PORE SPACES TO P-WAVES: RECONSTRUCTING PALEOCHANNEL GEOMETRIES ON A MIDDLE MISSISSIPPIAN SLOPE

The Fort Payne Formation, located in northern Tennessee and southern Kentucky, is a Middle Mississippian unit characterized by mixed carbonate and siliciclastic rocks. Within the Fort Payne, numerous paleochannels are observed filled with crinoidal grainstones, packstones, wackestones and siliciclastic shales. The channels incise approximately 5-10m into underlying carbonate and silica-rich muds. Diagenetic alteration to dolomite is common within the Fort Payne; however, many primary depositional structures appear to remain intact.

In this study, stratigraphic and petrographic observations are used to construct detailed cross sections of channel complexes in the Fort Payne. There are seven lithologic facies identified in more than 120m of stratigraphic section within and adjacent to paleochannels. Petrographic analyses of these facies show that the percent of siliciclastic or micritic clay between carbonate allochems ranges from <5% in grainstones to >95% in mudstones. Crinoids are the dominant allochem visible in hand sample, and siliceous sponge spicules are common at higher magnifications. Carbonate skeletal debris in the Fort Payne is disaggregated, and elongate fossil fragments show alignment parallel to bedding as well as imbrication suggesting they have been transported some distance.

To better characterize the orientation and geometry of channels in the Fort Payne, field observations were upscaled and simplified to create a series of synthetic 2D seismic cross sections. The results show that, for a dual lithology (carbonate-siliciclastic) model, individual channels like those observed in the Fort Payne are only visible at ultra high peak frequencies (> 150 Hz). This is important because the unit is a proven hydrocarbon reservoir in the region, and the geometry of slope channels may control reservoir distribution elsewhere in Tennessee and Kentucky.