The Kaskaskia sequence was a cratonic sequence that began in the mid-Devonian, peaked early in the Mississippian, and ended by mid-Mississippian time. A major unconformity separates it from the lower Tippecanoe sequence. Beginning in the late Devonian, black shales begin to dominate in the rocks, composed of detritus eroded from the uplifted Acadian highlands to the west; they also indicate widespread anoxic conditions across the sea floor. By mid-Mississippian time however, shallow-water carbonate deposition resumed, until the final regression of the epeiric seas late in the period.