On this fieldtrip, we visit outcrops of Middle Mississippian siliciclastic mounds that have affinities with the famous European Waulsortian mud mounds and younger submarine channels incised into the lower part of the Fort Payne Formation. The purpose of this fieldtrip is to stimulate discussion of these unique geometries in a mixed carbonate-clastic system. It is now generally conceded that these stratigraphic features were built in a basin plain setting, but their origin is poorly understood. Further, we will see other geologic strata (Chattanooga Shale and Maury Shale) whose origins have been, and continue to be, intensely debated in the geologic literature.

The mounds at the base of the Fort Payne are about the same age as the classic European Waulsortian mounds and have a similar fauna. The largest Tennessee mounds are as large as some in Europe, but differ in having a matrix of terrigenous clay rather than carbonate mud.

Channels in the Fort Payne are filled with a mix of alternating carbonates and fine-grained clastics. Deposition in the channels was likely due to carbonate-rich sediment gravity flows on the slope, evidenced by grainstones that exhibit grading and imbrication of crinoid skeletal fragments. Siliciclastic mudstones interbedded with carbonate facies suggest that event-driven flows punctuated periods of slope quiescence and hemipelagic deposition during the Mississippian.