstone. The evaluation of these formations was based on data collected from the US DOE-funded Illinois Basin -- Decatur Project being conducted by the Midwest Geological Sequestration Consortium (MGSC) in Macon County, Illinois. All three formations have significant potential. The Knox formation is composed of interconnected solution cavities that make CO2 plume prediction difficult. The St. Peter Sandstone is a potential sink but, at 52 m (170 feet) thick, it has less storage capacity than the Mt. Simon Sandstone. The Mt. Simon Sandstone is over 487 m (1600 feet thick) in the Decatur area with average porosities of 22% and permeabilities of 200 mD. However, individual intervals can have porosities as high as 28% and permeabilities of over a Darcy. Few wells have been drilled through these Cambro-Ordovician saline reservoirs because there are no recoverable hydrocarbons; therefore, seismic reflection data integrated with regional geologic models are absolutely necessary for evaluating potential sites and characterizing reservoirs with only one or two wells. Regional seismic profiles across the Illinois Basin were used to define areas of high and low risk for sequestration. Areas have been designated as high risk if the Mt. Simon Formation is thin or non-existent as a result of Precambrian topography or if it is a structurally complex area with extensive faulting. Seismic and regional well data suggested that the saline formation at Decatur, Illinois is an excellent sink for CO2. Seismic acquisition at the Illinois Basin -- Decatur Project has been challenging given that the site is located in close proximity

  7. An Evaluation of the Carbon Sequestration Potential of the Cambro-Ordovician Strata of the Illinois and Michigan Basins

    SciTech Connect

    Kirksey, Jim; Ansari, Sajjad; Malkewicz, Nick; Leetaru, Hannes

    2014-01-01

    The Knox Supergroup is a significant part of the Cambrian-Ordovician age sedimentary deposition in the Illinois Basin. While there is a very small amount of oil production associated with the upper Knox, it is more commonly used as a zone for both Class I and Class II disposal wells in certain areas around the state. Based on the three penetrations of the Knox Formation at the Illinois Basin – Decatur Project (IBDP) carbon dioxide (CO2) sequestration site in Macon County, Illinois, there is potential for certain zones in the Knox to be used for CO2 sequestration. More specifically, the Potosi member of the Knox Formation at about –3,670 feet (ft) subsea depth would be a candidate as all three penetrations had massive circulation losses while drilling through this interval. Each well required the setting of cement plugs to regain wellbore stability so that the intermediate casing could be set and successfully cemented to surface. Log and core analysis suggests significant karst porosity throughout the Potosi member. The purpose of this study is to develop a well plan for the drilling of a CO2 injection well with the capability to inject 3.5 million tons per annum (3.2 million tonnes per annum [MTPA] CO2 into the Knox Formation over a period of 30 years.

  8. An Evaluation of the Carbon Sequestration Potential of the Cambro-Ordovician Strata of the Illinois and Michigan Basins

    SciTech Connect

    Leetaru, Hannes

    2014-12-01

    The studies summarized herein were conducted during 2009–2014 to investigate the utility of the Knox Group and St. Peter Sandstone deeply buried geologic strata for underground storage of carbon dioxide (CO2), a practice called CO2 sequestration (CCS). In the subsurface of the midwestern United States, the Knox and associated strata extend continuously over an area approaching 500,000 sq. km, about three times as large as the State of Illinois. Although parts of this region are underlain by the deeper Mt. Simon Sandstone, which has been proven by other Department of Energy-funded research as a resource for CCS, the Knox strata may be an additional CCS resource for some parts of the Midwest and may be the sole geologic storage (GS) resource for other parts. One group of studies assembles, analyzes, and presents regional-scale and point-scale geologic information that bears on the suitability of the geologic formations of the Knox for a CCS project. New geologic and geo-engineering information was developed through a small-scale test of CO2 injection into a part of the Knox, conducted in western Kentucky. These studies and tests establish the expectation that, at least in some locations, geologic formations within the Knox will (a) accept a commercial-scale flow rate of CO2 injected through a drilled well; (b) hold a commercial-scale mass of CO2 (at least 30 million tons) that is injected over decades; and (c) seal the injected CO2 within the injection formations for hundreds to thousands of years. In CCS literature, these three key CCS-related attributes are called injectivity, capacity, and containment. The regional-scale studies show that reservoir and seal properties adequate for commercial-scale CCS in a Knox reservoir are likely to extend generally throughout the Illinois and Michigan Basins. Information distinguishing less prospective subregions from more prospective fairways is included in

  9. Terminal suturing of Gondwana along the southern margin of South China Craton: Evidence from detrital zircon U-Pb ages and Hf isotopes in Cambrian and Ordovician strata, Hainan Island

    NASA Astrophysics Data System (ADS)

    Xu, Yajun; Cawood, Peter A.; Du, Yuansheng; Zhong, Zengqiu; Hughes, Nigel C.

    2014-12-01

    Hainan Island, located near the southern end of mainland South China, consists of the Qiongzhong Block to the north and the Sanya Block to the south. In the Cambrian, these blocks were separated by an intervening ocean. U-Pb ages and Hf isotope compositions of detrital zircons from the Cambrian succession in the Sanya Block suggest that the unit contains detritus derived from late Paleoproterozoic and Mesoproterozoic units along the western margin of the West Australia Craton (e.g., Northampton Complex) or the Albany-Fraser-Wilkes orogen, which separates the West Australia and Mawson cratons. Thus, in the Cambrian the Sanya Block was not part of the South China Craton but rather part of the West Australian Craton and its environs. In contrast, overlying Late Ordovician strata display evidence for input of detritus from the Qiongzhong Block, which constituted part of the southeastern convergent plate margin of the South China Craton in the early Paleozoic. The evolving provenance record of the Cambrian and Ordovician strata suggests that the juxtaposition of South China and West Australian cratons occurred during the early to mid-Ordovician. The event was linked with the northern continuation of Kuungan Orogeny, with South China providing a record of final assembly of Gondwana.

  10. The 1997 core drilling through Ordovician and Silurian strata at Röstånga, S. Sweden: preliminary stratigraphic assessment and regional comparison

    USGS Publications Warehouse

    Bergstrom, Stig M.; Huff, W.D.; Koren', T.; Larsson, K.; Ahlberg, P.; Kolata, Dennis R.

    1999-01-01

    A core drilling at Ro??sta??nga, the first such drilling ever undertaken in this classical Lower Paleozoic outcrop area in W-central Scania, penetrated an approximately 96 m thick succession of Lower Silurian-upper Middle Ordovician marine rocks. The drilling was stopped at a depth of 132.59 m in an interval of crushed rocks, probably a prominent fault zone, that proved impossible to drill through. The core contains a stratigraphical sequence from the basal Upper Llandoverian (Telychian Stage) to the upper Middle Ordovician (Harjuan Stage). The following units are recognized in descending stratigraphic order (approximate thickness in parenthesis): Kallholn Formation (35 m), Lindega??rd Mudstone (27 m), Fja??cka Shale (13 m), Mossen Formation (0.75 m), Skagen Formation (2.5 m), and Sularp Shale (19 m+). Except for the Skagen Formation, the drilled sequence consists of shales and mudstones with occasional thin limestone interbeds and is similar to coeval successions elsewhere in Scania. There are 11 K-bentonite beds in the Kallholn Formation, 2(3?) in the Lindega??rd Mudstone, 1 in the Mossen Formation, 7 in the Skagen Formation, and 33 in the Sularp Shale. The core serves as an excellent Lower Silurian-upper Middle Ordovician reference standard not only for the Ro??sta??nga area but also for southernmost Sweden in general because the cored sequence is the stratigraphically most complete one known anywhere in this region.

  11. Geometry of the Iapetus Baltoscandian continental margin; evidence for basement highs from the external imbricate zone.

    NASA Astrophysics Data System (ADS)

    Rice, A. Hugh N.

    2015-04-01

    The geometry of the Iapetus Baltoscandian continental margin prior to Scandinavian Caledonian collision is important, since only with a detailed initial input can synthetic palaeogeographic and deformation models be correctly applied. The Scandes comprise ~SE-directed nappes pierced by tectonic windows exposing basement with condensed, post-Gaskiers-glaciation (582-580Ma) cover sequences. Here, evidence, largely from the Lower Allochthon (external imbricate zone), for major displacement of these basement rocks ('Window Allochthon'), is summarized; palaeogeographically they formed a topographic-high along the Baltoscandian continental margin. In the Oslo Graben and East Finnmark areas (southernmost/northernmost Scandinavia), the transition from (par)-autochthon to allochthon is preserved (Osen-Roa Nappe Complex/Gaissa Thrust Belt; ORNC/GTB). These areas give reliable templates for other parts of the orogen, where the orogen leading edge has been extensively eroded. In the ORNC and GTB, bulk shortening was ~50%, with values rising towards the hinterland; metamorphic grades also increase towards the hinterland. Balanced-sections restore the trailing-edges of the ORNC and GTB to Norwegian coastal areas. In Finnmark, restoration places pre-Marinoan (pre~650 Ma) GTB anchizone-grade rocks above epizone-grade post-Gaskiers rocks lying unconformably on basement in the Komagfjord tectonic window. In southern Norway, restored pre-Gaskiers ORNC rocks overlie Cambro-Ordovician sediments unconformable on basement in the Atnsjøen/Spekedalen windows and WGR. Caledonian Middle Allochthon deformation in Finnmark was SE-directed and in the GTB E- to ESE-directed. In the Komagfjord window basement, Caledonian imbrication was SE-directed, but the overlying basal Middle Allochthon mylonites have an out-of-sequence E-ESE overprint. Thus the Komagfjord basement/cover lies structurally between the Middle and Lower Allochthons. In the Atnsjøen/Spekedalen windows, SE-directed Caledonian

  12. Paleokarst, karst related diagenesis and reservoir development: Examples from Ordovician-Devonian age strata of west Texas and the Mid-continent

    SciTech Connect

    Candelaria, M.P.; Reed, C.L.

    1992-01-01

    This publication served as a guidebook for a Permian Basin Section-SEPM field trip to examine exposures of paleokarst in lower Paleozoic platform carbonates of West Texas and New Mexico. Included are road logs for the field trips and a collection of eighteen papers and abstracts that focus on various aspects of paleokarst in shallow-water carbonates including: (1) recognition and classification of karst-related textures in outcrop and the subsurface; (2) sequence stratigraphic analysis of karsted platforms; (3) diagenetic products of karstification; and (4) production characteristics of karst reservoirs. Collectively, these papers provide excellent documentation of sedimentary fabrics and diagenetic products associated with paleokarst development resulting from regional exposure of Cambro-Ordovician and Siluro-Devonian carbonates of the Great American Bank.'' The major value of this volume lies in the integration of a variety of approaches for examining processes and products related to karstification. These include the use of core, outcrop, well logs, and computer modeling to better understand paleokarst development and preservation. Some of the more interesting articles are highlighted below.

  13. An Evaluation of the Carbon Sequestration Potential of the Cambro-Ordovician Strata of the Illinois and Michigan Basins. Part 1. Evaluation of Phase 2 CO2 Injection Testing in the Deep Saline Gunter Sandstone Reservoir (Cambro-Ordovician Knox Group), Marvin Blan No. 1 Hancock County, Kentucky Part 2. Time-lapse Three-Dimensional Vertical Seismic Profile (3D-VSP) of Sequestration Target Interval with Injected Fluids

    SciTech Connect

    Bowersox, Richard; Hickman, John; Leetaru, Hannes

    2012-12-20

    Part 1 of this report focuses on results of the western Kentucky carbon storage test, and provides a basis for evaluating injection and storage of supercritical CO2 in Cambro-Ordovician carbonate reservoirs throughout the U.S. Midcontinent. This test demonstrated that the Cambro- Ordovician Knox Group, including the Beekmantown Dolomite, Gunter Sandstone, and Copper Ridge Dolomite in stratigraphic succession from shallowest to deepest, had reservoir properties suitable for supercritical CO2 storage in a deep saline reservoir hosted in carbonate rocks, and that strata with properties sufficient for long-term confinement of supercritical CO2 were present in the deep subsurface. Injection testing with brine and CO2 was completed in two phases. The first phase, a joint project by the Kentucky Geological Survey and the Western Kentucky Carbon Storage Foundation, drilled the Marvin Blan No. 1 carbon storage research well and tested the entire Knox Group section in the open borehole – including the Beekmantown Dolomite, Gunter Sandstone, and Copper Ridge Dolomite – at 1152–2255 m, below casing cemented at 1116 m. During Phase 1 injection testing, most of the 297 tonnes of supercritical CO2 was displaced into porous and permeable sections of the lowermost Beekmantown below 1463 m and Gunter. The wellbore was then temporarily abandoned with a retrievable bridge plug in casing at 1105 m and two downhole pressure-temperature monitoring gauges below the bridge plug pending subsequent testing. Pressure and temperature data were recorded every minute for slightly more than a year, providing a unique record of subsurface reservoir conditions in the Knox. In contrast, Phase 2 testing, this study, tested a mechanically-isolated dolomitic-sandstone interval in the Gunter.

  14. Trends in extend and depth of Ordovician infauna

    SciTech Connect

    Droser, M.L.; Bottjer, D.J.

    1987-05-01

    The Ordovician radiation has been particularly well documented from analyses of trends in marine familial diversity. Trace fossil diversity also increased during this time. However, there has not previously been an attempt to document the Ordovician radiation in terms of depth and extent of bioturbation and utilization of infaunal ecospace. In order to determine the relationship between the Ordovician radiation and the development of the infaunal biological benthic boundary layer, over 600 m of Ordovician strata (Nevada and Utah) deposited in shallow subtidal shelf environments were examined. The amount of bioturbation in these rocks was ranked using the following ichnofabric indices: (1) no bioturbation; (2) discrete isolated trace fossils, up to 10% bioturbated; (3) 10 to 40% bioturbated, but bedding is generally preserved; (4) 40 to 60% bioturbated, last vestiges of bedding preserved; (5) bedding completely disrupted; and (6) bedding nearly or totally homogenized. In the Lower and Middle Ordovician the most common ichnofabric index is 3, represented by 41% of the strata, whereas ichnofabric index 5 represents only 8%. Depth of bioturbation averages 2-3 cm with a maximum of 5 cm. Flat pebble conglomerates, previously suggested to indicate limited bioturbation, are abundant in these strata. By the late Caradoc, 67% of the strata are represented by ichnofabric index 5. Depth of bioturbation ranges from centimeters to tens of centimeters, with Thalassinoides dominating trace fossil assemblages. This nearly order-of-magnitude increase in the occurrence of completely bioturbated strata through the Ordovician is consistent with the hypotheses of others who have suggested that an increase in diversity can be accompanied by an increase in utilization of ecospace.

  15. Exploration in Ordovician of central Michigan Basin

    SciTech Connect

    Fisher, J.H.; Barratt, M.W.

    1985-12-01

    Deep wells in the central Michigan basin have provided sufficient data to define two new mappable formations - the Foster Formation and the Bruggers Formation. Recent conodont studies have corrected the age assignments of the strata containing these formations. Previously, the lower section (Foster) was classified as mostly Cambrian, and the upper unit (Bruggers) was identified as Early Ordovician. Conodont identifications indicate an Early and Middle Ordovician age for the Foster Formation and a Middle Ordovician age for the Bruggers Formation. The Michigan basin existed in embryonic form in the Late Cambrian, but the full outline of the present-day basin did not develop until Early Ordovician. Gas and condensate are produced from the Bruggers Formation as deep as 11,252 ft (3429 m). Geothermal investigations suggest that gas production is possible to the base of the Paleozoic section in the central basin (17,000 ft or 5181 m). Paleotemperatures were higher during the Paleozoic owing to 3000-4000 ft (914-1291 m) of additional sedimentary cover. Five wells are producing from the Bruggers Formation. All are deeper tests in anticlines producing from Devonian reservoirs discovered earlier. The structures are the result of vertical movements of basement fault blocks activated by regional stresses. 12 figures, 2 tables.

  16. Geochemistry of Ordovician Keli Group basalts associated with Besshi-type Cu-Zn deposits from the southern Trondheim and Sulitjelma mining districts of Norway

    NASA Astrophysics Data System (ADS)

    Smith, A. D.; Farquhar, J. S.; Smith, P.

    1990-01-01

    Besshi-type volcanogenic Cu-Zn deposits in the Scandinavian Caledonides are hosted by Ordovician metabasalts and clastic sediments of the Storen, Fundsjo and Sulitjelma groups. The basalts are transitional between T-MORB and marginal basin tholeiites in composition and are characterised by Nd and Pb isotopic compositions which overlap the more radiogenic values of Lower Palaeozoic MORB. These features, along with the intercalation of the basalts with tuffs and continentally derived sediments, indicate an epicontinental rift or marginal basin origin, possibly analogous to the present Red Sea and Gulf of Aden rifts. This implies the development of a restricted ocean basin in the north of Iapetus between the Laurentian and Baltoscandian microcontinents during the Cambrian and Early Ordovician.

  17. Kukersite--An oil shale of Ordovician age: Origin, occurrence, and geochemistry

    SciTech Connect

    Bauert, H. . Geology Dept.)

    1992-01-01

    Kukersite is the name originally given to Ordovician oil shale in the Baltic oil shale basin of Estonia. This basin covers about 50,000 sq km and extends eastward to the Leningrad district of Russia. The main oil shale sequence contains up to 50 kukersite beds alternating with argillaceous limestone. They accumulated in Llandeilo-early Caradoc (early Middle Ordovician) during a prominent regression of the Baltoscandian epicontinental sea. This oil shale contains up to 50--60% of total organic carbon. Kukersite consists mostly of accumulations of the microfossil Gloeocapsomorpha prisca, which was apparently an intertidal to very shallow subtidal, marine, mat-forming, benthonic cyanobacterium. Morphological and biogeochemical characteristics show strong similarities with modern mat-forming cyanobacterium Entophysalis major, which can be regarded as a modern analogue for G. prisca. Beside Estonia, the kukersite-type oil shales are known from several sedimentary basins in North America (in Michigan, Illinois, Wisconsin, North Dakota, Oklahoma) and in Australia (Amadeus and Canning basins), and all of these are exclusively of Ordovician age. G. prisca-dominated oil shales have a high hydrocarbon yield and are considered the main source for Ordovician oils in the USA. Hydrocarbons generated from kukersites have certain distinctive geochemical characteristics. These oils have the characteristic predominance of odd carbon number (C[sub 13]-C[sub 19]) n-alkanes with virtual absence of pristane and phytane. The worldwide distribution of kukersites and the related oils points to the fact that shallow-water widespread Ordovician cratonic seas were a favorable environment for C. prisca.

  18. Late Ordovician pelecypod faunas from the Cincinnati, Ohio area

    SciTech Connect

    Frey, R.C.

    1985-01-01

    The distribution of pelecypod faunas in the Late Ordovician strata exposed in the Cincinnati, Ohio area, points to a close relationship between lithofacies type and the life habits of these Ordovician bivalves. Muddy clastic shallow marine facies of Edenian, Maysvillian, and early Richmondian age support faunas dominated by endobyssate filter-feeding species, including a variety of modiomorphids and the genus Ambonychia, plus infaunal filter-feeding orthonotids, and in faunal deposit-feeding palaeotaxodonts. These pelecypod groups occur in claystones with a fauna of calymenid and asaphid trilobites, nautiloids, cyclomyan monoplacophorans, and occasionally crinoids and asterozoans. Younger Richmondian strata in the area are predominantly carbonate platform facies and support pelecypod faunas dominated by robust endobyssate and epibyssate ambonychiids, cyrtodontids, and colpomyids. These pelecypods are associated with diverse assemblage of articulate brachiopods, trepostome ectoprocts, solitary rugose corals, and mollusks in skeletal limestones representing storm-reworked thickets or ramos ectoprocts. This fundamental dichotomy in Late Ordovician pelecypod faunas is recognized not only in the Cincinnati area, but in Late Ordovician strata exposed on Manitoulin Island in Ontario and eastward into Quebec. Reconstructions of the life habits of these pelecypods demonstrates the dominance of the endobyssate mode of life in these Early Paleozoic pelecypods.

  19. Late Ordovician-Early Silurian chitinozoans from north-eastern and western Illinois, USA

    USGS Publications Warehouse

    Butcher, A.; Mikulic, Donald G.; Kluessendorf, Joanne

    2010-01-01

    Samples of uppermost Ordovician and Silurian strata from two cores from north-eastern and western Illinois were processed for chitinozoans. Due to apparent sea-floor oxidation or palaeoenvironmental constraints, very few samples yielded specimens, but those that did allow tentative correlation with established biostratigraphical zonations for the Chitinozoa. Samples from the Wilhelmi Formation of core DH76-21 in north-eastern Illinois yielded Spinachitina fragilis, a typically earliest Silurian taxon. A sample from the Maquoketa Group strata of core Principia #4, western Illinois, yielded a monospecific assemblage of Conochitina elegans, which is suggestive of a late Ordovician age. Higher in this core, a sample from the upper strata of the Bowling Green Dolomite yielded an assemblage indicating a late Rhuddanian to Aeronian age, including Angochitina hansonica, previously only described from strata in Nevada, and one new species, Fungochitina illinoisensis. ?? 2009 Elsevier B.V. All rights reserved.

  20. Depositional setting and paleogeography of Ordovician Vinini Formation, central Nevada

    SciTech Connect

    Finney, S.C.; Perry, B.D. )

    1991-02-01

    The eugeoclinal strata of the Ordovician Vinini Formation composes most of the Roberts Mountains allochthon (RMA). Its stratigraphy, reconstructed in the Roberts Mountains, can be precisely correlated throughout much of the RMA and into coeval strata of the autochthonous miogeocline by means of graptolite and conodont biostratigraphy. The Vinini is a mixture of clastic lithologies with some limestone and greenstone. Coarse clastics, characterized by well-rounded and well-sorted sands derived from cratonic sources, occur in two separate intervals and provide critical data on depositional and paleogeographic setting. The lower interval, hundreds of meters thick, was deposited in the latest Ibexian-earliest Whiterockian and can be closely correlated throughout central Nevada. It is a mixture of quartz sandstone, siltstone, limestone, and calcareous sandstone, deposited by turbidity flows during a lowstand of sea level. Both eastern and western sources have been interpreted for these sands. The upper interval is a prominent, pure quartzite up to 20 m thick deposited as a prograding blanket of sand in the latest Whiterockian-earliest Mohawkian. It occurs in the Vinini in the northern Toquima Range and in a parautochthonous sequence of transitional strata in the southern Toiyabe Range. This interval represents the most basinward edge of the Eureka Quartzite, which was also deposited across the miogeocline. The presence of sand of the Eureka Quartzite in the RMA indicates that the basin in which the RMA strata were deposited was immediately adjacent to the margin of North America in the Ordovician.

  1. Conodont biostratigraphy of lower Ordovician rocks, Arbuckle Group, southern Oklahoma

    SciTech Connect

    Dresbach, R.I.; Ethington, R.L. )

    1989-08-01

    The Arbuckle Group of southern Oklahoma displays the only complete exposure of the shallow-water carbonates that characterize the Lower Ordovician of interior North America. Trilobites have been described from some parts of this sequence and sporadic occurrences of other invertebrates are known, but much of the sequence is sparingly fossiliferous. As a consequence, these magnificent exposures have not contributed notably to continuing efforts toward development of a comprehensive biostratigraphic scheme for the Lower Ordovician of the North American platform. Samples collected at 25-ft intervals through the Arbuckle Group along and adjacent to Interstate Highway 35 on the south flank of the Arbuckle anticline near Ardmore, Oklahoma, produced conodonts in abundances ranging from a few tens to over a thousand elements per kilogram and displaying good to excellent preservation with low CAI. These conodonts document a biostratigraphic continuum that provides a standard for correlation of Lower Ordovician rocks in the subsurface of central US and of the many localized and incomplete outcrops of generally equivalent strata in the Ozark and Upper Mississippi Valley regions. The stratigraphic continuity of the collections makes the I-35 section an ideal standard reference section for graphic correlation of Lower Ordovician rocks containing conodonts of the Mid-Continent Province.

  2. Asteroid breakup linked to the Great Ordovician Biodiversification Event

    NASA Astrophysics Data System (ADS)

    Schmitz, Birger; Harper, David A. T.; Peucker-Ehrenbrink, Bernhard; Stouge, Svend; Alwmark, Carl; Cronholm, Anders; Bergström, Stig M.; Tassinari, Mario; Xiaofeng, Wang

    2008-01-01

    The rise and diversification of shelled invertebrate life in the early Phanerozoic eon occurred in two major stages. During the first stage (termed as the Cambrian explosion), a large number of new phyla appeared over a short time interval ~540Myrago. Biodiversity at the family, genus and species level, however, remained low until the second stage marked by the Great Ordovician Biodiversification Event in the Middle Ordovician period. Although this event represents the most intense phase of species radiation during the Palaeozoic era and led to irreversible changes in the biological make-up of Earth's seafloors, the causes of this event remain elusive. Here, we show that the onset of the major phase of biodiversification ~470Myrago coincides with the disruption in the asteroid belt of the L-chondrite parent body-the largest documented asteroid breakup event during the past few billion years. The precise coincidence between these two events is established by bed-by-bed records of extraterrestrial chromite, osmium isotopes and invertebrate fossils in Middle Ordovician strata in Baltoscandia and China. We argue that frequent impacts on Earth of kilometre-sized asteroids-supported by abundant Middle Ordovician fossil meteorites and impact craters-accelerated the biodiversification process.

  3. Stratigraphical distribution of the Ordovician conodont Erraticodon Dzik in Argentina

    NASA Astrophysics Data System (ADS)

    Heredia, S.; Carlorosi, J.; Mestre, A.; Soria, T.

    2013-08-01

    Three different species of the Ordovician genus Erraticodon Dzik are described and illustrated. Erraticodon patu Cooper is reported from the Lower-Midde Ordovician strata of the Acoite and Alto del Cóndor formations. E. cf. Erraticodon balticus and Erraticodon hexianensis from Middle Ordovician carbonate deposits of the San Juan Formation are analyzed and compared to specimens of these species from Australia, China, Newfoundland, and Baltica. E. patu and E. hexianensis are recorded for first time in the San Juan Formation of Precordillera. The elements of E. cf. E. balticus resemble closely E. balticus Dzik but lack the important denticle on the posterior process of the S elements. An evaluation of the stratigraphic occurrences of these species relative to those of key Lower and Middle Ordovician conodont species such as Trapezognathus diprion Lindström, Oepikodus intermedius Serpagli, Baltoniodus triangularis (Lindström), Baltoniodus navis Lindström, Yangtzeplacognathus crassus (Chen and Zhang) and Eoplacognathus pseudoplanus (Viira) indicates they value for biostratigraphic correlation.

  4. Paleogeography and evolution of the Ordovician/Silurian (Whiterockian-Llandoverian) continental margin in central Nevada

    SciTech Connect

    Britt, L.W. )

    1991-02-01

    In central Nevada, stratigraphic successions of Whiterockian-Llandoverian lithofacies, transitional with autochthonous platform/shelf carbonates to the east, occur in isolated windows in outer slope to basinal lithotopes of the Roberts Mountains allochthon. Petrologic, chronostratigraphic and lithostratigraphic, and paleontologic comparison of those successions with platform/shelf facies to the east is integral for reconstruction of Ordovician-Silurian platform margin paleogeography and pre-Antler genesis of the western North American continental margin. Numerous facies changes and/or stratigraphic omissions in central Nevada can be related to sea level fluctuation and aggradation/progradation of the carbonate platform to the east, and not to a postulated, offshore geanticline (i.e., the Toiyabe Ridge). Stratigraphic omission of the Eureka Quartzite above Pogonip equivalents in transitional successions of the Toquima Range and the presence of correlative quartzite in outer slope/basinal parautochthonous facies of the Toiyabe Range suggest development of a possible bypass-margin during the Middle Ordovician. Deposition of Late Ordovician platform margin dolostones (Ely Springs Dolostone) and upper ramp limestones (Hanson Creek Formation and Martin Ridge strata) followed Late Ordovician transgression that drowned the margin and reestablished the carbonate factory. Glacioeustatic drawdown of Late Ordovician-earliest Silurian seas due to the Gondwanan glacial fluctuation can be recognized in strata along the platform margin and upper ramp. Rapid, Early Silurian transgression produced dark-gray carbonates and may have induced marginal flexure and regional, massive slope failure in central Nevada, generating stratigraphic hiatuses west of the platform margin.

  5. Upper Ordovician-Lower Silurian shelf sequences of the Eastern Great Basin: Barn Hills and Lakeside Mountains, Utah

    SciTech Connect

    Harris, M.T. . Dept. of Geosciences); Sheehan, P.M. . Dept of Geology)

    1993-04-01

    Detailed stratigraphic sections through Upper Ordovician-Lower Silurian shelf strata of the Eastern Great Basin were measured in two Utah localities, Barn Hills (Confusion Range) and Lakeside Mountains. Six major subfacies occur in these strata: mud-cracked and crinkly laminated subfacies, Laminated mudstone subfacies, cross-bedded grainstone subfacies, cross-laminated packstone subfacies, grainy bioturbated subfacies, muddy bioturbated subfacies, and thalassinoides burrowed subfacies. These occur in 1--10 m thick cycles in three facies: muddy cyclic laminite facies (tidal flats), cross-bedded facies (subtidal shoals), and bioturbated facies (moderate to low-energy shelf). The vertical facies succession, stacking patterns of meter-scale cycles, and exposure surfaces define correlatable sequences. The authors recognize four Upper Ordovician sequences (Mayvillian to Richmondian). An uppermost Ordovician (Hirnantian) sequence is missing in these sections but occurs basinward. Lower Silurian sequences are of early Llandoverian (A), middle Llandoverian (B), early late Llandoverian (C1--C3), late late Llandoverian (C4--C5), latest Llandoverian (C6) to early Wenlock age. In general, Upper Ordovician and latest Llandoverian-Wenlockian facies are muddier than intervening Llandoverian facies. The shift to muddier shelf facies in latest Llandoverian probably corresponds to the development of a rimmed shelf. The sequence framework improves correlation of these strata by combining sedimentologic patterns with the biostratigraphic data. For example, in the Lakesides, the Ordovician-Silurian boundary is shifted 37 m downward from recent suggestions. In addition, the sequence approach highlights intervals for which additional biostratigraphic information is needed.

  6. Pre-Alleghenian (Pennsylvanian-Permian) hydrocarbon emplacement along Ordovician Knox unconformity, eastern Tennessee

    SciTech Connect

    Haynes, F.M.; Kesler, S.E.

    1989-03-01

    Cores taken during exploration for Mississippi Valley-type lead and zinc ores in the Mascot-Jefferson City zinc district of eastern Tennessee commonly contain hydrocarbon residues in carbonate rocks of the Knox Group immediately below the Lower Ordovician Knox unconformity. The location and number of these residue-bearing strata reveal information about the Paleozoic history of hydrocarbon emplacement in the region. Contour maps, generated from nearly 800 holes covering more than 20 km/sup 2/, indicate that zones with elevated organic content in the uppermost 30 m of the Lower Ordovician Mascot Dolomite show a strong spatial correlation with Middle Ordovician paleotopographic highs. These same zones show no spatial association with present-day structural highs, which were formed during Pennsylvanian-Permian Alleghenian tectonism. This suggests that the physical entrapment of hydrocarbons migrating through the upper permeable units of the Mascot must have occurred prior to the principal tectonism of the Alleghenian orogeny. 7 figures, 1 table.

  7. Thermal maturity patterns (CAI and %Ro) in the Ordovician and Devonian rocks of the Appalachian basin in West Virginia

    USGS Publications Warehouse

    Repetski, John E.; Ryder, Robert T.; Avary, Katharine Lee; Trippi, Michael H.

    2005-01-01

    The objective of this study is to enhance existing thermal maturity maps in West Virginia by establishing: 1) new subsurface CAI data points for the Ordovician and Devonian and 2) new %Ro and Rock Eval subsurface data points for Middle and Upper Devonian black shale units. Thermal maturity values for the Ordovician and Devonian strata are of major interest because they contain the source rocks for most of the oil and natural gas resources in the basin. Thermal maturity patterns of the Middle Ordovician Trenton Limestone are evaluated here because they closely approximate those of the overlying Ordovician Utica Shale that is believed to be the source rock for the regional oil and gas accumulation in Lower Silurian sandstones (Ryder and others, 1998) and for natural gas fields in fractured dolomite reservoirs of the Ordovician Black River-Trenton Limestones. Improved CAI-based thermal maturity maps of the Ordovician are important to identify areas of optimum gas generation from the Utica Shale and to provide constraints for interpreting the origin of oil and gas in the Lower Silurian regional accumulation and Ordovician Black River-Trenton fields. Thermal maturity maps of the Devonian will better constrain burial history-petroleum generation models of the Utica Shale, as well as place limitations on the origin of regional oil and gas accumulations in Upper Devonian sandstone and Middle to Upper Devonian black shale.

  8. Strata mechanics in coal mining

    SciTech Connect

    Jeremic, M.L.

    1985-01-01

    This book considers the following topics: coal measure; coal seam feature; roof and floor strata; virgin strata pressure; deformation and failure of structure; room and pillar mining; longwall mining; slice mining; open slope mining; sub-level caving; and coal pillar structure.

  9. First plants cooled the Ordovician

    NASA Astrophysics Data System (ADS)

    Lenton, Timothy M.; Crouch, Michael; Johnson, Martin; Pires, Nuno; Dolan, Liam

    2012-02-01

    The Late Ordovician period, ending 444 million years ago, was marked by the onset of glaciations. The expansion of non-vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets.

  10. Unusual Deep Water sponge assemblage in South China-Witness of the end-Ordovician mass extinction.

    PubMed

    Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim

    2015-01-01

    There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China. PMID:26538179

  11. Unusual Deep Water sponge assemblage in South China—Witness of the end-Ordovician mass extinction

    NASA Astrophysics Data System (ADS)

    Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim

    2015-11-01

    There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China.

  12. Unusual Deep Water sponge assemblage in South China—Witness of the end-Ordovician mass extinction

    PubMed Central

    Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim

    2015-01-01

    There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China. PMID:26538179

  13. Comparison of Late Ordovician epicontinental seas and their relative bathymetry in North American and China

    SciTech Connect

    Johnson, M.E.; Fox, W.T. ); Jia-Yu, Rong )

    1989-02-01

    Six widely separated areas with Upper Ordovician strata in Canada and the United States are compared with six localities in southern China. Cyclic sedimentation, including evaporites, carbonates, and phosphatic black shales, occurred in relatively shallow epicontinental seas of North America. As many as three Ashgill cycles of regionally different styles may have been coeval throughout North America in response to modest changes in sea level. Environments in South China primarily included carbonates and black shales with a far more uniform distribution. Absence of comparable sedimentary cycles confirms that the platform bathymetry of South China was consistently deeper than in North America. The almost complete exposure of North China (Sino-Korean Plate) by Late Ordovician time underscores the fact that independent cratons have different bathymetric histories. By mid-Silurian time, South China also was fully exposed. Such hypsographic variation is critical to the intercontinental correlation of features related to eustasy, water chemistry, and even the patterns of extinctions.

  14. Late Ordovician (post-Sardic) rifting branches in the North Gondwanan Montagne Noire and Mouthoumet massifs of southern France

    NASA Astrophysics Data System (ADS)

    Javier Álvaro, J.; Colmenar, Jorge; Monceret, Eric; Pouclet, André; Vizcaïno, Daniel

    2016-06-01

    Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded, and the subsequent Middle-Ordovician stratigraphic gap is related to the Sardic phase. Upper Ordovician sedimentation started in the rifting branches of Cabrières and Mouthoumet with deposition of basaltic lava flows and lahar deposits (Roque de Bandies and Villerouge formations) of continental tholeiite signature (CT), indicative of continental fracturing. The infill of both rifting branches followed with the onset of (1) Katian (Ka1-Ka2) conglomerates and sandstones (Glauzy and Gascagne formations), which have yielded a new brachiopod assemblage representative of the Svobodaina havliceki Community; (2) Katian (Ka2-Ka4) limestones, marlstones, and shales with carbonate nodules, reflecting development of bryozoan-echinoderm meadows with elements of the Nicolella Community (Gabian and Montjoi formations); and (3) the Hirnantian Marmairane Formation in the Mouthoumet massif that has yielded a rich and diverse fossil association representative of the pandemic Hirnantia Fauna. The sealing of the subaerial palaeorelief generated during the Sardic phase is related to Silurian and Early Devonian transgressions leading to onlapping patterns and the record of high-angle discordances.

  15. Geochemistry and origin of oil from Cambrian and Ordovician reservoirs in eastern and central Ohio

    SciTech Connect

    Ryder, R.T. ); Burruss, R.C.; Hatch, J.R. )

    1991-08-01

    Oil from stratigraphic traps along the Middle Ordovician Knox unconformity in Ohio was analyzed to determine its geochemical characteristics, source, and migration history. The following stratigraphic units were samples: Upper Cambrian( ) Rose Run Sandstone, sample number (n) = 7; Upper Cambrian Knox Dolomite, n = 6; Upper Cambrian Krysik sandstone, n = 1; and Middle Ordovician Black River Limestone, n = 1. These Ohio oils are geochemically similar to oils in North America that are correlated with Ordovician source rocks. Seventy-one core samples from Ohio and West Virginia were analyzed by Rock-Eval for total organic carbon (TOC) and pyrolysis products and by solvent extraction to evaluate the source of the Ohio oils. Three potential source-rock intervals were tested: (1) Middle and Upper Cambrian strata in the Rome trough, (2) the Middle Ordovician Wells Creek Formation and the equivalent part of the Beekmantown Group, and (3) the Middle and Upper Ordovician Antes Shale. The thermal maturity of many samples was too high to give T{sub max} values and to yield adequate solvent extracts for detailed characterization. The Antes Shale samples have moderate TOC values ({bar x} = 1.2, n = 12) and Rock-Eval production indices between 0.3 and 0.5 ({bar x} = 0.4) calculated from nine samples with TOC greater than 0.5. These geochemical characteristics, a stratigraphic position about 1,000 ft above the Knox unconformity, and a maximum burial depth of about 10,000 ft along the Ohio-West Virginia border suggests that the Antes Shale is the probable source rock for the Ohio oils.

  16. Partitioning of the Taconic foreland basin: Middle to Late Ordovician flysch and molasse sub-basins of New York State and Ontario

    SciTech Connect

    Lehmann, D.; Brett, C.E.; Ingram, S.L. . Dept. of Geological Sciences)

    1992-01-01

    Analysis of field and well data suggest that the foreland basin in New York and Ontario is divisible into two sub-basins containing siliciclastic fill which are separated by a moderately narrow, north/south oriented region of relatively thin siliciclastic strata. The eastern sub-basin contains a thick succession of late Middle and early Late Ordovician basinal black shales and turbiditic siltstones and sandstones (flysch). These strata thicken eastward to over 800 m beneath the thrust belt (Taconic allochthon) in the eastern most portion of the sub-basin. The flysch is, at least in part, time-correlative with ramp carbonates present in the western sub-basin. The western sub-basin contains a relatively thin succession of flysch deposits that overlie Upper Ordovician carbonates. The flysch deposits from the western sub-basin correlate with only the stratigraphically highest strata in the eastern sub-basin. In the western sub-basin, flysch deposits are overlain by Upper Ordovician shallow marine to non-marine mudstones and sandstones (molasse). The molasse is unconformably overlain by Lower Silurian strata. Due to the angularity of the unconformity surface, the molasse is stratigraphically most complete towards the western margin of the western sub-basin; thickest deposits in this sub-basin ([gt] 600 m) are not the most stratigraphically complete. The general sedimentary history of the New York portion of the Taconic siliciclastic wedge is bipartite: (1) rapid subsidence in the eastern sub-basin during the late Middle and early Late Ordovician accompanied by flysch-phase filling; (2) rapid subsidence in the western sub-basin during the middle to late Late Ordovician accompanied by molasse-phase filling.

  17. Middle Ordovician organic matter assemblages and their effect on Ordovician-derived oils

    SciTech Connect

    Jacobson, S.R.; Hatch, J.R.; Teerman, S.C.; Askin, R.A.

    1988-09-01

    Two distinct Middle Ordovician oil-prone organic-matter assemblages occur in thermally immature to marginally mature petroleum source rocks from Iowa. The substantially more oil-prone Assemblage A generates the unique Ordovician Oil fingerprint, which has been associated with the organic-walled microfossil Gloeocapsamorpha prisca. The second, Assemblage B, generates a more ordinary signature. The two assemblages, which are mixed or interbedded in many Ordovician sediments of North America, explain the variations in oils derived from Ordovician source rocks. These mixtures also aid in interpretation of the chemistry of G. prisca. 7 figures, 2 tables.

  18. Trepostome and cystoporate bryozoans from the Lexington Limestone and the Clays Ferry Formation (Middle and Upper Ordovician) of Kentucky

    USGS Publications Warehouse

    Karklins, O.L.

    1984-01-01

    The Lexington Limestone and the Clays Ferry Formation of Kentucky contain an abundant and diversified fossil invertebrate fauna. This report is concerned with the trepostome and cystoporate bryozoans that constitute a major part of that fauna. The Lexington Limestone, largely a biofragmental fossiliferous limestone, rests disconformably on the Tyrone Limestone (Middle Ordovician). The Clays Ferry Formation consists of approximately equal amounts of biofragmentallimestone and shale, and it overlies conformably, or intertongues with, the upper part of the Lexington Limestone. The Clays Ferry Formation is overlain by the Garrard Siltstone (Upper Ordovician) in central Kentucky and intertongues with the Kope Formation (Upper Ordovician) in northern Kentucky. The MiddleUpper Ordovician boundary falls within the upper part of the Lexington Limestone and laterally equivalent strata of the Clays Ferry Formation. The Lexington Limestone has been divided into 12 members, consisting of calcarenites, calcisiltites, calcilutites, nodular limestones, and shales in various amounts, that intertongue complexly. Because of the great abundance of bryozoans this study is generally limited to bryozoans recovered from, in ascending order, the Grier Limestone Member, the Perryville Limestone Member, the Brannon Member, the Tanglewood Limestone Member, and the Millersburg Member of the Lexington Limestone and from the Clays Ferry Formation and its Point Pleasant Tongue. The trepostome and cystoporate bryozoans discussed are referred to 36 species belonging to 22 genera. The trepostome component includes 29 species belonging to 16 genera: Amplexopora, Atactoporella, Balticopora, Batostoma, Cyphotrypa, Dekayia, Eridotrypa, Hetero-_ trypa, Homotrypa, Homotrypella, Mesotrypa, Parvohallopora, Peronopora, Prasopora, Stigmatella, and Tarphophragma, a new genus. Five of the trepostome species are new: Balticopora arcuatilis, Cyphotrypa switzeriensis, Dekayia epetrima, Eridotrypa sadievillensis

  19. Aeromagnetic anomalies over faulted strata

    USGS Publications Warehouse

    Grauch, V.J.S.; Hudson, Mark R.

    2011-01-01

    High-resolution aeromagnetic surveys are now an industry standard and they commonly detect anomalies that are attributed to faults within sedimentary basins. However, detailed studies identifying geologic sources of magnetic anomalies in sedimentary environments are rare in the literature. Opportunities to study these sources have come from well-exposed sedimentary basins of the Rio Grande rift in New Mexico and Colorado. High-resolution aeromagnetic data from these areas reveal numerous, curvilinear, low-amplitude (2–15 nT at 100-m terrain clearance) anomalies that consistently correspond to intrasedimentary normal faults (Figure 1). Detailed geophysical and rock-property studies provide evidence for the magnetic sources at several exposures of these faults in the central Rio Grande rift (summarized in Grauch and Hudson, 2007, and Hudson et al., 2008). A key result is that the aeromagnetic anomalies arise from the juxtaposition of magnetically differing strata at the faults as opposed to chemical processes acting at the fault zone. The studies also provide (1) guidelines for understanding and estimating the geophysical parameters controlling aeromagnetic anomalies at faulted strata (Grauch and Hudson), and (2) observations on key geologic factors that are favorable for developing similar sedimentary sources of aeromagnetic anomalies elsewhere (Hudson et al.).

  20. Complexity in benthic-pelagic marine ecosystems in the late Ordovician (central New York)

    SciTech Connect

    Byrne, S.M.

    1985-01-01

    Cisne and Chandlee (1982) outlined a paleogeographic model for marine invertebrates collected from Middle Ordovician strata in central New York. Subsequent interpretations of their stratigraphic and geographic distributions were based on control by levels of oxygen. Especially critical were the presumed distribution of the trilobite Triarthus and three graptolites, Orthograptus, Climacograptus, and Corynoides, which were supposed to have occupied vertically stratified habitats in the water column. In order to test this general thesis 42 stratigraphically discrete samples were collected from continuously exposed Late Ordovician mudstones in central New York, which contained taxa virtually identically to those employed by Cisne. The sampling interval spanned about 1.5 million years and over 1/4 of the samples contained relatively large numbers of graptolites. Over 3000 graptolite rhabdosomes were identified. The later Ordovician Orthograptus are preserved both with and without Climacograptus and with various benthic taxa. However neither Orthograptus nor Climacograptus display a consistent stratigraphic pattern, and Triarthus co-occurred with both graptolites, introducing a discordant note into any attempt at a simple modeling of early Paleozoic benthic/pelagic ecosystems.

  1. Stratigraphy and tectonic significance of Lower Paleozoic continental margin strata in northeastern Washington

    NASA Astrophysics Data System (ADS)

    Smith, Moira T.; Gehrels, George E.

    1992-06-01

    Lower Paleozoic eugeoclinal strata in the Kootenay Arc in northeastern Washington and southeastern British Columbia are transitional between autochthonous lower Paleozoic miogeoclinal strata and outboard volcanic arc terranes of uncertain paleogeographic affinity. They provide a record of lower Paleozoic continental margin depositional and tectonic processes oceanward of the continental shelf. The southernmost stratigraphic unit, the Covada Group, is divided into two formations, the Daisy Formation, a mid fan sequence of arkosic and subarkosic wacke and arenite, and the Early Ordovician Butcher Mountain Formation, consisting of alkalic(?) pillow basalt and tuff of within-plate affinity. Another unit, formerly part of the Covada Group, is excluded and informally named the Bradeen Hill assemblage. It contains chert, chert-quartz arenite, quartz arenite, chert pebble conglomerate, shale, and basalt, and may be Ordovician to Devonian on the basis of stratigraphic evidence and regional correlations. The Covada Group and Bradeen Hill assemblage record (1) deposition of continentally derived sediments in a submarine fan setting, (2) relatively quiescent starved basin conditions, (3) local faulting; and (4) intermittent periods of volcanism, perhaps reflecting local extension. They can be correlated with other stratigraphic units in the Kootenay Arc and resemble units as far north as the Selwyn basin in northern Canada and as far south as the Roberts Mountains allochthon in central Nevada. This unites the stratigraphic record and implies a high degree of synchroneity of tectonic events along over 2500 km of the outer continental margin during early Paleozoic time.

  2. Evidence for detachment of the Cambro-Ordovician carbonate sequence in the central Appalachians

    SciTech Connect

    Brezinski, D. ); Campbell, P.; Anderson, T.H. . Dept. of Geology and Planetary Science)

    1992-01-01

    Throughout the central Appalachians Cambro-Ordovician carbonate strata are commonly believed to conformably overlie Lower Cambrian clastic strata of the Chilhowee Group. A recently recognized interval of calc-mylonite, 3 to 15 m thick, within the lower Tomstown Formation near the base of the Cambrian carbonate sequence suggests that a structural break may exist. The calc-mylonite is a regional feature which may be recognized for at least 80 km along strike at a consistent stratigraphic level although it and adjacent strata are intricately folded and faulted. The interval includes very light gray to white marble with laminae of tan dolomite which exhibit pervasive mylonite foliation and an east-west stretching lineation. Asymmetric microstructures and detached isoclinal fold hinges suggest that this marble records a component of simple shear. Locally developed kinematic indicators record a top to the west sense of shear. A common mineral assemblage is dolomite + quartz + calcite + muscovite + epidote [+-] chlorite [+-] talc, suggesting that deformation occurred under greenschist facies conditions. Overlying the calc-mylonite is dark gray laminated mylonitic limestone 10--30 m thick, in which strain decreases stratigraphically upward. The calc-mylonite is interpreted as recording detachment of a rigid carbonate sequence from underlying clastic strata. The carbonates have moved westward an unknown distance from their original place of deposition. This detachment is an early structure that was subsequently folded and faulted with the Blue Ridge cover sequence.

  3. Ordovician carbonate formation waters in the Illinois Basin: Chemical and isotopic evolution beneath a regional aquitard

    SciTech Connect

    Stueber, A.M. ); Walter, L.M. . Dept. of Geological Sciences)

    1992-01-01

    Formation waters from carbonate reservoirs in the upper Ordovician Galena Group of the Illinois Basin have been analyzed geochemically to study origin of salinity, chemical and isotopic evolution, and relation to paleohydrologic flow systems. These carbonate reservoirs underlie the Maquoketa Shale Group of Cincinnatian age, which forms a regional aquitard. Cl-Br relations and Na/Br-Cl/Br systematics indicate that initial brine salinity resulted from subaerial evaporation of seawater to a point not significantly beyond halite saturation. Subsequent dilution in the subsurface by meteoric waters is supported by delta D-delta O-18 covariance. Systematic relations between Sr-87/Sr-86 and 1/Sr suggest two distinct mixing events: introduction of a Sr-87 enriched fluid from a siliciclastic source, and a later event which only affected reservoir waters from the western shelf of the basin. The second mixing event is supported by covariance between Sr-87/Sr-86 and concentrations of cations and anions; covariance between Sr and O-D isotopes suggests that the event is related to meteoric water influx. Systematic geochemical relations in ordovician Galena Group formation waters have been preserved by the overlying Maquoketa shale aquitard. Comparison with results from previous studies indicates that waters from Silurian-Devonian carbonate strata evolved in a manner similar to yet distinct from that of the Ordovician carbonate waters, whereas waters from Mississippian-Pennsylvanian strata that overlie the New Albany Shale Group regional aquitard are marked by fundamentally different Cl-Br-Na and Sr isotope systematics. Evolution of these geochemical formation-water regimes apparently has been influenced significantly by paleohydrologic flow systems.

  4. Ordovician paleomagnetism of eastern Yunnan, China

    SciTech Connect

    Fang, Wu; Van der Voo, R. ); Liang, Qizhong )

    1990-06-01

    Three magnetic components have been isolated in Ordovician formations of the Yangtze Paraplatform (South China Block). Two of these (Daqing A and Hongshiya B components) yield paleopoles that conform to the Carboniferous to Triassic segment of the apparent polar wander path for South China, and are therefore interpreted as remagnetizations. The third component (declination/inclination = 301{degree}/+66{degree}, N = 5 sites, k = 21.4, {alpha}{sub 95} = 17{degree}) passes the fold test and is interpreted as primary (late Early Ordovician). The paleopole, at 39{degree}S, 236{degree}E, and the paleolatitude of 48{degree}S support an Ordovician position of South China adjacent to Gondwana.

  5. A Russian record of a Middle Ordovician meteorite shower: Extraterrestrial chromite at Lynna River, St. Petersburg region

    NASA Astrophysics Data System (ADS)

    Lindskog, Anders; Schmitz, Birger; Cronholm, Anders; Dronov, Andrei

    2012-08-01

    Numerous fossil meteorites and high concentrations of sediment-dispersed extraterrestrial chromite (EC) grains with ordinary chondritic composition have previously been documented from 467 ± 1.6 Ma Middle Ordovician (Darriwilian) strata. These finds probably reflect a temporarily enhanced influx of L-chondritic matter, following the disruption of the L-chondrite parent body in the asteroid belt 470 ± 6 Ma. In this study, a Volkhovian-Kundan limestone/marl succession at Lynna River, northwestern Russia, has been searched for EC grains (>63 μm). Eight samples, forming two separate sample sets, were collected. Five samples from strata around the Asaphus expansus-A. raniceps trilobite Zone boundary, in the lower-middle Kundan, yielded a total of 496 EC grains in 65.5 kg of rock (average 7.6 EC grains kg-1, but up to 10.2 grains kg-1). These are extremely high concentrations, three orders of magnitude higher than "background" levels in similar condensed sediment from other periods. EC grains are typically about 50 times more abundant than terrestrial chrome spinel in the samples and about as common as terrestrial ilmenite. Three stratigraphically lower lying samples, close to the A. lepidurus-A. expansus trilobite Zone boundary, at the Volkhov-Kunda boundary, yielded only two EC grains in 38.2 kg of rock (0.05 grains kg-1). The lack of commonly occurring EC grains in the lower interval probably reflects that these strata formed before the disruption of the L-chondrite parent body. The great similarity in EC chemical composition between this and other comparable studies indicates that all or most EC grains in these Russian mid-Ordovician strata share a common source--the L-chondrite parent body.

  6. Ordovician faunas of Burgess Shale type.

    PubMed

    Van Roy, Peter; Orr, Patrick J; Botting, Joseph P; Muir, Lucy A; Vinther, Jakob; Lefebvre, Bertrand; el Hariri, Khadija; Briggs, Derek E G

    2010-05-13

    The renowned soft-bodied faunas of the Cambrian period, which include the Burgess Shale, disappear from the fossil record in the late Middle Cambrian, after which the Palaeozoic fauna dominates. The disappearance of faunas of Burgess Shale type curtails the stratigraphic record of a number of iconic Cambrian taxa. One possible explanation for this loss is a major extinction, but more probably it reflects the absence of preservation of similar soft-bodied faunas in later periods. Here we report the discovery of numerous diverse soft-bodied assemblages in the Lower and Upper Fezouata Formations (Lower Ordovician) of Morocco, which include a range of remarkable stem-group morphologies normally considered characteristic of the Cambrian. It is clear that biotas of Burgess Shale type persisted after the Cambrian and are preserved where suitable facies occur. The Fezouata biota provides a link between the Burgess Shale communities and the early stages of the Great Ordovician Biodiversification Event. PMID:20463737

  7. Ordovician chitinozoan zones of Great Basin

    SciTech Connect

    Hutter, T.J.

    1987-08-01

    Within the Basin and Range province of the Great Basin of the western US, Ordovician chitinozoans have been recovered in two major lithic facies; the western eugeosynclinal facies and the eastern miogeosynclinal facies. Chitinozoans recovered from these facies range in age from Arenig to Ashgill. Extensive collections from this area make possible the establishment of chitinozoan faunal interval zones from the Ordovician of this area. Selected species of biostratigraphic value include, in chronostratigraphic order, Lagenochitina ovoidea Benoit and Taugourdeau, 1961, Conochitina langei Combaz and Peniguel, 1972, Conochitinia poumoti Combaz and Penique, Desmochitina cf. nodosa Eisenack, 1931, Conochitina maclartii Combaz and Peniguel, 1972, Conochitina robusta Eisenack, 1959, Angochitina capitallata Eisenack, 1937, Sphaerochitina lepta Jenkins. 1970, and Ancyrochitina merga Jenkins, 1970. In many cases, these zones can be divided into additional sub-zones using chitinozoans and acritarchs. In all cases, these chitinozoan faunal zones are contrasted with established American graptolite zones of the area, as well as correlated with British standard graptolite zones. The composition of these faunas of the western US Great Basin is similar to that of the Marathon region of west Texas and the Basin Ranges of Arizona and New Mexico, to which direct comparisons have been made. There also appears to be a great similarity with the microfaunas and microfloras of the Ordovician of the Canning basin of western Australia. The Ordovician chitinozoan faunal interval zones established for the Basin and Range province of the Great Basin of the western US also appear to be applicable to the Marathon region of west Texas and the Basin Ranges of Arizona and New Mexico.

  8. Glacial onset predated Late Ordovician climate cooling

    NASA Astrophysics Data System (ADS)

    Pohl, Alexandre; Donnadieu, Yannick; Le Hir, Guillaume; Ladant, Jean-Baptiste; Dumas, Christophe; Alvarez-Solas, Jorge; Vandenbroucke, Thijs R. A.

    2016-06-01

    The Ordovician glaciation represents the acme of one of only three major icehouse periods in Earth's Phanerozoic history and is notorious for setting the scene for one of the "big five" mass extinction events. Nevertheless, the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained. Here using an Earth system model with an innovative coupling method between ocean, atmosphere, and land ice accounting for climate and ice sheet feedback processes, we report simulations portraying for the first time the detailed evolution of the Ordovician ice sheet. We show that the emergence of the ice sheet happened in two discrete phases. In a counterintuitive sequence of events, the continental ice sheet appeared suddenly in a warm climate. Only during the second act, and set against a background of decreasing atmospheric CO2, followed steeply dropping temperatures and extending sea ice. The comparison with abundant sedimentological, geochemical, and micropaleontological data suggests that glacial onset may have occurred as early as the Middle Ordovician Darriwilian, in agreement with recent studies reporting third-order glacioeustatic cycles during the same period. The second step in ice sheet growth, typified by a sudden drop in tropical sea surface temperatures by ˜8°C and the further extension of a single, continental-scale ice sheet over Gondwana, marked the onset of the Hirnantian glacial maximum. By suggesting the presence of an ice sheet over Gondwana throughout most of the Middle and Late Ordovician, our models embrace the emerging paradigm of an "early Paleozoic Ice Age."

  9. Ordovician impacts at sea in Baltoscandia

    NASA Technical Reports Server (NTRS)

    Lindstroem, M.; Puura, V.; Floden, T.; Bruun, A.

    1992-01-01

    Northern Europe has an assemblage of Ordovician probable impacts that is exceptional because the structures involved are relatively old yet well preserved because they formed at sea and because they formed within a restricted geological time in a relatively small area. The Tvaren, Kardla, and Lockne structures might not be strictly contemporaneous but all formed near the beginning of the Caradoc Age (about 460 Ma), whereas the Granby structure is about 20 Ma older. The range of diameters is from about 2 km (Tvaren, Granby) to 8 km (Lockne). The stratigraphic succession formed on impact at sea, as uniformly documented by these structures, begins with a breccia lens consisting of basement rocks that are intensely crushed. Owing to expulsion of sea water by the impact, this breccia formed under essentially dry conditions. Later on this breccia was in part hydrothermally altered. It is overlain by backsurge turbidite that formed from fragments of local sedimentary bedrock and crystalline basement when the sea water returned to the crater site. Either the turbidite is simply a Bouma sequence (although quite thick - as much as over 50 m) from very coarse rubble to mud, or it is more complex. After deposition of the backsurge turbidite, or turbidite complex, the craters still remained as 150-200-m-deep holes in the sea bed. Together with the presence of relatively shallow water over the rim wall, this situation created predictable hydrologic conditions for extended histories of sedimentation and biological development at the crater as well as within it. The presence of a concentration of craters within a limited area of well-preserved and accessible Ordovician deposits raises a question about the Ordovician, especially its middle portion, as potentially an age of relatively intense impact activity even in wider areas. In this connection it may be apposite to mention that the only fossil stony meteorites so far recorded in rocks are from the late Early and the Middle

  10. Unembellished graphic correlation: An example from the Ordovician of North America

    SciTech Connect

    Sweet, W.C. . Dept. of Geological Sciences)

    1993-03-01

    The graphic method, as originally described by Shaw, has now been applied in the correlation of Ordovician rocks in sections at 125 localities in the US and Canada. These sections, related to one another by the well-controlled distribution of 318 species of conodonts, form the basis for a chronostratigraphic framework that currently permits recognition in all major component sections of the equivalents of divisions 6 m thick in the Standard Reference Section. The latter is a graphically assembled composite of long sections in Nevada, Oklahoma, and the Cincinnati Region of Indiana, Kentucky, and Ohio. To demonstrate the graphic method, correlation of Middle and Late Ordovician rocks in New York, Minnesota, and Tennessee will be illustrated. Sections considered include stratotypes of the 7 or 8 stages into which the Mohawkian and Cincinnatian Series have traditionally been divided. Graphic assembly clearly documents the now well-known overlap between the upper Trentonian'' Cobourgian Stage of New York and strata typical of the Edenian and lower Maysvillian stages in the typical Cincinnatian sequence of Ohio, Indiana, and Kentucky.

  11. Microbialite morphostratigraphy as a tool for correlating Late Cambrian-Early Ordovician sequences.

    PubMed

    Shapiro, R S; Awramik, S M

    2000-03-01

    Microbialite morphostratigraphy is a new tool for intrabasinal correlation using diverse microbialite structures (morphotypes). The recognition of the succession of morphotypes over constrained temporal intervals and broad areas is a function of the complex interactions that operate to create the structure. Because so many nonlinked variables (e.g., biotic, sedimentological, physicochemical) are involved, similar morphotypes do not reoccur over long temporal intervals. To demonstrate the technique, the upper Cambrian-lowermost Ordovician shelf strata of the Great Basin, United States, were correlated using both morphostratigraphy and standard lithostratigraphy. Six morphozones and one morphosubzone were recognized, as were four main lithologic successions. Because the boundaries between the morphozones and lithologic successions did not coincide, it is inferred that the characteristics of the various microbialite structures are not solely controlled by physical factors. The principles for establishing a morphostratigraphy outlined in this article allow for the potential to correlate along other ancient marine margins in both the same Cambrian and Ordovician interval, as well as any interval in the Phanerozoic in which diverse microbialite structures occur. PMID:10736268

  12. Trace metal occurrences in acid-insoluble residues of the Ordovician Galena Group, southeastern Minnesota

    SciTech Connect

    Lively, R.S.; Mossler, J.H.; Morey, G.B. ); Hauck, S.A. . Natural Resources Research Inst.)

    1993-03-01

    Regional geochemical, studies on insoluble residues from Paleozoic carbonate rocks have become an integral part of the search for new Upper Mississippi Valley-type mineral deposits in the northern Midcontinent. The authors have extended these studies to southeastern Minnesota, an area well to the north of known lead-zinc deposits of commercial size and grade. In this region, a thin sequence of Upper Cambrian to Middle Ordovician strata unconformably overlies a complex Precambrian basement. More than 500 samples of limestone and dolomite from 40 drill holes and outcrops were analyzed for 29 related trace elements. Preliminary interpretations are based on the analysis of 380 samples of the Ordovician Galena Group from 37 localities. Results indicate that anomalous concentrations of Pb, Cu, zn, As, Cd, and Ni are confined to the southern half of the Galena subgroup area and extend less than 30 miles north of the Iowa border. The anomalous areas, as well as saddles between the, have a distinct northwest trend, coincident with structural features previously recognized in the Precambrian basement. The spatial relationships of the anomalies and the lack of direct correlation imply deposition from fluids moving north out of the main lead-zinc district along structural pathways. The lack of significant anomalies in the northern part of the subcrop area implies northwest weakening of the forces driving the metal-bearing fluids, as well as a decrease over distance in the absolute metal content of the migrating fluids.

  13. Late Ordovician to Early Silurian amalgamation of the Dalradian and adjacent Ordovician rocks in the British Isles

    NASA Astrophysics Data System (ADS)

    Bluck, B. J.; Leake, Bernard E.

    1986-11-01

    From detailed radiometric and pressure-temperature estimates of the metamorphic history, uplift, and erosion of the Dalradian rocks of the British Isles, we find that 15 25 km of erosion took place mainly in Ordovician time. None of this vast volume of material is apparently present in the Ordovician sedimentary basins that now flank the Dalradian block. We conclude that the Ordovician basins to the south of the Dalradian block are exotic terranes, and we document their emplacement into their present position during Late Ordovician to Early Silurian time (i.e., Taconic) by using evidence mainly from western Ireland.

  14. Detrital zircon U-Pb geochronology of Cambrian to Triassic miogeoclinal and eugeoclinal strata of Sonora, Mexico

    USGS Publications Warehouse

    Gehrels, G.E.; Stewart, John H.

    1998-01-01

    One hundred and eighty two individual detrital zircon grains from Cambrian through Permian miogeoclinal strata, Ordovician eugeoclinal rocks, and Triassic post-orogenic sediments in northwestern Sonora have been analyzed. During Cambrian, Devonian, Permian, and Triassic time, most zircons accumulating along this part of the Cordilleran margin were shed from 1.40-1.45 and 1.62-1.78 Ga igneous rocks that are widespread in the southwestern United States and northwestern Mexico. Zircons with ages of approximately 1.11 Ga are common in Cambrian strata and were apparently shed from granite bodies near the sample site. The sources of 225-280 Ma zircons in our Triassic sample are more problematic, as few igneous rocks of these ages are recognized in northwestern Mexico. Such sources may be present but unrecognized, or the grains could have been derived from igneous rocks of the appropriate ages to the northwest in the Mojave Desert region, to the east in Chihuahua and Coahuila, or to the south in accreted(?) arc-type terranes. Because the zircon grains in our Cambrian and Devonian to Triassic samples could have accumulated in proximity to basement rocks near their present position or in the Death Valley region of southern California, our data do not support or refute the existence of the Mojave-Sonora megashear. Ordovician strata of both miogeoclinal and eugeoclinal affinity are dominated by >1.77 Ga detrital zircons, which are considerably older than most basement rocks in the region. Zircon grains in the miogeoclinal sample were apparently derived from the Peace River arch area of northwestern Canada and transported southward by longshore currents. The eugeoclinal grains may also have come from the Peace River arch region, with southward transport by either sedimentary or tectonic processes, or they may have been shed from off-shelf slivers of continents (perhaps Antarctica?) removed from the Cordilleran margin during Neoproterozoic rifting. It is also possible that the

  15. Maps showing petroleum exploration intensity and production in major Cambrian to Ordovician reservoir rocks in the Anadarko Basin

    USGS Publications Warehouse

    Henry, Mitch; Hester, Tim

    1996-01-01

    The Anadarko basin is a large, deep, two-stage Paleozoic basin (Feinstein, 1981) that is petroleum rich and generally well explored. The Anadarko basin province, a geogrphic area used here mostly for the convenience of mapping and data management, is defined by political boundaries that include the Anadarko basin proper. The boundaries of the province are identical to those used by the U.S. Geological Survey (USGS) in the 1995 National Assessment of United Stated Oil and Gas Resources. The data in this report, also identical to those used in the national assessment, are from several computerized data bases including Nehring Research Group (NRG) Associates Inc., Significant Oil and Gas Fields of the United States (1992); Petroleum Information (PI), Inc., Well History Control System (1991); and Petroleum Information (PI), Inc., Petro-ROM: Production data on CD-ROM (1993). Although generated mostly in response to the national assessment, the data presented here arc grouped differently and arc displayed and described in greater detail. In addition, the stratigraphic sequences discussed may not necessarily correlate with the "plays" of the 1995 national assessment. This report uses computer-generated maps to show drilling intensity, producing wells, major fields, and other geologic information relevant to petroleum exploration and production in the lower Paleozoic part of the Anadarko basin province as defined for the U.S. Geological Survey's 1995 national petroleum assessment. Hydrocarbon accumulations must meet a minimum standard of 1 million barrels of oil (MMBO) or 6 billion cubic feet of gas (BCFG) estimated ultimate recovery to be included in this report as a major field or revoir. Mapped strata in this report include the Upper Cambrian to Lower Ordovician Arbuckle and Low Ordovician Ellenburger Groups, the Middle Ordovician Simpson Group, and the Middle to Upper Ordovician Viola Group.

  16. Geochemical character and origin of oils in Ordovician reservoir rock, Illinois and Indiana, USA

    SciTech Connect

    Guthrie, J.M.; Pratt, L.M.

    1995-11-01

    Twenty-three oils produced from reservoirs within the Ordovician Galena Group (Trenton equivalent) and one oil from the Mississippian Ste. Genevieve Limestone in the Illinois and Indiana portions of the Illinois basin are characterized. Two end-member oil groups (1) and (2) and one intermediate group (1A) are identified using conventional carbon isotopic analysis of whole and fractionated oils, gas chromatography (GC) of saturated hydrocarbon fractions, isotope-ratio-monitoring gas chromatography/mass spectrometry (irm-GC/MS) of n-alkanes ranging from C{sub 15} to C{sub 25}, and gas chromatography/mass spectrometry (GC/MS) of the aromatic hydrocarbon fractions. Group 1 is characterized by high odd-carbon predominance in mid-chain n-alkanes (C{sub 15}-C{sub 19}), low abundance Of C{sub 20+}, n-alkanes, and an absence of pristane and phytane. Group IA is characterized by slightly lower odd-carbon predominance of mid-chain n-alkanes, greater abundance of C{sub 20+} n-alkanes compared to group 1, and no pristane and phytane. Conventional correlations of oil to source rock based on carbon isotopic-type curves and hopane (m/z 191) and sterane (m/z 217) distributions are of limited use in distinguishing Ordovician-reservoired oil groups and determining their origin. Oil to source rock correlations using the distribution and carbon isotopic composition of n-alkanes and the m/z 133 chromatograms of n-alkylarenes show that groups 1 and 1A originated from strata of the Upper Ordovician Galena Group. Group 2 either originated solely from the Upper Ordovician Maquoketa Group or from a mixture of oils generated from the Maquoketa Group and the Galena Group. The Mississippian-reservoired oil most likely originated from the Devonian New Albany Group. The use of GC, irm-GC/MS, and GC/MS illustrates the value of integrated molecular and isotopic approaches for correlating oil groups with source rocks.

  17. 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

  18. Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry.

    PubMed

    Trotter, Julie A; Williams, Ian S; Barnes, Christopher R; Lécuyer, Christophe; Nicoll, Robert S

    2008-07-25

    The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth's history. Previous temperature estimates of up to approximately 70 degrees C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician-Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period. PMID:18653889

  19. Thermal maturity of carboniferous strata, Ouachita Mountains

    SciTech Connect

    Houseknecht, D.W.; Matthews, S.M.

    1985-03-01

    The Ouachita Mountains, a relatively untested, potential hydrocarbon province, contain a thick Paleozoic section of apparently favorable source beds, reservoir beds, and trap configurations. To estimate the thermal maturity of these strata, vitrinite reflectance was measured on 89 samples collected mostly from Carboniferous rocks from throughout the Ouachita outcrop area.

  20. A time like our own? Radioisotopic calibration of the Ordovician greenhouse to icehouse transition

    NASA Astrophysics Data System (ADS)

    Smith, M. Elliot; Singer, Brad S.; Simo, Toni

    2011-11-01

    Tiered interpolation, a new timescale methodology, was used to construct the first radioisotopically-calibrated composite δ 13C curve for the Ordovician period using sanidine 40Ar/ 39Ar age determinations and existing U-Pb geochronology and biostratigraphic zonation. Tiered interpolation intercalates and temporally scales the numerical age of lithostratigraphic horizons by conducting a series of nested projections between hierarchical temporal control points. For primary control points, new 40Ar/ 39Ar ages and legacy U-Pb geochronology were screened to avoid analyses affected by inheritance and daughter loss and calibrated to reflect modern decay constants and standard values. Ages for secondary, tertiary, etc.… control points are obtained via linear interpolation of between higher order control points. In scaling the Ordovician δ 13C composite, the following control point order was applied: (1) radioisotopic ages (2) graptolite Zones, (3) index taxa-based on speciation events (North Atlantic conodont Zones), (4) North American Mid-continent conodont zones, and (5) stratal thicknesses at δ 13C sampled sections. The resulting timescale utilizes the highest resolution of each component, is internally consistent, and is re-scalable as more precise radioisotopic ages become available. It provides a robust framework for independently assessing the accuracy of biostratigraphic composite timescales because it does not rely an assumption of quasi-continuous sediment accumulation and/or speciation. To better calibrate the Late Ordovician and resolve a discrepancy between U-Pb and 40Ar/ 39Ar ages, three new 40Ar/ 39Ar ages were determined via the laser fusion of multiple single sanidine phenocrysts from three bentonitic ash beds from the Late Ordovician marine strata of the upper Mississippi valley where the record of Taconic volcanism is most complete. Fusions of 275 individual sanidine crystals from the Millbrig, Dygerts, and Rifle Hill bentonites yield largely

  1. Supraregional seismites in Triassic - Jurassic boundary strata

    NASA Astrophysics Data System (ADS)

    Lindström, Sofie; Pedersen, Gunver K.; van de Schootbrugge, Bas; Johansson, Leif; Petersen, Henrik I.; Dybkjær, Karen; Weibel, Rikke; Hansen, Katrine H.; Erlström, Mikael; Alwmark, Carl; Nielsen, Lars Henrik; Oschmann, Wolfgang; Tegner, Christian

    2014-05-01

    The end-Triassic mass extinction event (201.564 Ma) was synchronous with the earliest volcanic phase during the emplacement of the Central Atlantic Magmatic Province (CAMP), a large igneous province (LIP) formed during the initial breakup of Pangea. Volcanic degassing of CO2 and other volatile gases, and/or thermogenic methane, from the CAMP is generally regarded as the main cause of the end-Triassic biotic crisis. However, discrepancies in the durations of the ETE (50 Kyrs) and the CAMP volcanism (600 Kyrs) as well as temporal offsets between carbon cycle perturbations and biotic turnovers suggest a more complex scenario that require further studies of the temporal succession of events in Triassic-Jurassic (TJ) boundary strata. Here, we present and examine multiple episodes of soft-sediment deformation (seismite) within uppermost Rhaetian marine and terrestrial strata of Denmark, Sweden and Germany. These seismites are stratigraphically constrained by palynology and C-isotopes to the latest Rhaetian, and are synchronous to the single seismite layer from the UK, which similarly predates the T/J boundary, and has been explained by an extraterrestrial bolide impact. Instead, we argue that the multiple episodes of soft-sediment deformation, interbedded by undisturbed strata, were formed from repeated intense earthquake activity restricted to an interval within the latest Rhaetian bracketed by two negative excursions in δ13C and also containing palynological evidence for deforestation and fern proliferation. The fact that these biotic changes coincide with repeated seismic activity has implications for the end-Triassic extinction and the CAMP scenario. We discuss the temporal position of the seismites in regards to other end-Triassic events, and argue that their supraregional distribution in pre-TJ-boundary strata of NW Europe may be linked to intensified earthquake activity during CAMP emplacement, rather than an extraterrestrial impact.

  2. Rank Ordovician wildcats staked in northern Mississippi counties

    SciTech Connect

    Petzet, G.A.

    1990-10-01

    This paper reports that Ordovician Knox dolomite is the objective at two rank wildcats in northern Mississippi. The wells appear to be the first modern drilling to Ordovician in the area, about 400 miles southeast of prolific Cambro-Ordovician Arbuckle gas production discovered in late 1987 in Wilburton field, Latimer County, Okla. The author discusses how an oil company plans a 12,500 ft Knox test at 1 Lay, in 27-25n-2e, in central Tallahatchie County, Miss., about 80 miles south of Memphis. This paper also reports on plans to drill 1 Jenkins 8-1, in 8-19n-15e, to 10,800 ft or Ordovician.

  3. Biostratigraphy and chronostratigraphy of the Cambrian-Ordovician great American carbonate bank

    USGS Publications Warehouse

    Taylor, John F.; Repetski, John E.; Loch, James D.; Leslie, Stephen A.

    2012-01-01

    The carbonate strata of the great American carbonate bank (GACB) have been subdivided and correlated with ever-increasing precision and accuracy during the past half century through use of the dominant organisms that evolved on the Laurentian platform through the Cambrian and the Ordovician. Trilobites and conodonts remain the primary groups used for this purpose, although brachiopods, both calcareous and phosphatic, and graptolites are very important in certain facies and intervals. A series of charts show the chronostratigraphic units (series and stages) currently in use for deposits of the GACB and the biostratigraphic units (zones, subzones, and biomeres) whose boundaries delineate them. Older and, in some cases obsolete, stages and faunal units are included in the figures to allow users to relate information from previous publications and/or industry databases to modern units. This chapter also provides a brief discussion on the use of biostratigraphy in the recognition and interregional correlation of supersequence boundaries within the Sauk and Tippecanoe megasequences, and the varied perspectives on the nature of biostratigraphic units and their defining taxa during the past half century. Also included are a concise update on the biomere concept, and an explanation of the biostratigraphic consequences of a profound change in the dynamics of extinction and replacement that occurred on the GACB in the Early Ordovician when the factors responsible for platformwide biomere-type extinctions faded and ultimately disappeared. A final section addresses recent and pending refinements in the genus and species taxonomy of biostratigraphically significant fossil groups, the potential they hold for greatly improved correlation, and the obstacles to be overcome for that potential to be realized.

  4. Formation waters from Cambrian-age strata, Illinois Basin, USA: Constraints on their origin and evolution

    NASA Astrophysics Data System (ADS)

    Panno, Samuel V.; Hackley, Keith C.; Locke, Randall A.; Krapac, Ivan G.; Wimmer, Bracken; Iranmanesh, Abbas; Kelly, Walton R.

    2013-12-01

    Recently, brine samples from the Cambrian-age Mount Simon Formation (the deepest, most inaccessible sedimentary rock formation of the Illinois Basin) and the overlying Ironton-Galesville Formation were collected as part of a major research effort evaluating the feasibility of sequestration of carbon dioxide in deep geologic formations. Halide and halide/cation ratios (especially Cl/Br and Na/Br ratios) from groundwater samples collected during this investigation suggest that the brines of the Cambrian-age strata formed by the evaporation of seawater well beyond the point of halite precipitation. The Cl/Br and Na/Br ratios, the presence of Mississippi-Valley-Type (MVT) ore mineralization in close proximity to the Illinois Basin, and the tectonic history of the region and the Illinois Basin suggest that components of ore-forming brines and perhaps crystalline basement brine are likely still present within the Mount Simon Formation. Halide and cation/halide ratio plots show that these brines have mixed with and have been diluted by subaerially evaporated seawater, seawater and dilute groundwater. Movement of brines out of the Mount Simon Formation and/or exchange with brines of other formations is constrained by the overlying, siltstone- and shale-rich Eau Claire Formation, a low-permeability layer. The most plausible interpretation of the halide and halide/cation ratio data is that the brines of the Cambrian-age strata were introduced to the Illinois Basin from outside of the basin, perhaps when the Illinois Basin was connected to the Arkoma (Oklahoma and Arkansas) and Black Warrior Basins (Alabama and Mississippi) via the Reelfoot Rift during Cambrian and early Ordovician time. In addition, the presence of some percentage of high NaCl, low Cl/Br brines from the crystalline basement is suggested given the geochemical relationships of the halide and cation/halide ratios and the tectonic history of the Illinois Basin. Finally, halide and cation/halide ratios determined

  5. Detrital Zircon Geochronology of Cambro-Ordovician Siliciclastic Units of the Humber Arm Allochthon, Newfoundland, Canada

    NASA Astrophysics Data System (ADS)

    Gittens, A.; Casey, J. F.; Lapen, T. J.; Dewey, J. F.; Reid, D.

    2012-12-01

    Paleogeographic reconstruction of the Newfoundland area suggests that various arc terranes developed during the opening of the Iapetus Ocean and development of the Cambro-Ordovician Laurentian stable continental margin. These terranes were then accereted to the continental passive-margin upon initial closure of the ocean basin in the Ordovician. The origin and age of these terranes are still questionable as they may contain older Pre-Cambrian basement according to some workers, and if so, they could be interpreted as originating from Laurentia or any other bordering landmass to the Iapetus Ocean at that time. The sedimentary packages of the Humber Arm allochthon in Newfoundland, Canada, were thrust upon autochthonous sedimentary rocks of the Laurentian passive-margin and deformed during the Taconic Orogeny. Zircon U-Pb ages in the syn- and post-rift siliciclastic strata of the Humber Arm Allochthon (the Bradore, Blow Me Down Brook, Summerside, Irishtown, Lower Head, and Goose Tickle Formations) were coupled with correlation to known source region ages in Laurentia and proposed younger arc terranes. Results show that: (1) there are predominantly Laurentian-derived contributions to detrital sediment deposited along the passive margin and foreland basin units during the early Cambrian to middle Ordovician, with relative age contributions ranging from the Archean (3070 Ma) to the Paleozoic (551 Ma), which agrees with previous interpretations and provides a better constraint on the duration of rifting (591 - 551 Ma); (2) only two grains yielded ages consistent with an arc age (482 Ma and 480 Ma), based on the method used, which are insufficient to constrain the age and nature of the Taconic Arc; (3) a biased analysis of small (50-100μm), euhedral zircons yielded an age range of 464 - 510 Ma and a peak age of 466 Ma (3 grains), which is consistent with the age of the colliding arc system; (4) the North Atlantic craton and adjacent terranes in the Labrador region

  6. The record of time in cratonic interior strata: Does exceptionally slow subsidence necessarily result in exceptionally poor stratigraphic completeness?

    USGS Publications Warehouse

    Runkel, Anthony C.; Miller, J.F.; McKay, R.M.; Palmer, A.R.; Taylor, John F.

    2008-01-01

    A newly constructed a high-resolution chronostratigraphic and lithostratigraphic framework for the Upper Cambrian and Lower Ordovician Sauk Sequence in the cratonic interior of North America provides insight into the long-standing question of how time is recorded in sedimentary packages deposited in shallow epeiric seas across regions with exceptionally slow subsidence. It reveals that time is recorded in these strata in a manner fundamentally similar to the way it is in a number of nearshore marine-dominated sedimentary packages that were deposited under conditions of markedly higher subsidence rates. The principal consequence of slow subsidence in the cratonic interior appears largely to be a pronounced shingling of chronostratigraphic units perpendicular to depositional strike. An evaluation of relative stratigraphic completeness of the Upper Cambrian and Lower Ordovician of this region suggests that a number of routine interpretations and assumptions must be re-evaluated. Our results are inconsistent with the common interpretation that: (1) cratonic interior sedimentary packages are exceptionally stratigraphically incomplete; and (2) that conditions of very slow subsidence and a bathymetrically shallow shelf by themselves preclude deposition of a relatively complete record of time. In refuting these conventional assumptions, our conclusions have implications for a variety of approaches that require a fundamental understanding of the stratigraphic record of time, such as efforts to construct eustatic sea level curves and evaluations of the fossil record of evolution.

