DEPOSITIONAL AND STRATIGRAPHIC ARCHITECTURE OF THE MISSISSIPPIAN-PENNSYLVANIAN MICHIGAN BASIN, USA

Core material was analyzed to better understand the depositional evolution of the Carboniferous Michigan basin. The main objectives of this study are to evaluate strata deposited in the south and central Michigan basin and better understand the eustatic, tectonic, and climatic controls on deposition across the Mississippian-Pennsylvanian sequence boundary. Study of pollen and spores from this interval indicates deposition during the Chesterian and Morrowan regional stages (Ravn, Personal Communication, 2011), across the Mississippian-Pennsylvanian boundary. This analysis indicates the Michigan Formation was deposited during the Chesterian Stage, conflicting with previous Chronostratigraphy, which designates the unit as Osagian-Mermecian in age.

Three distinct, disconformity-bounded, depositional successions are recognized and can be used for local and regional stratigraphic correlation on the basis of distinct sedimentary facies associations and biostratigraphy. The Michigan Formation comprises of heterolithic deposits of siltstone, sandstone, and gypsum deposited in an estuarine tidal-flat to back barrier bay setting in a periodically arid and restricted marine environment. The onset of rapidly fluctuating base-level conditions resulted in the deposition Bayport Limestone and the Parma Sandstone. The Parma Sandstone contains facies characteristics indicative of strong tidal influence and is inter-bedded with discontinuous, marine, arid tidal flat carbonates of the Bayport Limestone, possibly the result of 4th order (~500 Ky) eustatic sea-level fluctuations. Paleosols, coal, and fluvial-estuarine (?) sandstone in the Pennsylvanian Saginaw Formation reflects a significant regressive event and a transition to a terrestrial/marginal marine depositional system deposited in a distinctly humid environment during the early Morrowan regional North American stage.