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Abstract: New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostrati-graphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced [...]

The late Katian Elkhorn event is a biogeochemical perturbation preceding the Late Ordovician mass extinction (LOME) with an exceptional record in the United States (U.S.). Results of our recent studies in this interval allow revised temporal ordering to strata across multiple basins providing insights into the magnitude of environmental disturbance and associated processes and feedbacks. The record of the Elkhorn event spans portions of the Appalachian and Midcontinent basins in the eastern U.S. and the Williston Basin and Cordilleran margin in the west. Our work focuses heavily on the Midcontinent Basin in particular, as it shares many characteristics of size, tectonic setting, and lithofacies with the Baltic Basin, providing the potential for resolving global signatures of the event. In its type-area, the Cincinnatian Series ends with the Elkhorn event. The succession is marked by shallowing from subtidal to marginal marine facies, capped by a karstic sequence boundary. Our new conodont data demonstrate that an overlying white to pink crinoidal grainstone package, previously assigned to the basal Silurian “white” Brassfield Formation near the Ohio-Indiana state line, is in fact Upper Ordovician. Further, δ13Ccarb values in this unit are elevated, in line with later phases of the Elkhorn event (2‰ more positive than reported Rhuddanian values). These findings support a correlation of the grainstone interval with the Fernvale Formation of central Tennessee. To the east, much of the northern Appalachian Basin was overfilled with widespread marginal marine to terrestrial red beds by the onset of the Elkhorn event, while the Midcontinent Basin to the west remained relatively sediment starved. In the southern Midcontinent, the mid-Elkhorn event sequence boundary was onlapped by ironstone deposition (lower Fernvale Formation). The ironstones are overlain by sparry and hematitic grainstones with localized bioherms. In Arkansas, where the Fernvale is thickest (>30 m), the sparry phase gives way upward to manganese carbonates and bioherms. Across the region, the Fernvale is, in turn, cut by a sequence boundary, suggesting a yet higher Katian sequence, and is perforated by paleokarst pockets that are filled and overlain by upper Katian (Ka4) sediments. This sequence boundary is onlapped by black shales and the thickest (>10 m) phosphorite of the Ordovician at the end of the Elkhorn event. Previous studies have suggested age equivalence of the Elkhorn and Paroveja δ13Ccarb excursions in Laurentia and Baltica. Despite the attraction of aligning the latest Richmondian and Pirgu regional stages, our data sets demonstrate that this is a miscorrelation. Critical to this revision are new integrated biostratigraphic and chemostratigraphic data sets in a transect from the margin of the Appalachian Basin into the Midcontinent Basin. The new data reveal that the Elkhorn Shale and Fernvale Formation are overlain by the Brainard and laterally equivalent Sylvan, and Mannie shales. These shale successions contain graptolites of the complanatusand pacificus zones. Thus, the Elkhorn event occurred in the latest manitoulinensis Zone, suggesting correlation with the Baltic Moe δ13Ccarb excursion. Our extensive new data sets provide regional chronostratigraphic correlation of strata deposited during the Elkhorn event. When temporally ordered, these records provide evidence for high amplitude sea level oscillations, major redox fluctuations, and reef pulses that demonstrate the waxing and waning of continental ice sheets on Gondwana and the spread of oceanic anoxia only a few million years before the LOME. These findings further call into question traditional models of rapid glaciation during a long-lived greenhouse state as the sole driver of the LOME and emphasize the need for new integrated Upper Ordovician research initiatives to better characterize Katian events. [ABSTRACT FROM AUTHOR]

