CALCICLASTIC SEDIMENT GRAVITY FLOWS: LESSONS LEARNED FROM OUTCROPS OF THE MISSISSIPPIAN FORT PAYNE FORMATION
We use a combination of stratigraphic and petrographic analyses of Fort Payne outcrops to construct cross sections through proximal and distal slope deposits. Detrital components are almost entirely carbonate allochems including disaggregated crinoids, bryozoans, brachiopods, and siliceous sponge spicules. Sedimentary structures include normal grading of skeletal components as well as imbrication of crinoid columnals parallel to bedding. These observations suggest that while carbonate production may have dominated the updip shelf, transport on the slope was more closely linked to sediment gravity flow processes. Thus, we interpret observed lithofacies to reflect a continuum of hydrodynamic conditions resulting in debris flows, high- and low-concentration turbulent flows, and pelagic settling on the seafloor.
In the subsurface, the Fort Payne serves as a reservoir unit hosting oil and gas sourced from the Chattanooga Shale (Devonian). To date, most Mississippian-aged discoveries have been stratigraphic traps attributed to the development of carbonate mud mounds in the lowermost Fort Payne; however, our recent work suggests that porosity and permeability trends may also be controlled by paleochannel geometries and the distribution of proximal-to-distal slope sedimentary bodies.