The stratigraphic succession of the Michigan Basin has been studied for more than 100 years. However, there are still inconsistencies in the stratigraphic framework for Devonian strata. For example, the stratigraphic relationship between the alternating green-gray silty shale of the Ellsworth Formation and the underlying black shale of the Antrim Formation varies in the literature; these differences in proposed relationships are substantial with implications for chronostratigraphy in the Michigan Basin.

This study, conducted through the Keck Geology Consortium at Western Michigan University and Beloit College, aims to litho- and chemostratigraphically characterize the Ellsworth Formation in the Michigan Basin. More specifically, this study will define the base of the Ellsworth and the nature of its contact with the underlying Antrim, as well as the amount of lithologic and chemostratigraphic variation within the Ellsworth between two cores from north-central Michigan. Lithologic analysis of the two cores was conducted through the construction of detailed stratigraphic columns. Mineralogical and elemental analysis was accomplished using XRD and pXRF, respectively. Additionally, reflective light microscopy was used to analyze bulk samples.

Preliminary results indicate that the contact between the Lachine Member of the Antrim Formation and the overlying Ellsworth Formation is lithologically gradational, which may explain the variable stratigraphic descriptions in the previous literature. Lithologic and mineralogic differences observed among units and cores are attributed to more sediment input to the Michigan Basin during the Ellsworth compared to the Antrim, and one core being closer to the source of siliciclastic influx than the other, more basinal core. Future work will continue to use elemental chemostratigraphy through the contact interval to confirm the gradational contact and further characterize the units studied.