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Late Mississippian (Chesterian) through early Pennsylvanian (Atokan) strata, Michigan Basin, USA

Shannon M. Towne
Shannon M. Towne
Three Rivers Operating Company, 5301 Southwest Parkway, Suite 400, Austin, Texas 78735-8986, USA
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Niah B.H. Venable
Niah B.H. Venable
Watershed Science, Natural Resource Ecology Laboratory and Department of Ecosystem Science and Sustainability, Colorado State University, 1476 Campus Delivery, Fort Collins, Colorado 80523-1476, USA
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David A. Barnes
David A. Barnes
Western Michigan University, Department of Geosciences, 1903 W. Michigan Avenue, Kalamazoo, Michigan 49008-5241, USA
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09 June 201713 March 2018


The Carboniferous Michigan Basin is the subject of conflicting interpretations resulting from the lack of detailed stratigraphic analysis of relevant rock units. In this study, an ~610 m (2000 ft) section of recently acquired core material was evaluated on the basis of lithofacies and stacking patterns, stratigraphic contacts, and well-established regional geologic relations of Mississippian and Pennsylvanian strata.

The Bayport formation is composed of seven distinct primary depositional lithofacies reflecting open-marine and shoal-water to restricted peritidal environments, typically capped by an exposure surface. Carbonate-dominated strata of the Bay port formation are interstratified but ultimately transition up section into siliciclastic-dominated strata (previously called the Parma Sandstone) deposited in tidally influenced, estuarine facies. Late Mississippian Bayport strata are sharply overlain by Pennsylvanian-aged siliciclastic lithofacies of the Saginaw Formation. These facies were deposited in a range of terrestrial and marginal-marine environments, from coarse-grained fluvial sandstones at the base (previously known as the Grand River Formation), to the finer-grained channel sandstones and floodplain mudstones of mixed fluvial and estuarine systems in the middle Saginaw Formation. Carbonaceous shales, mudstones, and thin coal intervals characterize the middle to upper Saginaw Formation.

In the southern Michigan Basin, an important unconformity at the Mississippian- Pennsylvanian contact is represented by either an incised valley-fi ll succession or a prominent paleosol above the Bayport formation at the base of the Absaroka section in the Saginaw Formation. In upthrown areas adjacent to a major wrench fault, the Lucas fault in south-central Michigan, the Bayport formation is transitional upward from an intensely karsted limestone to a red-bed paleosol and then to primarily carbonaceous mudrock of the Saginaw Formation. In downthrown areas adjacent to the fault, the formation contact, and systemic unconformity, is a sandstone-on-sandstone contact. Climate-sensitive strata indicate a significant transition from predominantly arid conditions in the Mississippian Bayport formation to humid climate conditions in the Pennsylvanian Saginaw Formation across the Mississippian-Pennsylvanian systemic boundary. Previously, the Bayport formation was considered Meramecian in age; however, palynologic analyses of samples collected from core within the interval indicate a Chesterian (late Mississippian) age, representing a significant revision of existing Michigan Basin stratigraphy.

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GSA Special Papers

Paleozoic Stratigraphy and Resources of the Michigan Basin

Geological Society of America
ISBN electronic:




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