SUPRATENUOUS FOLDS AND SOFT-SEDIMENT DEFORMATION OF CRINOID REEFS OF THE LOWER MISSISSIPPIAN FORT PAYNE FORMATION ON STATE ROUTE 52 NEAR CELINA, TN

A series of road cuts southeast of Celina, TN, were recently constructed to improve Tennessee Highway 52, and the section was opened in November 2013 exposing 6 km (4mi) of lower Mississippian Fort Payne Formation (Mfp). One or several crinoid reef flanks are exposed in this new section; they consist of crinoid-rich mudstone-supported floatstone with a matrix of calcareous mud with locally interbedded and replacement chert, but the internal parts of the reef with crinoids in living position are not exposed. The reefs are unconformably overlain by greenish-gray Mfp calcareous shale and siltstone. The unconformity exhibits 2 to 10 m (6 to 30 ft.) of relief as supratenuous folds with limbs that dip off the reefs up to 35 degrees.

5.5 km (3.4 mi) northwest of Celina, TN, on State Route 52, is a similar Mfp reef complex that exhibits unusual structure. This reef may have consisted of three to four small crinoid mounds that moved down a gentle paleoslope to become imbricated and folded one onto the trailing edge of the next, with the southernmost reef recumbently folded with a small thrust in the transport direction. Transport would have occurred while the reefs were semi-lithified, but each fold hinge of green shale and siltstone has a weak, fanned axial-planar cleavage. While the exposures are two-dimensional, the three-dimensional shape of these transported reefs may be lobate, like lobes of hot molten road tar moving down-slope. The reefs are unconformably overlain by greenish-gray siltstone and shale with small supratenuous folds. All of the crinoid reefs occur within 1 to 15 m (3-50 ft.) of the Ft. Payne-Chattanooga Shale contact where the contact can be observed. Reefs of this type are prolific producers of oil and gas beneath the Eastern Highland Rim in Tennessee and southern Kentucky, and these exposures highlight their complexity and difficulty of location and exploration.