Study of a subsurface core (named F688) from northern Indiana provides integrated data sets linking Katian chronostratigraphic records of the Appalachian and Midcontinent basins. The F688 core shows a variety of shallow- and deep-water facies containing numerous, well-preserved and zonally significant fossil species and diagnostic chemostratigraphic patterns. The succession belonging to the Cincinnatian Regional Stage in the F688 core is 210 m thick. Detailed benchtop examination of the succession revealed several phosphatic intervals, rich brachiopod faunas, multiple graptolitic horizons, and at least two tephras. Elemental analysis was conducted at 60 cm spacing quantifying lithofacies composition. Based on these results, the succession was assigned to six previously defined lithostratigraphic units (Kope, Waynesville, Liberty, Whitewater, Elkhorn, and Fort Atkinson formations). This lithostratigraphic succession shares components with both the Appalachian and Midcontinent basins, suggesting deposition near their shared margin. Twenty samples yielded abundant, well-preserved, low-diversity conodont assemblages with long-ranging taxa that clearly demarcate the position of the Ordovician–Silurian boundary at the top of the succession in the core. More than fifty palynologic samples, targeting graptolite-bearing intervals, were processed for chitinozoans and produced important new insights. The Kope Formation contains the chitinozoan species Belonechitina kjellstromi, Hercochitina downiei, and Clathrochitina sp. nov., co-occurring with a graptolite assemblage suggestive of the Geniculograptus pygmaeus Zone. Samples from the overlying Waynesville Formation produced graptolites indicative of the upper G. pygmaeus to Paraorthograptus manitoulinensis zones co-occurring with the long-ranging chitinozoan species Belonechitina micracantha and Plectochitina spongiosa as well as several new species of the genera Tanuchitina and Hercochitina. Higher in the core, the Liberty, Whitewater, Elkhorn, and Fort Atkinson formations yielded chitinozoan species characteristic of the upper Katian biozones of Anticosti Island and Nevada, such as Tanuchitina anticostiensis, Hercochitina longi, and Eisenackitina ripae. Results of δ13Ccarb analysis reveal partial preservation of the Kope, Waynesville, and Elkhorn excursions. A tephra in the rising limb of the Waynesville Excursion yielded needle-shaped clear zircons that will provide a high-precision U-Pb age. The Fort Atkinson Formation is overlain by the Brassfield Formation containing Silurian conodonts and δ13Ccarb values suggesting an Aeronian age. Chronostratigraphic data from our study of the F688 core resolves longstanding uncertainty about correlations between strata of Katian Age in the Appalachian and Midcontinent basins. Integration of core F688 with our other regional chronostratigraphic data in the Midcontinent Basin demonstrates that the Fort Atkinson Formation of the Indiana and Illinois subsurface is age equivalent to the Fernvale Formation of Tennessee, Arkansas, and Oklahoma. Across this area, the Fernvale is overlain by graptolitic shales of the uppermost P. manitoulinensis to basal Dicellograptus complanatus graptolite zones. By contrast, the type Fort Atkinson Formation of Iowa is interpreted to occur completely within the younger D. complanatus Zone. These regional correlations taken as a whole suggest that the uppermost Katian (all of Ka4) and all but the uppermost Hirnantian are missing throughout much of the Appalachian Basin. By contrast, the Midcontinent Basin contains a much more complete upper Katian and Hirnantian succession. Our comprehensive approach is correcting temporal miscorrelation and providing robust chronostratigraphic context for study of biogeochemical events, which will further enable us to disentangle proxy data and identify the processes that drove the Katian diversity peak and culminated in the Late Ordovician mass extinction. [ABSTRACT FROM AUTHOR]