  7. Provenance of north Gondwana Cambrian-Ordovician sandstone: U-Pb SHRIMP dating of detrital zircons from Israel and Jordan

    USGS Publications Warehouse

    Kolodner, K.; Avigad, D.; McWilliams, M.; Wooden, J.L.; Weissbrod, T.; Feinstein, S.

    2006-01-01

    A vast sequence of quartz-rich sandstone was deposited over North Africa and Arabia during Early Palaeozoic times, in the aftermath of Neoproterozoic Pan-African orogeny and the amalgamation of Gondwana. This rock sequence forms a relatively thin sheet (1-3 km thick) that was transported over a very gentle slope and deposited over a huge area. The sense of transport indicates unroofing of Gondwana terranes but the exact provenance of the siliciclastic deposit remains unclear. Detrital zircons from Cambrian arkoses that immediately overlie the Neoproterozoic Arabian-Nubian Shield in Israel and Jordan yielded Neoproterozoic U-Pb ages (900-530 Ma), suggesting derivation from a proximal source such as the Arabian-Nubian Shield. A minor fraction of earliest Neoproterozoic and older age zircons was also detected. Upward in the section, the proportion of old zircons increases and reaches a maximum (40%) in the Ordovician strata of Jordan. The major earliest Neoproterozoic and older age groups detected are 0.95-1.1, 1.8-1.9 and 2.65-2.7 Ga, among which the 0.95-1.1 Ga group is ubiquitous and makes up as much as 27% in the Ordovician of Jordan, indicating it is a prominent component of the detrital zircon age spectra of northeast Gondwana. The pattern of zircon ages obtained in the present work reflects progressive blanketing of the northern Arabian-Nubian Shield by Cambrian-Ordovician sediments and an increasing contribution from a more distal source, possibly south of the Arabian-Nubian Shield. The significant changes in the zircon age signal reflect many hundreds of kilometres of southward migration of the provenance. ?? 2006 Cambridge University Press.

  8. Remagnetized cratonic Cambrian strata from southern Nevada

    NASA Astrophysics Data System (ADS)

    Gillett, Stephen L.

    1982-08-01

    Stratigraphic sections of Cambrian strata in southeastern Nevada are akin to thin, cratonic facies exposed in the Grand Canyon; their structural setting is much more complicated, however, from Mesozoic and Cenozoic tectonism. Paleomagnetic samples from two sections through these strata appear to have been completely remagnetized. Coarse-grained, lightcolored sandstone from the Tapeats Sandstone yields scattered magnetizations, residing in hematite, that appear to reflect protracted diagenetic acquisition of remanence. A hematitic sandstone in the Bright Angel Shale yields relatively consistent `Paleozoic' directions of magnetization, but petrographic study shows that the hematite results from diagenetic oxidation, and stratigraphic arguments suggest that the oxidation was not penecontemporaneous. Gray limestones of the Jangle and Muav Limestones yield a magnetization, residing in magnetite, that may reflect late Tertiary remagnetization, being imposed during uplift related to the onset of Basin and Range deformation. In any case, this magnetization differs greatly in direction from a hematite magnetization reported from slightly younger Muav Limestone in the Grand Canyon. Both the sampling sites also appear to have been tectonically rotated, but whether this rotation is true or a geometric artifact of the tilt correction cannot be determined from the present data. These results suggest that paleomagnetic data from rocks as old as Cambrian must be scrutinized very carefully before their magnetizations can be accepted as penecontemporaneous, and such scrutiny must include geologic data.

  9. Glacial recharge and paleohydrologic flow systems in the Illinois basin: Evidence from chemistry of Ordovician carbonate (Galena) formation waters

    SciTech Connect

    Stueber, A.M. ); Walter, L.M. )

    1994-11-01

    The Illinois basin provides an opportune setting for elucidating the roles of remnant evaporite brines and meteoric waters in the evolution of formation waters in an intracratonic sedimentary basin. Formation waters from carbonate reservoirs in the Upper Ordovician Galena Group have been analyzed geochemically to study the origin of their salinity, their chemical and isotopic evolution, and their relationship to paleohydrologic flow systems. Chloride/bromide ratios and Cl/Br-Na/Br relations indicate that initial brine salinity resulted from subaerial evaporation of seawater rather than from halite dissolution. Subsequent subsurface dilution of the brines by meteoric waters is disclosed by [delta]D-[delta][sup 18]O covariance; however, the remnant evaporite brine has not been completely expelled from these Ordovician strata. Galena formation waters have [sup 87]Sr/[sup 86]Sr ratios that range from 0.708 17 (a value nearly equal to that of coeval seawater) to 0.710 43. This is the greatest range of Sr isotopic ratios found in waters from any stratigraphic unit in the basin. Two fluid mixing events are revealed in plots of [sup 87]Sr/[sup 86]Sr vs. 1/Sr. 41 refs., 11 figs., 1 tab.

  10. Ordovician orogeny in the Alps: a reappraisal

    NASA Astrophysics Data System (ADS)

    Zurbriggen, Roger

    2015-03-01

    An important part of the pre-Mesozoic basement of the Alps is the product of orogenic processes occurred in Ordovician times. Most of the geological constrains for this reconstruction have been obtained by the study of the Strona-Ceneri zone in the Southern Alps, where Alpine overprint was weak. The erosion of late Pan-African belts delivered large amounts of greywackes and pelites into subduction zones along Gondwana. The sediments were subducted and accreted to form wide complexes. As a result of the large sediment input, subduction retreated and the mantle-derived magmas intruded the base of the fertile "mud pile." This initiated substantial anatexis to produce peraluminous magmas, which intruded and extruded syntectonically. Thereby, the predominantly steeply structured subduction-accretion complex provided ideal pathways for the uprising magmas, and down-thrusting host rocks to result in an isostatically stable crust. The SE Australian Lachlan fold belt is interpreted as an upper crustal analog of the Strona-Ceneri zone. Based on the combination of their geology, a crustal profile through an Alaskan type of orogen is drawn.

  11. Carbon isotope variation in mid-continent Ordovician-type oils: relationship to a major middle Ordovician carbon isotope shift

    SciTech Connect

    Hatch, J.R.; Jacobson, S.R.; Witzke, B.J.; Anders, D.E.; Watney, W.L.; Newell, K.D.

    1985-05-01

    Detailed organic geochemical comparisons of Mid-Continent Ordovician oils with extracts of potential source rocks show that in the Forest City basin of northeastern Kansas and southeastern Nebraska, oil source rocks are Middle Ordovician shales of the Simpson Group. For the Keota Dome field, Washington County, Iowa, the oil source rock is the Middle Ordovician Glenwood Shale Member of the Platteville Formation. Analyses of saturated and aromatic hydrocarbon fractions of Ordovician-type oils from the Forest City basin, Keota Dome field, and the Michigan basin show that sigma TC of the two fractions are similar and that sigma T varies over a considerable range, from -32.5 per mil to -25.5 per mil (PDB). This large range in sigma TC reflects a major shift in the carbon isotope composition of organic matter during the Middle Ordovician. This shift is shown in a 62.5-ft (19 m) interval of core from the Decorah and Platteville Formations in the E.M. Greene 1 well in Washington County, Iowa, where organic carbon sigma TC changes regularly upward from -32.2 per mil to -22.7 per mil (PDB). The change in organic carbon sigma TC in this core is not related to variations in amount (0.13-41.4% TOC) or type (hydrogen index = 69 to 1000 mg HC/g TOC) of the marginally mature (T/sub max/ = 440 +/- 5C) organic matter. Ordovician-type oils in both the Forest City and Michigan basins show variable sigma TC, suggesting that the sigma TC shift displayed in the Middle Ordovician rocks of southeastern Iowa is a regional and possibly a global effect, related to changes in the sigma TC of the ocean-atmosphere carbon reservoir. Isotopic analyses of coexisting carbonate minerals support this interpretation.

  12. An Ordovician variation on Burgess Shale-type biotas

    PubMed Central

    Botting, Joseph P.; Muir, Lucy A.; Jordan, Naomi; Upton, Christopher

    2015-01-01

    The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods. Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas. Here we clarify the early stages of the GOBE by describing a new open-marine Konservat-Lagerstätte from the Early Ordovician of Wales. The Afon Gam Biota includes many lineages typical of the Cambrian Burgess Shale-type biotas, but the most abundant groups were sponges, algae and worms, with non-trilobite arthropods being unexpectedly rare. Labile tissues occur abundantly in the sponges and are also present in other groups, including brachiopods and hyoliths. Taphonomic biases are considered and rejected as explanations for arthropod rarity; the preserved biota is considered to be an approximation to the original community composition. We note that other exceptionally preserved communities in the Welsh Ordovician are also sponge-dominated, suggesting a regional change in benthic ecology during the early stages of the GOBE. PMID:25909638

  13. Chemical correlation of K-bentonite beds in the Middle Ordovician Decorah Subgroup, upper Mississippi Valley

    NASA Astrophysics Data System (ADS)

    Kolata, Dennis R.; Frost, Joyce K.; Huff, Warren D.

    1987-03-01

    Strata of the Champlainian (Middle Ordovician) Decorah Subgroup in the upper Mississippi Valley region have been correlated on the basis of the chemical composition of K-bentonite beds in widely distributed outcrops and cores. The four principal K-bentonite beds in the Decorah—the Deicke, Millbrig, Elkport, and Dickeyville—can be differentiated by their unique chemical fingerprints, which were established using a linear discriminant function analysis. The elements that served as the best discriminators of differences between beds were, in order of atomic number, Na, Sc, Ti, Zr, Sm, Eu, Tb, Dy, Yb, Lu, Hf, Ta, and Th. Although no one element serves to delineate a K-bentonite bed completely from others, a combination of elements can do so. The chemical signatures of the Deicke and Millbrig K-bentonite Beds, the two thickest and most widespread K-bentonites in the Mississippi Valley, were recognized in outcrop and subsurface from southern Minnesota to southeastern Missouri, a distance of about 900 km. The Elkport and the Dickeyville K-bentonites were chemically identified in a limited area in northern Illinois, southwestern Wisconsin, and northern Iowa. The Decorah consists of widespread lithologic units that are approximately parallel to K-bentonite beds in some areas, but in other areas lateral gradation of lithologies, as shown by K-bentonite correlations, indicates contemporaneity of Decorah lithofacies.

  14. Comparative diversification dynamics among palaeocontinents during the Ordovician Radiation

    NASA Technical Reports Server (NTRS)

    Miller, A. I.

    1997-01-01

    The Ordovician Radiation was among the most extensive intervals of diversification in the history of life. However, a delineation of the proximal cause(s) of the Radiation remains elusive. Any such determination should involve an analysis of geographic overprints on diversification: did the Radiation occur randomly around the world or, alternatively, was it focused in particular geographic or depositional regimes? Here, I present a comparative evaluation of Ordovician diversification among several palaeocontinents to determine whether biotas associated with certain palaeocontinents exhibited different diversification patterns than others; in part, this involves a numerical "correction" to raw diversity trajectories. Clear disparities among palaeocontinents are indicated by the data, which appear to reflect differences in the extent of siliciclastic input partly in association with tectonic activity. Further testing will be required to fully substantiate the implication that siliciclastic influx was a predominant factor in the Ordovician Radiation, affecting a variety of higher taxa among all three Phanerozoic evolutionary faunas.

  15. Reconstructing Late Ordovician carbon cycle variations

    NASA Astrophysics Data System (ADS)

    Pancost, Richard D.; Freeman, Katherine H.; Herrmann, Achim D.; Patzkowsky, Mark E.; Ainsaar, Leho; Martma, Tõnu

    2013-03-01

    The role of carbon dioxide in regulating climate during the early Paleozoic, when severe glaciations occurred during a putative greenhouse world, remains unclear. Here, we present the first molecular carbon isotope proxy-based estimates for Late Ordovician (early Katian) pCO2 levels, and explore the limitations of applying this approach to the reconstruction of Paleozoic pCO2. Carbon isotope profiles from three sites in Laurentia (Iowa, Ontario and Pennsylvania) and one site in Baltica (Estonia) exhibit overall low isotope fractionation between organic and inorganic carbon during photosynthesis (ɛp) and these values declined during the early Katian carbonate carbon isotope excursion (or Guttenberg Carbon Isotope Excursion, GICE). Algal ɛp values are sensitive to changes in CO2 concentrations, algae cell morphologies, and cell growth rates. To constrain these factors, we present molecular evidence that a decrease in the relative abundance of cyanobacteria and a change in the eukaryotic algae community co-occurred with the GICE. Regardless of local biotic or oceanographic influences, a decline in ɛp values indicates photosynthesis was sensitive to carbon concentrations, and via analogy with modern taxa, constrains pCO2 to below ˜8× pre-industrial levels (PIL), or about half of previous estimates. In addition, the global, positive carbon isotope excursions expressed in a wide variety of sedimentary materials (carbonate, bulk organic matter, n-alkanes, acyclic and cyclic isoprenoid hydrocarbons), provide compelling evidence for perturbation of the global carbon cycle, and this was likely associated with a decrease in pCO2 approximately 10 million years prior to the Hirnantian glaciations. Isotopic records from deeper water settings suggest a complex interplay of carbon sources and sinks, with pCO2 increasing prior to and during the early stages of the GICE and then decreasing when organic carbon burial outpaced increased volcanic inputs.

  16. Vestiges of an Ordovician west-vergent thin-skinned Ocloyic thrust belt in the Argentine Precordillera, southern Central Andes

    NASA Astrophysics Data System (ADS)

    Thomas, William A.; Astini, Ricardo A.

    2007-08-01

    Collision of the down-going, Laurentia-derived Argentine Precordillera terrane with the Gondwanan margin drove the Ordovician Ocloyic orogeny, including subduction volcanism, metamorphism, and top-to-west shearing east of the Precordillera. In the Precordillera, above passive-margin carbonates (Lower Ordovician San Juan Limestone and older carbonates), a Middle to Upper Ordovician westward-prograding synorogenic clastic wedge of black shale (Gualcamayo Shale) and coarser clastic sediment (Las Vacas Conglomerate and Trapiche Formation) fills a peripheral foreland basin. New research has identified vestiges of a west-directed thin-skinned Ocloyic foreland thrust belt that has been fragmented by east-directed Andean thrusting. The El Corral thrust sheet, with hanging-wall detachment in the San Juan Limestone, extends over a west-directed footwall frontal ramp and extensive flat to low-angle footwall cutoff in the Gualcamayo and Las Vacas formations. Las Vacas conglomerates in the footwall include olistoliths (10-m scale) exclusively of San Juan Limestone and Gualcamayo Shale; the beds in some olistoliths are folded. The advancing El Corral thrust sheet successively supplied and overrode the stratigraphically restricted olistoliths. In the El Corral footwall, tight west-vergent folds and faults within an anticlinorium in the San Juan Limestone and Gualcamayo Shale suggest a deeper (unexposed) thrust fault, the Los Celestitos fault. West of the anticlinorium, easterly dip (restored to remove Andean deformation) beneath an angular unconformity between Las Vacas and Trapiche beds is consistent geometrically with the trailing limb of a west-vergent fault-propagation anticline in the hanging wall of the subsurface Los Celestitos fault. The same angular unconformity truncates the El Corral fault and hanging-wall strata. In the Trapiche Formation, contrasting sedimentary facies from sandy turbidites westward to limestone-clast megabeds and olistoliths suggest another frontal

  17. Organic geochemistry of mid-continent Ordovician oils

    SciTech Connect

    Palmer, S.E.

    1985-01-01

    Early Paleozoic oils retain the biochemical imprint of oceanic life prior to evolution of land plants and vertebrates. Thus, these oils have geochemical features which make them unique with respect to younger oils, but also share some common properties with the latter. Characteristic mid-continent Ordovician oil features include predominance of n-C/sub 14/ to n-C/sub 19/ over n-C/sub 20/+ alkanes in the C/sub 15/+ saturate hydrocarbon fraction, low amounts of isoprenoids and abundant C/sub 27/ and C/sub 29/ diasteranes relative to normal steranes. Properties common to both Ordovician and younger oils are: nearly equal amounts of C/sub 15/+ n-alkanes, cycloalkanes, and aromatics and pristane/phytane ratios of 0.7 to 1.6. Collectively, these Ordovician oils have a relatively negative stable carbon isotopic composition but are not unique with respect to other marine oils. Although terpane distributions are generally similar to geologically-younger oils, the Ordovician oils contain significant amounts of C/sub 19/, C/sub 20/, and C/sub 21/ tricyclic diterpanes relative to the C/sub 23/ homolog as well as large contributions by C/sub 31/+ pentacyclic triterpanes. Presence of long-chained n-alkanes, C/sub 29/ steranes, and C/sub 24/ tetracyclic terpanes, which are generally accepted as input from land plants in, e.g., Tertiary deposits, are also present in Ordovician oils. The characteristics listed above describe oils from the Williston and Michigan basins as well as Ordovician oils from Kansas and Oklahoma.

  18. Element distribution patterns in the ordovician Galena group, Southeastern Minnesota: Indicators of fluid flow and provenance of terrigenous material

    USGS Publications Warehouse

    Lively, R.S.; Morey, G.B.; Mossler, J.H.

    1997-01-01

    As part of a regional geochemical investigation of lower Paleozoic strata in the Hollandale embayment of southeastern Minnesota, elemental concentrations in acid-insoluble residues were determined for carbonate rock in the Middle Ordovician Galena Group. Elemental distribution patterns within the insoluble residues, particularly those of Ti, Al, and Zr, show that the Wisconsin dome and the Wisconsin arch, which contributed sediment to the embayment prior to Galena time, continued as weak sources of sediment during this period. In contrast, trace metals commonly associated with Mississippi Valley-type lead-zinc mineralization, including Pb, Zn, Cu, Ag, Ni, Co, As, and Mo, show dispersal patterns that are independent of those associated with primary depositional phenomena. These trace metals are concentrated in southern Minnesota in carbonate rocks near the interface between limestone- and dolostone-dominated strata. Dispersal patterns imply that the metals were carried by a north-flowing regional ground-water system. The results show that the geochemical attributes of insoluble residues can be used to distinguish provenance and transport directions of primary sediments within a depositional basin from effects of subsequent regional ground-water flow systems.

  19. Ohio operators setting sights on objectives in Cambrian, Ordovician

    SciTech Connect

    Petzet, G.A.

    1991-02-04

    Exploration for gas in rocks of Cambrian and Ordovician age is on the upswing as the Devonian Clinton and Medina tight gas sands play starts to wind down in the Ohio portion of the Appalachian basin. The area's intrepid independent operators refer to the objective formations as Ordovician Trempealeau dolomite, Rose Run sandstone, Copper Ridge dolomite, Knox dolomite, Beekmantown dolomite, and Cambrian Rome and Mount Simon sandstones. Rose Run drilling is centered in Coshocton, Holmes, and Tuscarawas counties. The formation underlies roughly the eastern half of the state and is the subject of a detailed geologic investigation.

  20. Palaeontological evidence bearing on global Ordovician-Silurian continental reconstructions

    NASA Astrophysics Data System (ADS)

    Fortey, Richard A.; Cocks, L. Robin M.

    2003-06-01

    The discreteness or otherwise of major Ordovician and Silurian terranes can be recognised by the shallow-water benthic faunas which lived upon them. Their borders are often indicated by the disposition of progressively shallow- to deep-water assemblages at the terrane edge as well as by structural features. Their positions relative to each other in the Early Palaeozoic can be best indicated by a combination of palaeomagnetic and faunal evaluation: the latter is the topic of this paper. Faunal evaluation is now possible quantitatively as well as quantitatively. Global palaeobiogeography is reviewed for the period as deduced from faunal evidence. There was one supercontinent, Gondwana, which stretched from West Gondwana (today's southern Europe and North Africa) at high latitudes to tropical East Gondwana (Australasia and adjacent areas), with intermediate palaeolatitudes in the Middle East and South America. Around Gondwana, especially to its north, were a large number of peri-Gondwanan terranes, particularly Avalonia, Perunica, parts of Turkey and Arabia and Sibumasu. In addition, there were the substantial independent continents of Laurentia, Baltica, Siberia, Annamia, North China and South China. Analysis of the shallow-water benthos, particularly trilobites and brachiopods, provides distinctive signatures for palaeo-position in most cases. Despite a large faunal turnover particularly corresponding with the latest Ordovician glacial event, the progressive evolution of the ecologies of benthic shelly faunas were also much influenced by changing geographies during the 80-Ma period. In the early Ordovician, oceans were at their widest, enabling Baltica and Laurentia to have different signatures from either East or West Gondwana. Siberia in early Ordovician times had faunal contact with Laurentia and East Gondwana, but in the mid-Ordovician, there were more endemics, and by the late Silurian, it was the only continent of substance in the northern hemisphere (hosting

  1. Stratigraphy of the cambo-ordovician succession in Illnois

    SciTech Connect

    Lasemi, Yaghoob; Khorasgani, Zohreh; Leetaru, Hannes

    2014-09-30

    The Upper Cambrian through Lower Ordovician succession (Sauk II-III sequences) in the Illinois Basin covers the entire state of Illinois and most of the states of Indiana and Kentucky. To determine lateral and vertical lithologic variations of the rocks within the Cambro-Ordovician deposits that could serve as reservoir or seal for CO2 storage, detailed subsurface stratigraphic evaluation of the succession in Illinois was conducted. The Cambro-Ordovician succession in the Illinois Basin consists of mixed carbonate-siliciclastic deposits. Its thickness ranges from nearly 800 feet in the extreme northwest to nearly 8000 feet in the Reelfoot Rift in the extreme southeastern part of the state. In northern and central Illinois, the Cambro-Ordovician rocks are classified as the Cambrian Knox and the Ordovician Prairie du Chien Groups, which consist of alternating dolomite and siliciclastic units. In the southern and deeper part of the Illinois Basin, the Cambro-Ordovician deposits consist chiefly of fine to coarsely crystalline dolomite capped by the Middle Ordovician Everton Formation. Detailed facies analysis indicates that the carbonate units consist mainly of mudstone to grainstone facies (fossiliferous/oolitic limestone and dolomite) with relics of bioclasts, ooids, intraclasts and peloids recording deposition on a shallow marine ramp setting. The dominant lithology of the Knox and the overlying Prairie du Chien Group is fine to coarsely crystalline, dense dolomite. However, porous and permeable vugular or fractured/cavernous dolomite intervals that grade to dense fine to coarsely crystalline dolomite are present within the dolomite units. Several hundred barrels of fluid were lost in some of these porous intervals during drilling, indicating high permeability. The sandstone intervals are porous and permeable and are texturally and compositionally mature. The permeable sandstone and porous dolomite intervals are laterally extensive and could serve as important

  2. Evaporites and strata-bound tungsten mineralization

    SciTech Connect

    Ririe, G.T. )

    1989-02-01

    Discoidal gypsum crystal cavities occur in quartzites that host varying amounts of strata-bound scheelite mineralization near Halls Creek in Western Australia. The host quartzites have been regionally metamorphosed to greenschist facies and are contained within a Middle Proterozoic sequence that includes pelites, mafic and felsic volcanics, and volcaniclastic rocks. Textural, fluid inclusion, and oxygen isotope data indicate that scheelite was present in the host quartzites prior to regional metamorphism. The presence of crystal cavities after gypsum in the quartzites implies an evaporitic origin for this sequence. The continental-sabkha playa basins of the Mojave Desert, California, are suggested to be possible modern analogs-e.g., Searles Lake, where the tungsten content is up to 70 ppm WO{sub 3} in brines and 118 ppm in muds, and exceeds the amount of tungsten in all known deposits in the United States. Metamorphism of a continental evaporitic sequence containing tungsten could produce an assemblage of rocks very similar to those reported from several stratabound tungsten deposits. Some of these, such as at Halls Creek, may be related to original accumulations of tungsten in nonmarine evaporitic environments.

  3. Geochronology of Early Eocene strata, Baja California

    SciTech Connect

    Flynn, J.J.; Cipolletti, R.M.

    1985-01-01

    Recent discoveries clearly indicate a Wasatchian (Early Eocene) land mammal age for fossil vertebrates from the Punta Prieta area, Baja California North, Mexico. This fauna provides a rare test for discriminating the temporal significance of mammalian faunas over a broad geographic area. The authors sampled intertonguing, fossiliferous terrestrial and marine strata for paleomagnetic and biostratigraphic analyses to provide an independent age determination for the Punta Prieta area mammal fauna. The marine macroinvertebrate assemblage is most likely upper Meganos to lower Capay West Coast Molluscan Stage based on the temporal ranges of all the taxa; also, none of the taxa occur in pre-Meganos stages. Two genera of planktonic forams indicate a probably Eocene age. They sampled seventeen paleomagnetic sites over 50 meters in the terrestrial mammal-bearing section, and thirteen sites over 25 meters in the marine section. The entire terrestrial sequence is reversely magnetized; initial results indicate the marine sequence probably also is reversely magnetized. Based on all the available biochronologic evidence this reversed sequence most likely should be correlated with the long reversed polarity Chron C24R. Clarkforkian to Early Wasatchian faunas in Wyoming also are associated with Chron C24R. All the available biostratigraphic and magnetostratigraphic evidence strongly supports an Early Eocene age for the Punta Prieta mammalian fauna and temporal equivalence of the Punta Prieta Wasatchian fauna with Wasatchian faunas from the Western United States. Land mammal ages are synchronous and applicable across broad geographic areas.

  4. High-resolution conodont oxygen isotope record of Ordovician climate change

    NASA Astrophysics Data System (ADS)

    Chen, J.; Chen, Z.; Algeo, T. J.

    2013-12-01

    The Ordovician Period was characterized by several major events, including a prolonged 'super greenhouse' during the Early Ordovician, the 'Great Ordovician Biodiversification Event (GOBE)' of the Middle and early Late Ordovician, and the Hirnantian ice age and mass extinction of the latest Ordovician (Webby et al., 2004, The Great Ordovician Biodiversification Event, Columbia University Press). The cause of the rapid diversification of marine invertebrates during the GOBE is not clear, however, and several scenarios have been proposed including widespread development of shallow cratonic seas, strong magmatic and tectonic activity, and climate moderation. In order to investigate relationships between climate change and marine ecosystem evolution during the Ordovician, we measured the oxygen isotopic composition of single coniform conodonts using a Cameca secondary ion mass spectrometer. Our δ18O profile shows a shift at the Early/Middle Ordovician transition that is indicative of a rapid 6 to 8 °C cooling. This cooling event marks the termination of the Early Ordovician 'super greenhouse' and may have established cooler tropical seawater temperatures that were more favorable for invertebrate animals, setting the stage for the GOBE. Additional cooling episodes occurred during the early Sandbian, early Katian, and Hirnantian, the last culminating in a short-lived (<1-Myr) end-Ordovician ice age. The much cooler conditions that prevailed at that time may have been an important factor in the end-Ordovician mass extinction. Our results differ from those of Trotter et al. (2008, 'Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry,' Science 321:550-554). Instead of a slow, protracted cooling through the Early and Middle Ordovician, our high-resolution record shows that cooling occurred in several discrete steps, with the largest step being at the Early/Middle Ordovician transition.

  5. Sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata

    SciTech Connect

    Jack C. Pashin; Robert A. Gastaldo

    2004-07-15

    The origin of coal-bearing strata has been debated vigorously for more than a century, and with the emergence of coalbed methane as a major energy resource and the possibility of sequestering greenhouse gas in coal, this debate has never been more relevant. This volume contains 10 chapters on coal-bearing strata of Carboniferous through Tertiary age and is based on a special session that was held at an AAPG Annual Meeting in New Orleans. Contributors have employed a multitude of approaches ranging from basin analysis to plant taphonomy to support a variety of views on the sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata.

  6. Geological Carbon Sequestration Storage Resource Estimates for the Ordovician St. Peter Sandstone, Illinois and Michigan Basins, USA

    SciTech Connect

    Barnes, David; Ellett, Kevin; Leetaru, Hannes

    2014-09-30

    The Cambro-Ordovician strata of the Midwest of the United States is a primary target for potential geological storage of CO2 in deep saline formations. The objective of this project is to develop a comprehensive evaluation of the Cambro-Ordovician strata in the Illinois and Michigan Basins above the basal Mount Simon Sandstone since the Mount Simon is the subject of other investigations including a demonstration-scale injection at the Illinois Basin Decatur Project. The primary reservoir targets investigated in this study are the middle Ordovician St Peter Sandstone and the late Cambrian to early Ordovician Knox Group carbonates. The topic of this report is a regional-scale evaluation of the geologic storage resource potential of the St Peter Sandstone in both the Illinois and Michigan Basins. Multiple deterministic-based approaches were used in conjunction with the probabilistic-based storage efficiency factors published in the DOE methodology to estimate the carbon storage resource of the formation. Extensive data sets of core analyses and wireline logs were compiled to develop the necessary inputs for volumetric calculations. Results demonstrate how the range in uncertainty of storage resource estimates varies as a function of data availability and quality, and the underlying assumptions used in the different approaches. In the simplest approach, storage resource estimates were calculated from mapping the gross thickness of the formation and applying a single estimate of the effective mean porosity of the formation. Results from this approach led to storage resource estimates ranging from 3.3 to 35.1 Gt in the Michigan Basin, and 1.0 to 11.0 Gt in the Illinois Basin at the P10 and P90 probability level, respectively. The second approach involved consideration of the diagenetic history of the formation throughout the two basins and used depth-dependent functions of porosity to derive a more realistic spatially variable model of porosity rather than applying a

  7. Terminal Ordovician extinction: geochemical analysis of the Ordovician/Silurian boundary, Anticosti Island, Quebec

    SciTech Connect

    Orth, C.J.; Gilmore, J.S.; Quintana, L.R.; Sheehan, P.M.

    1986-05-01

    Elemental abundances (including Ir), carbon and oxygen ratios in carbonates, mineral content, and thin sections have been measured in samples collected across the conodont-defined Ordovician/Silurian (O/S) boundary exposed on Anticosti Island, Quebec. The Ir concentrations ranged from 5 to a maximum at the boundary of 58 parts per trillion (ppt). However, there is no evidence, on the basis of these Ir results, for the association of a large-body-Earth impact with the O/S extinction, because the Ir concentrations, like those of most other trace elements, are simply proportional to the clay (Al) content in the carbonate sequence. The /sup 13/C//sup 12/C and /sup 18/O//sup 16/O ratios decrease abruptly at the boundary, then just as abruptly increase to a long period of higher than preboundary ratios. These patterns are probably related to the salinity in the seaway, which was shallowing up to boundary time and then deepened and developed patch-reefs. Fresh-water input from rivers would have been most influential during the shallow-water conditions. 32 references, 4 figures.

  8. Use of the Deicke and Millbrig K-bentonites to resolve Middle Ordovician stratigraphic problems in the central Appalachians

    SciTech Connect

    McVey, D.E.; Huff, W.D. . Dept. of Geology)

    1993-03-01

    It well known that numerous K-bentonite beds occur in Middle Ordovician strata in eastern North America. Two of these beds, the Deicke and Millbrig, have been correlated on a regional scale and have proven to be excellent time lines between the southern Appalachians and the upper Mississippi Valley. The purpose of this study is to extend the correlation of these two beds through the Central Appalachians (southern Virginia into central Pennsylvania) and to use them to investigate regional changes in carbonate and clastic facies. The Deicke and Millbrig can be correlated by chemical fingerprinting using whole rock chemical and mineralogical analyses. The immobile trace elements (Yb, Dy, Sc, Lu, Zr, and etc.) serve as effective discriminators when grouped in a hierarchical assemblage by discriminate function analysis. Distinctive mineral assemblages include labradorite as the principle plagioclase in the Deicke and andesine as the principle plagioclase in the Millbrig. Interpretation of Middle Ordovician stratigraphy in the central Appalachians has been hampered in the past by structural and facies complications. Both the Deicke and Millbrig have been correlated in this study from southern Virginia along strike northward into central Pennsylvania. Both the Deicke and Millbrig occur within the platform carbonates of the Eggleston Fm. at Hagan, Virginia, the shallow ramp carbonates of the Oranda Fm. at Strasburg and Mauzy, Virginia, the lower Martinsburg black shale and turbidite facies at Martinsburg, West Virginia, and the slope carbonates of the New Enterprise Member of the Salona Fm. in central Pennsylvania. This study supports the work done by Rosenkrans (1963) that dealt with the correlation of K-bentonites in the central Appalachians.

  9. Post-Knox Ordovician stratigraphic sequences and the significance of the Rocklandian K-bentonites, eastern United States

    SciTech Connect

    Haynes, J.T. . Dept. of Geography and Earth Science)

    1992-01-01

    The depositional sequences of the post-Knox Ordovician are reinterpreted and summarized, with emphasis on the stratigraphic importance of the Rocklandian K-bentonites relative to the various sequence-defining unconformities associated with them. The Deicke and Millbrig K-bentonite Beds can be traced through the subsurface to Cincinnati Arch exposures, where a remarkably similar stratigraphy occurs; fenestral micrites (Tyrone/Carters Fms.) unconformably underlie fossil-rich limestone (Lexington/Hermitage Fms.). The Deicke and Millbrig, however, both occur in the fenestral micrites below the unconformity, rather than above it, a stratigraphy which suggests that if this post-Tyrone unconformity is the same as the post-Quimbys Mill unconformity, it is a diachronous surface, climbing upsection and crossing the K-bentonites southeast of the Upper Mississippi Valley. In eastern belts two lesser unconformities are associated with the K-bentonites. Locally in Birmingham, AL, a post-Chickamauga unconformity is 4 m above the Millbrig and is overlain by a thin Sequatchie Fm., itself unconformably overlain by the Silurian Red Mountain Fm. In VA between Roanoke and Wytheville on the Pulaski and Cove Mountain thrust sheets, the Deicke is absent and a sub-Bays unconformity exists where the Walker Mountain Sandstone, a pebbly quartz arenite 18--28 m below the Millbrig, overlies Black River limestones. The post-Tyrone unconformity, like the older post-Knox unconformity, is a regionally extensive hiatus, suggestive of a eustatic sea-level change. By contrast, the unconformities that are restricted to only the eastern Valley and Ridge may be evidence of tectonism along the continental margin during the ordovician. Similarly localized unconformities are recognized in Silurian and Devonian strata as well throughout the southern Appalachians.

  10. Remagnetization and tectonic rotation of Upper Precambrian and Lower Paleozoic strata from the Desert Range, southern Nevada

    NASA Astrophysics Data System (ADS)

    Gillett, Stephen L.; van Alstine, David R.

    1982-12-01

    In the Desert Range of southern Nevada, miogeoclinal sedimentary rocks, mostly shallow-water limestones of latest Precambrian through Early Ordovician age, yield three components of magnetization having different blocking temperature spectra: (1) a low blocking temperature component near the direction of the present axial-dipole field; (2) an intermediate blocking temperature component with northerly declination and inclination ˜+60°; and (3) a characteristic component with southeasterly declination and inclination ˜-20°. Combinations of alternating field and thermal demagnetization indicate that the intermediate and characteristic components reside in magnetite. The intermediate magnetization probably reflects a viscous partial thermoremanent magnetization (VPTRM) imposed between the Late Cretaceous and mid-Cenozoic; it was probably acquired when the strata were dipping slightly eastward. The characteristic magnetization is probably a VPTRM imposed during regional uplift in the Late Permian. The degree of heating required to have destroyed any primary magnetization is consistent with the conodont color alteration index observed in the Ordovician rocks; additionally, the characteristic magnetization in those rocks is younger than bedding disruption caused by major, late stylolitization. Red-purple mudstones from the middle member of the Wood Canyon Formation, in which a directionally similar characteristic magnetization resides in fine-grained hematite, also appear to have been remagnetized; in these rocks, the remagnetization probably reflects partial recrystallization, as the blocking temperatures are too high to have been reset by burial heating. The sampled sections have undergone relative tectonic rotation about a vertical axis, consistent with late Tertiary oroflexural bending that had been proposed on independent geologic evidence. The characteristic magnetization probably provides a reliable estimate of the magnitudes of the vertical axis rotations, as

  11. Late Ordovician paleogeography of central Idaho and its tectonic implications

    SciTech Connect

    Measures, E.A. )

    1991-02-01

    The Late Ordovician (Cincinnatian, Ashgill) paleogeography of central Idaho has been weakly constrained in the past. Previously, this area was treated as a simple extension of the miogeocline-eugeocline paleogeography defined from units in the Great Basin (Nevada and Utah). Detailed analysis of the Upper Ordovician Fish Haven Dolomite enables a more refined paleogeographic interpretation to be made at this time. The Fish Haven Dolomite (260 m or 800 ft, average thickness) of central Idaho is composed of 16 different carbonate facies which can be grouped into three sequences; facies within each sequence are depositionally related. Overall, the facies and sequences indicate that a carbonate ramp formed in central Idaho outboard of the craton and a hinge zone, within a subsiding area of the miogeocline. Shallow subtidal ramp deposits were probably deposited in approximately 30 m (100 ft.), or less, of water depth. During this time interval, open ocean, anoxic bottom waters extended up into deep ;subtidal regions (60 m or 200 ft). This information indicates that the Late Ordovician carbonate ramp underwent backstepping at its outermost portion resulting n drowning of the western ramp and eventual migration of transitional facies deposits (Roberts Mountains Formation) over miogeoclinal deposits. Tectonics played an active part in the deposition of the Fish Haven Dolomite in the miogeocline of central Idaho. The ultimate cause of the tectonism is not known at this time, but could be related to changes in the rate of sea-floor spreading, active structures within the continental margin, proximity of the Ordovician Klamath Mountains island arc Terrane, or unknown processes.

  12. Echinoderms from Middle and Upper Ordovician rocks of Kentucky

    USGS Publications Warehouse

    Parsley, R.L.

    1981-01-01

    The Middle and Upper Ordovician limestones of Kentucky, especially the Lexington Limestone, have yielded a diverse silicified echinoderm fauna, including: Stylophora-Enoploura cf. E. punctata; Paracrinoidea-A mygdalocystites; Crinoidea, Inadunata-Hybocrir/us tumidus, Hybocystites problem,aticus, Carabocrinus sp., Cupulocrinus sp., Heterocrinus sp.; Cyclocystoidea-Cyclocystoides sp. A rhombiferan cystoid, A mecystis laevis, from the Edinburg Formation, Virginia, is also discussed. No new taxa are introduced.

  13. Relation of Middle and Late Triassic strata of N-C Nevada to contemporaneous strata of southern Nevada and Utah

    SciTech Connect

    Elison, M.W.

    1993-04-01

    Middle and Late Triassic shelf strata in north-central Nevada comprising dominantly carbonate rocks of the Star Peak Group and overlying siliciclastic and carbonate rocks are overlain tectonically by predominantly siliciclastic basinal strata. Late Triassic slope strata are preserved in the East and Humboldt Ranges. At present, these Triassic rocks are separated from contemporaneous deposits of Utah by roughly 300 km over which time-equivalent ( ) strata are limited to a small, isolated outcrop near Currie, NV. Mesozoic and Cenozoic tectonics and widespread absence of Triassic rocks immediately to the east complicate the relation between the north-central Nevada section and Triassic rocks of southern Nevada and Utah. The gap in Triassic rocks may have resulted from erosion of intervening strata or from tectonic separation of originally contiguous stratal sequences. Some depositional facies of the shelf uniformly cover the preserved outcrop area and do not constrain the scale of the depositional system. Where facies variations are present, they suggest sediment sources to the east and north and deeper water to the west. Facies patterns, however, were influenced by local tectonics and changes in sediment source and supply. Late Triassic strata of N-C Nevada probably are the shallow-marine equivalents of fluvial and lacustrine rocks to the east. Local tectonics and changes in sediment influx require caution regarding interpretation of the original proximity of preserved stratal sequences.

  14. Middle and Upper Ordovician nautiloid cephalopods of the Cincinnati Arch region of Kentucky, Indiana, and Ohio

    USGS Publications Warehouse

    Frey, R.C.

    1995-01-01

    This chapter of 'Contributions to the Ordovician paleontology of Kentucky and nearby states' deals with the stratigraphic distribution, paleoecology, biogeography, and systematic paleontology of 50 species of nautiloid cephalopods from the Midcontinent. The species are placed in 30 genera. Most of the specimens are silicified and from Middle Ordovician rocks of Kentucky. The study is augmented by unsilicified material from the Upper Ordovician Cincinnatian Provincial Series from the tri-state area of Kentucky, Indiana, and Ohio.

  15. Evolution of Cambrian-Ordovician carbonate shelf, United States Appalachians

    SciTech Connect

    Read, J.F.

    1985-02-01

    Cross sections and isopach maps (palinspastic) of the Cambrian-Ordovician continental shelf, US Appalachians, show that thickness and facies trends are controlled by the Adirondack, New Jersey, and Virginia highs and depocenters in Tennessee, Pennsylvania, and by the Rome trough. Carbonate sedimentation was initiated with drowning of Early Cambrian clastics, deposition of carbonate ramp and rimmed shelf facies followed by drowning, then regional regression and deposition of Early to Middle Cambrian red beds and platform margin rimmed shelf facies. During subsequent regional transgression, the Conasauga intrashelf shale basin formed, bounded toward the shelf edge and along depositional strike by Middle to Upper Cambrian oolitic ramp facies and cyclic peritidal carbonates. Intrashelf basin filling and regional regression caused progradation of Late Cambrian cyclic carbonates and clastics across the shelf. By this time, the margin had a relief of 2.5 km. During the Early Ordovician, incipient drowning of the shelf formed subtidal carbonates and bioherms that passed up into cyclic carbonate as sea level oscillations decreased in magnitude. Numerous unconformities interrupt this sequence in the northern Appalachians. The earlier high relief rimmed shelf was converted into a ramp, owing to uplift in the basin, heralding approaching collision. Subsidence rates on the margin were low (4 cm/1000 yr) and typical of a mature passive margin. Shelf sedimentation in the southern Appalachians ceased with arc-continent collision and development of the Knox unconformity, which dies out into the Pennsylvania depocenter. Major exploration targets are in the Late Cambrian-Early Ordovician Knox Group.

  16. Middle Ordovician carbonate ramp deposits of central Appalachians

    SciTech Connect

    Demicco, R.V.

    1986-05-01

    Middle Ordovician carbonates exposed in Maryland and Pennsylvania can be divided into six facies, each a few tens to hundreds of meters thick: (1) cyclic, meter-scale, alternating thin-bedded to massive limestones and mud-cracked, stromatolitic laminites; (2) thick-bedded to massive skeletal wackestones containing diverse fauna; (3) cross-stratified skeletal-oncoid grainstones; (4) graded, thin-bedded limestones with diverse fauna and internal planar lamination or hummocky cross-stratification; (5) nodular, thin-bedded limestones; and (6) shaly, thin-bedded to laminated limestones containing rare breccia beds. These facies are interpreted as deposits of: (1) tidal flats; (2) open, bioturbated muddy shelf; (3) lime-sand shoals; (4) below normal wave-base shelf; (5) deep ramp; and (6) basin. Palinspastic reconstructions of facies distribution in Maryland and Pennsylvania suggest that these facies developed during flooding of a carbonate ramp that deepened northeastward into a foreland basin. This northern depocenter of the Middle Ordovician Appalachian foreland basin is notably different that its southern counterpart in Virginia and Tennessee. Large skeletal bioherms did not develop on the northern carbonate ramp, where only one onlap package exists. Thus, although the record of the foundering of the passive Cambrian-Ordovician carbonate shelf is grossly similar in the southern and central Appalachians, there are several significant differences. The overlying Martinsburg Formation contains deep-water facies and taconic-style thrust sheets in the central Appalachians, which suggests that the two depocenters may have had different tectonic settings.

  17. Ordovician "sphinctozoan" sponges from Prince of Wales Island, southeastern Alaska

    USGS Publications Warehouse

    Rigby, J.K.; Karl, S.M.; Blodgett, R.B.; Baichtal, J.F.

    2005-01-01

    A faunule of silicified hypercalcified "sphinctozoan" sponges has been recovered from a clast of Upper Ordovician limestone out of the Early Devonian Karheen Formation on Prince of Wales Island in southeastern Alaska. Included in the faunule are abundant examples of the new genus Girtyocoeliana, represented by Girtyocoeliana epiporata (Rigby and Potter), and Corymbospongia adnata Rigby and Potter, along with rare Corymbospongia amplia n. sp., and Girtyocoelia(?) sp., plus common Amblysiphonella sp. 1 and rare Amblysiphonella(?) sp. 2. The assemblage is similar to that from Ordovician clasts from the eastern Klamath Mountains of northern California. This indicates that the Alexander terrane of southeastern Alaska is related paleogeographically to the lithologically and paleontologically similar terrane of the eastern Klamath Mountains. This lithology and fossil assemblage of the clast cannot be tied to any currently known local rock units on Prince of Wales Island. Other clasts in the conglomerate appear to have been locally derived, so it is inferred that the limestone clasts were also locally derived, indicating the presence of a previously undocumented Ordovician limestone unit on northern Prince of Wales Island. 

  18. Late Ordovician glacial record of the Anti-Atlas, Morocco

    NASA Astrophysics Data System (ADS)

    Le Heron, Daniel Paul

    2007-09-01

    Late Ordovician glaciogenic deposits are exposed intermittently along an 800 km long outcrop belt in the Anti-Atlas mountains of southern Morocco. These deposits are of economic significance as potential oil-bearing sandstones in the Tindouf and Boudenib basins and thus are here re-examined as analogues to subsurface hydrocarbon reservoirs. Glaciogenic deposits of the Upper Second Bani Formation rest unconformably upon underlying shallow marine clastic deposits. The unconformity is characterised by a series of palaeovalleys, some 0.5-1.0 km wide, and up to 100 m deep, which may have been cut under elevated hydrostatic pressures as tunnel valleys beneath a Late Ordovician ice sheet. The valleys and intervalley areas are filled with glaciogene sediments categorized into five facies associations, namely 1) a tabular sandstone association (shallow marine/shoreface deposits), 2) a massive sandstone and conglomerate (ice contact debrites), 3) meandriform sandstone deposits (ice proximal sandur), 4) stratified diamictites (ice-rafted debris) and 5) sigmoidally bedded sandstones (intertidal sandstones). Deformation in these sediments is ubiquitous and includes soft-sediment striated pavements, metre-scale duplex systems, thrust and fold belts of deformation affecting some tens of metres of sediment, and pervasive lineations. These features are interpreted to record the complex nature of deformation processes operating beneath a Late Ordovician ice sheet including sliding at the ice-bed interface, folding and deformation within the sediment column, and a series of complex ramps, detachments and shear zones within an unconsolidated pile of sediment beneath the ice sheet.

  19. Changes in the Style of Neritic Carbonate Production in the Tropics during the End-Ordovician Hirnantian Glaciation : atypical limestone facies from the Anticosti succession, eastern Canada

    NASA Astrophysics Data System (ADS)

    Desrochers, A.; Long, D. G. F.; Ghienne, J.-F.

    2012-04-01

    During the End-Ordovician (Hirnantian) glacial maxima, carbonate platforms in the tropics were exposed extensively and their own diverse endemic faunas, displaced to the continental margins, suffered massive extinction. One of the best exposed and most complete stratigraphic records from a paleotropical area spanning the Ordovician/Silurian (O/S) boundary is on Anticosti Island in eastern Canada. The Anticosti sequence developed within a far-field Taconic foreland basin along the eastern margin of Laurentia under the influence of high tectonic subsidence and sustained carbonate sediment supply. Our biostratigraphically well-controlled δ13C curves and depth sensitive facies analysis allow us to recognize a distinctive Hirnantian stratigraphic architecture and its related sea level curve at the Milankovitch-cyclicity scales. The sudden appearance of abundant oncolites and calcimicrobial-coral reefs marks the Anticosti succession near the O/S boundary at the same time of a major faunal turnover (conodont, chitinozoan, acritarch, shelly faunas). These microbial limestones, a prominent regional marker unit on Anticosti Island known as the Laframboise Member, formed mainly during the peak interval and falling limb of the main Hirnantian positive isotopic carbon excursion. A comparison with the sequence stratigraphy of Morocco suggests that the Laframboise limestones correspond to the Late Ordovician glacial climax (middle to upper Hirnantian in age), characterised by a continental-scale ice sheet. A comparison between the Laframboise succession and other coeval shallow-water tropical successions in Laurentia, Avalonia, Baltica, Siberia and South China shows that the style of carbonate production changed from one derived largely from various carbonate secreting organisms to one dominated by widespread microbial and/or oolitic production. In contrast to the normal marine shelly faunas of pre- and post- extinction Hirnantian strata, shallow water tropical carbonates appear

  20. Time-scale calibration by high-precision U sbnd Pb zircon dating of interstratified volcanic ashes in the Ordovician and Lower Silurian stratotypes of Britain

    NASA Astrophysics Data System (ADS)

    Tucker, R. D.; Krogh, T. E.; Ross, R. J.; Williams, S. H.

    1990-10-01

    High initial parent/daughter element ratios and a unique dual decay scheme make U sbnd Pb zicron ages more precise and reliable than most isotopic ages, and thus inherently superior for time-scale calibration. Employing improved techniques to the conventional method of U sbnd Pb dating, we have analyzed microgram-size (2-12 × 10 -8 g) zircon fractions from biostratigraphically controlled volcanic ashes and dated key Paleozoic time-markers with a precision better than 1% (±2Ma). Four of the stratotype samples from Britain for which fission-track ages [ 1] were previously reported have yielded improved ages of:438.7 ± 2.0Ma for the lower Silurian zone of Coronograptus cyphus from Llandovery strata at Dob's Linn, southern Scotland;457.5 ± 2.2 Ma for a Middle Ordovician Caradoc (Longvillian) ash near Bala, North Wales, and;465.7 ± 2.1and464.6 ± 1.8 Ma for the Didymograptus artus Zone and the type Didymograptus Murchisoni Zone, respectively, of the Llanvirn Series at Arenig Fawr and Abereiddi Bay, Wales. Another sample from the zone of Dicellograptus anceps ( P. pacificus Subzone) of the Ashgill Series at Dob's Linn has been dated at445.7 ± 2.4Ma, suggesting placement of the Ordovician-Silurian time boundary at approximately 441 Ma. A sixth bentonite from Caradocian age strata of North America (Spechts Ferry Shale, Decorah Formation, Missouri) is453.7 ± 1.8Ma old, indicating that the Rocklandian Stage of the Mohawkian Series is only slightly younger than the Longvillian Stage of the Caradoc Series in Britain.

  1. Silcrete in the uppermost Cambrian and Lower Ordovician of the Wisconsin arch and Michigan basin - Implications for subaerial exposure

    SciTech Connect

    Smith, G.L. )

    1991-03-01

    Silcrete within uppermost Cambrian strata and the Lower Ordovician Prairie du Chien Group delineates the basinward extent of subaerial exposure during three relative sea-level lowstands that exposed portions of the Wisconsin arch and Michigan basin before, during, and after Prairie du Chien deposition. Shallow-water Prairie du Chien carbonates and Cambrian sandstones were deposited in tropical, epeiric seas during relative sea-level highstands. Fabrics identical to Cenozoic silcretes consist of cryptocrystalline microquartz (chert), microquartz ({lt}0.02 mm), megaquartz ({lt}0.02 mm), and length-slow and length-fast chalcedony. Silicified crusts of oolitic grainstones and/or anhydrite nodule typically coat uppermost Cambrian and Prairie du Chien unconformities. Silicification associated with intra- and post-Prairie du Chien unconformities is generally restricted to within 5 m of the overlying unconformity. Highly permeable lithologies, such as oolitic grainstones, boundstones, and paleokarst breccias, were preferentially silicified during intra- and post-Prairie du Chien exposure. Reworked silcrete clasts typically overlie unconformities. Silcrete is a practical exposure indicator as it is easily identified in outcrop and well cuttings. Silcrete within uppermost Cambrian strata is generally restricted to the Wisconsin arch axis, but occurs as far east as western Michigan. Silcrete below the intra-Prairie du Chien unconformity indicates subaerial exposure of the entire arch and basin. In contrast, silcrete below the post-Prairie du Chien, pre-St. Peter unconformity indicates that exposure was restricted to the Wisconsin arch and western margin of the Michigan basin in eastern Wisconsin.

  2. CO{sub 2} Injectivity, Storage Capacity, Plume Size, and Reservoir and Seal Integrity of the Ordovician St. Peter Sandstone and the Cambrian Potosi Formation in the Illnois Basin

    SciTech Connect

    Leetaru, Hannes; Brown, Alan; Lee, Donald; Senel, Ozgur; Coueslan, Marcia

    2012-05-01

    The Cambro-Ordovician strata of the Illinois and Michigan Basins underlie most of the states of Illinois, Indiana, Kentucky, and Michigan. This interval also extends through much of the Midwest of the United States and, for some areas, may be the only available target for geological sequestration of CO{sub 2}. We evaluated the Cambro-Ordovician strata above the basal Mt. Simon Sandstone reservoir for sequestration potential. The two targets were the Cambrian carbonate intervals in the Knox and the Ordovician St. Peter Sandstone. The evaluation of these two formations was accomplished using wireline data, core data, pressure data, and seismic data from the USDOE-funded Illinois Basin Decatur Project being conducted by the Midwest Geological Sequestration Consortium in Macon County, Illinois. Interpretations were completed using log analysis software, a reservoir flow simulator, and a finite element solver that determines rock stress and strain changes resulting from the pressure increase associated with CO{sub 2} injection. Results of this research suggest that both the St. Peter Sandstone and the Potosi Dolomite (a formation of the Knox) reservoirs may be capable of storing up to 2 million tonnes of CO{sub 2} per year for a 20-year period. Reservoir simulation results for the St. Peter indicate good injectivity and a relatively small CO{sub 2} plume. While a single St. Peter well is not likely to achieve the targeted injection rate of 2 million tonnes/year, results of this study indicate that development with three or four appropriately spaced wells may be sufficient. Reservoir simulation of the Potosi suggest that much of the CO{sub 2} flows into and through relatively thin, high permeability intervals, resulting in a large plume diameter compared with the St. Peter.

  3. Supercritical strata in Lower Paleozoic fluvial rocks: a super critical link to upper flow regime processes and preservation in nature

    NASA Astrophysics Data System (ADS)

    Lowe, David; Arnott, Bill

    2015-04-01

    Recent experimental work has much improved our understanding of the lithological attributes of open-channel supercritical flow deposits, namely those formed by antidunes, chutes-and-pools and cyclic steps. However their limited documentation in the ancient sedimentary record brings into question details about their geological preservation. Antidune, chute-and-pool and cyclic step deposits are well developed in sandy ephemeral fluvial deposits of the Upper Cambrian - Lower Ordovician Potsdam Group in the Ottawa Embayment of eastern North America. These high energy fluvial strata form dm- to a few m-thick units intercalated within thick, areally expansive successions of sheet sandstones consisting mostly of wind ripple and adhesion stratification with common deflation lags. Collectively these strata record deposition in a semi-arid environment in which rare, episodic high-energy fluvial events accounted for most of the influx of sediment from upland sources. Following deposition, however, extensive aeolian processes reworked the sediment pile, and hence modified profoundly the preserved stratigraphic record. Antidune deposits occur as 0.2 - 1.6 m thick cosets made up of 2 - 15 cm thick lenticular sets of low angle (≤ 20o) cross-stratified, medium- to coarse-grained sandstone bounded by low-angle (5 - 15o) concave-upward scours and, in many cases, capped by low angle (10 - 15o) convex-upwards symmetrical formsets. Chute-and-pool deposits form single sets, 5 - 55 cm thick and 0.6 - 6 m wide, with scoured bases and low to high angle (5 - 25o) sigmoidal cross-strata consisting of medium- to coarse-grained sandstone. Cyclic step deposits consist of trough cross-stratified sets, 20 cm - 1.6 m thick, 2.5 - 12 m long and 7 - 35 m wide, typically forming trains that laterally are erosively juxtaposed at regularly-spaced intervals. They are composed of medium- to coarse-grained sandstone with concave-up, moderate to high angle (15 - 35o) cross-strata with tangential bases

  4. Kinematic Evolution of fold-and-thrust Belts in the Yubei Area: Implications for the Tectonic Events of Ordovician at the Southern Tarim Basin

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2015-12-01

    As a response to tecto-orogenic processes of the South Altun and the West Kunlun (Monlar P, 1975; He Bizhu, 2011), early Paleozoic tectonic evolution of the southern Tarim craton was distinctively one of the extensions and was followed by compression (Morris W.Leighton, 1990; Gao Zhiqian, 2015). From the late Ordovician, the Yubei area developed distinctively NE-SW trending fold-and-thrust belts in rows which were eroded and deformed through multiphase tectonic movement (Dengfa He, 2007), with similarities and dissimilarities between each other rows in many aspects, at the Southern Tarim inner basin (Fig. 1). The northern of Hetian paleo-uplift and the northwestern of NE-trending folds zone on Caledonian in Tangguzibasi depression should be favorable to the potential exploration area for the first large-scale period of hydrocarbon migration and accumulation (Brown LF, 1979). In this contribution, based on geophysical log, core and 2D/3D seismic data, we constructed its tectonic geometry morphology, controlled by detailed chronostratigraphic framework. According to the fault-related fold theory, rows of asymmetric fault-propagation folds grew in the Yubei area during the late Caledonian period, with the evidence of interpreted growth strata from the high resolution 3D seismic data (Suppe J et al., 1990). That intercontinental tecto-orogenic events from southern Tarim basin, leading to the transformation of its margins, affected inner basin at that time, modified the basin into the Tarim metacraton (Jean-Paul Liégeois, 2013; Zieglar P.A., 1998). Correlating the four tectonic groups of the identified with the axis variation of strata and fold amplitude distribution showed that fault evolution progressed in several superimposed stages: Precambrian, late Ordovician to early Carboniferous (Zhao Zongju, 2009), Carboniferous to Permian, Cenozoic. Analyzing the sedimentary development and structure evolution the tectonic paleo-geographic setting is reconstructed, providing

  5. Sedimentological cross section of Cambro-Ordovician carbonate shelf (Knox group, Conassauga Formation) in central Alabama: facies, diagenesis, potential reservoirs

    SciTech Connect

    Sternbach, L.R.

    1984-04-01

    Cambro-Ordovician thrust-imbricated carbonates in central Alabama are the focus of renewed exploration interest. Samples from east-west-trending core holes within the surface-most thrust plates reconstruct the carbonate shelf and shelf-edge facies before deformation. The Upper Cambrian shelf margin now is in the subsurface of Talledega County; coeval dolostones in the western part of the state represent the former shelf interior. Rock analogs to former environments include the following. (1) Barrier shoals (Conasauga Formation) - dark colored, partially dolomitized ooid and skeletal grainstones. (2) Submerged back-barrier and offshelf dolomitized sediments (lower Knox Group) - western belt: finely crystalline algal thrombolites, fenestral dolopelmicrites, rippled beds; eastern belt: finely laminated dolostones, slope-derived pebbles and graded beds. (3) Tidal flats (upper Knox Group) - light-colored, crystalline dolostones, dolomitized pellet grainstones, algal laminites, pseudomorphs after sulfates and early diagenetic chertification. (4) Former emergent shelf -(Knox unconformity)-pelmicrite, skeletal wackestones, erosional chert pebble conglomerate. Multiple possibilities for hydrocarbon reservoirs appear throughout the sequence. Vuggy and intercrystalline dolostone porosity is primarily in the lower Knox formations. Primary interparticle pores are retained in lower Knox algal buildups. Breccia porosity occurs in the strata below the Knox unconformity through solution of the underlying Knox Group. Fractures in the subsurface are believed to enhance permeability in all porosity types.

  6. Sedimentological cross section of Cambro-Ordovician carbonate shelf (Knox group, Conasauga Formation) in central Alabama: facies, diagenesis, potential reservoirs

    SciTech Connect

    Sternbach, L.R.

    1984-04-01

    Cambro-Ordovician thrust-imbricated carbonates in central Alabama are the focus of renewed exploration interest. Samples from east-west-trending core holes within the surface-most thrust plates reconstruct the carbonate shelf and shelf-edge facies before deformation. The Upper Cambrian shelf margin now is in the subsurface of Talledega County; coeval dolostones in the western part of the state represent the former shelf interior. Rock analogs to former environments include the following. (1) Barrier shoals (Conasauga Formation) - dark colored, partially dolomitized ooid and skeletal grainstones. (2) Submerged back-barrier and offshelf dolomitized sediments (lower Knox Group) - western belt: finely crystalline algal thrombolites, fenestral dolopelmicrites, rippled beds; eastern belt: finely laminated dolostones, slope-derived pebbles and graded beds. (3) Tidal flats (upper Knox Group) - light-colored, crystalline dolostones, dolomitized pellet grainstones, algal laminites, pseudomorphs after sulfates and early diagenetic chertification. (4) Former emergent shelf -(Knox unconformity)-pelmicrite, skeletal wackestones, erosional chert pebble conglomerate. Multiple possibilities for hydrocarbon reservoirs appear throughout the sequence. Vuggy and intercrystalline dolostone porosity is primarily in the lower Knox formations. Primary interparticle pores are retained in lower Knox algal buildups. Breccia porosity occurs in the strata below the Knox unconformity through solution of the underlying Knox Group. Fractures in the subsurface are believed to enhance permeability in all porosity types.

  7. Sedimentary and microbial record of the Middle/Late Ordovician phosphogenetic episode in the northern Holy Cross Mountains, Poland

    NASA Astrophysics Data System (ADS)

    Trela, Wiesław

    2008-01-01

    Numerous phosphorite beds and phosphatic nodules occur in the upper Middle and lower Upper Ordovician carbonate-shale succession of the Bukowiany Formation outcropping in the northern Holy Cross Mountains, central Poland. The vertical stacking pattern of this succession indicates that phosphatic and accompanying strata reflect a conformable sedimentary succession accumulated during a rise of relative sea level. The base of the Bukowiany Formation is marked by a conspicuous phosphorite horizon revealing a low net sediment accumulation rate reflecting a switch into a mesotrophic ecological system. This horizon was produced by reworking and redeposition of pristine phosphate sediment (e.g. by currents activity) during the late Darriwilian transgression. The overlying sedimentary record appears to reflect nucleation of the phosphate phase in the sediment-water interface and its subsequent burial by the accompanying sediment. The phosphatized tiny stromatolites and nodules preserved within the Bukowiany Formation indicate that benthic microbial communities played an important role in redistribution and concentration of phosphate during deposition of this succession.

  8. Dissecting global diversity patterns: examples from the Ordovician Radiation.

    PubMed

    Miller, A I

    1997-01-01

    Although the history of life has been characterized by intermittent episodes of radiation that can be recognized in global compilations of biodiversity, it does not necessarily follow that these episodes are caused by processes that occurred uniformly around the world. Major diversity increases could be generated by the cumulative effects of different mechanisms operating simultaneously at several geographic or environmental scales. The purpose of this review is to describe ongoing research on the manifestations, at several scales, of the Ordovician Radiation, which was among the most extensive intervals of diversification in the history of life. Through much of the period, diversity was concentrated most heavily near regions of active mountain building and volcanism; differences in diversity patterns from continent to continent, and among regions within continents, reflect this overprint. While this suggests a linkage of the Radiation and tectonic activity, this is by no means the only mediating agent. Outcrop-based research in North America has demonstrated that tectonic activity was detrimental to some biotic elements, in contrast to its effects on other organisms. Moreover, in the Great Basin of North America where the local stratigraphic record is of particularly high quality, biotic transitions characteristic of the period occurred far more rapidly than observed in global compilations of diversity, suggesting that the global rate of transition may represent the aggregate sum of transitions that occurred abruptly, but at different times, around the world. Finally, it has been demonstrated that, in concert with an increase in average age, the environmental and geographic ranges of Ordovician genera both increased significantly through the period, indicating a role for intrinsic factors in producing Ordovician biotic patterns. PMID:11541187

  9. Early middle Ordovician (Whiterockian) paleogeography of basin ranges

    SciTech Connect

    Ross, R.J. Jr. ); James, N.P. ); Hintze, L.F. ); Ketner, K.B. )

    1991-02-01

    During a highstand of the Canadian shield over the Archean mantle root in the early Whiterock (Orthidiella zone), the western rimmed shelf evolved from a late Ibexian ramp. Calathid-sponge mounds initiated the rim on shelf, and micritic carbonate mounds formed on the upper slope. Large bodies of coeval upper slope mound lithology occur in northern nevada from Reed's Station on the west to The Narrows on the east; these Ordovician olistoliths (anomalously within Devonian deepwater facies) imply an early middle Ordovician carbonate escarpment from which huge blocks slid into deep water. Lowering of sea level at or after the close of the Ordovician may have resulted in displacement of such blocks. In the lower Anomalorthis zone, southwest of a line from Lytle Ranch to Cortex, shallow subtidal to oncolitic shoal water deposits form a vast prograding platform rim. To the northeast lay the partly euxinic, intrashelf Kanosh Basin. The boundary between the subsiding shale basin and the widening, upward shallowing oncolitic rim may have been a zone of hydrocarbon accumulation. Accelerated relative subsidence in the upper Anomalorthis zone resulted in transgression of the burrowed subtidal facies over the Kanosh basin. Southeastward over the site of the oncolitic rim, expansive tidal flat beds accreted repeatedly. Lastly, during Lichenaria-Opikina deposition, brief extensive transgression in the north was smothered by prograding quartz sand (Eureka Quartzite). The sands thinned and bypassed tectonically emergent islands along the Tooele arch. In the south, the sand appears to have poured into karst cavities in a belt from the Talc City Hills to the Sheep Range.

  10. Fibrous calcite from the Middle Ordovician Holston Formation (east Tennessee)

    SciTech Connect

    Tobin, K.J.; Walker, K.R. . Dept. of Geological Sciences)

    1993-03-01

    Fibrous calcite from buildups, which occur near the top of the Middle Ordovician Holston Formation, were examined from two localities near Knoxville, TN (Alcoa Highway and Deanne Quarry). Buildups at these localities were deposited under open-marine conditions, slightly down-slope from the platform edge. Fibrous calcite (mainly radiaxial fibrous) occur most commonly as cements in mainly stromatactis structures present in bioherms and intergranular porosity in beds that flank bioherms. Fibrous calcite is interpreted to have been precipitated in a marine setting. Fibrous calcite is uniformly turbid or banded with interlayered turbid and clearer cement. Fibrous calcite most commonly shows patchy or blotchy dull-non-luminescence under cathodoluminescence. Bands of uniformly non-luminescent and relatively bright luminescent calcite are present. [delta][sup 13]C compositions of fibrous calcite vary little (0.6 to 1.0%) but [delta][sup 18]O values are highly variable ([minus]4.8 to [minus]7.1%). Post-marine cement consists of ferroan and non-ferroan, dull luminescent equant calcite ([delta][sup 13]C = 0.3 to 0.8; [delta][sup 18]O = [minus]8.6 to [minus]11.5) and is interpreted as precipitated in a deep meteoric or burial setting. Depleted [delta][sup 18]O compositions of fibrous calcite reflect addition of post-depositional calcite during stabilization. Most enriched [delta][sup 13]C and [delta][sup 18]O fibrous calcite composition are similar to enriched values from other Middle Ordovician southern Appalachian buildups (other localities of Holston (TN) and Effna (VA) formations) ([delta][sup 13]C = 0.3 to 0.8; [delta][sup 18]O = [minus]3.9 to [minus]4.8) and may reflect fibrous calcite precipitated in isotopic equilibrium with Middle Ordovician sea water.

  11. Dissecting global diversity patterns: examples from the Ordovician Radiation

    NASA Technical Reports Server (NTRS)

    Miller, A. I.

    1997-01-01

    Although the history of life has been characterized by intermittent episodes of radiation that can be recognized in global compilations of biodiversity, it does not necessarily follow that these episodes are caused by processes that occurred uniformly around the world. Major diversity increases could be generated by the cumulative effects of different mechanisms operating simultaneously at several geographic or environmental scales. The purpose of this review is to describe ongoing research on the manifestations, at several scales, of the Ordovician Radiation, which was among the most extensive intervals of diversification in the history of life. Through much of the period, diversity was concentrated most heavily near regions of active mountain building and volcanism; differences in diversity patterns from continent to continent, and among regions within continents, reflect this overprint. While this suggests a linkage of the Radiation and tectonic activity, this is by no means the only mediating agent. Outcrop-based research in North America has demonstrated that tectonic activity was detrimental to some biotic elements, in contrast to its effects on other organisms. Moreover, in the Great Basin of North America where the local stratigraphic record is of particularly high quality, biotic transitions characteristic of the period occurred far more rapidly than observed in global compilations of diversity, suggesting that the global rate of transition may represent the aggregate sum of transitions that occurred abruptly, but at different times, around the world. Finally, it has been demonstrated that, in concert with an increase in average age, the environmental and geographic ranges of Ordovician genera both increased significantly through the period, indicating a role for intrinsic factors in producing Ordovician biotic patterns.

  12. Ordovician ash geochemistry and the establishment of land plants

    PubMed Central

    2012-01-01

    The colonization of the terrestrial environment by land plants transformed the planetary surface and its biota, and shifted the balance of Earth’s biomass from the subsurface towards the surface. However there was a long delay between the formation of palaeosols (soils) on the land surface and the key stage of plant colonization. The record of palaeosols, and their colonization by fungi and lichens extends well back into the Precambrian. While these early soils provided a potential substrate, they were generally leached of nutrients as part of the weathering process. In contrast, volcanic ash falls provide a geochemically favourable substrate that is both nutrient-rich and has high water retention, making them good hosts to land plants. An anomalously extensive system of volcanic arcs generated unprecedented volumes of lava and volcanic ash (tuff) during the Ordovician. The earliest, mid-Ordovician, records of plant spores coincide with these widespread volcanic deposits, suggesting the possibility of a genetic relationship. The ash constituted a global environment of nutrient-laden, water-saturated soil that could be exploited to maximum advantage by the evolving anchoring systems of land plants. The rapid and pervasive inoculation of modern volcanic ash by plant spores, and symbiotic nitrogen-fixing fungi, suggests that the Ordovician ash must have received a substantial load of the earliest spores and their chemistry favoured plant development. In particular, high phosphorus levels in ash were favourable to plant growth. This may have allowed photosynthesizers to diversify and enlarge, and transform the surface of the planet. PMID:22925460

  13. Reservoir potential in Lower Devonian strata of Illinois

    SciTech Connect

    Whitaker, S.T. )

    1989-08-01

    Lower Devonian strata have considerable potential for hydrocarbon reserves in the Illinois basin; however, there has not yet been a major exploration effort for Lower Devonian reservoirs in the basin, nor has an adequate model been developed to explain distribution of these reservoirs. Due to the lack of exploration, production from these strata is presently limited to a few fields in south-central and southwestern Illinois. A review of data available at the Illinois State Geological Survey indicates that most Lower Devonian production in Illinois is from dolomitized cherty limestones in the Clear Creek Formation and Grassy Knob Chert. Minor production has also been noted in similar facies in the Bailey Limestone. Reservoir development within these strata is caused by dolomitization of slightly porous limestone beds and occurs in proximity to the beds' subcrop at the sub-Kaskaskia (pre-Middle Devonian) unconformity. The best reservoir development appears to be along paleotopographic highs on the Lower Devonian surface. Traps are most commonly formed where porous dolomitic beds, truncated at the sub-Kaskaskia unconformity are underlain by tight cherty limestones and overlain by tight Middle Devonian carbonates. Traps may also be formed downdip from porosity truncations where trends of porous Lower Devonian strata coincide with structural closures. The geometry and distribution of known reservoirs and traps in Lower Devonian carbonates indicate there may be several productive fairways in the basin. Exploration for and exploitation of these plays will depend on an increased understanding of Lower Devonian strata utilizing exploration models such as the one presented here.

  14. (U-Th)/He Ages of Detrital Zircons From Paleozoic Strata of the Severnaya Zemlya Archipelago (Russian High Arctic): implication for testing the different tectonic models

    NASA Astrophysics Data System (ADS)

    Ershova, Victoria; Anfinson, Owen; Prokopiev, Andrei; Khudoley, Andrei; Stockli, Daniel; Faleide, Jan Inge; Gaina, Carmen; Malyshev, Nikolay

    2016-04-01

    The Severnaya Zemlya archipelago comprises four main islands (Pioneer, October Revolution, Komsomolets and Bol'shevik), along with numerous other small islands, islets and island groups. It contains rocks varying in age from Late Cambrian to Permian and is a key area for understanding the tectonic evolution of the North Kara and Laptev Sea basins. Various models have been proposed for the Paleozoic history of the Kara Terrane: 1) Kara terrane inferred as a part of a larger continent block called Arctida (Zonenshain et al, 1990). 2) Lorenz et al. (2008a, 2008b) described the Kara terrane as a marginal part of Baltica. 3) The Kara Terrane existed as a separate terrane or microcontinent during the Paleozoic (Bogdanov et al., 1998; Gramberg & Ushakov, 2000; Metelkin et al., 2000, 2005) Here we present (U-Th)/He ages of detrital zircons collected from Ordovician - Devonian strata of Pioneer and October Revolution islands) along with Sedov Islands. All detrital zircon (U-Th)/He ages are older than age of host rocks indicating the samples were not buried deep enough (less than ~6-8 km) to reset the (U-Th)/He isotopic system. Thus, (U-Th)/He ages indicate the exhumational history of the clastic source region. The (U-Th)/He detrital zircon ages from Ordovician- Silurian strata, with a peak age of ca. 465 Ma, suggest the primary source region was located within the Caledonian Orogen, which is unknown in the modern vicinity of Severnaya Zemlya. The abundance of Caledonian (U-Th)/He zircon ages in the studied samples suggests a continuation of Caledonides northeastward across Barents shelf as previously inferred from pre-Permo-Carboniferous rifting restoration and illustrated by geophysical data. In contrast to older clastic rocks, (U-Th)/He detrital zircon ages from the Devonian deposits show a mixture of Ellesmerian and Caledonian ages with age peaks at ca. 365 Ma and 465 Ma and the youngest grains nearing the depositional age of the strata. The ages suggest the clastic

  15. Seawater fluid inclusions preserved within Cambrian-Ordovician marine cements indicate Cambrian-Ordovician seawater precipitated low-magnesium calcite

    SciTech Connect

    Johnson, W.J.; Goldstein, R.H. . Dept. of Geology)

    1992-01-01

    The San Saba Member of the Wilberns Formation (Llano Uplift, Texas) contains a series of Late Cambrian-Early Ordovician hardgrounds. Bladed low-Mg calcite cements are truncated at hardground surfaces and overlain by shallow marine limestones, indicating a syndepositional shallow marine origin. Primary one-phase fluid inclusions within bladed cements have marine salinities, suggesting that these low-Mg calcite cements formed as a precipitate from Late Cambrian and Early Ordovician seawater and have not undergone recrystallization. Stable isotope analysis of the bladed cement yields delta O-18 values that cluster between [minus]5.6--[minus]6.0 ([per thousand] PDB) which is comparable to those previously reported for Early Ordovician marine calcite. The delta C-13 values are more positive than those reported for this time interval (0.6--1.3 [per thousand] PDB). Trace element analysis indicates that strontium content ranges from 200 to 2,200 ppm. Iron ranges from below detection by electron microprobe to 800 ppm. Mg is generally below detection, however, cements in one hardground display Mg contents that increase progressively toward pore centers. Trace element data lack covariance that would suggest recrystallization. In addition, closed system recrystallization cannot be supported here due to a lack of microdolomite inclusions. Stable isotope, trace element, and fluid inclusion data are consistent with submarine cementation at or below the sediment-water interface. These cements have not undergone significant recrystallization and preserve a primary low Mg calcite mineralogy. These data suggest that early Paleozoic seawater differed chemically from modern seawater. Moreover, preservation of ancient seawater, within fluid inclusions, may provide a direct means of determining those differences.

  16. Did intense volcanism trigger the first Late Ordovician icehouse?

    USGS Publications Warehouse

    Buggisch, Werner; Joachimski, Michael M.; Lehnert, Oliver; Bergstrom, S. M.; Repetski, John E.

    2009-01-01

    Oxygen isotopes measured on Late Ordovician conodonts from Minnesota and Kentucky (United States) were studied to reconstruct the paleotemperature history during late Sandbian to Katian (Mohawkian–Cincinnatian) time. This time interval was characterized by intense volcanism, as shown by the prominent Deicke, Millbrig, and other K-bentonite beds. A prominent carbon isotope excursion (Guttenberg δ13C excursion, GICE) postdates the Millbrig volcanic eruptions, and has been interpreted to reflect a drawdown of atmospheric carbon dioxide and climatic cooling. The oxygen isotope record in conodont apatite contradicts this earlier interpretation. An increase in δ18O of 1.5‰ (Vienna standard mean ocean water) just above the Deicke K-bentonite suggests an abrupt and short-lived cooling that possibly initiated a first short-term glacial episode well before the major Hirnantian glaciation. The decrease in δ18O immediately after the mega-eruptions indicates warming before the GICE, and no cooling is shown in the GICE interval. The coincidence of the Deicke mega-eruption with a cooling event suggests that this major volcanic event had a profound effect on Late Ordovician (late Mohawkian) climate.

  17. Rapid recovery from the Late Ordovician mass extinction

    NASA Technical Reports Server (NTRS)

    Krug, A. Z.; Patzkowsky, M. E.

    2004-01-01

    Understanding the evolutionary role of mass extinctions requires detailed knowledge of postextinction recoveries. However, most models of recovery hinge on a direct reading of the fossil record, and several recent studies have suggested that the fossil record is especially incomplete for recovery intervals immediately after mass extinctions. Here, we analyze a database of genus occurrences for the paleocontinent of Laurentia to determine the effects of regional processes on recovery and the effects of variations in preservation and sampling intensity on perceived diversity trends and taxonomic rates during the Late Ordovician mass extinction and Early Silurian recovery. After accounting for variation in sampling intensity, we find that marine benthic diversity in Laurentia recovered to preextinction levels within 5 million years, which is nearly 15 million years sooner than suggested by global compilations. The rapid turnover in Laurentia suggests that processes such as immigration may have been particularly important in the recovery of regional ecosystems from environmental perturbations. However, additional regional studies and a global analysis of the Late Ordovician mass extinction that accounts for variations in sampling intensity are necessary to confirm this pattern. Because the record of Phanerozoic mass extinctions and postextinction recoveries may be compromised by variations in preservation and sampling intensity, all should be reevaluated with sampling-standardized analyses if the evolutionary role of mass extinctions is to be fully understood.

  18. Tunneling trilobites: Habitual infaunalism in an Ordovician carbonate seafloor

    NASA Astrophysics Data System (ADS)

    Cherns, Lesley; Wheeley, James R.; Karis, Lars

    2006-08-01

    Asaphus trilobites preserved in tunnel systems of the trace fossil Thalassinoides from the mid-Ordovician (ca. 465 Ma) Holen Limestone, Sweden, are interpreted as the trace makers, enabled by shallow carbonate firm grounds to construct open tunnel networks and develop habitual infaunal behavior. Their in situ preservation confirms an infaunal ethology inferred for some trilobite taxa from functional morphology. We suggest that predation pressure from large omnivorous nautiloid cephalopods (“Orthoceras” Limestone facies) may have triggered ecologic opportunism. In trilobites well adapted for predatory-scavenging behavior as well as excavation, the tunnel networks functioned primarily for protection, possibly assisting in feeding, breathing, and breeding strategies. Previously, “trilobite burrows” have referred to seafloor traces of locomotion, feeding, and resting (Cruziana, Rusophycus). Infaunal, tunneling trilobites provide new evidence of mid-Ordovician partitioning of the skeletal benthos, adding to an ecologic and trophic tier hitherto interpreted as occupied by soft-bodied organisms. Such trilobites also provide an identity for Thalassinoides tracemakers prior to Devonian evolution of decapod crustaceans.

  19. Did intense volcanism trigger the first Late Ordovician icehouse?

    USGS Publications Warehouse

    Buggisch, Werner; Joachimski, Michael M.; Lehnert, Oliver; Bergström, Stig M.; Repetski, John E.; Webers, Gerald F.

    2010-01-01

    Oxygen isotopes measured on Late Ordovician conodonts from Minnesota and Kentucky (United States) were studied to reconstruct the paleotemperature history during late Sandbian to Katian (Mohawkian–Cincinnatian) time. This time interval was characterized by intense volcanism, as shown by the prominent Deicke, Millbrig, and other K-bentonite beds. A prominent carbon isotope excursion (Guttenberg δ13C excursion, GICE) postdates the Millbrig volcanic eruptions, and has been interpreted to reflect a drawdown of atmospheric carbon dioxide and climatic cooling. The oxygen isotope record in conodont apatite contradicts this earlier interpretation. An increase in δ18O of 1.5‰ (Vienna standard mean ocean water) just above the Deicke K-bentonite suggests an abrupt and short-lived cooling that possibly initiated a first short-term glacial episode well before the major Hirnantian glaciation. The decrease in δ18O immediately after the mega-eruptions indicates warming before the GICE, and no cooling is shown in the GICE interval. The coincidence of the Deicke mega-eruption with a cooling event suggests that this major volcanic event had a profound effect on Late Ordovician (late Mohawkian) climate.

  20. Evolution of Cambrian-Ordovician carbonate shelf, US Appalachians

    SciTech Connect

    Read, J.F.

