Re-Examination of a Middle Mississippian Carbonate Mud-Mound Complex from the Fort Payne Formation in South-Central, Kentucky

This study examines the origin of a 213-m (700-ft) long, Middle Mississippian, carbonate “mud-mound complex” in the Fort Payne Formation of south-central Kentucky. The complex’s well-exposed, easily accessible, and well-preserved nature provides an opportunity to understand how mounds like this developed during a time of sediment starvation, basinward of the largely abandoned Borden-Grainger Delta complex. The mound complex is formed of small, accretionary mounds that accreted onto the flanks of an eroded structural high and onto the backs of each other, apparently for protection from storms. Each sub-mound is composed of micrite-rich wackestone, comprising one of two biofacies: 1) alternating layers of microbial micrite and storm-razed communities of fenestrate bryozoans, crinoids and sponges, and 2) irregularly arranged accumulations of microbial micrite and small intercalated bryozoan-dominated communities, the former generating more massive wackestone lithofacies, and the latter, a vuggier lithofacies. The mound complex is also divided by three thin shale intervals overlying reworked surfaces that appear to represent flooding surfaces at possible parasequence boundaries. So much microbial micrite suggests occurrence in the photic zone. Additionally, the presence of dascyclad algae indicates depths no deeper than 40 m (130 ft). Overall, Fort Payne carbonate-mound development and the related proliferation of mound communities is related to a period of sediment starvation and a paleoclimatic/paleogeographic setting that suggests the possibility of upwelling. Repeated storms were major contributors to mound growth.