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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. 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.

  2. 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.

  3. 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.

  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. 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

  11. 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.

  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. 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

  17. 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.

  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. 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

  20. 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.

  1. 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

  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. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. (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

  14. 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.

  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. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  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. 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.

  20. 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

  1. 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.

  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. 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

  13. 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

  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. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  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

    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 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

  9. 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.

  10. 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.

  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. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  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. 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.

  9. 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.

  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. 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

  19. 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

  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. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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

  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. 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.

  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

    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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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

  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.