    1985-01-01

    Newly compiled cross sections and isopach maps of the Cambro-Ordovician continental shelf, U.S. Appalachians shows that thickness and facies trends are controlled by the Adirondack, New Jersey and Virginia and Alabama arches, and depocenters in Tennessee, Pennsylvania and the Rome Trough. Carbonate sedimentation was initiated with drowning of Early Cambrian clastics, deposition of carbonate ramp facies followed by drowning, regional regression and deposition of Early to Middle Cambrian red beds and platform margin rimmed shelf lime sands and reefs. During subsequent regional transgression the Conasauga intrashelf shale basin formed, bounded toward the shelf edge and along depositional strike by Middle to Upper Cambrian oolitic ramp facies and cyclic peritidal carbonates. During Middle Cambrian rifting, the Rome Trough was filled by thick clastics and carbonates. Intrashelf basin filling and regional regression caused progradation of Late Cambrian cyclic carbonates and clastics across the shelf. By this time, the margin had a relief of 2.5 kms. During the Early Ordovician, incipient drowning of the shelf formed subtidal carbonates and bioherms that passed up into cyclic carbonates which grade seaward into lime sands and reefs. Numerous unconformities interrupt this sequence in the Northern Appalachians. Early dolomitization patterns were controlled by regional highs. Subsidence rates on the margin were low (4 cm/1000 yrs) and typical of a mature passive margin. Shelf sedimentation in the Southern Appalachians ceased with arc-continent collision and development of the Knox unconformity, which dies out into the Pennsylvania depocenter.

  1. Evidence for Late Ordovician glaciation of Al Kufrah Basin, Libya

    NASA Astrophysics Data System (ADS)

    Le Heron, Daniel Paul; Howard, James

    2010-09-01

    Fieldwork at the flanks of Al Kufrah Basin, Libya, reveals that Late Ordovician ice sheets were present in the eastern Sahara and that they extended northeastward toward Egypt. Evidence for grounded ice sheets is preserved at the both the southeastern (Jabal Azbah) and northern (Jabal az-Zalmah) basin margins. Characteristic soft-sediment deformation structures, including soft-sediment folds, small-scale faults and striated pavements indicate subglacial shearing and the formation of glacial erosion surfaces. These findings support the presence of a Late Ordovician ice margin in the eastern Sahara and add vital new constraints to reconstructions of the morphology of North African grounded ice sheets. Prior to our study, there existed two plausible models on ice sheet geometry. The first was that separate ice sheets - namely a north and west African ice sheet and an Arabian ice sheet - extended over this part of western North Gondwana. The second was that ice cover was continuous. The presence of a suite of subglacially-generated deformation structures adds considerable credence to the latter interpretation.

  2. Preliminary paleomagnetic study of the Thetford Mines Ordovician Ophiolite (Canada)

    NASA Astrophysics Data System (ADS)

    Di Chiara, Anita; Morris, Antony; Anderson, Mark

    2016-04-01

    Extension associated with oceanic ridges at divergent plate boundaries is characterized by normal faulting and episodic magma supply. Studies in modern oceanic settings suggest locally along ridges both lower crust and upper mantle peridotites may be exhumed to the seafloor in features known as oceanic core complexes (OCC). OCC are characterized by long-lived low-angle detachment faults that extend for 10s of km, and that are crosscut by high-angle normal faults oriented parallel to the rift axis. Here we present preliminary results from 12 paleomagnetic sites sampled on an example of fossilized Ordovician OCC preserved in the in the Canadian Appalachians, the Southern Quebec ophiolites. These were obducted and subjected to polyphase deformation during Palaeozoic orogeny along the Laurentian margin of Iapetus. Although locally obscured by tectonic fabrics and structures, the original relationships between the ophiolitic mantle, the overlying plutonic section, and onlapping Ordovician siliciclastic rocks can be reconstructed within the Thetford-Mines ophiolite. Preliminary results from AMS and Thermal demagnetization experiments record a remarkably consistent overprint from the youngest (Acadian) phase of Paleozoic orogeny. Although complicating further study of intra-oceanic deformation along the detachment fault in the original OCC, the results provide further insights into the progressive overprint of deformation events as recorded by AMS.

  3. Reconstructing Cambro-Ordovician Seawater Composition using Clumped Isotope Paleothermometry on Calcitic and Phosphatic Brachiopods

    NASA Astrophysics Data System (ADS)

    Bergmann, K.; Robles, M.; Finnegan, S.; Hughes, N. C.; Eiler, J. M.; Fischer, W. W.

    2012-12-01

    A secular increase in δ18O values of marine fossils through early Phanerozoic time raises questions about the evolution of climate and the water cycle. This pattern suggests two end-member hypotheses 1) surface temperatures during early Paleozoic time were very warm, in excess of 40°C (tropical MAT), or 2) the isotopic composition of seawater increased by up to 7-8‰. It has been difficult to evaluate these hypotheses because the δ18O composition of fossils depends on both temperature and the δ18O of water. Furthermore, primary isotopic signatures can be overprinted by diagenetic processes that modify geological materials. This too could explain the decrease in δ18O values of marine fossils with age. Carbonate clumped isotope thermometry can constrain this problem by providing an independent measure of crystallization temperature and, when paired with classical δ18O paleothermometry, can determine the isotopic composition of the fluid the mineral last equilibrated with. Combined with traditional tools, this method has the potential to untangle primary isotopic signatures from diagenetic signals. We measured the isotopic ordering of CO3 groups (Δ47) substituted into the phosphate lattice of phosphatic brachiopods in Cambrian strata. Phosphatic fossils are generally less soluble than carbonates in surface and diagenetic environments, and so are hypothesized to provide a more robust record of primary growth conditions. They also provide an archive prior to the rise of thick shelled calcitic fossils during the Ordovician Radiation. Additionally, measurements of the δ18O of the CO3 groups can be compared with the δ18O of PO4 groups to test whether their mutual fractionation is consistent with primary growth and the apparent temperature recorded by carbonate clumped isotope measurements. We are constructing a phosphatic brachiopod calibration for carbonate clumped isotope thermometry, and Δ47 values of CO2 extracted from modern phosphatic brachiopods suggest

  4. High-resolution Chemostratigraphy Through a Nearshore, Mixed Carbonate-shale Succession of Late Ordovician Age (Sandbian-Katian) in the Laurentian Cratonic Interior

    NASA Astrophysics Data System (ADS)

    Anderson, N. T.; Steenberg, J.; Walters, A.; Retzler, A.; Frahm, E.; Feinberg, J. M.; Dworkin, S. I.; Cowan, C. A.; Runkel, A.

    2015-12-01

    High-resolution (20cm sampling interval) δ13Ccarb, δ13Corg, and pXRF data from core and outcrop exposures of a mixed carbonate-shale succession of Late Ordovician age (Sandbian-Katian) provide insight into the nearshore paleoceanography of Laurentian epeiric seas during a time of global marine perturbations. These strata occur along a 250km transect in Minnesota and Iowa. They represent deposition in a tectonically stable, marginal marine setting that records the interplay of (1) seafloor topography, (2) sea level change, (3) terrigenous influx that periodically smothered a benthic heterozoan faunal community, and (4) production of micritic carbonate that eludes assignment to obvious depositional conditions. Preliminary analyses of δ13Ccarb data from closely spaced sections of the Platteville Formation reveal km-scale lateral variation in the isotopic record. Amid current debate over the interpretation of isotopically distinct "aquafacies" in epeiric seas (reported in these and similar strata elsewhere), our data appear to distinguish regional lithofacies and allow correlation through an otherwise sedimentologically-opaque carbonate rock. Comparison of δ13Ccarb with δ13Corg from carbonate and shale units through the Platteville, Decorah and Cummingsville Formations permits time correlation across significant facies and paleoceanographic gradients in the study area. High-resolution lithostratigraphic data from pXRF allows comparison with this isotopic chronostratigraphy. This time interval includes cooling at the onset of global ice-house conditions (under relatively elevated atmospheric CO2 levels), perturbations of the carbon cycle evinced by δ13C excursions (e.g., GICE) and unusual marine ashfalls preserved as well known K-bentonites in the study area (Millbrig, Deicke, etc.). These strata provide an opportunity to study the dynamics of the most inshore and possibly most sensitive setting preserved for this system.

  5. New paleontological and geological data on the Ordovician and Silurian of Bolivia

    NASA Astrophysics Data System (ADS)

    Gagnier, P. Y.; Blieck, A.; Emig, C. C.; Sempere, T.; Vachard, D.; Vanguestaine, M.

    1996-11-01

    The oldest vertebrates of South America are from the thick Anzaldo (=Cuchupunata) Formation in central Bolivia. At the scale of the basin, the Anzaldo is overlain by the San Benito, Tokochi, Cancañiri, Llallagua and Kirusillas/Uncía formations. The Anzaldo was classically dated Caradoc (early Late Ordovician), but recent paleontological data have suggested a Llanvirn age (early Middle Ordovician). The only significant fossil invertebrates recently collected in the Anzaldo, viz., lingulid brachiopods, give an age not older than Late Ordovician. Fossils from the Tokochi suggest a Caradoc age. The microfossils (acritarchs and foraminifers mainly) collected in the Cancañiri and Kirusillas/Uncía formations indicate an Ashgill to Wenlock age (late Late Ordovician to late Early Silurian) for these formations. A Caradoc (or perhaps older) age thus seems more correct for the Anzaldo Formation. These new paleontological data have major implications on our knowledge of the Ordovician-Silurian basins of Bolivia: 1) transition from a Middle Ordovician marine foreland basin to a Late Ordovician-Llandovery glacial-marine to turbidite trough in the Altiplano occurred in the (late?) Caradoc; 2) a major sea-level rise developed around the Llandovery-Wenlock boundary; 3) a fossiliferous limestone member of shallow origin and early Wenlock age is present approximately between Cochabamba and Santa Cruz.

  6. Magnetostratigraphy of displaced Upper Cretaceous strata in southern California

    NASA Astrophysics Data System (ADS)

    Fry, J. Gilbert; Bottjer, David J.; Lund, Steve P.

    1985-09-01

    A magnetostratigraphic study of Upper Cretaceous marine strata from the Santa Ana Mountains in southern California has identified a Campanian reversed magnetozone. This reversed interval, corresponding to marine magnetic anomaly 33 34 (Chron 33r) of Campanian age, can be correlated with a Campanian reversed magnetozone that has been reported from strata of the Great Valley Sequence in central California. The Late Cretaceous paleolatitude of the Santa Ana Mountains is estimated from this study to be 26.6°N. This is significantly different from the region's expected Cretaceous paleolatitude of 43.8°N as part of the North American stable craton, and indicates that this region (part of the Peninsular Ranges terrane) was 1900 km farther south in Cretaceous time relative to the stable craton. *Present address: Mobil Oil Corp., P.O. Box 900, Dallas, Texas 75221

  7. Climatic and tectonic control of Ordovician sedimentation in the western and central High Atlas (Morocco)

    NASA Astrophysics Data System (ADS)

    Chacrone, Choukri; Hamoumi, Naïma; Attou, Ahmed

    2004-06-01

    The sedimentology of Ordovician deposits in the western and central High Atlas mountains defines several depositional environments: tidal-dominated littoral; wave- and storm-dominated delta, tidal-dominated delta; wave- and storm-dominated shelf. The sediments are mainly siliciclastic and mixed limestone-sili ciclastic, with sparse deposits of ooidal ironstone, basal transgressive sand, and glauconite. The sediments were derived from different levels of the Pan-African chain in the Lower and Middle Ordovician, and from the Sahara in the Upper Ordovician. The sedimentary and sequential evolution indicate that deposition occurred in two independents epeiric seas, influenced mainly by the interplay of tectonics and climate.

  8. Sequence stratigraphic framework of Neogene strata in offshore Nigeria

    SciTech Connect

    Pacht, J.A.; Bowen, B.E.; Hall, D.J.

    1996-08-01

    The western portion of the Nigerian continental margin (Dahomey Basin) exhibits stable to moderately unstable progradation. Systems tracts are similar to those described by Vail for stable progradational margins. In contrast, strata off the central and eastern portions of the Nigerian coast (Niger Delta Complex) exhibit highly unstable progradation, and systems tracts are similar to those in Neogene strata of the offshore Gulf of Mexico. Lowstand basin floor fans in both areas are defined by a well-developed upper reflection. This reflection downlaps along the sequence boundary or abuts against the downthrown side of a growth fault surface. Most lower lowstand (slope fan) strata exhibit discontinuous to semi-continuous subparallel reflections. However, this systems tract also contains channel complexes characterized by chaotic bedding with small bright spots and less common large channels, which exhibit concave-upward reflections. In the western portion of the study area, lower lowstand deposits commonly pinch out on the slope. Deposition occurred largely from point sources. In contrast, contemporaneous shallow-water facies are developed in lower lowstand systems tracts in the Niger Delta Complex. Deposition occurred along a line source. Large amplitude anomalies in the upper lowstand (prograding wedge) suggest well-developed sheet sands occur in shallow-water and deep-water in the Niger Delta complex. However, in the Dahomey Basin there is little evidence of deep-water sands in this interval. The transgressive and highstand systems tracts are usually very thin in outer shelf to basin floor strata in both areas. Both the Dahomey Basin and Niger Delta Complex exhibit different stratigraphic geometries, and therefore, require different exploration strategies.

  9. Ordovician reef-hosted Jiaodingshan Mn-Co deposit and Dawashan Mn deposit, Sichuan Province, China

    USGS Publications Warehouse

    Fan, Delian; Hein, James R.; Ye, Jie

    1999-01-01

    The Jiaodingshan Mn-Co and Dawashan Mn deposits are located in the approximately 2-m thick Daduhe unit of the Wufengian strata of Late Ordovician (Ashgill) age. Paleogeographic reconstruction places the deposits at the time of their formation in a gulf between Chengdu submarine rise and the Kangdian continent. The Jiaodingshan and Dawashan deposits occur in algal-reef facies, the former in an atoll-like structure and the latter in a pinnacle reef. Ores are mainly composed of rhodochrosite, kutnahorite, hausmannite, braunite, manganosite, and bementite. Dark red, yellowish-pink, brown, green-gray, and black ores are massive, banded, laminated, spheroidal, and cryptalgal (oncolite, stromatolite, algal filaments) boundstones. Blue, green, and red algal fossils show in situ growth positions. Samples of high-grade Jiaodingshan and Dawashan ores assay as much as 66.7% MnO. Jiaodingshan Mn carbonate ores have mean contents of Ba, Co, and Pb somewhat higher than in Dawashan ores. Cobalt is widely distributed and strongly enriched in all rock types as compared to its crustal mean content. Cobalt is correlated with Cu, Ni, and MgO in both deposits and additionally with Ba and Zn in the Dawashan deposit. The δ13C(PDB) values of Mn carbonate ores (-7.8 to -16.3‰) indicate contributions of carbon from both seawater bicarbonate and the bacterial degradation of organic matter, the latter being 33% to 68%, assuming about -24‰ for the δ13C(PDB) of the organic matter. Host limestones derived carbon predominantly from seawater bicarbonate δ1313C(PDB) of +0.2 to -7‰). NW-trending fault zones controlled development of lithofacies, whereas NE-trending fault zones provided pathways for movement of fluids. The source of Co, Ni, and Cu was mainly from weathering of mafic and ultramafic rocks on the Kangdian continent, whereas contemporaneous volcanic eruptions were of secondary importance. The reefs were likely mineralized during early diagenesis under shallow burial. The reefs

  10. Late Ordovician (Ashgillian) glacial deposits in southern Jordan

    NASA Astrophysics Data System (ADS)

    Turner, Brian R.; Makhlouf, Issa M.; Armstrong, Howard A.

    2005-11-01

    The Late Ordovician (Ashgillian) glacial deposits in southern Jordan, comprise a lower and upper glacially incised palaeovalley system, occupying reactivated basement and Pan-African fault-controlled depressions. The lower palaeovalley, incised into shoreface sandstones of the pre-glacial Tubeiliyat Formation, is filled with thin glaciofluvial sandstones at the base, overlain by up to 50 m of shoreface sandstone. A prominent glaciated surface near the top of this palaeovalley-fill contains intersecting glacial striations aligned E-W and NW-SE. The upper palaeovalley-fill comprises glaciofluvial and marine sandstones, incised into the lower palaeovalley or, where this is absent, into the Tubeiliyat Formation. Southern Jordan lay close to the margin of a Late Ordovician terrestrial ice sheet in Northwest Saudi Arabia, characterised by two major ice advances. These are correlated with the lower and upper palaeovalleys in southern Jordan, interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest. Thus, four ice advances are now recorded from the Late Ordovician glacial record of southern Jordan. Disturbed and deformed green sandstones beneath the upper palaeovalley-fill in the Jebel Ammar area, are confined to the margins of the Hutayya graben, and have been interpreted as structureless glacial loessite or glacial rock flour. Petrographic and textural analyses of the deformed sandstones, their mapped lateral transition into undeformed Tubeiliyat marine sandstones away from the fault zone, and the presence of similar sedimentary structures to those in the pre-glacial marine Tubeiliyat Formation suggest that they are a locally deformed facies equivalent of the Tubeiliyat, not part of the younger glacial deposits. Deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre-existing faults, previously weakened by epeirogenesis, triggering sediment

  11. Possible late middle Ordovician organic carbon isotope excursion: evidence from Ordovician oils and hydrocarbon source rocks, Mid-Continent and east-central United States

    SciTech Connect

    Hatch, J.R.; Jacobson, S.R.; Witzke, B.J.; Risatti, J.B.; Anders, D.E.; Watney, W.L.; Newell, K.D.; Vuletich, A.K.

    1987-11-01

    A possible coeval excursion in organic-matter delta/sup 13/C is recognized in different late Middle Ordovician lithologic facies over a distance of 480 mi (770 km), perhaps 930 mi (1500 km), in the Mid-Continent and east-central US. The large variability in the carbon isotope compositions of Ordovician oils from the Mid-Continent and east-central US is a direct result of the variable carbon isotope composition of organic matter in the Middle Ordovician hydrocarbon source rocks. The excursion in organic-matter delta/sup 13/C in late Middle Ordovician rocks may reflect significantly increased organic matter productivity and/or preservation. The excursion is not directly related to maceral composition of the organic matter. Limited dissolved CO/sub 2/ availability, possibly a result of continued high organic matter productivity, and limited circulation in the Middle Ordovician seas may have increased the size of the excursion in organic matter delta/sup 13/C. 5 figures, 4 tables.

  12. 43 CFR 2806.32 - How does BLM determine the population strata served?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false How does BLM determine the population... does BLM determine the population strata served? (a) BLM determines the population strata served as follows: (1) If the site or facility is within a designated RMA, BLM will use the population strata of...

  13. 43 CFR 2806.32 - How does BLM determine the population strata served?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false How does BLM determine the population... does BLM determine the population strata served? (a) BLM determines the population strata served as follows: (1) If the site or facility is within a designated RMA, BLM will use the population strata of...

  14. 43 CFR 2806.32 - How does BLM determine the population strata served?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false How does BLM determine the population... does BLM determine the population strata served? (a) BLM determines the population strata served as follows: (1) If the site or facility is within a designated RMA, BLM will use the population strata of...

  15. 43 CFR 2806.32 - How does BLM determine the population strata served?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false How does BLM determine the population... does BLM determine the population strata served? (a) BLM determines the population strata served as follows: (1) If the site or facility is within a designated RMA, BLM will use the population strata of...

  16. Cambrian-Ordovician Rose Run sandstone in northeastern Ohio

    SciTech Connect

    Glenn, R.V.; Kostka, G.

    1987-09-01

    The Rose Run Sandstone Member of the Knox Group has been an elusive target for many years. Many wells had been drilled to the Rose Run in northeastern Ohio, but with very little success. The completion of the Park-Ohio 3 Rhoa in April of 1982 sparked renewed interest in the play. During its first 2 years of production, the 3 Rhoa produced more than 700 mmcf of gas and 700 bbl of condensate. Data obtained from a detailed core analysis and stratigraphic interpretation of the seismic data indicate a depositional environment more complex and variable than prior interpretations from well data alone. These depositional trends, combined with the local structural and erosional complexities at the unconformity, explain the prior lack of success in the Cambrian-Ordovician of northeastern Ohio.

  17. Ordovician-Silurian tectonism in northern California: The Callahan event

    SciTech Connect

    Cotkin, S.J. )

    1992-09-01

    Middle Ordovician to Early Silurian volcanism, plutonism, metamorphism, deformation, and sedimentation in the Yreka and Trinity terranes, eastern Klamath Mountains, northern California, are considered to be related phenomena that occurred in response to an episode of tectonism known as the Callahan event. A diverse array of evidence is used to construct a tectonic model for the Callahan event that involves a subduction zone, a magnetic arc, and a back-arc spreading center, and to show that tectonism likely occurred within the framework of the North American continental margin. Evidence pertaining to subduction polarity is meager, but is consistent with an eastward dip. The Callahan event represents the earliest Phanerozoic convergent-margin tectonic event recognized within the U.S. Cordillera.

  18. Nucularcidae: A new family of palaeotaxodont Ordovician pelecypods (Mollusca) from North America and Australia

    USGS Publications Warehouse

    Pojeta, J., Jr.; Stott, C.A.

    2007-01-01

    The new Ordovician palaeotaxodont family Nucularcidae and the new genus Nucularca are described. Included in Nucularca are four previously described species that have taxodont dentition: N. cingulata (Ulrich) (the type species), N. pectunculoides (Hall), N. lorrainensis (Foerste), and N. gorensis (Foerste). All four species are of Late Ordovician (Cincinnatian; Katian) age and occur in eastern Canada and the northeastern USA. Ctenodonta borealis Foerste is regarded as a subjective synonym of Nucularca lorrainensis. No new species names are proposed. The Nucularcidae includes the genera Nucularca and Sthenodonta Pojeta and Gilbert-Tomlinson (1977). Sthenodonta occurs in central Australia in rocks of Middle Ordovician (Darriwilian) age. The 12 family group names previously proposed for Ordovician palaeotaxodonts having taxodont dentition are reviewed and evaluated in the Appendix. ?? 2007 NRC Canada.

  19. The Ordovician Radiation: A Follow-up to the Cambrian Explosion?

    PubMed

    Droser, Mary L; Finnegan, Seth

    2003-02-01

    There was a major diversification known as the Ordovician Radiation, in the period immediately following the Cambrian. This event is unique in taxonomic, ecologic and biogeographic aspects.While all of the phyla but one were established during the Cambrian explosion, taxonomic increases during the Ordovician were manifest at lower taxonomic levels although ordinal level diversity doubled. Marine family diversity tripled and within clade diversity increases occurred at the genus and species levels. The Ordovician radiation established the Paleozoic Evolutionary Fauna; those taxa which dominated the marine realm for the next 250 million years. Community structure dramatically increased in complexity. New communities were established and there were fundamental shifts in dominance and abundance.Over the past ten years, there has been an effort to examine this radiation at different scales. In comparison with the Cambrian explosion which appears to be more globally mediated, local and regional studies of Ordovician faunas reveal sharp transitions with timing and magnitudes that vary geographically. These transitions suggest a more episodic and complex history than that revealed through synoptic global studies alone.Despite its apparent uniqueness, we cannot exclude the possibility that the Ordovician radiation was an extension of Cambrian diversity dynamics. That is, the Ordovician radiation may have been an event independent of the Cambrian radiation and thus requiring a different set of explanations, or it may have been the inevitable follow-up to the Cambrian radiation. Future studies should focus on resolving this issue. PMID:21680422

  20. Organic geochemistry of Mid-Continent middle and Late Ordovician oils

    SciTech Connect

    Longman, M.W.; Palmer, S.E.

    1987-08-01

    Ordovician oils in Mohawkian and Cincinnatian reservoirs of the US Mid-Continent retain the biochemical imprint of Middle and Upper Ordovician oceanic life before the evolution of land plants and most vertebrates. Thus, these oils have some geochemical features that distinguish them from younger oils. These features include (1) a predominance of n-C/sub 15/, n-C/sub 17/, and n-C/sub 19/ alkanes in the saturated hydrocarbon fraction, (2) relatively low amounts of longer chain n-alkanes, (3) low amounts of chlorophyll-derived isoprenoids, such as pristane and phytane, and (4) abundant C/sub 29/ sterane relative to C/sub 27/ with rearranged forms (diasteranes) predominant over normal steranes. Ordovician oils also generally contain little sulfur and have a somewhat variable light stable carbon isotopic composition with delta/sup 13/C/sub sat/ and delta/sup 13/C/sub aro/ values of -28 to -31 per thousand (PDB), but these features are typical of many marine oils. The unusual chemistry of these Ordovician oils supports the interpretation of Reed, Illich, and Horsfield (1986) that prokaryotic organisms provided the organic matter for most Ordovician oils. Although their claim for Gloeocapsamorpha (a problematic unicellular prokaryote, possibly a blue-green alga or an unusually large bacterium) cannot be proven from oil chemistry alone, knowing that indigenous Mid-Continent Ordovician oils were derived from prokaryotic organisms may aid in future exploration for these reservoirs. 7 figures, 3 tables.

  1. Detrital zircons from the Ordovician rocks of the Pyrenees: Geochronological constraints and provenance

    NASA Astrophysics Data System (ADS)

    Margalef, Aina; Castiñeiras, Pedro; Casas, Josep Maria; Navidad, Marina; Liesa, Montserrat; Linnemann, Ulf; Hofmann, Mandy; Gärtner, Andreas

    2016-06-01

    The first LA-ICP-MS U-Pb detrital zircon ages from quartzites located below (three samples) and above (one sample) the Upper Ordovician unconformity in the Central Pyrenees (the Rabassa Dome, Andorra) were investigated. The maximum depositional age for the Jújols Group, below the unconformity, based on the youngest detrital zircon population, is around 475 Ma (Early Ordovician), whereas for the Bar Quartzite Fm., above the unconformity, the presence of only two zircons of 442 and 443 Ma precludes obtaining a precise maximum sedimentation age. A time gap of ~ 20 million years for the Upper Ordovician unconformity in the Pyrenees can be proposed, similar to that of the Sardic unconformity in Sardinia. The similar age patterns obtained on both sides of the Upper Ordovician unconformity suggest that there was no change in the source area of these series, while the absence of a Middle Ordovician age population may be due to a lack of sedimentation at that time. The four study samples present very similar U-Pb age patterns: the main age populations correspond to Neoproterozoic (Ediacarian-Cryogenian, ca. 550-750 Ma); Grenvillian (Tonian-Stenian, ca. 850-1100 Ma); Paleoproterozoic (Orosirian, ca.1900-2100 Ma) and Neoarchean (ca. 2500-2650 Ma). The similarity with the Sardinian age distribution suggests that these two terranes could share the same source area and that they were paleogeographically close in Ordovician times in front of the Arabian-Nubian Shield.

  2. Orbital-scale glacio-eustasy during the transition between the Early Ordovician warm period (greenhouse) and the Late Ordovician cool period (icehouse)

    NASA Astrophysics Data System (ADS)

    Elrick, M.; Reardon, D.; Labor, W. A.

    2011-12-01

    Recent studies using oxygen isotopes from conodont apatite and carbonate clumped isotopes suggest that the transition from the Early Ordovician warm period (greenhouse) to the Latest Ordovician glacial period (icehouse) occurred in two stages- cooling during the Early and Middle Ordovician and another, more abrupt cooling in the Latest Ordovician (Hirnantian). These results come from samples collected at time intervals of >0.5 My; therefore, the data does not resolve orbital-scale climatic changes. This study utilizes oxygen isotopes from conodont apatite collected across multiple, orbital-scale carbonate cycles (or parasequences) in the early Late Ordovician to evaluate high-frequency paleoclimate changes. More specifically, we are addressing whether the observed carbonate cycles formed in response to orbital-scale, glacio-eustasy and to shed light on the dynamics of the Ordovician warm-to-cool climatic transition. The Upper Ordovician (early Katian) Lexington Limestone of Kentucky is characterized by cyclic carbonates and shales deposited in southern subtropical waters of the Laurentian craton. Orbital-scale (~15-130 ky) subtidal cycles (1-3 m) are composed of offshore limestone and shale, overlain by lower shoreface, then upper shoreface skeletal carbonates and show no evidence of subaerial exposure at cycle tops. δ18Oapatite values from multiple cycles range from ~18-19.5%. The majority of cycles record low isotopic values in the deepest water facies (during sea-level rise and highstand) and higher isotopic values in the shallowest water facies (during sea-level fall and lowstand). The magnitude of isotopic shift across individual cycles is up to ~1%. Estimated subtropical SSTs range from ~28°-34°C. If the intracycle isotopic shifts were due only to SST changes, then the temperatures fluctuated up to 4°C during individual cycle formation; estimated thermo-eustatic changes given these SST changes are not sufficient in magnitude to generate the observed

  3. Ordovician and Silurian Phi Kappa and Trail Creek formations, Pioneer Mountains, central Idaho; stratigraphic and structural revisions, and new data on graptolite faunas

    USGS Publications Warehouse

    Dover, James H.; Berry, William B.N.; Ross, Reuben James, Jr.

    1980-01-01

    clastic rocks reported in previously measured sections of the Phi Kappa, as well as the sequence along Phi Kappa Creek from which the name originates, are excluded from the Phi Kappa as revised and are reassigned to two structural plates of Mississippian Copper Basin Formation; other strata now excluded from the formation are reassigned to the Trail Creek Formation and to an unnamed Silurian and Devonian unit. As redefined, the Phi Kappa Formation is only about 240 m thick, compared with the 3,860 m originally estimated, and it occupies only about 25 percent of the outcrop area previously mapped in 1930 by H. G. Westgate and C. P. Ross. Despite this drastic reduction in thickness and the exclusion of the rocks along Phi Kappa Creek, the name Phi Kappa is retained because of widely accepted prior usage to denote the Ordovician graptolitic shale facies of central Idaho, and because the Phi Kappa Formation as revised is present in thrust slices on Phi Kappa Mountain, at the head of Phi Kappa Creek. The lithic and faunal consistency of this unit throughout the area precludes the necessity for major facies telescoping along individual faults within the outcrop belt. However, tens of kilometers of tectonic shortening seems required to juxtapose the imbricated Phi Kappa shale facies with the Middle Ordovician part of the carbonate and quartzite shale sequence of east central Idaho. The shelf rocks are exposed in the Wildhorse structural window of the northeastern Pioneer Mountains, and attain a thickness of at least 1,500 m throughout the region north and east of the Pioneer Mountains. The Phi Kappa is in direct thrust contact on intensely deformed medium- to high-grade metamorphic equivalents of the same shelf sequence in the Pioneer window at the south end of the Phi Kappa-Trail Creek outcrop belt. Along East Pass, Big Lake, and Pine Creeks, north of the Pioneer Mountains, some rocks previously mapped as Ramshorn Slate are lithologically and faunally equivalent to the P

  4. The Strata-l Experiment on Microgravity Regolith Segregation

    NASA Technical Reports Server (NTRS)

    Fries, M.; Abell, P.; Brisset, J.; Britt, D.; Colwell, J.; Durda, D.; Dove, A.; Graham, L.; Hartzell, C.; John, K.; Leonard, M.; Love, S.; Sanchez, D. P.

    2016-01-01

    The Strata-1 experiment studies the segregation of small-body regolith through long-duration exposure of simulant materials to the microgravity environment on the International Space Station (ISS). Many asteroids feature low bulk densities, which implies high values of porosity and a mechanical structure composed of loosely bound particles, (i.e. the "rubble pile" model), a prime example of a granular medium. Even the higher-density, mechanically coherent asteroids feature a significant surface layer of loose regolith. These bodies will evolve in response to very small perturbations such as micrometeoroid impacts, planetary flybys, and the YORP effect. A detailed understanding of asteroid mechanical evolution is needed in order to predict the surface characteristics of as-of-yet unvisited bodies, to understand the larger context of samples from sample return missions, and to mitigate risks for both manned and unmanned missions to asteroidal bodies. Due to observation of rocky regions on asteorids such as Eros and Itokawa, it has been hypothesized that grain size distribution with depth on an asteroid may be inhomogeneous: specifically, that large boulders have been mobilized to the surface. In terrestrial environments, this size-dependent sorting to the surface of the sample is called the Brazil Nut Effect. The microgravity and acceleration environment on the ISS is similar that of a small asteroid. Thus, Strata-1 investigates size segregation of regolith in an environment analogous to that of small bodies. Strata-1 consists of four regolith simulants in evacuated tubes, as shown in Figure 1 (Top and Middle). The simulants are (1) a crushed and sieved ordinary chondrite meteorite to simulate an asteroidal surface, (2) a carbonaceous chondrite simulant with a mixture of fine and course particles, and two simplified silicate glass simulants; (3) one with angular and (4) another with spherical particles. These materials were chosen to span a range of granular

  5. Segmentation of skin strata in reflectance confocal microscopy depth stacks

    NASA Astrophysics Data System (ADS)

    Hames, Samuel C.; Ardigò, Marco; Soyer, H. Peter; Bradley, Andrew P.; Prow, Tarl W.

    2015-03-01

    Reflectance confocal microscopy is an emerging tool for imaging human skin, but currently requires expert human assessment. To overcome the need for human experts it is necessary to develop automated tools for automatically assessing reflectance confocal microscopy imagery. This work presents a novel approach to this task, using a bag of visual words approach to represent and classify en-face optical sections from four distinct strata of the skin. A dictionary of representative features is learned from whitened and normalised patches using hierarchical spherical k-means. Each image is then represented by extracting a dense array of patches and encoding each with the most similar element in the dictionary. Linear discriminant analysis is used as a simple linear classifier. The proposed framework was tested on 308 depth stacks from 54 volunteers. Parameters are tuned using 10 fold cross validation on a training sub-set of the data, and final evaluation was performed on a held out test set. The proposed method generated physically plausible profiles of the distinct strata of human skin, and correctly classified 81.4% of sections in the test set.

  6. Baseline characteristics of different strata of astronaut corps

    NASA Technical Reports Server (NTRS)

    Hamm, Peggy B.; Pepper, L. J.

    1993-01-01

    The Longitudinal Study of Astronaut Health (LSAH) is an epidemiological study designed to study the effects of the occupational exposures incurred by astronauts in health outcomes and changes in physiological variables. Between 1959 and 1991, 195 individuals were selected for the program. The medical standards for selection have remained essentially unchanged since the Mercury Program, but the range and stringency of these criteria have been modified. Demographic and physiological variables identified during the selection year are examined for various strata of the Astronaut Corps. Specifically, age, sex, race, education, usual occupation, military affiliation, medical history, family medical history, visual and hearing measurements, physical exam variables, and specific laboratory values are investigated. Differences are examined in astronauts for the following criteria: (1) were selected prior to 1970 (n = 73) versus those selected after 1970 (n = 122); (2) have flown multiple missions versus those who have flown less than two missions; (3) have walked in space versus all others; (4) have more than 500 hours of mission time versus all others; and (5) have gone to the Moon versus all others. Length of time served in the Astronaut Corps is examined for each of these strata.

  7. Ordovician platform, slope, and basin facies in subsurface of southern North America

    SciTech Connect

    Alberstadt, L.P.; Colvin, G.; Sauve, J.

    1986-05-01

    Ordovician carbonates of the Nashville dome and Ozark dome regions have long been considered typical shelf deposits. In the subsurface to the south, in the Black Warrior basin, Mississippi Embayment, and Arkoma basin, these shelf carbonate units changed facies. The most significant change is the occurrence of a thick limestone unit characterized by a faunal and floral assemblage of Nuia, Girvanella (isolated long strands), Sphaerocodium, a delicate stacked-chambered organism (.algal), and sponge spicules and sponge mudstone clumps. In ascending order, the complete Ordovician sequence consists of: a lower dolostone, the Nuia-sponge limestone, a dolostone, and a limestone. The upper part of this four-fold sequence changes character westward into the Arkoma basin. The lower two units maintain their character for long distances along depositional strike and occur in parts of the Appalachians as far north as Newfoundland, and on the opposite side of the continent in Nevada. The Nuia-sponge assemblage is a distinctive petrographic marker and seems to be a persistent Ordovician rock and fossil assemblage of widespread occurrence. In Nevada, it occurs on the surface where it is associated with slump and slide features that suggest that it is an outer shelf or upper slope deposit. Coeval carbonates in the Ouachita Mountains are different and show indications of being deep water (basinal). Biostratigraphic evidence indicates that the succession in the subsurface is continuous; the regional Lower Ordovician-Middle Ordovician unconformity is absent. The Lower Ordovician-Middle Ordovician boundary falls near the top of the Nuia-sponge mudstone unit and not at the top of the underlying thick dolostone unit.

  8. Seismic-geochemical exploration mix reveals Ordovician dolomite chimneys

    SciTech Connect

    Tedesco, S.A.

    1995-07-01

    The Cincinnati, Findlay and Algonquin arch system extends from central Tennessee to southern Ontario, and along this trend are found shallow but prolific dolomite breccias, or chimneys, or Ordovician age. The reservoirs are difficult to explore for and, until the discovery of Stoney Point Field in 1983, were essentially found by accident. The Stoney Point Field in southern Michigan was found by an integrated approach utilizing surface geochemical and seismic methods. In southern Ontario, central Kentucky and Tennessee, the use of 2-D, 2-D swathe and, most recently, 3-D seismic surveys in conjunction with surface geochemistry has caused, sustained and increased success rates for exploration for these types of reserves. The Stoney Point Field was discovered using seismic and four surface geochemical methods. A dry hole was drilled first, and its location was based on seismic. Subsequently, a new location was drilled 100 feet to the west and encountered thick pay and is productive. These two wells and their close proximity indicate the difficulty in exploring for these reservoirs and the need for an integrated approach.

  9. An acercostracan marrellomorph (Euarthropoda) from the Lower Ordovician of Morocco

    NASA Astrophysics Data System (ADS)

    Legg, David A.

    2016-04-01

    Enosiaspis hrungnir gen. et sp. nov., a new species of marrellomorph arthropod from the Lower Ordovician (Tremadocian) Fezouata biota of Morocco, is described. This taxon is characterised by the possession of a cordiform dorsal carapace with an anterior notch and a doublure-like structure formed from fused marginal spines, covering the entire body. The head comprises at least five segments which bear an anterior pair of antenna, followed by three pairs of potentially biramous, geniculate appendages. The trunk possesses around 25 pairs of delicate, almost filamentous appendages, which decrease in size posteriorly. Similar features are also found in Xylokorys chledophilia from the Silurian of England, and Vachonisia rogeri from the Devonian of Germany, indicating acercostracan affinities for E. hrungnir. This was tested using a phylogenetic analysis which resolved this taxon as sister taxon to a group composed of the formerly mentioned taxa. The similarities between the ventral spinose carapace doublure of E. hrungnir and the mediolateral spines of marrellid marrellomorphs further support claims that the dorsal shield of acercostracans evolved from the fusion of spinose anlagen, akin to the formation of the carapace of crustaceans.

  10. An acercostracan marrellomorph (Euarthropoda) from the Lower Ordovician of Morocco.

    PubMed

    Legg, David A

    2016-04-01

    Enosiaspis hrungnir gen. et sp. nov., a new species of marrellomorph arthropod from the Lower Ordovician (Tremadocian) Fezouata biota of Morocco, is described. This taxon is characterised by the possession of a cordiform dorsal carapace with an anterior notch and a doublure-like structure formed from fused marginal spines, covering the entire body. The head comprises at least five segments which bear an anterior pair of antenna, followed by three pairs of potentially biramous, geniculate appendages. The trunk possesses around 25 pairs of delicate, almost filamentous appendages, which decrease in size posteriorly. Similar features are also found in Xylokorys chledophilia from the Silurian of England, and Vachonisia rogeri from the Devonian of Germany, indicating acercostracan affinities for E. hrungnir. This was tested using a phylogenetic analysis which resolved this taxon as sister taxon to a group composed of the formerly mentioned taxa. The similarities between the ventral spinose carapace doublure of E. hrungnir and the mediolateral spines of marrellid marrellomorphs further support claims that the dorsal shield of acercostracans evolved from the fusion of spinose anlagen, akin to the formation of the carapace of crustaceans. PMID:26922777

  11. Petroleum source rock evaluation of the Alum and Dictyonema Shales (Upper Cambrian-Lower Ordovician) in the Baltic Basin and Podlasie Depression (eastern Poland)

    NASA Astrophysics Data System (ADS)

    Kosakowski, Paweł; Kotarba, Maciej J.; Piestrzyński, Adam; Shogenova, Alla; Więcław, Dariusz

    2016-05-01

    We present geochemical characteristics of the Lower Palaeozoic shales deposited in the Baltic Basin and Podlasie Depression. In the study area, this strata are represented by the Upper Cambrian-Lower Ordovician Alum Shale recognized in southern Scandinavia and Polish offshore and a equivalent the Lower Tremadocian Dictyonema Shale from the northern Estonia and the Podlasie Depression in Poland. Geochemical analyses reveal that the Alum Shale and Dictyonema Shale present high contents of organic carbon. These deposits have the best source quality among the Lower Palaeozoic strata, and they are the best source rocks in the Baltic region. The bituminous shales complex has TOC contents up to ca. 22 wt%. The analysed rocks contain low-sulphur, oil-prone Type-II kerogen deposited in anoxic or sub-oxic conditions. The maturity of the Alum and Dictyonema Shales changes gradually, from the east and north-east to the west and south-west, i.e. in the direction of the Tornquist-Teisseyre Zone. Samples, located in the seashore of Estonia and in the Podlasie region, are immature and in the initial phase of "oil window". The mature shales were found in the central offshore part of the Polish Baltic Basin, and the late mature and overmature are located in the western part of the Baltic Basin. The Alum and Dictyonema Shales are characterized by a high grade of radioactive elements, especially uranium. The enrichment has a syngenetic or early diagenetic origin. The measured content of uranium reached up to 750 ppm and thorium up to 37 ppm.

  12. Ordovician of the Siberian Platform: sea-level and long-term lithological changes

    NASA Astrophysics Data System (ADS)

    Dronov, A.

    2012-04-01

    Comparative analysis of the Ordovician successions of the Siberian and North American platforms demonstrates a striking similarity in the long-term lithological changes and sea-level curve interpretation. On both platforms Ordovician succession starts with tropical stromatolite-bearing carbonates which abruptly changes to siliciclastic deposits (Baykit Sandstone in Siberia and Eureka Sandstone in North America respectively) and terminates with cool-water carbonates (Ettensohn, 2010; Herrmann et al., 2004; Kanygin et al., 2010). Numerous K-bentonite beds in the Upper Ordovician of North American and Siberian platforms stressed this similarity (Huff et al., 2010; Dronov et al., 2011). The sea-level curve for the Ordovician of North American platform assumes a prominent sea-level drop at the base of the Middle Ordovician and a long-term lowstand during all the Dapingian and Darriwilian (80-100 m lower than in the Lower and Upper Ordovician), (Vail eat al., 1977; Ross and Ross, 1992; 1995). The sea-level curve for the Ordovician of Siberian platform looks roughly the same (Dronov et al., 2009; Kanygin et al, 2010). On the other hand, sea-level curves for the Ordovician of the Gondwanan platforms (North Africa, Yangtze platform, South America, Avalonia) seems to share different patterns (Videt et al., 2010; Su, 2007; Heredia and Beresi, 1995; Woodcock, 1990). The Middle Ordovician represents rather a highstand interval in these reconstructions. As for the Baltica, there are two different sea-level models for this paleocontinent. The sea-level curve suggested by A. Nielsen (2004) demonstrate close similarity to the North American model while the sea-level curve presented by A. Dronov (2005) seems to fit better to the platforms rifted from the Gondwana paleocontinent (Munnecke et al., 2010). This contradiction reflects opposite opinions in the interpretation of limestone units within the deep water setting of the Ordovician basin of Baltoscandia. The invasion of carbonate

  13. Detrital zircon U-Pb and (U-Th)/He double-dating of Upper Cretaceous-Cenozoic Zagros foreland basin strata in the Kurdistan Region of northern Iraq

    NASA Astrophysics Data System (ADS)

    Barber, D. E.; Stockli, D. F.; Koshnaw, R. I.; Horton, B. K.; Tamar-Agha, M. Y.; Kendall, J. J.

    2014-12-01

    The NW Zagros orogen is the result of the multistage collisional history associated with Late Cretaceous-Cenozoic convergence of the Arabian and Eurasian continents and final closure of Neotethys. Siliciclastic strata preserved within a ~400 km segment of the NW Zagros fold-thrust belt and foreland basin in the Iraqi Kurdistan Region (IKR) provide a widespread record of exhumation and sedimentation. As a means of assessing NW Zagros foreland basin evolution and chronostratigraphy, we present coupled detrital zircon (DZ) U-Pb and (U-Th)/He geo-thermochronometric data of Upper Cretaceous to Pliocene siliciclastic strata from the Duhok, Erbil, and Suleimaniyah provinces of IKR. LA-ICP-MS U-Pb age analyses reveal that the foreland basin fill in IKR in general was dominantly derived from Pan-African/Arabian-Nubian, Peri-Gondwandan, Eurasian, and Cretaceous volcanic arc terrenes. However, the provenance of these strata varies systematically along strike and through time, with an overall increase in complexity upsection. DZ age distribution of Paleocene-Eocene strata is dominated by a ~95 Ma grain age population, likely sourced from the Late Cretaceous Hassanbag-Bitlis volcanic arc complex along the northern margin of Arabia. In contrast, DZ U-Pb age distributions of Neogene strata show a major contribution derived from various Eurasian (e.g., Iranian, Tauride, Pontide; ~45, 150, 300 Ma) and Pan-African (~550, 950 Ma) sources. The introduction of Eurasian DZ ages at the Paleogene-Neogene transition likely records the onset of Arabian-Eurasian collision. Along strike to the southeast, the DZ U-Pb spectra of Neogene strata show a decreased percentage of Pan-African, Peri-Gondwandan, Tauride, and Ordovician ages, coupled with a dramatic increase in 40-50 Ma DZ ages that correspond to Urumieh-Dokhtar magmatic rocks in Iran. Combined with paleocurrent data, this suggests that Neogene sediments were transported longitudinally southeastward through an unbroken foreland basin

  14. Bioerosion of Inorganic Hard Substrates in the Ordovician of Estonia (Baltica)

    PubMed Central

    Vinn, Olev; Wilson, Mark A.; Toom, Ursula

    2015-01-01

    The earliest bioeroded inorganic hard substrates in the Ordovician of Estonia appear in the Dapingian. Hardgrounds are also known from the Sandbian and Katian. Most of the bioerosion of inorganic hard substrates occurs as the boring Trypanites Mägdefrau, 1932 along with some possible Gastrochaenolites borings. North American hardground borings are more diverse than those in Baltica. In contrast to a worldwide trend of increasing boring intensity, the Estonian record seems to show no increase in boring intensities during the Middle and Late Ordovician. Hardgrounds seem to be more common during the temperate climate interval of the Ordovician calcite sea in Estonia (seven hardgrounds during 15 my) than in the part with a tropical climate (four hardgrounds during 12 my). Bioerosion is mostly associated with carbonate hardgrounds, but cobbles and pebbles broken from the hardgrounds are also often penetrated by Trypanites borings. The general diversity of boring ichnotaxa in Baltica increased from one ichnospecies in the Cambrian to seven by the end of Ordovician, showing the effect of the GOBE on bioeroding ichnotaxa. The diversity of inorganic hard substrate borers increased by only two times. This difference can be explained by the wider environmental distribution of organic as compared to inorganic substrates in the Ordovician seas of Baltica, and their more continuous temporal availability, which may have caused increased specialization of several borers. The inorganic substrates may have been bioreroded only by the generalists among boring organisms. PMID:26218582

  15. Ordovician carbonate buildups: Potential gas reservoirs in the Ordos basin, central China

    SciTech Connect

    Huaida Hsu )

    1991-03-01

    The Ordos basin of central China covers an area of about 25,000 km{sup 2}. A series of eastward moving overthrusts developed along its western flank, but most of the basin consists of a stable slope that dips westward less than one degree. The basin contains sediments from Sinian to Middle Ordovician and from the Middle Carboniferous to Cretaceous. Its evolutionary history is similar to that of the Alberta basin. Recently drilled wildcat wells have produced commercial gas flows that are closely associated with Ordovician carbonate buildups and a weathered surface between the Ordovician and Carboniferous. Most of the buildups consist of agal mounds; however, some Middle Ordovician reefs developed in the western portion and along the southern margin of the Ordos basin. More than 200 buildups were delineated using seismic stratigraphic techniques. They can be divided into four distinct types. The growth and distribution of buildups were controlled by sea-level fluctuations. The interpretations made in this study were based on the integration of results from a variety of analyses including vertical profiling, differential interformational velocity analysis, amplitude versus offset comparisons, G-log analysis, seismic modeling techniques, and high-precision gravity surveys. The best gas prospects are the Ordovician carbonate buildups distributed around the basin's central uplift. The delineation of carbonate buildups and the demonstration that they are associated with commercial gas flows open the gate for future gas exploration in this area.

  16. EMD Method Applied to Identification of Logging Sequence Strata

    NASA Astrophysics Data System (ADS)

    Zhao, Ni; Li, Rui

    2015-10-01

    In this work, we compare Fourier transform, wavelet transform, and empirical mode decomposition (EMD), and point out that EMD method decomposes complex signal into a series of component functions through curves of local mean value. Each of Intrinsic Mode Functions (IMFs - component functions) contains all the information on the original signal. Therefore, it is more suitable for the interface identification of logging sequence strata. Well logging data reflect rich geological information and belong to non-linear and non-stationary signals and EMD method can deal with non-stationary and non-linear signals very well. By selecting sensitive parameters combination that reflects the regional geological structure and lithology, the combined parameter can be decomposed through EMD method to study the correlation and the physical meaning of each intrinsic mode function. Meanwhile, it identifies the stratigraphy and cycle sequence perfectly and provides an effective signal treatment method for sequence interface.

  17. Regional contemporaneity of eustatic, subsidence, and tectonic events in the Middle-Upper Ordovician of the Appalachians and Ouachita orogens and the southern Oklahoma aulacogen

    SciTech Connect

    Finney, S.C.; Bergstroem, S.M.

    1985-01-01

    On-going graptolite and conodont studies in the Southern Appalachians, the Ouachitas, and the Arbuckle Mountains have revealed contemporaneity of important geological events of regional significance. Reassessment of previous graptolite biostratigraphy has resulted in a revised zonation that has solved some correlation problems and is tied to the Midcontinent and North Atlantic conodont zonations. These zonations are used to date significant geological events in geographically separate regions during two time intervals in the Middle-Upper Ordovician. The base of the graptolite shale succession (Athens) in the Southern Appalachians (Alabama-Tennessee) belongs to the G. teretiusculus Zone, or locally (Georgia) possibly a slightly older unit, and marks the initial shelf-basin development and uplift of source areas to the east reflecting a phase of the Taconic Orogeny. The bases of the Womble and Woods Hollow shales in the Ouachita Orogen represent about the same level. Slightly younger N. gracilis Zone strata tend to be transgressive throughout the world and appear to represent a global eustatic event. In the Arbuckle Mountains this event is reflected by the Tulip Creek Shale. A major subsidence event in the Oklahoma aulacogen, contemporaneous with the regression, produced a transgressive lithofacies sequence represented by the lower Viola Springs Formation in the Arbuckle Mountains. The regressive and subsidence events appear to have been coeval with the emplacement of the Taconic allochthon and Hamburg Klippe in the Northern Appalachians.

  18. Three-dimensional structural interrelationships within Cambrian-Ordovician lithotectonic unit of central Appalachians

    SciTech Connect

    Wilson, T.H.; Shumaker, R.C.

    1988-05-01

    A block diagram of the Cambrian-Ordovician lithotectonic unit illustrates three-dimensional structural relationships within that sequence along the length of the central Appalachian Valley and Ridge and High Plateau provinces. The diagram shows that the Valley and Ridge province is divisible into areas within which shortening is relatively constant in the Cambrian-Ordovician lithotectonic unit. These areas are bounded by zones across which significant differences in shortening occur. These transitions zones contain major cross-strike structural discontinuities in surface structure; in some instances, these discontinuities extend across the Valley and Ridge province and into the High Plateau province. Increases in fold amplitude and number occur in the cover of the Plateau, across strike from the more intensely deformed areas of the Valley and Ridge, where shortening within the Cambrian-Ordovician unit is significantly greater than elsewhere within that province. Structurally controlled gas accumulations are more prevalent in these areas of the Plateau. 7 figures, 2 tables.

  19. Stratigraphic significance of Cruziana: New data concerning the Cambrian-Ordovician ichnostratigraphic paradigm

    SciTech Connect

    Magwood, J.P.A.; Pemberton, S.G. )

    1990-08-01

    The classic Cambrian-Ordovician ichnostratigraphic paradigm originally developed in Europe is based on the assumption that Cruziana - ichnofossils presumably produced by trilobites - can be used in much the same way as trilobite body fossils have been used in chronostratigraphy. That these ichnofossils can be found in many otherwise unfossiliferous, shallow-marine siliciclastic deposits has made them extremely valuable as correlation tools. The paradigm has been used to date lower Paleozoic units in eastern Canada and Europe. It has also been used as supporting evidence to show close affinities between (1) eastern North America, Wales, and Spain and (2) Spain, northern Africa, and southern Asia. Ichnospecies indicative of the Lower Ordovician (Tremadocian and Arenigian), according to the paradigm, have been recovered from the Lower Cambrian (Atdabanian) Gog Group, near Lake Louise, Alberta, Canada. This discovery indicates that these ichnospecies cannot be used as global Lower Ordovician index fossils.

  20. Map showing high-purity silica sand of Middle Ordovician age in the Midwestern states

    USGS Publications Warehouse

    Ketner, Keith B.

    1979-01-01

    Certain quartz sands of Middle Ordovician age in the Midwestern States are well known for their purity and are exploited for a wide variety of industrial uses. The principal Middle Ordovician formations containing high-purity sands are the St. Peter Sandstone which crops out extensively from Minnesota to Arkansas; the Everton Formation principally of Arkansas; and the Oil Creek, McLish, and Tulip Creek Formations (all of the Simpson Group) of Oklahoma. The St. Peter and sandy beds in the other formations are commonly called "sandstones," but a more appropriate term is "sands" for in most fresh exposures they are completely uncemented or very weakly cemented. On exposure to air, uncemented sands usually become "case hardened" where evaporating ground water precipitates mineral matter at the surface; but this is a surficial effect. This report summarizes the available information on the extent of exposures, range of grain size, and chemical composition of the Middle Ordovician sands.

  1. Association of orogenic activity with the Ordovician radiation of marine life

    NASA Technical Reports Server (NTRS)

    Miller, A. I.; Mao, S.

    1995-01-01

    The Ordovician radiation of marine life was among the most substantial pulses of diversification in Earth history and coincided in time with a major increase in the global level of orogenic activity. To investigate a possible causal link between these two patterns, the geographic distributions of 6576 individual appearances of Ordovician vician genera around the world were evaluated with respect to their proximity to probable centers of orogeny (foreland basins). Results indicate that these genera, which belonged to an array of higher taxa that diversified in the Middle and Late Ordovician (trilobites, brachiopods, bivalves, gastropods, monoplacophorans), were far more diverse in, and adjacent to, foreland basins than they were in areas farther removed from orogenic activity (carbonate platforms). This suggests an association of orogeny with diversification at that time.

  2. Palaeomagnetic evidence from the Ordovician and Silurian of northwest Peninsular Malaysia

    NASA Astrophysics Data System (ADS)

    Haile, N. S.

    1980-06-01

    The Ordovician and Silurian Setul Limestone of the Langkawi Islands, northwest Peninsular Malaysia, has a mean magnetic vector of D = 338°, I = 62° after cleaning and correction for tilt. This is equivalent to a palaeolatitude of 43°, and a palaeomagnetic pole at 46°N, 76°E. The Silurian part of the Setul limestone also shows a similar direction. The Ordovician results are equivalent to a palaeolatitude of 43°, N or S. Recent reconstructions, based on palaeontology, place Indochina and China in the northern hemisphere in the Ordovician; if this is correct, a palaeolatitide of 43° for Langkawi would imply that Malaya-Indochina was the most northerly continental fragment at that time.

  3. High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician

    NASA Astrophysics Data System (ADS)

    Porada, P.; Lenton, T. M.; Pohl, A.; Weber, B.; Mander, L.; Donnadieu, Y.; Beer, C.; Pöschl, U.; Kleidon, A.

    2016-07-01

    It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km3 rock) yr-1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today's global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate.

  4. Hydrocarbon charging histories of the Ordovician reservoir in the Tahe oil field, Tarim Basin, China.

    PubMed

    Li, Chun-Quan; Chen, Hong-Han; Li, Si-Tian; Zhang, Xi-Ming; Chen, Han-Lin

    2004-08-01

    The Ordovician reservoir of the Tahe oil field went through many tectonic reconstructions, and was characterized by multiple hydrocarbon chargings. The aim of this study was to unravel the complex charging histories. Systematic analysis of fluid inclusions was employed to complete the investigation. Fluorescence observation of oil inclusions under UV light, and microthermometry of both oil and aqueous inclusions in 105 core samples taken from the Ordovician reservoir indicated that the Ordovician reservoir underwent four oil chargings and a gas charging. The hydrocarbon chargings occurred at the late Hercynian, the Indo-Sinian and Yanshan, the early Himalaya, the middle Himalaya, and the late Himalaya, respectively. The critical hydrocarbon charging time was at the late Hercynian. PMID:15236484

  5. El Paso Formation - a Lower Ordovician platform carbonate deposit

    SciTech Connect

    Clemons, R.E.

    1987-05-01

    The eastward-transgressive Lower Ordovician El Paso Formation conformably overlies Bliss Sandstone in southern New Mexico. Locally, lower El Paso was deposited on low hills of plutonic and volcanic rocks. The region subsided gradually throughout Canadian time, receiving the El Paso carbonate rock blanket up to 460 m thick. Lithologic and chronologic correlative rocks were deposited over most of the southwestern US as the first Paleozoic carbonate platform sequence. The El Paso Formation contains four members, listed here in ascending order: Hitt Canyon, Jose, McKelligon, and Padre. Gradually decreasing sand content upward through the Hitt Canyon indicates deepening water and/or greater distance to shore. Girvanella(.) oncolites are locally abundant. Stromatolite mounds near the top of the Hitt Canyon, combined with an influx of sand, ooids, and rounded bioclasts in the Jose Member, recorded a shoaling phase. The overlying McKelligon Member contains little or no sand, and sponge-Calathium mounds are prominent at some locales. Stromatolite mounds are interbedded with sponge-Calathium mounds in a few sections. Lower Padre Member beds are typically silty to sandy and locally contain thinly-laminated zones. The Padre contains more restricted fauna that includes traces of ostracods. Pervasive bioturbation of El Paso beds and fauna consisting of echinoderms, sponges, gastropods, trilobites, Nuia, Calathium, cephalopods, and algae plus minor brachiopods and Pulchrilamina indicate predominating shallow-subtidal environments. Low-energy platform environments, in which a large volume of micritic muds accumulated, were disturbed thousands of times by storms producing abundant thin, poorly washed biosparite, intrasparite, and intrasparrudite lenses.

  6. Geochemistry of Middle Ordovician carbonate rocks in the Illinois basin

    SciTech Connect

    Li, W.; Anderson, T.F. . Dept. of Geology)

    1993-03-01

    Middle Ordovician carbonate rocks in the Illinois Basin have been studied using petrographic and geochemical techniques. Platteville limestones have higher [delta][sup 18]O values than those of the Galena Group while their carbon isotope compositions are similar. Everton dolomite occurs below the St. Peter Sandstone and is characterized by very low [delta][sup 13]C values ([minus]9.2 to [minus]5.0). Joachim dolomite occurs above the St. Peter Sandstone and is characterized by somewhat higher [delta][sup 13]C values than the Everton Dolomite. The dolomites of the Platteville and Galena Groups have higher [delta][sup 13]C values than the Joachim dolomite. Their oxygen isotopic compositions are higher than those of associated limestones. Dolomite of possible hydrothermal origin is represented by Galena and Platteville core samples from Stephenson County in northern Illinois. It is coarse-grained and associated with lead-zinc ore deposits and is characterized by [delta][sup 13]C values similar to that of Galena dolomite, but considerably lower [delta][sup 18]O values. Saddle dolomite occurs as a minor phase in cavities or as cross-cutting veins throughout the basin. It often is associated with fluorite and was followed by a later-stage calcite cement. It has high [delta][sup 13]C values but low [delta][sup 18]O values ([minus]9.0 to [minus]6.5). [sup 87]Sr/[sup 86]Sr ratios and trace element data, as well as stable isotopes and petrographic evidence, suggest that the majority of the dolomites were formed in seawater (perhaps in hypersaline environments) during early diagenesis before significant compaction. Some dolomites underwent recrystallization and/or hydrothermal alteration after initial dolomitization.

  7. Phylogenetic Clustering of Origination and Extinction across the Late Ordovician Mass Extinction

    PubMed Central

    Krug, Andrew Z.; Patzkowsky, Mark E.

    2015-01-01

    Mass extinctions can have dramatic effects on the trajectory of life, but in some cases the effects can be relatively small even when extinction rates are high. For example, the Late Ordovician mass extinction is the second most severe in terms of the proportion of genera eliminated, yet is noted for the lack of ecological consequences and shifts in clade dominance. By comparison, the end-Cretaceous mass extinction was less severe but eliminated several major clades while some rare surviving clades diversified in the Paleogene. This disconnect may be better understood by incorporating the phylogenetic relatedness of taxa into studies of mass extinctions, as the factors driving extinction and recovery are thought to be phylogenetically conserved and should therefore promote both origination and extinction of closely related taxa. Here, we test whether there was phylogenetic selectivity in extinction and origination using brachiopod genera from the Middle Ordovician through the Devonian. Using an index of taxonomic clustering (RCL) as a proxy for phylogenetic clustering, we find that A) both extinctions and originations shift from taxonomically random or weakly clustered within families in the Ordovician to strongly clustered in the Silurian and Devonian, beginning with the recovery following the Late Ordovician mass extinction, and B) the Late Ordovician mass extinction was itself only weakly clustered. Both results stand in stark contrast to Cretaceous-Cenozoic bivalves, which showed significant levels of taxonomic clustering of extinctions in the Cretaceous, including strong clustering in the mass extinction, but taxonomically random extinctions in the Cenozoic. The contrasting patterns between the Late Ordovician and end-Cretaceous events suggest a complex relationship between the phylogenetic selectivity of mass extinctions and the long-term phylogenetic signal in origination and extinction patterns. PMID:26658946

  8. Phylogenetic Clustering of Origination and Extinction across the Late Ordovician Mass Extinction.

    PubMed

    Krug, Andrew Z; Patzkowsky, Mark E

    2015-01-01

    Mass extinctions can have dramatic effects on the trajectory of life, but in some cases the effects can be relatively small even when extinction rates are high. For example, the Late Ordovician mass extinction is the second most severe in terms of the proportion of genera eliminated, yet is noted for the lack of ecological consequences and shifts in clade dominance. By comparison, the end-Cretaceous mass extinction was less severe but eliminated several major clades while some rare surviving clades diversified in the Paleogene. This disconnect may be better understood by incorporating the phylogenetic relatedness of taxa into studies of mass extinctions, as the factors driving extinction and recovery are thought to be phylogenetically conserved and should therefore promote both origination and extinction of closely related taxa. Here, we test whether there was phylogenetic selectivity in extinction and origination using brachiopod genera from the Middle Ordovician through the Devonian. Using an index of taxonomic clustering (RCL) as a proxy for phylogenetic clustering, we find that A) both extinctions and originations shift from taxonomically random or weakly clustered within families in the Ordovician to strongly clustered in the Silurian and Devonian, beginning with the recovery following the Late Ordovician mass extinction, and B) the Late Ordovician mass extinction was itself only weakly clustered. Both results stand in stark contrast to Cretaceous-Cenozoic bivalves, which showed significant levels of taxonomic clustering of extinctions in the Cretaceous, including strong clustering in the mass extinction, but taxonomically random extinctions in the Cenozoic. The contrasting patterns between the Late Ordovician and end-Cretaceous events suggest a complex relationship between the phylogenetic selectivity of mass extinctions and the long-term phylogenetic signal in origination and extinction patterns. PMID:26658946

  9. Stratigraphic framework of Cambrian and Ordovician rocks across Rome Trough, central Appalachian basin

    SciTech Connect

    Ryder, R.T.

    1987-09-01

    Restored stratigraphic cross sections drawn primarily through the subsurface of parts of Pennsylvania, Ohio, West Virginia, Kentucky, and Tennessee provide new detailed information to further the understanding of Cambrian and Ordovician sedimentation and tectonics associated with the Rome trough sector of the Appalachian basin. Drilled thickness of the Cambrian and Ordovician sequence ranges from a maximum of about 14,500 ft (4.5 km) along the axis of the trough to a minimum of about 3500 ft (1 km) on the western flank.

  10. Limestones of western Newfoundland that magnetized before Devonian folding but after Middle Ordovician lithification

    SciTech Connect

    Hodych, J.P. )

    1989-01-01

    A positive fold test and a negative conglomerate test help determine when and how stable remanence was acquired in the Middle Ordovician Table Head Group limestones of the Port au Port Peninsula of Newfoundland. The limestones magnetized after lithification and incorporation as clasts into a Middle Ordovician breccia. Hence, the limestones do not carry a detrital or other primary remanence despite their very low conodont color alteration index. The remanence may be thermoviscous or diagenetic and was acquired before Devonian folding. This suggests the need for caution in interpreting paleomagnetic results from other early Paleozoic limestones whose remanence resides in magnetite of blocking temperature lower than 400C.

  11. Resistivity imaging of strata and faults in Bangladesh

    NASA Astrophysics Data System (ADS)

    Hosain, A.; Steckler, M. S.; Akhter, S. H.

    2015-12-01

    The Ganges-Brahmaputra-Meghna Delta, the largest in the world, is subject to deformation by active tectonics and dynamic river systems. It lies near the juncture of the Indian, Eurasian and Burmese plates and is being overthrust by both the Shillong Massif and the Indo-Burman Ranges. There are multiple major and minor active faults in Bangladesh, many of which are buried by the sedimentation. For example, the Madhupur tract is a Pleistocene upland in the middle part of Bengal Basin. Whether it is a passive interfluve of the river system or a tilted and tectonically uplifted block has been debated for decades. The Tippera Surface, in Comilla at the eastern part of the basin, is composed of uplifted and oxidized Holocene strata and overlies buried anticlines of the Indo-Burman fold belt. Furthermore, the rivers are subject to migrations, avulsions and other changes in course. The last major avulsion of the Brahmaputra River was only ~200 years ago. During the sea level fall in the last glaciation the major rivers created large incised valleys. In much of the exposed uplands there was the development of a weathered clay surface. This now forms a clay layer separating the Pleistocene and Holocene strata in large parts of Bangladesh. We use electrical resistivity surveying and hand-drilled borehole lithological data to better understand the subsurface discontinuities and structures. The resistivity system consists of an 84 electrode array powered by 2 car batteries and is capable of imaging lithologies to ~100m depth, similar to the depths of the boreholes used to calibrate the data. We extend our previous work on the western margin of the Madhupur Tract with additional lines on the eastern flank of Madhupur. Resistivity lines along the exposed Lalmai anticline in Comilla image the now tilted Holocene-Pleistocene clay layer. Additional lines along the subsurface continuation of the anticline provide additional information on the subsurface lithologies associated with

  12. Palynology of the Vermillion Creek coal bed and associated strata

    SciTech Connect

    Nichols, D.J.

    1987-01-01

    Fifty-four species of spores, pollen, fungi, and algal palynomorphs were identified from the Vermillion Creek coal bed and associated strata, including underlying and overlying deposits and partings within the coal. The stratigraphic distribution and relative abundances of these plant microfossils were determined in samples from three cores. The palynomorph assemblage, which is late early Eocene in age, includes 8 species of pterophyte spores, 4 species of gymnosperm pollen, 39 species of angiosperm pollen, 2 species of algal coenobia or cysts, and 1 species of fungal spore. The assemblage is dominated by the pollen species Platycarya paltycaryoides and Arecipites tenuiexinous. Ten species appear to have biostratigraphic importance, based on their stratigraphic ranges in the Rocky Mountain region. The record of their occurrence in a well-dated stratigraphic section is a contribution to Tertiary biostratigraphy in the central Rockies. Palynologic evidence supplements stratigraphic, sedimentologic, geochemical, coal petrographic and other paleontologic evidence on the nature of the depositional environment. The Vermillion Creek coal was deposited in a paludal environment adjacent to a nonsaline lacustrine system. Evidence from botanical affinities of palynomorph species and habitats of living relatives indicates that the region had a moist subtropical climate in late early Eocene time.

  13. A review of Arbuckle Group strata in Kansas from a sedimentologic perspective: Insights for future research from past and recent studies

    USGS Publications Warehouse

    Franseen, E.K.

    2000-01-01

    Arbuckle Group and equivalent-age rocks (Cambrian and Lower Ordovician) represent an important record of sediment deposition in the history of the North American continent and they contain important accumulations of hydrocarbons (oil and gas) and base metal deposits. This is true for Kansas as well where Arbuckle strata account for approximately 40% of the volume of produced petroleum and known reserves. However, in comparison to their counterparts in other areas, such as the Ellenburger and Knox, Arbuckle rocks in Kansas remain relatively understudied, especially with respect to sedimentology and diagenesis. The Arbuckle is present in the subsurface in most of Kansas and is absent only in areas of northeastern and northwestern Kansas, and over ancient uplifts and buried Precambrian highs. Arbuckle rocks thicken from north to south and are up to 1,390 feet in the southeastern corner of Kansas. Arbuckle Group and equivalent-age rocks from Kansas and surrounding areas are similar, consisting of platform deposits dominated by ramp-type subtidal to peritidal carbonates (mostly dolomitized) which can be subdivided into cycles, less than 0.5 m to 40 m thick, based on facies type and depositional patterns. Recent studies from central Kansas show that major depositional facies consist of coarse-grained packstones/ grainstones, fine-grained packstones/wackestones/mudstones, stromatolites-thrombolites, intraclastic conglomerate and breccia, and shale. In addition, secondary features include dolomitization, breccia, fracture, and conglomerate related to early subaerial exposure and later karst, burial or structural processes, silicification, and local mineralization. Arbuckle and equivalent strata in the Midcontinent were affected by prolonged subaerial exposure that began immediately after Arbuckle deposition, forming the sub-Tippecanoe to sub-Absaroka unconformity. Favorable reservoir qualities generally are thought to be related directly to basement structural elements and

  14. Possible extrinsic controls on the Ordovician radiation: Stratigraphic evidence from the Great Basin, western USA

    SciTech Connect

    Droser, M.L. . Dept. of Earth Sciences); Fortey, R.A. . Dept. of Palaeontology)

    1993-04-01

    The Ordovician radiation has been previously examined by looking at 1/analyses of patterns of diversification within small clades, 2/analyses of large databases to elucidate large-scale paleoecological patterns such as increased tiering and onshore-offshore shifts associated with this radiation. In order to resolve the relationships between these two scales of analysis there is critical need to examine in detail the paleoecology and possible biofacies shifts associated with the Ordovician radiation. The authors have examined the base of the Whiterock Series (Lower-Middle Ordovician) in the Great Basin as it represents one of the most complete records of the Ordovician radiation on the North American continent. Detailed field evidence suggests that the base of the Whiterock does not represent a simple faunal turnover but corresponds with the first occurrences in the region of groups that come to dominate the rest of the Paleozoic. Among the trilobites, this includes the lichides, calymenids, proetides, and phacopides. Similar patterns are found among the dominate Paleozoic bivalve, cephalopod, brachiopod and graptolite clades. Global correlation of this time interval suggests that this pattern of first broad geographic occurrences is not unique to North America. This boundary corresponds with a globally recognized sea level lowstand. In the Great Basin, significant facies shifts are present in shallow and deep water settings. While extrinsic controls are commonly reserved for extinctions, these data suggest that extrinsic factors may have been significant in the timing of the Paleozoic fauna rose to dominance.

  15. Petroleum potential of the Upper Ordovician Maquoketa Group in Illinois: A coordinated geological and geochemical study

    SciTech Connect

    Crockett, J.E.; Oltz, D.F. ); Kruge, M.A. )

    1990-05-01

    The Ordovician Maquoketa Group in Illinois, predominantly composed of shale, calcareous shale, and carbonates, has long been considered a potential source for Illinois basin hydrocarbons. Methods used to better define the petroleum potential of the Maquoketa in the Illinois basin were lithostratigraphic study, Rock-Eval (pyrolysis) analyses, comparison of molecular markers from whole-rock extracts and produced oil, and construction of burial history models. Organic-rich submature Maquoketa potential source rocks are present in western Illinois at shallow depths on the basin flank. Deeper in the basin in southern Illinois, Rock-Eval analyses indicate that the Maquoketa shale is within the oil window. Solvent extracts of the Maquoketa from western Illinois closely resemble the Devonian New Albany Shale, suggesting that past studies may have erroneously attributed Maquoketa-generated petroleum to a New Albany source or failed to identify mixed source oils. Subtle differences between Maquoketa and New Albany solvent extracts include differences in pristane/phytane ratios, proportions of steroids, and distribution of dimethyldibenzothiophene isomers. Maquoketa solvent extracts show little resemblance to Middle Ordovician oils from the Illinois or Michigan basins. Lithostratigraphic studies identified localized thick carbonate facies in the Maquoketa, suggesting depositional response to upper Ordovician paleostructures. Sandstone facies in the Maquoketa in southwestern Illinois offer a potential source/trap play, as well as serving as potential carrier beds for hydrocarbon migration. Maquoketa source and carrier beds may feed older Ordovician rocks in faulted areas along and south of the Cottage Grove fault system in southern Illinois.

  16. Paleomagnetism and magnetostratigraphy of the Middle Ordovician Everton Formation, northern Arkansas

    SciTech Connect

    Farr, M.R.; Sprowl, D.R. )

    1991-03-01

    Paleomagnetic study of the Everton Formation (Chazyan) indicates the presence of both early and late Paleozoic components resident in magnetite. The Fisher mean direction of this apparent primary component is D = 97.9{degree}, I = 1.8{degree} (k = 22, A{sub 95} = 11.2{degree}). Based on a number of factors, the authors believe this early Paleozoic component represents a primary remanence in detrital magnetic. The calculated paleopole for this component (6.1{degree}N, 171.5{degree}E) falls near the Lower Ordovician pole from the Oneata Formation but away from other Middle Ordovician paleopoles. This pole constrains the apparent polar wander path for North America during a period of rapid apparent polar wander. Approximately 70% of the characteristic directions of the early Paleozoic component have reversed polarity; 30% have normal polarity. There is a magnetic reversal from normal to reversed at the contact with the underlying Lower Ordovician Powell Formation. At least six magnetic reversals in the Everton Formation can be correlated between four sampled sections within the area. These correlations are consistent with member boundaries within the Everton. The lateral consistency of the reversals permits time correlation through the Everton section as well as construction of a preliminary magnetostratigraphy for a portion of the Middle Ordovician.

  17. Lower Silurian-Upper Ordovician subsurface glacial outwash deposits, northern Saudi Arabia

    SciTech Connect

    Dobson, P.B. )

    1991-08-01

    Recently acquired seismic data reinterpreted well information in northwest Saudi Arabia extends outcropping Lower Silurian to Upper Ordovician Zarqa/Sarah glacial and periglacial deposits into the subsurface. These deposits range from northeast-trending outwash-filled channels deeply incised into the underlying Ordovician Qasim and the Cambrian-Ordovician Saq Formation in the east. A southwest source for these sediments is implied by this new data. This supports previously interpreted source directions mapped from outcrop. It also correlates with the position of the Arabian plate relative to known Gonwanaland ice caps during the Early Silurian-Late Ordovician. The recognition of glacial outwash sediments in the subsurface provides new insight into the continuity and environments of deposition of the Qasim Formation members in northwest Saudi Arabia. The hydrocarbon-prone Lower Silurian Qusaiba Member of the Qalibah Formation overlies the Zarqa/Sarah Formations. The Qusaiba represents a rapid transgression of the Paleo-Tethys Sea during the final melting of the Gondwanaland ice caps. The seal-source characteristics of the Qusaiba Member, combined with the good porosity and permeability of the underlying outwash deposits, suggest a prospective hydrocarbon exploration play. Gas is produced from this reservoir in the Risha field of eastern Jordan.

  18. Onset of main Phanerozoic marine radiation sparked by emerging Mid Ordovician icehouse

    PubMed Central

    Rasmussen, Christian M. Ø.; Ullmann, Clemens V.; Jakobsen, Kristian G.; Lindskog, Anders; Hansen, Jesper; Hansen, Thomas; Eriksson, Mats E.; Dronov, Andrei; Frei, Robert; Korte, Christoph; Nielsen, Arne T.; Harper, David A.T.

    2016-01-01

    The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals – at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ13C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE. PMID:26733399

  19. Onset of main Phanerozoic marine radiation sparked by emerging Mid Ordovician icehouse.

    PubMed

    Rasmussen, Christian M Ø; Ullmann, Clemens V; Jakobsen, Kristian G; Lindskog, Anders; Hansen, Jesper; Hansen, Thomas; Eriksson, Mats E; Dronov, Andrei; Frei, Robert; Korte, Christoph; Nielsen, Arne T; Harper, David A T

    2016-01-01

    The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals - at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ(13)C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE. PMID:26733399

  20. Onset of main Phanerozoic marine radiation sparked by emerging Mid Ordovician icehouse

    NASA Astrophysics Data System (ADS)

    Rasmussen, Christian M. Ø.; Ullmann, Clemens V.; Jakobsen, Kristian G.; Lindskog, Anders; Hansen, Jesper; Hansen, Thomas; Eriksson, Mats E.; Dronov, Andrei; Frei, Robert; Korte, Christoph; Nielsen, Arne T.; Harper, David A. T.

    2016-01-01

    The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals - at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ13C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE.

  1. Transition metal catalysis in the generation of petroleum: A genetic anomaly in Ordovician oils

    SciTech Connect

    Mango, F.D. )

    1992-10-01

    The transition metals, captured from sedimentary waters by chlorophyll, have been proposed as the catalytic agents that convert n-alkane biolipids into the rearranged light hydrocarbons in petroleum. Certain ancient oils (Ordovician) display a depletion in chlorophyll, suggesting that they may have been derived from sedimentary rocks also depleted in transition metals. These oils show anomalously high concentrations of n-heptane relative to their respective rearranged isoalkane and cycloalkane products. This extraordinary enrichment in light n-alkanes appears unique to the chlorophyll-deficient Ordovician oils. The high concentrations of n-heptane may have resulted from the thermal cracking of higher n-alkanes, which are known to be dominant components of the kerogenous precursors to the Ordovician oils. However, the methylhexanes, which have no thermolytic precursors enriched in the kerogenous source, show a proportionate increase in concentration. The contention, therefore, that thermal cracking might explain the n-heptane anomaly is untenable since a kerogenous starting material enriched in n-alkanes and depleted in isoalkanes cannot reasonably crack to a light hydrocarbon product enriched in both n-alkanes and isoalkanes. According to a postulated catalytic cycle, n-alkane and isoalkane concentrations are controlled by the relative rates of two divergent pathways. If the various transition metals that may catalyze these reactions differ in activity, then a unique distribution of metals created by a chlorophyll deficiency could explain the Ordovician anomaly.

  2. Ordovician magmatic belt upon pre-Variscan basement in the internal Sardinian Variscides

    NASA Astrophysics Data System (ADS)

    Helbing, H.; Frisch, W.; Tiepolo, M.