New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostratigraphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced at 1.0-1.5 m intervals, were sampled from the New Associated Consolidated Paper (NACP) drill core and analyzed for major and trace elemental composition by portable X-ray fluorescence analyzer (pXRF). Select micrite and calcareous shale powders were then analyzed for δ13Ccarb (number of samples, N = 364) and 87Sr/86Sr ( N = 25). Our results indicate a Floian to early Darriwilian (F3-Dw1) age for the Romaine Formation, a middle Darriwilian to Sandbian (Dw2-Sa1) age for the Mingan Formation, a lower to mid-Katian (Ka1-Ka2) age for the Macasty Formation, an upper Katian (Ka3) age for the lower Vauréal Formation, an uppermost Katian (Ka4) age for the upper Vauréal, and a Hirnantian (H1) age for the Ellis Bay Formation. This integrated chemostratigraphic and biostratigraphic synthesis establishes the position of numerous unconformities, the duration of the intervening depositional sequences, and rates of sedimentation. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Facies and carbon isotope analysis of a series of four drill cores from Cincinnati, Ohio provide an opportunity to assess Late Ordovician paleoenvironmental variability along the margin of the Sebree Trough, an intracratonic basin associated with Taconian far-field tectonics. The cores provide stratigraphic data for an approximately 50km long NE-SW transect that roughly parallels the margin of the trough. The cores span the upper High Bridge Group through much of the equivalents of the Lexington Formation, and in one case into the overlying Cincinnatian strata (Kope). The cores were logged at centimeter-scale for litho-, bio-, and tapho-facies. A number of marker beds that are present in the cores, including K-bentonites, fossil epiboles (e.g., Prasopora bryozoans), and deformed beds, have been previously documented in the central Kentucky outcrop belt. We also sampled one core for carbon isotopes as a means of providing additional constraints on correlation into the central Kentucky outcrop belt. The facies succession in the lower half of the cores matches that of the lower members of the Lexington Formation in Kentucky (Curdsville, Logana, and lower Grier members). The upper half of the cores contain a more shale-rich facies succession, recording offshore environments that were substantially deeper than those of the Lexington Platform of the central Kentucky outcrop belt. These results corroborate previous studies, which indicated that the Sebree Trough expanded during the earliest Katian. Two positive carbon isotope excursions identified from outcrops of the Logana Member and the Macedonia bed on the Lexington Platform, are clearly recognizable in the sampled Cincinnati region drill core. We believe that one or both of these excursions are equivalent to the Guttenberg carbon isotope excursion (GICE) of the upper Mississippi Valley. [ABSTRACT FROM AUTHOR]

Recent detailed studies of the physical, bio-, and chemostratigraphy of upper Llandovery to middle Wenlock strata of the Cincinnati Arch area, primarily SW Ohio and SE Indiana and to a lesser extent west-central Kentucky, indicate a regionally extensive pattern of units, correlatable in detail overmore than 30,000 sq. km. This relatively simple stratigraphy has been obscured by the development of local names and by different usage of the same name in different areas. Here in we review and update this stratigraphical succession to provide uniformnomenclature and correlation of these units throughout the study area. The units as redefined and/or extended in this study include the Lee Creek, Dayton, Osgood, Lewisburg, Massie, and Laurel formations. Extension of the unit name Salamonie Dolomite is herein discouraged south of the Salamonie type area in NE Indiana. The term Dayton Dolostone is herein redefined; it is overlain by the Osgood Formation, which is also redefined here as equivalent to Foerste's (1897) 'Lower Osgood Clay'. The Lewisburg Limestone/Dolostone is reintroduced here as a formal name at the rank of formation to include a thin interval of pelmatozoan-brachiopod dolomitic pack- to grainstone formerly termed 'Middle Osgood Limestone' in Indiana and 'Laurel of Ohio' (in part) in SWO hio. The term Massie Shale, defined in SWO hio, is extended at formation rank throughout the study area as equivalent to the 'Upper Osgood Clay' and unnamed shale unit of the lower part of the Laurel (subunit 2) in Kentucky. [ABSTRACT FROM AUTHOR]

A restudy of the palynology of the Whirlpool Formation and Power Glen Formation in New York (USA) yielded a diverse fossil assemblage with cryptospores, glomalean fungi, acritarchs, chitinozoans, scolecodonts, and small carbonaceous fossils. These new data, and particularly the presence of the chitinozoan index fossil Hercochitina crickmayi, combined with emerging stable carbon isotope data, suggest a Late Ordovician (Katian or Hirnantian) age for these formations, which is older than their previously suggested Silurian (Rhuddanian) age. [ABSTRACT FROM AUTHOR]