ABSTRACT

Sandstones in the isolated Pennsylvanian section of the Michigan Basin range in age from Morrowan through Desmoinesian. They are dominantly of fluvial origin, as indicated by dispersal pattern geometry and field characteristics. During Morrowan time, the basin was characterized by deltaic sedimentation, with sediment dispersal controlled mainly by pre-Pennsylvanian topography. Sand detritus was localized in high energy lowlands, primarily as distributary channel deposits. The delta originated near Saginaw Bay and prograded across the basin in southerly and westerly directions, subduing much of the initial basin relief.

In succeeding Atokan and Desmoinesian time, the basin became the site of a broad alluvial plain, which contained an aggrading stream system that drained down a regional paleoslope to the west or southwest. Sand was concentrated by point-bar deposition in the higher energy stream channels, whereas finer clastics were localized in inter-channel flood plain areas. The alluvial plain was substantially inland from Pennsylvanian seaways, and only occasionally inundated by marine transgressions.

Provenance of Pennsylvanian sandstones was relatively constant, with the primary avenue of detrital influx being consistently from the northeast. Sandstone petrology indicates a multicycle origin, with probable derivation from older Paleozoic arenites.