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 are highly fractured; tectonic extension and related thermal subsidence have resulted in the formation of two major sedimentary basins. These basins, known as the Illinois Basin and Michigan Basin, facilitated extensive deposition of sedimentary rock during the Paleozoic Era.