Carbonate buildups are a common feature in Mississippian sections worldwide. Yet despite intense study, questions remain about depositional processes that form such structures and their interrelations, if any, to each other. Carbonate buildups located in siliciclastic basins are particularly understudied and poorly understood.
This study focuses on a new exposure of buildups in the siliciclastic-dominated Fort Payne basin (Osagean) of south central Kentucky. It represents a first attempt to combine field and petrographic descriptions of facies in the buildup interval of the Fort Payne with the concepts of sequence stratigraphy to gain better insight into their depositional histories. The buildup interval is composed of five distinct facies. Two of these, the fossiliferous green shale and the tabular crinoidal packstone-grainstone, represent the background sedimentation during buildup nucleation and growth. The remaining three facies make up the buildups themselves. The shaly packstone marks the inception of buildup growth, the massive wackestone represents the core of the buildups, and the crinoidal grainstone is a buildup-flank facies deposited near the end of buildup growth. The buildups of the Fort Payne Formation grew during the transgressive phase of one third-order sequence in the early Osagean. The time at which buildup growth ceased cannot be determined precisely with available data but likely occurred either at the maximum flooding surface or during the early highstand.
Three commonly used depositional models, abbreviated as the lithoherm model, the baffling model, and the microbial model, are evaluated with respect to the Fort Payne buildups. None of the models is deemed adequate to explain all of the features of the buildups. Rather, a combination of all three seems to be required to account fully for all of the characteristics noted in this study. This multi-faceted depositional model compares favorably with other Carboniferous buildups worldwide, suggesting commonalities that transcend the properties of the basins in which they grew.