TECTONICS OF PART OF THE CUMBERLAND PLATEAU: DATA FROM DETAILED GEOLOGIC MAPPING AND SUBSURFACE MAPPING OF STRATIGRAPHIC HORIZONS IN OIL AND GAS WELLS

The Cumberland Plateau is located between the Cincinnati arch to the west and the Valley and Ridge foreland fold-thrust belt to the east, and consists of three structural provinces: (1) the mostly undeformed Plateau where the primary structure is a regional dip of ~25 ft/mile (5 m/km) to the southeast off the Cincinnati arch/Nashville dome; (2) the Pine Mountain thrust sheet; and (3) the Cumberland Plateau overthrust sheet that includes the Sequatchie anticline.

Detailed geologic mapping of Fox Creek, Hebbertsburg, and Lancing 7.5-minute quadrangles reveals the Cumberland Plateau overthrust to be a complex series of thrusts and tear faults, bounded to the northeast by the Emory River dextral tear fault. The difference in outcrop pattern of the Cumberland Plateau overthrust and the Pine Mountain thrust has been attributed to changes in stratigraphy and the mechanical strength of the Chattanooga Shale. The relationship between the Sequatchie Valley fault and Cumberland Plateau overthrust has been illustrated through field relationships and in cross sections in the three quadrangles.

Subsurface mapping of several key stratigraphic horizons demonstrates the relationship of subsurface structure to surface geology and the location of upper Fort Payne carbonate mounds on the northern Cumberland Plateau in Anderson, Cumberland, Fentress, Morgan, and Scott Counties, Tennessee. The Middle Ordovician Deicke bentonite, the Missississippian-Devonian Chattanooga Shale, and the Fort Payne Formation were identified in well logs and interpolated using empirical Bayesian kriging, a geostatistical technique, and analyzed by creating trend surface residual anomaly maps.

Carbonate mounds in the upper Fort Payne Formation of the northern Cumberland Plateau have been of economic interest to the hydrocarbon industry for over 50 years, and subsurface mapping shows that these carbonate mounds are located in a structurally unique setting. Trend surface residual anomaly mapping reveals that the mounds are located: (1) along the crest of a broad NE-SW-striking anticline; (2) in a structurally low area relative to the remainder of the anticline; (3) above small-scale, along-strike anticlines on the Chattanooga Shale surface; and (4) in the Fort Payne Formation where it drastically decreases thickness.