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Carbonate Margin Depositional Dynamics of the Lower Silurian Taconic and Salinic Foreland Basins: a High Frequency Eustatic Signal Superimposed on Long-Term Basin Evolution

Patrick I. McLaughlin1 and Carlton E. Brett2

1Bucknell University, Geology Department, Lewisburg, PA 17837

2University of Cincinnati, Department of Geology, Cincinnati OH 45221

New sequence stratigraphic analysis along the Cincinnati Arch reveals striking similarity between classic Lower Silurian sections of the Niagara region and outcrop and subsurface data from southwestern Ohio. The strata of these two regions contain a Llandovery succession made up of couplets of hardground-bearing glauconitic grainstone-ironstone and (largely barren) shale-dominated intervals, forming 4th-order depositional sequences. Three complete lower Llandovery depositional sequences and the lower part of a fourth, deposited during the Taconic Orogeny, show little change from southern Ohio southwestward into central Kentucky (~150 km), indicating depositional strike. However, these strata show a high degree of facies change in sections to the northwest of this strike line, indicating the direction of depositional dip. These strata are removed under a late Llandovery age erosional unconformity that is regionally angular. The erosion is so extensive that across western Ohio, northwestern Kentucky, and eastern Indiana only a portion of the lowermost depositional sequence is preserved, similar to the pattern of stratal overstepping developed in the Niagara region. The erosion is to extensive on the Cincinnati Arch that the uppermost Llandovery age strata rest upon the Upper Ordovician in parts of eastern Indiana, suggesting the axis of the Cincinnati Arch resided several tens of kilometers west of its present location during the Llandovery (nearly coincident with the Upper Ordovician Sebree Trough). The uplift of the arch during the late Llandovery is coincident with renewed basin subsidence further to the east and is interpreted as far-field tectonic response to the onset of the Salinic Orogeny.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York