Richard Krause¹

(1) University of Cincinnati, Cincinnati, OH

ABSTRACT: Carbonate debris flows and biotic sedimentation in a toe-of-slope environment; Fort Payne Formation, south-central Kentucky

The Lower Mississippian Fort Payne Formation of south-central Kentucky contains mound-like carbonate mud structures that have confounded workers for decades. These structures have been compared to the classic Lower Carboniferous Waulsortian Mounds of northern Europe and New Mexico. However, evidence also exists indicating they may represent multiple generations of debris flows from a prograding shelf margin, which were then colonized by mound-building organisms.

The present study utilized a series of new road cuts, which are unique in terms of their stratigraphic completeness and lateral continuity. The outcrops show a complete vertical section of the lower Fort Payne Formation, including the basal contact with the underlying Devonian black shales. Of particular interest is the contact between the crinoidal wackestone bodies (the putative mud mounds), and the fossiliferous green shale that represents background sedimentation. The lower contact of the wackestone bodies with the green shale may be erosional, and is associated with synsedimentary deformation, whereas the upper contact shows onlapping and tends to be gradational. These critical relationships have been studied at multiple scales, from outcrop to thin section.

Implications of this study are far reaching, as similar facies are relatively common in Lower Carboniferous shelf-margin environments. Understanding the mode of formation of these structures offers important insight into many disparate problems such as the process of stabilization of a prograding shelf during low stand deposition and recovery of biotic communities after an extinction.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado