Reports: UNI850242-UNI8: Testing Depositional Models Across an Upper Ordovician Facies Transition in Kentucky, Ohio, and Indiana

Benjamin F. Dattilo, PhD , Indiana University-Purdue University (Fort Wayne)

The bulk of work for the first year has been to gather data and begin analysis for surface and subsurface sections.  Undergraduate student employees are heavily involved in all phases of the work. In the subsurface we have gathered and begun correlating geophysical logs from approximately 450 boreholes from 72 counties in adjoining parts of Ohio, Indiana, and Kentucky.  To insure correct correlations, the interval correlated in each log is about 300 m (100 ft) spanning from the middle Ordovician Deicke and Millbrig bentonite marker beds at the base to the Silurian Waldron Shale or the Devonian Shale markers at the top.

We studied the 50 Upper Ordovician interval of particular interest, about 40 m (120 ft) from within the interval, in 10 core samples from boreholes across the region to establish a link between the outcrop sections, which are known at meter-scale resolution, and the less well studied subsurface geophysical logs.

Field work expenses included trips to the Ohio geological survey for well logs in addition to field descriptions of outcrops from around the Cincinnati region and deeper into Kentucky. The sediments exposed at these localities were deposited in the intertidal and supratidal environments and differ significantly from sediments of the same age further north. Our effort to make high-resolution correlations to these localities has involved collection of about 100 rock samples from which we have made thin sections and polished slabs to help characterize sediment types and establish criteria for the recognition of cyclicity in the peritidal rocks.

As this point a lot of tedious groundwork has been completed.  As correlations come together, an integrated picture will emerge.  One publication in review presents some of the preliminary work and outlines the surprising structure of a few single shell beds as it is traced from the shallow water deposits in Kentucky to the deeper-water deposits in the subsurface of Indiana. Conference presentations have concentrated on the recognition of cycles within the Maysville and the tracing some of these cycles from normal marine environments into peritidal environments.

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