    2003-04-01

    A middle Ordovician angular unconformity overlain by conglomerates is exposed in the foreland of the Sardinian Variscides and marks the Sardic phase. Towards the orogen, the foreland is bordered by the nappe zone, in which calc-alkaline suite-derived porphyroids occur in the stratigraphic position of middle Ordovician, but such an unconformity as documented in the foreland is not exposed. The nappe zone records increasing metamorphism from low- to medium-grade towards internal parts and is juxtaposed against the high-grade axial zone along a late Variscan fault. Towards the internal parts, the stratigraphy and the porphyroid occurrence become increasingly uncertain. The Ordovician orthogneisses from Lodè and Tanaunella appear respectively in the medium-grade nappe zone and high-grade axial zone as plutonic equivalents to the porphyroids and rise the question whether these orthogneisses intruded in a sedimentary sequence or in an older basement. In order to solve this classical basement problem, we obtained the following results at the transition between nappe zone and axial zone in NE Sardinia. We discovered porphyroids in the low-grade nappe zone south of the village Lula. Furthermore, the earliest foliation S1 is restricted to the medium-grade nappe zone and high-grade axial zone, but is not developed neither in the orthogneisses nor in the porphyroid-interlayered low-grade nappe zone. In-situ U-Pb isotopic data obtained by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on zircon yield 485 +/- 11 Ma for the low-grade Lula porphyroid, 493 +/- 11 Ma for the medium-grade Lodè orthogneiss, and 453 +/- 8 Ma for the high-grade Tanaunella orthogneiss. Besides these Ordovician ages, Neoproterozoic ages are inherited from a Pan-African episode. According to these results we can draw the following conclusions. The internal Sardinian Variscides are made up by an Ordovician magmatic belt upon a pre-Variscan basement. The displacement at the late

  3. Calcified algae and bryozoans from the Ordovician - Silurian successions of the Spiti Himalaya, India

    NASA Astrophysics Data System (ADS)

    Pandey, Shivani; Parcha, Suraj Kumar

    2015-04-01

    The Tethys Himalaya contains an extensive record of sediments ranging from Precambrian to Cretaceous. These successions are well exposed in Pin, Parahio, Kunzum La and in the Takche sections. The present work is focused on the Ordovician and Silurian succession in the Pin Valley. The Ordovician succession consists of purple coloured quartzite, shale, siltstone, grits, dolarenites etc. Whereas, the Silurian succession comprises of thick sequence of slate, dolomite, calcarenites, olive green shale, limestone and pink dolomite. Both the successions contain a rich assemblage of the microfossils along with other body fossils. These successions show a wide variety of marine calcareous algae, along with corals and bryozoans. The calcified algae and bryozoans reported from the Ordovician - Silurian succession are mostly in carbonate beds. The various genera of bryozoan identified are as Calloporella, Cyphotrypa, Dekayai, Eridotrypa, Insignia, Trematopora, etc. along with them are various forms of calcified algae which were found in association in the same thin sections. The prominent genera of calcified algae are as: Dasyporella, Moniliporella, and Vermiporella. The algal assemblages mainly consist of the order Dasycladales, which predominants in the entire successions. Three genera of Dasycladacean algae were identified, among them genus Moniliporella was reported first time from the Pin section. The presence of bryozoans and calcified green algae in these successions indicates shallow marine to near shore environmental conditions followed by different stages of regression and transgression during this time span. Based on the faunal elements, middle to late Ordovician age can be assigned to Thango Formation and late Ordovician to late Silurian to the Takche Formation.The bryozoan communities identified indicates a correlation with that of southern China, Russia, Siberia, Kazakhstan and Mongolia. The genera Insignia and Tremaptopora which are reported from the Spiti Basin

  4. Depositional history and petroleum potential of Middle and Upper Ordovician of Alabama Appalachians

    SciTech Connect

    Benson, J.D.; Mink, R.M.

    1983-09-01

    Middle and Upper Ordovician deposits occupy a significant position in the Paleozoic sequence in the southern Appalachians, since they represent a transition from passive margin carbonate to active margin clastic deposition. Middle Ordovician units show a transition from shallow-water deposits in the west to deeper water basinal deposits in the east. West of the Helena fault the Middle Ordovican is represented by peritidal to shallow subtidal lithologic characteristics of the Chickamauga Limestone. East of the Helena these shallow-water deposits are replaced by deeper water carbonates of the Lenoir and Little Oak Limestones and graptolitic shales of the Athens Formation. Red-green mudrocks of the Greensport Formation were deposited in shallow-shelf to tidal-flat environments and were in turn overlain by quartz arenites of the Colvin Mountain Sandstone, deposited as part of a shallow-barrier system. With continued uplift during the Late Ordovician, additional clastics prograded westward over the filled basin. Early Late Ordovician shallow-shelf to tidal-flat mudrocks of the Sequatchie Formation grade westward into shallow-water carbonates of the Inman and Leipers Formations. With continued input, Sequatchie clastics prograded westward and over-rode the westerly carbonates. A relative sea-level rise during the late Late Ordovican was accompanied by deposition of open-marine shelf, bioclastic limestones of the Sequatchie throughout much of the western Valley and Ridge. The petroleum potential of the Middle and Upper Ordovician sequence in the Alabama Appalachians appears to range from marginal to moderate. The existence of significant reservoirs in this area appears dependent upon the development of fracture porosity associated with Appalachian structures.

  5. Episodic potassic alteration of Ordovician tuffs in the Upper Mississippi Valley

    SciTech Connect

    Lee, M.; Hay, R.L.; Kolata, D.R.

    1985-01-01

    Tuffs of middle and late Ordovician age are altered to mixed-layer illite-smectite (I/S) and to K-feldspar in the Upper Mississippi Valley in northeast Iowa, southeast Minnesota, and southwest Wisconsin. Some and perhaps much of the I/S replaces previously feldspathized tuff, as shown by field and petrographic relationships. Samples for K-Ar dating were collected over a 200 km southeast-northwest traverse. Dates from authigenic K-feldspar are early Devonian and range from 397 +/- 13 to 406 +/- 18, averaging 400 m.y. in three samples, including a middle Ordovician tuff in Iowa and Minnesota and a late Ordovician tuff in Minnesota. Ages of illite layers in I/S are late Devonian and early Mississippian and range from 356 +/- 16 to 371 +/- 17, averaging 366 m.y. in 5 samples including 4 from two middle Ordovician tuffs in Minnesota and Iowa and the late Ordovician tuff in Minnesota. Oxygen-isotopic composition of the K-feldspar and I/S shows that the two minerals crystallized under different conditions and probably reflect introduction of waters of varying chemistry and temperature. K-feldspar very likely crystallized under higher temperatures and possibly lower salinity than the I/S. Introduction of these pore waters may have been caused by groundwater movements resulting from recharge in distal areas undergoing tectonic uplift. K-feldspar alteration was concurrent with early Devonian uplift on the Northeast Missouri Arch and possibly the Transcontinental Arch. Age of the illite layers corresponds to movements on the Sangamon Arch and possibly the Wisconsin Arch.

  6. The Origin and Initial Rise of Pelagic Cephalopods in the Ordovician

    PubMed Central

    Kröger, Björn; Servais, Thomas; Zhang, Yunbai

    2009-01-01

    Background During the Ordovician the global diversity increased dramatically at family, genus and species levels. Partially the diversification is explained by an increased nutrient, and phytoplankton availability in the open water. Cephalopods are among the top predators of todays open oceans. Their Ordovician occurrences, diversity evolution and abundance pattern potentially provides information on the evolution of the pelagic food chain. Methodology/Principal Findings We reconstructed the cephalopod departure from originally exclusively neritic habitats into the pelagic zone by the compilation of occurrence data in offshore paleoenvironments from the Paleobiology Database, and from own data, by evidence of the functional morphology, and the taphonomy of selected cephalopod faunas. The occurrence data show, that cephalopod associations in offshore depositional settings and black shales are characterized by a specific composition, often dominated by orthocerids and lituitids. The siphuncle and conch form of these cephalopods indicate a dominant lifestyle as pelagic, vertical migrants. The frequency distribution of conch sizes and the pattern of epibionts indicate an autochthonous origin of the majority of orthocerid and lituitid shells. The consistent concentration of these cephalopods in deep subtidal sediments, starting from the middle Tremadocian indicates the occupation of the pelagic zone early in the Early Ordovician and a subsequent diversification which peaked during the Darriwilian. Conclusions/Significance The exploitation of the pelagic realm started synchronously in several independent invertebrate clades during the latest Cambrian to Middle Ordovician. The initial rise and diversification of pelagic cephalopods during the Early and Middle Ordovician indicates the establishment of a pelagic food chain sustainable enough for the development of a diverse fauna of large predators. The earliest pelagic cephalopods were slowly swimming vertical migrants

  7. A Laurentian margin back-arc: the Ordovician Wedowee-Emuckfaw-Dahlonega basin

    USGS Publications Warehouse

    Barineau, Clinton I.; Tull, James F.; Holm-Denoma, Christopher S.

    2015-01-01

    Independent researchers working in the Talladega belt, Ashland-Wedowee-Emuckfaw belt, and Opelika Complex of Alabama, as well as the Dahlonega gold belt and western Inner Piedmont of Alabama, Georgia, and the Carolinas, have mapped stratigraphic sequences unique to each region. Although historically considered distinct terranes of disparate origin, a synthesis of data suggests that each includes lithologic units that formed in an Ordovician back-arc basin (Wedowee-Emuckfaw-Dahlonega basin—WEDB). Rocks in these terranes include varying proportions of metamorphosed mafic and bimodal volcanic rock suites interlayered with deep-water metasedimentary rock sequences. Metavolcanic rocks yield ages that are Early–Middle Ordovician (480–460 Ma) and interlayered metasedimentary units are populated with both Grenville and Early–Middle Ordovician detrital zircons. Metamafic rocks display geochemical trends ranging from mid-oceanic-ridge basalt to arc affinity, similar to modern back-arc basalts. The collective data set limits formation of the WEDB to a suprasubduction system built on and adjacent to upper Neoproterozoic–lower Paleozoic rocks of the passive Laurentian margin at the trailing edge of Iapetus, specifically in a continental margin back-arc setting. Overwhelmingly, the geologic history of the southern Appalachians, including rocks of the WEDB described here, indicates that the Ordovician Taconic orogeny in the southern Appalachians developed in an accretionary orogenic setting instead of the traditional collisional orogenic setting attributed to subduction of the Laurentian margin beneath an exotic or peri-Laurentian arc. Well-studied Cenozoic accretionary orogens provide excellent analogs for Taconic orogenesis, and an accretionary orogenic model for the southern Appalachian Taconic orogeny can account for aspects of Ordovician tectonics not easily explained through collisional orogenesis.

  8. Ordovician K-bentonites in the Argentine Precordillera: relations to Gondwana margin evolution

    USGS Publications Warehouse

    Huff, W.D.; Bergstrom, Stig M.; Kolata, Dennis R.; Cingolani, C.A.; Astini, R.A.

    1998-01-01

    This paper is included in the Special Publication entitled 'The proto- Andean margin of Gondwana', edited by R.J. Pankhurst and C.W. Rapela. Ordovician K-bentonites have now been recorded from >20 localities in the vicinity of the Argentine Precordillera. Most occur in the eastern thrust belts, in the San Juan Limestone and the overlying the Gualcamayo Formation, but a few ash beds are known also from the central thrust belts. The oldest occur in the middle Arenig I, victoriae lunatus graptolite (Oe. evae conodont) Zone, and the youngest in the middle Llanvirn P. elegans (P. suecicus) Zone. Mineralogical characteristics, typical of other Ordovician K-bentonites, include a matrix of illite/smectite mixed-layer clay and a typical felsic volcanic phenocryst assemblage: biotite, beta-form quartz, alkali and plagioclase feldspar, apatite, and zircon, with lesser amounts of hornblende, clinopyroxene, titanite and Fe-Ti oxides. The proportions of the mineral phases and variations in their crystal chemistry are commonly unique to individual (or small groups of) K-bentonite beds. Glass melt inclusions preserved in quartz are rhyolitic in composition. The sequence is unique in its abundance of K-bentonite beds, but a close association between the Precordillera and other Ordovician sedimentary basins cannot be established. The ash distribution is most consistent with palaeogeographical reconstructions in which early Ordovician drifting of the Precordillera occurred in proximity to one or more volcanic arcs, and with eventual collision along the Andean margin of Gondwana during the mid-Ordovician Ocloyic event of the Famatinian orogeny. The Puna-Famatina terrane northeast of the Precordillera might have served as the source of the K-bentonite ashes, possibly in concert with active arc magmatism on the Gondwana plate itself.

  9. A Cenozoic-Style Scenario for the End-Ordovician Glaciation

    NASA Astrophysics Data System (ADS)

    Desrochers, André; Ghienne, Jean-François; Vandenbroucke, Thijs R. A.; Achab, Aicha; Asselin, Esther; Dabard, Marie-Pierre; Farley, Claude; Loi, Alfredo; Paris, Florentin; Wickson, Steven; Veizer, Jan

    2015-04-01

    The end-Ordovician (Hirnantian) was an enigmatic interval in the Phanerozoic, known for massive glaciation potentially at elevated CO2 levels, biogeochemical cycle disruptions recorded as large isotope anomalies and a devastating extinction event. Such linkage of eustatic, biological and isotopic records to the climatically forced development of an ice sheet can only be contemplated within a framework of high-resolution sequence stratigraphy that integrates allo-, chemo- or biostratigraphic markers. We develop sequence stratigraphic correlations for two superbly exposed and exceptionally well-developed latest Ordovician successions, the Anti-Atlas of Morocco and Anticosti Island in Canada. Both offer sections, on a 100-km scale, from the basin edge to the axis of active sedimentary depocentres. Relative to the end-Ordovician ice-sheet centre (present-day north-central Africa), they provide a near-field (Anti-Atlas, siliciclastic platform) and a far-field (Anticosti Island, mixed carbonate and siliciclastic) stratigraphic records. These two successions, up to 300 and 100m thick, respectively, were deposited in basins with notable subsidence rates and significant (ca. 100 m) initial water depths, enabling the development of comprehensive archives of the latest Ordovician glaciation. This framework, driven by glacio-eustatic cycles tied to the evolution of polar continental-scale ice sheets over west Gondwana, enables the correlation of eustatic cycles at a level that is beyond the resolution capability of most absolute dating methods and of biozones, the latter typically of Myr duration. A proposed Cenozoic-style scenario including three main glacial cycles and higher-order phenomena necessitates the revision of the end-Ordovician, glaciation-related sequence of events.

  10. Parallel retreat of rock slopes underlain by alternation of strata

    NASA Astrophysics Data System (ADS)

    Imaizumi, Fumitoshi; Nishii, Ryoko; Murakami, Wataru; Daimaru, Hiromu

    2015-06-01

    Characteristic landscapes (e.g., cuesta, cliff and overhang of caprock, or stepped terrain) formed by differential erosion can be found in areas composed of variable geology exhibiting different resistances to weathering. Parallel retreat of slopes, defined as recession of slopes without changes in their topography, is sometimes observed on slopes composed of multiple strata. However, the conditions needed for such parallel retreat have not yet been sufficiently clarified. In this study, we elucidated the conditions for parallel retreat of rock slopes composed of alternating layers using a geometric method. In addition, to evaluate whether various rock slopes fulfilled the conditions for parallel retreat, we analyzed topographic data obtained from periodic measurement of rock slopes in the Aka-kuzure landslide, central Japan. Our geometric analysis of the two-dimensional slopes indicates that dip angle, slope gradient, and erosion rate are the factors that determine parallel retreat conditions. However, dip angle does not significantly affect parallel retreat conditions in the case of steep back slopes (slope gradient > 40°). In contrast, dip angle is an important factor when we consider the parallel retreat conditions in dip slopes and gentler back slopes (slope gradient < 40°). Geology in the Aka-kuzure landslide is complex because of faulting, folding, and toppling, but spatial distribution of the erosion rate measured by airborne LiDAR scanning and terrestrial laser scanning (TLS) roughly fulfills parallel retreat conditions. The Aka-kuzure landslide is characterized by repetition of steep sandstone cliffs and gentle shale slopes that form a stepped topography. The inherent resistance of sandstone to weathering is greater than that of shale. However, the vertical erosion rate within the sandstone was higher than that within the shale, due to direct relationship between slope gradient and vertical erosion rate in the Aka-kuzure landslide.

  11. New interpretation of the so-called Nubian strata in northeast Africa

    SciTech Connect

    Klitzsch, E.H.; Squyres, C.H.

    1988-08-01

    Stratigraphical interpretation of the so-called Nubian Sandstone of Egypt and northern Sudan have led to new ideas on the structural and paleogeographical development of northeast Africa. The strata formerly comprised under the term Nubian Sandstone include sediments from Cambrian to Paleocene age. Based on field work and paleontological investigations during the last 10 years, these strata can be subdivided into three major cycles, each characterizing a certain structural situation of northeast Africa. The first or Paleozoic cycle comprises strata of Cambrian to Early Carboniferous age. These strata were deposited during a period of generally northern dip of northeast Africa; continental sediments transported northward interfinger with marine strata resulting from southward transgressions. Sediments of the second cycle were deposited during and after Gondwana and northern continents collided, which caused updoming of large areas of Egypt and bordering areas to the west and east. As a result, most of Egypt became subject to erosion; transgressions remained near the present northern edge of the continent, and purely continental deposition took place in northern Sudan and bordering areas in Chad and Libya. The resulting strata are similar to the Karroo of East Africa. Strata of the third cycle were deposited after Pangea began to disintegrate. Northeast Africa now had a generally northern dip again, and consequently deposition was controlled - as during the first cycle - by northward drainage and southward transgressions. This last cycle began during Late Jurassic time.

  12. New paleomagnetic results from Late Ordovician rocks of the Yangtze Block, South China, and their paleogeographic implications

    NASA Astrophysics Data System (ADS)

    Han, Zhirui; Yang, Zhenyu; Tong, Yabo; Jing, Xianqing

    2015-07-01

    The paleogeographic relationship between South China and Australia during the Ordovician is important for understanding the configuration of South China in Gondwana. However, high-quality Ordovician paleomagnetic results for the Yangtze Block are scarce. Here we report the results of a new paleomagnetic study of the Late Ordovician limestones of Wangcang County in the northern Yangtze Block, performed in order to constrain the paleoposition of South China. Two magnetic components were isolated by detailed stepwise thermal demagnetization. The low-temperature component falls close to the local current Earth's field direction. The site-mean direction obtained from the high-temperature component (HTC) carried by magnetite is D/I = 132.6°/-35.2° (α95 = 3.6°) after bedding correction, yielding a paleomagnetic pole at 45.8°S, 191.3°E (dp = 2.4°, dm = 4.2°). The HTC direction passed reversal and fold tests, and its corresponding pole differs from the available paleomagnetic poles since the Silurian of the South China Block. These results suggest that the remanent magnetization was probably acquired during the earliest stage of sedimentation. The high-temperature component yields a paleolatitude of 19.5°S, implying that the Yangtze Block was at tropic latitudes during the Late Ordovician. These new and reliable paleomagnetic results bridge the Ordovician data gap and favor the proximity between South China and Australia during the Late Ordovician.

  13. Sands of West Gondwana: An archive of secular magmatism and plate interactions — A case study from the Cambro-Ordovician section of the Tassili Ouan Ahaggar (Algerian Sahara) using U-Pb-LA-ICP-MS detrital zircon ages

    NASA Astrophysics Data System (ADS)

    Linnemann, Ulf; Ouzegane, Khadidja; Drareni, Amar; Hofmann, Mandy; Becker, Sindy; Gärtner, Andreas; Sagawe, Anja

    2011-04-01

    zircons are Meso- to Paleoarchaean ones and provide evidence for the input of very old cratonic basement, most likely from cratonic inliers of the West African craton (Leonian, Liberian). Because of the potential input of detrital zircon from the Amazonian craton, which is reflected in the Mesoproterozoic and late Paleoproterozoic grains, we speculate that some of the Paleoproterozoic to Neoarchean (2.0 Ga to 2.6 Ga) zircons were also derived from Amazonia. Due to the total lack of 1.0-1.2 Ga old zircon, our data set excludes all crustal domains situated in the Arabian-Nubian shield and the East African belt, as well as the Sunsás belt of Amazonia ("Sunsás-Grenvillian") as potential sediment sources. Sedimentation in the Tassili Ouan Ahaggar basin started in uppermost Cambrian to Ordovician time due to the opening of the Rheic Ocean. This event led to subsidence related to the rift and drift of Avalonia and related terranes from the northwestern Gondwanan margin. The basal Early Tassili quartzite has detrital zircon populations that suggest a local provenance either from West African or from a related terrane in the Tuareg shield. A dramatic change occurs in the deltaic to shallow marine strata of the Lower Ordovician Ajjers Formation and in the overlying marine sandstones of the Middle Ordovician d'In Azaoua Formation. Our data for both formations indicate the Pan-African orogen, and very likely Cadomian terranes as the main source for the detritus. During this time, the region was affected by rift tectonics due to the opening of the Rheic Ocean and therefore amenable to erosion at rift shoulders and escarpments. Our data also indicate that glacial erosion in Upper Ordovician (Hirnantian) time must have affected larger areas of old cratonic surfaces as the populations of Paleoproterozoic to Archaean zircons are significantly higher than in other age clusters. Large parts of highly mature sands of the Cambro-Ordovician section in the Tassili Ouan Ahaggar basin were

  14. Effects of sequence stratigraphy on distribution of Cambro-Ordovician siliciclastic hydrocarbon reservoirs in Michigan basin

    SciTech Connect

    Horne, J.C.; Reel, C.L.; Cummins, G.D. )

    1989-08-01

    The lateral and vertical distribution of Cambrian-Ordovician siliciclastic reservoir-potential rock types in the Michigan basin is governed by the sequence stratigraphy. The sequence stratigraphy is controlled primarily by the interaction of four variables: subsidence, eustasy, volume of sediments, and climate. Seven sequential stratigraphic intervals can be defined in the pre-Utica, Cambrian-Ordovician deposits of the Michigan basin. Each of these unconformity-bounded sequences begins with a siliciclastic unit deposited over a lowstand surface of erosion. These lowstand surfaces developed during periods when eustatic sea level decline exceeded the rate of subsidence in the basin, and much or all of the basin became exposed. Where the sedimentation rate was less than the sum of the rate of subsidence and sea level change, a transgressive sequence developed with more open-marine carbonates overlying shallower water and/or non-marine facies. Reservoir-potential siliciclastics accumulated in incised valley-fill and transgressive reworked deposits.

  15. Exceptionally preserved 450-million-year-old ordovician ostracods with brood care.

    PubMed

    Siveter, David J; Tanaka, Gengo; Farrell, Una C; Martin, Markus J; Siveter, Derek J; Briggs, Derek E G

    2014-03-31

    Ostracod crustaceans are the most abundant fossil arthropods and are characterized by a long stratigraphic range. However, their soft parts are very rarely preserved, and the presence of ostracods in rocks older than the Silurian period [1-5] was hitherto based on the occurrence of their supposed shells. Pyritized ostracods that preserve limbs and in situ embryos, including an egg within an ovary and possible hatched individuals, are here described from rocks of the Upper Ordovician Katian Stage Lorraine Group of New York State, including examples from the famous Beecher's Trilobite Bed [6, 7]. This discovery extends our knowledge of the paleobiology of ostracods by some 25 million years and provides the first unequivocal demonstration of ostracods in the Ordovician period, including the oldest known myodocope, Luprisca incuba gen. et sp. nov. It also provides conclusive evidence of a developmental brood-care strategy conserved within Ostracoda for at least 450 million years. PMID:24631241

  16. Iridium abundance maxima at the latest Ordovician mass extinction horizon, Yangtze Basin, China: Terrestrial or extraterrestrial

    SciTech Connect

    Kun Wang; Chatterton, B.D.E. ); Attrep, M. Jr; Orth, C.J. )

    1992-01-01

    Neutron activation analyses of the Chinese Ordovician/Silurian (O/S) boundary sections at two distant localities in the Yangtze Basin, spanning the horizon of a major latest Ordovician global extinction event, show the maxima of iridium abundances to be coincident with the extinction horizon at the base of the graptolite Glyptograptus persculputs zone. The 0.23 ppb Ir maximum in the Yichang type section is almost as large as the late Eocene impact Ir anomaly. However, the authors have observed that the Ir abundances in the Chinese sections are closely correlated with the sedimentation rates, and therefore have concluded that Ir maxima do not indicate a cataclysmic extraterrestrial impact at this extinction level.

  17. The conodont Iapetognathus and its value for defining the base of the Ordovician System

    USGS Publications Warehouse

    Miller, J. E.; Repetski, John E.; Nicoll, R. S.; Nowlan, G. S.; Ethington, R. L.

    2014-01-01

    Nicoll et al. (1999, Brigham Young University Geology Studies 44, 27–101) published the taxonomy of species of the ramiform conodont Iapetognathus Landing in Fortey et al. (1982, The Cambrian–Ordovician boundary: sections, fossil distributions, and correlations, National Museum of Wales, Geological Series No. 3, Cardiff, 95–129) and its ancestorIapetonudus Nicoll et al., 1999. Cooper et al. (2001, Episodes 24, 19–28) used the First Appearance Datum of Iapetognathus fluctivagus Nicoll et al., 1999 to mark the base of the Ordovician System at Green Point, Newfoundland. Terfelt et al. (2012, Lethaia 45, 227–237) re-evaluated Iapetognathus at Green Point and made several taxonomic and stratigraphic conclusions, nearly all of which we refute herein.

  18. A new technique for surface and shallow subsurface paleobarometry using fluid inclusions: An example from the Upper Ordovician Viola Formation, Kansas, USA

    USGS Publications Warehouse

    Newell, K.D.; Goldstein, R.H.

    1999-01-01

    This research illustrates a new approach for paleobarometry employing heterogeneously entrapped fluid inclusions to determine timing and depth of diagenesis. Heterogeneously entrapped fluid inclusions (gas + water) in vug-filling quartz from the Upper Ordovician Viola Formation in the Midcontinent of the United States were analyzed for their internal pressure with a fluid-inclusion crushing stage. The free gas in fluid inclusions was entrapped at near-surface temperature, as indicated by the presence of all-liquid fluid inclusions and fluid inclusions with low homogenization temperatures ( <40??C). Crushing the crystal and measuring the change in bubble size determines the pressure of entrapment directly. Heterogeneous trapping is indicated by widely varying L:V ratios, from all-liquid to vapor-rich. Gas bubbles in most fluid inclusions analyzed expanded upon release to atmospheric pressure, but some collapsed. A mode of 1.5 to 2.0 atm internal pressure was indicated by the crushing runs, but pressures up to 42.9 atm were recorded. Quartz precipitation and associated fluid-inclusion entrapment therefore occurred over a wide depth-range, but principally at depths of approximately 10 m. Crushing runs done in kerosene confirmed the presence of hydrocarbon gases in most of these inclusions, and bulk analyses of gases in the quartz by quadrupole mass spectrometer revealed methane, ethane, and atmospheric gases. The hydrocarbon gases may have originated in deeper thermogenically mature sedimentary strata, and then leaked to the near-surface where they were entrapped in the precipitating quartz cement. Freezing data indicate an event of quartz precipitation from fluids of marine-fresh water intermediate salinity and other events of precipitation from more saline fluids. Considering the determined pressures, the precipitating fluids probably originated at surfaces of subaerial exposure (unconformities) and surfaces of evaporite precipitation in the overlying Silurian

  19. Slope-apron deposition in an ordovician arc-related setting: The Vuelta de Las Tolas Member (Suri Formation), Famatina Basin, northwest Argentina

    USGS Publications Warehouse

    Mangano, M.G.; Buatois, L.A.

    1997-01-01

    The Ordovician Suri Formation is part of the infill of the Famatina Basin of northwest Argentina, which formed in an active setting along the western margin of early Paleozoic Gondwana. The lower part of this formation, the Vuelta de Las Tolas Member, records sedimentation on a slope apron formed in an intra-arc basin situated on a flooded continental arc platform. The coincidence of a thick Arenig-Llanvirn sedimentary succession and volcanic-plutonic arc rocks suggests an extensional or transtensional arc setting, and is consistent with evidence of an extensional regime within the volcanic arc in the northern Puna region. The studied stratigraphic sections consist of volcanic rocks and six sedimentary facies. The facies can be clustered into four facies associations. Association 1, composed of facies A (laminated siltstones and mudstones) and B (massive mudstones and siltstones), is interpreted to have accumulated from silty-muddy high-and low-density turbidity currents and highly fluid, silty debris flows, with subsequent reworking by bottom currents, and to a lesser extent, hemipelagic suspension in an open-slope setting. Facies association 2 is dominated by facies C (current-rippled siltstones) strata. These deposits are interpreted to record overbank sedimentation from fine-grained turbidity currents. Facies E (matrix-supported volcanic breccias) interbedded with andesitic lava units comprises facies association 3. Deposition was contemporaneous with subaqueous volcanic activity, and accumulated from cohesive debris flows in a coarse-grained wedge at the base of slope. Facies association 4 is typified by facies D (vitric fine-grained sandstones and siltstones) and F (channelized and graded volcanic conglomerates and breccias) deposits. These strata commonly display thinning-and fining-upward trends, indicating sedimentation from highly-concentrated volcaniclastic turbidity currents in a channelized system. The general characteristics of these deposits of fresh

  20. Evidence for multi-cycle sedimentation and provenance constraints from detrital zircon U-Pb ages: Triassic strata of the Lusitanian basin (western Iberia)

    NASA Astrophysics Data System (ADS)

    Pereira, M. F.; Gama, C.; Chichorro, M.; Silva, J. B.; Gutiérrez-Alonso, G.; Hofmann, M.; Linnemann, U.; Gärtner, A.

    2016-06-01

    Laser ablation ICP-MS U-Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U-Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U-Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296 Ma), which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa-Morena and Central Iberian zones that outcrop in and close to the Porto-Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian-Carboniferous ages (< ca. 315 Ma) found in detrital zircons provide evidence of the denudation of Variscan and Cimmerian granites during the infilling of continental rift basins in western Iberia. The zircon age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin, which probably acted as an intermediate sediment repository. U-Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived from local source areas with features typical of Gondwana, with no sediment from external sources from Laurussia or southwestern Iberia.

  1. Gas reservoir potential of the Lower Ordovician Beekmantown Group, Quebec Lowlands, Canada

    SciTech Connect

    Dykstra, J.C.F.; Longman, M.W.

    1995-04-01

    The Beekmantown Group in the Quebec Lowlands was deposited as part of an extensive Early Ordovician coastal and shallow marine complex on the eastern margin of the North American craton. The Beekmantown is stratigraphically equivalent to the Beekmantown, Knox, Arbuckle, and Ellenburger rocks of the United States, and is subdivided into two formations: the sandstone-rich Theresa Formation and the overlying dolomite-rich Beauharnois. Dolomites of the Beekmantown provide an important exploration target in both the autochthon and the overlying thrust sheets of the Canadian and U.S. Appalachians. The reservoir potential of the autochthonous Beekmantown Group in the Quebec Lowlands can be determined from seismic data, well logs, cuttings, and petrographic analyses of depositional and diagenetic textures. Deposition of the Beekmantown occurred alongson the western passive margin of the Iapetus Ocean. By the Late Ordovician, the passive margin had been transformed into a foreland basin. Faulting locally positioned Upper Ordovician Utica source rocks against the Beekmantown and contributed to forming hydrocarbon reservoirs. The largest Beekmantown reservoir found to date is the St. Flavien field, with 7.75 bcf of original gas (methane) in place in fractured and possibly karst-influenced allochthonous dolomites within a thrust-fault anticline. Seven major depositional units can be distinguished in cuttings and correlated with wireline logs. Dolomites in the Beekmantown contain vuggy, moldic, intercrystalline, and fracture porosity. Early porosity formed at the top of the major depositional units in peritidal dolomites; however, much of this porosity was later filled by late-stage calcite cement after hydrocarbon migration. Thus, a key to finding gas reservoirs in the autochthonous Beekmantown is to define Ordovician poleostructures in which early and continuous entrapment of hydrocarbons prevented later cementation.

  2. Geochemistry of the Cambrian-Ordovician aquifer system in the northern midwest, United States

    SciTech Connect

    Siegel, D.I.

    1989-01-01

    The geochemistry of the Cambrian-Ordovician aquifer system was modified during the Pleistocene by large-scale emplacement of glacial meltwater, as indicated by large-scale emplacement of glacial meltwater, as indicated by the investigation of stable isotopes of water, and a plume of dilute water that trends perpendicular to the direction of ground-water flow in Iowa and Missouri. Ground water in this part of the aquifer system could be hundreds of thousands of years old.

  3. Tectonically reset Rb-Sr system during Late Ordovician terrane assembly in lapetus, western Ireland

    SciTech Connect

    Kennan, P.S.; Murphy, F.C.

    1987-12-01

    The uncertainty of a ca. 460 Ma age of mylonitization of acid igneous rocks in the western Irish Caledonides required reevaluation of the published Rb-Sr whole-rock data. The authors found that the data support an alternative ca. 426 +/- 10 Ma age of mylonitic resetting. This time of deformation relates to the assembly of suspect terranes during Late Ordovician closure of the Iapetus ocean.

  4. Tectonic vs. eustatic controls on Ordovician deposition in the Alabama Appalachians

    SciTech Connect

    Benson, D.J. . Dept. of Geology)

    1992-01-01

    The Lower Ordovician section consists of a thick (> 1,500 ft.) sequence of peritidal to shallow subtidal carbonates deposited on a broad, stable platform. Initial Taconic orogenic activity during Late Canadian time downwarped the southeastern margin of the continent and resulted in deposition of a unique subtidal unit. A fall in eustatic sea level during Early Whiterockian time exposed the majority of the platform and produced the Post-Knox unconformity, a major regional unconformity that truncates Upper Cambrian-Lower Ordovician carbonates across the Alabama Appalachians. Middle Ordovician deposition began as a result of eustatic sea level rise and continued downwarping of the SE margin of the North American continent. Initial Middle Ordovician deposits are peritidal carbonates that onlap the Post-Knox unconformity from SE to NW. Continued loading of the margin of the continent led to formation of a deep-water basin to the SE and the concurrent development of a peripheral bulge in the vicinity of what is now the Birmingham anticlinorium. Peritidal carbonates to the SE pass upward into shallow ramp carbonates, deep-ramp mixed carbonate/clastic deposits, and, finally, basinal organic shales. As the deep-water basin evolved, shallow ramp carbonates onlapped the peripheral bulge to the NW. The rapidly evolving basin trapped terrigeneous deposits shed from tectonic highlands to the E and SE permitting deposition of shallow to deep ramp, skeletal carbonates to the NW. Continued tectonic loading led to migration and the ultimate inundation of the peripheral bulge. By Late Mohawkian time, filling of the basin allowed terrigeneous sediments derived from the tectonic highlands to prograde westward, onlap and carbonate ramp, and, finally, terminate carbonate deposition.

  5. Allochthonous Ordovician eugeoclinal rocks on Turner Island, eastern Gulf of California, and their paleotectonic significance

    SciTech Connect

    Poole, F.G. ); Berry, W.B.N. . Dept. of Geology and Geophysics); Madrid, R.J. )

    1993-04-01

    A dark-gray meta-argillite unit within a strongly deformed allochthonous sequence of interbedded chert, siliceous argillite, siltite, and minor limestone or dolostone on the northern part of Turner Island contains poorly preserved, carbonized graptolites of late Middle to early Late Ordovician age. The Ordovician meta-argillite on Turner Island correlates with graptolitic Ordovician oceanic rocks in the Somoran orogen exposed on the mainland of Mexico about 90 km east-southeast of Hermosillo, in central Sonora. Turner Island lithofacies, together with fossil types and ages, indicate that the graptolitic meta-argillite unit is part of the Paleozoic eugeoclinal sequence that makes up the Somoran orogen, and is the westernmost sedimentary facies of this orogen within Mexico. Like other eugeoclinal rocks of the Sonoran orogen, the rocks on Turner Island were faulted and isoclinally folded. This assemblage of deformed Paleozoic rocks was tectonically emplaced and metamorphosed before intrusion by Mesozoic or Tertiary dikes and sills. Paleozoic rocks on Turner Island and the Mexican mainland to the east are located east of the East Pacific Rise and the transform faults that segment it in the Gulf of California. The Paleozoic rocks on Turner Island and mainland Mexico are dissimilar to Paleozoic rocks in Baja California, which lie west of the transform fault systems in the Gulf. Consequently, the author interpret the Paleozoic rocks in Baja California to represent displaced terranes that have no physical correlatives to the eugeoclinal rocks of Turner Island and mainland Mexico. The Ordovician rocks on Turner Island, therefore, indicate that the Sonoran orogen occurs as far west as the eastern Gulf of California but east of the transform fault systems.

  6. Conodont biostratigraphy of the Ordovician-Silurian boundary in the Central Appalachian Valley and Ridge Province

    SciTech Connect

    Philips, P.L. Jr.; Hall, J.C. . Dept. of Earth Sciences)

    1993-03-01

    Conodont biostratigraphy of the Ordovician-Silurian boundary in the Central Appalachian Valley and Ridge Province is based primarily on lithologic criteria. Although the boundary is precisely defined lithologically, virtually nothing is known about the biostratigraphic relationships in this interval due to a historic lack of detailed studies in this region. The present study is based on nearly 50 samples from 7 sections in Tennessee and Virginia, aimed at establishing a conodont-based biostratigraphic framework useful for local and regional correlation of lithostratigraphic units and boundaries. The data at hand show uppermost Ordovician rocks in this region have conodont faunas which are characterized by species of Oulodus, Aphelognathus, Phragmodus, and Plectodina. These faunas represent associations which locally correspond to the Oulodus velicuspis to Aphelognathus divergens Zones. Lowermost Silurian rocks contain faunas dominated by species of Ozarkodina, Distomodus, Pranognathus, and Walliserodus that correspond to the faunas of the Distomodus kentuckyensis Zone. Conodont ages indicate that the uppermost Ordovician rocks in the Central Appalachians range in age from upper Edenian to upper Richmondian and lowermost Silurian rocks range in age from upper Rhuddanian to lower Telychian in age. No conodont faunas which characterize the uppermost Richmondian, Gamachian, or lowermost Rhuddanian have yet been identified. The results of this study are in agreement with those of out previous study of the Southern Appalachian Valley and Ridge Province.

  7. Progradational sequences in lower Ordovician portion of Deadwood Formation, Williston basin

    SciTech Connect

    Anderson, D.

    1988-07-01

    In the Williston basin, the Cambrian and Ordovician Deadwood Formation can be divided into six informal members based on gamma-ray log characteristics. Members C through F are Early Ordovician (Tremadocian to Arenigian) and consist of three progradational sequences. In ascending order, the sequences consist of (1) a mixed sandstone-limestone lithotype, (2) limestone lithotypes ranging from mudstone to grainstone, (3) bioturbated, peloidal, calcareous, siliciclastic mudstone and siltstone, (4) bioturbated to planar-laminated, peloidal, calcareous siltstone and sandstone, (5) Skolithos-bored, cross-bedded to planar-laminated quartzarenite, (6) bioturbated dolomite and anhydrite-cemented fossiliferous quartz wacke, and (7) silty laminated dolomudstone. The asymmetrical sequences represent progradation of a siliciclastic shoreline, back-barrier lagoon, and intertidal algal flat over a siliciclastic shelf and a distal carbonate shoal. The present distribution of the sequences and individual lithotypes in the Williston basin is a function of the limited eastward advance of the carbonate shoal during transgression, the limited westward advance of the shoreline during progradation, deep shoreface erosion of the previous sequence during rapid transgression, and Middle Ordovician erosion.

  8. Quantitative paleobathymetric analysis from subsidence data: example from middle Ordovician of Michigan basin

    SciTech Connect

    Howell, P.D.; Budai, J.M.

    1989-03-01

    Quantitative paleobathymetry is difficult to determine for any rock sequence with a significant subtidal component. Water depth estimates are traditionally obtained from detailed sedimentology and paleontology, but this type of data is seldom available in subsurface work. Further, a good geological data base may be inconclusive for paleobathymetry in subtidal or substorm-wave base environments. More accurate facies prediction would be possible if paleobathymetry could be determined from the conventional subsurface data normally available to explorationists. Subsidence analysis of sedimentary basins has the potential to provide precise paleobathymetric estimates for a variety of depositional settings. This technique is illustrated using the Middle Ordovician carbonates of the Michigan basin. Tectonic subsidence patterns established from stratigraphic and subsidence modeling of the Lower-Middle Ordovician Prairie du Chien Group in Michigan are projected forward through the Middle Ordovician. Isopach thicknesses of the Black River and Trenton carbonates are superimposed on the tectonic subsidence patterns to provide a quantitative basin-fill model. The model paleobathymetry is then compared with core data from exploration wells to evaluate the model facies interpretation. An excellent fit is achieved for the shallow to deep subtidal platform and basinal Trenton carbonates. This technique allows paleobathymetry to be calculated in many basins where tectonic subsidence patterns can be accurately modeled.

  9. Tectonic influence on sedimentation patterns, Upper Ordovician of eastern North America

    SciTech Connect

    Keith, B.D.

    1987-09-01

    The upper part of the Champlainian Series and all of the Cincinnatian Series (both parts of the Upper Ordovician Series on the newly published COSUNA charts) can be divided up into seven time slices; the late part of the Blackriverian Age, Rocklandian, Kirkfieldian, Shermanian, Edenian, Maysvillian Ages, and early part of Richmondian Age. Analysis of the rocks, using these time slices in eastern North America, shows five regional facies packages: (1) clean carbonates, (2) mixed carbonates and terrigenous clastics, (3) shale, (4) terrigenous clastics coarser than shale, and (5) terrigenous clastics prograded over carbonates. The latter is considered a facies because of this style of sedimentation is integral to the Upper Ordovician. Regional tectonic events related to plate collision along the eastern margin of North America had a direct influence on the sedimentation pattern of these facies packages. the extensive clean carbonate platform represented by upper Blackriverian rocks was replaced by wide-spread argillaceous carbonates during Rocklandian, Kirkfieldian, and Shermanian time. Also, by Shermanian time, a linear belt of shale deposition bisected the carbonate platform from the southwest to the northeast. South of this trend, carbonate sedimentation continued essentially without interruption in response to tectonic stability until the end of the Ordovician Period. To the north, the carbonate platform deepened and was later flooded by shale during Edenian and Maysvillian time. Starting during the Maysvillian and continuing into the Richmondian, upwarping and erosion of the Taconic highlands caused large-scale terrigenous clastic progradation over the northeastern part of the platform.

  10. Climate change and the selective signature of the Late Ordovician mass extinction.

    PubMed

    Finnegan, Seth; Heim, Noel A; Peters, Shanan E; Fischer, Woodward W

    2012-05-01

    Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia. PMID:22511717

  11. Origin of the Cambrian-Ordovician sedimentary cycles of Wisconsin using tectonic subsidence analysis

    SciTech Connect

    Watso, D.C.; deV Klein, G. )

    1989-10-01

    Cambrian-Ordovician stratigraphy of the Wisconsin dome is organized into five cycles consisting of basal quartzose sandstone, overlain by glauconitic sandstone and capped by limestone or dolostone. Unconformities at the base of each cycle are found to be coeval with known times of rapid tectonic subsidence in the Illinois basin at approximately 512, 502, 495, and 461 Ma. These times of rapid basin subsidence in the Illinois basin are interpreted to represent resurgent faulting events concurrent with thermal subsidence. Such regional extensional faulting would cause concomitant minor uplift of the Wisconsin dome, developing erosional unconformities observed at the base of each Cambrian-Ordovician stratigraphic cycle. Because sea level was rising at a constant global rate during deposition of the Cambrian-Ordovician cycles, stabilization of minor uplift permitted local transgression and deposition of a successive cycle. Repeated faulting during thermal subsidence in the Illinois basin caused repeated minor uplift on the Wisconsin dome, each time initiating a new stratigraphic cycle. Exceptions to this model include initial Late Cambrian transgression onto the midcontinent and a global drop in sea level at 485 Ma. The findings suggest that geodynamic models proposing a two-stage process from mechanical fault-controlled subsidence to thermal subsidence during evolution of extensional basins may need to be modified to include the occurrence of coeval extensional faulting and thermal subsidence during initial stages of basin thermal subsidence.

  12. Climate change and the selective signature of the Late Ordovician mass extinction

    PubMed Central

    Finnegan, Seth; Heim, Noel A.; Peters, Shanan E.; Fischer, Woodward W.

    2012-01-01

    Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia. PMID:22511717

  13. Late Ordovician land plant spore 13C fractionation records atmospheric CO2 and climate change

    NASA Astrophysics Data System (ADS)

    Beerling, D. J.; Nelson, D. M.; Pearson, A.; Wellman, C.

    2008-12-01

    Molecular systematics and spore wall ultrastructure studies indicate that late Ordovician diad and triad fossil spores were likely produced by plants most closely related to liverworts. Here, we report the first δ13C estimates of Ordovician fossil land plant spores, which were obtained using a spooling wire micro-combustion device interfaced with an isotope-ratio mass spectrometer (Sessions et al., 2005, Analytical Chemistry, 77, 6519). The spores all originate from Saudi Arabia on the west of Gondwana and date to before (Cardadoc, ca. 460 Ma), during (443Ma) and after (Llandovery, ca. 440Ma) the Hirnantian glaciation. We use these numbers along with marine carbonate δ13C records to estimate atmospheric CO2 by implementing a theoretical model that captures the strong CO2-dependency of 13C fractionation in non-vascular land plants (Fletcher et al., 2008, Nature Geoscience, 1, 43). Although provisional at this stage, reconstructed CO2 changes are consistent with the Kump et al. (2008) (Paleo. Paleo. Paleo. 152, 173) 'weathering hypothesis' whereby pre-Hirnantian cooling is caused by relatively low CO2 (ca. 700ppm) related to enhanced weathering of young basaltic rocks during the early phase of the Taconic uplift, with background values subsequently rising to around double this value by the earliest Silurian. Further analyses will better constrain atmospheric CO2 change during the late Ordovician climatic perturbation and address controversial hypotheses concerning the causes and timing of the Earth system transition into an icehouse state.

  14. Ordovician-Carboniferous tectono-sedimentary evolution of the North Nuratau region, Uzbekistan (Westernmost Tien Shan)

    NASA Astrophysics Data System (ADS)

    McCann, T.; Nurtaev, B.; Kharin, V.; Valdivia-Manchego, M.

    2013-04-01

    The Tien Shan is a c. 2500 km long orogenic belt of which the Nuratau region of eastern Uzbekistan forms the western part. Petrographical and field analysis of the Ordovician-Carboniferous succession in the North Nuratau region provided the basis for a reconstruction of the depositional settings along part of the northern margin of the Alai continent and their evolution during the period of closure of the Turkestan Ocean, which separated the Alai and the Kazakh-Kyrgyz continents. Initial sedimentation (Ordovician) was broadly carbonate dominated, although by Mid-Late Ordovician times siliciclastic input predominated in some areas. These variations, between clastic- and carbonate-dominated regions may have been related to tectonic activity within the Alai continent. Carbonate sedimentation was reestablished in the ?Wenlock, with broad shelf systems forming along the continental margin. Volcanic activity in the Early Devonian records a period of tectonic instability, and this was followed by the reestablishment of the carbonate mosaic, albeit with a greater degree of instability (as indicated by stratigraphic gaps) than in the Silurian. This pattern extended up into the Carboniferous culminating in backarc-related magmatic activity. Final closure of the Turkestan Ocean involved significant folding and thrusting, as well as a major change from compressional to strike-slip movement.

  15. Climate change and the selective signature of the Late Ordovician mass extinction

    NASA Astrophysics Data System (ADS)

    Finnegan, Seth; Heim, Noel A.; Peters, Shanan E.; Fischer, Woodward W.

    2012-05-01

    Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia.

  16. Review of the Ordovician stratigraphy and fauna of the Anarak Region in Central Iran

    NASA Astrophysics Data System (ADS)

    Popov, Leonid E.; Hairapetian, Vachik; Evans, David H.; Pour, Mansoureh Ghobadi; Holmer, Lars E.; Baars, Christian

    2015-12-01

    The Ordovician sedimentary succession of the Pol-e Khavand area, situated on the northern margin of the Yazd block, has important differences from those in other parts of Central Iran. It has been established that the presumably terminal Cambrian to Lower Ordovician volcano-sedimentary Polekhavand Formation, exposed in the Pol-e Khavand area, has non-conformable contact with greenschists of the Doshakh Metamorphic Complex. The succeeding, mainly siliciclastic Chahgonbad Formation contains low to moderately diverse faunal assemblages, including brachiopods, cephalopods, trilobites and tentaculitids. The Darriwilian age of the lower part of the formation is well established by the co-occurrence of brachiopod genera Camerella, Phragmorthis, Tritoechia and Yangtzeella. The associated rich cephalopod fauna is different from the Darriwilian cephalopod associations of the Alborz terrane and may show some affinity with warm water faunas of North China and South Korea. It is likely that the Mid Ordovician fauna recovered from the lower part of the Chahgonbad Formation settled in the area sometime during a warming episode in the late Darriwilian. By contrast the low diversity mid Katian brachiopod association includes only three taxa, which occur together with the trilobite Vietnamia cf. teichmulleri and abundant, but poorly preserved tentaculitids questionably assigned to the genus Costatulites. This faunal association bears clear signatures linking it to the contemporaneous cold water faunas of the Arabian, Mediterranean and North African segments of Gondwana. Four brachiopod species recovered from the Chahgonbad Formation, including Hibernodonta lakhensis, Hindella prima, Lomatorthis? multilamellosa and Yangtzeella chupananica are new to science.

  17. Calibrating the Ordovician Radiation of marine life: implications for Phanerozoic diversity trends

    NASA Technical Reports Server (NTRS)

    Miller, A. I.; Foote, M.

    1996-01-01

    It has long been suspected that trends in global marine biodiversity calibrated for the Phanerozoic may be affected by sampling problems. However, this possibility has not been evaluated definitively, and raw diversity trends are generally accepted at face value in macroevolutionary investigations. Here, we analyze a global-scale sample of fossil occurrences that allows us to determine directly the effects of sample size on the calibration of what is generally thought to be among the most significant global biodiversity increases in the history of life: the Ordovician Radiation. Utilizing a composite database that includes trilobites, brachiopods, and three classes of molluscs, we conduct rarefaction analyses to demonstrate that the diversification trajectory for the Radiation was considerably different than suggested by raw diversity time-series. Our analyses suggest that a substantial portion of the increase recognized in raw diversity depictions for the last three Ordovician epochs (the Llandeilian, Caradocian, and Ashgillian) is a consequence of increased sample size of the preserved and catalogued fossil record. We also use biometric data for a global sample of Ordovician trilobites, along with methods of measuring morphological diversity that are not biased by sample size, to show that morphological diversification in this major clade had leveled off by the Llanvirnian. The discordance between raw diversity depictions and more robust taxonomic and morphological diversity metrics suggests that sampling effects may strongly influence our perception of biodiversity trends throughout the Phanerozoic.

  18. High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician.

    PubMed

    Porada, P; Lenton, T M; Pohl, A; Weber, B; Mander, L; Donnadieu, Y; Beer, C; Pöschl, U; Kleidon, A

    2016-01-01

    It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km(3) rock) yr(-1), defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today's global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate. PMID:27385026

  19. Marine Ostracod Provinciality in the Late Ordovician of Palaeocontinental Laurentia and Its Environmental and Geographical Expression

    PubMed Central

    Mohibullah, Mohibullah; Williams, Mark; Vandenbroucke, Thijs R. A.; Sabbe, Koen; Zalasiewicz, Jan A.

    2012-01-01

    Background We examine the environmental, climatic and geographical controls on tropical ostracod distribution in the marine Ordovician of North America. Methodology/Principal Findings Analysis of the inter-regional distribution patterns of Ordovician Laurentian ostracods, focussing particularly on the diverse Late Ordovician Sandbian (ca 461 to 456 Ma) faunas, demonstrates strong endemicity at the species-level. Local endemism is very pronounced, ranging from 25% (e.g. Foxe basin) to 75% (e.g. Michigan basin) in each basin, a pattern that is also reflected in other benthic faunas such as brachiopods. Multivariate (ordination) analyses of the ostracod faunas allow demarcation of a Midcontinent Province and a southern Marginal Province in Laurentia. While these are most clearly differentiated at the stratigraphical level of the bicornis graptolite biozone, analyses of the entire dataset suggest that these provinces remain distinct throughout the Sandbian interval. Differences in species composition between the provinces appear to have been controlled by changes in physical parameters (e.g. temperature and salinity) related to water depth and latitude and a possible regional geographic barrier, and these differences persist into the Katian and possibly the Hirnantian. Local environmental parameters, perhaps operating at the microhabitat scale, may have been significant in driving local speciation events from ancestor species in each region. Conclusions/Significance Our work establishes a refined methodology for assessing marine benthic arthropod micro-benthos provinciality for the Early Palaeozoic. PMID:22900000

  20. High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician

    PubMed Central

    Porada, P.; Lenton, T. M.; Pohl, A.; Weber, B.; Mander, L.; Donnadieu, Y.; Beer, C.; Pöschl, U.; Kleidon, A.

    2016-01-01

    It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km3 rock) yr−1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today's global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate. PMID:27385026

  1. POSSIBLE LATE MIDDLE ORDOVICIAN ORGANIC CARBON ISOTOPE EXCURSION: EVIDENCE FROM ORDOVICIAN OILS AND HYDROCARBON SOURCE ROCKS, MID-CONTINENT AND EAST-CENTRAL UNITED STATES.

    USGS Publications Warehouse

    Hatch, Joseph R.; Jacobson, Stephen R.; Witzke, Brian J.; Risatti, J. Bruno; Anders, Donald E.; Watney, W. Lynn; Newell, K. David; Vuletich, April K.

    1987-01-01

    Oils generated by Middle Ordovician rocks are found throughout the Mid-Continent and east-central regions of the United States. Gas chromatographic characteristics of these oils include a relatively high abundance of n-alkanes with carbon numbers less than 20, a strong predominance of odd-numbered n-alkanes between C//1//0 and C//2//0, and relatively small amounts of branched and cyclic alkanes. The wide ranges in delta **1**3C for oils and rock extracts reflect a major, positive excursion(s) in organic matter delta **1**3C in late Middle Ordovician rocks. This excursion has at least regional significance in that it can be documented in sections 480 mi apart in south-central Kansas and eastern Iowa. The distance may be as much as 930 mi. The parallel shifts in organic and carbonate delta **1**3C in core samples from 1 E. M. Greene well, Washington County, Iowa, imply changes in the isotope composition of the ocean-atmosphere carbon reservoir. These and other aspects of the subject are discussed.

  2. Deciphering evolutionary strata on plant sex chromosomes and fungal mating-type chromosomes through compositional segmentation.

    PubMed

    Pandey, Ravi S; Azad, Rajeev K

    2016-03-01

    Sex chromosomes have evolved from a pair of homologous autosomes which differentiated into sex determination systems, such as XY or ZW system, as a consequence of successive recombination suppression between the gametologous chromosomes. Identifying the regions of recombination suppression, namely, the "evolutionary strata", is central to understanding the history and dynamics of sex chromosome evolution. Evolution of sex chromosomes as a consequence of serial recombination suppressions is well-studied for mammals and birds, but not for plants, although 48 dioecious plants have already been reported. Only two plants Silene latifolia and papaya have been studied until now for the presence of evolutionary strata on their X chromosomes, made possible by the sequencing of sex-linked genes on both the X and Y chromosomes, which is a requirement of all current methods that determine stratum structure based on the comparison of gametologous sex chromosomes. To circumvent this limitation and detect strata even if only the sequence of sex chromosome in the homogametic sex (i.e. X or Z chromosome) is available, we have developed an integrated segmentation and clustering method. In application to gene sequences on the papaya X chromosome and protein-coding sequences on the S. latifolia X chromosome, our method could decipher all known evolutionary strata, as reported by previous studies. Our method, after validating on known strata on the papaya and S. latifolia X chromosome, was applied to the chromosome 19 of Populus trichocarpa, an incipient sex chromosome, deciphering two, yet unknown, evolutionary strata. In addition, we applied this approach to the recently sequenced sex chromosome V of the brown alga Ectocarpus sp. that has a haploid sex determination system (UV system) recovering the sex determining and pseudoautosomal regions, and then to the mating-type chromosomes of an anther-smut fungus Microbotryum lychnidis-dioicae predicting five strata in the non

  3. The ages and tectonic setting of the Faja Eruptiva de la Puna Oriental, Ordovician, NW Argentina

    NASA Astrophysics Data System (ADS)

    Bahlburg, Heinrich; Berndt, Jasper; Gerdes, Axel

    2016-07-01

    The Ordovician Faja Eruptiva de la Puna Oriental is a magmatic, predominantly intrusive belt in the Puna of northwestern Argentina with a N-S extension of ca. 400 km. Scarce isotope geochemical ages and biostratigraphic data on some of the folded Faja Eruptiva country rocks assign the magmatism either to the Lower and lower Middle Ordovician, or to the latest Ordovician. Interpretations of origin and tectonic framework of the Faja Eruptiva are controversial and vary between arc, back-arc and collisional-orogenic settings. We present high-resolution La-ICP-MS U-Pb age and Hf isotope data on zircons from 10 plutonic samples covering the magmatic belt along a length of 200 km in the northern Argentinian Puna. The xenocrystic and magmatic zircon age data have a wide spread between 2700 Ma and 440 Ma. Concordia and weighted mean age data document protracted magmatism in two phases between 480 and 460 Ma, and between 453 and 444 Ma, and constrain the time of the last intrusions at 444 ± 3 Ma and at 445 ± 2 Ma thus defining this last and main phase of intrusion at 444 Ma. εHf(t) values define a main vertical trend centered at 500 Ma with εHf(t) values between + 3 and - 16 indicating significant mixing of juvenile early Paleozoic melts with Paleoproterozoic crustal components. A second trend is formed by zircons with ages between 1.1 Ga and c. 500 Ma and predominantly positive εHf values between + 8 and - 3 and originates in juvenile mantle compositions between 1.6 and 1.1 Ga. The spread of the zircon and Hf data document that the Faja Eruptiva intrusives have experienced large-scale contamination by the hosting crustal basement. It follows that the basement of the Puna is formed either by the upper Proterozoic-lower Cambrian Puncoviscana Formation as an erosional product of the Proterozoic orogenic belts of SW Amazonia or that the Puna including its Puncoviscana basement is underlain by a crust shaped by these orogenies. The main intrusive event at 444 Ma has been

  4. The Late Ordovician Extinction: How it became the best understood of the five major extinctions.

    NASA Astrophysics Data System (ADS)

    Sheehan, P.

    2003-04-01

    The end Ordovician extinction has become arguably the best-understood major extinction event in Earth History. A plethora of workers have established the pattern of faunal change and causes of the extinction with remarkably little disagreement. The first indication of increased extinction at the end of the Ordovician was a graph of global diversity patterns by Norman Newell in 1967, although he did not recognize it as a major event. The presence of a major extinction event became clear as William Berry and Art Boucot assembled data for Silurian correlation charts in the late 1960s. The first reports of North African glaciation in the late 1960s provided a cause for the extinction and study of the event snowballed. It was no accident that recognition of the extinction began in North America, because it was there that the extinction completely overturned faunas in the epicontinental seas. Glacio-eustatic regression of shallow seaway coincided with the disappearance of endemic Laurentian faunas and replacement by a highly cosmopolitan fauna in the Silurian. Once the event was established in North America, paleontologists soon found evidence of the event around the globe. The well-documented Hirnantia Fauna was found to correspond to the glacial interval, and Pat Brenchley soon recognized that there were two pulses of extinction, at the beginning and end of the glaciation. At the same time that the faunal changes were being documented geologic studies of the glaciation provided information on the environmental changes associated with the extinction. The timing of the glacial maximum was established in Africa and by the presence of dropstones in high latitude marine rocks. The 1990s saw geochemical techniques employed that allowed examination of atmospheric CO2 and temperature changes. In many places carbonate deposition declined. Glacio-eustatic regression was obvious in many areas, and a sea-level decline in the range of 50-100 m was established. Shallow

  5. Selenium Concentrations in Middle Pennsylvanian Coal-Bearing Strata in the Central Appalachian Basin

    USGS Publications Warehouse

    Neuzil, Sandra G.; Dulong, Frank T.; Cecil, C. Blaine; Fedorko, Nick; Renton, John J.; Bhumbla, D.K.

    2007-01-01

    Introduction This report provides the results of a reconnaissance-level investigation of selenium (Se) concentrations in Middle Pennsylvanian coal-bearing strata in the central Appalachian basin. Bryant and others (2002) reported enrichments of Se concentrations in streams draining areas disturbed by surface mining relative to Se concentrations in streams that drain undisturbed areas; the study was conducted without the benefit of data on Se concentrations in coal-bearing strata prior to anthropogenic disturbance. Thus, the present study was conducted to provide data on Se concentrations in coal-bearing strata prior to land disturbance. The principal objectives of this work are: 1) determine the stratigraphic and regional distribution of Se concentrations in coal-bearing strata, 2) provide reconnaissance-level information on relations, if any, between Se concentrations and lithology (rock-type), and 3) develop a cursory evaluation of the leachability of Se from disturbed strata. The results reported herein are derived from analyses of samples obtained from three widely-spaced cores that were collected from undisturbed rock within a region that has been subjected to extensive land disturbance principally by either coal mining or, to a lesser extent, highway construction. The focus was on low-organic-content lithologies, not coal, within the coal-bearing interval, as these lithologies most commonly make up the fill materials after coal mining or in road construction.

  6. Analysis of Cretaceous (Aptian) strata in central Tunisia, using 2D seismic data and well logs

    NASA Astrophysics Data System (ADS)

    Zouaghi, Taher; Ferhi, Issam; Bédir, Mourad; Youssef, Mohamed Ben; Gasmi, Mohamed; Inoubli, Mohamed Hédi

    2011-08-01

    This paper presents a structural and depositional model of lower Cretaceous (Aptian) strata in central Tunisia, using detailed facies relations in outcrops, seismic reflection data, and wells. The study interval (called the "Aptian supersequence") is subdivided into four seismic sequences containing third-order sequences. Sequence architecture was strongly affected by syndepositional tectonic movements, which controlled sequence position and distribution. Specifically, the seismic sections show irregular distribution of different zones of subsidence and uplift. The observed structures identified through the detailed mapping suggest that lower Cretaceous rifting created depressions and grabens that filled with strata characterized by divergent reflectors striking against dipping growth faults. The Aptian-Albian unconformity ("crisis") marked a change of the extensional stress field from NNW-SSE to NE-SW induced rotation of blocks and an evolution of sedimentary basin filling related to the regional tectonic deformation. Local salt tectonic movement accentuated the formation of asymmetric depocenters. The salt ascended at the junction of master faults, resulting in cross-cutting of the strata and local reworking of Triassic evaporites in Aptian strata. Basinward to landward variations of the thickness and facies associated with strata pinch-outs and unconformities are related to the main synsedimentary tectonic events that were synchronous with salt tectonic movements. Triassic salt domes and salt intrusions along faults accentuated the border elevations between basin depocenters and uplifts. These sedimentary phenomena in central Tunisia are interpreted as causally related aspects of a local and global tectonic event during the Aptian.

  7. Modeling of multi-strata forest fire severity using Landsat TM Data

    NASA Astrophysics Data System (ADS)

    Meng, Qingmin; Meentemeyer, Ross K.

    2011-02-01

    Most of fire severity studies use field measures of composite burn index (CBI) to represent forest fire severity and fit the relationships between CBI and Landsat imagery derived differenced normalized burn ratio (dNBR) to predict and map fire severity at unsampled locations. However, less attention has been paid on the multi-strata forest fire severity, which represents fire activities and ecological responses at different forest layers. In this study, using field measured fire severity across five forest strata of dominant tree, intermediate-sized tree, shrub, herb, substrate layers, and the aggregated measure of CBI as response variables, we fit statistical models with predictors of Landsat TM bands, Landsat derived NBR or dNBR, image differencing, and image ratioing data. We model multi-strata forest fire in the historical recorded largest wildfire in California, the Big Sur Basin Complex fire. We explore the potential contributions of the post-fire Landsat bands, image differencing, image ratioing to fire severity modeling and compare with the widely used NBR and dNBR. Models using combinations of post-fire Landsat bands perform much better than NBR, dNBR, image differencing, and image ratioing. We predict and map multi-strata forest fire severity across the whole Big Sur fire areas, and find that the overall measure CBI is not optimal to represent multi-strata forest fire severity.

  8. Study of the strata formation during the explosion of a wire in vacuum

    NASA Astrophysics Data System (ADS)

    Rousskikh, A. G.; Oreshkin, V. I.; Chaikovsky, S. A.; Labetskaya, N. A.; Shishlov, A. V.; Beilis, I. I.; Baksht, R. B.

    2008-10-01

    The formation of strata during fast electrical explosions of aluminum wires at current densities of (1-1.4)×108 A/cm2 has been studied experimentally. To observe the strata, the soft x radiation generated at the hot point of an x-pinch was used. It has been revealed that strata are formed before the voltage collapse, that is, at the stage of heating of the wire metal. Two wire explosion modes were realized: with and without cutoff of the current carried by the exploding wire. Analysis of the experimental results shows that the stratification is most probably due to the thermal instability that develops as a consequence of the increase in metal resistivity with temperature.

  9. Capture-recapture studies for multiple strata including non-markovian transitions

    USGS Publications Warehouse

    Brownie, C.; Hines, J.E.; Nichols, J.D.; Pollock, K.H.; Hestbeck, J.B.

    1993-01-01

    We consider capture-recapture studies where release and recapture data are available from each of a number of strata on every capture occasion. Strata may, for example, be geographic locations or physiological states. Movement of animals among strata occurs with unknown probabilities, and estimation of these unknown transition probabilities is the objective. We describe a computer routine for carrying out the analysis under a model that assumes Markovian transitions and under reduced parameter versions of this model. We also introduce models that relax the Markovian assumption and allow 'memory' to operate (i.e., allow dependence of the transition probabilities on the previous state). For these models, we sugg st an analysis based on a conditional likelihood approach. Methods are illustrated with data from a large study on Canada geese (Branta canadensis) banded in three geographic regions. The assumption of Markovian transitions is rejected convincingly for these data, emphasizing the importance of the more general models that allow memory.

  10. Study of the strata formation during the explosion of a wire in vacuum

    SciTech Connect

    Rousskikh, A. G.; Oreshkin, V. I.; Chaikovsky, S. A.; Labetskaya, N. A.; Shishlov, A. V.; Beilis, I. I.; Baksht, R. B.

    2008-10-15

    The formation of strata during fast electrical explosions of aluminum wires at current densities of (1-1.4)x10{sup 8} A/cm{sup 2} has been studied experimentally. To observe the strata, the soft x radiation generated at the hot point of an x-pinch was used. It has been revealed that strata are formed before the voltage collapse, that is, at the stage of heating of the wire metal. Two wire explosion modes were realized: with and without cutoff of the current carried by the exploding wire. Analysis of the experimental results shows that the stratification is most probably due to the thermal instability that develops as a consequence of the increase in metal resistivity with temperature.

  11. Greenhouse‑icehouse transition in the Late Ordovician marks a step change in extinction regime in the marine plankton

    NASA Astrophysics Data System (ADS)

    Crampton, James S.; Cooper, Roger A.; Sadler, Peter M.; Foote, Michael

    2016-02-01

    Two distinct regimes of extinction dynamic are present in the major marine zooplankton group, the graptolites, during the Ordovician and Silurian periods (486-418 Ma). In conditions of "background" extinction, which dominated in the Ordovician, taxonomic evolutionary rates were relatively low and the probability of extinction was highest among newly evolved species ("background extinction mode"). A sharp change in extinction regime in the Late Ordovician marked the onset of repeated severe spikes in the extinction rate curve; evolutionary turnover increased greatly in the Silurian, and the extinction mode changed to include extinction that was independent of species age ("high-extinction mode"). This change coincides with a change in global climate, from greenhouse to icehouse conditions. During the most extreme episode of extinction, the Late Ordovician Mass Extinction, old species were selectively removed ("mass extinction mode"). Our analysis indicates that selective regimes in the Paleozoic ocean plankton switched rapidly (generally in <0.5 My) from one mode to another in response to environmental change, even when restoration of the full ecosystem was much slower (several million years). The patterns observed are not a simple consequence of geographic range effects or of taxonomic changes from Ordovician to Silurian. Our results suggest that the dominant primary controls on extinction throughout the lifespan of this clade were abiotic (environmental), probably mediated by the microphytoplankton.

  12. New paleomagnetic results from Ordovician sedimentary rocks from NW Anatolia: Tectonic implications for the paleolatitudinal position of the Istanbul Terrane

    NASA Astrophysics Data System (ADS)

    Oksum, Erdinc; Hisarlı, Z. Mümtaz; Çinku, Mualla Cengiz; Ustaömer, Timur; Orbay, Naci

    2015-11-01

    The Istanbul terrane, classically known as the "Paleozoic of Istanbul", is geologically one of the important continental components of NW Turkey. The terrane comprises an Early Ordovician to Early Carboniferous transgressive sedimentary sequence and appears as an exotic unit with respect to its present surroundings. The paleogeographical position of the Ordovician rocks is unknown. We have therefore conducted a paleomagnetic study from a total of 56 sites in red fluvial clastics of the Kurtkoy formation and shallow marine quartzites of the Aydos formation to determine the paleolatitude of the Istanbul terrane during the Ordovician. The Lower Ordovician group mean direction calculated from 17 reliable sites provides a mean inclination of I = 19.4°, (α95 = 2.3°, k = 146.0) accepting only inclination data. A paleolatitude of 16.4° is obtained after considering an inclination correction factor of f = 0.6 due to the E/I results. The Early Ordovician paleolatitude of the Istanbul terrane shows a lower paleolatitudinal position closer to the equatorial zone than previously inferred.

  13. South East Asia as a part of an Ordovician Gondwanaland—a palaeobiogeographic test of a tectonic hypothesis

    NASA Astrophysics Data System (ADS)

    Burrett, Clive; Stait, Bryan

    1985-10-01

    The hypothesis that Thailand and Malaysia (the Sibumasu block) were adjacent to Australia in the Early Palaeozoic has been tested by an examination of the Ordovician sequences and faunas of Sibumasu and Australia. The relatively stenogeographic nautiloids of the two areas are remarkably similar and have a Simpson Index of 0.92 at the generic level. Two new genera of discosorids are restricted to the two blocks and Georgina and Mesaktoceras are found elsewhere only in Tibet. Very close affinities are also evident between the gastropod, polyplacophoran and rostroconch molluscs. The Ordovician brachiopod faunas are also very close including the genus Spanodonta. Other very close similarities are found between the Upper Cambrian trilobite faunas and the Ordovician conodonts and stromatoporoids. No Ordovician faunas younger than Upper Whiterockian were found during this study in either northern Australia or Sibumasu and a stratigraphic gap probably exists from the Upper Whiterockian to the Upper Ordovician over most of the two blocks. These remarkably close faunal similarities are good evidence in favour of the hypothesis that Sibumasu was adjacent to Australia during the Early Palaeozoic. Similarly close faunal relationships between North China, South East Asia, Tibet and Australia may also suggest close proximity of those blocks during the Early Palaeozoic.

  14. Greenhouse-icehouse transition in the Late Ordovician marks a step change in extinction regime in the marine plankton.

    PubMed

    Crampton, James S; Cooper, Roger A; Sadler, Peter M; Foote, Michael

    2016-02-01

    Two distinct regimes of extinction dynamic are present in the major marine zooplankton group, the graptolites, during the Ordovician and Silurian periods (486-418 Ma). In conditions of "background" extinction, which dominated in the Ordovician, taxonomic evolutionary rates were relatively low and the probability of extinction was highest among newly evolved species ("background extinction mode"). A sharp change in extinction regime in the Late Ordovician marked the onset of repeated severe spikes in the extinction rate curve; evolutionary turnover increased greatly in the Silurian, and the extinction mode changed to include extinction that was independent of species age ("high-extinction mode"). This change coincides with a change in global climate, from greenhouse to icehouse conditions. During the most extreme episode of extinction, the Late Ordovician Mass Extinction, old species were selectively removed ("mass extinction mode"). Our analysis indicates that selective regimes in the Paleozoic ocean plankton switched rapidly (generally in <0.5 My) from one mode to another in response to environmental change, even when restoration of the full ecosystem was much slower (several million years). The patterns observed are not a simple consequence of geographic range effects or of taxonomic changes from Ordovician to Silurian. Our results suggest that the dominant primary controls on extinction throughout the lifespan of this clade were abiotic (environmental), probably mediated by the microphytoplankton. PMID:26811471

  15. Greenhouse−icehouse transition in the Late Ordovician marks a step change in extinction regime in the marine plankton

    PubMed Central

    Crampton, James S.; Cooper, Roger A.; Sadler, Peter M.; Foote, Michael

    2016-01-01

    Two distinct regimes of extinction dynamic are present in the major marine zooplankton group, the graptolites, during the Ordovician and Silurian periods (486−418 Ma). In conditions of “background” extinction, which dominated in the Ordovician, taxonomic evolutionary rates were relatively low and the probability of extinction was highest among newly evolved species (“background extinction mode”). A sharp change in extinction regime in the Late Ordovician marked the onset of repeated severe spikes in the extinction rate curve; evolutionary turnover increased greatly in the Silurian, and the extinction mode changed to include extinction that was independent of species age (“high-extinction mode”). This change coincides with a change in global climate, from greenhouse to icehouse conditions. During the most extreme episode of extinction, the Late Ordovician Mass Extinction, old species were selectively removed (“mass extinction mode”). Our analysis indicates that selective regimes in the Paleozoic ocean plankton switched rapidly (generally in <0.5 My) from one mode to another in response to environmental change, even when restoration of the full ecosystem was much slower (several million years). The patterns observed are not a simple consequence of geographic range effects or of taxonomic changes from Ordovician to Silurian. Our results suggest that the dominant primary controls on extinction throughout the lifespan of this clade were abiotic (environmental), probably mediated by the microphytoplankton. PMID:26811471

  16. Arenig volcanic and sedimentary strata, central New Brunswick and eastern Maine

    USGS Publications Warehouse

    Poole, W.H.; Neuman, R.B.

    2002-01-01

    Arenig strata in the Napadogan area of the Miramichi Highlands of west-central New Brunswick are similar to those of the Lunksoos anti-clinorial area of eastern Maine. Strata from both areas were deposited in a volcanic back-arc setting upon Cambrian-Tremadoc, deep-water, turbiditic quartzose strata on the northwest-facing Gander margin of Gondwana. Tremadoc southeastward obduction of the Penobscot Arc, formed in the lapetus Ocean to the northwest of the margin, was followed by local uplift, rift faulting, erosion, and finally by local deposition of late Arenig gravel within the early stages of a subsiding back-arc basin that was related to a younger, northwest-facing, early Arenig-Llanvirn Popelogan Arc lying to the northwest. These strata became overlain by late Arenig marine felsic tuff, sandy and silty tuff and mudstone, coarse textured and many hundreds of metres thick in the Lunksoos area but much finer and only a few metres thick farther from the volcanic centres, in the Napadogan area. During Llanvirn, the strata became covered with deep-water, commonly manganiferous, ferruginous shale-chert in a basin shielded from currents carrying coarse detritus. Arenig strata of the Napadogan area probably developed to the southeast of the main rift-volcanism zone that perhaps extended between the Lunksoos and northeastern Miramichi Highlands during the Arenig. Brachiopods of the Celtic paleogeographic assemblage colonized newly formed shelves flanking islands along the zone. Shell beds developed upon fresh layers of ash in a nutrient-rich environment between episodes of volcanism. These Celtic brachiopods developed in cool waters of high southern latitudes off Gondwana, different from those on the Laurentian margin in warm waters of low southern latitudes.

  17. From northern Gondwana passive margin to arc dismantling: a geochemical discrimination of Ordovician volcanisms (Sardinia, Italy)

    NASA Astrophysics Data System (ADS)

    Gaggero, L.; Oggiano, G.; Buzzi, L.; Funedda, A.

    2009-04-01

    In Sardinia, one of the southernmost remain of the European Variscan belt, a crustal section through northern Gondwanan paleodomains is largely preserved. It bears significant evidence of igneous activity, recently detailed in field relationships and radiometric dating (Oggiano et al., submitted). A Cambro - Ordovician (491.7 ± 3.5 Ma ÷ 479.9 ± 2.1 Ma, LA-ICP-MS U-Pb zircon age) bimodal volcanic suite occurs with continuity in external and inner Variscan nappes of Sardinia below the so-called Sardic unconformity. The igneous suite represents an intraplate volcanic activity developed through subsequent episodes: i) an intermediate explosive and effusive volcanism, i.e. pyroclastic fall deposits and lava flows, embedded into epicontinental clastic sediments, culminating in silicic ignimbrite eruptions, and ii) mafic effusives. Geochemical data document a transitional, within-plate signature, e.g. the average Th/Ta (4.5) and La/Nb (2.7) overlap the upper continental crust values. The volcanites are characterized by slight fractionation of LREEs, nearly flat HREE abundance. The negative Eu anomaly increases towards evolved compositions. Some prominent HREE depletion (GdCN/YbCN = 13.8), and the high Nb/Y suggest a garnet-bearing source. The high 87Sr radiogenic content (87Sr/86Sr 490 Ma = 0.71169) and the epsilon Nd 490 Ma value of -6.54 for one dacite sample, imply a time integrated LREE-enriched source with a high Rb/Sr, such as a metasedimentary source. The stratigraphy of the succession and the geochemical composition of igneous members suggest a volcanic passive margin along the northern Gondwana at the early Ordovician. The bimodal Mid-Ordovician arc volcanism (465.4 ± 1.4 Ma, U-Pb zircon age; Oggiano et al., submitted) is developed in the external nappes (e.g. in Sarrabus and Sarcidano) and in the foreland occurs as clasts at the base of the Hirnantian succession (Leone et al. 1991). The Mid Ordovician sub-alkalic volcanic suite has reliable stratigraphic and

  18. 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.

  19. Hydrocarbon potential of Cambrian-Ordovician Knox Group in south-central Kentucky

    SciTech Connect

    Gooding, P.J.

    1987-09-01

    In the eastern US, the carbonate rocks of the Cambrian-Ordovician Knox Group were deposited on a broad, gently sloping continental shelf in shallow hypersaline waters. A major unconformity occurs at the top of the Knox Group. This regional unconformity developed when the Sauk Sea retreated at the close of the Early Ordovician. In south-central Kentucky, the paleotopographic surface is characterized by extensive paleokarst developed on the upper Knox surface. The study area is located on the crest of the Cincinnati arch, a major structural feature that separates the Appalachian basin to the east from the Illinois basin on the west. Oil and gas are being produced from Cambrian-Ordovician rocks throughout the US, and south-central Kentucky is no exception. In south-central Kentucky, the Knox is of considerable economic importance. Hydrocarbon entrapment occurs at or near the unconformity at the top of the Knox. Approximately 3500 oil and gas wells and mineral exploration holes have penetrated the upper Knox Group in south-central Kentucky. Over 32 million bbl of oil have been recovered from 11 relatively shallow stratigraphic zones in 120 oil pools. These stratigraphic zones are generally encountered at depths of less than 2000 ft. A substantial amount of oil has been recovered from pools that produce exclusively from the Knox. Brecciated and fractured zones at the top of the Knox have also served as the host rock for sulfide mineralization, and these deposits may contain significant amounts of lead, zinc, and barium resources for future exploitation.

  20. Sedimentation and tectonic implications of Cambrian-Ordovician clastics, Renville county, North Dakota

    SciTech Connect

    Mescher, P.K.; Pol, J.C.

    1985-02-01

    Cambrian-Ordovician clastics of the Deadwood Formation were studied in detail from Newporte field in Renville County, North Dakota. This small Cambrian-Ordovician oil pool was extensively cored, often to the Precambrian basement, allowing close examination of clastic deposition influenced by local basement tectonics. In Renville County, the basal unit consists of a well-rounded, fine to medium-grained glauconitic quartz sandstone. Paleohighs appear to have had a pronounced effect on Deadwood sedimentation. Sands, from quiet water settings, show poor to moderate sorting, are commonly finely laminated, and/or show traces of minor small-scale cross-bedding. In places, bedding planes are highly disrupted, suggesting intervals of intense bioturbation (Skolithos). Sands associated with paleohighs are clean, well sorted, and commonly friable. Their association with basement structure is suggestive of beach-barrier-bar sequences related to irregularly upthrown basement blocks. In one example, this clean basal sand is associated with an upthrown basement block and is sharply truncated by the pre-Winnipeg (early Ordovician) unconformity. The first unit above the basal sandstone in structurally lower wells is an anomalous conglomerate unit. Large angular basement clasts up to cobble size were viewed in core. This unit grades upward into a fine sand sequence and distally grades into a marine sand. It terminates abruptly in upthrown wells and indicates rapid fault movement and offset during middle Deadwood deposition, with development of localized fanglomerate sequences associated with fault scarps. Immediately capping this sequence is a dark-gray marine shale that thins depositionally toward paleohighs.

  1. Paleoenvironment and the oxygen isotope geochemistry of ironstone of the Upper Ordovician Neda Formation, Wisconsin, USA

    SciTech Connect

    Yapp, C.J. )

    1993-05-01

    Geological evidence suggests that the goethite-dominated, oolitic ironstone of the Upper Ordovician Neda Formation in the north central United States was subaerially weathered in the Late Ordovician. The oxygen isotope ratios of the goethites in the [open quotes]hard[close quotes] and [open quotes]soft[close quotes] ores of this deposit are rather uniform with a [delta][sup 18]O value of about [minus]1.0[per thousand]. This [delta][sup 18]O value indicates the presence of meteoric water at the time of goethite formation and supports the idea that the goethites in hard and soft ores were formed in the same chemical weathering environment 440 million years ago. The [delta][sup 18]O value of accessory phosphate in some soft ore goethite-rich ooids was measured and combined with the goethite [delta][sup 18]O value to calculate a temperature of formation of about 23[degrees]C. The corresponding [delta][sup 18]O value of the ancient water was calculated to have been [minus]7.3[per thousand]. The relatively [open quotes]cool[close quotes] temperature calculated for the low-altitude, tropical site occupied by the Neda ironstone in the Late Ordovician is consistent with published evidence from fossil marine invertebrates for global cooling at that time. The [delta][sup 18]O value of [minus]7.3[per thousand] for the ancient tropical precipitation could indicate intense rainfall of a seasonal (perhaps monsoonal) character. 27 refs., 7 figs., 3 tabs.

  2. 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.

