Over 2000 linear feet of recently acquired conventional core and hundreds of well logs were analyzed to reevaluate regional, middle Carboniferous litho- and bio-stratigraphic relationships in the Michigan Basin, USA. The main objective of this workshop is to interpret the evolution of the Michigan Basin relative to other more extensively studied, North American cratonic interior basin successions in the Illinois and Appalachian basins. Stratigraphic relationships are evaluated in the Michigan, Bayport, and Saginaw formations on the basis of sedimentary lithofacies, contact relationships, and facies stacking patterns, in addition to new age determinations from several distinct pollen and spore assemblages. Core and well-log cross sections are presented to establish regional stratal geometry and corroborate stratigraphic relationships established in core studies. Biostratigraphic analysis has established the age range of these middle Carboniferous strata, which range from late Mississippian (Chesterian) through the early–middle Pennsylvanian (Morrowan and Atokan) North American stages, with no indication of significant hiatus relative to existing chronostratigraphic resolution. Significant soil horizons and incised valley-fill deposits found at the Mississippian-Pennsylvanian systemic boundary, however, are interpreted to represent the basal Absaroka sequence boundary.

Significant variations in eustatic, climatic, and tectonic signals recorded in Carboniferous strata of the Michigan Basin are found to be in close agreement with regional geological relationships established in recent sequence stratigraphic and basin analysis studies conducted in adjacent cratonic interior basins. Shallow, mostly restricted marine, mixed clastic, carbonate, and evaporite strata of the Mississippian Michigan and Bayport formations are overlain by carbonaceous debris-rich, terrigenous clastics dominated marginal marine and terrestrial strata of the Pennsylvanian Saginaw Formation. These strata record the complex interplay among second and higher order eustatic changes, global climate variations, and the culmination of Appalachian orogenic activity along the eastern margin of North America during the middle Carboniferous. These geological factors resulted in the dramatic transition from carbonate-dominated, stable cratonic interior basin sedimentation during the Siluro-Devonian to siliciclastic-dominated strata in the latest Devonian through Carboniferous in the Michigan Basin.