Michigan Basin

The Michigan Basin is a geologic basin centered on the Lower Peninsula of the US state of Michigan. The feature is represented by a nearly circular pattern of geologic sedimentary strata in the area with a nearly uniform structural dip toward the center of the peninsula.

The basin is centered in Gladwin County where the Precambrian basement rocks are 16,000 feet (4,900 m) deep. Around the margins, such as under Mackinaw City, Michigan, the Precambrian surface is around 4,000 feet (1,200 m) down. This 4,000-foot (1,200 m) contour on the bedrock clips the northern part of the lower peninsula and continues under Lake Michigan along the west. It crosses the southern counties of Michigan and continues on to the north beneath Lake Huron.

On the north in the Canadian Shield, which includes the western part of Michigan's Upper Peninsula, Precambrian rocks are exposed at the surface. The eastern margins of Wisconsin along Green Bay are along the margins of the basin, while Precambrian rocks crop out to the west in central Wisconsin. The northeastern margin of Illinois around Chicago are on the southwestern margin of the basin. The southeast striking Kankakee Arch continuation of the Cincinnati Arch forms the southwest boundary of the basin underlying northeastern Illinois and northern Indiana. To the east, the Findlay Arch forms the southeast margin of the basin as it strikes to the northeast across northwestern Ohio, under the bed of Lake Erie and on as the Algonquin Arch through the southwestern prong of Ontario. The Wisconsin Arch forms the western boundary of the basin.

The rocks of the basin include Cambrian-Ordovician sandstones and carbonate rocks around the margins and at depth. Above or basinward are found the Silurian-Devonian dolostones and limestones with Carboniferous (Mississippian and Pennsylvanian) strata filling the center. A relatively thin veneer of Jurassic sediments are found in the center of the basin at the surface.

The basin appears to have subsided concurrently with basin filling as the sediments within the basin are all relatively shallow-water sediments, many of which are richly fossiliferous. The location was on a geologically passive portion of crust. The development of the basin and the surrounding arches were likely affected by the tectonic activity of the long-term Appalachian orogeny several hundred miles to the south and east.

Within the Precambrian rocks beneath and just west of the center of the basin lies a generally north to northwest trending linear feature that appears to be an ancient rift in the Earth's crust. This rift appears to be contiguous with the rift zone under Lake Superior. This, the Midcontinent Rift System, turns west under Lake Superior and then southwest through southern Minnesota, central and western Iowa and on through southeastern Nebraska and into eastern Kansas.