  3. Cambrian-Ordovician craton margin section, southern Great Basin: A sequence stratigraphic perspective

    SciTech Connect

    Cooper, J.D. ); Edwards, J.C. )

    1991-02-01

    The Upper Cambrian through Upper Ordovician cratonal to miogeoclinal transition section in southern Nevada and eastern California accumulated on a gentle homoclinal ramp and includes a variety of peritidal and subtidal carbonate facies. This section consists of a westward-thickening wedge assigned to the Nopah and Mountain Springs formations and can be related to one type 1 and least four type 2 sequences. The basal part of the section is the Dunderberg Shale Member of the Nopah Formation, which is composed of meter-scale cyclical shale-carbonate bundles. Carbonate interbeds signify a variety of peritidal to deep subtidal paleoenvironments that comprise shelf margin and transgressive systems tracts. The progradation of a thrombolitic bank complex in the overlying upper Nopah may reflect emergence on the craton, evidenced by the Sauk II-Sauk III cratonic disconformity. The overlying A' member of the Mountain Springs Formation rests in sharp and, in places, slightly discordant contact with the top of the Nopah. This contact is interpreted as a marine flooding surface and type 2 sequence boundary. Member A consists of Lower Ordovician transgressive and highstand systems tracts comprised of oolitic shoal and back-shoal to intertidal carbonates. The type 1 unconformity that separates member A from overlying B' member is the top of the first-order Sauk Sequence. The B' member is a thin stratal interval of late Middle to Late Ordovician age and consists of dark, burrow-mottled skeletal wackestone and mudstone that is part of a transgressive systems tract. It is bounded above by another type 1 unconformity and therefore represents the first-order Tippecanoe sequence of Sloss.

  4. Shelf to basin transition in Middle Ordovician carbonates in Alabama Appalachians

    SciTech Connect

    Benson, D.J.

    1986-05-01

    In the Alabama valley and ridge, Middle Ordovician carbonates are exposed in two northeast-southwest-trending outcrop belts separated by the Helena fault. Northwest to southeast transits across these outcrop belts illustrate a well-defined shallow to deep water transition. West of the Helena fault, the Middle Ordovician is represented by a transgressive-regressive sequence of peritidal and shallow subtidal carbonates of the Chickamauga Limestone, deposited in tidal-flat, low-energy open-shelf, and high-energy shoal environments. Tidal-flat deposits consist of peloidal and intraclastic wackestones and packstones containing abundant exposure indicators. These grade into light-colored, skeletal wackestones and packstones containing a diverse faunal assemblage rich in algae, indicating deposition in a shallow, low-energy, open-shelf setting. High energy shoal deposition is represented by a 20-80 ft thick sequence of cross-bedded skeletal grainstone. Included within the grainstone are pods of bryozoan-sponge-algal bafflestone and bindstone that represent small mud-rich bioherms. East of the Helena fault, the Middle Ordovician series consists of deeper water carbonates of the Lenoir and Little Oak Limestones and graptolitic shales of the Athens Formation. The Lenoir and Little Oak are composed of dark-colored, even-bedded, skeletal wackestones which, with the exception of scattered Nuia, lack algae, indicating deposition in the deeper part of the photic zone. These wackestones grade southeastward into very finely laminated, argillaceous mudstones and calcareous shales of the Athens Formation. The Athens is dark colored, organic-rich, lacking in bottom-dwelling fauna, and contains common synsedimentary slump structures suggesting deposition in an anoxic, lower slop environment.

  5. The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade

    PubMed Central

    Coates, Michael I.; Karatajūtė-Talimaa, Valentina; Shelton, Richard M.; Cooper, Paul R.

    2016-01-01

    The Mongolepidida is an Order of putative early chondrichthyan fish, originally erected to unite taxa from the Lower Silurian of Mongolia. The present study reassesses mongolepid systematics through the examination of the developmental, histological and morphological characteristics of scale-based specimens from the Upper Ordovician Harding Sandstone (Colorado, USA) and the Upper Llandovery–Lower Wenlock Yimugantawu (Tarim Basin, China), Xiushan (Guizhou Province, China) and Chargat (north-western Mongolia) Formations. The inclusion of the Mongolepidida within the Class Chondrichthyes is supported on the basis of a suite of scale attributes (areal odontode deposition, linear odontocomplex structure and lack of enamel, cancellous bone and hard-tissue resorption) shared with traditionally recognized chondrichthyans (euchondrichthyans, e.g., ctenacanthiforms). The mongolepid dermal skeleton exhibits a rare type of atubular dentine (lamellin) that is regarded as one of the diagnostic features of the Order within crown gnathostomes. The previously erected Mongolepididae and Shiqianolepidae families are revised, differentiated by scale-base histology and expanded to include the genera Rongolepisand Xinjiangichthys, respectively. A newly described mongolepid species (Solinalepis levis gen. et sp. nov.) from the Ordovician of North America is treated as family incertae sedis, as it possesses a type of basal bone tissue (acellular and vascular) that has yet to be documented in other mongolepids. This study extends the stratigraphic and palaeogeographic range of Mongolepidida and adds further evidence for an early diversification of the Chondrichthyes in the Ordovician Period, 50 million years prior to the first recorded appearance of euchondrichthyan teeth in the Lower Devonian. PMID:27350896

  6. The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade.

    PubMed

    Andreev, Plamen; Coates, Michael I; Karatajūtė-Talimaa, Valentina; Shelton, Richard M; Cooper, Paul R; Wang, Nian-Zhong; Sansom, Ivan J

    2016-01-01

    The Mongolepidida is an Order of putative early chondrichthyan fish, originally erected to unite taxa from the Lower Silurian of Mongolia. The present study reassesses mongolepid systematics through the examination of the developmental, histological and morphological characteristics of scale-based specimens from the Upper Ordovician Harding Sandstone (Colorado, USA) and the Upper Llandovery-Lower Wenlock Yimugantawu (Tarim Basin, China), Xiushan (Guizhou Province, China) and Chargat (north-western Mongolia) Formations. The inclusion of the Mongolepidida within the Class Chondrichthyes is supported on the basis of a suite of scale attributes (areal odontode deposition, linear odontocomplex structure and lack of enamel, cancellous bone and hard-tissue resorption) shared with traditionally recognized chondrichthyans (euchondrichthyans, e.g., ctenacanthiforms). The mongolepid dermal skeleton exhibits a rare type of atubular dentine (lamellin) that is regarded as one of the diagnostic features of the Order within crown gnathostomes. The previously erected Mongolepididae and Shiqianolepidae families are revised, differentiated by scale-base histology and expanded to include the genera Rongolepisand Xinjiangichthys, respectively. A newly described mongolepid species (Solinalepis levis gen. et sp. nov.) from the Ordovician of North America is treated as family incertae sedis, as it possesses a type of basal bone tissue (acellular and vascular) that has yet to be documented in other mongolepids. This study extends the stratigraphic and palaeogeographic range of Mongolepidida and adds further evidence for an early diversification of the Chondrichthyes in the Ordovician Period, 50 million years prior to the first recorded appearance of euchondrichthyan teeth in the Lower Devonian. PMID:27350896

  7. Tectonic Setting of Explosive Volcanic Eruptions in the UPPER Ordovician of the Siberian Platform

    NASA Astrophysics Data System (ADS)

    Huff, W. D.; Dronov, A.; Sell, B. K.; Kanygin, A. V.

    2014-12-01

    In recent years 8 K-bentonite beds have been discovered in the Upper Ordovician of the Tungus basin on the Siberian Platform. All the beds were identified in the outcrops of the Baksian, Dolborian and Burian regional stages, which correspond roughly to the Upper Sandbian, Katian and probably lowermost Hirnantian Global Stages. The 4 lowermost beds from the Baksian and Dolborian Regional Stages were studied in detail. They are represented by thin beds (1-2 cm) of soapy light gray or yellowish plastic clays and usually easily identifiable in the outcrops. The beds were traced in the outcrops over a distance of more than 60 km along the Podkamennaya Tunguska River valley. All K-bentonite beds have been found within the Upper Ordovician cool-water carbonate succession. The four lowermost K-bentonite beds, which were sampled, have been studied by powder X-ray diffraction and scanning electron microscopy together with energy dispersive X-ray analysis. The low percent of smectite in mixed-layer phases reflects a high degree of burial metamorphism since the time of their origin. The K-bentonites provide evidence of intensive explosive volcanism on or near the western margin of the Siberian craton in Late Ordovician time. The K-bentonite beds from the Baksian and Dolborian regional stages (Katian) of the southwestern part of the Tungus basin in Siberia are thus derived from the alteration of volcanic ash falls. All four beds contain volcanogenic euhedral zircon and apatite phenocrysts. Zircon crystals from the uppermost K-bentonite bed within the Baksian regional stage provide a 206Pb/238U age of 450.58±0.27 Ma. The timing of volcanism is surprisingly close to the period of volcanic activity of the Taconic arc near the eastern margin of Laurentia. The Yenisei arc had its continuation along the western continental margin of Siberia and both of them constitute a single Taconic-Yenisei volcanic arc. Field studies of the Upper Ordovician succession along the Moyero River in

  8. Effect of the Ordovician paleogeography on the (in)stability of the climate

    NASA Astrophysics Data System (ADS)

    Pohl, A.; Donnadieu, Y.; Le Hir, G.; Buoncristiani, J.-F.; Vennin, E.

    2014-11-01

    The Ordovician Period (485-443 Ma) is characterized by abundant evidence for continental-sized ice sheets. Modeling studies published so far require a sharp CO2 drawdown to initiate this glaciation. They mostly used non-dynamic slab mixed-layer ocean models. Here, we use a general circulation model with coupled components for ocean, atmosphere, and sea ice to examine the response of Ordovician climate to changes in CO2 and paleogeography. We conduct experiments for a wide range of CO2 (from 16 to 2 times the preindustrial atmospheric CO2 level (PAL)) and for two continental configurations (at 470 and at 450 Ma) mimicking the Middle and the Late Ordovician conditions. We find that the temperature-CO2 relationship is highly non-linear when ocean dynamics are taken into account. Two climatic modes are simulated as radiative forcing decreases. For high CO2 concentrations (≥ 12 PAL at 470 Ma and ≥ 8 PAL at 450 Ma), a relative hot climate with no sea ice characterizes the warm mode. When CO2 is decreased to 8 PAL and 6 PAL at 470 and 450 Ma, a tipping point is crossed and climate abruptly enters a runaway icehouse leading to a cold mode marked by the extension of the sea ice cover down to the mid-latitudes. At 450 Ma, the transition from the warm to the cold mode is reached for a decrease in atmospheric CO2 from 8 to 6 PAL and induces a ~9 °C global cooling. We show that the tipping point is due to the existence of a 95% oceanic Northern Hemisphere, which in turn induces a minimum in oceanic heat transport located around 40° N. The latter allows sea ice to stabilize at these latitudes, explaining the potential existence of the warm and of the cold climatic modes. This major climatic instability potentially brings a new explanation to the sudden Late Ordovician Hirnantian glacial pulse that does not require any large CO2 drawdown.

  9. Effect of the Ordovician paleogeography on the (in)stability of the climate

    NASA Astrophysics Data System (ADS)

    Pohl, A.; Donnadieu, Y.; Le Hir, G.; Buoncristiani, J.-F.; Vennin, E.

    2014-07-01

    The Ordovician is a particular Period during Earth History highlighted by abundant evidence for continental-size polar ice-sheets. Modelling studies published so far require a sharp CO2 drawdown to initiate this glaciation. They mostly used non-dynamic slab mixed-layer ocean models. Here, we use a general circulation model with coupled components for ocean, atmosphere and sea ice to examine the response of Ordovician climate to changes in CO2 and paleogeography. We conduct experiments for a wide range of CO2 (from 16 to 2 times the preindustrial atmospheric CO2 level (PAL)) and for two continental configurations (at 470 Ma and at 450 Ma) mimicking the Middle and the Late Ordovician conditions. We find that the temperature-CO2 relationship is highly non-linear when ocean dynamics is taken into account. Two climatic modes are simulated as radiative forcing decreases. For high CO2 concentrations (≥ 12 PAL at 470 Ma and ≥ 8 PAL at 450 Ma), a relative hot climate with no sea ice characterises the warm mode. When CO2 is decreased to 8 PAL and 6 PAL at 470 and 450 Ma, a tipping-point is crossed and climate abruptly enters a runaway icehouse leading to a cold mode marked by the extension of the sea ice cover down to the mid-latitudes. At 450 Ma, the transition from the warm to the cold mode is reached for a decrease in atmospheric CO2 from 8 to 6 PAL and induces a ~ 9 °C global cooling. We show that the tipping-point is due to the existence of a quasi-oceanic Northern Hemisphere, which in turn induces a minimum in oceanic heat transport located around 40° N. The peculiar shape of the oceanic heat transport in the Northern Hemisphere explains the potential existence of the warm and of the cold climatic modes. This major climatic instability potentially brings a new explanation to the sudden Late Ordovician Hirnantian glacial pulse that does not require any large CO2 drawdown.

  10. New evidence for land plants from the lower Middle Ordovician of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Strother, Paul K.; Al-Hajri, Said; Traverse, Alfred

    1996-01-01

    Macerations of Middle Ordovician (Llanvirnian) shales from Saudi Arabia yield an assemblage of spores of probable land plants (cryptospores), acritarchs, and chitinozoa. The production of sporopollenin-containing, sporelike tetrads is considered a fundamental character of the embryophytes, because no extant algae produce spores of this type. No trilete spores were found at this horizon, reinforcing previous assertions that obligate meiotic tetrads predate the earliest trilete spores. Sporomorph tetrads and dyads, in conjunction with cuticlelike fragments, were probably derived from terrestrial plants at a bryophyte grade. Although there are reports of possibly older cryptospores, the Hanadir assemblage described herein clearly establishes their presence by Llanvirnian time.

  11. Palynological tracers of eustatic and climatic changes in the Late Ordovician on the North Gondwanan Margin

    NASA Astrophysics Data System (ADS)

    Le Hérissé, A.; Vecoli, M.

    2003-04-01

    The short-lived Hirnantian glacio-eustatic interval (1 My or less) caused about 60 per cent loss of total marine animal genera. This icehouse climate is also responsible for significant changes on the evolution of the plankton and the distribution of related microfossil assemblages, from pre-glacial to post-glacial episodes. This is clearly confirmed on different upper Ordovician sections from various paleogeographic location on the North Gondwanan margin. The effects of the glaciation did not correspond exactly to a cataclysmic event, because the palynomorphs do not show accelerated rates of extinction, in the inhospitable environment. It could also be noted that the origins of the Silurian communities are rooted in the upper Ordovician prior to the glaciation, with appearance of precursors (or -ahead of time-) forms, that diversified later in the Silurian. Nevertheless, the harsh climatic conditions associated to sea-level drop, caused a reduction in the number of taxa, with a scenario composed of three separate critical events: 1. a selective survival of ubiquitous taxa which are tolerant to the sea-level drawdown and of few taxa that appear specifically adapted to cold environments (Rawtheyan-early Hirnantian); 2. an adaptation of the sympagic microflora, to the variations of the sea-ice cover during deglaciation, including polymorphism and speciations (Hirnantian); 3. a slow recovery acompanying the climatic restoration and transgression in the latest Ordovician and early Silurian. Modifications in abundance and diversity of the microfossil assemblages, in the percentages of reworked elements and of amorphic organic matter are interpreted as evidence of a series of advances and retreats of the continental ice, of important changes of sea-surface conditions, of differences in the rate of melting of the icebergs during the deglaciation, as well as post-glacial isostatic rebounds. Our investigation demonstrates that the analysis of the evolution of palynomorph

  12. Cambrian-lower Middle Ordovician passive carbonate margin, southern Appalachians: Chapter 14

    USGS Publications Warehouse

    Read, J. Fred; Repetski, John E.

    2012-01-01

    The southern Appalachian part of the Cambrian–Ordovician passive margin succession of the great American carbonate bank extends from the Lower Cambrian to the lower Middle Ordovician, is as much as 3.5 km (2.2 mi) thick, and has long-term subsidence rates exceeding 5 cm (2 in.)/k.y. Subsiding depocenters separated by arches controlled sediment thickness. The succession consists of five supersequences, each of which contains several third-order sequences, and numerous meter-scale parasequences. Siliciclastic-prone supersequence 1 (Lower Cambrian Chilhowee Group fluvial rift clastics grading up into shelf siliciclastics) underlies the passive margin carbonates. Supersequence 2 consists of the Lower Cambrian Shady Dolomite–Rome-Waynesboro Formations. This is a shallowing-upward ramp succession of thinly bedded to nodular lime mudstones up into carbonate mud-mound facies, overlain by lowstand quartzose carbonates, and then a rimmed shelf succession capped by highly cyclic regressive carbonates and red beds (Rome-Waynesboro Formations). Foreslope facies include megabreccias, grainstone, and thin-bedded carbonate turbidites and deep-water rhythmites. Supersequence 3 rests on a major unconformity and consists of a Middle Cambrian differentiated rimmed shelf carbonate with highly cyclic facies (Elbrook Formation) extending in from the rim and passing via an oolitic ramp into a large structurally controlled intrashelf basin (Conasauga Shale). Filling of the intrashelf basin caused widespread deposition of thin quartz sandstones at the base of supersequence 4, overlain by widespread cyclic carbonates (Upper Cambrian lower Knox Group Copper Ridge Dolomite in the south; Conococheague Formation in the north). Supersequence 5 (Lower Ordovician upper Knox in the south; Lower to Middle Ordovician Beekmantown Group in the north) has a basal quartz sandstone-prone unit, overlain by cyclic ramp carbonates, that grade downdip into thrombolite grainstone and then storm

  13. Correlation of upper Triassic strata between southern Colorado Plateau and southern High Plains, New Mexico

    SciTech Connect

    Lucas, S.G. )

    1989-09-01

    Almost 600 m of Upper Triassic strata are exposed in the Hagan basin. They pertain to the basal Agua Zarca member of the Chinle Formation (as much as 80 m), overlain by about 500 m of mud-rock-dominated red beds of the Petrified Forest Member of the Chinle Formation. The top of the Triassic section here is the 5.5-24 m-thick Correo Sandstone Bed of Chinle Formation, which is disconformably overlain by the medial silty member of the Middle Jurassic Entrada Sandstone. At Lamy, approximately 370 m of Upper Triassic strata represent the westernmost outcrops of the Triassic section typical of the Tucumcari basin. This Triassic section consists of about 140 m of Santa Rosa Formation (divisible into three members) overlain by a mud-rock-dominated section (Chinle Formation) split by a medial sandy interval, the Cuervo member (Trujillo Formation of the Palo Duro basin). The youngest Triassic strata near Lamy are rhythmically bedded sediments of the Redonda Member. Based on lithologic similarity, stratigraphic position, and limited paleontological data, the central New Mexico Upper Triassic strata support for the following correlations (from west to east): (1) Shinarump = Agua Zarca = Santa Rosa; (2) lower Petrified Forest = lower shale member of the Chinle = Tecovas; (3) Sonsela = Poleo = Cuervo = Trujillo; (4) upper Petrified Forest = upper shale member of the Chinle; and (5) Owl Rock = Redonda = Correo. These correlations reflect homotaxis of sedimentary cycles across a broad region of the southern Western Interior during the Late Triassic.

  14. Neogene marine isotopic evolution and the erosion of Lesser Himalayan strata: Implications for Cenozoic tectonic history

    NASA Astrophysics Data System (ADS)

    Myrow, Paul M.; Hughes, Nigel C.; Derry, Louis A.; Ryan McKenzie, N.; Jiang, Ganqing; Webb, A. Alexander G.; Banerjee, Dhiraj M.; Paulsen, Timothy S.; Singh, Birendra P.

    2015-05-01

    An extensive, northward deepening blanket of Neoproterozoic and Cambrian sedimentary rocks once extended from the Himalayan margin far onto the Indian craton. Cambrian deposits of this "upper Lesser Himalayan" succession, which include deposits of the "outer" Lesser Himalaya tectonic unit, are enriched in radiogenic 187Os. They make up part of a proximal marine facies belt that extends onto the craton and along strike from India to Pakistan. By contrast, age-equivalent facies in the Tethyan Himalaya are more distal in nature. Neoproterozoic to Cambrian strata of the upper Lesser Himalayan succession are now missing in much of the Lesser Himalaya, with their erosion exposing older Precambrian Lesser Himalayan strata. We suggest that exhumation and weathering of the upper Lesser Himalaya and related strata caused dramatic changes in the 187Os/188Os and 87Sr/86Sr Neogene record of seawater starting at ∼ 16 Ma. First-order estimates for the volume of upper Himalayan strata, as well as the volume of all LH rock eroded since this time, and geochemical box modeling, support this idea. Exhumation at 16 Ma is a fundamental event in the evolution of the Himalayan orogeny and the geochemical evolution of the oceans, and will be a critical part of the construction of future models of Himalayan thrust belt evolution.

  15. Stratigraphic patterns, sedimentology, and diagenesis of Capitan backreef strata, Permian, Guadalupe Mnts, New Mexico

    SciTech Connect

    Mutti, M. ); Simo, T. )

    1991-03-01

    Capitan backreef strata, Yates Formation, are characterized by six cycles, each with a lower siliciclastic and an upper carbonate unit. The factors controlling the deposition of these packages remain controversial. Traditional sedimentary and stratigraphic approaches have been integrated with diagenetic events to understand the main controls on the genesis of these cycles. Syndepositional and syn-unconformity diagenetic features are: (1) marine calcite or aragonite cementation, (2) dissolution of metastable mineral phases, and (3) dolomitization (both replacive and primary precipitate). Geochemistry of dolomites is consistent with evaporation-concentrated and slightly reducing marine waters. Meteoric calcite cements were not found associated with the subaerial exposure surfaces at cycle tops in shelf strata. Arid climate probably prevented the establishment of stable freshwater lenses. Postdepositional diagenesis includes meteoric and shallow burial calcite cements, dissolution vugs, kalinite, and vadose calcite cements. Combination of sedimentologic and diagenetic studies of Guadalupe Mountains outcrops suggests that sea level fluctuations probably were responsible for the deposition of cyclic strata and syndepositional diagenetic features. Relative sea level falls exposed parts of the shelf driving dolomitizing fluids through shelf strata. Relative sea level rises flooded the shelf and deposited subtidal to intertidal siliciclastic and carbonate rocks.

  16. Analysis of safety precautions for coal and gas outburst-hazardous strata

    SciTech Connect

    Hudecek, V.

    2008-09-15

    The author analyses coal and gas outbursts and generalizes the available data on the approaches to solving the problematics of these gas-dynamic events in the framework of Czech Republic Grant 'Estimate of the Safety Precautions for Coal and Gas Outburst Hazardous Strata'.

  17. New uppermost Cambrian U-Pb date from Avalonian Wales and age of the Cambrian-Ordovician boundary

    USGS Publications Warehouse

    Davidek, K.; Landing, E.; Bowring, S.A.; Westrop, S.R.; Rushton, A.W.A.; Fortey, R.A.; Adrain, J.M.

    1998-01-01

    A crystal-rich volcaniclastic sandatone in the lower Peltura scarabaeoides Zone at Ogof-odi near Criccieth, North Wales, yields a U-Pb zircon age of 491 ?? 1 Ma. This late Late Cambrian date indicates a remarkably young age for the Cambrian-Ordovician boundary whose age must be less than 491 Ma. Hence the revised duration of the post-Placentian (trilobite-bearing) Cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparble to that provided by Ordovician graptolites and Mesozoic ammonites.

  18. A new Lagerstätte from the Middle Ordovician St. Peter Formation in northeast Iowa, USA

    NASA Astrophysics Data System (ADS)

    Liu, Huaibao P.; McKay, Robert M.; Young, Jean N.; Witzke, Brian J.; McVey, Kathlyn J.; Liu, Xiuying

    2006-11-01

    A new fossil fauna has been discovered from a recently recognized shale unit within the middle Ordovician St. Peter Formation in northeast Iowa. It contains a variety of invertebrates and vertebrates, including soft body tissues, impressions, and 3-dimensionalpreservations. The exceptional preservation reveals a new Konservat-Lagerstätte, the Winneshiek Lagerstätte, and opens a unique window into the community that inhabited the margins of the Laurentian cratonic seaway during Middle Ordovician transgression. Among the fossils, several conodont assemblages, including the apparatus of enigmatic coleodontids, are preserved. Some conodont assemblages associated with soft body tissues are particularly noteworthy.

  19. A new Lagerstätte from the Middle Ordovician St. Peter formation in northeast Iowa, USA

    USGS Publications Warehouse

    Liu, Huaibao P.; McKay, Robert M.; Young, Jean N.; Witzke, Brian J.; McVey, Kathlyn J.; Liu, Xiuying

    2006-01-01

    A new fossil fauna has been discovered from a recently recognized shale unit within the middle Ordovician St. Peter Formation in northeast Iowa. It contains a variety of invertebrates and vertebrates, including soft body tissues, impressions, and 3-dimensionalpreservations. The exceptional preservation reveals a new Konservat-Lagerstätte, the Winneshiek Lagerstätte, and opens a unique window into the community that inhabited the margins of the Laurentian cratonic seaway during Middle Ordovician transgression. Among the fossils, several conodont assemblages, including the apparatus of enigmatic coleodontids, are preserved. Some conodont assemblages associated with soft body tissues are particularly noteworthy.

  20. Natural gas production from Ordovician Queenston Formation in West Auburn field, Cayuga County, New York

    SciTech Connect

    Ward, T.L.

    1988-08-01

    Gas has been produced from the Upper Ordovician Queenston Formation at West Auburn field, Cayuga County, New York, for over 20 years. This field indicates Queenston production to be long lived, with substantially economic reserves found at depths shallower than 2,000 ft. Locally, The Queenston is comprised of sand and silty shale with the primary reservoirs found in quartzose sandstones. The overall thickness of the Queenston clastic interval is over 700 ft with gas found in the upper 300 ft. Three primary gas sands are continuous across the field area and have high average porosities of as much as 13.0% and average permeabilities of 0.20 md. Extreme examples show peak porosities approaching 20% and permeabilities of over 5.0 md. The reservoir is composed of very fine to medium-grained, moderately sorted, red sandstone. Sand grains are predominantly quartz with minor amounts of feldspar. The main pore-filling constituent is abundant authigenic clay with iron oxides, thus contributing to reduced permeabilities. These sands vary in reservoir quality through the field and, hence, allow for stratigraphic trapping of the gas. Other factors involved include the updip accumulation of gas against the Silurian-Ordovician unconformity at the top of the Queenston. Some of the pay sands are absent due to this unconformity in the area farthest updip and, therefore, decrease the overall reserve potential of the individual well in that part of the field.

  1. Biostratigraphic utility of organic-walled phytoplankton, Upper Ordovician-Lower Silurian of Appalachian basin

    SciTech Connect

    Colbath, G.K.

    1986-05-01

    Upper Ordovician-Lower Silurian marine mudstones in the Appalachian basin, which have not been subjected to extensive heating or oxidation, contain abundant organic-walled phytoplankton (prasinophycean algal phycomata and acritarchs). In most areas graptolites and conodonts have not been recovered from these rocks, making the phytoplankton particularly important for biostratigraphic correlation. Recent advances have improved the precision with which these microfossils can be used. By tabulating relative abundance data carefully, an abrupt change in the composition of phytoplankton associations can be recognized at the Ordovician-Silurian boundary can be located with greater precision and confidence than is possible using the stratigraphic ranges of individual species. Many supposedly long-ranging species have relatively short stratigraphic ranges, and thus greater utility, as a result of detailed taxonomic studies. Therefore, type and comparative material are important considerations. Also, vesicle wall architecture and dehiscent structures are valuable taxonomic characters. Scanning electron microscopy examination has improved our understanding of small forms (less than 20 ..mu..m in diameter), and has thus increased the number of taxa available for use in biostratigraphy. Further study of samples from vertically extensive stratigraphic sections of established age should help workers refine the biostratigraphy of these microfossils.

  2. Simulating Late Ordovician deep ocean O2 with an earth system climate model. Preliminary results.

    NASA Astrophysics Data System (ADS)

    D'Amico, Daniel F.; Montenegro, Alvaro

    2016-04-01

    The geological record provides several lines of evidence that point to the occurrence of widespread and long lasting deep ocean anoxia during the Late Ordovician, between about 460-440 million years ago (ma). While a series of potential causes have been proposed, there is still large uncertainty regarding how the low oxygen levels came about. Here we use the University of Victoria Earth System Climate Model (UVic ESCM) with Late Ordovician paleogeography to verify the impacts of paleogeography, bottom topography, nutrient loading and cycling and atmospheric concentrations of O2 and CO2 on deep ocean oxygen concentration during the period of interest. Preliminary results so far are based on 10 simulations (some still ongoing) covering the following parameter space: CO2 concentrations of 2240 to 3780 ppmv (~8x to 13x pre-industrial), atmospheric O2 ranging from 8% to 12% per volume, oceanic PO4 and NO3 loading from present day to double present day, reductions in wind speed of 50% and 30% (winds are provided as a boundary condition in the UVic ESCM). For most simulations the deep ocean remains well ventilated. While simulations with higher CO2, lower atmospheric O2 and greater nutrient loading generate lower oxygen concentration in the deep ocean, bottom anoxia - here defined as concentrations <10 μmol L-1 - in these cases is restricted to the high-latitue northern hemisphere. Further simulations will address the impact of greater nutrient loads and bottom topography on deep ocean oxygen concentrations.

  3. Mass extinction of the marine biota at the Ordovician-Silurian transition due to environmental changes

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2014-11-01

    The terminal Ordovician was marked by one of five great mass extinction events of the Phanerozoic (445.6-443.0 Ma ago), when up to 86% of the marine species became extinct. The rapid onset of the continental glaciation on Gondwana determined by its position in the South Pole area; the cooling; the hydrodynamic changes through the entire water column in the World Ocean; and the corresponding sea level fall, which was responsible for the reduction of shelf areas and shallow-water basins, i.e., the main ecological niche of the Ordovician marine biota, were main prerequisites of the stress conditions. Similar to other mass extinction events, these processes were accompanied by volcanism, impact events, a corresponding reduction of the photosynthesis and bioproductivity, the destruction of food chains, and anoxia. The appearance and development of terrestrial plants and microphytoplankton, which consumed atmospheric carbon dioxide, thus, diminishing the greenhouse effect and promoting the transition of the climatic system to the glacial mode, played a unique role in that period.

  4. Probable Middle Cambrian and Middle-Late Ordovician seismites, a record of extensional to compressional tectonics

    SciTech Connect

    Pope, M.C.; Read, J.F. . Dept. of Geology)

    1992-01-01

    Facies resembling seismites, in situ shock deformation of sediments related to earthquake activity, appear to be developed in a Middle Cambrian intrashelf basinal setting in Virginia, and in a Middle-Late Ordovician foreland basin setting throughout Virginia and Kentucky. The Middle Cambrian facies developed during Rome trough and Conasauga basin extensional tectonics, whereas the Middle and Late Ordovician examples developed during eastward subduction of the North American plate (Taconic Orogeny). The seismites are characterized by contorted bedding, abundant ball and pillow structures, upward injection of sediment, in-place foundering of large blocks with erosional tops, development of mud-supported chaotic conglomerate fabrics and perhaps compacted sediment filled dikes in shale. The seismites occur in both clastic and carbonate, fine-to-carose grained sediments and vary in scale from centimeters to meters. The contorted bedding probably relates to seismically induced liquefaction of sediments within the upper few meters of section, whereas ball and pillow formation and sediment injection is due to water escape. The low sedimentation rates in the intrashelf basin and on the foreland ramp would tend to preclude these features resulting from high sedimentation rates causing loading of water-rich mud sections, even though some beds related to storm deposition. In fact, most of the storm beds, even thicker ones, show little evidence of ball and pillow formation. Seismites may provide an important temporal record of earthquakes affecting these basins, and need to be recognized if one is to separate tectonic from eustatic effects in these basins.

  5. Controls on deposition of the St. Peter Sandstone (Middle-Late Ordovician), Michigan basin

    SciTech Connect

    Nadon, G.C.; Simo, A.; Byers, C.W.; Dott, R.H, Jr. )

    1991-08-01

    The St. Peter Sandstone (Middle-late Ordovician) of the Michigan basin represents an approximately 10-m.y. interval of clastic deposition in an otherwise carbonate-dominated Ordovician succession. This interval, up to 320 m thick, also coincides with a change in basin configuration from the nearly circular depocenter of the underlying Shakopee Formation to an east-west elongate trough situated west to Saginaw Bay. Interpretation of well logs and core from throughout the basin indicates that the clastics are composed of 20-25 sequences upper shoreface to tidal-flat environments. The sequences are interbedded with heavily bioturbated, shaly, lower shoreface sandstones (1-14 m thick) and, in the central and southeastern parts of the basin, with carbonate shales, stromatolites, and oolitic grain-stones (2-39 m thick). The eastern and southeastern margins of the basin contain the thickest carbonate accumulations. Hydrocarbons fields are located over structural highs formed by reactivation of basement structures. Detailed comparison of well logs within field shows that sedimentary cycles thin over the structures as a result of the local reduction in the formation of accommodation space by syndepositional movements on the faults. The presence of thick carbonates along the southeastern margin of the basin is a result of the combination of distance form the clastic source and the episodic formation of accommodation space by syndepositional normal faulting along the basin margin.

  6. New gas discoveries in the Ordovician sandstones, Risha area; northeast Jordan

    SciTech Connect

    Sabbah, A.A.; Ramini, H.M. )

    1996-01-01

    Over thirty wells for exploration and production purposes were drilled in the Risha Area, northeast Jordan by the Natural Resources Authority since 1986. Commercial gas was discovered in the sandstones of Dubeidib Formation (Late Ordovician age). These sandstones are believed to have been deposited in the form of marine sand bars trending NNE-SSW. During the Early Paleozoic time, Jordan has undergone periods of epirogenic movements ending in Late Ordovician. Two major lineament trends are dominant, one oriented northwest-southeast and the other ENE-WSW. A third trend oriented north-south to NNW-SSE also appears but more discontinuous. Four source rock horizons were developed within the Early Paleozoic times. Oil generation of Lower Paleozoic source horizons took place in the Late Paleozoic. The upper Mudawwara hot shales of Silurian age is believed to have generated liquid hydrocarbons in the Late Cretaceous times, in a second phase of hydrocarbon generation. Dry gas was originated through organic maturation of the Lower Paleozoic source horizons. The Risha Gas Field is producing 30 MMcfgd since it was first discovered in 1987.

  7. New gas discoveries in the Ordovician sandstones, Risha area; northeast Jordan

    SciTech Connect

    Sabbah, A.A.; Ramini, H.M.

    1996-12-31

    Over thirty wells for exploration and production purposes were drilled in the Risha Area, northeast Jordan by the Natural Resources Authority since 1986. Commercial gas was discovered in the sandstones of Dubeidib Formation (Late Ordovician age). These sandstones are believed to have been deposited in the form of marine sand bars trending NNE-SSW. During the Early Paleozoic time, Jordan has undergone periods of epirogenic movements ending in Late Ordovician. Two major lineament trends are dominant, one oriented northwest-southeast and the other ENE-WSW. A third trend oriented north-south to NNW-SSE also appears but more discontinuous. Four source rock horizons were developed within the Early Paleozoic times. Oil generation of Lower Paleozoic source horizons took place in the Late Paleozoic. The upper Mudawwara hot shales of Silurian age is believed to have generated liquid hydrocarbons in the Late Cretaceous times, in a second phase of hydrocarbon generation. Dry gas was originated through organic maturation of the Lower Paleozoic source horizons. The Risha Gas Field is producing 30 MMcfgd since it was first discovered in 1987.

  8. Did a Gamma-Ray Burst Initiate the Late Ordovician Mass Extinction?

    NASA Technical Reports Server (NTRS)

    Melott, A. L.; Lieberman, B. S.; Laird, C. M.; Martin, L. D.; Medvedov, M. V.; Thomas, B. C.; Cannizzo, J. K.; Gehrels, N.; Jackman, C. H.

    2004-01-01

    Gamma-ray bursts (hereafter GRB) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average several times per billion years. At leastfive times in the history of lfe, the Earth experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRB may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. Due to severe depletion of the ozone layer, intense solar ultraviolet radiation is expected to result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identijied as the probable cause of this mass extinction, may have resultedfiom a GRB.

  9. Palaeogeographic implications of a new iocrinid crinoid (Disparida) from the Ordovician (Darriwillian) of Morocco

    PubMed Central

    Rahman, Imran A.; Ausich, William I.

    2015-01-01

    Complete, articulated crinoids from the Ordovician peri-Gondwanan margin are rare. Here, we describe a new species, Iocrinus africanus sp. nov., from the Darriwilian-age Taddrist Formation of Morocco. The anatomy of this species was studied using a combination of traditional palaeontological methods and non-destructive X-ray micro-tomography (micro-CT). This revealed critical features of the column, distal arms, and aboral cup, which were hidden in the surrounding rock and would have been inaccessible without the application of micro-CT. Iocrinus africanus sp. nov. is characterized by the presence of seven to thirteen tertibrachials, three in-line bifurcations per ray, and an anal sac that is predominantly unplated or very lightly plated. Iocrinus is a common genus in North America (Laurentia) and has also been reported from the United Kingdom (Avalonia) and Oman (middle east Gondwana). Together with Merocrinus, it represents one of the few geographically widespread crinoids during the Ordovician and serves to demonstrate that faunal exchanges between Laurentia and Gondwana occurred at this time. This study highlights the advantages of using both conventional and cutting-edge techniques (such as micro-CT) to describe the morphology of new fossil specimens. PMID:26664800

  10. Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction.

    PubMed

    Finnegan, Seth; Rasmussen, Christian M Ø; Harper, David A T

    2016-04-27

    The Late Ordovician mass extinction (LOME) coincided with dramatic climate changes, but there are numerous ways in which these changes could have driven marine extinctions. We use a palaeobiogeographic database of rhynchonelliform brachiopods to examine the selectivity of Late Ordovician-Early Silurian genus extinctions and evaluate which extinction drivers are best supported by the data. The first (latest Katian) pulse of the LOME preferentially affected genera restricted to deeper waters or to relatively narrow (less than 35°) palaeolatitudinal ranges. This pattern is only observed in the latest Katian, suggesting that it reflects drivers unique to this interval. Extinction of exclusively deeper-water genera implies that changes in water mass properties such as dissolved oxygen content played an important role. Extinction of genera with narrow latitudinal ranges suggests that interactions between shifting climate zones and palaeobiogeography may also have been important. We test the latter hypothesis by estimating whether each genus would have been able to track habitats within its thermal tolerance range during the greenhouse-icehouse climate transition. Models including these estimates are favoured over alternative models. We argue that the LOME, long regarded as non-selective, is highly selective along biogeographic and bathymetric axes that are not closely correlated with taxonomic identity. PMID:27122567

  11. Ordovician paleosols at Arisaig, Nova Scotia, and the evolution of the atmosphere

    NASA Technical Reports Server (NTRS)

    Feakes, C. R.; Holland, H. D.; Zbinden, E. A.

    1989-01-01

    A series of Late Ordovician andesite flows are exposed along the coastline near Arisaig, Nova Scotia. Field relationships, textural and mineralogical evidence, and chemical analyses of three interflow units confirm that they are paleosols. The chemical variations observed in these paleosols are quite similar to those of modern soils developed on mafic volcanic rocks. Virtually all of the iron in the paleosols was oxidized and retained during weathering; however, in two of the three paleosols a small fraction of the ferrous iron escaped oxidation and was precipitated near the base of the paleosols. This redistribution of ferrous iron may reflect the presence of nonvascular land plants. The variations in the concentration of the major oxides produced by weathering of the andesites at Arisaig are consistent with the probable lower limit of 0.04 atm for the partial pressure of O2 in the atmosphere during the Late Ordovician. The current data base for Paleozoic and Precambrian paleosols indicates that a significant increase in the PO2/PCO2 ratio in the atmosphere took place about 2.0 x 10(9) years ago; since then the ratio of PO2/PCO2 in the atmosphere has been high enough to oxidize all of the iron in soils developed on igneous rocks.

  12. Ordovician paleosols at Arisaig, Nova Scotia, and the evolution of the atmosphere.

    PubMed

    Feakes, C R; Holland, H D; Zbinden, E A

    1989-01-01

    A series of Late Ordovician andesite flows are exposed along the coastline near Arisaig, Nova Scotia. Field relationships, textural and mineralogical evidence, and chemical analyses of three interflow units confirm that they are paleosols. The chemical variations observed in these paleosols are quite similar to those of modern soils developed on mafic volcanic rocks. Virtually all of the iron in the paleosols was oxidized and retained during weathering; however, in two of the three paleosols a small fraction of the ferrous iron escaped oxidation and was precipitated near the base of the paleosols. This redistribution of ferrous iron may reflect the presence of nonvascular land plants. The variations in the concentration of the major oxides produced by weathering of the andesites at Arisaig are consistent with the probable lower limit of 0.04 atm for the partial pressure of O2 in the atmosphere during the Late Ordovician. The current data base for Paleozoic and Precambrian paleosols indicates that a significant increase in the PO2/PCO2 ratio in the atmosphere took place about 2.0 x 10(9) years ago; since then the ratio of PO2/PCO2 in the atmosphere has been high enough to oxidize all of the iron in soils developed on igneous rocks. PMID:11542236

  13. A Cenozoic-style scenario for the end-Ordovician glaciation

    PubMed Central

    Ghienne, Jean-François; Desrochers, André; Vandenbroucke, Thijs R.A.; Achab, Aicha; Asselin, Esther; Dabard, Marie-Pierre; Farley, Claude; Loi, Alfredo; Paris, Florentin; Wickson, Steven; Veizer, Jan

    2014-01-01

    The end-Ordovician was an enigmatic interval in the Phanerozoic, known for massive glaciation potentially at elevated CO2 levels, biogeochemical cycle disruptions recorded as large isotope anomalies and a devastating extinction event. Ice-sheet volumes claimed to be twice those of the Last Glacial Maximum paradoxically coincided with oceans as warm as today. Here we argue that some of these remarkable claims arise from undersampling of incomplete geological sections that led to apparent temporal correlations within the relatively coarse resolution capability of Palaeozoic biochronostratigraphy. We examine exceptionally complete sedimentary records from two, low and high, palaeolatitude settings. Their correlation framework reveals a Cenozoic-style scenario including three main glacial cycles and higher-order phenomena. This necessitates revision of mechanisms for the end-Ordovician events, as the first extinction is tied to an early phase of melting, not to initial cooling, and the largest δ13C excursion occurs during final deglaciation, not at the glacial apex. PMID:25174941

  14. The significance of 24-norcholestanes, triaromatic steroids and dinosteroids in oils and Cambrian-Ordovician source rocks from the cratonic region of the Tarim Basin, NW China

    USGS Publications Warehouse

    Li, Meijun; Wang, T.-G.; Lillis, Paul G.; Wang, Chunjiang; Shi, Shengbao

    2012-01-01

    Two oil families in Ordovician reservoirs from the cratonic region of the Tarim Basin are distinguished by the distribution of regular steranes, triaromatic steroids, norcholestanes and dinosteroids. Oils with relatively lower contents of C28 regular steranes, C26 20S, C26 20R + C27 20S and C27 20R regular triaromatic steroids, dinosteranes, 24-norcholestanes and triaromatic dinosteroids originated from Middle–Upper Ordovician source rocks. In contrast, oils with abnormally high abundances of the above compounds are derived from Cambrian and Lower Ordovician source rocks. Only a few oils have previously been reported to be of Cambrian and Lower Ordovician origin, especially in the east region of the Tarim Basin. This study further reports the discovery of oil accumulations of Cambrian and Lower Ordovician origin in the Tabei and Tazhong Uplifts, which indicates a potential for further discoveries involving Cambrian and Lower Ordovician sourced oils in the Tarim Basin. Dinosteroids in petroleum and ancient sediments are generally thought to be biomarkers for dinoflagellates and 24-norcholestanes for dinoflagellates and diatoms. Therefore, the abnormally high abundance of these compounds in extracts from the organic-rich sediments in the Cambrian and Lower Ordovician and related oils in the cratonic region of the Tarim Basin suggests that phytoplankton algae related to dinoflagellates have appeared and might have flourished in the Tarim Basin during the Cambrian Period. Steroids with less common structural configurations are underutilized and can expand understanding of the early development history of organisms, as well as define petroleum systems.

  15. Relationship of Ordovician and Silurian reservoir development to unconformities at Midland farms and Inez fields, Andrews County, Texas

    SciTech Connect

    Mear, C.E.; Becher, J.W.

    1986-03-01

    Hydrocarbons are being produced at Midland Farms and Inez fields from Ellenburger dolomites and Fusselman limestones. Reservoirs developed there during Ordovician and Silurian periods of minor folding and faulting, followed by regional uplift and subaerial exposure of the carbonates. Vuggy, cavernous, and solution-enlarged fracture porosity was developed in the Lower Ordovician Ellenburger dolomites prior to deposition of the overlying Middle Ordovician shales of the Simpson Group. Vuggy and cavernous porosity developed in the Lower Silurian Fusselman crinoid-ostracod-pellet packstones and grainstones before deposition of the overlying Silurian Wristen shales. Montoya siliceous limestones of Late Ordovician age were truncated during a period of pre-Silurian erosion, but porosity development is not indicated in Montoya rock cuttings. Only minor amounts of porosity developed in the Lower to Middle Devonian Thirty-one packstones and wackestones as a result of uplift and erosion in the Middle Devonian. Regional compression during the post-Mississippian enhanced doubly plunging anticlines now having up to 91 m (300 ft) of closure at the Ellenburger through Thirty-one formations at Midland Farms and Inez fields. Fractures may have developed in Paleozoic limestones during this period of folding, but reservoir enhancement appears to have resulted only in the Ellenburger dolomites. Representative porosity measurements of the Ellenburger and Fusselman pay zones cannot be made from wireline log calculations, due to the fractured, vuggy, and cavernous nature of the porosity.

  16. A Lower Ordovician sponge/algal facies in the southern United States and its counterparts elsewhere in North America

    SciTech Connect

    Alberstadt, L. ); Repetski, J.E. )

    1989-06-01

    Subsurface Ordovician rocks in the Black Warrior Basin, Mississippi Embayment, and the eastern part of the Arkoma Basin reflect a different depositional history than coeval rocks exposed in the Nashville Basin, Ozark Dome, and southern Appalachians. The succession consists of four informal lithologic units. From top to bottom these are: (1) Stones River limestones, (2) upper dolostone, (3) sponge/algal limestones characterized by the presence of Nuia, and (4) lower dolostone. Of these, the sponge/algal limestone unit is the most atypical. It has a conspicuous biotic assemblage which can be recognized petrographically in well cuttings. The diagnostic fossil allochems are: sponges, sponge spicules, Nuia, Girvanella, and Sphaerocodium. Conodonts from the sponge/algal limestones are probably entirely Early Ordovician (Canadian) and include cold- and deep-water species found in the North Atlantic Province, whereas those in the overlying dolostones represent exclusively warm-water, shelf environments. The conodonts in the Black Warrior Basin suggest that an unconformity between Lower and Middle Ordovician carbonates (Knox unconformity) does not exist in much of that region. The sponge/algal limestones represent a different facies than their coeval shelf rocks in the interior of the continent. The limestone contains a distinctive biotic assemblage recognized in Lower Ordovician rocks in Newfoundland, in the Arbuckle and Wichita mountains of Oklahoma, in West Texas, and in the Great Basin of Nevada and Utah.

  17. The roles of Lazarus taxa and refugia through the Ordovician-Silurian transition: data from the Brachiopoda

    NASA Astrophysics Data System (ADS)

    Rong, J.-Y.; Boucot, A. J.; Harper, D. A.; Zhan, R.-B.; Neuman, R. B.

    2003-04-01

    Global analyses of nearly 90 families and 275 genera of brachiopods from the middle Ashgill through the Hirnantian (Ordovician) to the lower-middle Rhuddanian (Silurian) suggest that about 60% and 40% of the total number of genera were eliminated at the first and second phases of the end Ordovician extinction event, respectively. Among the 85 surviving genera, about 50 with declining and 10 with proliferating abundances are known from the Hirnantian together with about 20 provisional Lazarus taxa. The Lazarus taxa are essentially survivors and form the extremity of the declining genera. The distributions of declining genera and relicts during the crisis interval shows a random and sporadic pattern, suggesting there was no single, common refugium for end Ordovician brachiopods. In addition to their biological attributes, a markedly decreased population size together with taphonomic failure and poor preservation, and collecting bias have contributed towards the distributional trends apparent during the event. The development of declining genera during the extinction may be linked to their palaeogeographical setting, the phylogenetic history of the taxa, and the ambient environmental conditions. This new global database has significantly reduced the number of Lazarus taxa and minimizes the number of possible locations for collective refugia during the end Ordovician crisis. Nevertheless, the atrypids, athyridids, pentamerids, and spiriferids had more limited distributions during the crisis interval but formed the locus for a Silurian diversification of the phylum into carbonate environments possibly around the Rhuddanian-Aeronian boundary.

  18. Leperditicopid ostracodes from Ordovician rocks of Kentucky and nearby states and characteristic features of the order Leperditicopida

    USGS Publications Warehouse

    Berdan, J.M.

    1984-01-01

    Leperditicopid ostracodes from the Ordovician formations of Kentucky occur in micritic to fine-grained carbonate rocks believed to represent shallow-water facies. They are found at widely separated horizons in the Middle Ordovician High Bridge Group, the Middle and Upper Ordovician Lexington Limestone, and the Upper Ordovician Ashlock, Bull Fork, and Drakes Formations. In this sequence, the leperditicopes are represented by two genera of leperditiids, Eoleperditia Swartz, 1949 and Bivia Berdan, 1976, and six isochilinid genera, Isochilina Jones, 1858, Teichochilina Swartz, 1949, Ceratoleperditia Harris, 1960, Parabriartina n. gen., Kenodontochilina n. gen., and Saffordellina Bassler and Kellett, 1934; the type species of the hitherto poorly known genus Saffordellina, S. muralis (Ulrich and Bassler, 1923), is redescribed and refigured. In all, 18 taxa, of which 2 are in open nomenclature, are described and illustrated. In addition, the family Isochilinidae Swartz, 1949 is redefined to include genera without marginal brims and with straight ventral contact margins. The morphological characteristics of leperditicopid genera are discussed, and a table listing described genera and their diagnostic features is included.

  19. Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Great Ordovician Biodiversification Event.

    PubMed

    Buatois, Luis A; Mángano, Maria G; Olea, Ricardo A; Wilson, Mark A

    2016-06-21

    Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal-substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation. PMID:27247396

  20. The Environmental Context of Gastropods on Western Laurentia (Basin and Range Province) during the Great Ordovician Biodiversification Event

    ERIC Educational Resources Information Center

    Dahl, Robyn Mieko

    2015-01-01

    Gastropods are a major component of modern marine ecosystems and can be found in nearly every type of marine ecosystem. They experienced their first notable radiation during the Great Ordovician Biodiversification Event (~470 Ma), during which their diversity tripled. This study examines the gastropod assemblage preserved in the Basin and Range…

  1. Cambrian to Lower Ordovician complexes of the Kokchetav Massif and its fringing (Northern Kazakhstan): Structure, age, and tectonic settings

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.; Tolmacheva, T. Yu.; Tretyakov, A. A.; Kotov, A. B.; Shatagin, K. N.

    2016-01-01

    A comprehensive study of the Lower Palaeozoic complexes of the Kokchetav Massif and its fringing has been carried out. It has allowed for the first time to discover and investigate in detail the stratified and intrusive complexes of the Cambrian-Early Ordovician. Fossil findings and isotope geochronology permitted the determination of their ages. The tectonic position and internal structures of those complexes have also been defined and their chemical features have been analyzed as well. The obtained data allowed us to put forward a model of the geodynamic evolution of Northern Kazakhstan in the Late Ediacaran-Earliest Ordovician. The accumulation of the oldest Ediacaran to Earliest Cambrian siliciclastics and carbonates confined to the Kokchetav Massif and its fringing occurred in a shallow shelf environment prior to its collision with the Neoproterozoic Daut island arc: complexes of the latter have been found in the northeast of the studied area. The Early Cambrian subduction of the Kokchetav Massif under the Daut island arc, their following collision and exhumation of HP complexes led to the formation of rugged ground topography, promoting deposition of siliceous-clastic and coarse clastic units during the Middle to early Late Cambrian. Those sediments were mainly sourced from eroded metamorphic complexes of the Kokchetav Massif basement. At the end of the Late Cambrian to the Early Ordovician within the boundaries of the massif with the Precambrian crust, volcanogenic and volcano-sedimentary units along with gabbros and granites with intraplate affinities were formed. Simultaneously in the surrounding zones, which represent relics of basins with oceanic crust, N-MORB- and E-MORB-type ophiolites were developed. These complexes originated under extensional settings occurred in the majority of the Caledonides of Kazakhstan and Northern Tian Shan. In the Early Floian Stage (Early Ordovician) older heterogeneous complexes were overlain by relatively monotonous

  2. Applications of sequence stratigraphy to Pennsylvanian strata in the Illinois Basin

    USGS Publications Warehouse

    Weibel, C.P.

    1996-01-01

    Sequence stratigraphy concepts have been applied previously to the interpretation of Pennsylvanian strata in the Illinois Basin with the use of the 'cycle' by J.A. Udden in 1912 and the cyclothem by H. Wanless and J. Weller in 1932. The unconformity-bounded cyclothem was recognized in Pennsylvanian strata throughout the basin and is a small-scale version of the cratonic sequence of L.L. Sloss. Recent applications indicate that the transgressive-regressive unit, a genetic succession bounded by marine-flooding surfaces, is a more practical stratigraphic unit that has applications for stratigraphic control, structural control, sedimentology, and hydrostratigraphy. Transgressive-regressive units conveniently fit within a sequence stratigraphic framework.

  3. Investigation of deep permeable strata in the permian basin for future geothermal energy reserves

    SciTech Connect

    Erdlac, Richard J., Jr.; Swift, Douglas B.

    1999-09-23

    This project will investigate a previously unidentified geothermal energy resource, opening broad new frontiers to geothermal development. Data collected by industry during oil and gas development demonstrate deep permeable strata with temperatures {ge} 150 C, within the optimum window for binary power plant operation. The project will delineate Deep Permeable Strata Geothermal Energy (DPSGE) assets in the Permian Basin of western Texas and southeastern New Mexico. Presently, geothermal electrical power generation is limited to proximity to shallow, high-temperature igneous heat sources. This geographically restricts geothermal development. Delineation of a new, less geographically constrained geothermal energy source will stimulate geothermal development, increasing available clean, renewable world energy reserves. This proposal will stimulate geothermal reservoir exploration by identifying untapped and unrealized reservoirs of geothermal energy. DPSGE is present in many regions of the United States not presently considered as geothermally prospective. Development of this new energy source will promote geothermal use throughout the nation.

  4. Algebraic investigations in landau model of structural phase transitions: II. Orbits, strata and epikernels

    NASA Astrophysics Data System (ADS)

    Kopský, V.

    1983-07-01

    First we introduce the basic notions of the theory of permutation representations: stabilizers, orbits, stable subsets and strata. Then we consider the relation between permutation and linear representations which lead to some formulae connecting subduction coefficients, Clebsch-Gordan coefficients, and dimensions of stability spaces. This relation also leads to the concept of suborbits. Epikernels, the subgroups which are stabilizers of vectors of irreducible subspaces (either on the complex or on the real field) — are, studied and several theorems about them are proved. Further we consider the relation between epikernels, stability spaces and strata for subspaces irreducible on the real field as compared with subspaces irreducible on the complex field. Finally, the exomorphism is defined with use of permutation representations. The vectors of irreducible subspaces and corresponding epikernels (their stabilizers) for real ireps (representations irreducible on the real) of the classical crystal point groups are given in the appendix.

  5. Balanoglossites ichnofabrics from the Middle Ordovician Volkhov formation (St. Petersburg Region, Russia)

    NASA Astrophysics Data System (ADS)

    Knaust, D.; Dronov, A.

    2013-05-01

    The limestone succession of the Middle Ordovician Volkhov Formation in the St. Petersburg region (Russia) exposes numerous horizons with firm- and hardgrounds below omission surfaces, which contain trace fossils attributable to the ichnogenus Balanoglossites Mägdefrau, 1932. Although known from the literature since 75 years, such trace fossils were previously only informally described as "Korrosionsgruben", "Karandashi", or ascribed to different ichnotaxa such as Trypanites, Arenicolites and Pseudopolydorites. Owing to their complexity and often high bioturbation density, the morphology of these trace fossils is difficult to capture. Ichnofabrics containing Balanoglossites triadicus were studied in detail from sawn rock faces, broken rock blocks and sectioned slabs, including those from historical buildings in St. Petersburg. Accordingly, different trace-fossil elements can be revealed in dependence on the original substrate consistency, reflecting various stages of lithification: Mineral-stained and Trypanites-perforated hardground surfaces are bioeroded with long elongated grooves which are assigned to the ichnogenus Sulcichnus. Subtle openings lead into the partly lithified limestone where they branch into complex galleries of B. triadicus. They are characterized by J-, U- and Y-shaped shafts and multiply branched tunnels, which gradually continue into the underlying firmground. Other portions of the ichnofabric only exhibit biodeformational structures or the strongly compacted and branched burrow networks Labyrintichnus, which is due to the original soft sediment consistency. Balanoglossites ichnofabrics demarcate certain omission surfaces within the Dikari Limestone and can be traced for more than 300 km, supporting the regional lithostratigraphical correlation. The trace maker of B. triadicus and related trace fossils is interpreted to be a eunicid polychate with the ability to bioerode and burrow the sediment. The studied material from the Ordovician is

  6. Stratigraphy and correlation of Upper Triassic strata between west Texas and eastern New Mexico

    SciTech Connect

    Lucas, S.G. ); Anderson, O.J. )

    1992-04-01

    Lithostratigraphy and vertebrate biochronology allow precise correlation of Upper Triassic strata between west Texas and eastern New Mexico. Upper Triassic strata are well exposed in west Texas from Oldham to Scurry counties, and are assigned to the Dockum Formation of the Chinle Group. Fossil vertebrates from the Camp Springs and Tecovas Members are of late Carnian age, whereas those from the Copper Member are of early Norian age. Upper Triassic strata in east-central New Mexico, across the Llano Estacado from the west Texas outcrops, correlate as follows: Camper Springs = lower Santa Rose; Tecovas = upper Santa Rosa/Garita Creek; Trujillo = Trujillo ('Cuervo'); Cooper = lower Bull Canyon. Upper Triassic strata in southeastern New Mexico and in Howard and adjacent counties in Texas are the lower Santa Rosa/Camper Springs overlain by mudstones and sandstones that contain late Carnian vertebrates and are informally termed upper member of Dockum Formation. Available data refute several long-held ideas about the Upper Triassic of west Texas. These data demonstrate that: (1) there is a pervasive unconformity at the base of the Dockum Formation that represents much of Triassic time; (2) the Trujillo Member is not correlative with the Santa Rosa of eastern New Mexico: Trujillo is a medial Dockum unit, whereas Santa Rosa is at the base of the Upper Triassic section; (3) very little Dockum mudrock was deposited in lakes; and (4) Dockum rivers flowed almost exclusively to the north, northwest, and west, so there was no closed depositional basin in west Texas during the Late Triassic.

  7. Overpressure and hydrocarbon accumulations in Tertiary strata, Gulf Coast of Louisiana

    USGS Publications Warehouse

    Nelson, Philip H.

    2012-01-01

    Many oil and gas reservoirs in Tertiary strata of southern Louisiana are located close to the interface between a sand-rich, normally pressured sequence and an underlying sand-poor, overpressured sequence. This association, recognized for many years by Gulf Coast explorationists, is revisited here because of its relevance to an assessment of undiscovered oil and gas potential in the Gulf Coast of Louisiana. The transition from normally pressured to highly overpressured sediments is documented by converting mud weights to pressure, plotting all pressure data from an individual field as a function of depth, and selecting a top and base of the pressure transition zone. Vertical extents of pressure transition zones in 34 fields across southern onshore Louisiana range from 300 to 9000 ft and are greatest in younger strata and in the larger fields. Display of pressure transition zones on geologic cross sections illustrates the relative independence of the depth of the pressure transition zone and geologic age. Comparison of the depth distribution of pressure transition zones with production intervals confirms previous findings that production intervals generally overlap the pressure transition zone in depth and that the median production depth lies above the base of the pressure transition zone in most fields. However, in 11 of 55 fields with deep drilling, substantial amounts of oil and gas have been produced from depths deeper than 2000 ft below the base of the pressure transition zone. Mud-weight data in 7 fields show that "local" pressure gradients range from 0.91 to 1.26 psi/ft below the base of the pressure transition zone. Pressure gradients are higher and computed effective stress gradients are negative in younger strata in coastal areas, indicating that a greater potential for fluid and sediment movement exists there than in older Tertiary strata.

  8. Numerical and experimental study of strata behavior and land subsidence in an underground coal gasification project

    NASA Astrophysics Data System (ADS)

    Sirdesai, N. N.; Singh, R.; Singh, T. N.; Ranjith, P. G.

    2015-11-01

    Underground Coal Gasification, with enhanced knowledge of hydrogeological, geomechanical and environmental aspects, can be an alternative technique to exploit the existing unmineable reserves of coal. During the gasification process, petro-physical and geomechanical properties undergo a drastic change due to heating to elevated temperatures. These changes, caused due to the thermal anisotropy of various minerals, result in the generation of thermal stresses; thereby developing new fracture pattern. These fractures cause the overhead rock strata to cave and fill the gasification chamber thereby causing subsidence. The degree of subsidence, change in fluid transport and geomechanical properties of the rock strata, in and around the subsidence zone, can affect the groundwater flow. This study aims to predict the thermo-geomechanical response of the strata during UCG. Petro-physical and geomechanical properties are incorporated in the numerical modelling software COMSOL Multiphysics and an analytical strength model is developed to validate and further study the mechanical response and heat conduction of the host rock around the gasification chamber. Once the problems are investigated and solved, the enhanced efficiency and the economic exploitation of gasification process would help meet country's energy demand.

  9. Numerical Modeling of Mechanical Behavior for Buried Steel Pipelines Crossing Subsidence Strata

    PubMed Central

    Han, C. J.

    2015-01-01

    This paper addresses the mechanical behavior of buried steel pipeline crossing subsidence strata. The investigation is based on numerical simulation of the nonlinear response of the pipeline-soil system through finite element method, considering large strain and displacement, inelastic material behavior of buried pipeline and the surrounding soil, as well as contact and friction on the pipeline-soil interface. Effects of key parameters on the mechanical behavior of buried pipeline were investigated, such as strata subsidence, diameter-thickness ratio, buried depth, internal pressure, friction coefficient and soil properties. The results show that the maximum strain appears on the outer transition subsidence section of the pipeline, and its cross section is concave shaped. With the increasing of strata subsidence and diameter-thickness ratio, the out of roundness, longitudinal strain and equivalent plastic strain increase gradually. With the buried depth increasing, the deflection, out of roundness and strain of the pipeline decrease. Internal pressure and friction coefficient have little effect on the deflection of buried pipeline. Out of roundness is reduced and the strain is increased gradually with the increasing of internal pressure. The physical properties of soil have a great influence on the mechanical properties of buried pipeline. The results from the present study can be used for the development of optimization design and preventive maintenance for buried steel pipelines. PMID:26103460

  10. Stable isotopic perturbation at the Ordovician-Silurian transition in NE Poland

    SciTech Connect

    Hoffman, A.; Gruszczynski, M.; Malkowski, K. . Paleobiology Inst.); Satir, M. ); Halas, S. . Physics Inst.)

    1992-01-01

    An interpretation of the time series of stable isotopic proportions of carbon, oxygen, and sulfur in rock samples from subsurface Ordovician-Silurian transition in north-eastern Poland demonstrates a clearcut perturbation that must imply some global scale controlling factors. This perturbation is particularly emphasized by its comparison to the sustained secular Paleozoic trend in isotopic characteristics of the oceanic system. On the other hand, this isotopic perturbation contrasts with unidirectional local changes in geochemical elemental proportions in the same rock samples. The perturbation is most parsimoniously explained as linked to the onset of a major glaciation. Its relationship to the second largest mass extinction in the history of the biosphere still remains to be elucidated.

  11. Testing for possible cyclicity in carbonate sediments of Middle Ordovician of east Tennessee

    SciTech Connect

    Ghazizadeh, M.; Walker, K.R.

    1986-05-01

    Middle Ordovician carbonate sediments (Chickamauga Group) near Decatur, Tennessee, consist of 450 m of complex tidal-flat and subtidal sediments. Fourteen facies are recognized: (1) cherty dolostone (supratidal environment); (2) green and red silty mudstone (supratidal mud flat); (3) greenish-gray micrite-biomicrite (supratidal mud flat); (4) red silty, intrapelbiosparite-biosparite (intertidal channel); (5) green and red, loosely packed, ostracod-rich pelbiomicrite (intertidal pond); (6) stromatolitic mudstone (intertidal levee); (7) bryozoan-ostracod-brachiopod-rich pelbiomicrite (subtidal lagoon type I); (8) silty, packed pelbiomicrite-pelbiosparite (subtidal lagoon type II); (9) ostracod-gastropod-rich, bioturbated pelbiomicrite (subtidal lagoon type III); (10) bioturbated brachiopod-molluscan-rich biomicrite (subtidal lagoon type IV); (11) bioturbated green and red silty mudstone to silty sparse biomicrite (lagoon); (12) gray-tan mudstone to sparse biomicrite (quiet water, deeper subtidal lagoon); (13) intrapelbiosparite-pelbiosparite (subtidal channel); and (14) Tetradium-rich packstone (subtidal wave baffle).

  12. Carbonate-shelf depositional environments of the Ordovician Viola formation in South-Central Kansas

    USGS Publications Warehouse

    Newell, K.D.

    2000-01-01

    The Upper Ordovician Viola Formation, an important petroleum reservoir in the Midcontinent, is a carbonate unit present over much of the subsurface in Kansas. The Viola is composed of two fining-upward sedimentary packages that are separated from each other by a minor karstic surface representing a brief period of exposure. Each package represents a third-order sedimentary cycle and consists of an echinoderm-rich packstone overlain by a thicker lime mudstone. The echinoderm-rich packstone was deposited nearshore in agitated waters, but subsequently was bioturbated. The overlying lime mudstone was deposited in deeper, quiet waters, and locally contains storm-deposited carbonate sands. Subtle growth of the Central Kansas Arch and Pratt Anticline (structures transecting the depositional shelf) is indicated by packstones and grainstones being thicker over these arches, whereas finer grained lithologies dominate in basinal areas on the arch flanks. Structureless lime mudstones, probably intensely bioturbated, grade into laminated lime mudstones farther basinward.

  13. Evidence of a tectonically driven sequence succession in the Middle Ordovician Taconic foredeep

    NASA Astrophysics Data System (ADS)

    Joy, Michael P.; Mitchell, Charles E.; Adhya, Soumava

    2000-08-01

    The late Mohawkian through early Cincinnatian (Ordovician) Trenton Group carbonates and coeval siliciclastic succession of the central Mohawk Valley, New York State, were deposited in a foreland basin during the Taconic orogeny. Development of this facies mosaic records changes in stacking patterns that took place during episodic basin deepening and simultaneous carbonate-ramp shallowing along a ramp to basin transect located on the distal slope of the foreland basin. Differential rates of subsidence across the region produced accommodation rates that increased by an order of magnitude from west to east. High rates of siliciclastic sediment supply and even higher subsidence rates resulted in a thick, deep-water succession in the eastern part of the study region. The coeval Trenton Group succession in the west formed under conditions of moderate sediment supply and lower subsidence rate, resulting in a net shallowing-upward succession. These relationships suggest that active margin tectonism was the proximate cause of the Mohawk Valley facies architecture.

  14. Ordovician-Silurian tectonism in northern California:The Callahan event

    NASA Astrophysics Data System (ADS)

    Cotkin, Spencer J.

    1992-09-01

    Middle Ordovician to Early Silurian volcanism, plutonism, metamorphism, deformation, and sedimentation in the Yreka and Trinity terranes, eastern Klamath Mountains, northern California, are considered to be related phenomena that occurred in response to an episode of tectonism known as the Callahan event. A diverse array of evidence is used to construct a tectonic model for the Callahan event that involves a subduction zone, a magmatic arc, and a back-arc spreading center, and to show that tectonism likely occurred within the framework of the North American continental margin. Evidence pertaining to subduction polarity is meager, but is consistent with an eastward dip. The Callahan event represents the earliest Phanerozoic convergent-margin tectonic event recognized within the U.S. Cordillera.

  15. Eurypterid trackways from the Table Mountain Group (Ordovician) of South Africa

    NASA Astrophysics Data System (ADS)

    Braddy, Simon J.; Almond, John E.

    1999-07-01

    Eurypterid trackways in paralic facies of the Graafwater and Peninsula Formations, lower Table Mountain Group (Ordovician) of the Western Cape Province, South Africa, are reviewed. The ichnotaxonomy of trackways preserved on the 'Brandenburg slab' from the Graafwater area is reassessed, with the recognition of two distinct forms: (1) Palmichnium capensis (Anderson, 1975), consisting of a series of four tracks, many accessory imprints and (usually) an intermittent bilobed medial impression; and (2) Petalichnus brandenburgensis isp. nov., a much narrower trackway with nine to ten tracks per series and no medial impression. Palmichnium capensis is interpreted as the locomotory trace of an onychopterellan eurypterid (Chelicerata: Eurypterida). Petalichnus brandenbergensis is provisionally ascribed to the Trilobita. The likely walking techniques employed by onychopterellan eurypterids are assessed from the revised ichnological evidence, comparisons with extant taxa and modelling procedures; subaqueous locomotion was achieved by a series of short hops across the substrate and on land these animals were slow-moving and cumbersome, employing an ungainly, undulatory gait.

  16. The anatomy, taphonomy, taxonomy and systematic affinity of Markuelia: Early Cambrian to Early Ordovician scalidophorans

    USGS Publications Warehouse

    Dong, X.-P.; Bengtson, S.; Gostling, N.J.; Cunningham, J.A.; Harvey, T.H.P.; Kouchinsky, A.; Val'Kov, A.K.; Repetski, J.E.; Stampanoni, M.; Marone, F.; Donoghue, P.C.J.

    2010-01-01

    Markuelia is a vermiform, annulated introvertan animal known as embryonic fossils from the Lower Cambrian to Lower Ordovician. Analysis of an expanded and revised dataset for Introverta shows that the precise position of Markuelia within this clade is dependent on the taxa included. As a result, Markuelia is assigned to the scalidophoran total group to reflect uncertainty as to whether it is a stem-scalidophoran or a stem-priapulid. The taxonomy of the genus is revised to provide an improved taxonomic framework for material assigned to Markuelia. Five species are recognized: M. secunda Val'kov, M. hunanensis Dong and Donoghue, M. lauriei Haug et al., M. spinulifera sp. nov. and M. waloszeki sp. nov. Finally, the preservation of Markuelia is evaluated in the light of both the taphonomy of the fossil embryos themselves and the experimental taphonomy of the priapulid Priapulus caudatus, which has been proposed as both a close relative and an anatomical analogue of Markuelia. ?? The Palaeontological Association.

  17. Unraveling the Phylogenetic Relationships of the Eccoptochilinae, an Enigmatic Array of Ordovician Cheirurid Trilobites

    PubMed Central

    Gapp, I. Wesley; Congreve, Curtis R.; Lieberman, Bruce S.

    2012-01-01

    The Cheiruridae are a diverse group of trilobites and several subfamilies within the clade have been the focus of recent phylogenetic studies. This paper focuses on the relationships of one of those subfamilies, the Ordovician Eccoptochilinae. We analyze sixteen species from six genera within the traditionally defined group, using the pilekiid Anacheirurus frederici as an outgroup. To assess the monophyly of the Eccoptochilinae seven sphaerexochine species, Kawina arnoldi, Sphaerexochus arenosus, S. atacius, S. latifrons, S. mirus, S. parvus, and S. scabridus were included in the analysis as well. The results of this analysis show that the genus Eccoptochile represents a paraphyletic grade and species traditionally assigned to Parasphaerexochus and Skelipyx plot within Pseudosphaerexochus. Also, representative species of Sphaerexochinae plot within the traditionally defined Eccoptochilinae, suggesting Eccoptochilinae itself is paraphyletic. To resolve this, we propose all species of Pseudosphaerexochus be placed within Sphaerexochinae and Eccoptochilinae be restricted to a monotypic Eccoptochile clavigera. PMID:23173046

  18. Distal orogenic effects on peripheral bulge sedimentation: Middle and Upper Ordovician of the Nashville Dome

    SciTech Connect

    Holland, S.M.; Patzkowsky, M.E.

    1997-03-01

    A major switch in depositional style in the Ordovician carbonates of the Nashville Dome corresponds closely with the onset of the late Middle Ordovician Taconic orogeny. This time marks a shift from tropical-type to temperate-type carbonates, the initiation of widespread major phosphate deposition, the introduction of large amounts of terrigenous silt and clay, the occurrence of widespread seismically induced soft-sediment deformation, and a change from a low-energy flat-topped carbonate shelf to a high-energy doubly dipping carbonate ramp. Soft-sediment deformation and the introduction of siliciclastics are direct effects of the Taconic orogeny; the switch from tropical-type to temperate-type carbonates, the initiation of phosphate deposition, and the switch in carbonate ramp are largely oceanographic effects triggered by the orogeny. In particular, phosphate deposition and the switch to temperate-type limestones appears to have been driven by upwelling along the eastern side of the Nashville Dome within the newly deepened Taconic foreland basin. A fourfold decrease in the rate of relative sea-level rise occurred on the Nashville Dome nearly 3 m.y. following the onset of thrusting and foreland basin initiation. Subsidence rates were constant before and after this decrease, and no evidence of a change in subsidence rates is seen to coincide with the onset of thrusting. The slowing of subsidence may reflect viscoelastic uplift of the Nashville Dome, but the abrupt change from one constant subsidence rate to another is not predicted by existing foreland basin models.

  19. Diagenesis of the Cambro-Ordovician sedimentary rocks of west-central Wisconsin

    SciTech Connect

    Carpenter, T.L.; Hooper, R.L. . Dept. of Geology)

    1994-04-01

    Shales and siltstones of the Cambro-Ordovician sedimentary rocks of west-central Wisconsin record a complex history of diagenesis. This study examined clays and other minerals within clay-rich layers from fresh surface outcrops of the Cambro-Ordovician sedimentary rocks using XRD and SEM/EDX. Feldspar authigenesis in the base of the Mt. Simon Fm. represents the earliest recorded period of authigenesis. These early formed feldspars ([approximately] 60[mu]M in size) have been completely pseudomorphed by kaolinite. These feldspathization and kaolinization events are limited to the lower 80 feet of the Mt. Simon Fm. Later periods of authigenesis resulted in corrosion of the kaolinite, feldspar authigenesis and illitization with production of I/S ([approximately] 90%I) and minor neoformed filamentous illite throughout the section from the base of the Mt Simon Fm. to at least the Glenwood Fm. In rare instances the filamentous illites have been replaced by kaolinite during a second period of kaolinization. Some of the shales contain abundant authigenic pyrite and at least two generations of authigenic gypsum. Complete dissolution of K-feldspars within some of the samples is evidenced by the presence of small euhedral pits in phosphatic brachiopod shells and suggests that organic acids may have played a role in the diagenesis. The complexity of the authigenic relationships identified in these rocks indicates that they have been subjected to multiple periods of diagenesis with fluids of divergent compositions. This is most readily explained if the rocks behaved as an open system with periodic flushing of K-rich and K-poor fluids.

  20. Hydrocarbon biomarkers from Ordovician sediments and the fossil alga Gloeocapsomorpha prisca Zalessky 1917

    NASA Astrophysics Data System (ADS)

    Hoffmann, C. F.; Foster, C. B.; Powell, T. G.; Summons, R. E.

    1987-10-01

    Numerous Ordovician oils worldwide are known to show unusual and distinctive distributions of hydrocarbons which, it has been suggested, are derived from a "unique benthonic mat-forming non-photosynthetic prokaryotic organism", Gloeocapsomorpha prisca Zalessky 1917, which is the major contributor of organic matter. Organic matter-rich sediments from the Canning and Amadeus Basins of Australia, known to contain G. prisca fossils and to have the characteristic predominance of odd carbon number (C 13-C 19) n-alkanes, were investigated to determine other hydrocarbon distributions. Sediments from both basins contained abundant n-alkylcyclohexanes with odd carbon number predominance (C 13-C 19) and methyl- n-alkylcyclohexanes (C 14-C 20) which, in immature sediments, showed an even carbon number predominance. The isomer distribution of these latter compounds was determined by direct comparison with synthetic standards. The sediments from both basins also contained very similar distributions of steranes and pentacyclic triterpanes and the derived kerogens had a characteristically light carbon isotope signature. Pyrolysis of a G. prisca-rich kerogen yielded a hydrocarbon mixture with a similar composition to the sediment extract, except that there was a marked increase in the relative abundance of pristane, phytane, alkylcyclohexanes, steranes and hopanes relative to n-alkanes. We argue on the basis of the geological, geochemical and palynological data that G. prisca was probably planktonic, photosynthetic and very possibly eukaryotic and that the striking character of Ordovician oils and sediments derive from bacterial and other diagenetic imprints superimposed on the primary signature of this organism.

  1. Black shale source rocks and oil generation in the Cambrian and Ordovician of the central Appalachian Basin, USA

    USGS Publications Warehouse

    Ryder, R.T.; Burruss, R.C.; Hatch, J.R.

    1998-01-01

    Nearly 600 million bbl of oil (MMBO) and 1 to 1.5 trillion ft3 (tcf) of gas have been produced from Cambrian and Ordovician reservoirs (carbonate and sandstone) in the Ohio part of the Appalachian basin and on adjoining arches in Ohio, Indiana, and Ontario, Canada. Most of the oil and gas is concentrated in the giant Lima-Indiana field on the Findlay and Kankakee arches and in small fields distributed along the Knox unconformity. Based on new geochemical analyses of oils, potential source rocks, bitumen extracts, and previously published geochemical data, we conclude that the oils in both groups of fields originated from Middle and Upper Ordovician blcak shale (Utica and Antes shales) in the Appalachian basin. Moroever, we suggest that approximately 300 MMBO and many trillions of cubic feet of gas in the Lower Silurian Clinton sands of eastern Ohio originated in the same source rocks. Oils from the Cambrian and Ordovician reservoirs have similar saturated hydrocarbon compositions, biomarker distributions, and carbon isotope signatures. Regional variations in the oils are attributed to differences in thermal maturation rather than to differences in source. Total organic carbon content, genetic potential, regional extent, and bitument extract geochemistry identify the balck shale of the Utica and Antes shales as the most plausible source of the oils. Other Cambrian and Ordovician shale and carbonate units, such as the Wells Creek formation, which rests on the Knox unconformity, and the Rome Formation and Conasauga Group in the Rome trough, are considered to be only local petroleum sources. Tmax, CAI, and pyrolysis yields from drill-hole cuttings and core indicate that the Utica Shale in eastern and central Ohio is mature with respect to oil generation. Burial, thermal, and hydrocarbon-generation history models suggest that much of the oil was generated from the Utica-Antes source in the late Paleozoic during the Alleghanian orogeny. A pervasive fracture network

  2. Structural Determinants of Drug Partitioning in Surrogates of Phosphatidylcholine Bilayer Strata

    PubMed Central

    Lukacova, Viera; Natesan, Senthil; Peng, Ming; Tandlich, Roman; Wang, Zhanbin; Lynch, Sandra; Subramaniam, Rajesh; Balaz, Stefan

    2013-01-01

    The knowledge of drug concentrations in bilayer headgroups, core, and at the interface between them is a prerequisite for quantitative modeling of drug interactions with many membrane-bound transporters, metabolizing enzymes and receptors, which have the binding sites located in the bilayer. This knowledge also helps understand the rates of trans-bilayer transport because balanced interactions of drugs with the bilayer strata lead to high rates, while excessive affinities for any stratum cause a slowdown. Experimental determination of bilayer location is so tedious and costly that the data are only available for some fifty compounds. To extrapolate these valuable results to more compounds at a higher throughput, surrogate phases have been used to obtain correlates of the drug affinities for individual strata. We introduced a novel system, consisting of a diacetyl phosphatidylcholine (DAcPC) solution with the water content of the fluid bilayer as the headgroup surrogate and n-hexadecane (C16) representing the core. The C16/DAcPC partition coefficients were measured for 113 selected compounds, containing structural fragments that are frequently occurring in approved drugs. The data were deconvoluted into the ClogP-based fragment solvation characteristics and processed using a solvatochromic correlation. Increased H-bond donor ability and excess molar refractivity of compounds promote solvation in the DAcPC phase as compared to bulk water, contrary to H-bond acceptor ability, dipolarity/polarizability, and volume. The results show that aromates have more balanced distribution in bilayer strata, and thus faster trans-bilayer transport, than similar alkanes. This observation is in accordance with the frequent occurrence of aromatic rings in approved drugs and with the role of rigidity of drug molecules in promoting intestinal absorption. Bilayer locations, predicted using the C16/DAcPC system, are in excellent agreement with available experimental data, in contrast to

  3. Paleogeographic and structural setting of Miocene strata in central western Nevada

    SciTech Connect

    Stewart, J.H. )

    1993-04-01

    Late Cenozoic sedimentary rocks as old as 19 Ma are widely distributed in central western Nevada. They are greatly more abundant than older Cenozoic strata and are commonly interpreted to have formed in fault-bounded basins that mark the onset of widespread extension in the Basin and Range Province. Miocene strata are largely coeval with a magmatic arc that extended south southeast near the boundary of the Basin and Range and Sierra Nevada Provinces. This arc produced voluminous andesitic flows and lahars that locally interfinger with the Miocene strata. Miocene depositional basins apparently varied greatly in size. The largest that can be defined clearly is the Esmeralda Basin that was at least 65 km long and 45 km wide. Other basins may have been larger but are difficult to reconstruct; still other basins may be small and isolated, particularly within the magmatic arc. Lacustrine deposits and minor interfingering deltaic and distal fluvial units predominate; near-source, coarse alluvial-fan and megabreccia landslide deposits are locally conspicuous. coarse near-source deposits, particularly landslide deposits, are interpreted to be adjacent to basin-bounding normal faults. The Esmeralda, Coal Valley, and Gabbs Valley-Stewart Valley-Tonopah Basins are interpreted to be related to large-scale Miocene extension. Other basins may be (1) pull-apart structures related to strike-slip faults, (2) downdropped blocks in areas of cross-cutting normal and/or strike-slip faults related to changes in the extension direction or (3) grabens or half-grabens related to uniform extension. Younger Cenozoic basins, including present-day basins, overprint and cut across the Miocene basins.

