Western Shelf
Location
Western Illinois and adjacent parts of Missouri
(fig. 2)
References
Bell et al. 1964
Description
The Western Shelf is the west flank of the Illinois Basin lying west of the Fairfield Basin and east of the Ozark Dome and the axis of the Mississippi River Arch. Its boundaries are quite indefinite in most places except along the Du Quoin Monocline, which forms part of the eastern border. The Western Shelf was a carbonate platform during much of the Paleozoic Era and it was characterized by slow rates of deposition, open marine circulation, and low elastic input. The shelf experienced only mild structural deformation, most of which apparently took place late in the Mississippian Period or early in the Pennsylvanian Period and produced northwest-trending anticlines and faulted monoclines. The southern part of the Western Shelf is commonly called the Sparta Shelf.
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