--> Subsurface Facies Analysis of the Cambrian Mt

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Subsurface Facies Analysis of the Cambrian Mt. Simon Sandstone in Western Ohio



Department of Geology, Bowling Green State University, Bowling Green, OH  43403.


     In Ohio, the Precambrian basement and overlaying Cambrian section is subsurface. On the western flank of the Cincinnati Arch, the Cambrian Mt. Simon Sandstone is the first sedimentary unit deposited above the basal unconformity, and is of interest as a potential hydrocarbon reservoir and as a target for hazardous waste deep-well injection. Detailed subsurface facies analysis of the Mt. Simon Sandstone was conducted from continuous cores and geophysical logs from two wells: the Ohio Department of Natural Resources (ODNR) Warren County well (DGS 2627) and the British Petroleum Company (BP) Allen County well (BP 4).

     In the ODNR well, the Mt. Simon Sandstone shows a generally coarsening- and thickening-upward sequence of sandstone, siltstone and minor mudstone. Tidal rhythmites, flaser and lenticular bedding, mud drapes, interclasts, and significant bioturbation structures attest to a shallow marine, tidally influenced depositional setting. The coarsening-and thickening-upward sequence is interpreted as a transgressive barrier sequence, documenting migration of the barrier itself (the bulk of the Mt. Simon Sandstone) above basal lagoonal/estuarine succession. Independent tests of the geophysical logs shows a characteristic signature of the facies described and interpreted from core samples.

     On the basis of the geophysical logs, depositional facies were predicted in the BP well then confirmed by facies analysis of the core samples from that well. Facies were predictably recognized, however it became apparent that previous workers had misidentified the upper contact between the Mt. Simon Sandstone and Eau Clair Formation in this well.  A regional interpretation based upon both wells suggests the Cambrian coastline was oriented NE-SW, and transgression proceeded to the NW during this interval.