  4. Tide-dominated delta model for coal-bearing Wilcox strata in south Texas

    SciTech Connect

    Breyer, J.A.

    1984-04-01

    Coal-bearing Wilcox strata near Uvalde in south Texas are the deposits of a tide-dominated delta. The delta of the Klang and Langat Rivers, Malaysia, provides a modern analog for these strata. Five facies have been identified from a study of core and well logs: lignite; underclay; interbedded sand and mud with lenticular, wavy, and flaser bedding; ripple-laminated or cross-bedded sand; and greenish, very strongly bioturbated sand. On the Klang-Langat delta, the modern equivalents of these facies are peat formed in fresh water swamps; root horizons developed beneath the peat; interbedded sand and mud deposited on tidal flats; channel sands; and shallow marine sand and mud. Tidal flat deposits are the most abundant type of sediment on the Klang-Langat delta and in the coal-bearing Wilcox strata. The tidal flats of the modern delta are crossed by small tidal creeks and by larger tidal streams. The tidal channels are cut into tidal flat sediments and separate peat-forming areas. Channel sands in the Wilcox are cut into tidal flat deposits and form washouts in the lignite. Two types of channel-fill sand are present in the Wilcox, sands 5-15 ft (1.5-4.5 m) thick and sands more than 30 ft (9m) thick. The thinner sands, deposits of small tidal creeks, have sharp, erosive bases, fine upward and pass into interbedded sand and mud. The thicker sands have sharp tops as well as sharp bases and show no grain-size trends; they are fills of larger tidal streams.

  5. Study of the strata formation during the explosion of foils in vacuum

    NASA Astrophysics Data System (ADS)

    Zhigalin, A. S.; Rousskikh, A. G.; Oreshkin, V. I.; Chaikovsky, S. A.; Ratakhin, N. A.; Khishchenko, K. V.; Baksht, R. B.

    2015-11-01

    The formation of the strata during fast explosion of metal foils at current densities of 0.1 GA/cm2 has been studied experimentally. To observe the strata, the soft x-ray radiation generated by an X-pinch was used. The study of the process of stratification during the foil explosion was carried out with a setup consisting of three generators. One of the generators (WEG-2), was operated to initiate the explosion of the foils, while the others (XPG radiographs) were used for diagnostics. The generator WEG-2 has the capacitance of 250 nF, the charge voltage of 20 kV, and the current rate of 16 A/ns. The radiographs XPG have the capacitance of 1 μF, the charge voltage of 43 kV, the current of 300 kA, and the current rise time of 180 ns. X-pinch produced by four Mo wires was a load for the radiographs. The delay between the operation of the WEG-2 and XPG generators was set using a DPG trigger pulse generator. We performed the experiments with the Al and Cu foils. The length of foil was 2 cm, the foil width was 1 mm, and the foil thickness was 6 μm. It has been revealed that strata were formed early in the explosion, i.e. at the stage when the metal melted. Analysis of the experimental results suggests that the most probable reason for the stratification is the thermal instability developing because of the increase in resistivity of the foil metal with temperature.

  6. Growth status of small for gestational age Indian children from two socioeconomic strata

    PubMed Central

    Khadilkar, Vaman V.; Mandlik, Rubina M.; Palande, Sonal A.; Pandit, Deepa S.; Chawla, Meghna; Nadar, Ruchi; Chiplonkar, Shashi A.; Kadam, Sandeep S.; Khadilkar, Anuradha A.

    2016-01-01

    Aims: To assess growth and factors associated with growth in children born small for gestational age (SGA) from two socioeconomic strata in comparison to age- and sex-matched healthy controls. Methods: Retrospective study conducted at two hospitals in Pune, 0.5–5 years, 618 children: 189-SGA from upper socioeconomic strata (USS), 217-SGA from lower socioeconomic strata (LSS), and 212 appropriate for gestational age healthy controls were randomly selected. Birth and maternal history, socioeconomic status, length/height, and weight of children were recorded. Anthropometric data were converted to Z scores (height for age Z-score [HAZ], weight for age Z-score [WAZ]) using WHO AnthroPlus software. Results: The HAZ and WAZ of the SGA group were significantly lower as compared to the controls and that of the LSS SGAs were lower than USS SGAs (P < 0.05). Thirty two percent children were stunted (HAZ <−2.0) in USS and 49% in LSS (P < 0.05). Twenty nine percent children in the USS SGA group were stunted at 2 years and 17% at 5 years. In the LSS SGA group, 54% children were stunted at 2 years and 46% at 5 years. Generalized linear model revealed normal vaginal delivery (β = 0.625) and mother's age (β =0.072) were positively associated and high SES (β = −0.830), absence of major illness (β = −1.01), higher birth weight (β = −1.34) were negatively associated for risk of stunting (P < 0.05). Conclusion: Children born SGA showed poor growth as compared to controls. Special attention to growth is necessary in children from LSS, very low birth weight babies, and those with major illnesses during early years of life. PMID:27366721

  7. Seismic evidence for Mesozoic strata in the northern Nansha waters, South China Sea

    NASA Astrophysics Data System (ADS)

    Wang, Yanlin; Qiu, Yan; Yan, Pin; Zheng, Hongbo; Liu, Hailing; Wang, Jun

    2016-05-01

    According to previous studies, Mesozoic deposits have been unequivocally identified in the northeastern Nansha waters (southern margin of the South China Sea, SCS). Thick lower structural layers in the north Nansha waters have not clearly been identified as either Mesozoic or Cenozoic strata. These strata are characterized by strong top erosion, tilted layer or folded anticlines. New long-offset multi-channel seismic data show refracted phases from the top of the lower structural layer in the northern Nansha waters. A major velocity leap (approximately from 1.6 km/s to 3.8 km/s or 2.9 km/s to 5.3 km/s), calculated from the refraction wave of seismic data, is found across a prominent angular unconformity, indicating a major sedimentary hiatus. According to the stratigraphic characteristics and velocity range of the lower structural layer, velocity leap at the top of lower structural layer and ubiquitous absence of upper Cretaceous strata in the Nansha waters, the lower structural layer of the northern Nansha waters are interpreted as Mesozoic. Based on the similarities in stratigraphic characteristics of the lower structural layers between the northern and central Nansha waters, previous studies from gravity data and multi-channel seismic data, we propose that lower structural layers over central Nansha waters may also Mesozoic. This further suggests that the intensity of upper crustal extension was moderate in Nansha waters during the Cenozoic, which related to a combination of the Cenozoic slab pull of the proto-SCS and lithosphere delamination over an ancient orogenic belt between the northern and southern continental margins of the SCS, which may weaken extension of upper crust over the Nansha waters.

  8. Ordovician meteoric carbon and oxygen isotopic values: Implications for the latitudinal variations of ancient stable isotopic values

    USGS Publications Warehouse

    Tobin, K.J.; Steinhauff, D.M.; Walker, K.R.

    1999-01-01

    Columnar and clear blocky calcite cement from a Middle Ordovician carbonate succession in east Tennessee is interpreted as meteoric in origin. Columnar and clear blocky calcite from this succession does not show extremely large 13C depletions reported from meteoric phases of younger rocks. Meteoric fluid ??18O values calculated from clear blocky calcite are ??? 2 to 3??? more negative than approximately coeval sea water; a relationship typical of modern, low-latitude, coastal meteoric water. Comparison with meteoric ??18O values from Ordovician units elsewhere suggests that the geographic distribution of these values may be broadly similar to that observed today. Therefore, we tentatively suggest that geographic distribution of meteoric ??18O values during both icehouse and greenhouse eras are similar.

  9. Paleomagnetic poles and polarity zonation from Cambrian and Devonian strata of Arizona

    USGS Publications Warehouse

    Elston, D.P.; Bressler, S.L.

    1977-01-01

    Basal Paleozoic Tapeats Sandstone (Early and Middle Cambrian) in northern and central Arizona exhibits mixed polarity and a low-latitude paleomagnetic pole. Carbonates of Middle and early Late Cambrian age, and directly superposed carbonate and carbonate-cemented strata of latest Middle(?) and early Late Devonian age, are characterized by reversed polarity and high-latitude poles. The high-latitude Middle Cambrian pole, which appears to record a large but brief excursion of the polar wandering path, is considered provisional pending additional work. The Devonian data from Arizona indicate that a shift of the pole to a "late Paleozoic" position had occurred by Middle Devonian time. ?? 1977.

  10. Reconstruction of Eolian Bedforms from Cross-Bedded Strata at Victoria Crater, Meridiani Planum, Mars

    NASA Astrophysics Data System (ADS)

    Hayes, A. G.; Grotzinger, J. P.; Squyres, S. W.; Lewis, K.; Metz, J.; Bell, J. F.; Athena Science Team

    2007-12-01

    Outcrop exposures imaged by the Opportunity rover at Meridiani Planum have depicted cross-bedded strata with geometries and scales similar to eolian and subaqeous deposits on Earth. On Earth preserved cross-strata are rich in geologic information, providing insight into the depositional environment and sediment transport directions. The high-resolution stratigraphy of these cross-bedded strata can be used to reconstruct sedimentary bedforms on Mars to infer formation process and describe the depositional environment. Meter-scale cross bedding at Victoria Crater is similar to terrestrial eolian deposits and is interpreted as a dry dune field. Sets of cross-strata in the Cape St. Vincent and Cape St. Mary sections of Victoria Crater are comparable to Jurassic-age eolian deposits of the western US. The Opportunity Rover has spent ~300 sols traversing 90 degrees of the rim of Victoria crater, obtaining images of rock outcrops exposed by several promontories along the way. The outcrops at the Cape St. Mary and Cape St. Vincent promontories, which are located at opposite ends of the traverse, have proven to be the best examples of meter scale cross-bedding observed on Mars to date. Super-resolution imaging techniques and long baseline stereo observations were utilized during an extended imaging campaign of both outcrop faces. Cape St. Mary is characterized by meter-scale trough-style cross bedding, suggesting sinuous crested dunes with scour pits migrating perpendicular to the outcrop face. Cape St. Vincent, which is striking 110° away from Cape St. Mary, has layering indicative of a single climbing bedform with dune heights of several meters. The findings at Cape St. Mary and Cape St. Vincent are combined with other bedding faces to produce an eolian deposition model for layering exposed at Victoria Crater. Any depositional model used to explain the bedding must conform to an observed N-S paleo-flow direction. In addition to bedded layering, a bright band is observed

  11. Integrated depositional model for the Cenomanian Turonian organic-rich strata in North Africa

    NASA Astrophysics Data System (ADS)

    Lüning, S.; Kolonic, S.; Belhadj, E. M.; Belhadj, Z.; Cota, L.; Barić, G.; Wagner, T.

    2004-01-01

    During the Late Cenomanian-Early Turonian (C/T) Oceanic Anoxic Event (OAE2), organic-rich strata was deposited in rift shelf basins and slopes across North Africa and in deep-sea basins of the adjacent oceans. Based on a review of published and unpublished information, this paper documents the distribution and organic-richness of C/T strata across the whole region within a palaeogeographic framework and systematically analyses the conditions and processes, which controlled their deposition. Previously, the C/T in North Africa has been most intensively studied in southern Morocco (Tarfaya) and Tunisia. Only little data is availabe for other parts of North Africa, namely Algeria, Libya and Egypt, because distribution of C/T Corg strata there becomes more patchy. A general decrease in peak organic richness and black shale thickness occurs from west to east, partly as a result of upwelling along the Moroccan Atlantic coast and the absence of upwelling in the eastern Mediterranean area. Furthermore, in the confined central Atlantic, the oxygen minimum zone (OMZ) in many places reached down to the deep-sea floor (3-4 km), while the lower limit of the OMZ along the North African Tethys was much shallower and underlain by oxic water masses. As documented by high resolution biostratigraphic and chemostratigraphic data, C/T black shale deposition in most areas outside the upwelling zone are restricted to a strong, eustatic, latest Cenomanian transgressive phase. Triggered by this sea-level rise, the OMZ impinged onto the North African continental shelf and the margins of intrashelf basins, which mostly formed during the Early Cretaceous as halfgrabens. Important units containing C/T organic-rich strata in the region are the Atlantic Tarfaya black shales (Morocco, Western Sahara), black shales and phtanites in the Moroccan and Algerian Atlas, the Bahloul Fm. in the SE Constantine Basin and in northern and central Tunisia, the Etel Fm. in the Sirte Basin, the Al Hilal Fm. in

  12. The Occurrence of Knickpoints in Soluble Strata in the Buffalo River Basin, Arkansas

    NASA Astrophysics Data System (ADS)

    Thaler, E.; Covington, M. D.; Myre, J. M.; Perne, M.; Holcomb, G.

    2014-12-01

    Prior field and theoretical work has suggested that bedrock channels adjust to lower stream power when encountering highly soluble strata, exhibiting an increase in channel width and/or a decrease in channel slope. However, in apparent contradiction to this expectation, many channels within the Buffalo River Basin, Arkansas, contain knickpoints, in the form of waterfalls and slot canyons, that are developed at the contact between the Mississippian Batesville Sandstone and the underlying Boone Limestone. To improve understanding of bedrock channel response to contrasts in rock solubility, longitudinal surveys were conducted in three channels that cross the Boone Limestone. Additionally, channel widths and a profile were obtained for the main stem of the Buffalo River using aerial photography and a digital elevation model. Schmidt scores for the Boone and Batesville suggest that the two strata have similar compressive strengths, which is a measure of relative resistance to mechanical erosion. Two of the four studied reaches show significant knickpoint development, and in both cases the basin area above the knickpoint is less than 3 km2. One possible explanation is that these knickpoints have been arrested at a critical threshold basin area. However, at least four other such knickpoints are known from the area, and in all cases the knickpoint is highly correlated to the contact rather than a specific basin area, suggesting that the properties of the strata are an important factor. We identify three potential mechanisms that may often act in concert to develop knickpoints at contacts with underlying soluble rocks. (1) If chemical erosion in the soluble reach outpaces uplift, and knickpoint retreat through the overlying layer is sufficiently slow, then a knickpoint will develop. (2) Karstification can divert geomorphic work to the subsurface, resulting in a steep surface channel and possible stalling of upstream knickpoint migration within the soluble strata. (3) The

  13. Regional structural cross sections, mid-permian to quaternary strata, Texas Panhandle and Eastern New Mexico

    SciTech Connect

    McGookey, D.A.; Gustavson, T.C.; Hoadley, A.D.

    1989-01-01

    Twelve regional cross sections (with text) of the Palo Duro, Dalhart, and Anadarko Basins illustrating the tabular geometry of Permian evaporite beds, areas where salt has been lost by dissolution, and the effects of dissolution-induced subsidence on Permian and post-Permian strata. The authors identify areas of dissolution beneath the High Plains, the Caprock Escarpment, the Rolling Plains, the Pecos Plains, and along the Canadian River valley. The cross sections are printed at a vertical scale of 1 inch equals 400 feet and a horizontal scale of 1 inch equals approximately 8 miles and were constructed using geophysical logs, sample logs, and surficial geologic data.

  14. Algebraic varieties in the Birkhoff strata of the Grassmannian Gr(2): Harrison cohomology and integrable systems

    NASA Astrophysics Data System (ADS)

    Konopelchenko, B. G.; Ortenzi, G.

    2011-11-01

    The local properties of the families of algebraic subsets Wg in the Birkhoff strata Σ2g of Gr(2) containing the hyperelliptic curves of genus g are studied. It is shown that the tangent spaces Tg for Wg are isomorphic to the linear spaces of 2-coboundaries. Particular subsets in Wg are described by the integrable dispersionless coupled KdV systems of hydrodynamical type defining a special class of 2-cocycles and 2-coboundaries in Tg. It is demonstrated that the blows-ups of such 2-cocycles and 2-coboundaries and gradient catastrophes for associated integrable systems are interrelated.

  15. Palynology of Albian-Cenomanian strata in Mersa Matruh well, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Sultan, Ismail Z.

    Plant microfossils have been recovered from the Albian and lower Cenomanian strata encountered in Mersa Matruh well No. 1, drilled in the northern part of the Western Desert of Egypt. The microflora includes 56 miospore species belonging to 35 genera; most of them are derived from pteridophyte, gymnosperm and angiosperm vegetations. Differences in miospore assemblages of the Albian and Lower Cenomanian are described. Correlation with coeval palynofloral assemblages in West Africa and South and North America reveals that the Mersa Matruh area, Egypt belongs to the mid-Cretaceous African-South American phytogeoprovince.

  16. The Environmental Context of Gastropods on Western Laurentia (Basin and Range Province) During the Great Ordovician Biodiversification Event

    NASA Astrophysics Data System (ADS)

    Dahl, Robyn Mieko

    Gastropods are a major component of modern marine ecosystems and can be found in nearly every type of marine ecosystem. They experienced their first notable radiation during the Great Ordovician Biodiversification Event (~470 Ma), during which their diversity tripled. This study examines the gastropod assemblage preserved in the Basin and Range Province of the Western United States to establish the environmental context for the Ordovician gastropod radiation. Gastropods are present within every facies examined, but their relative abundance and distribution varies. Gastropods are rare in normal marine settings and abundant in harsh (i.e., dysoxic, hypersaline) environments. Their environmental context is shown to impact survivorship through the end-Ordovician extinction event and throughout the Paleozoic and Mesozoic. Collecting accurate density data for fossil deposits can prove challenging, especially when beds are not exposed in plane view. In these cases, paleontologists are tasked with reconstructing shellbed density from cross section exposure. This study presents a mathematical model to calculate the density of fossil material within a bed from bedding cross section counts. The model is calibrated against an Ordovician biofacies comprised of oncoids, macluritid gastropods and receptaculitids exposed in the Arrow Canyon Range of Southern Nevada, where unique preservation provides both cross section exposures and plan view of fossil concentrations. University Earth Science Departments seeking to establish impactful geoscience outreach programs often pursue large-scale, grant funded programs. While this type of outreach is highly successful, it is also extremely costly, and grant funding can be difficult to secure. Here, we present the Geoscience Education Outreach Program (GEOP), a small-scale, very affordable model tested over five years in the Department of Earth Sciences at UCR. GEOP provides a variety of outreach events and allows UCR Earth Sciences to

  17. Late Ordovician volcanism in Korea constrains the timing for breakup of Sino-Korean Craton from Gondwana

    NASA Astrophysics Data System (ADS)

    Cho, Deung-Lyong; Lee, Seung Ryeol; Koh, Hee Jae; Park, Jun-Beom; Armstrong, Richard; Choi, Duck K.

    2014-12-01

    In the early Paleozoic the Sino-Korean Craton (SKC) and South China Craton (SCC) were situated along the margin of east Gondwana. The SKC was connected to core Gondwana by an epeiric sea which was the site for deposition of lower Paleozoic sequences of SKC. The SKC and SCC may have drifted away from core Gondwana sometime during the mid-Paleozoic and would have been outboard microcontinents in the late Paleozoic, until they collided to form the East Asian continent in the Triassic. The breakup of SCC from Gondwana was suggested to have taken place at ∼380 Ma, while no reliable suggestions have hitherto been made for breakup of SKC from Gondwana. This study presents a convincing evidence for breakup of SKC from Gondwana, based on the recognition of Late Ordovician volcanism in Korea. New SHRIMP U-Pb zircon ages, 445.0 ± 3.7 Ma and 452.5 ± 3.2 Ma, are obtained from trachytic rocks of the Ongnyeobong Formation of Taebaeksan Basin in Korea which occupied the marginal part of the SKC in the early Paleozoic. This Late Ordovician volcanism along with previous records of Ordovician volcanic activities along the western margin of the SKC is interpreted indicating the development of an incipient oceanic ridge. The oceanic ridge uplifted the SKC including the epeiric sea, which subsequently resulted in terminating the early Paleozoic sedimentation of the epeiric sea. The paucity of lower Paleozoic volcanic rocks across much of the SKC however suggests that the oceanic ridge did not extend into the epeiric sea. Instead, spreading of oceanic ridge entailed dextral movement of associated transform faults, which may have played a major role in breakup of SKC from mainland Gondwana by the end of Ordovician.

  18. Relationship between paleotopographic surface of Cambrian-Ordovician Knox Group and oil and gas entrapment in Kentucky

    SciTech Connect

    Gooding, P.J.

    1987-09-01

    Cambrian-Ordovician dolostones of the Knox Group constitute one of the largest occurrences of this rock type known in the US. In Kentucky, the Knox carbonate sequence attains thicknesses of more than 3500 ft. Mudstone and wackestone are dominant in the upper Knox, with lesser amounts of packstone and grainstone. The Upper Cambrian to Lower Ordovician carbonate sequences in Kentucky resulted from carbonate sedimentation on a cratonic platform in shallow, low-energy marine environments. Relative structural quiescence existed during this time. The thick sequence of shallow-water carbonates suggests that the rate of deposition generally kept pace with subsidence of the craton. Geologic environments and climatic conditions during this period were similar to those of the Bahamas today. Warm climate, sporadic rainfall, and dry trade winds probably accounted for the net loss of water by evaporation and the resulting hypersaline conditions. The paleotopographic surface that developed on top of the Knox Group is of considerable economic importance because of potential hydrocarbon entrapment at or near the unconformity. Areas where permeable and porous zones developed on the exposed Knox surface due to erosion and weathering provide reservoir conditions; also, the unconformable surface of the Knox was sealed by an overlapping impermeable formation capable of entrapping hydrocarbons. Because of pressures exerted, hydrocarbons driven by fluids or gas may migrate along the eroded Knox surface laterally and upward onto paleotopographic highs. These conditions increase the probability of finding commercial oil and gas deposits in the Cambrian-Ordovician Knox in Kentucky.

  19. Chronostratigraphy of the Trenton Group and Utica Shale, Pt. II: Stratigraphic correlations using Ordovician glasses in K-bentonites

    SciTech Connect

    Delano, J.W.; Tice, S. . Dept. of Geological Sciences); Mitchell, C.E.; Goldman, D. . Dept. of Geology); Samson, S.D. . Dept. of Geology)

    1992-01-01

    Rhyolitic glasses in the form of pristine melt inclusions that occur within quartz phenocrysts are being used for the geochemical fingerprinting of Ordovician K-bentonites in the northern Appalachian Basin. These melt inclusions are samples of pre-eruptive magma that became trapped during phenocryst growth in the deep crustal magma chambers. Plinian eruptions led to quenching of the enclosed rhyolitic magma to form glass when the quartz phenocrysts were blasted into the atmosphere. Preservation of this Ordovician glass is due to its being hermetically sealed within a mineral (quartz) that is resistant to weathering and diagenetic alteration. Chemical compositions of glasses in four Ordovician K-bentonites from the Mohawk Valley of New York State have been acquired using high-precision, electron microprobe analyses. The elements Mg, Cl, Ca, Ti, and Fe are often diagnostic. The accompanying figure illustrates one combination of elements that is effective in distinguishing K-bentonites, which are not stratigraphically equivalent. These K-bentonites were selected to test competing chronostratigraphies of the northern Appalachian Basin and indicate problems with the model by Cisne et al.

  20. Distribution of linear mesostructures in oblique folded surfaces: Unravelling superposed Ordovician and Variscan folds in the Pyrenees

    NASA Astrophysics Data System (ADS)

    Casas, Josep Maria; Queralt, Pilar; Mencos, Joana; Gratacós, Oscar

    2012-11-01

    Detailed mapping and structural analysis yielded new data on the geometry of Ordovician folds in the Pyrenees. These folds caused the Variscan mainphase folds to develop over non-horizontal bedding surfaces in the pre-Upper Ordovician rocks. As a result, the Variscan mainphase fold axes and intersection lineations in these rocks present a wide range of orientations. Bedding surfaces exhibit a complex pattern in map view making it necessary to reconstruct the structure in 3D. Computer aided reconstruction tools such as FoldPlot proved useful for visualizing and reconstructing the geometry of such refolded structures in 3D. In the absence of map-scale key horizons, evidence of superposed folds is provided by detailed mapping of mesostructures. This requires a good and continuous outcrop over an extended area since one single fold system can account for a complex distribution of the subsequent intersection lineation. As a result, a cartographic study and a structural analysis are warranted because the direction of the Ordovician folds cannot be established only by the orientation of the L2 mesostructures.

  1. Iapetonudus (N. gen.) and Iapetognathus Landing, unusual Earliest Ordovician multielement conodont taxa and their utility for biostratigraphy

    USGS Publications Warehouse

    Nicoll, R.S.; Miller, J.F.; Nowlan, G.S.; Repetski, J.E.; Ethington, Raymond L.

    1999-01-01

    The Early Ordovician (Tremadocian) multielement conodont genus Iapetognathus is one of the oldest denticulate euconodont genera known. The ramiform-ramiform apparatus structure of Iapetognathus is not similar morphologically to other Late Cambrian to Earliest Ordovician denticulate multielement taxa, such as Eodentatus or Cordyloduts, because the major denticulate process has a lateral rather than a posterior orientation as it is in the other two examples. For this reason the genus is believed to have developed from the coniform-coniform apparatus Iapetonudus ibexensis (N.gen., n.sp.) through the development of the denticulate lateral processes. The two genera have a number of morphologic features in common and appear in stratigraphic succession. Iapetognathus aengensis (Lindstro??m) is redefined as a multielement taxon using topotype material and Ig. preaengensis Landing is placed in synonymy with it. Iapetognathus sprakersi, recently described by Landing in Landing and others (1996), is recognized as a multielement species and the new multielement species, Ig. fluctivagus, Ig. jilinensis and Ig. landingi n. spp. are described herein, based on type specimens from Utah (U.S.A.), Jilin (China) and Colorado (U.S.A.) respectively. Iapetonudus and Iapetognathus are important genera in defining the level of the Cambrian-Ordovician boundary. Iapetonudus is currently recognized only from Utah, Texas and Oklahoma, but Iapetognathus is cosmopolitan in its distribution.

  2. Organic geochemical evidence for nitrogen-limited oligotrophic seas in the Late Ordovician

    NASA Astrophysics Data System (ADS)

    Rohrssen, M.; Love, G. D.

    2011-12-01

    The Late Ordovician (~450-44 Ma) was a period of drastic environmental change, beginning in a hothouse climate with epeiric seaways near a Phanerozoic high and concluding with the Hirnantian glaciation, large positive carbon isotope excursion(s) (Hirnantian isotopic carbon excursion, HICE) and one of the Big Five mass extinctions. Warm sea temperatures and low oxidant concentrations relative to modern likely made intervals of the Late Ordovician particularly suited to the development of extensive denitrification in oxygen minimum zones (OMZs), contributing to nitrogen limitation of marine ecosystems. Mixed carbonate/siliciclastic deposits on Anticosti Island, Canada, provide an excellent opportunity to assemble stratigraphic lipid biomarker records of microbial community structure and response to environmental change associated with the Hirnantian glaciation in a tropical epeiric seaway. Lipid biomarkers extracted from Anticosti rocks yield low thermal maturities, consistent with the shallow burial history of the island and lack molecules likely derived from contamination (e.g. zero oleanane from angiosperms). In addition, Anticosti bitumens bear the C29 sterane predominance and low C28/C29 sterane ratio expected from Lower Paleozoic rocks. Anticosti biomarkers reveal unusual environmenal conditions throughout the Hirnantian at Anticosti. Despite the presence of unequivocally marine fossils, Anticosti bitumens contain no detectable 24-n-propylcholestane, usually a robust marker of marine environmental conditions. Anticosti bitumen have high abundances of 3β-methylhopanes (4-11% of C30 αβ-hopane), molecules which are commonly associated with Type I methanotrophic bacteria. Moderate abundances of 2α-methylhopane (2-4% C30 αβ-hopane) with only trace quantities of gammacerane are found. Hopane/sterane ratios, reflecting a highercontribution of bacteria relative to eukaryotes, range from 1.8 to 11.2 (average 4.8), higher than the Phanerozoic marine average of 0

  3. Late Ordovician Seawater Sulfate δ34S in Well-preserved Brachiopods

    NASA Astrophysics Data System (ADS)

    Present, T. M.; Paris, G.; Burke, A.; Fischer, W. W.; Adkins, J. F.

    2014-12-01

    In the end-Ordovician Hirnantian stage, pyrite-sulfur and carbon isotope excursions coincide with a mass extinction and major glaciation [1]. The sulfur isotopic composition of Carbonate Associated Sulfate (δ34SCAS) is routinely measured as a proxy for the composition of ancient seawater sulfate, which offers a measure of Earth's surface redox balance during this time. However, the variance among bulk-rock CAS samples commonly greatly exceeds analytical precision. CAS analytical techniques typically require large samples (normally >30g CaCO3), so integration of different synsedimentary and diagenetic components may explain this scatter. Using a new sulfur isotope MC-ICP-MS analytical technique [2], we analyzed 5-10mg of well-preserved secondary layer fibrous calcite of brachiopod fossils collected from Late Ordovician-early Silurian sections on Anticosti Island, Canada, and compared these values to those obtained from texture-specific sampling of other carbonate phases found in these rocks. Brachiopod secondary layer calcites show a range of δ34SCAS values with only 2‰ variability—much less than the 21‰ range observed among less well-preserved and/or diagenetic components. Notably, micrite— a phase often valued for CAS analysis— is as much as 15‰ lower than brachiopods in the same hand sample. Recrystallized fossils and late diagenetic cements are enriched up to 6‰ from brachiopods. Thus, diagenetic processes can strongly impact and overprint CAS signals, even in carbonate rocks of exceptionally low thermal maturity. Our analysis of brachiopod CAS from these sections indicates that there was no marine sulfate excursion coeval with the Hirnantian carbon isotope excursion and glacial maximum. These observations support Jones and Fike's interpretation of the noisier bulk-rock δ34SCAS record from Anticosti Island [1]. In addition, we measured the sulfur isotopic composition of CAS in a modern brachiopod to confirm that it provides a robust archive of

  4. Modeling oxygenation of an ocean-atmosphere system during the Late Ordovician-Devonian

    NASA Astrophysics Data System (ADS)

    Ozaki, K.

    2013-12-01

    Throughout the Earth's history, the redox state of surface environments, biogeochemical cycles, and biological innovation/extinction have been intimately related. Therefore, understanding the long-term (over millions of years) evolution of the redox state of an ocean-atmosphere system and its controlling factors is one of the fundamental topics of Earth Sciences. In particular, Early Paleozoic is marked by the prominent biological evolution/diversification events (Cambrian explosion and Great Ordovician Biodiversification Event), implying the causal linkage between ocean oxygenation and biological innovation. On the other hand, multiple lines of evidence (such as black shale deposition, low C/S ratio of buried sediments, low molybdenum isotopic value, and iron speciation data) suggest that ocean interior had been kept in low oxygen condition until the Devonian. Dahl et al. (2010) PNAS found an increase in molybdenum isotopic value from ~1.4‰ to ~2.0‰ between ~440 Ma and ~390 Ma, implying the oceanic redox transition to a well-oxygenated condition. It was proposed that this ocean oxygenation event correlates with the diversification of vascular land plants; an enhanced burial of terrigenous organic matter increases the oxygen supply rate to an ocean-atmosphere system. Although this hypothesis for a causal linkage between the diversification of land plants and oxidation event of an ocean-atmosphere system is intriguing, it remains unclear whether the radiation of land plant is necessary to cause such redox transition. Because oxygen is most likely regulated by a combination of several feedbacks in the Earth system, it is essential to evaluate the impact of plant diversification on the oxygenation state of an ocean-atmosphere system by use of a numerical model in which C-N-P-O-S coupled biogeochemical cycles between ocean-atmosphere-sediment systems are take into account. In this study, the paleoredox history of an ocean-atmosphere system during the Paleozoic is

  5. Comparison of iron isotope variations in modern and Ordovician siliceous Fe oxyhydroxide deposits

    NASA Astrophysics Data System (ADS)

    Moeller, Kirsten; Schoenberg, Ronny; Grenne, Tor; Thorseth, Ingunn H.; Drost, Kerstin; Pedersen, Rolf B.

    2014-02-01

    Formation pathways of ancient siliceous iron formations and related Fe isotopic fractionation are still not completely understood. Investigating these processes, however, is difficult as good modern analogues to ancient iron formations are scarce. Modern siliceous Fe oxyhydroxide deposits are found at marine hydrothermal vent sites, where they precipitate from diffuse, low temperature fluids along faults and fissures on the seafloor. These deposits exhibit textural and chemical features that are similar to some Phanerozoic iron formations, raising the question as to whether the latter could have precipitated from diffuse hydrothermal fluids rather than from hydrothermal plumes. In this study, we present the first data on modern Fe oxyhydroxide deposits from the Jan Mayen hydrothermal vent fields, Norwegian-Greenland Sea. The samples we investigated exhibited very low δ56Fe values between -2.09‰ and -0.66‰. Due to various degrees of partial oxidation, the Fe oxyhydroxides are with one exception either indistinguishable from low-temperature hydrothermal fluids from which they precipitated (-1.84‰ and -1.53‰ in δ56Fe) or are enriched in the heavy Fe isotopes. In addition, we investigated Fe isotope variations in Ordovician jasper beds from the Løkken ophiolite complex, Norway, which have been interpreted to represent diagenetic products of siliceous ferrihydrite precursors that precipitated in a hydrothermal plume, in order to compare different formation pathways of Fe oxyhydroxide deposits. Iron isotopes in the jasper samples have higher δ56Fe values (-0.38‰ to +0.89‰) relative to modern, high-temperature hydrothermal vent fluids (ca. -0.40‰ on average), supporting the fallout model. However, formation of the Ordovician jaspers by diffuse venting cannot be excluded, due to lithological differences of the subsurface of the two investigated vent systems. Our study shows that reliable interpretation of Fe isotope variations in modern and ancient marine

  6. Sulfate sulfur isotope stratigraphy reveals a record of ocean ventilation during the Latest Ordovician

    NASA Astrophysics Data System (ADS)

    Gill, B. C.; Lyons, T. W.; Young, S.; Kaljo, D.; Saltzman, M.

    2012-12-01

    The Hirnantian (445 to 443 Ma)—the last stage of the Ordovician—is marked by several important historical events, including large-scale continental glaciation; a large perturbation to the global carbon cycle; and, most notably, the second largest extinction interval in Earth history. Several recent models for Late Ordovician extinction have invoked the expansion of euxinia (anoxic, H2S-containing marine waters) as a kill mechanism. A positive sulfur isotope excursion found in sedimentary pyrite that parallels the well-known Hirnantian positive carbon isotope excursion or HICE is cited as one of the main lines of evidence for enhanced marine euxinia. Following this line of argument, the pyrite-S and organic-C excursions should track changes in the isotopic compositions of the marine sulfate and dissolved inorganic carbon pools attributed to enhanced burial rates for both pyrite and organic carbon during a global expansion of euxinia in the oceans. Our data for marine sulfate, however, suggest something different. Specifically, to further constrain the changes to the global sulfur cycle over the late Ordovician, we present sulfur isotope data from both carbonate-associated sulfate (δ34SCAS) and pyrite (δ34Spyrite) paired with carbon isotope data from successions from the paleo-contintents of Laurentia and Baltica. δ34SCAS data from both successions show little variation during the Hirnantian. The lack a positive sulfate-S isotope excursion parallel to the HICE suggests a driver other than organic carbon burial for the carbon isotope excursion, such as enhanced weathering of carbonate rocks as proposed by others. Consistent with this alternative, we argue that the positive sulfur isotope excursion seen in pyrite in the Hirnantian successions, including our section from Baltica, reflects changes in local sedimentary environments. Specifically, eustatic shallowing of sedimentary environments and ventilation of the oceans pushed the local zone of microbial sulfate

  7. Magnetic history of Early and Middle Ordovician sedimentary sequence, northern Estonia

    NASA Astrophysics Data System (ADS)

    Plado, J.; Preeden, U.; Pesonen, L. J.; Mertanen, S.; Puura, V.

    2010-01-01

    Alternating field and thermal demagnetization of lime- and dolostones from the Lower and Middle Ordovician (Floian to Darriwilian stages) subhorizontally bedded sequences in NW and NE Estonia reveal two characteristic magnetization components (named P and S). The intermediate-coercivity (demagnetized at 30-60 mT, up to 300-350°C) reversed polarity component P (mean of Floian Stage: Dref = 147.8 +/- 10.8°, Iref = 65.8 +/- 5.4° combined mean of Dapingian and Darriwilian stages: Dref = 166.0 +/- 8.4°, Iref = 56.1 +/- 6.5°) is regarded as the primary remanence of early diagenetic (chemical) origin. On the Baltica's apparent polar wander path (APWP), the palaeopoles (Floian: Plat = 25.0°N, Plon = 50.8°E, K = 52.7, A95 = 7.2° Dapingian and Darriwilian: Plat = 11.4°N, Plon = 39.1°E, K = 33.8, A95 = 6.7°) are placed on the Lower and Middle Ordovician segment. The poles indicate that Estonia was located at southerly latitudes, decreasing with time (Floian: ~48°S Dapingian and Darriwilian: ~37°S), when the remanence was acquired. A high-coercivity and high-unblocking-temperature component S (mean of samples: Dref = 33.7 +/- 6.3°, Iref = 51.9 +/- 5.7°) that is regarded as a secondary remanence has both normal and reversed polarities. On the European APWP, its palaeopole (Plat = 52.5°N, Plon = 157.9°E, K = 38.9, A95 = 5.3°) gives middle to late Permian age. According to mineralogical (SEM and optical microscopy) and rock magnetic (three-component induced remnant magnetization) studies, component P is carried by magnetite (coexisting with glauconite) and component S by haematite. Magnetite is of chemical origin, formed in the course of early diagenesis and/or dolomitization. During the Permian continental period haematite, the carrier of component S, was likely precipitated from oxidizing meteoric fluids in the already existing or simultaneously formed pore space between the dolomite crystals.

  8. Automated Segmentation of Skin Strata in Reflectance Confocal Microscopy Depth Stacks.

    PubMed

    Hames, Samuel C; Ardigò, Marco; Soyer, H Peter; Bradley, Andrew P; Prow, Tarl W

    2016-01-01

    Reflectance confocal microscopy (RCM) is a powerful tool for in-vivo examination of a variety of skin diseases. However, current use of RCM depends on qualitative examination by a human expert to look for specific features in the different strata of the skin. Developing approaches to quantify features in RCM imagery requires an automated understanding of what anatomical strata is present in a given en-face section. This work presents an automated approach using a bag of features approach to represent en-face sections and a logistic regression classifier to classify sections into one of four classes (stratum corneum, viable epidermis, dermal-epidermal junction and papillary dermis). This approach was developed and tested using a dataset of 308 depth stacks from 54 volunteers in two age groups (20-30 and 50-70 years of age). The classification accuracy on the test set was 85.6%. The mean absolute error in determining the interface depth for each of the stratum corneum/viable epidermis, viable epidermis/dermal-epidermal junction and dermal-epidermal junction/papillary dermis interfaces were 3.1 μm, 6.0 μm and 5.5 μm respectively. The probabilities predicted by the classifier in the test set showed that the classifier learned an effective model of the anatomy of human skin. PMID:27088865

  9. Astrochronologic Testing in Deep-Time Strata: Historical Overview and Recent Advances

    NASA Astrophysics Data System (ADS)

    Meyers, S. R.

    2014-12-01

    The quest for astronomical-climate rhythms ("Milankovitch cycles") in Phanerozoic strata is now commonplace, and has yielded fundamental advancements in our understanding of climate change, paleoceanography, astrodynamics, geochronology and chronostratigraphy. Of central importance to this success has been the development of astrochronologic testing methods for the evaluation of astronomical-climate influence on sedimentation; this can be especially challenging for deep-time strata that lack sufficient independent time control (e.g., radioisotopic data) to unambiguously calibrate observed spatial rhythms to temporal periods. Most deep-time (pre-Pleistocene) astrochronologic testing methods fall into one of two categories: (1) those that test for expected amplitude or frequency modulation imposed by an astronomical signal, or (2) those that test for bedding hierarchies ("frequency ratios") that are predicted by the dominant astronomical periods. In this talk, I discuss the historical context of these methods, recent advances that overcome subjective evaluation and circular reasoning, and their implementation in a new "open source" software package for astrochronology (Meyers, 2014, astrochron: An R Package for Astrochronology).

  10. The Alabama, U.S.A., seismic event and strata collapse of May 7, 1986

    NASA Astrophysics Data System (ADS)

    Long, Leladd Timothy; Copeland, Charles W.

    1989-09-01

    On May 7, 1986, the residents of Tuscaloosa, Alabama, felt a seismic event of local magnitude 3.6 that occurred at the same time as a rock burst and roof collapse in an active longwall coal mine. Visual inspection of the seismograms reveals a deficiency in energy at frequencies above 20 Hz compared to tectonic earthquakes or surface blasts. The predominance of energy below 5 Hz may explain reports of body wave magnitudes ( m b ) greater than 4.2. Also, 1.0 Hz surface waves were more strongly excited than body waves and may explain local felt effects more typically associated with greater epicentral distances. All recorded first motions were dilatational. The concentration of stations in the northern hemisphere allows reverse motion on an east-trending near-vertical plane or strike-slip motion on northwest or southeast trending planes. The reverse focal mechanism is preferred, because the area of roof collapse and the area of active longwall mining are located between two east-striking loose vertical fracture zones. The characteristics of the seismic event suggest that it might have been sudden shear failure resulting from accumulated strain energy in overlying strata behind an active longwall. Although an alternate interpretation of the focal mechanism as an implosion or shear failure in the strata above previously mined out areas is also allowed by the first motion data, this alternate intepretation is not supported by geological data.

  11. Automated Segmentation of Skin Strata in Reflectance Confocal Microscopy Depth Stacks

    PubMed Central

    Hames, Samuel C.; Ardigò, Marco; Soyer, H. Peter; Bradley, Andrew P.; Prow, Tarl W.

    2016-01-01

    Reflectance confocal microscopy (RCM) is a powerful tool for in-vivo examination of a variety of skin diseases. However, current use of RCM depends on qualitative examination by a human expert to look for specific features in the different strata of the skin. Developing approaches to quantify features in RCM imagery requires an automated understanding of what anatomical strata is present in a given en-face section. This work presents an automated approach using a bag of features approach to represent en-face sections and a logistic regression classifier to classify sections into one of four classes (stratum corneum, viable epidermis, dermal-epidermal junction and papillary dermis). This approach was developed and tested using a dataset of 308 depth stacks from 54 volunteers in two age groups (20–30 and 50–70 years of age). The classification accuracy on the test set was 85.6%. The mean absolute error in determining the interface depth for each of the stratum corneum/viable epidermis, viable epidermis/dermal-epidermal junction and dermal-epidermal junction/papillary dermis interfaces were 3.1 μm, 6.0 μm and 5.5 μm respectively. The probabilities predicted by the classifier in the test set showed that the classifier learned an effective model of the anatomy of human skin. PMID:27088865

  12. Sandstone units of the Lee Formation and related strata in eastern Kentucky

    USGS Publications Warehouse

    Rice, Charles L.

    1984-01-01

    Most of the Cumberland Plateau region of southeastern Kentucky is underlain by thick sequences of quartzose sandstone which are assigned for the most part to the Lee Formation. Much new information has been gathered about the Lee and related strata as a result of the cooperative mapping program of the U. S. Geological Survey and the Kentucky Geological Survey between 1960 and 1978. This report summarizes the age, lithology, distribution, sedimentary structures, and stratigraphic relations of the sandstone units of the Lee within and between each of three major outcrop belts in Kentucky: Cumberland Mountain, Pine Mountain, and the Pottsville Escarpment area. The Lee Formation generally has been regarded as Early Pennsylvanian in age and separated from Mississippian strata in Kentucky by an unconformity. However, lithostratigraphic units included in the formation as presently defined are broadly time-transgressive and range in age from Late Mississippian in parts of the Cumberland Mountain outcrop belt to Middle Pennsylvanian in the Pottsville Escarpment area. Members of the Lee intertongue with and grade into the underlying Pennington Formation and overlying Breathitt Formation. Sandstone and conglomeratic sandstone members of the Lee of Mississippian age found only in parts of the Cumberland overthrust sheet are closely associated with marine rocks; Pennsylvanian members are mostly associated with continental coal-bearing strata. Sandstone members of the Lee are mostly quartz rich and range from more than 90 percent to more than 99 percent quartz. They are relatively coarse grained, commonly pebbly, and in places conglomeratic. The units are southwest-trending linear or broadly lobate bodies. The Lee Formation is as much as 1,500 ft thick in the type area in Cumberland Mountain where it has been divided into eight members. The Pinnacle Overlook, Chadwell, White Rocks Sandstone, Middlesboro, Bee Rock Sandstone, and Naese Sandstone Members are mostly quartzose

  13. Late Ordovician (Turinian-Chatfieldian) carbon isotope excursions and their stratigraphic and paleoceanographic significance

    USGS Publications Warehouse

    Ludvigson, Greg A.; Witzke, B.J.; Gonzalez, Luis A.; Carpenter, S.J.; Schneider, C.L.; Hasiuk, F.

    2004-01-01

    Five positive carbon isotope excursions are reported from Platteville-Decorah strata in the Upper Mississippi Valley. All occur in subtidal carbonate strata, and are recognized in the Mifflin, Grand Detour, Quimbys Mill, Spechts Ferry, and Guttenberg intervals. The positive carbon isotope excursions are developed in a Platteville-Decorah succession in which background ??13C values increase upward from about -2??? at the base to about 0??? Vienna Pee Dee belemnite (VPDB) at the top. A regional north-south ??13C gradient, with lighter values to the north and heavier values to the south is also noted. Peak excursion ??13C values of up to +2.75 are reported from the Quimbys Mill excursion, and up to +2.6 from the Guttenberg excursion, although there are considerable local changes in the magnitudes of these events. The Quimbys Mill, Spechts Ferry, and Guttenberg carbon isotope excursions occur in units that are bounded by submarine disconformities, and completely starve out in deeper, more offshore areas. Closely spaced chemostratigraphic profiles of these sculpted, pyrite-impregnated hardground surfaces show that they are associated with very abrupt centimeter-scale negative ??13C shifts of up to several per mil, possibly resulting from the local diagenetic effects of incursions of euxinic bottom waters during marine flooding events. ?? 2004 Elsevier B.V. All rights reserved.

  14. Statistically significant faunal differences among Middle Ordovician age, Chickamauga Group bryozoan bioherms, central Alabama

    SciTech Connect

    Crow, C.J.

    1985-01-01

    Middle Ordovician age Chickamauga Group carbonates crop out along the Birmingham and Murphrees Valley anticlines in central Alabama. The macrofossil contents on exposed surfaces of seven bioherms have been counted to determine their various paleontologic characteristics. Twelve groups of organisms are present in these bioherms. Dominant organisms include bryozoans, algae, brachiopods, sponges, pelmatozoans, stromatoporoids and corals. Minor accessory fauna include predators, scavengers and grazers such as gastropods, ostracods, trilobites, cephalopods and pelecypods. Vertical and horizontal niche zonation has been detected for some of the bioherm dwelling fauna. No one bioherm of those studied exhibits all 12 groups of organisms; rather, individual bioherms display various subsets of the total diversity. Statistical treatment (G-test) of the diversity data indicates a lack of statistical homogeneity of the bioherms, both within and between localities. Between-locality population heterogeneity can be ascribed to differences in biologic responses to such gross environmental factors as water depth and clarity, and energy levels. At any one locality, gross aspects of the paleoenvironments are assumed to have been more uniform. Significant differences among bioherms at any one locality may have resulted from patchy distribution of species populations, differential preservation and other factors.

  15. An Upper Ordovician sponge-bearing micritic limestone and implication for early Palaeozoic carbonate successions

    NASA Astrophysics Data System (ADS)

    Park, Jino; Lee, Jeong-Hyun; Hong, Jongsun; Choh, Suk-Joo; Lee, Dong-Chan; Lee, Dong-Jin

    2015-04-01

    A potentially new type of non-reef sponge-bearing micritic limestone is reported from the Upper Ordovician Xiazhen Formation of south-eastern China. The sponges are preserved as incomplete skeletons that consist of curved bifurcated and trifurcated spicules embedded in dark micrite, and can only be recognized under a petrographic microscope. The characteristics of the spicule networks suggest that the sponges are probably belonging to demosponges. However, based on the absence of features such as desma, zygome, a distinct dermal layer, and a canal system, they are not considered to be lithistids. The majority of the sponges are found in a lime mudstone facies, together with some micritic portions of wackestone to grainstone facies, comprising approximately 13% of the 50-m thick micritic limestone successions. It is interpreted that the non-lithistid demosponges flourished on soft substrates over shallow marine carbonate platform. Such sponge-bearing carbonates are similar to spiculites and spongolites in terms of being a major constituent of the sedimentary rocks and their potential contribution as sediment producers, but affinity and modes of preservation of the Xiazhen sponges are significantly different to those of the spiculites and spongolites. In light of the present finding, it is suggested that non-lithistid demosponges may have been more widespread in early Palaeozoic non-reef carbonates than has previously been recognized, thus indicating the critical need for further detailed studies if we are to understand their distributions and sedimentological contributions.

  16. Paleokarst and reservoir porosity in the Ordovician Beekmantown Dolomite of the central Appalachian basin

    USGS Publications Warehouse

    Smosna, R.; Bruner, K.R.; Riley, R.A.

    2005-01-01

    A karst-unconformity play at the top of the Ordovician Beekmantown Dolomite is judged to have great petroleum potential in Ohio and adjacent states; wells have high ultimate reserves and large areas remain untested. To better understand the origin, development, and distribution of Beekmantown porosity, we conducted a petrologic-stratigraphic study of cores and thin sections from 15 oil and gas wells. The massive dolomite, characterized by a hypidiotopic-idiotopic texture, formed by the replacement of stacked peritidal carbonate cycles. Secondary porosity occurs at two scales: (1) mesoscopic - breccia porosity, solution-enlarged fractures, large vugs, and caverns, and (2) microscopic - intercrystalline, intracrystalline, molds, small vugs, and microfractures. Mesoscopic pores (providing the major storage capacity in this reservoir) were produced by intrastratal solution and collapse of carbonate layers, whereas microscopic pores (connecting the larger pores) generally formed by the leaching of individual carbonate grains and crystals. Most pore types developed during periods of subaerial exposure across the carbonate bank, tied to either the numerous, though brief falls of relative sea level during Beekmantown deposition or more importantly the prolonged Knox unconformity at the close of sedimentation. The distribution of reservoir-quality porosity is quite heterogeneous, being confined vertically to a zone immediately below the unconformity and best developed laterally beneath buried hills and noses of this erosion surface. The inferred, shallow flow of ground water in the Beekmantown karst, primarily below topographic highs and above a diagenetic base level close to the water table, led to this irregular distribution of porosity.

  17. A new type of solar-system material recovered from Ordovician marine limestone

    PubMed Central

    Schmitz, B.; Yin, Q. -Z.; Sanborn, M. E.; Tassinari, M.; Caplan, C. E.; Huss, G. R.

    2016-01-01

    From mid-Ordovician ∼470 Myr-old limestone >100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the L-chondrite parent body. Recently one anomalous meteorite, Österplana 065 (Öst 65), was found in the same beds that yield L chondrites. The cosmic-ray exposure age of Öst 65 shows that it may be a fragment of the impactor that broke up the L-chondrite parent body. Here we show that in a chromium versus oxygen-isotope plot Öst 65 falls outside all fields encompassing the known meteorite types. This may be the first documented example of an ‘extinct' meteorite, that is, a meteorite type that does not fall on Earth today because its parent body has been consumed by collisions. The meteorites found on Earth today apparently do not give a full representation of the kind of bodies in the asteroid belt ∼500 Myr ago. PMID:27299793

  18. Provenance of the Middle Ordovician Blount clastic wedge, Georgia and Tennessee

    NASA Astrophysics Data System (ADS)

    Mack, Greg H.

    1985-04-01

    Convergent tectonism along the Appalachian continental margin in Middle Ordovician time resulted in cratonward-prograding clastic wedges. Detrital modes of 52 sandstones of the Blount clastic wedge in Georgia and Tennessee are dominated by monocrystalline quartz (68%), feldspar (10%, plagioclase >K-feldspar), and pelitic rock fragments (10%), with lesser amounts of polycrystalline quartz (6%), chert (2%), low-grade metamorphic rock fragments (2%), and quartzofeldspathic rock fragments (0.3%). The primary source rocks were sedimentary; subordinate contributions were from low-grade metamorphic and plagioclase-rich plutonic and/or gneissic rocks. The composition of sandstones from the Martinsburg clastic wedge, based on point-counting 18 samples from the collection of McBride, and from the Taconic clastic wedge, based on data of Hiscott, is similar to the Blount clastic wedge except that Martinsburg and Taconic sandstones have additional evidence of derivation from intermediate or mafic volcanic and deep-water sedimentary source rocks, which were lacking in the Blount source terrane. The differences in provenance among the clastic wedges may indicate along-strike variations in tectonic style, or variations in the distribution of rock types, or differences in the level of erosion within orogenic terranes of similar origin.

  19. Internal-tide deposits in an Ordovician submarine channel: Previously unrecognized facies

    SciTech Connect

    Gao Zhenzhong; Eriksson, K.A. )

    1991-07-01

    A Middle Ordovician submarine-channel deposit in the southern Appalachians is capped by an interval of fine-grained, predominantly cross-laminated sandstones that are interpreted as internal-tide deposits. Two facies are recognized: (1) bidirectional cross-laminated, very fine grained sandstones, and (2) unidirectional cross-bedded and cross-laminated, medium- to fine-grained sandstones. Facies 1 is dominated by bidirectional cross-laminations that dip both landward and seaward parallel to the paleochannel axis. This facies is related to up-channel and down-channel currents caused by internal tides. Facies 2 has both low-angle, tabular cross-beds and cross-laminations that dip landward. The formative up-channel currents are attributed to superimposition of internal waves on internal tides. The vertical transition from high-concentration gravity-flow deposits to intercalated low-concentration turbidites and internal-tide deposits is related to a rise in sea level that resulted in storage of coarse debris landward of the submarine channel.

  20. Diagenesis of hydrocarbon-bearing rocks in the Middle Ordovician Simpson Group, southeastern Anadarko Basin, Oklahoma

    USGS Publications Warehouse

    Pitman, Janet K.; Burruss, Robert A.

    1989-01-01

    Quartzarenites and subarkoses in the Middle Ordovician Simpson Group in the Gulf Costello No. 1 and Sunray-DX Parker No. 1 Mazur wells, southeastern Anadarko basin, have undergone a complex diagenetic and petroleum-migration history. During early burial, petroleum migrated locally through sandstones; patches of bitumen in calcite and bitumen-lined quartz overgrowths containing oil-bearing inclusions reflect the introduction of petroleum-bearing fluids at shallow depths. Stable-isotope data reveal that early calcite precipitated at near-surface temperatures from fluids dominated by marine carbon. At moderate to deep burial, calcite dissolution, followed by ferroan-dolomite and clay-mineral precipitation, occurred at about the same time as the rocks reached levels of thermal maturity sufficient for the generation of hydrocarbons. Maximum paleotemperatures during deep burial are estimated from maturation models to have reached 250°F in the Costello well and 300°F in the Mazur well. Maturation-derived temperatures in the Costello well are consistent with preliminary homogenization temperatures (210-250°F) for oil inclusions along microscopic healed fractures that formed during deep burial, thus supporting an Early to Middle Pennsylvanian timing for the generation and migration of late-stage hydrocarbons. The early petroleum phase, emplaced while the rocks were at shallow burial depths, migrated from mature source rocks deeper in the basin.

  1. Bedded cherts in the Early Ordovician Arbuckle Group of southwestern Oklahoma

    SciTech Connect

    Donovan, R.N. ); Ragland, D.A.

    1991-03-01

    Bedded cherts are a rarely occurring but environmentally significant facies in the Early Ordovician Arbuckle Group. Two such units have been identified: one in the Cool Creek Formation and one in the Kindblade Formation. In each, microcrystalline calcite and dolomite alternate in thin laminae with microcrystalline silica in units up to 25 cm in thickness. The areal extent of the bedded cherts encompasses more than 130 km{sup 2}. It is hypothesized that the interlaminated cherts and micrites were deposited in very shallow marine conditions. A relatively small part of the Oklahoma Aulacogen was cut off from open ocean circulation, resulting in an isolated lagoon. The chert/micrite couplets may represent seasonal deposits in the lagoon. During seasonal flooding, slightly deeper water resulted in algal growth with accompanying precipitation of carbonates and solution of detrital quartz sand. During the dry season, the dissolved silica precipitated, resulting in thin layers of microcrystalline chart. Some carbonate layers contain small pseudomorphs after what may have been gypsum and anhydrite crystals and nodules, indicating that salinities increased enough to permit formation of evaporites. At least ten couplets occur in the thickest units, suggesting that the lagoon existed for ten wet-dry seasons.

  2. A new type of solar-system material recovered from Ordovician marine limestone.

    PubMed

    Schmitz, B; Yin, Q-Z; Sanborn, M E; Tassinari, M; Caplan, C E; Huss, G R

    2016-01-01

    From mid-Ordovician ∼470 Myr-old limestone >100 fossil L-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to Earth following the breakup of the L-chondrite parent body. Recently one anomalous meteorite, Österplana 065 (Öst 65), was found in the same beds that yield L chondrites. The cosmic-ray exposure age of Öst 65 shows that it may be a fragment of the impactor that broke up the L-chondrite parent body. Here we show that in a chromium versus oxygen-isotope plot Öst 65 falls outside all fields encompassing the known meteorite types. This may be the first documented example of an 'extinct' meteorite, that is, a meteorite type that does not fall on Earth today because its parent body has been consumed by collisions. The meteorites found on Earth today apparently do not give a full representation of the kind of bodies in the asteroid belt ∼500 Myr ago. PMID:27299793

  3. Graptolite community responses to global climate change and the Late Ordovician mass extinction

    NASA Astrophysics Data System (ADS)

    Sheets, H. David; Mitchell, Charles E.; Melchin, Michael J.; Loxton, Jason; Štorch, Petr; Carlucci, Kristi L.; Hawkins, Andrew D.

    2016-07-01

    Mass extinctions disrupt ecological communities. Although climate changes produce stress in ecological communities, few paleobiological studies have systematically addressed the impact of global climate changes on the fine details of community structure with a view to understanding how changes in community structure presage, or even cause, biodiversity decline during mass extinctions. Based on a novel Bayesian approach to biotope assessment, we present a study of changes in species abundance distribution patterns of macroplanktonic graptolite faunas (˜447–444 Ma) leading into the Late Ordovician mass extinction. Communities at two contrasting sites exhibit significant decreases in complexity and evenness as a consequence of the preferential decline in abundance of dysaerobic zone specialist species. The observed changes in community complexity and evenness commenced well before the dramatic population depletions that mark the tipping point of the extinction event. Initially, community changes tracked changes in the oceanic water masses, but these relations broke down during the onset of mass extinction. Environmental isotope and biomarker data suggest that sea surface temperature and nutrient cycling in the paleotropical oceans changed sharply during the latest Katian time, with consequent changes in the extent of the oxygen minimum zone and phytoplankton community composition. Although many impacted species persisted in ephemeral populations, increased extinction risk selectively depleted the diversity of paleotropical graptolite species during the latest Katian and early Hirnantian. The effects of long-term climate change on habitats can thus degrade populations in ways that cascade through communities, with effects that culminate in mass extinction.

  4. Graptolite community responses to global climate change and the Late Ordovician mass extinction.

    PubMed

    Sheets, H David; Mitchell, Charles E; Melchin, Michael J; Loxton, Jason; Štorch, Petr; Carlucci, Kristi L; Hawkins, Andrew D

    2016-07-26

    Mass extinctions disrupt ecological communities. Although climate changes produce stress in ecological communities, few paleobiological studies have systematically addressed the impact of global climate changes on the fine details of community structure with a view to understanding how changes in community structure presage, or even cause, biodiversity decline during mass extinctions. Based on a novel Bayesian approach to biotope assessment, we present a study of changes in species abundance distribution patterns of macroplanktonic graptolite faunas (∼447-444 Ma) leading into the Late Ordovician mass extinction. Communities at two contrasting sites exhibit significant decreases in complexity and evenness as a consequence of the preferential decline in abundance of dysaerobic zone specialist species. The observed changes in community complexity and evenness commenced well before the dramatic population depletions that mark the tipping point of the extinction event. Initially, community changes tracked changes in the oceanic water masses, but these relations broke down during the onset of mass extinction. Environmental isotope and biomarker data suggest that sea surface temperature and nutrient cycling in the paleotropical oceans changed sharply during the latest Katian time, with consequent changes in the extent of the oxygen minimum zone and phytoplankton community composition. Although many impacted species persisted in ephemeral populations, increased extinction risk selectively depleted the diversity of paleotropical graptolite species during the latest Katian and early Hirnantian. The effects of long-term climate change on habitats can thus degrade populations in ways that cascade through communities, with effects that culminate in mass extinction. PMID:27432981

  5. Oolitic and pisolitic ironstones in the early Ordovician (Arenig) of the Amadeus Basin, central Australia

    NASA Astrophysics Data System (ADS)

    Gorter, John D.

    Early Ordovician oolitic ironstone was first reported from the subsurface Pacoota Sandstone of the Amadeus Basin in the Tempe Vale 1 petroleum exploration well in 1982, and found subsequently in Tent Hill 1 and Mt Winter 2 coreholes. Density log correlations and descriptions of cuttings show the presence of ironstones in other wells in the northwestern part of the basin. Several measured sections in the same general area also contain discrete beds of oolitic or pisolitic ironstone. All known occurrences are in the Early Arenig upper Pacoota Sandstone. Two types of deposition are apparent: Type 1 oolitic ironstones gradationally overlie a shallowing-upward marine clastic cycle, commencing with deeper water shales and passing upward through bioturbated siltstones to cross-bedded sandstones, and terminating in bioturbated oolitic ironstones; and Type 2 oolitic ironstones are invariably sharply bounded, non-bioturbated, generally structureless but sometimes cross-bedded, occur interbedded with marine clastics, and do not always occur at the top of shallowing-upward cycles. Type 1 oolithic ironstones are interpreted to have been deposited in-situ upon shoaling barrier bars in a low energy, shallow intracratonic sea. Type 2 ironstones are interpreted to have been reworked from the tops of such barrier bars, possibly during storms, and redeposited in offshore to lower shoreface environments.

  6. Cambrian-Ordovician Knox production in Ohio: Three case studies of structural-stratigraphic traps

    USGS Publications Warehouse

    Riley, R.A.; Wicks, J.; Thomas, Joan

    2002-01-01

    The Knox Dolomite (Cambrian-Ordovician) in Ohio consists of a mixed carbonate-siliciclastic sequence deposited in a tidal-flat to shallow-marine environment along a broad continental shelf. Knox hydrocarbon production occurs in porous sandstone and dolomite reservoirs in the Copper Ridge dolomite, Rose Run sandstone, and Beekmantown dolomite. In Ohio, historical Knox exploration and development have been focused on paleogeomorphic traps within the prolific Morrow Consolidated field, and more recently, within and adjacent to the Rose Run subcrop. Although these paleogeomorphic traps have yielded significant Knox production, structural and stratigraphic traps are being largely ignored. Three Knox-producing pools demonstrate structural and stratigraphic traps: the Birmingham-Erie pool in southern Erie and southwestern Lorain counties, the South Canaan pool in northern Wayne County, and the East Randolph pool in south-central Portage County. Enhanced porosity and permeability from fractures, as evident in the East Randolph pool, are also an underexplored mechanism for Knox hydrocarbon accumulation. An estimated 800 bcf of gas from undiscovered Knox resources makes the Knox one of the most attractive plays in the Appalachian basin.

  7. An evaluation of strata behavior and tailgate support performance at Eagle Nest Mine

    SciTech Connect

    Mucho, T.P.; Compton, C.S.; Oyler, D.C.; Horvath, S.

    1996-12-01

    Strata behavior and support performance were evaluated in a longwall tailgate test area at the Eagle Nest Mine near Van, WV. The mine operates in the Eagle coalbed which ranges in height from 4 to 6 ft (1.2 to 1.8 m) on the mine property. Rugged topography results in rapid changes in overburden which ranges from 200 to 1200 ft (61 to 366 m). The immediate roof at this mine transitions from sandstone to shale. In some areas the sandstone appears to be massive while in many locations it is highly laminated, fossilized, and interspersed with coal streaks. Horizontal stress levels appear to be sufficient to create instabilities in the roof in some locations, especially where the roof is thinly laminated. Traditionally, hardwood cribs have been used at the mine to provide secondary support for longwall tailgates; Strata Products` Hercules cribs are installed on 8 ft (2.4 m) centers staggered left and right in the tailgate entry. In a 250 ft (75 m) tailgate test area, however, cable bolts were installed in lieu of cribs. The bolts were 12 ft (3.6 m) long tensionable cables anchored with 5 ft (1.5 m) of resin. Four cables were installed across the entry and rows were spaced on 6 ft (1.8 m) centers. Primary. roof support was maintained in the vicinity of the test area using 42 in (1.1 m), grade 60, No. 6 (19 mm diameter) resin bolts installed on 4 ft (1.2 m) centers through T-2 channels. The cable test area was located under a stream valley in an area of relatively shallow overburden. Strata instabilities consistently had been associated with the stream valley in both the Eagle and the overlying Powellton coalbeds. In an effort to further expose the cables to the most difficult stress conditions available at the time of the test, the specific site chosen was directly beneath a barrier pillar remaining in the upper Powellton mine (approximately 150 ft (45 m) of interburden separates the two coalbeds).

  8. Paleomagnetism and rock magnetism of Quaternary volcanic rocks and Late Paleozoic strata, VC-1 core hole, Valles Caldera, New Mexico, with emphasis on remagnetization of Late Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Geissman, John W.

    1988-06-01

    Paleomagnetic and rock magnetic data obtained from azimuthally unoriented core samples, collected at approximately 1- to 3-m intervals, of Continental Scientific Drilling Program core hole VC-1 have prompted reinterpretations of the Quaternary volcanic stratigraphy intersected by the bore and have aided in evaluating the thermal regime within late Paleozoic strata attending fluid circulation and mineral deposition during and after development of the Toledo and Valles calderas. The results from Quaternary units (Banco Bonito Obsidian: I = +35.4°, a95 = 2.8° (inclination only determinations), n = 33; Battleship Rock Tuff: D = 359.6°, I = +42.4°, a95 = 2.8°, n = 5 site means (surface sites); VC-1 Rhyolite: I = +39.2°, a95 = 12.8°, n = 7; Upper VC-1 Tuff: I = +37.2°, a95 = 10.7°, n = 13; Middle VC-1 Tuff: I = +42.1°, a95 = 2.1°, n = 39; South Mountain Rhyolite: D = 350.9°, I = +49.9°, a95 = 3.4°, n = 10 (one surface site)) are consistent with isotopic age data, indicating that the entire moat volcanic sequence intersected is less than 650 kyr. Monitoring of natural remanent magnetization (NRM) intensity, NRM directions, directions of magnetizations isolated during progressive demagnetization, median destructive forces, and rock magnetization parameters has identified systematic variations within the thick Banco Bonito Obsidian and VC-1 Tuff units. The Permian Abo Formation, Pennsylvanian to earliest Permian Madera Limestone, and Pennsylvanian Sandia Formation typically contain a moderate positive inclination magnetization component (Abo Formation: I = +52.2°, a95 = 7.4°, n = 16; Madera Limestone: I = +58.4°, a95 = 2.8°, n = 105; Sandia Formation: I = +53.9°, a95 = 4.8°, n = 21); when residing in magnetite, it is usually unblocked in the laboratory by 350°C; when carried by hematite it is unblocked by 550°C. A moderate negative inclination (e.g., Madera and Abo strata: D = 173.1°, I = -46.6°, a95 = 5.5°; n = 47 samples; assuming a north seeking

  9. Lower Cretaceous bentonitic strata in southwestern Montana assigned to Vaughn Member of Mowry Shale (East) and of Blackleaf Formation (West)

    USGS Publications Warehouse

    Tysdal, R.G.; Dyman, T.S.; Nichols, D.J.

    1989-01-01

    The Vaughn Member, newly assigned to the Mowry Shale in this report, comprises strata that crop out in the Greenhorn, Gravelly, Madison, and Gallatin ranges, and the Centennial and Beartooth mountains of southwestern Montana. Herein the member is correlated with the Vaughn Member of the Blackleaf Formation, which crops out to the west in the Lima Peaks area, Snowcrest Range, and Pioneer Mountains. Strata assigned to the Vaughn Member of the Blackleaf Formation in southwestern Montana exhibit the same contrasting relationships that exist in northwestern Montana. The Vaughn Member of the Mowry is late Albian in age, determined by bracketing with shallow water marine bivalves in the Muddy Sandstone below and palynomorphs in Mowry strata above. Palynomorphs from the Vaughn Member itself are typically mid-Cretaceous, but do not permit a more exact determination of age. -from Authors

  10. A Martian analog in Kansas: Comparing Martian strata with Permian acid saline lake deposits

    NASA Astrophysics Data System (ADS)

    Benison, Kathleen C.

    2006-05-01

    An important result of the Mars Exploration Rover's (MER) mission has been the images of sedimentary structures and diagenetic features in the Burns Formation at Meridiani Planum. Bedding, cross-bedding, ripple marks, mud cracks, displacive evaporite crystal molds, and hematite concretions are contained in these Martian strata. Together, these features are evidence of past saline groundwater and ephemeral shallow surface waters on Mars. Geochemical analyses of these Martian outcrops have established the presence of sulfates, iron oxides, and jarosite, which strongly suggests that these waters were also acidic. The same assemblage of sedimentary structures and diagenetic features is found in the salt-bearing terrestrial red sandstones and shales of the middle Permian (ca. 270 Ma) Nippewalla Group of Kansas, which were deposited in and around acid saline ephemeral lakes. These striking sedimentological and mineralogical similarities make these Permian red beds and evaporites the best-known terrestrial analog for the Martian sedimentary rocks at Meridiani Planum.

  11. Method, system and computer program product for monitoring and optimizing fluid extraction from geologic strata

    DOEpatents

    Medizade, Masoud; Ridgely, John Robert

    2009-12-15

    An arrangement which utilizes an inexpensive flap valve/flow transducer combination and a simple local supervisory control system to monitor and/or control the operation of a positive displacement pump used to extract petroleum from geologic strata. The local supervisory control system controls the operation of an electric motor which drives a reciprocating positive displacement pump so as to maximize the volume of petroleum extracted from the well per pump stroke while minimizing electricity usage and pump-off situations. By reducing the electrical demand and pump-off (i.e., "pounding" or "fluid pound") occurrences, operating and maintenance costs should be reduced sufficiently to allow petroleum recovery from marginally productive petroleum fields. The local supervisory control system includes one or more applications to at least collect flow signal data generated during operation of the positive displacement pump. No flow, low flow and flow duration are easily evaluated using the flap valve/flow transducer arrangement.

  12. Contribution to the discussion of folded Pannonian strata in the Southern Vienna Basin

    NASA Astrophysics Data System (ADS)

    Häusler, H.

    2012-04-01

    It is well known that Neogene Basins in Eastern Austria were formed by regional extensional tectonics. Nevertheless Peresson & Decker (1997) reported local folding in the Vienna Basin, which they interpreted as a result of post-Miocene compression. Based on their hypothesis we now present three locations of folded Pannonian formations, which we interpret as tectonic ones. First the coal bearing Neufeld formation of the Neufeld-Zillingdorf mining area, second the folded Neufeld formation of Steinbrunn, the coming into existence of which currently is under discussion, and third the folded Pannonian beds of Oberlaa near Vienna. In 1952 Ruttner described big inclined folds in the coal bearing Pannonian of the Neufeld open coal pit with NNE plunging axes. The well mapped faults of the entire mining area revealed an en echelon pattern, which can be interpreted as a result of sinistral strike slip faulting along the crystalline belt of the Central Alpine basement (Leitha Mountains - Rosalia). Historic photographs proof the existence of folds with wavelengths and amplitudes on the order of several meters, horizontally inclined and overturned, indicating local post-Miocene folding. In Steinbrunn, only a few kilometers east of Zillingdorf, another outcrop reveals folded deposits of the Neufeld formation, and was subject to several tectonic and sedimentological investigations. While Peresson & Decker (1997) implied a tectonic origin, Exner et al. (2008) favoured the hypothesis of a synsedimentary evolution of these folds. Grundtner et al. (2009) identified a coarsening upward and shallowing upward of these Upper Pannonian strata, and interpreted the brackish-limnic succession as deposits in a floodplain depositional environment. Within such an environment a paleo-slope enabling slumping and sliding of Upper Pannonian soft sediments forming sedimentary folds with a wavelength and amplitude of several meters is quite unlikely. Eventual high resolution geophysical investigations

  13. Origin of discontinuities in coal-bearing strata at roaring creek (basal Pennsylvanian of Indiana)

    USGS Publications Warehouse

    Nelson, W.J.; Eggert, D.L.; DiMichele, W.A.; Stecyk, A.C.

    1985-01-01

    Basal Pennsylvanian coal-bearing strata exposed along Roaring Creek, west-central Indiana, exhibit extreme lateral discontinuity. Coal seams abruptly change in thickness and elevation; they split, grade into shale, are cut out by channels and disrupted by soft-sediment deformational structures. Initial sediments were laid down by a network of southwest-flowing streams that traversed a deeply channelized upland surface of Mississippian carbonate rocks. Channels aggraded rapidly as uplands were worn down, so the region changed through time from uplands to upper deltaic plain. Local environments included channels, localized point bars, small natural levees and crevasse splays, overbank deposits, and swamps. Differential compaction and subsidence, slumping stream banks, and possibly collapsing sinkholes influenced sedimentation. As a consequence, coals are too discontinuous for economical mining, although they are locally thick and high in quality. ?? 1985.

  14. [Stunting and emaciation in children under 5 in distinct regions and strata in Mexico].

    PubMed

    Rivera-Dommarco, J; González-Cossío, T; Flores, M; Hernández-Avila, M; Lezana, M A; Sepúlveda-Amor, J

    1995-01-01

    Data from a National Nutrition Survey conducted in 1988 in a probability sample of 13,236 households and 17,426 children under five, representative at the national level and for four regions (North, Center, South, and Mexico City), were analyzed. Risks for wasting and stunting and odds ratios were obtained by region, by district according to proportion of indigenous population and by level of urbanization, by level of education of both parents, by gender, and by various combinations of the former strata. A high risk of stunting and a low risk of wasting were found. The risk of stunting is greater in predominantly indigenous and rural districts, in the South and Center, and in families of mothers with low education and poor housing conditions. The results can be used for food and nutrition policy planning and for targeting nutrition intervention programs. PMID:7618120

  15. The emplacement time of the Hegenshan ophiolite: Constraints from the unconformably overlying Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Zhou, Jian-Bo; Han, Jie; Zhao, Guo-Chun; Zhang, Xing-Zhou; Cao, Jia-Lin; Wang, Bin; Pei, Sheng-Hui

    2015-11-01

    Controversy has long surrounded the emplacement time of the Hegenshan ophiolite that is considered to mark a suture zone, called the Hegenshan-Heihe suture, resulting from the closure of a back-arc basin in the Paleo-Asian Ocean. The Hegenshan ophiolite in the Xiaobaliang area is unconformably overlain by a sequence of Paleozoic strata, called the Zhesi Formation that consists of conglomerate, sandstone, siltstone and limestone, some of which contain Permian marine fossils of Brachiopods. Therefore, the ages of these Paleozoic strata can be used to constrain the emplacement time of the Hegenshan ophiolite. Four samples of the Zhesi Formation collected in the Xiaobaliang area yield the detrital zircon U-Pb ages of 285-272 Ma (with the peak at 279 Ma), 315-288 Ma (with a peak at 300 Ma), 320-358 Ma (with a peak at 336 Ma), and 406 ± 3 Ma, of which the ~ 280 and ~ 300 Ma age groups are remarkably similar to the ages of latest Carboniferous-Early Permian Gegenaobao/Dashizai Formation, or A-type granites, which formed under a post-collisional setting. However, the age groups of 320 to 358 Ma with a peak at 336 Ma, show the features of mafic-ultramafic zircons in CL image, most likely derived from local mafic-ultramafic rocks of the Hegenshan ophiolite in the Xiaobaliang area, which is supported by the fact of the ophiolite unconformably overlain by the Middle Permian Zhesi Formation. Therefore, we propose that the emplacement time of the Hegenshan ophiolite must have happened at some time before the Middle Permian (~ 280 Ma), most likely between 300 and 335 Ma, not in the Silurian, Devonian or Mesozoic as previously considered.

  16. Structure of arboreal and herbaceous strata in a neotropical seasonally flooded monodominant savanna of Tabebuia aurea.

    PubMed

    Bueno, M L; Damasceno-Junior, G A; Pott, A; Pontara, V; Seleme, E P; Fava, W S; Salomão, A K D; Ratter, J A

    2014-05-01

    Large areas in the Pantanal wetland are covered by monodominant formations, e.g. typical landscapes with local names such as "paratudal", dominated by T. aurea. Studies on structure of these formations generally include only woody strata, consequently the species richness registered is usually low due to the absence of the 'ground layer' of herbaceous and others low species. We recorded 13 species, 12 genera and 11 families for the arboreal stratum. Considering arboreal flora without the dominant (T. aurea) individuals showed great establishment in relation to the flood level between 35 - 45 cm while the individuals of the dominant species of 30 - 45 cm. The diameter distribution revealed that the population of T. aurea did not show the reverse J curve, the usual pattern for species in constant regeneration, also evidenced in inconstant Licourt quotient, indicating an episodic recruitment that could lead to future changes in structure. In the herbaceous strata we recorded 78 species, included in 62 genera and 27 families. Using plots method we sampled 46 species, 40 genera and 22 families, while in line interception we found 65 species distributed in 57 genera and 26 families. The floristic similarity of Sørensen between both methods was 59.4%, with 33 species in common, and the method of line interception was more efficient in detecting richness, with 35% more species found in the same time. According to the methods of plots and line interception applied on the woody stratum, our results gave similar detailed information on the structure of this type of savanna, and in spite of being monodominant it shows high species richness when the herbaceous stratum is taken into account. Plots and line interception methods showed similar results for the woody stratum and high species richness of the herbaceous stratum. PMID:25166317

  17. Solute concentrations influence microbial methanogenesis in coal-bearing strata of the Cherokee basin, USA

    DOE PAGESBeta

    Kirk, Matthew F.; Wilson, Brien H.; Marquart, Kyle A.; Zeglin, Lydia H.; Vinson, David S.; Flynn, Theodore M.

    2015-11-18

    In this study, microorganisms have contributed significantly to subsurface energy resources by converting organic matter in hydrocarbon reservoirs into methane, the main component of natural gas. In this study, we consider environmental controls on microbial populations in coal-bearing strata of the Cherokee basin, an unconventional natural gas resource in southeast Kansas, USA. Pennsylvanian-age strata in the basin contain numerous thin (0.4–1.1 m) coalbeds with marginal thermal maturities (0.5–0.7% Ro) that are interbedded with shale and sandstone. We collected gas, water, and microbe samples from 16 commercial coalbed methane wells for geochemical and microbiological analysis. The water samples were Na–Cl typemore » with total dissolved solids (TDS) content ranging from 34.9 to 91.3 g L–1. Gas dryness values [C1/(C2 + C3)] averaged 2640 and carbon and hydrogen isotope ratios of methane differed from those of carbon dioxide and water, respectively, by an average of 65 and 183‰. These values are thought to be consistent with gas that formed primarily by hydrogenotrophic methanogenesis. Results from cultivation assays and taxonomic analysis of 16S rRNA genes agree with the geochemical results. Cultivable methanogens were present in every sample tested, methanogen sequences dominate the archaeal community in each sample (avg 91%), and few archaeal sequences (avg 4.2%) were classified within Methanosarcinales, an order of methanogens known to contain methylotrophic methanogens. Although hydrogenotrophs appear dominant, geochemical and microbial analyses both indicate that the proportion of methane generated by acetoclastic methanogens increases with the solute content of formation water, a trend that is contrary to existing conceptual models. Consistent with this trend, beta diversity analyses show that archaeal diversity significantly correlates with formation water solute content. In contrast, bacterial diversity more strongly correlates with location

  18. Generation and Migration of Natural Gas in Miocene Strata, Offshore Southeastern Korea

    NASA Astrophysics Data System (ADS)

    Son, Byeong-Kook

    2016-04-01

    Natural gas and condensate are produced from Miocene strata of the Tertiary marine basin, called Ulleung Basin, which is located offshore southeastern Korea. Petroleum system in the basin has not been fully understood, because effective source rocks have not been identified in the area. However, 1-D petroleum system modelling and isotope data indicate that the source rock of the natural gas and condensate might be present at deeper strata than 5,000 m in the basin. In addition, the analysis of diamondoids in the condensate shows that the gas was transformed from type II kerogen. Based on this source rock information and other geological data, 2-D petroleum system modelling was conducted on two cross sections in the southwestern margin of the basin. The 2-D models show two phase generation and migration, which are caused by the geometry of source bed and the maturity level of each pod of the bed. In addition, the accumulation of hydrocarbon is constrained greatly by the timing of development of the regional seal. The first generation and migration of oil and gas begins with a high rate of sedimentation at a deeply and early buried pod of the source bed at 15 Ma. The hydrocarbon, however, migrates upward and diffuses toward the surface. The second generation and migration occurs at around 11 Ma from the other pod of the source bed. This hydrocarbon migrates updip toward anticlines and accumulates into the traps of anticlines. On the other hand, the model shows that the generation and migration is dominated by gas, rather than oil. This model indicates that the accumulation of hydrocarbon can be completed only by the proper and sophisticated combination of the geological elements and the timing of hydrocarbon migration in time and space. This 2-D feature of generation and migration is supported by additional 1-D models of two pseudo-wells drilled on the 2-D section.

