A Revised Stratigraphic Framework for the Middle and Upper Devonian of the Northern Michigan Basin
High-resolution stratigraphic correlation of Middle and Upper Devonian strata in the northern Michigan Basin has been hindered by a lack of outcrops, lithofacies changes across the basin, and a deficiency of subsurface lithostratigraphic analysis. In this study, a combined approach of sequence- and biostratigraphy is used to reconstruct a high-resolution stratigraphic framework for the Michigan Basin. Stratigraphic units included in this study are the Antrim Shale and the Traverse Group, both of which have a long history of oil and gas production in Michigan. Stratigraphic data from both outcrop and core is utilized. The recognition of third- and, possibly, fourth-order depositional sequences in different facies allows tentative stratigraphic correlations across depositional strike in the Michigan Basin. A key stratigraphic datum is the Taghanic Onlap, a late Middle Devonian transgression that has been recognized globally. Additionally, the limited conodont biostratigraphy undertaken to date provides a means for correlating the Michigan Basin strata with the global stratigraphic framework. Brachiopod biostratigraphy in the Michigan Basin, however, is in contrast with other stratigraphic data. In particular, the first appearance of brachiopod taxa with paleoequatorial affinities that are associated with the Taghanic Onlap occur later in the Michigan Basin than expected in comparison to other basins based on sequence- and conodont biostratigraphic correlation. This may be related to the isolated nature of the northern Michigan Basin, suggested by paleogeographic reconstructions, which would have allowed the shallow portions of the Michigan Basin to serve as a refuge for endemic taxa during the Taghanic Onlap incursions. In order to reconcile the stratigraphic framework and allow correlation of the Michigan Basin succession with other basins, carbonate carbon isotope chemostratigraphy is the most promising approach for future work. A recently reconstructed, high-resolution carbonate carbon isotopic profile for the northern Appalachian Basin has recognized a global positive isotopic excursion, and provides a guide for testing the proposed sequence stratigraphic framework, and the contradicting brachiopod biostratigraphic data, in Middle and Upper Devonian strata of the northern Michigan Basin.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013