STRATIGRAPHY AND SEDIMENTOLOGY OF THE DEVONIAN ANTRIM SHALE IN THE SCHMUCKER 3-30 CORE, NORTHWEST OHIO

The Late Devonian Antrim Shale of the Michigan Basin is a widespread, black shale-dominated unit. In the Schmucker 3-30 core (Fulton County, northwest Ohio), deposited on the southeasternmost margin of the Michigan Basin, the Antrim Shale and its component members are herein recognized and described. Regional subsurface studies and gamma log correlation along a transect from the Schmucker 3-30 well into the center of the basin show that the well intersects the following Devonian strata, from oldest to youngest: the Eifelian Dundee Limestone, overlain unconformably by the Givetian Traverse Group (Silica Shale and Tenmile Creek Dolostone), overlain unconformably by shale and dolostone of the probable Frasnian “Traverse Formation”, which transitions into the Frasnian Norwood and Paxton members and the Famennian Lachine and upper members of the Antrim Shale. In this core, the Ellsworth Shale interfingers with the Antrim between the Lachine and upper members. Additionally, the upper member of the Antrim is unconformably overlain by glacial deposits in this core. Only two portions of the succession were cored and available for sedimentological study, however, specifically the 1) the mid-Norwood through mid-Paxton, and, 2) the mid-Lachine. Norwood strata in the core consist of dark gray and black pyritic shale. The contact with the overlying Paxton is abrupt in the core, with Paxton strata piped down into the Norwood within burrow fills. Paxton strata in the core consist of variably calcareous and pyritic, heavily bioturbated, fossiliferous gray mudstone. Lachine strata in the core consist of dark gray and black pyritic shale. Remarkably, the Antrim Shale in this core from the basin margin closely resembles other Michigan Basin Antrim successions lithologically, and demonstrates the widespread nature of this (overall) transgressive unit. This study provides a better understanding of the stratigraphy of the Antrim Shale on the southeasternmost edge of the Michigan Basin and refines correlations of the Antrim Shale from the study area into the basin center.