  19. The Lower Cretaceous strata in Svalbard and the Barents Sea; basin infill dynamics and palaeobathymetry

    NASA Astrophysics Data System (ADS)

    Midtkandal, Ivar; Faleide, Jan Inge; Evensen Dahlberg, Maria; Dimitriou, Myrsini; Petter Nystuen, Johan

    2014-05-01

    Data from cliff sections on Svalbard and seismic sections from the Barents Sea indicate an Early Cretaceous depositional system of far greater reach than the Svalbard archipelago, with a source area to the northwest of Svalbard and a basin deepening to the southeast in the western Barents Sea. Seismic imagery shows large-scale, low-angle clinoforms that demonstrate progradation of shallow-marine clastic deposits hundreds of kilometres into the present day Barents Sea, sourced from areas near the High Arctic Large Igneous Province (HALIP) to the northwest. Field data and seismic imagery are coupled to map architectural patterns that provide information on basin physiography and scale. The results of the study show that the sediment infill of the epicontinental basin was largely controlled by availability of accommodation space, and how the formation of localized syn- and post-depositional troughs and highs altered the position and orientation of the Early Cretaceous shoreline, and thereby its corresponding facies distribution. The Early Cretaceous accommodation space covering a wider part of the Barents Shelf, was created by regional subsidence of a possible deep-seated origin. In the SW Barents Sea additional accommodation space was formed by prominent rift events during Late Jurassic-Early Cretaceous times. Cenozoic uplift and erosion, increasing northwards, has removed most of the Lower Cretaceous strata in the NW Barents Sea. Thus, a direct tie between the prograding units in the southern Barents Sea and the exposed more proximal Lower Cretaceous strata on Svalbard is not possible. An on-going analysis of seismic profiles along with well data will provide new constraints for estimating palaeo-water depths and facies distribution for the Cretaceous in the Barents Sea.

  20. Westward overstepping of Lower Mississippian by Upper Mississippian strata in eastern Nevada

    SciTech Connect

    Nichols, K.M.; Silberling, N.J.; Macke, D.L. )

    1993-04-01

    The Mississippian section in western Utah includes three complete, successive stratigraphic sequence, each representing a distinct third-order transgressive-regressive (T-R) cycle. In ascending order, these sequences are informally named the Morris (MO), Sadlick (SA), and Maughan (MA) (Silberling and others, this volume). In west-central Utah, the MO is represented by strata customarily regarded as the lower part of the Joana Limestone, SA by the upper part of the Joana and the Needle Siltstone Member of the Chainman Shale, and MA by the Skunk Spring Limestone Bed and part of the overlying Chainman Shale. The systems tracts that define the stratigraphic boundaries between these three sequences can be traced westward to the southern Egan Range in Nevada. Farther west, in the White Pine Range, MA rests disconformably on MO, and SA is cut out between them. Still farther west, in the north-central Pancake Range where MO limestones are 22 m thick, terra-rossa soil and/or a sedimentary breccia of MO limestone separate MO from a few meters of micritic radiolarian limestone below a thick section of MA argillite. Through stratigraphic thicknesses of as much as a few tens of meters, discontinuous units of this micrite, along with units of encrinite, are interstratified with argillite similar to that which forms much of the overlying strata of the Dale Canyon Formation or Chainman Shale. This sequence, directly overlying the Pilot Shale, could either be MA, and thus mid or late Meramecian in age at its base, or be an older Mississippian sequence unrelated to the sequences occurring farther east in Nevada and in Utah.

  1. Vertical-axis rotations determined from paleomagnetism of Mesozoic and Cenozoic strata of the Bolivian Andes

    NASA Astrophysics Data System (ADS)

    Richards, David R.; Butler, Robert F.; Sempere, Thierry

    2004-07-01

    Thermal demagnetization and principal component analysis allowed determination of characteristic remanent magnetization (ChRM) directions from 256 sites at 22 localities in Mesozoic and Cenozoic sedimentary strata of the Bolivian Altiplano and Eastern Cordillera. An inclination-only fold test of site-mean ChRM directions from Cenozoic units (principally the Santa Lucía Formation) indicates optimum unfolding at 97.1% unfolding, consistent with a primary origin for the ChRM. For Mesozoic strata, optimum unfolding occurred at 89.2%, perhaps indicating secondary remagnetization at some locations. For Cenozoic units, comparison of locality-mean directions with expected paleomagnetic directions indicates vertical-axis rotations from 33° counterclockwise to 24° clockwise. Euler pole analysis of along-strike variation in crustal shortening within the Subandean and Interandean zones indicates 18° clockwise rotation south of the axis of curvature of the Bolivian Andes and 6° counterclockwise rotation northwest of the axis during the past 10 m.y. Along-strike variation of shortening within the Eastern Cordillera indicates 8° clockwise rotation south of the axis and 8° counterclockwise rotation northwest of the axis from 35 to 10 Ma. These vertical-axis rotations produced by along-strike variations in crustal shortening during development of the Bolivian fold-thrust belt agree well with observed rotations determined from paleomagnetism of Cenozoic rocks in the Eastern Cordillera and in the Subandean and Interandean zones. However, local rotations are required to account for complex rotations in the Cochabamba Basin and within the Altiplano. The curvature of the Bolivian Andes has been progressively enhanced during Cenozoic fold-thrust belt deformation.

  2. Solute Concentrations Influence Microbial Methanogenesis in Coal-bearing Strata of the Cherokee Basin, USA.

    PubMed

    Kirk, Matthew F; Wilson, Brien H; Marquart, Kyle A; Zeglin, Lydia H; Vinson, David S; Flynn, Theodore M

    2015-01-01

    Microorganisms have contributed significantly to subsurface energy resources by converting organic matter in hydrocarbon reservoirs into methane, the main component of natural gas. In this study, we consider environmental controls on microbial populations in coal-bearing strata of the Cherokee basin, an unconventional natural gas resource in southeast Kansas, USA. Pennsylvanian-age strata in the basin contain numerous thin (0.4-1.1 m) coalbeds with marginal thermal maturities (0.5-0.7% R o ) that are interbedded with shale and sandstone. We collected gas, water, and microbe samples from 16 commercial coalbed methane wells for geochemical and microbiological analysis. The water samples were Na-Cl type with total dissolved solids (TDS) content ranging from 34.9 to 91.3 g L(-1). Gas dryness values [C1/(C2 + C3)] averaged 2640 and carbon and hydrogen isotope ratios of methane differed from those of carbon dioxide and water, respectively, by an average of 65 and 183‰. These values are thought to be consistent with gas that formed primarily by hydrogenotrophic methanogenesis. Results from cultivation assays and taxonomic analysis of 16S rRNA genes agree with the geochemical results. Cultivable methanogens were present in every sample tested, methanogen sequences dominate the archaeal community in each sample (avg 91%), and few archaeal sequences (avg 4.2%) were classified within Methanosarcinales, an order of methanogens known to contain methylotrophic methanogens. Although hydrogenotrophs appear dominant, geochemical and microbial analyses both indicate that the proportion of methane generated by acetoclastic methanogens increases with the solute content of formation water, a trend that is contrary to existing conceptual models. Consistent with this trend, beta diversity analyses show that archaeal diversity significantly correlates with formation water solute content. In contrast, bacterial diversity more strongly correlates with location than solute content

  3. Comparative Sex Chromosome Genomics in Snakes: Differentiation, Evolutionary Strata, and Lack of Global Dosage Compensation

    PubMed Central

    Zektser, Yulia; Mahajan, Shivani; Bachtrog, Doris

    2013-01-01

    Snakes exhibit genetic sex determination, with female heterogametic sex chromosomes (ZZ males, ZW females). Extensive cytogenetic work has suggested that the level of sex chromosome heteromorphism varies among species, with Boidae having entirely homomorphic sex chromosomes, Viperidae having completely heteromorphic sex chromosomes, and Colubridae showing partial differentiation. Here, we take a genomic approach to compare sex chromosome differentiation in these three snake families. We identify homomorphic sex chromosomes in boas (Boidae), but completely heteromorphic sex chromosomes in both garter snakes (Colubridae) and pygmy rattlesnake (Viperidae). Detection of W-linked gametologs enables us to establish the presence of evolutionary strata on garter and pygmy rattlesnake sex chromosomes where recombination was abolished at different time points. Sequence analysis shows that all strata are shared between pygmy rattlesnake and garter snake, i.e., recombination was abolished between the sex chromosomes before the two lineages diverged. The sex-biased transmission of the Z and its hemizygosity in females can impact patterns of molecular evolution, and we show that rates of evolution for Z-linked genes are increased relative to their pseudoautosomal homologs, both at synonymous and amino acid sites (even after controlling for mutational biases). This demonstrates that mutation rates are male-biased in snakes (male-driven evolution), but also supports faster-Z evolution due to differential selective effects on the Z. Finally, we perform a transcriptome analysis in boa and pygmy rattlesnake to establish baseline levels of sex-biased expression in homomorphic sex chromosomes, and show that heteromorphic ZW chromosomes in rattlesnakes lack chromosome-wide dosage compensation. Our study provides the first full scale overview of the evolution of snake sex chromosomes at the genomic level, thus greatly expanding our knowledge of reptilian and vertebrate sex chromosomes

  4. Solute Concentrations Influence Microbial Methanogenesis in Coal-bearing Strata of the Cherokee Basin, USA

    PubMed Central

    Kirk, Matthew F.; Wilson, Brien H.; Marquart, Kyle A.; Zeglin, Lydia H.; Vinson, David S.; Flynn, Theodore M.

    2015-01-01

    Microorganisms have contributed significantly to subsurface energy resources by converting organic matter in hydrocarbon reservoirs into methane, the main component of natural gas. In this study, we consider environmental controls on microbial populations in coal-bearing strata of the Cherokee basin, an unconventional natural gas resource in southeast Kansas, USA. Pennsylvanian-age strata in the basin contain numerous thin (0.4–1.1 m) coalbeds with marginal thermal maturities (0.5–0.7% Ro) that are interbedded with shale and sandstone. We collected gas, water, and microbe samples from 16 commercial coalbed methane wells for geochemical and microbiological analysis. The water samples were Na–Cl type with total dissolved solids (TDS) content ranging from 34.9 to 91.3 g L−1. Gas dryness values [C1/(C2 + C3)] averaged 2640 and carbon and hydrogen isotope ratios of methane differed from those of carbon dioxide and water, respectively, by an average of 65 and 183‰. These values are thought to be consistent with gas that formed primarily by hydrogenotrophic methanogenesis. Results from cultivation assays and taxonomic analysis of 16S rRNA genes agree with the geochemical results. Cultivable methanogens were present in every sample tested, methanogen sequences dominate the archaeal community in each sample (avg 91%), and few archaeal sequences (avg 4.2%) were classified within Methanosarcinales, an order of methanogens known to contain methylotrophic methanogens. Although hydrogenotrophs appear dominant, geochemical and microbial analyses both indicate that the proportion of methane generated by acetoclastic methanogens increases with the solute content of formation water, a trend that is contrary to existing conceptual models. Consistent with this trend, beta diversity analyses show that archaeal diversity significantly correlates with formation water solute content. In contrast, bacterial diversity more strongly correlates with location than solute content

  5. Shale gas reservoir characteristics of Ordovician-Silurian formations in the central Yangtze area, China

    NASA Astrophysics Data System (ADS)

    Shan, Chang'an; Zhang, Tingshan; Wei, Yong; Zhang, Zhao

    2016-07-01

    The characteristics of a shale gas reservoir and the potential of a shale gas resource of Ordovician-Silurian age in the north of the central Yangtze area were determined. Core samples from three wells in the study area were subjected to thin-section examination, scanning electron microscopy, nuclear magnetic resonance testing, X-ray diffraction mineral analysis, total organic carbon (TOC) testing, maturity testing, gas-bearing analysis, and gas component and isothermal adsorption experiments. A favorable segment of the gas shale reservoir was found in both the Wufeng Formation and the lower part of the Longmaxi Formation; these formations were formed from the late Katian to early Rhuddanian. The high-quality shale layers in wells J1, J2, and J3 featured thicknesses of 54.88 m, 48.49 m, and 52.00 m, respectively, and mainly comprised carbonaceous and siliceous shales. Clay and brittle minerals showed average contents of 37.5% and 62.5% (48.9% quartz), respectively. The shale exhibited type II1 kerogens with a vitrinite reflectance ranging from 1.94% to 3.51%. TOC contents of 0.22%-6.05% (average, 2.39%) were also observed. The reservoir spaces mainly included micropores and microfractures and were characterized by low porosity and permeability. Well J3 showed generally high gas contents, i.e., 1.12-3.16 m3/t (average 2.15 m3/t), and its gas was primarily methane. The relatively thick black shale reservoir featured high TOC content, high organic material maturity, high brittle mineral content, high gas content, low porosity, and low permeability. Shale gas adsorption was positively correlated with TOC content and organic maturity, weakly positive correlated with quartz content, and weakly negatively correlated with clay content. Therefore, the Wufeng and Longmaxi formations in the north of the central Yangtze area have a good potential for shale gas exploration.

  6. Glaciation and deglaciation of the Libyan Desert: The Late Ordovician record

    NASA Astrophysics Data System (ADS)

    Le Heron, D. P.; Armstrong, H. A.; Wilson, C.; Howard, J. P.; Gindre, L.

    2010-01-01

    Detailed outcrop studies at the flanks of Al Kufrah Basin, Libya, reveal the nature of glacially-related sedimentation and post-depositional deformation styles produced in association with the Late Ordovician glaciation, during which ice sheets expanded northward over North Africa to deposit the Mamuniyat Formation. At the SE basin flank (Jabal Azbah), the Mamuniyat Formation is sand-dominated, and incises interfingering braidplain and shallow marine deposits of the Hawaz Formation. The glacially-related sediments include intercalations of mud-chip bearing tabular sandstones and intraformational conglomerates, which are interpreted as turbidite and debrite facies respectively. These record aggradation of an extensive sediment wedge in front of a stable former ice margin. An increase in mudstone content northward is accompanied by the occurrence of more evolved turbidites. A widespread surface, bearing streamlined NW-SE striking ridges and grooves, punctuates this succession. The structures on the surface are interpreted to have formed during a regional north-westward ice advance. Above, siltstones bearing Arthrophycus burrows, and Orthocone-bearing sandstones beneath tidal bars testify to glaciomarine conditions for deposition of the underflow deposits beneath. By contrast, the northern basin margin (Jabal az-Zalmah) is appreciably different in recording shallower water/paralic sedimentation styles and major glaciotectonic deformation features, although facies analysis also reveals northward deepening. Here, a siltstone wedging from 8 to 50 m toward the north was deposited (lower delta plain), succeeded by climbing ripple cross-laminated sandstones up to 60 m in thickness (distal through proximal delta mouth bar deposits) with occasional diamictite interbeds. These rocks are deformed by thrusts and > 50 m amplitude fault-propagation folds, the deformation locally sealed by a diamictite then overlain by conglomeratic lag during ultimate deglaciation. Integrating

  7. Structure and tectonics of a Lower Ordovician forearc ophiolite in central western Maine

    SciTech Connect

    Stetzer, L.M.; Dilek, Y. . Dept. of Geology and Geography)

    1993-03-01

    The Lower Ordovician Boil Mountain ophiolite complex (BMO) in central western Maine occurs in the Gander tectonic zone, nearly 100 km SE of the main Appalachian ophiolite belt, and represents part of the Iapetus oceanic domain. It is exposed in an ENE trending narrow zone immediately south of the Precambrian Chain Lakes massif (CLM). The contact between the CLM and the BMO is characterized by a steeply to vertically south-dipping shear zone composed of several fault planes, which display subhorizontal slickenside lineations with sinistral sense of shearing and counterclockwise rotated porphyroclasts. The BMO consists mainly of pyroxenite, gabbro, diorite, plagiogranite, autobreccia, mafic to felsic volcanic, volcaniclastic, and hemipelagic sedimentary rocks, and contacts between these lithologic units are commonly vertical and faulted. Autobreccia outcrops containing clasts and blocks of serpentinite, diabase, pillowed basalt, and radioalarian chert in a medium-grained hemipelagic matrix indicates deposition penecontemporaneous with ocean floor tectonism during evolution of the ophiolite. Extrusive rocks include basaltic, massive to pillow-lava flows, and andesites, dacites, and rhyolites and are commonly metamorphosed up to a lower-greenschist facies. The BMO is overlain to the SE by a melange-flysch sequence composed mainly of metapelite, metagraywacke, phyllite, and slate with abundant volcanic material suggesting alternated shallow- and deep-water sedimentation in a forearc basin. These relations and the observed structures in the ophiolite indicate its development in an oceanic environment with a low magma budget and active vertical tectonism. The available geochemical data show low Ti, Zr, Y, Cr, and REE contents of volcanic rocks suggesting a depleted magma source in a suprasubduction zone tectonic setting for the ophiolite.

  8. Evolutional trends and palaeobiogeography of the Ordovician trilobite Ovalocephalus Koroleva 1959

    PubMed Central

    Zhiyi, Zhou; Wenwei, Yuan; Zhiqiang, Zhou

    2010-01-01

    Ovalocephalus has a long stratigraphic range and wide geographical distribution in Ordovician peri-Gondwana. Based largely on the well-preserved specimens recently collected from China, all known forms are revised and listed. Phylogenetic analysis was conducted on the genus, involving 10 species. As suggested by the strict consensus tree, evolutional trends of the genus include mainly the isolation of the anterior glabellar portion anterior to S1, the forward shifting of eyes and the related lengthening (exsag.) of the posterior fixigena, the reduction of the number of pygidial axial segments and pleural abaxial rounded free tips, the shortening of the pygidial postaxial region, and the development of cranidial genal spines. Ovalocephalus may have originated in shallow-water sites of the South China Plate in the Early Floian, but migrated into the deep-water regions from the Darriwilian onwards. All the records of the genus from the Early Floian to Early Katian were confined to eastern peri-Gondwanan plates and terranes in low-latitude zones. It was only restricted to the South China, Tarim and North China plates until the Middle Darriwilian, but the Late Darriwilian eustatic sea-level rise and especially the Sandbian–Early Katian immense transgression may have brought about its dispersal to Alborz, Sibumasu and central Asian terranes. Following the closure of the Tornquist Sea, the genus was even able to spread to Baltica during the latest Katian, and the pre-Hirnantian warming (the Boda event) may have promoted a wider distribution of Ovalocephalus to western peri-Gondwana (the Taurides and Armorica terranes) in the then-high latitudes. PMID:19403533

  9. Deep-to-shallow carbonate ramp transition in Viola Limestone (Ordovician), southwest Arbuckle Mountains, Oklahoma

    SciTech Connect

    Glavin, P.K.

    1983-03-01

    The Viola Limestone (Middle and Upper Ordovician) of the southwest Arbuckle Mountains was deposited on a carbonate ramp within the southern Oklahoma Aulacogen. Depositional environments include (1) anaerobic, deep-ramp setting represented by microfacies RL, CH, CGL, and A, (2) dysaerobic, mid-ramp setting represented by microfacies B, and (3) aerobic, shallow-ramp setting represented by microfacies C and D. Deposition in the deep- and mid-ramp environments was dominated by bottom-hugging currents produced by off-platform flow of denser waters. Primary sedimentary structures include millimeter-size laminations, starved ripples, and concave-up and inclined erosional surfaces. Shelly benthic fauna are rare in A and B; trace fossils are common only in B. Deposits associated with the line-source gully, microfacies RL, CH, and CGL, are laterally confined; they have been observed only in the southwest Arbuckle Mountains. Primary sedimentary structures present in RL include wavy and ripple-cross laminae. Microfacies CH, contained within RL and interpreted as a submarine channel deposit, is present only at one locality. Primary sedimentary structures present in CH include an erosional base and several internal erosional surfaces, lateral accretionary sets, and imbricated, locally derived intraclasts. High total organic carbon (TOC) values have been reported for the lower Viola. TOC values of 1% have been reported from microfacies A, and TOC values of 5% have been reported from microfacies RL. These high values suggest that A and RL may act as hydrocarbon source rocks. Recognition of these microfacies in the subsurface will contribute to our knowledge of the Viola Limestone as an exploration target.

  10. Global analyses of brachiopod faunas through the Ordovician and Silurian transition: Reducing the role of the Lazarus effect

    USGS Publications Warehouse

    Rong, J.-Y.; Boucot, A.J.; Harper, D.A.T.; Zhan, R.-B.; Neuman, R.B.

    2006-01-01

    Global analyses of 88 families and 284 genera of brachiopods from middle Ashgill, Late Ordovician, to early-middle Rhuddanian, Early Silurian, indicate that 18.6% and 12.5% of families and 51.0% and 41.3% of genera were eliminated in the first and second phases of the end-Ordovician mass extinction, respectively, with the total loss of 28.4% of families and 69.0% of genera in the crisis. New investigation demonstrates that brachiopods, at both generic and familial levels, suffered greater during the first phase than during the second phase. Four groups (victims, relicts, survivors, and new arrivals) are distinguished by their stratigraphical ranges. Generic survivors, occurring in the Kosov Province during the Hirnantian, can be split into three types with respect to their changing abundance: increasing, declining, and Lazarus taxa. Among the 88 genera that survived, numerous declining genera occurred in the Hirnantian: 16 Lazarus families and 18 Lazarus genera are provisionally known and may be regarded as end members of the declining type. Comparison of the abundance, population size, and distribution patterns of declining and Lazarus taxa shows important similarities between these two types which contribute to a better understanding of the nature of Lazarus taxa. In addition to these biological attributes, taphonomic failure and generally poor preservation, together with collecting bias and inadequate systematic data, are clearly involved. More collections will undoubtedly globally reduce the number of Lazarus taxa. A single, common refugium for end-Ordovician brachiopods probably did not exist; rather, these taxa used paleogeographically scattered locations in a range of environments for survival. ?? 2006 NRC Canada.

  11. High potential for chemical weathering and climate effects of early lichens and bryophytes in the Late Ordovician

    NASA Astrophysics Data System (ADS)

    Porada, Philipp; Lenton, Tim; Pohl, Alexandre; Weber, Bettina; Mander, Luke; Donnadieu, Yannick; Beer, Christian; Pöschl, Ulrich; Kleidon, Axel

    2016-04-01

    Non-vascular vegetation in the Late Ordovician may have considerably increased global chemical weathering, thereby reducing atmospheric CO2 concentration and contributing to a decrease in global temperature and the onset of glaciations. Usually, enhancement of weathering by non-vascular vegetation is estimated using field experiments which are limited to small areas and a low number of species. This makes it difficult to extrapolate to the global scale and to climatic conditions of the past, which differ markedly from the recent climate. Here we present a global, spatially explicit modelling approach to estimate chemical weathering by non-vascular vegetation in the Late Ordovician. During this period, vegetation probably consisted of early forms of today's lichens and bryophytes. We simulate these organisms with a process-based model, which takes into account their physiological diversity by representing multiple species. The productivity of lichens and bryophytes is then related to chemical weathering of surface rocks. The rationale is that the organisms dissolve rocks to extract phosphorus for the production of new biomass. To account for the limited supply of unweathered rock material in shallow regions, we cap biotic weathering at the erosion rate. We estimate a potential global weathering flux of 10.2 km3 yr‑1 of rock, which is around 12 times larger than today's global chemical weathering. The high weathering potential implies a considerable impact of lichens and bryophytes on atmospheric CO2 concentration in the Ordovician. Moreover, we find that biotic weathering is highly sensitive to atmospheric CO2, which suggests a strong feedback between chemical weathering by lichens and bryophytes and climate.

  12. A unique Middle Ordovician K-bentonite bed succession at Röstånga, S. Sweden

    USGS Publications Warehouse

    Bergstrom, Stig M.; Huff, Warren D.; Kolata, Dennis R.; Yost, Deborah A.; Hart, Charles P.

    1997-01-01

    An approximately 8.5 m thick sequence of upper Viruan (upper Middle Ordovician) shales, mudstones, and limestones in an outcrop at Kyrkbäcken near Röstånga in W‐central Skåne contains 19 K‐bentonite beds, several of which are as much as 40–67 cm thick. Thirteen of these beds are in the upper part of the Sularp Fm., four in the Skagen Fm., and two questionable beds in the Mossen Fm. Evidence from macrofossils, chitinozoans, and conodonts are used for biostratigraphic age assessment of the K‐bentonite succession. Regional comparison of the sequence with those at Kinnekulle (Kullatorp), Koängen, and Tommarp suggests that its total stratigraphie thickness is smaller than those at the two former sites but the thicknesses of several of the Kyrkbacken ash beds are greater than those in similar stratigraphic positions in the other successions. The K‐bentonites at Kyrkbacken have a similar clay mineralogy and major and trace element composition as other Ordovician K‐bentonites, and these data indicate that the parental magma was of felsic, probably rhyolitic composition. Based on amphibole geoba‐rometry, the magma chamber is interpreted to have been at a depth of 14–20 km. The relatively large number of unusually thick ash beds of Middle Ordovician age makes the easily accessible Kyrkbäcken outcrop unique not only in Baltoscandia but, as far as we are aware, also on the entire northern hemisphere, and only one comparable exposure is known in the southern hemisphere, namely in the Precordillera of northern Argentina.

  13. Storm deposits as graves in Early Life: the Fezouata Lagerstätte case (Lower Ordovician, Morocco)

    NASA Astrophysics Data System (ADS)

    Vaucher, Romain; Pittet, Bernard; Hormière, Hélène; Martin, Emmanuel L. O.; Lefebvre, Bertrand

    2016-04-01

    The Fezouata Shale (Early Ordovician, Morocco) is renowned in the palaeontological community for its Konservat-Lagerstätte (Tremadocian in age) that yielded thousands of exceptionally well-preserved fossils (EPF) from the Great Ordovician Biodiversification Event. Lower Ordovician deposits in the central Anti-Atlas Mountain (Zagora area) are expressed by the Fezouata Shale and the Zini Formation. They consist in ca. 900m of siltstones and sandstones deposited in an epicontinental sea at the periphery of the Gondwanaland. Sedimentologic field analysis and sequence analysis were achieved on ten stratigraphic sections in order to constrain the palaeoenvironmental context of the Fezouata Biota and to predict the location (geographically and stratigraphically) of new Lagerstätten. Sedimentary structures (cm- to m-scale symmetrical ripples) and geometries (lobe, lobe-channel) point to storm dominance on the sedimentation but peculiar sedimentary features suggest a tide modulation. Thus, a wave-dominated tide-modulated model of deposition recording proximal offshore to shoreface environments for the Fezouata Shale and shoreface to foreshore environments for the overlying Zini Fm is proposed. Layers yielding EPF are argillaceous siltstones (with wave ripples of cm-scale wavelength) always overlain by fine-grained sandstones (distal storm deposits, few cm-thick, several m-long, with cm- to dm-scale hummocky cross-stratifications). Fast burying by storm deposits appear to be of prime importance to initiate the exceptional preservation of the soft tissues of animals in the fossil record. According to the model of deposition it correspond to environments close to the storm weather wave base. Lower Ordovician succession was deposited during a 2nd order cycle, although 3rd and 4th order cycles were also identified. Encoding these different orders of sea level fluctuations giving a value of "1" for the deepest part of sequences (for each order) and a value of "0" for the

  14. Main consistent patterns of Stromatoporoid Development in the Late Ordovician and Silurian in the North Urals Palaeobasin

    NASA Astrophysics Data System (ADS)

    Antropova, E.

    2009-04-01

    In the history of the Earth there have been no basins with similar characteristics. The North Urals palaeobasin had its own unique features. The dominant benthic organisms of basin ecosystem during the Ordovician and Silurian were stromatoporoids, corals, and brachiopods. This fauna is vitally important for the aims of stratigraphy so long as conodonts are extremely rare in sections of the Northern Urals area. The most complete ordering of stromatoporoid complexes has been established and made it possible to estimate rates and measures of extinction at a level of the province. It was also found out that stromatoporoids were organisms responsive to subtle changes of environment and that they accommodated differently to those changing conditions. The evolution of stromatoporoids was accompanied by phylogenetic reorganization and formation of endemic communities in the Late Ordovician and Early Silurian. In the Late Silurian taxonomical diversity of stromatoporoids was mainly controlled by migration processes and cosmopolites with wide palaeogeographic links prevailed in the palaeobasin. Therefore palaeobasin at that time was open to stromatoporoid fauna migration which is confirmed by the occurrence of genera and species that disperse in coeval deposits of many areas, for example, Baltic States, Sweden, Ukraine (Podolia), Western Siberia, Arctic islands of Russia, Mongolia, Canada (islands). The evolution of stromatoporoid communities in the Ordovician-Silurian was intermitted by biotic crises. The analysis of stromatoporoid development helps to define crucial points of ecosystem's reorganizations coinciding with critical geological and biotic events in the history of the North Urals palaeobasin existence, as well as global events during the Ordovician and Silurian (Hirnantian Event, Ireviken Event, Lau Event). The analysis of crises indicates local dependence of stromatoporoid biodiversity on depositional environments. Large local biocenos reorganizations and biotic

  15. Structural plays in Ellesmerian sequence and correlative strata of the National Petroleum Reserve, Alaska

    USGS Publications Warehouse

    Moore, Thomas E.; Potter, Christopher J.

    2003-01-01

    Reservoirs in deformed rocks of the Ellesmerian sequence in southern NPRA are assigned to two hydrocarbon plays, the Thrust-Belt play and the Ellesmerian Structural play. The two plays differ in that the Thrust-Belt play consists of reservoirs located in allochthonous strata in the frontal part of the Brooks Range fold-and-thrust belt, whereas those of the Ellesmerian Structural play are located in autochthonous or parautochthonous strata at deeper structural levels north of the Thrust-Belt play. Together, these structural plays are expected to contain about 3.5 TCF of gas but less than 6 million barrels of oil. These two plays are analyzed using a two-stage deformational model. The first stage of deformation occurred during the Neocomian, when distal strata of the Ellesmerian sequence were imbricated and assembled into deformational wedges emplaced northward onto regionally south-dipping authochon at 140-120 Ma. In the mid-Cretaceous following cessation of the deformation, the Colville basin, the foreland basin to the orogen, was filled with a thick clastic succession. During the second stage of deformation at about 60 Ma (early Tertiary), the combined older orogenic belt-foreland basin system was involved in another episode of north-vergent contractional deformation that deformed pre-existing stratigraphic and structurally trapped reservoir units, formed new structural traps, and caused significant amounts of uplift, although the amount of shortening was relatively small in comparison to the first episode of deformation. Hydrocarbon generation from source strata (Shublik Formation, Kingak Shale, and Otuk Formation) and migration into stratigraphic traps occurred primarily by sedimentary burial principally between 100-90 Ma, between the times of the two episodes of deformation. Subsequent burial caused deep stratigraphic traps to become overmature, cracking oil to gas, and some new generation to begin progressively higher in the section. Structural disruption of

  16. Magnetostratigraphy of syntectonic growth strata and implications for the late Cenozoic deformation in the Baicheng Depression, Southern Tian Shan

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiliang; Sun, Jimin; Tian, Zhonghua; Gong, Zhijun

    2016-03-01

    The collision between India and Eurasia in the Cenozoic has caused a series of intracontinental deformation in the foreland basins of Tian Shan, but there are debates about the timing of tectonic deformation and the relationship between tectonic uplift and sediment accumulation in the foreland basins. Based on the magnetostratigraphy of growth strata in the Baicheng Depression, Southern Tian Shan, we suggest that an episode of crustal shortening in the late Cenozoic evidenced by syntectonic growth strata in the Kelasu-Yiqikelike structural belt (KYSB) initiated at ∼5.3 Ma, since then the sedimentation rate accelerated abruptly and coarse molasse deposits accumulated. Combined with the results of growth strata on both flanks of Tian Shan and the fact that the Xiyu Formation on the southern limb of the Kasangtuokai Anticline was involved into the growth strata, we conclude that the period from ∼7-5 Ma to the early Pleistocene was one of the important episodes of intracontinental deformation in the foreland basins of Tian Shan, as a response to the Cenozoic collision between India and Eurasia.

  17. 78 FR 56944 - Strata Energy, Inc. (Ross In Situ Recovery Uranium Project); Notice of Atomic Safety and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-16

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  18. 77 FR 12087 - Atomic Safety and Licensing Board Panel; Strata Energy, Inc.; Memorandum and Order (Notice of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-28

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  19. Assessment of undiscovered oil and gas resources in Jurassic and Cretaceous strata of the Gulf Coast, 2010

    USGS Publications Warehouse

    Dubiel, Russell F.; Warwick, Peter D.; Swanson, Sharon; Burke, Lauri; Biewick, Laura R.H.; Charpentier, Ronald R.; Coleman, James L., Jr.; Cook, Troy A.; Dennen, Kris; Doolan, Colin; Enomoto, Catherine; Hackley, Paul C.; Karlsen, Alexander W.; Klett, Timothy R.; Kinney, Scott A.; Lewan, Michael D.; Merrill, Matt; Pearson, Krystal; Pearson, Ofori N.; Pitman, Janet K.; Pollastro, Richard M.; Rowan, Elizabeth L.; Schenk, Christopher J.; Valentine, Brett

    2011-01-01

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated means of 147.4 trillion cubic feet of undiscovered natural gas, 2.4 billion barrels of undiscovered oil, and 2.96 billion barrels of undiscovered natural gas liquids in Jurassic and Cretaceous strata in onshore lands and State waters of the Gulf Coast.

  20. Scalable Generalization of Hydraulic Conductivity in Quaternary Strata for Use in a Regional Groundwater Model

    NASA Astrophysics Data System (ADS)

    Jatnieks, J.; Popovs, K.; Klints, I.; Timuhins, A.; Kalvans, A.; Delina, A.; Saks, T.

    2012-04-01

    The cover of Quaternary sediments especially in formerly glaciated territories usually is the most complex part of the sedimentary sequences. In regional hydro-geological models it is often assumed as a single layer with uniform or calibrated properties (Valner 2003). However, the properties and structure of Quaternary sediments control the groundwater recharge: it can either direct the groundwater flow horizontally towards discharge in topographic lows or vertically, recharging groundwater in the bedrock. This work aims to present calibration results and detail our experience while integrating a scalable generalization of hydraulic conductivity for Quaternary strata in the regional groundwater modelling system for the Baltic artesian basin - MOSYS V1. We also present a method for solving boundary transitions between spatial clusters of lithologically similar structure. In this study the main unit of generalization is the spatial cluster. Clusters are obtained from distance calculations combining the Normalized Compression Distance (NCD) metric, calculated by the CompLearn parameter-free machine learning toolkit, with normalized Euclidean distance measures for coordinates of the borehole log data. A hierarchical clustering solution is used for obtaining cluster membership identifier for each borehole. Using boreholes as generator points for Voronoi tessellation and dissolving resulting polygons according to their cluster membership attribute, allows us to obtain spatial regions representing a certain degree of similarity in lithological structure. This degree of similarity and the spatial heterogeneity of the cluster polygons can be varied by different flattening of the hierarchical cluster model into variable number of clusters. This provides a scalable generalization solution which can be adapted according to model calibration performance. Using the dissimilarity matrix of the NCD metric, a borehole most similar to all the others from the lithological structure

  1. Migrated hydrocarbons in exposure of Maastrichtian nonmarine strata near Saddle Mountain, lower Cook Inlet, Alaska

    USGS Publications Warehouse

    LePain, D.L.; Lillis, P.G.; Helmold, K.P.; Stanley, R.G.

    2012-01-01

    Magoon and others (1980) described an 83-meter- (272-foot-) thick succession of Maastrichtian (Upper Cretaceous) conglomerate, sandstone, mudstone, and coal exposed on the south side of an unnamed drainage, approximately 3 kilometers (1.8 miles) east of Saddle Mountain in lower Cook Inlet (figs. 1 and 2). The initial significance of this exposure was that it was the first reported occurrence of nonmarine rocks of this age in outcrop in lower Cook Inlet, which helped constrain the Late Cretaceous paleogeography of the area and provided important information on the composition of latest Mesozoic sandstones in the basin. The Saddle Mountain section is thought to be an outcrop analog for Upper Cretaceous nonmarine strata penetrated in the OCS Y-0097 #1 (Raven) well, located approximately 40 kilometers (25 miles) to the south–southeast in Federal waters (fig. 1). Atlantic Richfield Company (ARCO) drilled the Raven well in 1980 and encountered oil-stained rocks and moveable liquid hydrocarbons between the depths of 1,760 and 3,700 feet. Completion reports on file with the Bureau of Ocean Energy Management (BOEM; formerly Bureau of Ocean Energy Management, Regulation and Enforcement, and prior to 2010, U.S. Minerals Management Service) either show flow rates of zero or do not mention flow rates. A fluid analysis report on file with BOEM suggests that a wireline tool sampled some oil beneath a 2,010-foot diesel cushion during the fl ow test of the 3,145–3,175 foot interval, but the recorded fl ow rate was still zero (Kirk Sherwood, written commun., January 9, 2012). Further delineation and evaluation of the apparent accumulation was never performed and the well was plugged and abandoned. As part of a 5-year comprehensive evaluation of the geology and petroleum systems of the Cook Inlet forearc basin, the Alaska Division of Geological & Geophysical Surveys obtained a research permit from the National Park Service to access the relatively poorly understood

  2. Sporomorphs from the Jackson Group (upper Eocene) and adjacent strata of Mississippi and western Alabama

    USGS Publications Warehouse

    Frederiksen, Norman O.

    1980-01-01

    This palynological study is based on 71 outcrop and core samples of the Jackson Group and adjacent strata from the type area of the group in western Mississippi and also from eastern Mississippi and western Alabama. The Jackson Group consists entirely of marine strata in the region of study. It includes the fossiliferous greensands of the Moodys Branch Formation at the base and the calcareous Yazoo Clay at the top. One hundred seventy-four sporomorph (spore and pollen) types are known from the Jackson Group and adjacent strata in the area of study; all but four of them were observed by the writer. The 174 types are assigned to 74 form genera, 37 modern genera, and 25 new species. Eleven species of pollen grains appear to have accurately determined restricted stratigraphic ranges within the sequence studied. Parsonsidites conspicuus Frederiksen and Ericipites aff. E. ericius (Potonie) Potonie have first occurrences (range bottoms) at the base of the Jackson Group. Aglaoreidia pristina Fowler has its first occurrence near the top of the Jackson. Eight species have last occurrences at or just below the top of the Jackson Group. These are Casuarinidites cf. C. granilabratus (Stanley) Srivastava, Chrysophyllum brevisulcatum (Frederiksen) n. comb., Cupanieidites orthoteichus Cookson and Pike, Symplocos gemroota n. sp., Nudopollis terminalis (Pflug and Thomson) Elsik, Sabal cf. S. granopollenites Rouse, Caprifoliipites tantulus n. sp., and Nypa echinata (Muller) n. comb. From the upper part of the Claiborne Group up through most of the Jackson, the dominant sporomorph types are Cupuliferdipollenites spp., Momipites coryloides Wodehouse, Cupuliferoidaepollenites liblarensis (Thomson) Potonie, Momipites micTofoveolatus (Stanley) Nichols, Quercoidites microhenricii (Potonie) Potonie, and Araliaceoipollenites granulatus (Potonie) n. comb. All these were probably produced by trees of the Juglandaceae and Fagaceae. Relative frequencies of each of these pollen types fluctuate

  3. An integrated geophysical study on the Mesozoic strata distribution and hydrocarbon potential in the South China Sea

    NASA Astrophysics Data System (ADS)

    Hu, Weijian; Hao, Tianyao; Jiang, Weiwei; Xu, Ya; Zhao, Baimin; Jiang, Didi

    2015-11-01

    A series of drilling, dredge, and seismic investigations indicate that Mesozoic sediments exist in the South China Sea (SCS) which shows a bright prospect for oil and gas exploration. In order to study the distribution of Mesozoic strata and their residual thicknesses in the SCS, we carried out an integrated geophysical study based mainly on gravity data, gravity basement depth and distribution of residual Mesozoic thickness in the SCS were obtained using gravity inversion constrained with high-precision drilling and seismic data. In addition, the fine deep crustal structures and distribution characteristics of Mesozoic thicknesses of three typical profiles were obtained by gravity fitting inversion. Mesozoic strata in the SCS are mainly distributed in the south and north continental margins, and have been reformed by the later tectonic activities. They extend in NE-trending stripes are macro-controlled by the deep and large NE-trending faults, and cut by the NW-trending faults which were active in later times. The offset in NW direction of Mesozoic strata in Nansha area of the southern margin are more obvious as compared to the north margin. In the Pearl River Mouth Basin and Southwest Taiwan Basin of the north continental margin the Mesozoic sediments are continuously distributed with a relatively large thickness. In the Nansha area of the south margin the Mesozoic strata are discontinuous and their thicknesses vary considerably. According to the characteristics of Mesozoic thickness distribution and hydrocarbon potential analyses from drilling and other data, Dongsha Uplift-Chaoshan Depression, Southwest Taiwan Basin-Peikang Uplift and Liyue Bank have large thickness of the Mesozoic residual strata, have good hydrocarbon genesis capability and complete source-reservoir-cap combinations, show a bright prospect of Mesozoic oil/gas resources.

  4. Solute concentrations influence microbial methanogenesis in coal-bearing strata of the Cherokee basin, USA

    SciTech Connect

    Kirk, Matthew F.; Wilson, Brien H.; Marquart, Kyle A.; Zeglin, Lydia H.; Vinson, David S.; Flynn, Theodore M.

    2015-11-18

    In this study, microorganisms have contributed significantly to subsurface energy resources by converting organic matter in hydrocarbon reservoirs into methane, the main component of natural gas. In this study, we consider environmental controls on microbial populations in coal-bearing strata of the Cherokee basin, an unconventional natural gas resource in southeast Kansas, USA. Pennsylvanian-age strata in the basin contain numerous thin (0.4–1.1 m) coalbeds with marginal thermal maturities (0.5–0.7% Ro) that are interbedded with shale and sandstone. We collected gas, water, and microbe samples from 16 commercial coalbed methane wells for geochemical and microbiological analysis. The water samples were Na–Cl type with total dissolved solids (TDS) content ranging from 34.9 to 91.3 g L–1. Gas dryness values [C1/(C2 + C3)] averaged 2640 and carbon and hydrogen isotope ratios of methane differed from those of carbon dioxide and water, respectively, by an average of 65 and 183‰. These values are thought to be consistent with gas that formed primarily by hydrogenotrophic methanogenesis. Results from cultivation assays and taxonomic analysis of 16S rRNA genes agree with the geochemical results. Cultivable methanogens were present in every sample tested, methanogen sequences dominate the archaeal community in each sample (avg 91%), and few archaeal sequences (avg 4.2%) were classified within Methanosarcinales, an order of methanogens known to contain methylotrophic methanogens. Although hydrogenotrophs appear dominant, geochemical and microbial analyses both indicate that the proportion of methane generated by acetoclastic methanogens increases with the solute content of formation water, a trend that is contrary to existing conceptual models. Consistent with this trend, beta diversity analyses show that archaeal diversity significantly correlates with formation water solute content. In contrast

  5. Analysing the Types of TV Programmes Viewed by Children from Different Socio-Economic Strata Based on Their Self-Report in the Turkish Context

    ERIC Educational Resources Information Center

    Kabadayi, Abdulkadir

    2006-01-01

    This research investigated the amount of time that children from different socio-economic strata spend watching television per week and whether there was a difference among children from low, middle and upper socio-economic strata with regard to viewing programme types, including action adventure, news and information, competitions, sports,…

  6. The petroleum system of the lower Palaeozoic strata in the central part of the Baltic basin

    NASA Astrophysics Data System (ADS)

    Lazauskiene, Jurga; Zdanaviciute, Onyte

    2013-04-01

    stable carbon isotope analyses allow three genetic oil groups to be distinguished in the Kaliningrad region. These oils appear to be confined to tectonically distinct areas suggesting that the hydrocarbons were derived from different kitchens. The hydrocarbon generation in the Baltic Basin started by the end of Silurian, while the basic phase is thought to occur in Devonian and Permian. Different source rocks contributed to the hydrocarbon expulsion. Slow deposition and tectonically stable regime ensured slow formation of the oil and gase-condensate fields with replenishing oil portions incoming with time: e.g. Cambrian oil traps could accumulate also Ordovician and Silurian oils.

  7. Correlation of the Ordovician Deicke and Millbrig K-bentonites between the Mississippi Valleyand the southern Appalachians

    SciTech Connect

    Huff, W.D.; Kolata, D.R. )

    1990-11-01

    Two widespread Rocklandian age (Middle Ordovician) K-bentonite beds, the Deicke and Millbrig, can be correlated from southern Minnesota and northwestern Iowa through eastern Missouri across Kentucky and central Tennessee to the valley and Ridge of the southern Appalachian Mountains. They are equivalent to beds previously called T-3 or Pencil Cave and T-4 or Mud Cave metabentonites, and thus constitute Ordovician chronostratigraphic marker horizons throughout much of the eastern Mid-Continent. Previous correlations of these beds in the Mississippi Valley by chemical fingerprinting is extended toward the southern Appalachian basin by tracing in surface exposures and on wireline logs. Both beds thicken toward the southeast indicating a volcanic source area that was probably east of South Carolina. The interval between the K-bentonite beds also thickens toward the southeast owing to increased rates of carbonate deposition between the two volcanic episodes. The areal extent of known correlatives of the Deicke and Millbrig is minimally estimated to be 600,000 km{sup 2} and at least 1,122 km{sup 3} of pre-compaction Deicke K-bentonite accumulated as ash in eastern North America. The volume of both beds suggests they rank among the largest air-fall ash deposits documented in the stratigraphic record. 7 figs.

  8. Gigantic Ordovician volcanic ash fall in North America and Europe: Biological, tectonomagmatic, and event-stratigraphic significance

    SciTech Connect

    Huff, W.D. ); Bergstroem, S.M. ); Kolata, D.R. )

    1992-10-01

    Biostratigraphical, geochemical, isotopic, and paleogeographic data suggest that the Millbrig K-bentonite, one of the thickest and most widespread Ordovician volcanic ash beds in eastern North America, is the same as the so-called 'Big Bentonite' in Baltoscandia. This is the first time that the same K-bentonite has been identified in both North America and Europe, and it serves as a unique event-stratigraphic marker over a large portion of the Northern Hemisphere. This eruption produced at least 340 km[sup 3] of dense-rock-equivalent ash that was deposited in a layer up to 1-2 m thick over several million square kilometers. As much as 800 km[sup 3] of additional ash may have fallen into the Iapetus Ocean, for a total of 1,140 km[sup 3]. Trace element geochemistry shows that the ash was derived from a felsic calc-alkalic magmatic source characteristic of volcanism in a continental crust-based, destructive plate-margin setting. This is one of the largest, if not the largest, ash falls recorded in Earth's Phanerozoic stratigraphic record, but its recognizable effect on faunas and floras was minimal, and it did not result in a global extinction event. The Millbrig-Big Bentonite bed provides accurate time control for sedimentologic, paleoecologic, and paleogeographic reconstructions across plates positioned in tropical (Laurentia) and temperate (Baltica) latitudes during Middle Ordovician time.

  9. Changes in depositional environments from Ordovician to tertiary of carbonate rocks in Tak-Mae Sod area, Northwest Thailand

    NASA Astrophysics Data System (ADS)

    Ratanasthien, Benjavun

    Carbonate rocks ranging in age from Ordovician to Tertiary along the Tak-Mae Sod and Mae Sod-Umphang highways were analysed mineralogically, petrographically, and geochemically. The study revealed the depositional environment of the mainly chemical precipitated Ordovician carbonate rocks to be in shallow (lagoonal?) waters of a warm climate. The Carboniferous carbonates were chemically deposited in moderately deep to deep water as indicated by siliceous limestone composed mainly of calcite and radiolarian chert and/or interbedded chert bands. The environment changed to shallower water during the Permo-Carboniferous as seen in the Pra Woh Limestone. The carbonates are characterized by pale colour dolomite, dolomitic limestone and calcareous sandstone. They are sometimes, fossiliferous, mainly bryozoa, foraminifera, corals, gastropods and bivalves. During Triassic to Jurassic, the carbonates were deposited in comparatively shallow and/or closed basins as indicated by alternating sequences of dark to black limestone, calcareous shale and calcareous sandstone. The rocks are composed of high carbonaceous material and clays with few fossils associated. The environment changed to brackish and eventually to fresh water during the Tertiary indicated by fossiliferous limestone (pelycypods and gastropods) and dolomitic limestone which are chemically precipitated in fresh water.

  10. Conodonts, stratigraphy, and relative sea-level changes of the tribes hill formation (lower ordovician, east-central New York)

    USGS Publications Warehouse

    Landing, E.D.; Westrop, S.R.; Knox, L.A.

    1996-01-01

    Tremadocian onlap is recorded by the Tribes Hill Formation. The formation is a lower Lower Ordovician (upper conodont Fauna B Interval(?)- Rossodus manitouensis Zone) depositional sequence that unconformably overlies the Upper Cambrian Little Falls Formation. Depositional environments and stratigraphy indicate that the Tribes Hill was deposited on a wave-, not tide-, dominated shelf and that a uniform, 'layer-cake' stratigraphy is present. The deepening-shoaling sequence of the Tribes Hill includes the: 1) Sprakers Member (new; peritidal carbonate and overlying tempestite limestone and shale); 2) Van Wie Member (new; subtidal shale and limestone); 3) Wolf Hollow Member (revised; massive carbonates with thrombolitic cap); and 4) Canyon Road Member (new; glauconitic limestone and overlying evaporitic dolostone). The shoaling half-cycle of the Tribes Hill is older than a shoaling event in western Newfoundland, and suggests epeirogenic factors in earliest Ordovician sea-level change in east Laurentia. Conodont and trilobite biofacies track lithofacies, and Rossodus manitouensis Zone conodonts and Bellefontia Biofacies trilobites appear in the distal, middle Tribes Hill Formation. Twenty-four conodont species are illustrated. Ansella? protoserrata new species, lapetognathus sprakersi new species, Leukorhinion ambonodes new genus and species, and Laurentoscandodus new genus are described.

  11. Cambro-ordovician sea-level fluctuations and sequence boundaries: The missing record and the evolution of new taxa

    USGS Publications Warehouse

    Lehnert, O.; Miller, J.F.; Leslie, Stephen A.; Repetski, J.E.; Ethington, Raymond L.

    2005-01-01

    The evolution of early Palaeozoic conodont faunas shows a clear connection to sea-level changes. One way that this connection manifests itself is that thick successions of carbonates are missing beneath major sequence boundaries due to karstification and erosion. From this observation arises the question of how many taxa have been lost from different conodont lineages in these incomplete successions. Although many taxa suffered extinction due to the environmental stresses associated with falling sea-levels, some must have survived in these extreme conditions. The number of taxa missing in the early Palaeozoic tropics always will be unclear, but it will be even more difficult to evaluate the missing record in detrital successions of higher latitudes. A common pattern in the evolution of Cambrian-Ordovician conodont lineages is appearances of new species at sea-level rises and disappearances at sea-level drops. This simple picture can be complicated by intervals that consistently have no representatives of a particular lineage, even after extensive sampling of the most complete sections. Presumably the lineages survived in undocumented refugia. In this paper, we give examples of evolution in Cambrian-Ordovician shallowmarine conodont faunas and highlight problems of undiscovered or truly missing segments of lineages. ?? The Palaeontological Association.

  12. A new look at age and area: the geographic and environmental expansion of genera during the Ordovician Radiation

    NASA Technical Reports Server (NTRS)

    Miller, A. I.

    1997-01-01

    Although available paleobiological data indicate that the geographic ranges of marine species are maintained throughout their entire observable durations, other evidence suggests, by contrast, that the ranges of higher taxa expand as they age, perhaps in association with increased species richness. Here, I utilize a database of Ordovician genus occurrences collected from the literature for several paleocontinents to demonstrate that a significant aging of the global biota during the Ordovician Radiation was accompanied by a geographic and environmental expansion of genus ranges. The proportion of genera occurring in two or more paleocontinents in the database, and two or more environmental zones within a six-zone onshore-offshore framework, increased significantly in the Caradocian and Ashgillian. Moreover, widespread genera tended to be significantly older than their endemic counterparts, suggesting a direct link between their ages and their environmental and geographic extents. Expansion in association with aging was corroborated further by demonstrating this pattern directly among genera that ranged from the Tremadocian through the Ashgillian. Taken together, these results are significant not only for what they reveal about the kinetics of a major, global-scale diversification, but also for what they suggest about the interpretation of relationships between diversity trends at the alpha (within-community) and beta (between-community) levels.

  13. Chloritization of Late Ordovician K-bentonites from the northern Baltic Palaeobasin influence from source material or diagenetic environment?

    NASA Astrophysics Data System (ADS)

    Hints, Rutt; Kirsimäe, Kalle; Somelar, Peeter; Kallaste, Toivo; Kiipli, Tarmo

    2006-09-01

    The Baltic Ordovician-Silurian sedimentary succession embodies numerous altered volcanic ash beds that are illite-smectite dominated. Only a few beds rich in chlorite-smectite are known from the Upper Ordovician Pirgu Stage of Estonia. Mixed-layer chlorite-smectite occurs commonly in low-grade metamorphic and hydrothermal environments. However, chloritic K-bentonites of the Pirgu Stage have never been buried deeply and lack signs of metamorphic overprinting. In order to understand the origin of chloritization, three distinct beds were sampled in 14 drillcores from Estonia and Latvia and analysed by means of XRD and SEM. The principal authigenic assemblage of the bulk samples consists of chlorite-smectite (corrensite) together with illite-smectite and K-feldspar. The actual mineral composition of K-bentonites though varies from sample to sample. The clay mineral assemblages range from virtually pure chlorite-smectite to illite-smectite dominated assemblages with minor or no chlorite-smectite. The proportion of chlorite-smectite in K-bentonites shows systematic lateral variations: the share of chloritic phases is highest in the shallower-water part of the palaeobasin and decreases towards the deeper part of the basin. Such regular lateral variations suggest a possible link between chloritization and the configuration of ancient palaeobasin. The present study suggests that the chloritization of primary felsic ashes occurred during early diagenesis and that it was caused by an influx of Mg-rich water probably from a marine sabkha-type environment.

  14. A record of astronomically forced climate change in a late Ordovician (Sandbian) deep marine sequence, Ordos Basin, North China

    NASA Astrophysics Data System (ADS)

    Fang, Qiang; Wu, Huaichun; Hinnov, Linda A.; Wang, Xunlian; Yang, Tianshui; Li, Haiyan; Zhang, Shihong

    2016-07-01

    The late Ordovician Pingliang Formation on the southwestern margin of the Ordos Basin, North China, consists of rhythmic alternations of shale, limestone, and siliceous beds. To explore the possible astronomical forcing preserved in this lithological record, continuous lithological rank and magnetic susceptibility (MS) stratigraphic series were obtained from a ~ 34 m thick section of the Pingliang Formation at Guanzhuang. Power spectral analysis of the MS and rank series reveal 85.5 cm to 124 cm, 23 cm to 38 cm, and 15 cm to 27 cm thick sedimentary cycles that in ratio match that of late Ordovician short eccentricity, obliquity and precession astronomical cycles. The power spectrum of the MS time series, calibrated to interpreted short orbital eccentricity cycles, aligns with spectral peaks to astronomical parameters, including 95 kyr short orbital eccentricity, 35.3 kyr and 30.6 kyr obliquity, and 19.6 kyr and 16.3 kyr precession cycles. The 15 cm to 27 cm thick limestone-shale couplets mainly represent precession cycles, and siliceous bed deposition may be related to both precession and obliquity forcing. We propose that precession-forced sea-level fluctuations mainly controlled production of lime mud in a shallow marine environment, and transport to the basin. Precession and obliquity controlled biogenic silica productivity, and temperature-dependent preservation of silica may have been influenced by obliquity forcing.

  15. Sedimentary characteristics of carbonate intra-platform shoals and their formation in Ordovician Tarim Basin, West China

    NASA Astrophysics Data System (ADS)

    Meng, M.

    2015-12-01

    The widely distributed carbonate intra-platform shoals has become a new important exploration target within the Tarim Basin, where reservoirs of Yubei oil-field (discovered in 2011) and the Shunnan oil-field (discovered in 2013) occur. Better understanding of the sedimentary characteristics and formation of intra-platform shoals is significant for predicting the distribution of Ordovician shoal reservoirs. The sedimentary characteristics, distribution patterns and formation mechanisms of carbonate intra-platform shoals in Ordovician Tarim Basin were studied based on outcrop analogue, core data, thin section observation, seismic, and well log data. Those shoals include oolitic shoal, intraclast shoal and bioclastic shoal. The intra-platform shoal consists of three sedimentary units: shoal base, shoal core and shoal cover, which are adjacent to intershoal sea faces. Laterally, the intra-platform shoals occurred as a more continuous sheet-like body.The intra-platform shoals deposited mainly in the lowstand systems tract and late stage of highstand systems tract. Several factors were probably responsible for the occurrence of intra-platform shoals, including: (i) a relatively shallow-water condition with a strong hydrodynamic environment, (ii) high-frequency oscillations of the sea level, and (iii) Subtle paleo-highs and relatively weak structural activities, which are important for the spatial distribution of reservoir facies.

  16. Using Apatitic Conodont Oxygen Isotopic Values to Determine the Cause of Late Ordovician Third-Order Stratigraphic Sequences

    NASA Astrophysics Data System (ADS)

    Tyra, T. A.; Maya, E.; Atudorei, V.; Stephen, L. A.

    2007-12-01

    Recent work suggests a link between third-order (~1-5 Myr) sea-level fluctuations and climate change, even in greenhouse periods. Upper Ordovician third-order transgressive-regressive sequences are pervasive in the stratigraphic record, can be correlated worldwide (i.e. North America, Baltica, China), and ambiguous in cause. We are evaluating climate's role in third-order sea-level change by analyzing the δ18O of conodont apatite, which is a proxy for both glacio-eustasy and paleotemperature. Conodont phosphatic oxygen is a more robust repository of primary oxygen isotope values than more extensively-studied calcareous fossils, which have been extensively studied. If sea-level change is climatically-driven (glacio-eustasy and thermo-eustasy), δ18O values will decrease with sea-level rise and increase with sea-level fall. We report preliminary results from Upper Ordovician sequences in the Monitor Range of central Nevada. The six stratigraphic sequences (30m-95m thick) preserve basinal-to-outer-shelf carbonates with the youngest sequence representing the Hirnantian glaciation. We collected conodont samples at a 2-10m resolution and also determined bulk carbonate δ13C for additional chemostratigraphy. With this information, we hope to determine if glacio-eustasy has a role within the five pre-Hirnantian sequences.

  17. Comparative analysis of the geological evolution of the northern and southern Appalachian orogen: Late Ordovician-Permian

    USGS Publications Warehouse

    Hibbard, J.P.; van Staal, C.R.; Rankin, D.W.

    2010-01-01

    Review of the major post-Middle Ordovician lithotectonic elements of the Appalachian orogen indicates that the middle to late Paleozoic geologic evolution of the Appalachian margin was less uniform than that of the early Paleozoic. Evolutionary divergence betweenthe northern and southern segments of the orogen started in the Late Ordovician to Silurian with staggered accretion of the first peri-Gondwanan elements to reach the Laurentia margin, Carolinia in the south and Ganderia in the north. Divergence was amplified duringthe Silurian, specifi cally with respect to the nature of the Laurentian margin and the history of accretion. During this time frame, the northern margin was convergent, whereas the amagmatic southern margin may well have been a transform boundary. In terms of accretion, the Late Silurian-Early Devonian docking of Avalonia was restricted to the northern segment, whereas the southern Appalachians appear to have been largely quiescent during this interval. The evolutionary paths of the two segments of the margin converge on a commonhistory in the Late Devonian during the Famennian event; we suggest that this tectonism was related to the initial marginwide interaction of Laurentia with the peri-Gondwanan blocks of Meguma and Suwanee, providing a uniform tectonic template for margin evolution. The Laurentian-Gondwanan collision is marked by second-order divergences in history. Specifi cally, during the Carboniferous, the southern segment records a larger component of shortening than the northern Appalachians. ?? 2010 Geological Society of America.

  18. Health risk assessment of ochratoxin A for all age-sex strata in a market economy

    PubMed Central

    Kuiper-Goodman, T.; Hilts, C.; Billiard, S.M.; Kiparissis, Y.; Richard, I.D.K.; Hayward, S.

    2009-01-01

    In order to manage risk of ochratoxin A (OTA) in foods, we re-evaluated the tolerable daily intake (TDI), derived the negligible cancer risk intake (NCRI), and conducted a probabilistic risk assessment. A new approach was developed to derive ‘usual’ probabilistic exposure in the presence of highly variable occurrence data, such as encountered with low levels of OTA. Canadian occurrence data were used for various raw food commodities or finished foods and were combined with US Department of Agriculture (USDA) food consumption data, which included data on infants and young children. Both variability and uncertainty in input data were considered in the resulting exposure estimates for various age/sex strata. Most people were exposed to OTA on a daily basis. Mean adjusted exposures for all age-sex groups were generally below the NCRI of 4ng OTA kg bw−1, except for 1–4-year-olds as a result of their lower body weight. For children, the major contributors of OTA were wheat-based foods followed by oats, rice, and raisins. Beer, coffee, and wine also contributed to total OTA exposure in older individuals. Predicted exposure to OTA decreased when European Commission maximum limits were applied to the occurrence data. The impact on risk for regular eaters of specific commodities was also examined. PMID:20013446

  19. Forward propagation of the Zagros Simply Folded Belt constrained from magnetostratigraphy of growth strata

    NASA Astrophysics Data System (ADS)

    Ruh, Jonas B.; Hirt, Ann M.; Burg, Jean-Pierre; Mohammadi, Ali

    2014-08-01

    The temporal evolution of the Zagros Simply Folded Belt is constrained by a magnetostratigraphic sequence containing a progressive unconformity on the southern limb of the Kuh-e Ghol Ghol anticline, in the Central Fars. The investigated ~1400 m thick sequence exposes a regressive megacycle containing, from bottom to top, open and shallow marine marls and sandy limestones, fine- to coarse-grained fluvial deposits and alluvial conglomerates. Correlating the magnetostratigraphic section with the geomagnetic polarity time scale constrains the transition from marine to fluvial sediment deposition at ~6 Ma. This transition was accompanied by a change in the accumulation rate from ~15 cm/ka to ~40 cm/ka, as measured on lithified sediments. Alluvial river deposits first occurred at ~3.2 Ma. The Kuh-e Ghol Ghol anticline began to grow at ~3.8 Ma, witnessing fastest limb rotation rates of 40°/Ma at ~3.3 Ma. Reporting magnetostratigraphic sections and ages of growth strata on a map of NE Fars reveal an ~1 cm/a, southwestward migration rate of the deformation front during the middle and late Miocene.

  20. New occurrence of Lower Eocene (Capay Stage) strata, lower Piru Creek, Topatopa Mountains, southern California

    SciTech Connect

    Squires, R.L.; Yamashiro, D.A.

    1986-04-01

    A 900-m thick siltstone unit between Canton Canyon and Piru Creek, 16 km north of the town of Piru, California, previously was unnamed and considered as undifferentiated Eocene or middle Eocene in age. The Siltstone unconformably overlies the Whitaker Peak granodiorite basement complex. At the base of the siltstone is a veneer of gruss (weathered granodiorite). The gruss is usually overlain by about a few meters of shoreface carbonaceous sandstone that grades vertically upward into transition-zone siltstone (500 m) with storm-deposit accumulations of macrofossils. Collections made at 53 localities from these lower 500 m of strata yielded numerous shallow marine gastropods and bivalves, as well as specimens of discocyclinid foraminifers, colonial corals, calcareous worm tubes, and spataganoid echinoids. This fauna is indicative of the West Coast provincial molluscan Capay Stage (lower Eocene). Common age-diagnostic species are Turritella uvasana infera, T. Andersoni, and Ostrea haleyi. Overlying and gradational with the transition-zone siltstone is 400 m of muddy siltstone with rare storm-deposit accumulations of macrofossils. This muddy siltstone thickens westward and passes into deep-sea slope and inner-fan turbidite deposits. Collections made at three localities in the muddy siltstone yielded many shallow marine gastropods and bivalves indicative of the Domengine stage (upper lower through lower middle Eocene). Common age-diagnostic species are Turritella uvasana applinae and Pitar (Lamelliconcha) joaquinensis.

  1. Uniparental Markers in Italy Reveal a Sex-Biased Genetic Structure and Different Historical Strata

    PubMed Central

    Sarno, Stefania; Harmant, Christine; Useli, Antonella; Sanz, Paula; Yang-Yao, Daniele; Manry, Jeremy; Ciani, Graziella; Luiselli, Donata; Quintana-Murci, Lluis; Comas, David; Pettener, Davide

    2013-01-01

    Located in the center of the Mediterranean landscape and with an extensive coastal line, the territory of what is today Italy has played an important role in the history of human settlements and movements of Southern Europe and the Mediterranean Basin. Populated since Paleolithic times, the complexity of human movements during the Neolithic, the Metal Ages and the most recent history of the two last millennia (involving the overlapping of different cultural and demic strata) has shaped the pattern of the modern Italian genetic structure. With the aim of disentangling this pattern and understanding which processes more importantly shaped the distribution of diversity, we have analyzed the uniparentally-inherited markers in ∼900 individuals from an extensive sampling across the Italian peninsula, Sardinia and Sicily. Spatial PCAs and DAPCs revealed a sex-biased pattern indicating different demographic histories for males and females. Besides the genetic outlier position of Sardinians, a North West–South East Y-chromosome structure is found in continental Italy. Such structure is in agreement with recent archeological syntheses indicating two independent and parallel processes of Neolithisation. In addition, date estimates pinpoint the importance of the cultural and demographic events during the late Neolithic and Metal Ages. On the other hand, mitochondrial diversity is distributed more homogeneously in agreement with older population events that might be related to the presence of an Italian Refugium during the last glacial period in Europe. PMID:23734255

  2. Drill Monitor with Strata Strength Classification in Near-Real Time

    NASA Astrophysics Data System (ADS)

    2002-01-01

    The process of drilling and bolting the roof is currently one of the most dangerous jobs in underground mining, resulting in about 1,000 accidents with injuries each year in the United States. Researchers from the Spokane Research Laboratory of the National Institute for Occupational Safety and Health are studying the use of a drill monitoring system to estimate the strength of successive layers of rock and assess the integrity of a mine roof so that roof drill operators can be warned when a weak layer is being drilled. Measurements taken during drilling can be converted to suitably scaled features so that a neural network can classify mine roof strata in terms of relative strength. The feasibility of this concept has been demonstrated in the laboratory. The research project was undertaken in order to increase the safety of underground miners, especially those involved in roof bolting. The system should be applicable to the mobile drills used in underground mining and would likely find wider application as well.

  3. Eustatic and tectonic control of sedimentation in the Pennsylvanian strata of the Central Appalachian Basin

    SciTech Connect

    Chesnut, D.R. Jr. . Kentucky Geological Survey)

    1992-01-01

    Analysis of the Breathitt Group of the Central Appalachian Basin reveals three orders of depositional cycles or trends. The Breathitt coarsening-upward trend (20 million years (my)) represents increasing intensity of the Alleghenian Orogeny. The major transgression (MT) cycle (2.5 my) was controlled by an unknown eustatic or tectonic mechanism. The major coal beds and intervening strata make up the coal-clastic cycle (CC cycle) (=Appalachian cyclothem) which has a 0.4 my periodicity. This periodicity supports eustatic control of sedimentation modulated by an orbital periodicity. Extensive coastal peats deposited at lowstand (CC cycle) were preserved as coals, whereas highstand peats were eroded during the subsequent drop in sea level. Autocyclic processes such as delta switching and avulsion occurred within CC cycles. An Early Pennsylvanian unconformity represents uplift and erosion of mid-Carboniferous foreland basin deposits. Alluvial deposits (Breathitt Group) derived from the highlands were transported to the northwest toward the forebulge. During lowstand, the only outlet available to further sediment transport (Lee sandstones) was toward the southwest (Ouachita Trough), along the Black Warrior-Appalachian foreland basins. The Middle Pennsylvanian marks a period of intermittent overfilling of the foreland basin and cresting of the forebulge. Marine transgressions entered through the foreland basins and across saddles in the forebulge. After the Ouachita Trough was destroyed during the late Middle Pennsylvanian, marine transgressions migrated only across saddles in the forebulge. In the Late Pennsylvanian, marine waters entered the basin only across the diminished forebulge north of the Jessamine Dome.

  4. Strata-1: An International Space Station Experiment into Fundamental Regolith Processes in Microgravity

    NASA Technical Reports Server (NTRS)

    Fries, M.; Abell, P.; Brisset, J.; Britt, D.; Colwell, J.; Durda, D.; Dove, A.; Graham, L.; Hartzell, C.; John, K.; Love, S.

    2016-01-01

    The Strata-1 experiment will study the evolution of asteroidal regolith through long-duration exposure of simulant materials to the microgravity environment on the International Space Station (ISS). Many asteroids feature low bulk densities, which implies high values of porosity and a mechanical structure composed of loosely bound particles, (i.e. the "rubble pile" model), a prime example of a granular medium. Even the higher-density, mechanically coherent asteroids feature a significant surface layer of loose regolith. These bodies are subjected to a variety of forces and will evolve in response to very small perturbations such as micrometeoroid impacts, planetary flybys, and the YORP effect. Our understanding of this dynamical evolution and the inter-particle forces involved would benefit from long-term observations of granular materials exposed to small vibrations in microgravity. A detailed understanding of asteroid mechanical evolution is needed in order to predict the surface characteristics of as-of-yet unvisited bodies, to understand the larger context of samples collected by missions such as OSIRIS-REx and Hayabusa 1 and 2, and to mitigate risks for both manned and unmanned missions to asteroidal bodies. Understanding regolith dynamics will inform designs of how to land and set anchors, safely sample/move material on asteroidal surfaces, process large volumes of material for in situ resource utilization (ISRU) purposes, and, in general, predict behavior of large and small particles on disturbed asteroid surfaces.

  5. Organic geochemistry of DSDP Site 467, offshore California, Middle Miocene to Lower Pliocene strata

    NASA Astrophysics Data System (ADS)

    Katz, Barry J.; Elrod, Louis W.

    1983-03-01

    Results of the analyses of twenty-three samples from the Middle Miocene to Lower Pliocene strata from DSDP Site 467, offshore California, are presented. The analyses were performed with the aim of determining the origin of the organic matter, the stratigraphic section's hydrocarbon generation potential and extent of organic diagenesis. Organic carbon contents are an order of magnitude greater than those typically found in deep sea sediments, suggesting an anoxic depositional environment and elevated levels of primary productivity. Hydrocarbon generation potentials are above average for most samples. The results of elemental analyses indicate that the kerogens are primarily composed of type II organic matter and are thermally immature. Analysis of the bitumen fractions confirms that the samples are immature. In cores from 541 to 614 meters, the gas chromatograms of the C 15+ non-aromatic hydrocarbon fractions are dominated by a single peak which was identified as 17α(H), 18α(H), 21β(H)-28, 30-bisnorhopane. This interval is the same area in which the highest degrees of anoxia are observed as reflected by the lowest pristane/phytane ratios. This correlation may have some implications with regard to the origin of the bisnorhopane and its possible use as an indicator of anoxic depositional conditions within thermally immature sediments.

  6. Late Quaternary strata and carbon burial records in the Yellow River delta, China

    NASA Astrophysics Data System (ADS)

    Zhao, Guangming; Ye, Siyuan; Li, Guangxue; Ding, Xigui; Yuan, Hongming

    2015-06-01

    Sediment carbon sequestration plays an essential role in mitigating atmospheric CO2 increases and the subsequently global greenhouse effect. To clarify the late Quaternary strata and carbon burial records in Yellow River delta (YRD), detailed analysis of benthic foraminifera, total carbon (TC), organic carbon (Corg), sedimentary characteristics and moisture contents of sediments, was performed on core ZK3, 30.3 m in length and obtained from YRD in 2007. Eight depositional units (designated U1-U8 in ascending order) were identified. A comprehensive analysis method of historical geography and sedimentary geology was used to determine the precise depositional ages of the modern Yellow River delta (MYRD), from which pre-MYRD ages were deduced. The results indicates that the maximum burial rates of TC, inorganic carbon (IC) and Corg occurred in the delta front (U5), and the minimum in the shallow sea (U3). Remarkable high sedimentation rates in the MYRD are responsible for burial efficiency of carbon, with an average rate of Corg burial reaching 2087±251 g (m2 yr)-1, and that of IC reaching 13741±808 g (m2 yr)-1, which are much higher than those of other regions with high contents of Corg. Therefore, YRD has a significant burial efficiency for carbon sequestration.

  7. Health risk assessment of ochratoxin A for all age-sex strata in a market economy.

    PubMed

    Kuiper-Goodman, T; Hilts, C; Billiard, S M; Kiparissis, Y; Richard, I D K; Hayward, S

    2010-02-01

    In order to manage risk of ochratoxin A (OTA) in foods, we re-evaluated the tolerable daily intake (TDI), derived the negligible cancer risk intake (NCRI), and conducted a probabilistic risk assessment. A new approach was developed to derive 'usual' probabilistic exposure in the presence of highly variable occurrence data, such as encountered with low levels of OTA. Canadian occurrence data were used for various raw food commodities or finished foods and were combined with US Department of Agriculture (USDA) food consumption data, which included data on infants and young children. Both variability and uncertainty in input data were considered in the resulting exposure estimates for various age/sex strata. Most people were exposed to OTA on a daily basis. Mean adjusted exposures for all age-sex groups were generally below the NCRI of 4 ng OTA kg bw(-1), except for 1-4-year-olds as a result of their lower body weight. For children, the major contributors of OTA were wheat-based foods followed by oats, rice, and raisins. Beer, coffee, and wine also contributed to total OTA exposure in older individuals. Predicted exposure to OTA decreased when European Commission maximum limits were applied to the occurrence data. The impact on risk for regular eaters of specific commodities was also examined. PMID:20013446

  8. A model of shield-strata interaction and its implications for active shield setting requirements

    SciTech Connect

    Barczak, T.M.; Oyler, D.C.

    1991-12-01

    This book reports that this U.S. Bureau of Mines study evaluates factors that influence longwall support and strata interaction. The longwall system is composed of an immediate and main roof structure and three supporting foundations: longwall structure that is generally supported by all three foundations, while the immediate roof acts as a beam that cantilevers from the coal face to the powered support. In most cases, shield loading involves a complex interaction of both main roof and immediate roof behavior and is a combination of loads produced from convergence of the main roof and displacements of the immediate roof caused by deformations of the cantilevered roof beam. Since the shield stiffness remains constant for all leg pressures and main roof convergence is irresistible in terms of shield capacity, the shield must be able to control the behavior of the immediate roof or floor structure for shield loading to be sensitive to setting pressures. If the goal is to minimize total shield loading, any active setting force must be offset by reduced passive shield loading to justify the active setting loads. Field data suggest that the typical reductions in passive loading do not justify the required increases in setting pressure in some applications.

  9. Application of deterministic deconvolution of ground-penetrating radar data in a study of carbonate strata

    USGS Publications Warehouse

    Xia, J.; Franseen, E.K.; Miller, R.D.; Weis, T.V.

    2004-01-01

    We successfully applied deterministic deconvolution to real ground-penetrating radar (GPR) data by using the source wavelet that was generated in and transmitted through air as the operator. The GPR data were collected with 400-MHz antennas on a bench adjacent to a cleanly exposed quarry face. The quarry site is characterized by horizontally bedded carbonate strata with shale partings. In order to provide groundtruth for this deconvolution approach, 23 conductive rods were drilled into the quarry face at key locations. The steel rods provided critical information for: (1) correlation between reflections on GPR data and geologic features exposed in the quarry face, (2) GPR resolution limits, (3) accuracy of velocities calculated from common midpoint data and (4) identifying any multiples. Comparing the results of deconvolved data with non-deconvolved data demonstrates the effectiveness of deterministic deconvolution in low dielectric-loss media for increased accuracy of velocity models (improved at least 10-15% in our study after deterministic deconvolution), increased vertical and horizontal resolution of specific geologic features and more accurate representation of geologic features as confirmed from detailed study of the adjacent quarry wall. ?? 2004 Elsevier B.V. All rights reserved.

  10. Tectonic development of Upper Cretaceous to Eocene strata of southwestern Utah

    SciTech Connect

    Goldstrand, P.M. )

    1994-01-01

    Upper Cretaceous to Paleogene nonmarine sedimentary rocks of southwest Utah record Sevier foreland basin sedimentation, Laramide-style folding and intermontane sedimentation, and cessation of Laramide deformation. The formations that record this tectonic evolution arc, from oldest to youngest, the Iron Springs, Kaiparowits, Canaan Peak, Grand Castle (informal name), Pine Hollow, and basal part of the Claron. The upper part of the Santonian to lower Campanian( ) Iron Springs Formation represents synorogenic, fluvial deposits derived from the Wah Wah and Blue Mountain thrust sheets of southwestern Utah. The middle to upper Campanian Kaiparowits and upper Campanian( ) to lower Paleocene Canaan Peak Formations are an upward-coarsening sequence derived from southeastern California and southern Nevada. Initial Laramide-style deformation occurred during latest Cretaceous or early Paleocene time, influencing the depositional pattern of the Canaan Peak fluvial system. The lower Paleocene Grand Castle formation represents an east- to southeast-flowing, braided-river system with the same source as the Iron Springs Formation (the Wah Wah and Blue Mountain thrust sheets). Conglomerate of Grand Castle onlaps the easternmost Sevier thrusts and is folded by Laramide structures. Although strata of the Grand Castle formation represent post-thrust and, in part, pre-Laramide deposition, initial development of a south-southwest-trending, Laramide-style upwarp controlled the geometry of the Grand Castle basin. 55 refs., 11 figs.

  11. Geochronology of upper Paleocene and lower Eocene strata, eastern Gulf Coastal Plain

    SciTech Connect

    Mancini, E.A.; Tew, B.H. Geological Survey of Alabama, Tuscaloosa, AL )

    1994-03-01

    Four samples of glauconitic sand from upper Paleocene and lower Eocene strata of the eastern Gulf Coastal Plain were analyzed for conventional potassium-argon (K-Ar) age determination. Results from these analyses are as follows: Coal Bluff Marl Member of the Naheola Formation of the Midway Group (58.2 [+-] 1.5 MA), Ostrea thirsae beds of the Nanafalia Formation of the Wilcox Group (56.3 [+-] 1.5 MA), upper Tuscahoma Sand of the Wilcox Group (54.5 [+-] 1.4 MA), and Bashi Marl Member of the Hatchetigbee Formation of the Wilcox Group (53.4 [+-] 1.4 MA). The Nanafalia Formation (Wilcox Group) disconformably overlies the Naheola Formation (Midway Group), and based on the data presented here, the age of this unconformity is bracketed between 59.7 and 54.8 MA. The Paleocene-Eocene Epoch boundary occurs in the Wilcox Group and coincides with the lithostratigraphic contact of the upper Paleocene Tuscahoma Sand with the lower eocene Hatchetigbee Formation. The age of this boundary, which is also an unconformity, can be placed between 55.9 and 52.0 MA. The K-Ar age dates for this boundary in the Gulf Coastal Plain compare favorably with the numerical limits placed on the Paleocene-Eocene boundary in the published literature. Generally, the Paleocene-Eocene Epoch boundary is reported as approximately 54 to 55 MA.

