OBSERVATIONS OF THE SEQUATCHIE FAULT AND GEOLOGIC MAPPING IN NORTHEASTERN ALABAMA

The Sequatchie fault is a southeast-dipping thrust fault that, in places, cuts the forelimb of the Sequatchie anticline, the leading (northwesternmost) structure of the Appalachian thrust belt in northeastern Alabama. Recent, detailed geologic mapping in the Mt. Carmel 7.5-minute quadrangle in the northeastern part of Alabama suggests that the Sequatchie fault becomes blind within the quadrangle. This interpretation agrees with previous geologic mapping by Hayes (1896), whereas Sanford (1966) did not map a fault in the area. Hayes (1896) first mapped a fault from Tennessee south along the northwest limb of the Browns Valley anticline into Alabama, and this fault was later named the Sequatchie fault by Rodgers (1950). New field observations, previously published data, and the topography in the area document the geometry of the Sequatchie fault in the Mt. Carmel quadrangle.

In the Mt. Carmel quadrangle, the trace of the fault extends from the eastern boundary southwestward and cuts down section in both the hanging wall and footwall from Mississippian rocks into the Upper Ordovician south of Roden Ridge. The trace of the fault continues within the Middle Ordovician Nashville and Stones River Groups and becomes a blind thrust further southwest. To the northeast, the Mississippian Monteagle Limestone is in the footwall of the fault. Continuing southwestward, the fault cuts down section in the footwall to the Nashville and Stones River Groups at the terminus of the surface fault trace. In the hanging wall, the Mississippian Tuscumbia Limestone, Fort Payne Chert, and Maury Formation undifferentiated is juxtaposed against the Mississippian Monteagle Limestone from the eastern edge of the quadrangle to a small inlet of Guntersville Lake, beyond which rocks in the hanging wall become progressively older, ending in the Nashville and Stones River Groups at the terminus of the mapped fault in the quadrangle. The exact location at which the Sequatchie fault becomes blind is unknown.