Late Frasnian sedimentation cycles in the Appalachian basin—possible evidence for high frequency eustatic sea-level changes

Abstract

During the late Frasnian, 11 fourth-order progradational/retrogradational marine sedimentation cycles were deposited in the Appalachian foreland basin. Mapping based primarily on subsurface data demonstrates the continuity of these cycles over a distance of 700 km. Cyclicity in distal facies occurs as alternations of organic-rich and organic-poor shales, two of the organic shales can be correlated with the transgressive “Kellwasser Beds” of Europe. In more proximal facies, recurring lobes of siltstone and sandstone were deposited. Based on lithologic indices, the temporal pattern shows significant variation in the strength of relative facies change during deposition. In particular, two times of particularly pronounced progradation correspond to previously recognized eustatic sea-level falls. The correlation of portions of Appalachian basin depositional cyclicity with global sea-level events suggests that the entire sequence of 11 cycles, with estimated average duration of around 100–150 ka, were the result of high-frequency eustatic sea-level changes. This in turn would be consistent with a brief period of late Frasnian glaciation, as others have previously suggested.