Style and origin of mid-Carboniferous deformation in the Illinois Basin, USA — Ancestral Rockies deformation?

Abstract

The integration of outcrop, borehole, and seismic reflection data from the Illinois Basin and adjacent eastern Ozark Dome in Illinois and Missouri sheds new light on the style and origin of intra-cratonic deformation. Typical structures of this region are high-angle reverse faults in Precambrian basement that propagated upward to monoclines and asymmetrical anticlines in Paleozoic sedimentary cover. These are compressive-block structures directly analogous to (although smaller than) `Laramide-style' structures of the Colorado Plateau and Rocky Mountain foreland. Central Illinois Basin structures were active chiefly during late Chesterian through Atokan (i.e., late Mississippian to middle Pennsylvanian; mid-Carboniferous) time, with continued intermittent movement through the late Pennsylvanian. Both the style and timing of deformation match those of the `Ancestral Rocky Mountains' orogeny of the southern Midcontinent and Rocky Mountain region of the USA. Deformation in the central Illinois Basin has generally been attributed to the nearby late Paleozoic Appalachian–Ouachita orogeny, even though the Illinois Basin's compressive block structural style is foreign to the Appalachian foreland. We suggest that the Ancestral Rockies event may have played a significant role in the development of Pennsylvanian-age compressive-block structures in Illinois and Missouri.