SUBSURFACE FACIES ANALYSIS AND PARAGENESIS OF THE UPPER ORDOVICIAN TRENTON LIMESTONE IN NORTHWESTERN OHIO

Previous studies of the Upper Ordovician Trenton Limestone in Northwestern Ohio interpreted an extensive subtidal carbonate platform on the northwest margin of Taconic foreland basin. This study focused on the subsurface facies analysis and paragenesis of the Trenton Limestone using five different wells (3564, 2878, 2972, 2971 and 3374) in Hancock, Wood, and Wyandot counties. Both core sections and thin sections were available from well 3564, while only thin sections or well sections were available from the other wells. The wells were correlated using gamma-ray and density logs. Paragenesis was studied using petrography, SEM, and cathodoluminescence. The Trenton Limestone mainly consists of bioclastic carbonates (mudstone, wackestone, packstone and grainstone) with minor siliciclastic shale. The dominant lithofacies in order of importance, are heterolithic carbonate mudstone and siliciclastic shale (lithofacies CMl) which are interpreted as tidalites, massive gray mudstone (Cmm), massive light gray mudstone with Stromatactis (Cms), bioclastic grainstone (Cgm)which are interpreted as storm layers, grainstone with lithoclasts (Cgmi) which are interpreted as reworked beachrock, packstone (Cpf), dolomicrite(Dmm) and dolograinstone(Dgm). Because of tidalites, mudcracks, lithoclasts, shell debris, and storm layers the Trenton Limestone in northwestern Ohio is interpreted to have been deposited in a peritidal environment. The unit has undergone multiple cementation and dissolution intervals, including replacement of original minerals and fabrics by calcite, chert, and dolomite. Secondary porosity often includes petroleum (bitumen) stains. Work is continuing on the order of diagenetic events preceding and following petroleum migration.