Precambrian rocks of Illinois are highly faulted; tectonic extension and related thermal subsidence have led to the formation of two major sedimentary basins. These basins, termed the Illinois Basin and Michigan Basin, allowed for extensive deposition of sedimentary rock during the Palaeozoic Era.
Precambrian rocks of Illinois exhibit extensive fracturing, which is attributed to tectonic extension and related thermal subsidence. This has led to the formation of two major sedimentary basins: the Illinois Basin and the Michigan Basin. These basins were instrumental in accumulating significant amounts of sedimentary rock during the Paleozoic Era.