EVIDENCE FOR THE OSAGEAN FORCED REGRESSION IN THE MICHIGAN BASIN AND COMPARISON WITH DATA FROM THE BORDEN DELTA (EARLY MISSISSIPPIAN) OF NORTHEASTERN KENTUCKY

Depositional histories of intracratonic basins have always been quite intriguing and problematic. The Michigan Basin is one of the most noticeable geologic structures in North America. Historically, the Paleozoic sediments in the Michigan Basin were deposited as classic ‘basin-fill’, responding to tectonic activity within the surrounding craton through shoreline migrations. The late Early Mississippian succession in Michigan consists of the Coldwater Shale overlain by the Marshall Sandstone (Kinderhookian-Osagean). The Marshall Sandstone is believed to have been deposited within the Michigan Basin in response to uplift and erosion of adjacent areas (i.e. Wisconsin Highlands, Canadian Shield). In northeastern Kentucky, the Kinderhookian-Osagean boundary is marked by the occurrence is the Osagean forced regression. The Osagean forced regression developed in response to glaciations in Gondwana. Although still debated, evidences for this glaciation can be found using lithologic characteristics, sequence stratigraphic interpretations, and chemostratigraphic data. In northeastern Kentucky, as the sea level dropped in response to the glaciations, large amounts of sediment was eroded and transported into the basin. This sediment bypass resulted in the deposition of the Farmers Member. Palynomorph data suggests the sediments in northeastern Kentucky originated in the Acadian Highlands. In the Michigan Basin, evidence of the glacially driven sea level drop at the Kinderhookian-Osagean boundary (Osagean forced regression) resulted in the erosion and transportation of sediments into the Michigan Basin, leading to the deposition of the Marshall Sandstone on top the Coldwater Shale. These two units are believed to represent the highstand (Coldwater) and lowstand (Marshall) conditions of two separate third order sequences. Preliminary palynomorph data reveal at least some of these clastic sediments originated in the Canadian Shield.