Samples from 35 exploratory wells penetrating a complete section of Silurian rocks in the Michigan basin are analyzed by conventional quantitative chemical methods. Chemical analysis yields numerical lithologic data not available from study of published subsurface information. The numerical lithologic data are used to construct clastic ratio, sand-shale ratio, evaporite ratio, and isopach maps which depict gross aspects of Silurian sedimentation, history, and environmental tectonics of the basin.

Analysis of the lithofacies maps reveals eight areal subdivisions of the Michigan basin that are interpreted in terms of sedimentation and regional tectonics. Most significant of the eight subdivisions are the Central Michigan basin, East Michigan basin, and Battle Creek trough. Positive elements influencing history of the basin are the Findlay and Kankakee arches. Battle Creek trough was a major link between the Illinois and Michigan basins, but was severed at time of isolation of the Salina sea.

Silurian rocks in the Michigan basin have produced only insignificant amounts of oil and relatively minor amounts of gas, but more exploration is indicated. A tectonic and lithofacies "hinge" across south-central Michigan, separating the Central Michigan basin from a southern shelf area, is suggested as a possible locale for development of important biohermal structures in the late Middle Silurian with resultant petroleum entrapment.