A NEW GEOLOGIC MODEL FOR THE SOUTHERN APPALACHIAN BASIN AND THE CONTINUATION OF THE ROME TROUGH SOUTHWARD AND SEQUATCHIE VALLEY THRUST NORTHWARD INTO NORTHERN TENNESSEE

Hydrocarbon exploration in the Cumberland Plateau is difficult because there are inadequate data to generate new geologic models. Regional-scale subsurface structures that have been identified (such as the Eureka structure in the western Valley and Ridge) have not been systematically investigated, which reflects a general reluctance to test deeper targets. This is mainly due to most oil and gas production in Tennessee and Kentucky is from shallow Mississippian and Ordovician limestones. Well data and new regional cross sections, however, indicate there are also shallow targets in the region that have not been prospected. We propose that the Rome trough continues southward from East-central Kentucky into northern Tennessee, but the full extent of the structure cannot be resolved because of paucity of seismic and basement well data. The trough exhibits a pronounced thickening of the Rome and Conasauga Formations (up to 2,000 ft) and a linear low in Precambrian–Ordovician trend surface residual anomaly (TSRA) maps. It is also proposed that Sequatchie Valley (SV) thrust extends northward beneath part of the Wartburg basin, based on well data and cross-section interpretation. In the Wartburg basin the Knox Group is shallower than expected, when compared to its elevation West of the Pine Mountain thrust. It is possible the extrapolated SV fault has not been identified before because most wells stop in Knox Group and no wells have yet drilled through the repeated section. The SV thrust is projected to ramp up-section in the northern part of the Wartburg basin and sole into the Chattanooga Shale, because the unit is structurally weak and the Pennsylvanian strata are not folded at the surface. This would also help explain a series of northwest-trending TSRA trends above the Chattanooga Shale that may correlate with blind structures, the marked thickening of the Chattanooga Shale (up to 300 ft) northwest of the Pine Mountain thrust, and tectonic stylolites suggesting pressure solution in the Mississippian section west of Sequatchie anticline where there are no known structures below the Cumberland Plateau overthrust.