Upper Mississippian (Lower Carboniferous) carbonate stratigraphy and syndepositional faulting reveal likely Ouachita flexural forebulge effects, eastern Kentucky, U.S.A.

Abstract

Stratigraphic analysis of late Middle to early Late Mississippian (Early Carboniferous; late Meramecian–early Chesterian) carbonates in east-central and northeastern Kentucky, U.S.A., shows six unconformity-bound sequences. The earliest, late Meramecian, St. Louis sequence shows a relatively uniform distribution and a typical eastward Appalachian gradient along the ENE-trending outcrop belt on the western margin of the Appalachian Basin. However, abrupt uplift and exposure of deeper water St. Louis deposits, indicated by erosional thinning and well-developed exposure features, at the Meramecian–Chesterian transition signal inception of regional early Chesterian uplift that intensively altered the nature and distribution of the five overlying early Chesterian carbonate sequences. Uplift was related to the syndepositional reactivation of WNW-trending basement faults that broke up the St. Louis platform and generated a mosaic-like distribution of the overlying five sequences due to structurally related erosional incision and paleoslope change to the southwest. These early Chesterian events coincide with a major phase of northeast-directed Ouachita Orogeny on the southern margin of Laurussia and concomitant forebulge migration to the ENE. Modeling of regional stress distribution, as well as timing and location during bulge migration, strongly indicate that a migrating Ouachita bulge reactivated basement structures and generated the noted stratigraphic anomalies in eastern Kentucky and nearby areas. The likelihood of low-amplitude flexural waves, like the Ouachita bulge, migrating across areas where they were not previously considered, has major implications for understanding structural, stratigraphic, and eustatic anomalies in supposedly stable cratonic areas far removed from active tectonism.