  12. Diffusive anisotropy in low-permeability Ordovician sedimentary rocks from the Michigan Basin in southwest Ontario.

    PubMed

    Xiang, Y; Al, T; Scott, L; Loomer, D

    2013-12-01

    Diffusive anisotropy was investigated using samples from Upper Ordovician shale and argillaceous limestone from the Michigan Basin of southwest Ontario, Canada. Effective diffusion coefficients (De) were determined for iodide (I(-)) and tritiated water (HTO) tracers on paired cm-scale subsamples oriented normal (NB) and parallel to bedding (PB) prepared from preserved drill cores within one year from the date of drilling. For samples with porosity >3%, an X-ray radiography method was used with I(-) tracer for determination of De and porosity accessible to I(-) ions. A through-diffusion method with I(-) and HTO tracers was used for most siltstone and limestone samples with low-porosity (<3%). The De values range from 7.0×10(-13) to 7.7×10(-12) m(2)·s(-1) for shale, 2.1×10(-13) to 1.3×10(-12) m(2)·s(-1) for limestone, and 5.3×10(-14) to 5.6×10(-13) m(2)·s(-1) for siltstone and limestone interbeds within the Georgian Bay Formation shale. The sample-scale anisotropy ratios (De-PB:De-NB) for De values obtained using the I(-) tracer are 0.9 to 4.9, and the anisotropy ratios for the HTO tracer are in the range of 1.1 to 7.0. The influence of porosity distribution on diffusive anisotropy has been investigated using one-dimensional spatially-resolved profiles of I(-)-accessible porosity (shale only) and the use of AgNO3 for fixation of I(-) tracer in the pores, allowing for SEM visualization of I(-)-accessible pore networks. The porosity profiles at the sample scale display greatest variability in the direction normal to bedding which likely reflects sedimentary depositional processes. The SEM imaging suggests that diffusion pathways are preferentially oriented parallel to bedding in the shale and that diffusion occurs dominantly within the argillaceous component of the limestone. However, the fine clay-filled intergranular voids in the dolomitic domains of the limestone are also accessible for diffusive transport. PMID:24121139

  13. Crystal growth history of quartz in the Ordovician Millbrig K-bentonite

    NASA Astrophysics Data System (ADS)

    Huff, W. D.; Inanli, F. O.

    2011-12-01

    Crystal size distribution (CSD) analysis has been applied to quartz crystals of the Ordovician Millbrig K-bentonite, which represents one of the largest known fallout ash deposits in the Phanerozoic Era, to establish crystal growth histories and conditions in the magma chamber prior to eruption. Specific CSDs of the quartz crystals of the Millbrig K-bentonite were examined to establish their growth conditions prior to the eruption. On the crystal size distribution plot, all Millbrig samples exhibit concave-down shapes in agreement with previously reported CSDs on large silicic systems [1] but in contrast to more mafic systems characterized by linear CSDs. Crystal growth mechanisms responsible for the concave down CSDs are thought to be surface-controlled crystal growth followed by a episode of textural coarsening. Although all samples follow concave-down shapes, two samples exhibit rather different CSD shapes. These findings appear to fingerprint a separate magma batch with different crystal growth conditions. These ash beds appear to be a product of a series of separate eruptions that represent separate magma layers or batches, each with slightly different crystal growth conditions. Haynes [2] interpreted the multiple ash layers as either a product of several periods of eruptive activity or the cumulative effect of an evolving magma chamber during a single massive eruptive event. Our data support the model of several periods of eruptive activity that was closely spaced in time. The two of the eight Millbrig samples must have come from an earlier phase eruption and are part of a basal section that have not been preserved in the stratigraphic record and lacks lateral continuity in distal parts of the deposits. Therefore, the multiple ash beds in the Millbrig must have been a product of series of separate eruptions that represent separate magma layers or batches that had different crystal growth conditions. Although conclusions on crystallization processes and the

  14. Devonian-Ordovician Magmatism in Chiapas Massif, Southern Maya Block, Mexico

    NASA Astrophysics Data System (ADS)

    Pompa-Mera, V.; Schaaf, P.; Weber, B.; Solis-Pichardo, G.; Hernandez-Trevino, T.; Ortega-Gutierrez, F.

    2008-12-01

    The Chiapas Massif (CM) is located in SE Mexico and extends over an area of more than 20,000 Km2 parallel to the Pacific coast between the Isthmus of Tehuantepec and the Guatemalan border. It constitutes the largest batholitic complex in Mexico and belongs to the Maya Block. The CM is predominantly formed by igneous, metaigneous and metasedimentary rocks. In the central CM several magmatic and metamorphic events have been identified in igneous rocks between Late Permian and Triassic times (220-240 Ma), together with a Jurassic tectonothermal event. Recent geochronological studies have been focused on granitic rocks from the central-southeastern CM and from this area, single grain zircon ages were also obtained from metasedimentary rocks. The results suggest that the basement rocks of the eastern CM and the Maya Block underwent several tectonothermal events since Ordovician and Devonian times. In this work, we present new data of magmatic and metamorphic rocks from the easternmost part of CM which confirms this hypothesis. Additionally, we present a semi-detailed geological map of this area showing some field relationship between the different units. We identified a new basal sequence significantly older than the Santa Rosa Formation, which has been considered up to now as forming the major underlying sequence of the CM, as well as the occurrence of several magmatic events in the Maya Block and in rocks from surrounding areas. The petrological, geochemical and geochronological features of these rocks show continuous crust recycling, the occurrence of within-plate magmatism in some parts with inherited Greenvillian and Archaean zircon grains as well as the occurrence of arc magmatism previous to accretion, deformation and terrane separation of the crustal blocks. Our new geochronological results obtained from the south easternmost part of the CM include a Rb-Sr biotite-muscovite age of 392+/-9 Ma and an Ar-Ar muscovite age of 406+/- 4 Ma from a tectonized granitic

  15. Distribution and significance of crystalline, perlitic and vesicular textures in the Ordovician Garth Tuff (Wales)

    NASA Astrophysics Data System (ADS)

    McArthur, A. N.; Cas, R. A. F.; Orton, G. J.

    Diverse spherulitic and granular crystalline fabrics, perlitic textures and fabrics related to the growth and migration of vesicles occur in the Garth Tuff, a largely welded Ordovician ignimbrite. Defining the distribution of such textures helps to constrain the ignimbrite's cooling and degassing history. Suites of spherulitic and perlitic textures closely reflect variation in cooling rates. Seven facies are defined based on the style and intensity of crystallisation: (1) a medium to coarsely crystalline, equigranular facies; (2) an intensely spherulitic facies; (3) a sparsely spherulitic facies; (4) a pectinate facies; (5) a microcrystalline to cryptocrystalline, equigranular facies; (6) a lithophysal facies; and (7) a transitional perlite-pectinate facies. Textural changes from facies 1 to 5 reflect progressively higher cooling rates. Facies 1 occurs in proximal settings in the ignimbrite's core. Facies 2 to 5 successively envelop facies 1, with facies 2 becoming the dominant fabric in the ignimbrite's core in medial settings. Facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite's welded margins. Crystallisation under hydrous conditions is reflected by second-boiling textures in the sporadically developed lithophysal facies. The seventh facies reflects a subtle interplay between cooling, hydration and crystallisation which locally prevented perlitic fracturing. The distribution of amygdales reflects patterns of volatile migration and entrapment. In the lower levels of the ignimbrite, amygdales occur in irregular concentrations or rare subvertical pipe-like structures. Pipe-like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state. Amygdales are widespread and evenly distributed in the upper levels of the ignimbrite. However, the top of the welding profile is characterised by a thin, poorly vesiculated, originally vitrophyric horizon that abruptly caps an intense concentration of amygdales

  16. Hurricane Mountain Formation melange: history of Cambro-Ordovician accretion of the Boundary Mountains terrane within the northern Appalachian orthotectonic zone

    SciTech Connect

    Boone, G.M.; Boudette, E.L.

    1985-01-01

    The Hurricane Mountain Formation (HMF) melange and associated ophiolitic and volcanogenic formations of Cambrian and lowermost Ordovician age bound the SE margin of the Precambrian Y (Helikian) Chain Lakes Massif in western Maine. HMF melange matrix, though weakly metamorphosed, contains a wide variety of exotic greenschist to amphibolite facies blocks as components of its polymictic assemblage, but blocks of high-grade cratonal rocks such as those of Chain Lakes or Grenville affinity are lacking. Formations of melange exposed in structural culminations of Cambrian and Ordovician rocks NE of the HMF in Maine and in the Fournier Group in New Brunswick are lithologically similar and probably tectonically correlative with the HMF; taken together, they may delineate a common pre-Middle Ordovician tectonic boundary. The authors infer that the Hurricane Mountain and St. Daniel melange belts define the SE and NW margins of the Boundary Mountains accreted terrane (BMT), which may consist of cratonal basement of Chain Lakes affinity extending from eastern Gaspe (deBroucker and St. Julien, 1985) to north-central New Hampshire. The Laurentian continental margin, underlain by Grenville basement, underplated the NW margin of this terrane, marked by the SDF suture zone, in late Cambrian to early Ordovician time, while terranes marked by Cambrian to Tremadocian (.) lithologies dissimilar to the Boundary Mountains terrane were accreted to its outboard margin penecontemporaneously. The docking of the Boundary Mountains terrane and the initiation of its peripheral melanges are equated to the Penobscottian disturbance.

  17. Depositional setting of Ordovician and Cambrian rocks in central Appalachian basin along a section from Morrow County, Ohio, to Calhoun County, West Virginia

    SciTech Connect

    Ryder, R.T.

    1988-08-01

    A 200-mi (320 km) long restored stratigraphic section from Morrow County, Ohio, to Calhoun County, West Virginia, contrasts Ordovician and Cambrian rocks deposited on a relatively stable shelf with those deposited in rift and postrift basins. Lithologic data are from commercial logs and from detailed descriptions of cores in five of the nine drill holes used to construct the section. Particularly instructive was the 2,352 ft (717 m) of core from the Hope Natural Gas 9634 Power Oil basement test in Wood County, West Virginia. Rift basin deposits are dominated by medium to dark-gray argillaceous limestone, argillaceous siltstone, and by green-gray to black shale of probable subtidal origin. Dolomite is the dominant rock type in the postrift basin and adjacent stable shelf deposits. The upper part of the postrift sequence, composed of the Middle Ordovician Black River Limestone, the Middle Ordovician Trenton Limestone, and Middle and Upper Ordovician Antes (Utica) Shale with a high organic content, represents deposition in gradually deepening water on an open shelf.

  18. Tectonic setting of the North Gondwana margin during the Early Ordovician: A comparison of the Ollo de Sapo and Famatina magmatic events

    NASA Astrophysics Data System (ADS)

    Del Greco, Kassandra; Johnston, Stephen T.; Shaw, Jessica

    2016-06-01

    This paper presents a comparison of compiled geochronological and geochemical data from the Ollo de Sapo and Famatina magmatic events. The Ollo de Sapo magmatic sequence is located in northwest Iberia and was emplaced during the early-Ordovician from 495 to 474 Ma. The Famatina Complex is a magmatic sequence located in Northern Argentina that was emplaced during the early- to mid-Ordovician from 483 to 463 Ma. These magmatic events are currently interpreted to have been emplaced in different tectonic settings despite both having occurred along the North Gondwana margin. Geochronological data indicates that these magmatic events occurred contemporaneously over at least 9 m.y. and therefore can provide a snapshot of the northern Gondwana margin during the mid-Ordovician. Major element data indicates that both magmatic suites are calc-alkaline to alkali-calcic and trace element and REE data show magmatic signatures that are indistinguishable. This study highlights the similarity between the Ollo de Sapo and the Famatina magmatic suites and discusses alternative models for their emplacement based on paleomagnetic and paleobiogeographical data. These data indicate that the Ollo de Sapo was likely emplaced in a subduction zone setting, while the Famatina magmatic suite may be of parautochthonous origin to Gondwana, implying that the Pampeanan margin may not have been active during the early- to mid-Ordovician.

  19. High-resolution delineation of chlorinated volatile organic compounds in a dipping, fractured mudstone: depth- and strata-dependent spatial variability from rock-core sampling

    USGS Publications Warehouse

    Goode, Daniel J.; Imbrigiotta, Thomas E.; Lacombe, Pierre J.

    2014-01-01

    Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale distribution of CVOCs in dipping, fractured mudstones of the Lockatong Formation of Triassic age, of the Newark Basin in West Trenton, New Jersey. From these results, a refined conceptual model for more than 55 years of migration of CVOCs and depth- and strata-dependent rock-matrix contamination was developed. Industrial use of trichloroethene (TCE) at the former Naval Air Warfare Center (NAWC) from 1953 to 1995 resulted in dense non-aqueous phase liquid (DNAPL) TCE and dissolved TCE and related breakdown products, including other CVOCs, in underlying mudstones. Shallow highly weathered and fractured strata overlie unweathered, gently dipping, fractured strata that become progressively less fractured with depth. The unweathered lithology includes black highly fractured (fissile) carbon-rich strata, gray mildly fractured thinly layered (laminated) strata, and light-gray weakly fractured massive strata. CVOC concentrations in water samples pumped from the shallow weathered and highly fractured strata remain elevated near residual DNAPL TCE, but dilution by uncontaminated recharge, and other natural and engineered attenuation processes, have substantially reduced concentrations along flow paths removed from sources and residual DNAPL. CVOCs also were detected in most rock-core samples in source areas in shallow wells. In many locations, lower aqueous concentrations, compared to rock core concentrations, suggest that CVOCs are presently back-diffusing from the rock matrix. Below the weathered and highly fractured strata, and to depths of at least 50 meters (m), groundwater flow and contaminant transport is primarily in bedding-plane-oriented fractures in thin fissile high-carbon strata, and in fractured, laminated strata of the gently

  20. High-resolution delineation of chlorinated volatile organic compounds in a dipping, fractured mudstone: Depth- and strata-dependent spatial variability from rock-core sampling.

    PubMed

    Goode, Daniel J; Imbrigiotta, Thomas E; Lacombe, Pierre J

    2014-12-15

    Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale distribution of CVOCs in dipping, fractured mudstones of the Lockatong Formation of Triassic age, of the Newark Basin in West Trenton, New Jersey. From these results, a refined conceptual model for more than 55years of migration of CVOCs and depth- and strata-dependent rock-matrix contamination was developed. Industrial use of trichloroethene (TCE) at the former Naval Air Warfare Center (NAWC) from 1953 to 1995 resulted in dense non-aqueous phase liquid (DNAPL) TCE and dissolved TCE and related breakdown products, including other CVOCs, in underlying mudstones. Shallow highly weathered and fractured strata overlie unweathered, gently dipping, fractured strata that become progressively less fractured with depth. The unweathered lithology includes black highly fractured (fissile) carbon-rich strata, gray mildly fractured thinly layered (laminated) strata, and light-gray weakly fractured massive strata. CVOC concentrations in water samples pumped from the shallow weathered and highly fractured strata remain elevated near residual DNAPL TCE, but dilution by uncontaminated recharge, and other natural and engineered attenuation processes, have substantially reduced concentrations along flow paths removed from sources and residual DNAPL. CVOCs also were detected in most rock-core samples in source areas in shallow wells. In many locations, lower aqueous concentrations, compared to rock core concentrations, suggest that CVOCs are presently back-diffusing from the rock matrix. Below the weathered and highly fractured strata, and to depths of at least 50 meters (m), groundwater flow and contaminant transport is primarily in bedding-plane-oriented fractures in thin fissile high-carbon strata, and in fractured, laminated strata of the gently

  1. High-resolution delineation of chlorinated volatile organic compounds in a dipping, fractured mudstone: Depth- and strata-dependent spatial variability from rock-core sampling

    NASA Astrophysics Data System (ADS)

    Goode, Daniel J.; Imbrigiotta, Thomas E.; Lacombe, Pierre J.

    2014-12-01

    Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale distribution of CVOCs in dipping, fractured mudstones of the Lockatong Formation of Triassic age, of the Newark Basin in West Trenton, New Jersey. From these results, a refined conceptual model for more than 55 years of migration of CVOCs and depth- and strata-dependent rock-matrix contamination was developed. Industrial use of trichloroethene (TCE) at the former Naval Air Warfare Center (NAWC) from 1953 to 1995 resulted in dense non-aqueous phase liquid (DNAPL) TCE and dissolved TCE and related breakdown products, including other CVOCs, in underlying mudstones. Shallow highly weathered and fractured strata overlie unweathered, gently dipping, fractured strata that become progressively less fractured with depth. The unweathered lithology includes black highly fractured (fissile) carbon-rich strata, gray mildly fractured thinly layered (laminated) strata, and light-gray weakly fractured massive strata. CVOC concentrations in water samples pumped from the shallow weathered and highly fractured strata remain elevated near residual DNAPL TCE, but dilution by uncontaminated recharge, and other natural and engineered attenuation processes, have substantially reduced concentrations along flow paths removed from sources and residual DNAPL. CVOCs also were detected in most rock-core samples in source areas in shallow wells. In many locations, lower aqueous concentrations, compared to rock core concentrations, suggest that CVOCs are presently back-diffusing from the rock matrix. Below the weathered and highly fractured strata, and to depths of at least 50 meters (m), groundwater flow and contaminant transport is primarily in bedding-plane-oriented fractures in thin fissile high-carbon strata, and in fractured, laminated strata of the gently

  2. Biostratigraphy, taxonomic diversity and patterns of morphological evolution of Ordovician acritarchs (organic-walled microphytoplankton) from the northern Gondwana margin in relation to palaeoclimatic and palaeogeographic changes

    NASA Astrophysics Data System (ADS)

    Vecoli, Marco; Le Hérissé, Alain

    2004-10-01

    Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant component of marine organic-walled microfossils in the Palaeozoic. The majority of acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features, as well as distributional patterns in the sediments. The production of these organic-walled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle (autecology) of the planktonic parent organisms. Calculation of evolutionary rates and development of a detailed diversity curve at specific level, form the basis for discussing the influence of global palaeoenvironmental perturbations on the evolution of organic-walled microphytoplankton in northern Gondwana during latest Cambrian through Ordovician times. The potential of acritarchs for biostratigraphic correlation at the regional scale (northern Gondwana domain) is much improved by our detailed revision of distributional patterns of 245 acritarch taxa. The most important Cambro-Ordovician acritarch bio-events are short periods of diversification, which also correspond to introduction of morphological innovations, observed in latest Cambrian and earliest Tremadoc, late Tremadoc, early Arenig, basal Llanvirn, and latest Ashgill, and an important extinction phase in the early Caradoc. Overall, acritarch diversity increased from the basal Ordovician up to the middle Llanvirn, then declined in the early and middle Caradoc. During Ashgill times, the assemblages are poorly diversified at the generic level as a result of a combined effect of sea level drawdown and onset of glacial conditions, but no major extinction event is observed in connection with the end-Ordovician biotic crisis. The peak in acritarch diversity during Middle Ordovician times appears to be correlated to maximum spread of palaeogeographical assembly. Acritarch dynamics appear largely

  3. Natural hydraulic fractures and the mechanical stratigraphy of shale-dominated strata

    NASA Astrophysics Data System (ADS)

    Imber, Jonathan; Armstrong, Howard; Atar, Elizabeth; Clancy, Sarah; Daniels, Susan; Grattage, Joshua; Herringshaw, Liam; Trabucho-Alexandre, João; Warren, Cassandra; Wille, Jascha; Yahaya, Liyana

    2016-04-01

    The aim of this study is to investigate stratigraphic variations in the spatial distribution and density of natural hydraulic and other fractures within oil mature, shale-dominated strata from the Cleveland Basin, northeast England. The studied interval includes the Pliensbachian Cleveland Ironstone and Toarcian Whitby Mudstone Formations. The Cleveland Ironstone Formation (ca. 25m thick) consists of silt- and mudstone units with discrete ironstone layers (seams). Ironstones account for 20% of the thickness of the formation. The Whitby Mudstone Formation is up to ca. 100 m thick; up to 2% of its total thickness consists of discrete calcium carbonate horizons, such as the Top Jet Dogger. Natural hydraulic fractures, characterised by plumose marks and concentric arrest lines on fracture surfaces are ubiquitous throughout both formations; shear fractures with mm- to cm-scale displacements occur locally, particularly within silt- and mudstones. Natural hydraulic fractures locally contain thin, sometimes fibrous, calcite fills and are commonly observed to terminate at bedding plane interfaces between silt- or mudstone and carbonate beds. We have recorded fracture locations and apertures along 139 transects in both shale (i.e. silt- and mudstone intervals) and carbonate strata. Natural hydraulic and shear fractures, measured along transects up to 50m long within all lithologies in both formations, typically display uniform distributions. There is no correlation between spacing distribution and bulk extension in any lithology. Median fracture densities recorded within the Cleveland Ironstone Formation are higher in intervening ironstone beds (<2.1 fractures per m in ironstone layers) compared with dominant shales (<0.9 fractures per m in silt- and mudstones). A qualitatively similar pattern occurs within the Whitby Mudstone Formation. However, the absolute values of median fracture density within different members of the Whitby Mudstone Formation range from 2

  4. Ion drag as a mechanism of plasma dust structure rotation in a strata in a magnetic field

    NASA Astrophysics Data System (ADS)

    Dzlieva, E. S.; Karasev, V. Yu.; Mashek, I. Ch.; Pavlov, S. I.

    2016-06-01

    In experiments on complex plasmas, afixed strata region in which the levitation of dust structures is observed is investigated using the method of probing by calibrated dust particles of different sizes in an applied magnetic field under elevated pressures. The measured azimuthal velocity of the probing particles corresponds to the action of the ion drag force for 4 μm-size particles and to the entrainment by the rotating gas owing to the electron vortex flow inside the strata for 1 μm-size particles. Extrapolation to pressures and magnetic fields in which the rotation inversion of dust structures is observed in experiments shows that the ion drag is the dominating force causing rotation with a negative projection of the angular velocity onto the magnetic induction.

  5. Detrital zircon geochronology of Neoproterozoic to Middle Cambrian miogeoclinal and platformal strata: Northwest Sonora, Mexico

    USGS Publications Warehouse

    Gross, E.L.; Stewart, John H.; Gehreis, G.E.

    2000-01-01

    Eighty-five detrital zircon grains from Mesoproterozoic and/or Neoproterozoic to Middle Cambrian sedimentary strata in northwest Sonora, Mexico, have been analyzed to determine source terranes and provide limiting depositional ages of the units. The zircon suites from the Mesoproterozoic and/or Neoproterozoic El Alamo Formation and El Aguila unit yield ages between 1.06 Ga and 2.67 Ga, with predominant ages of 1.1 to 1.2 Ga. Zircons from the Lower? and Middle Cambrian Bolsa Quartzite show age groups from 525 Ma to 1.63 Ga, with a dominant population of 1.1 to 1.2 Ga grains. Grains older than 1.2 Ga in the samples were most likely derived from basement terranes and ???1.4 Ga granitic bodies of the southwest U.S. and northwest Mexico. It is also possible that the sediments were transported from the south, although source rocks of the appropriate age are not presently exposed south of the study area in northern Mexico. Three possibilities for the dominant 1.1 to 1.2 Ga grains include derivation from: (I) exposures of the Grenville belt in southern North America, (2) local 1.1-1.2 Ga granite bodies, or (3) a southern source, such as the Oaxaca terrane, that was subsequently rifted away. Sampling of additional units in the western U.S. and northern Mexico may help resolve the ambiguity surrounding the source of the 1.1 to 1.2 Ga grains.

  6. Mesoporous Hybrid Polypyrrole-Silica Nanocomposite Films with a Strata-Like Structure.

    PubMed

    Farghaly, Ahmed A; Collinson, Maryanne M

    2016-06-14

    Using a single-potential-step coelectrodeposition route, Ppy-SiO2 nanocomposite films characterized by a multimodal porous structure were cathodically deposited from ethanolic solutions on oxidizable and nonoxidizable substrates for the first time. The materials produced have an interesting and unique strata-like pore structure along their depth. With the exception of a silica-rich inner region, the nanocomposite films are homogeneous in composition. Because the region closest to the electrode surface is silica-rich, the fabrication of Ppy-SiO2 and Ppy free-standing films become possible using a multistep etching strategy. Such films can be captured on a variety of different supports depending on the application, and they maintain their conductivity when interfaced with an electrode surface. These mesoporous composite films form through a unique mechanism that involves the production of two catalysts, OH(-) and NO(+). Through the process of understanding the reaction mechanism, we highlighted the effect of two simultaneous competing redox reactions occurring at the electrode interface on the morphology of the electrodeposited Ppy nanocomposite films and how solvent can influence the Ppy electropolymerization reaction mechanism and hence control the morphology of the final material. In an ethanolic solvent system, the pyrrole monomers undergo a step-growth polymerization, and particulate-like nanostructured films were obtained even upon changing the monomer or acid concentration. In an aqueous-based system, nanowire-like structures were produced, which is consistent with a chain-growth mechanism. Such materials are promising candidates for a wide range of applications including electrochemical sensing, energy storage, and catalysis. PMID:27245273

  7. Selenium speciation in Lower Cambrian Se-enriched strata in South China and its geological implications

    NASA Astrophysics Data System (ADS)

    Fan, Haifeng; Wen, Hanjie; Hu, Ruizhong; Zhao, Hui

    2011-12-01

    To understand the impact of Selenium (Se) into the biogeochemical cycle and implications for palaeo-redox environment, a sequential extraction method was utilized for samples including black shales, cherts, a Ni-Mo-Se sulfide layer, K-bentonite and phosphorite from Lower Cambrian Se-enriched strata in southern China. Seven species (water-soluble, phosphate exchangeable, base-soluble, acetic acid-soluble, sulfide/selenide associated, residual Se) and different oxidation states (selenate Se(VI), selenite Se(IV), organic Se, Se (0) and mineral Se(-II)) were determinated in this study. We found that the Ni-Mo-Se sulfide layer contained a significantly greater amount of Se(-II) associated with sulfides/selenides than those in host black shales and cherts. Furthermore, a positive correlation between the degree of sulfidation of iron (DOS) and the percentage of the sulfide/selenide-associated Se(-II) was observed for samples, which suggests the proportion of sulfide/selenide-associated Se(-II) could serve as a proxy for palaeo-redox conditions. In addition, the higher percentage of Se(IV) in K-bentonite and phosphorite was found and possibly attributed to the adsorption of Se by clay minerals, iron hydroxide surfaces and organic particles. Based on the negative correlations between the percentage of Se(IV) and that of Se(-II) in samples, we propose that the K-bentonite has been altered under the acid oxic conditions, and the most of black shale (and cherts) and the Ni-Mo-Se sulfide layer formed under the anoxic and euxinic environments, respectively. Concerning Se accumulation in the Ni-Mo-Se sulfide layer, the major mechanism can be described by (1) biotic and abiotic adsorption and further dissimilatory reduction from oxidized Se(VI) and Se(IV) to Se(-II), through elemental Se, (2) contribution of hydrothermal fluid with mineral Se(-II).

  8. Assessing subsurface strata using geophysical and geotechnical methods for designing structures near ground cracks

    NASA Astrophysics Data System (ADS)

    AlFouzan, F.; Dafalla, M.; Mutaz, E.

    2012-04-01

    This paper presents a combined approach using both geophysical and geotechnical approaches to study and evaluate the subsurface strata near ground for sites suffering from faults and cracks. It demonstrates how both techniques can be utilized to gather useful information for design geotechnical engineers. The safe distance for construction close to a ground crack is mainly dependant on the subsurface stratification and the engineering properties of underlying soils or rocks. Other factors include the area geology and concepts of safety margins. This study is carried out for a site in Al-Qassim region, Saudi Arabia. This type of faults and cracks can normally occur due to a geological or physical event or due to the nature and properties of the subsurface material. The geotechnical works included advancing rotary boreholes to depths of 25m to 31m with sampling and testing. The geophysical method used included performing 2D electrical resistivity profiles. The results of geophysical and geotechnical works showed good and close agreement. The use of 2D electrical resistivity was found useful to establish the layer thicknesses of shale and highly plastic clay. This cannot be determined without deep and expensive direct boring investigation. The results showed that a thick layer of expansive soil, which is considered a high-risk soil type containing large percentage of highly plastic clay materials, underlies the site. The volume changes due to humidity variations can result in either swelling or shrinking. These changes can have significant impact on engineering structures such as light buildings and roads. The logic of placing structures in close vicinity of the cracks is based on lateral stresses exerted on the crack face. The layer thickness is a detrimental factor to establish a safe design distance. Stress distribution analysis procedure is explained.

  9. Time Scale Optimization and the Hunt for Astronomical Cycles in Deep Time Strata

    NASA Astrophysics Data System (ADS)

    Meyers, Stephen R.

    2016-04-01

    A valuable attribute of astrochronology is the direct link between chronometer and climate change, providing a remarkable opportunity to constrain the evolution of the surficial Earth System. Consequently, the hunt for astronomical cycles in strata has spurred the development of a rich conceptual framework for climatic/oceanographic change, and has allowed exploration of the geologic record with unprecedented temporal resolution. Accompanying these successes, however, has been a persistent skepticism about appropriate astrochronologic testing and circular reasoning: how does one reliably test for astronomical cycles in stratigraphic data, especially when time is poorly constrained? From this perspective, it would seem that the merits and promise of astrochronology (e.g., a geologic time scale measured in ≤400 kyr increments) also serves as its Achilles heel, if the confirmation of such short rhythms defies rigorous statistical testing. To address these statistical challenges in astrochronologic testing, a new approach has been developed that (1) explicitly evaluates time scale uncertainty, (2) is resilient to common problems associated with spectrum confidence level assessment and 'multiple testing', and (3) achieves high statistical power under a wide range of conditions (it can identify astronomical cycles when present in data). Designated TimeOpt (for "time scale optimization"; Meyers 2015), the method employs a probabilistic linear regression model framework to investigate amplitude modulation and frequency ratios (bundling) in stratigraphic data, while simultaneously determining the optimal time scale. This presentation will review the TimeOpt method, and demonstrate how the flexible statistical framework can be further extended to evaluate (and optimize upon) complex sedimentation rate models, enhancing the statistical power of the approach, and addressing the challenge of unsteady sedimentation. Meyers, S. R. (2015), The evaluation of eccentricity

  10. Origin of sulfide and phosphate deposits in Upper Proterozoic carbonate strata, Irece basin, Bahia, Brazil

    SciTech Connect

    Kyle, J.R. ); Misi, A. )

    1991-03-01

    Carbonate strata of the Una Group represent late Proterozoic platform sedimentation in the Irece basin of north-central Brazil. Stratabound sulfide- and phosphate-rich units occur within a 50-m thick tidal flat sequence of dolomitic limestone and cherty dolomite. Three types of primary phosphate concentrations are present: columnar stromatolitic, laminar stromatolitic, and intraclastic. Resedimented phosphate clasts and phosphatic units interbedded with non phosphatic dolomites suggest early diagenetic replacement of algal carbonate units. Local stratabound Zn-Pb-Ag sulfide concentrations at the Tres Irmas prospect occur within silty dolomite with shallow water sedimentary structures and local disturbed laminae, synsedimentary faults, and breccias. Sulfide minerals include pyrite, sphalerite, galena, marcasite, jordanite, tetrahedrite, and covellite. Pyrite crystal aggregates commonly show bladed forms. Nodular aggregates of length-slow quartz are locally associated with sulfides. Sulfur isotope analyses indicate relatively uniform heavy {delta}{sup 34}S values. Barite shows a {delta}{sup 34}S range from +25.2 to +29.6{per thousand}, CDT. Pyrite and sphalerite representative of a variety of textural types have a {delta}{sup 34}S range of +20.2 to +22.6{per thousand}. Late Proterozoic evaporite sulfates show a wide range of {delta}{sup 34} S values from about +10 to +28{per thousand}. Thus, the {delta}{sup 34}S values for Irece barite could reflect original seawater sulfate values. However, the relatively heavy {delta}{sup 34}S values of the associated sulfides suggests that the original seawater sulfate was modified by bacterial sulfate reduction processes in shallow sea floor sediments. Textural and {delta}{sup 34}S evidence suggests that a later stage of metallic mineralization scavenged sulfur from preexisting sulfides or from direct reduction of evaporitic sulfate minerals.

  11. Hydrogeophysical investigation of aquifer properties and lithological strata in Abraka, Nigeria

    NASA Astrophysics Data System (ADS)

    Anomohanran, Ochuko

    2015-02-01

    The purpose of this study is to investigate the aquifer properties and lithological strata of Abraka, Nigeria. This was carried out by employing the geoelectric, geophysical well logging and pumping test methods. Ten vertical electrical soundings using the Schlumberger configuration were occupied to investigate the geoelectric properties of the subsurface, while two wells were drilled to evaluate the lithology and aquifer parameters of the study area. The result of the lithological study showed that the subsurface formations consist of lateritic sand, fine and medium grain sand mixed with clay, coarse sand, medium coarse sand and very coarse sand. The interpretation of the geoelectric data using a combination of curve matching and Win Resist computer iteration showed close correlation with the well record. The geoelectric result revealed that the fifth layer with a resistivity range of between 509 and 1033 Ω m and a depth range of between 31.5 and 45.9 m is the preferred layer to source for good quality water in the area. The result of well logs also showed that the electrical conductivity and the total dissolve solid which were obtained as 0.0105 mS/m and 67.43 mg/m3 respectively falls within the World Health Organisation benchmark for potable water. The result of pumping test further revealed that the transmissivity, storativity and specific capacity of the aquifer are 0.0713 m2/min, 1.3 × 10-5 and 0.39 m2/min respectively. It is inferred from this survey that the aquifer is confined and capable of yielding adequate and good quality water for the people.

  12. The impact of child safety promotion on different social strata in a WHO Safe Community

    PubMed Central

    Lindqvist, Kent; Dalal, Koustuv

    2012-01-01

    Abstract: Background: The objective of the current study was to evaluate outcomes of a program to prevent severe and less severe unintentional child injuries among the different social strata under WHO Safe Community program. Specifically, the aim was to study effectiveness of Safe Community program for reducing child injury. Methods: A quasi-experimental design was used, with pre- and post-implementation registrations covering the children (0 -15 years) in the program implementation area (population 41,000) and in a neighboring control municipality (population 26,000) in Östergötland County, Sweden. Results: Boys from not vocationally active households displayed the highest pre-intervention injury rate in both the control and intervention areas. Also in households in which the vocationally significant member was employed, boys showed higher injury rates than girls. Households in which the vocationally significant member was self-employed, girls exhibited higher injury rates than boys in the intervention area. After 6 years of program activity, the injury rates for boys and girls in employed category and injury rates for girls in self-employed category displayed a decreasing trend in the intervention area. However, in the control area injury rate decreased only for boys of employed families. Conclusions: The study indicated that almost no changes in injury rates in the control area suggested that the reduction of child injuries in the intervention area between 1983 and 1989 was likely to be attributable to the safety promotion program. Therefore, the current study indicates that Safe Community program seems to be successful for reducing child injuries. PMID:21502791

  13. Petrology and geochemistry of Ordovician K-bentonites in New York State: Constraints on the nature of a volcanic arc

    SciTech Connect

    Delano, J.W.; Schirnick, C.; Bock, B.; Kidd, W.S.F.; Heizler, M.T.; Putman, G.W.; De Long, S.E.; Ohr, M. )

    1990-03-01

    Altered volcanic ashes (K-bentonites) in the late Ordovician (Caradocian) Utica shale of New York State are the product of explosive arc volcanism. Most of the 30 K-bentonites examined in this investigation contain fragmental crystals and rock fragments (microliths) up to 600 {mu}m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts. The dominant phases are garnet (two groups; Gr{sub 15-20}Alm{sub 45-75}Py{sub 35-0}Sp{sub 2-5}; Gr{sub 2-5}Alm{sub 55-85}Py{sub 10-40}Sp{sub 1}), plagioclase feldspar (An{sub 80-10}), alkali feldspar (Or{sub 99-0}), clinopyroxene (Wo{sub 50-40}En{sub 50-30}Fs{sub 0-30}), and orthopyroxene (Wo{sub 1-2}En{sub 77-32}Fs{sub 32-66}), accompanied by lesser quantities of hornblende, aluminosilicate, quartz, sphene, Fe-Ti oxides, apatite, and zircon. Most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths, which possess minerals with similar compositions. Both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the Ordovician arc was constructed. They became entrained in the volcanic plume during explosive eruptions. A Precambrian age acquired on K-feldspars from one K-bentonite using the {sup 40}Ar/{sub 39}Ar method shows that these xenocrysts were derived from depths of less than 5-10 km in the microcontinent at the time of late Ordovician volcanism. The occurrence of xenocrysts and xenoliths in these K-bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks (e.g., isotopic age determinations; regional stratigraphic correlations of K-bentonites based upon chemical compositions).

  14. Paleomagnetism of Ordovician carbonate rocks from Malopolska Massif, Holy Cross Mountains, SE Poland — Magnetostratigraphic and geotectonic implications

    NASA Astrophysics Data System (ADS)

    Schätz, M.; Zwing, A.; Tait, J.; Belka, Z.; Soffel, H. C.; Bachtadse, V.

    2006-04-01

    The structural and geodynamic history of the Malopolska Massif (Holy Cross Mountains — Poland), situated within the Trans-European Suture Zone (TESZ) is still a matter of debate. Recent provenance studies and biogeographical data indicate that the Malopolska is a Gondwana-derived terrane accreted to Baltica between late Mid-Cambrian and Tremadocian times. Existing paleomagnetic data, however, are equivocal. They indicate either close proximity and coherence with Baltica since Silurian times or a significant Variscan dextral strike-slip displacement of Malopolska with respect to the latter along the Teisseyre-Tornquist Line. In order to address this problem a detailed paleomagnetic study of a condensed sequence of Middle to Upper Ordovician carbonate rocks from the Malopolska Massif (Mójcza quarry) has been undertaken. Samples were taken every 10 to 15 cm through the 4.5 m sequence which covers the Upper Llanvirnian and Caradocian. After detailed stepwise thermal demagnetization, a high unblocking temperature direction of magnetization with mixed polarities is identified. The directions pass the reversal test and yield an overall mean direction of Dec.: 323°, Inc.:- 63°, k: 16.6, α95: 5.8 after bedding correction. This corresponds to a paleo-(south)pole of 11°N, 46.8°E (d p: 7.2°, d m: 9.1°), which plots directly on the Ordovician segment of the apparent polar wander path for Baltica, thus rendering major post-Ordovician rotations of the area relative to Baltica unlikely. The paleomagnetic results reveal three zones of each reversed (R1-R3) and normal polarity (N1-N3). The section starts with a reversed polarity interval in the mid-Llanvirnian stage (R1). The transitions from R1 to N1 and from N1 to R2 in Middle Llanvirnian and from R2 to N2 during Upper Llanvirnian correspond well with previous paleomagnetic results based on graptolite biostratigraphy. After a short normal polarity interval (N2) the lower Caradocian is dominated by inverse polarity (R3

  15. Palaeocopid and podocopid Ostracoda from the Lexington Limestone and Clays Ferry Formation (Middle and Upper Ordovician) of central Kentucky

    USGS Publications Warehouse

    Warshauer, S.M.; Berdan, J.M.

    1982-01-01

    The Middle through lower Upper Ordovician Lexington Limestone and lower part of the Clays Ferry Formation contain an abundant and diversified ostracode fauna. More than 10,000 specimens belonging to 39 genera and 53 species have been found in 73 collections made by members of the U.S. Geological Survey in cooperation with the Kentucky Geological Survey between 1961 and 1970. Five of the genera and 17 of the species are new. New taxa include the genera Gephyropsis, Ningulella, Phelobythocypris, Quasibollia, and Uninodobolba and the following species: Americoncha dubia, Ballardina millersburgia, Brevidorsa strodescreekensis, Ceratopsis asymme , trica C. fimbriata, Ctenobolbina ventrispinifera, Cystomatochilina reticulotiara, Easchmidtella sinuidorsata, Gephyropsis trachyreticulata, Jonesella gonyloba, Laccoprimitia claysferryensis, L. cryptomorphologica, Leperditella? perplexa, Ningulella paupera, Parenthatia sadievillensis, Silenis kentuckyensis, and Uninodobolba franklinensis. In addition, a new species, Quasibollia copelandi, is described from the Middle Ordovician of Ontario. The type specimens of ostracodes previously described from these formations but not represented in the recent collections are redescribed and refigured. The genus Warthinia Spivey, 1939, is reinstated for Ordovician bolliids with two to four nodes, and the genus Ceratopsis Ulrich, 1894, is reviewed with new figures of all known North American species of the genus. Forty-four collections included enough specimens to warrant quantitative analysis. The temporal and spatial distribution of the genera were defined by using Q-mode cluster analysis based on Sorensen's quantified coefficient of association. The resulting phenogram indicated the existence of eight clusters; these clusters were characterized by calculation of constancy and fidelity measures for each of the variables. Generic diversity, compound generic diversity, and lithologic associations were scanned in an attempt to delineate the

  16. Evidence for an allocyclic origin of marine strata bounding the Upper Carboniferous Mary Lee coal zone, Warrior Basin, Alabama

    SciTech Connect

    Gastaldo, R.A. . Dept. of Geology); Demko, T.M. . Dept. of Geosciences)

    1992-01-01

    The Black Warrior Basin, a triangular foreland basin of Carboniferous age, is located at the southern end of the Appalachian orogen. A southwestward wedge of Mississippian and Lower Pennsylvanian sedimentary rocks occurs in the basin. The generally accepted model for basin-fill involves the progradation of a single delta, or multiple deltas (the Pottsville Formation), over an offshore carbonate bank (the Bangor Limestone). The Pottsville Formation is typical of Euramerican Carboniferous strata and is composed of the cyclical alternation of marine and terrestrial facies. The deposition of marine facies overlying terrestrial facies has been interpreted to have been the result of delta lobe switching and the compaction of underlying sediments, hence, autocyclic processes. Sedimentological features associated with the marine strata bounding the Mary Lee coal zone, the informal Jagger bedrock sandstone below and the Morris Shale above, are not indicative of circumstances generated by autocyclic processes. Rather, the marine strata highlight features resulting from allocyclic processes. The Jagger bedrock sandstone is a thick (> 15 m) sublitharenite interpreted as representing subtidal, shore-parallel bars. It is a sandstone body that was stranded on the shoreline during regional regression. The terrestrial coal-bearing strata are truncated by an erosional surface, marking the base of the Morris Shale. This ravinement surface is overlain by a ravinement bed representing a substrate developed by regional transgressive erosion that was subsequently colonized by open-marine macroinvertebrates. The ravinement bed is interpreted as a condensed section that accumulated under maximum water depth. Both of these features are indicative of development in response to extrinsic causes rather than intrinsic ones.

  17. Stratigraphic correlation by integrating photostratigraphy and remote sensing multispectral data: An example from Jurassic-Eocene strata, Northern Somalia

    SciTech Connect

    Sgavetti, M.; Ferrari, M.C.; Chiari, R.

    1995-11-01

    Integrated analyses of aerial photographs and multispectral remote sensing images were used for stratigraphic correlation in mainly carbonate and evaporitic rocks. These rocks crop out in an area of northern Somalia characterized by an arid climate. By the aerial photo analysis, we recognized photostratigraphic logs and stratal patterns and established correlations based on the tracing of physical surfaces with chronostratigraphic significance, such as photohorizons and photostratigraphic discontinuities. A limited number of field sections provided the lithological interpretation of the packages of strata delineated in aerial photos. By satellite multispectral (Landsat Thematic Mapper{trademark}) data analysis we identified image facies that represent packages of strata with different lithological characteristics. To interpret the image facies, we compared the responses in the thematic mapper (TM) bands with the laboratory spectroscopic properties of rock samples from the study area, and interpreted the absorption features by petrographic analysis. The Mesozoic and Tertiary strata analyzed herein are part of several formations deposited on a passive margin preceding the Oligocene-Miocene Gulf of Aden rifting and initial drifting. Following this approach, a number of stratigraphic units were recognized and mapped on aerial photos, and a framework of photostratigraphic correlation surfaces was delineated over significantly wide areas. These surfaces approximate time surfaces and are traced both within and across the lithostratigraphic units, improving existing maps. This method represents a mapping tool preliminary to more detailed field work, and is particularly useful in areas of difficult access.

  18. Yellow-tailed woolly monkey (Lagothrix flavicauda) proximal spacing and forest strata use in La Esperanza, Peru.

    PubMed

    Shanee, Sam

    2014-10-01

    Inter-individual spacing of primates and their use of forest strata depend on temporal and spatial changes in the environment and on predator avoidance, group demography, and social conditions. Greater proximity also increases the chances of agonistic and affinitive contact between individuals. I collected behavioral data for three groups of yellow-tailed woolly monkeys (Lagothrix flavicauda) by instantaneous sampling of focal animals for 15 months in La Esperanza, northeastern Peru. By use of combined data for all groups I examined the effects of season, activity, and age/sex class on nearest-neighbor distances and forest strata use. Small differences were observed for nearest-neighbor distances, forest strata use by different age/sex classes, and activity. Adult males had the lowest contact index scores. Contact index scores were low for juvenile females, for which nearest-neighbor distances were largest. Very little aggressive behavior was observed. Focal animals preferred upper levels of the forest with little difference in height for different activities. Lagothrix flavicauda have very cohesive groups with little seasonal or activity-dependent difference between nearest-neighbor distances or proximity. These results suggest that this species has less variable social organization and greater group cohesion than other Atelini. However, more studies are needed on other populations of L. flavicauda to better determine the species' social organization. Studies are also required to determine the extent to which dispersal times and kinship affect proximity, nearest-neighbor distances, and aggression. PMID:24906420

  19. Middle Jurassic strata link Wallowa, Olds Ferry, and Izee terranes in the accreted Blue Mountains island arc, northeastern Oregon

    SciTech Connect

    White, J.D.L. ); Vallier, T. ); Stanley, G.D. Jr. ); Ash, S.R. ); White, D.L.

    1992-08-01

    Middle Jurassic strata atop the Wallowa terrane in northeastern Oregon link the Wallowa, Izee, and Olds Ferry terranes as related elements of a single long-lived and complex oceanic feature, the Blue Mountains island arc. Middle Jurassic strata in the Wallowa terrane include a dacitic ash-flow deposit and contain fossil corals and bivalves of North American affinity. Plant fossils in fluvial sandstones support a Jurassic age and indicate a seasonal temperate climate. Corals in a transgressive sequence traditionally overlying the fluvial units are of Bajocian age and are closely related to endemic varieties of the Western Interior embayment. They are unlike Middle Jurassic corals in other Cordilleran terranes; their presence suggests that the Blue Mountains island arc first approached the North American craton at high paleolatitudes in Middle Jurassic time. The authors consider the Bajocian marine strata and underlying fluvial volcaniclastic units to be a basin-margin equivalent of the Izee terrane, a largely Middle Jurassic (Bajocian) succession of basinal volcaniclastic and volcanic rocks known to overlie the Olds Ferry and Baker terranes.

  20. Ordovician klippen structures of the Sierra de Umango: New insights on Tectonic evolution of the Western Sierras Pampeanas, Argentina

    NASA Astrophysics Data System (ADS)

    Meira, Vinícius Tieppo; Campos Neto, Mario da Costa; González, Pablo Diego; Stipp Basei, Miguel Ângelo; Varela, Ricardo

    2012-08-01

    The basement rock of the Pampean flat-slab (Sierras Pampeanas) in the Central Andes was uplifted and rotated in the Cenozoic era. The Western Sierras Pampeanas are characterised by meta-igneous rocks of Grenvillian Mesoproterozoic age and metasedimentary units metamorphosed in the Ordovician period. These rocks, known as the northern Cuyania composite terrane, were derived from Laurentia and accreted toward Western Gondwana during the Early Paleozoic. The Sierra de Umango is the westernmost range of the Western Sierras Pampeanas. This range is bounded by the Devonian sedimentary rocks of the Precordillera on the western side and Tertiary rocks from the Sierra de Maz and Sierra del Espinal on the eastern side and contains igneous and sedimentary rocks outcroppings from the Famatina System on the far eastern side. The Sierra de Umango evolved during a period of polyphase tectonic activity, including an Ordovician collisional event, a Devonian compressional deformation, Late Paleozoic and Mesozoic extensional faulting and sedimentation (Paganzo and Ischigualasto basins) and compressional deformation of the Andean foreland during the Cenozoic. A Nappe System and an important shear zone, La Puntilla-La Falda Shear Zone (PFSZ), characterise the Ordovician collisional event, which was related to the accretion of Cuyania Terrane to the proto-Andean margin of Gondwana. Three continuous deformational phases are recognised for this event: the D1 phase is distinguished by relics of S1 preserved as internal foliation within interkinematic staurolite porphyroblasts and likely represents the progressive metamorphic stage; the D2 phase exhibits P-T conditions close to the metamorphic peak that were recorded in an S2 transposition or a mylonitic foliation and determine the main structure of Umango; and the D3 phase is described as a set of tight to recumbent folds with S3 axial plane foliation, often related to thrust faults, indicating the retrogressive metamorphic stage. The

  1. Assessment of undiscovered oil and gas resources of the Ordovician Utica Shale of the Appalachian Basin Province, 2012

    USGS Publications Warehouse

    Kirschbaum, Mark A.; Schenk, Christopher J.; Cook, Troy A.; Ryder, Robert T.; Charpentier, Ronald R.; Klett, Timothy R.; Gaswirth, Stephanie B.; Tennyson, Marilyn E.; Whidden, Katherine J.

    2012-01-01

    The U.S. Geological Survey assessed unconventional oil and gas resources of the Upper Ordovician Utica Shale and adjacent units in the Appalachian Basin Province. The assessment covers parts of Maryland, New York, Ohio, Pennsylvania, Virginia, and West Virginia. The geologic concept is that black shale of the Utica Shale and adjacent units generated hydrocarbons from Type II organic material in areas that are thermally mature for oil and gas. The source rocks generated petroleum that migrated into adjacent units, but also retained significant hydrocarbons within the matrix and adsorbed to organic matter of the shale. These are potentially technically recoverable resources that can be exploited by using horizontal drilling combined with hydraulic fracturing techniques.

  2. New aspects of deformed cross-strata in fluvial sandstones: Examples from Neoproterozoic formations in northern Norway

    NASA Astrophysics Data System (ADS)

    Røe, Signe-Line; Hermansen, Marita

    2006-05-01

    Extensive (20-200 m long) exposures of tabular cross-sets in Neoproterozoic fluvial sandstone in Northern Norway demonstrate that deformed cross-strata, in the form of recumbently folded cross-strata with associated massive sand, are localized features passing in both up- and down-current direction into undeformed, concave-upward or sigmoidal cross-strata. The deformation occurs in down-current inclined, tangential wedge-shaped zones beneath reactivation surfaces, and less commonly as flat-topped lenticular zones. The localized nature of the sediment deformation is attributed to local liquefaction below the top of the bed in the case of the flat-topped lenses and at the dune front in the case of the more common tangential wedges. The position of the flat-topped lenses suggests deformation by the shear stress of high-velocity, suspension-laden currents. Although liquefaction of the dune front implies the action of gravity forces, it is argued that the fluvial currents were the main driving force at the instant of bed liquefaction. Post-folding gravitational shearing probably enhanced the deformation within the upper part of the wedges, with their long, flat-lying toeset resulting from redeposition of downslope-moving liquefied sand. The down-current alternation of deformed tangential wedges and undeformed cross-strata suggests that the mechanism that triggered the liquefaction of the dune lee side was related to the fluvial system itself and hence was of autokinetic origin. The tabular cross-sets have previously been interpreted as a product of the dune upper-stage plane-bed flow regime. In this flow context, it can be speculated that the liquefaction and deformation occurred when the flow conditions approached the plane-bed phase, probably inducing a highly differential turbulent pattern and pressure fluctuations sufficient to liquefy the fine/medium sand. The small flat-topped deformation lenses also suggest liquefaction by cyclic loading, whereas the solitary

  3. Very low-temperature metamorphism in Ordovician metasedimentary rocks above and below the Sardic unconformity, SW Sardinia, Italy

    NASA Astrophysics Data System (ADS)

    Franceschelli, M.; Battaglia, S.; Cruciani, G.; Pasci, S.; Puxeddu, M.

    2016-07-01

    In the Iglesiente region, the Cabitza and Monte Argentu Formations are separated by an angular unconformity known as the Sardic unconformity. This is related to an early Ordovician mild compressional phase, known as the "Sardic phase". The pelitic samples from the structurally lower Cabitza Formation consist of alternating reddish phyllosilicate-rich and whitish phyllosilicate-poor, sialic layers, whose S0 bedding plane is parallel to a pre-Variscan S1P schistosity overprinted by the Variscan S1V schistosity. Pelitic samples from the Monte Argentu Formation are characterized by a Variscan S1V axial plane schistosity. Samples from the two formations consist of quartz and phyllosilicates. The latter are potassic white mica, chlorite, paragonite, locally kaolinite, and pyrophyllite. The illite crystallinity values determined for the Cabitza samples are 0.25-0.31, with an average of 0.29; meanwhile, the Monte Argentu samples produce values of 0.33-0.38, with an average of 0.35. The chlorite crystallinity and b0 of potassic white mica values show greater heterogeneity in the Cabitza than the Monte Argentu samples. The b0 values and P-T pseudosections allow us to confirm that there is no significant difference in the P-T metamorphism conditions between the Cabitza and Monte Argentu samples. The Iglesiente region, which is considered to be the rift zone behind the Middle Ordovician Sarcidano-Barbagia volcanic arc, underwent the "Sardic phase", giving rise to E-W folds. These were first overprinted by weak E-W, and then by stronger N-S-oriented Variscan deformation events.

  4. Repetitive, multistage near surface and subsequent burial diagenesis in the Middle Ordovician Chickamauga organic buildups from Alabama

    SciTech Connect

    Tobin, K.J.; Walker, K.R.; Srinivasan, K. . Dept. of Geological Sciences)

    1992-01-01

    Middle Ordovician Chickamauga organic buildups from Red Mountain Expressway (RME) and Tidwell Hollow (TWH) in A have a complex diagenetic history when compared to approximately coeval Holston and Effna buildups of TN and VA. Near surface diagenetic history of the AL buildups at RME consists of two phases of marine and meteoric diagenesis. At TWH meteoric diagenesis occurred between initial and final generations of marine diagenesis. Initial marine diagenesis consisted of decay of sponges and dasyclad algae forming molds, micritization of fossils, and minor precipitation of fibrous calcite and turbid syntaxial overgrowths. A relative sea level rise at the top of the chickamauga is recorded by minor precipitation of fibrous calcite in selective voids and on equant calcite substrates suggestive of replacement of meteoric fluids in voids by marine waters. Extensive development of selective and non-selective porosity occurred during the final meteoric phase. Voids have the following occlusion history: (1) [+-] initial precipitation of a thin layer of equant calcite, (2) peloidal and/or micritic internal sedimentation, (3) [+-] deposition of turbid vadose silt, and (4) precipitation of pore-central equant (drusy) calcite. All meteoric features described above occurred during single generation at TWH and were associated with an exposure surface. A meteoric origin for equant calcite cements is supported by stable isotopic data which is slightly depleted relative to original marine compositions obtained from other Middle Ordovician buildups in the Southern Appalachians. In summary, porosity development is related to extensive subaerial exposure and the lack of continuously increasing burial immediately after deposition. The Holston and Effna buildups were buried under thick onlap sequences immediately after deposition.

  5. Early to Middle Ordovician organized and disorganized supra-subduction zone spreading along the Laurentian margin of Iapetus, Newfoundland Appalachians

    NASA Astrophysics Data System (ADS)

    Zagorevski, Alexandre; van Staal, Cees R.; McNicoll, Vicki J.; Cutts, Jamie A.

    2013-04-01

    The Annieopsquotch accretionary tract (AAT) comprises a thrust stack of Lower to Middle Ordovician arc and backarc terranes that were accreted to the Laurentian margin of Iapetus during Middle to Upper Ordovician. Geological relationships suggest that the constituent terranes of the AAT initially formed outboard of composite Laurentian margin in an extensional arc that underwent multiple rifting episodes prior to its accretion. The initiation of AAT magmatism led to the development of Tremadocian to Floian supra-subduction zone ophiolites with organized ridges indicated by well developed sheeted dyke complexes. This spreading centre propagated through a fragment of Laurentian crust and separated it from the composite Laurentian margin. This crustal block formed the basement to subsequent Floian to Darriwilian AAT arc magmatism. The Floian arc rifted leading to organized spreading in the Lloyds River backarc basin which was floored by juvenile backarc ophiolitic crust. The latest Floian to earliest Dapingian arc magmatism occurred above thickened crust, locally leading to eruption of andesitic rocks. The establishment of the Darriwilian arc was in part coeval with and followed yet another stage of rifting. Darriwilian magmatism is characterised by great along-strike variability, ranging from continental to intraoceanic calc-alkaline arc to tholeiitic back-arc magmatism, and lack of sheeted dyke complexes. The diversity of the magmatism can be attributed to fragmentation and magmatic reworking of the Laurenia-derived basement along strike in the same arc that is undergoing disorganized spreading. The constituent terranes of AAT were underplated beneath the composite Laurentian margin within ~5 Ma following their formation, coeval with extensional arc magmatism. This and other constraints suggest that the AAT thrust stack formed following subduction initiation in the backarc. AAT magmatism was terminated by the closure of the main tract of Iapetus and arrival of the

  6. Carbonate facies changes in the Upper Ordovician (Late Katian) of the Cincinnati Arch region: Implications for paleoclimate

    NASA Astrophysics Data System (ADS)

    Schwalbach, C. E.; Brett, C. E.; Aucoin, C. D.; Dattilo, B. F.

    2015-12-01

    The Upper Ordovician Rowland Member (Drakes Formation) exposed in the Cincinnati Arch region displays a suite of unusual facies that appear to record an environmental transition during the Late Ordovician. The Rowland displays four well-defined lithofacies, each containing a distinct biofacies. Proximal facies consist of green to gray shaly lime mudstones (often dolomitized), with ripples and desiccation cracks; these facies are sparsely fossiliferous, but show an abundance of infaunal filter feeders indicated by glauconite-filled burrows. These facies pass downramp into pale medium-bedded argillaceous micritic limestones, which are also sparsely fossiliferous but locally contain abundant deposit feeding organisms including brachiopods, small bryozoans, mollusks, and non-calcified algae. Select horizons yield rugosan and large colonial corals. These micritic beds often interfinger with a series of thick skeletal grainstone lenses that represent tidally influenced high-energy shoals and are exceptionally rich in well-preserved gastropods. To the north, these grainstones pass abruptly into offshore gray shaly packstone facies more typical of the Cincinnatian and contain a higher diversity of epifaunal brachiopods and ramose bryozoans. Compared to upramp facies of older Cincinnatian cycles, those of the Rowland show a greater thickness, relatively more micrite and glauconite, and higher abundance of corals and gastropods. These changes appear to be associated with a strong transgression underlain by a regional (and possibly global) lowstand erosional surface, as well as the Waynesville carbon isotope excursion. Additionally, these facies are correlative with similar transgressive facies in other regions, which also overlie regional lowstand unconformities. Increased micrite production instead of skeletal carbonates and the abundance of herbivorous? gastropods rather than echinoderms and bryozoans may indicate large-scale eutrophication and algal production

  7. Significance of nearshore trace-fossil assemblages of the cambro-ordovician deadwood formation and Aladdin Sandstone, South Dakota

    USGS Publications Warehouse

    Stanley, T.M.; Feldmann, R.M.

    1998-01-01

    The Cambro-Ordovician Deadwood Formation and Aladdin Sandstone represent intertidal and subtidal, nearshore deposystems that contain few well-preserved body fossils, but contain abundant trace fossils. The present study uses the much neglected trace-fossil fauna to describe the diverse paleoenvironments represented in the Deadwood-Aladdin deposystems, and to better understand the environmental conditions that controlled benthic life in the Early Paleozoic. The Deadwood-Aladdin ichnotaxa can be separated into three distinct assemblages based on the changing sedimentologic and hydrodynamic conditions that existed across the Cambro-Ordovician shelf. Trace-fossil assemblages and corresponding lithofacies characteristics indicate that the Deadwood-Aladdin deposystems formed within an intertidal-flat and subtidal-shelf environment. Based on the distribution and numbers of preserved ichnotaxa, the intertidal flat can be subdivided further into an ecologically stressful inner sand-flat environment, and a more normal marine outer sand-flat environment, both of which belong to a mixed, Skolithos-Cruziana softground ichnofacies. The inner sand flat is characterized by low diversity, low numbers, and a general lack of complexly constructed ichnotaxa. Trace fossils common to both assemblages tend to be smaller in the inner flat compared to the outer sand flat. Taphonomic effects, such as substrate type and sediment heterogeneity, also aid in differentiating between the inner and outer sand-flat assemblages. The subtidal shelf environment is categorized in the Cruziana Ichnofacies. Ichnological evidence of periodic tempestite deposition and hardground development within this subtidal regime is manifested by high diversity and low abundance of ichnogenera.

  8. Tephrochronology of rare Plio-Pleistocene fossiferous strata in south-central Afar, Ethiopia

    NASA Astrophysics Data System (ADS)

    DiMaggio, E.; Arrowsmith, R.; Campisano, C. J.; Deino, A. L.

    2013-12-01

    Sedimentary basins in the south and central Afar Depression archive the complex structural, climatic, volcanic, and biologic development of the region during the Pliocene and Pleistocene. The lower Awash Valley in central Afar has long served as a focus for these investigations, including the extensive work conducted to place fossil assemblages (including hominins) into stratigraphic and temporal context. Here we present a detailed analysis of tephra chemistry, correlations, and ages of the newly mapped and fossiliferous area of eastern Ledi-Geraru (ELG) in the lower Awash Valley (~3-2.5 Ma). Our results allow us to construct a tephrostratigraphic framework that provides important constraints for regional studies previously lacking a calibrated sedimentary record spanning 3 to 2.7 Ma. Based on glass chemistry and morphology, 40Ar/39Ar dating of feldspars, and stratigraphic mapping, we identified 23 distinct tephras (8 of which were dated) in >100 m of newly mapped fluvial and lacustrine sediments at ELG. The oldest tuff at ELG (Kuhulta Tuff; 2.994 Ma) is exposed in lake sediments (diatomite) that lie 3-5 m above basalt flows dated to ca. 3 Ma. The youngest ELG tephra (ca. 2.44 Ma) outcrops as a lenticular channel tuff in sediments faulted against older strata (~2.7 Ma). Between these two tephras lies the Gurumaha Tuff (ca. 2.82 Ma) and the Daáma and Bulinan Tuffs (both ca. 2.85 Ma), which provide excellent stratigraphic ties across a distance of 7.5 km, allowing us to document a lateral facies change from lacustrine in northern ELG to more nearshore in the south. These tuffs also confirm the presence of a fossiferous sedimentary record spanning the late Pliocene sedimentary gap in lower Awash Valley stratigraphy (ca. 2.94 - 2.7 Ma). While the youngest and oldest tephras at ELG temporally overlap with dated tephras from the well-described Hadar (3.8 - 2.94 Ma) and Busidima (2.7 - 0.016 Ma) Formations, we have yet to confirm geochemical correlates to any tephra

  9. Paleogeography and Depositional Systems of Cretaceous-Oligocene Strata: Eastern Precordillera, Argentina

    NASA Astrophysics Data System (ADS)

    Reat, Ellen J.; Fosdick, Julie C.

    2016-04-01

    New data from the Argentine Precordillera in the southern Central Andes document changes in depositional environment and sediment accumulation rates during Upper Cretaceous through Oligocene basin evolution, prior to the onset Miocene foredeep sedimentation. This work presents new sedimentology, detrital geochronology, and geologic mapping from a series of continental strata within this interval to resolve the timing of sedimentation, nature of depositional environments, and basin paleogeography at the nascent phase of Andean orogenic events, prior to the uplift and deformation of the Precordillera to the west. Five stratigraphic sections were measured across both limbs of the Huaco Anticline, detailing sedimentology of the terrestrial siliciclastic upper Patquía, Ciénaga del Río Huaco (CRH), Puesto la Flecha, Vallecito, and lower Cerro Morado formations. Paleocurrent data indicate a flow direction change from predominantly NE-SW in the upper Patquía and the lower CRH to SW-NE directed flow in the upper CRH, consistent with a large meandering river system and a potential rise in topography towards the west. This interpretation is further supported by pebble lag intervals and 1-3 meter scale trough cross-bedding in the CRH. The thinly laminated gypsum deposits and siltstones of the younger Puesto la Flecha Formation indicate an upsection transition into overbank and lacustrine sedimentation during semi-arid climatic conditions, before the onset of aeolian dune formation. New maximum depositional age results from detrital zircon U-Pb analysis indicate that the Puesto la Flecha Formation spans ~57 Myr (~92 to ~35 Ma) across a ~48 m thick interval without evidence for major erosion, indicating very low sedimentation rates. This time interval may represent distal foredeep or forebulge migration resultant from western lithospheric loading due to the onset of Andean deformation at this latitude. Detrital zircon U-Pb age spectra also indicate shifts in sediment routing

  10. Stratigraphic analysis of 3-D and 2-D seismic data to delineate porous carbonate debris flow in permian strata along the northwestern margin of the Midlan

    SciTech Connect

    Pacht, J.A.; Brooks, L.; Messa, F.

    1995-12-31

    Carbonate debris flow are very important plays in Leonard strata along the northwestern margin of the Midland Basin. Delineation of these strata, however, is difficult and detailed stratigraphic analysis of both 2D and 3D seismic data is important in reducing risk. Porous debris flows are best developed during lowstand time. When sea-level falls to a point at or below the shelf margin, sand to boulder-sized clasts created by reef-front erosion are funneled through slope gullies onto the base of the slope. Large debris flows exhibit well-defined mounds which downlap onto the sequence boundary. Many of these flows, however, are too thin to exhibit discrete reflections. 3D seismic data are used to define subtle changes in amplitude and frequency which suggest presence of porous strata. Along the northwest shelf, porous debris flows exhibit lower amplitude (dim spots) and lower frequency than surrounding strata. They are commonly developed immediately downdip of major slump scars.

  11. Eustatic control on early dolomitization of cyclic peritidal carbonates: Evidence from the Early Ordovician Upper Knox Group, Appalachians and Middle to Late Cambrian Bonanza King Formation, southern Great basin

    SciTech Connect

    Montanez, I.P. )

    1991-03-01

    The origin of massive dolomite in ancient cyclic carbonate successions remains a poorly resolved issue reflecting the lack of modern analogs of extensive dolomitization. This paper presents evidence for extensive synsedimentary dolomitization of peritidal cyclic carbonates of the Early Ordovician upper Knox Group, Appalachians, and of the Middle to Late Cambrian Bonanza King Formation, southern Great basin. Early dolomitization of these Cambro-Ordovician carbonates was synchronous with regressive conditions governed by superimposed sea-level oscillations (fifth-, fourth-, and third-order).

  12. Differences in the epidemiology of theileriosis on smallholder dairy farms in contrasting agro-ecological and grazing strata of highland Kenya.

    PubMed Central

    Gitau, G. K.; McDermott, J. J.; Katende, J. M.; O'Callaghan, C. J.; Brown, R. N.; Perry, B. D.

    2000-01-01

    A prospective cohort study was conducted in five purposively-sampled agro-ecological zone (AEZ)-grazing system strata in Murang'a District, Kenya, between March 1995 and June 1996. The study strata were selected based on a preliminary characterization study to represent the widest range of risks to East Coast fever (ECF) in the District and included zero-grazing and open-grazing farms. In total, 225 calves from 188 smallholder farms were examined from birth to 6 months of age and visited within the first 2 weeks of life and thereafter at bi-weekly intervals for up to 14 visits. The purpose of the study was to characterize the differences in epidemiology (risks of infection, morbidity and mortality) and potential control of ECF between the selected strata. Evidence of Theileria parva infection was assessed by increased antibody levels as measured in an indirect ELISA assay by the percent positivity (PP) of serum samples relative to a strong positive reference serum. Sero-conversion risks of T. parva were highest in the open-grazing strata. Antibody prevalence in adult cattle and ECF morbidity and mortality risks were also highest in open-grazing strata. While different, all five AEZ-grazing strata were considered to be endemically unstable for ECF. East Coast fever challenge was low in all zero-grazing strata and this challenge is likely to remain low due to continuing intensification of smallholder farming in the central highlands. In the open-grazing strata, there was higher challenge and a greater impact of ECF. PMID:10813159

  13. The Siljan Ring in central Sweden - a window into the Palaeozoic history of Baltoscandia

    NASA Astrophysics Data System (ADS)

    Lehnert, O.; Meinhold, G.; Bergström, S. M.; Calner, M.; Ebbestad, J. O. R.; Egenhoff, S.; Frisk, Å. M.; Högström, A. E. S.; Maletz, J.

    2012-04-01

    The Siljan meteorite crater, the largest known impact crater in Europe, is a main target of the research project 'Concentric Impact Structures in the Palaeozoic (CISP)', an integral of the Swedish Deep Drilling Program (SDDP). A set of new drillcores now provides possibilities to document the associated Early Palaeozoic sedimentary strata that form the crater ring-structure. In 2011 our research team has sampled the core sections for carbon isotope chemostratigraphy, thermal maturity analysis, sediment provenance, facies and microfacies studies. A dug trench at Nittsjö in the south-eastern part of the ring-structure forms complement to the drillcores and the total data set will allow intra- and intercontinental correlation of the succession and help to reconstruct Caledonian tectonic movements in the region. Based on initial analysis of the core sections, the Palaeozoic succession starts with the Tremadocian Obolus conglomerate whereas the youngest pre-Caledonian strata are Mid-Silurian shales of the Nederberga Formation. Our first preliminary studies show that different, and yet undefined, facies belts are preserved in the Siljan District. This part of Sweden, previously regarded to represent a stable cratonic area unaffected by the Caledonian collision between Baltica and Laurentia, locally has a complex tectonic history. In the western part of the crater, the Lower to Middle Ordovician carbonate succession is about 21 m thick, with a sharp flooding surface on top of the Mid-Ordovician Holen Formation. The immediately overlying shales are of upper Llandovery age based on graptolite data and comprises a minimum thickness of about 224 m. The erosional unconformity and substantial hiatus between these units suggest an extended period of uplift and erosion, presumably related to forebulge migration towards the east due to tectonic loading by the Caledonian nappes to the west. Megaslumps, debris flows, turbidites and several synsedimentary tectonic features in the

  14. /sup 40/Ar//sup 39/Ar age of detrital muscovite within Lower Ordovician sandstone in the coastal plain basement of Florida: implications for west African terrane linkages

    SciTech Connect

    Dallmeyer, R.D.

    1987-11-01

    Detrital muscovite was concentrated from a core of Lower Ordovician sandstone recovered from 1282 m in the Sun Oil Company, H.T. Parker No.1 well, Marion County, Florida. The concentrate records a /sup 40/Ar//sup 39/Ar plateau age of 504.1 +/- 2.1 Ma. The Paleozoic sedimentary section penetrated in this well is part of an extensive subsurface Lower Ordovician-Middle Devonian sedimentary succession characterized by Gondwanan paleontological affinities. The succession has been correlated with sequences of similar age in the Bove Basin of west Africa which unconformably overlie metamorphic units of the Bassaride and Rokelide orogens in Senegal and Guinea. Muscovite within these metamorphic rocks records ca. 500-510 Ma postmetamorphic /sup 40/Ar//sup 39/Ar cooling ages and was likely a proximal source for the lower Paleozoic clastic detritus represented in the pre-Mesozoic sedimentary sequences beneath the southeastern US coastal plain.

  15. First results of U-Pb dating of detrital zircons from the Upper Ordovician sandstones of the Bashkir uplift (Southern Urals)

    NASA Astrophysics Data System (ADS)

    Kuznetsov, N. B.; Belousova, E. A.; Degtyarev, K. E.; Pyzhova, E. S.; Maslov, A. V.; Gorozhanin, V. M.; Gorozhanina, E. N.; Romanyuk, T. V.

    2016-04-01

    The first results of U-Pb dating of detrital zircons from Upper Ordovician sandstones of the Bashkir uplift in the Southern Urals and U-Pb isotopic ages available for detrital zircons from six stratigraphic levels of the Riphean-Paleozoic section of this region are discussed. It is established that the long (approximately 1.5 Ga) depositional history of sedimentary sequences of the Bashkir uplift includes a peculiar period lasting from the Late Vendian to the Emsian Age of the Early Devonian (0.55-0.41 Ga). This period is characterized by the following features: (1) prevalence of material from eroded Mesoproterozoic and Early Neoproterozoic crystalline complexes among clastics with ages atypical of the Volga-Urals segment of the East European Platform basement; (2) similarity of age spectra obtained for detrital zircons from different rocks of the period: Upper Vendian-Lower Cambrian lithic sandstones and Middle Ordovician substantially quartzose sandstones.

  16. Tropical shoreline ice in the late Cambrian: Implications for earth's climate between the Cambrian Explosion and the Great Ordovician Biodiversification Event

    USGS Publications Warehouse

    Runkel, Anthony C.; MacKey, T.J.; Cowan, Clinton A.; Fox, David L.

    2010-01-01

    Middle to late Cambrian time (ca. 513 to 488 Ma) is characterized by an unstable plateau in biodiversity, when depauperate shelf faunas suffered repeated extinctions. This poorly understood interval separates the Cambrian Explosion from the Great Ordovician Biodiversification Event and is generally regarded as a time of sustained greenhouse conditions. We present evidence that suggests a drastically different climate during this enigmatic interval: Features indicative of meteoric ice are well preserved in late Cambrian equatorial beach deposits that correspond to one of the shelf extinction events. Thus, the middle to late Cambrian Earth was at least episodically cold and might best be considered a muted analogue to the environmental extremes that characterized the Proterozoic, even though cooling in the two periods may have occurred in response to different triggers. Such later Cambrian conditions may have significantly impacted evolution preceding the Ordovician radiation.

  17. Petrophysical, Lithological and Mineralogical Characteristics of the Shale Strata of the Volga- Ural Region

    NASA Astrophysics Data System (ADS)

    Morozov, Vladimir P.; Plotnikova, Irina N.; Pronin, Nikita V.; Nosova, Fidania F.; Pronina, Nailya R.

    2014-05-01

    The objects of the study are Upper Devonian carbonate rocks in the territory of South-Tatar arch and Melekess basin in the Volga- Urals region. We studied core material of Domanicoid facies from the sediments of Mendymski and Domanik horizons of middle substage of Frasnian stage of the Upper Devonian. Basic analytical research methods included the following: study of the composition, structural and textural features of the rocks, the structure of their voids, filter and reservoir properties and composition of the fluid. The complex research consisted of macroscopic description of the core material, optical microscopy analysis, radiographical analysis, thermal analysis, x-ray tomography, electron microscopy, gas-liquid chromatography, chromate-mass spectrometry, light hydrocarbons analysis using paraphase assay, adsorbed gases analysis, and thermal vacuum degassing method. In addition, we performed isotopic studies of hydrocarbons saturating shale rocks. Shale strata are mainly represented by carbonate-chert rocks. They consist mainly of calcite and quartz. The ratio of these rock-forming minerals varies widely - from 25 to 75 percent. Pyrite, muscovite, albite, and microcline are the most common inclusions. Calcareous and ferruginous dolomite (ankerite), as well as magnesian calcite are tracked down as secondary minerals. While performing the tests we found out that the walls of open fractures filled with oil are stacked by secondary dolomite, which should be considered as an indication moveable oil presence in the open-cut. Electron microscopy data indicate that all the studied samples have porosity - both carbonates and carbonate-siliceous rocks. Idiomorphism of the rock-forming grains and pores that are visible under a microscope bring us to that conclusion. The analysis of the images indicates that the type of reservoir is either porous or granular. The pores are distributed evenly in the volume of rock. Their size is very unstable and varies from 0.5 microns

  18. Interpreting Fracture Patterns in Sandstones Interbedded with Ductile Strata at the Salt Valley Anticline, Arches National Park, Utah

    SciTech Connect

    LORENZ, JOHN C.; COOPER, SCOTT P.

    2001-12-01

    Sandstones that overlie or that are interbedded with evaporitic or other ductile strata commonly contain numerous localized domains of fractures, each covering an area of a few square miles. Fractures within the Entrada Sandstone at the Salt Valley Anticline are associated with salt mobility within the underlying Paradox Formation. The fracture relationships observed at Salt Valley (along with examples from Paleozoic strata at the southern edge of the Holbrook basin in northeastern Arizona, and sandstones of the Frontier Formation along the western edge of the Green River basin in southwestern Wyoming), show that although each fracture domain may contain consistently oriented fractures, the orientations and patterns of the fractures vary considerably from domain to domain. Most of the fracture patterns in the brittle sandstones are related to local stresses created by subtle, irregular flexures resulting from mobility of the associated, interbedded ductile strata (halite or shale). Sequential episodes of evaporite dissolution and/or mobility in different directions can result in multiple, superimposed fracture sets in the associated sandstones. Multiple sets of superimposed fractures create reservoir-quality fracture interconnectivity within restricted localities of a formation. However, it is difficult to predict the orientations and characteristics of this type of fracturing in the subsurface. This is primarily because the orientations and characteristics of these fractures typically have little relationship to the regional tectonic stresses that might be used to predict fracture characteristics prior to drilling. Nevertheless, the high probability of numerous, intersecting fractures in such settings attests to the importance of determining fracture orientations in these types of fractured reservoirs.

  19. ‘Teach a Man to Fish’: The Doctrine of Sustainability and Its Effects on Three Strata of Malawian Society

    PubMed Central

    Swidler, Ann; Watkins, Susan Cotts

    2009-01-01

    This paper analyzes the social impacts of the commitment to “sustainability” in donor-funded AIDS programs. Using survey, interview, and ethnographic data from rural Malawi, we examine how efforts to mobilize and empower local communities affect three strata of Malawian society: the villagers these programs are meant to help, the insecure local elites whose efforts directly link programs to their intended beneficiaries, and, more briefly, national elites who implement AIDS policies and programs. We describe indirect effects of sustainability on the experiences, identities, and aspirations of Malawians—effects that are much broader and deeper than the direct impacts of funding. PMID:20161458

  20. Structure-Based Prediction of Drug Distribution Across the Headgroup and Core Strata of a Phospholipid Bilayer Using Surrogate Phases

    PubMed Central

    2015-01-01

    Solvation of drugs in the core (C) and headgroup (H) strata of phospholipid bilayers affects their physiological transport rates and accumulation. These characteristics, especially a complete drug distribution profile across the bilayer strata, are tedious to obtain experimentally, to the point that even simplified preferred locations are only available for a few dozen compounds. Recently, we showed that the partition coefficient (P) values in the system of hydrated diacetyl phosphatidylcholine (DAcPC) and n-hexadecane (C16), as surrogates of the H- and C-strata of the bilayer composed of the most abundant mammalian phospholipid, PC, agree well with the preferred bilayer location of compounds. High P values are typical for lipophiles accumulating in the core, and low P values are characteristic of cephalophiles preferring the headgroups. This simple pattern does not hold for most compounds, which usually have more even distribution and may also accumulate at the H/C interface. To model complete distribution, the correlates of solvation energies are needed for each drug state in the bilayer: (1) for the H-stratum it is the DAcPC/W P value, calculated as the ratio of the C16/W and C16/DAcPC (W for water) P values; (2) for the C-stratum, the C16/W P value; (3) for the H/C interface, the P values for all plausible molecular poses are characterized using the fragment DAcPC/W and C16/W solvation parameters for the parts of the molecule embedded in the H- and C-strata, respectively. The correlates, each scaled by two Collander coefficients, were used in a nonlinear, mass-balance based model of intrabilayer distribution, which was applied to the easily measurable overall P values of compounds in the DMPC (M = myristoyl) bilayers and monolayers as the dependent variables. The calibrated model for 107 neutral compounds explains 94% of experimental variance, achieves similar cross-validation levels, and agrees well with the nontrivial, experimentally determined bilayer

  1. Carbon isotope stratigraphy of an ancient (Ordovician) Bahamian-type carbonate platform: Implications for preservation of global seawater trends

    NASA Astrophysics Data System (ADS)

    Saltzman, M.; Leslie, S. A.; Edwards, C. T.; Diamond, C. W.; Trigg, C. R.; Sedlacek, A. R.

    2013-12-01

    . Few studies of ancient carbonates have attempted to explicitly compare C-isotope trends in both restricted platform settings and open marine settings (e.g., Immenhauser et al. 2002). We studied a restricted Bahamian-type carbonate platform of Middle-Late Ordovician (Darriwilian-early Sandbian) age included in the St. Paul Group of Maryland, notable for sedimentologic evidence of severe restriction and a general lack of open marine macrofauna. We are able to correlate the C-isotope curve from the St. Paul Group to other sections globally by using a combination of conodont microfossils and measurement of Sr isotopes on conodont apatite. Coeval C-isotope trends from open marine settings in the western United States and Estonia are comparable to the restricted platform in Maryland. In our Ordovician example, local factors appear to have modified the magnitude of the global trends, but not the timing and direction. A remaining question is whether magnitude differences are a function of sedimentation rate and completeness. We continue to test hypotheses of global correlations of C-isotope trends in the Middle-Late Ordovician by utilizing the rapidly changing Sr isotope curve at that time.

  2. Large-magnitude Middle Ordovician volcanic ash falls in North America and Europe: Dimensions, emplacement and post-emplacement characteristics

    USGS Publications Warehouse

    Huff, W.D.; Kolata, Dennis R.; Bergstrom, Stig M.; Zhang, Y.-S.

    1996-01-01

    Middle Ordovician K-bentonites represent some of the largest known fallout ash deposits in the Phanerozoic Era. They cover minimally 2.2 ?? 106 km2 in eastern North America and 6.9 ?? 105 km2 in northwestern Europe, and represents the coeval accumulation of plinian and co-ignimbrite ash on both Laurentia and Baltica during the closure of the Iapetus Ocean. The three most widespread beds are the Deicke and Millbrig K-bentonites in North America and the Kinnekulle K-bentonite in northwestern Europe. The vents were located near the Laurentian margin of Iapetus on an arc or microplate undergoing collision with Laurentia. The volume of ash preserved in the stratigraphic record converted to dense rock equivalent (DRE) of silicic magma is minimally estimated to be 943 km3 for the Deicke, 1509 km3 for the Millbrig and 972 km3 for the Kinnekulle. The Millbrig and Kinnekulle beds are coeval and possibly equivalent, yielding a combined DRE volume of nearly 2500 km3. Some unknown bu