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Comparative Sequence Stratigraphy of the Black River to Lower Trenton Group Interval (Upper Ordovician): Implications for Climatic and Associated Faunal Changes

Cornell, Sean R. and Carlton E. Brett
H. N. Fisk Laboratory for Sedimentary Geology, Department of Geology, University of Cincinnati, Cincinnati, OH 

The construction of high-resolution sequence stratigraphic frameworks from the upper Black River to Lower Trenton Groups from ancestral North America has allowed the detailed spatio-temporal comparison of two shelf-to-basin ramps from the eastern United States. Five 3rd-to-4th-order depositional sequences, each approximately 0.5 m.y. duration, have been established for this interval from both Ontario/New York and Kentucky/Ohio. Sequence comparisons help to constrain the timing and initial development of the Taconic foreland basin and related far-field topographic features on the craton. Despite an offset in timing of sequence depocenter migration patterns, large-scale magnafacies show relatively synchronous facies change and water-depth histories, suggesting that deposition in both regions was eustatically controlled. However, detailed comparisons of 4th order sequences have led to the recognition of a short- term asynchronous facies adjustment between regions in the M5A sequence (the immediate Black River/Trenton Group boundary interval). Specifically, facies development during the M5A TST, in KY/OH shows a shift to widespread coarse-grained skeletal grainstones (Curdsville Limestone), which is in stark contrast to underlying High Bridge Group. This rapid facies change, and associated faunal turnover has been interpreted to be the result of a change to relatively cooler water conditions in this region. Conversely, the same interval in the NY/Ontario region shows continuation of micrite-dominated wackestones and packstones through the M5A MFS. Thereafter, the two regions show a return to nearly identical facies types with the synchronous introduction of siliciclastics in both regions. This rather distinctive event is coincident with the as yet unexplained Guttenberg Carbon Isotopic Excursion.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004