DISTURBED BEDS IN LOWER FRASNIAN BLACK SHALES OF TENNESSEE AND KENTUCKY: THEIR POSSIBLE CONNECTION TO IMPACTS

Devonian black shales of Tennessee and Kentucky consist of three packages separated by regional unconformities. The lowermost package (package 1) encompasses rocks that range in age from the Upper Givetian into the lower to mid-Frasnian, and is unconformably overlain by mid to upper Frasnian black shales (package 2; also known as the Dowelltown member of the Chattanooga Shale). In various places from southern Tennesse to southern Kentucky the contact between package 1 and 2 is marked by angular unconformities. Although angular unconformities typically imply tectonic deformation in the lower package, in this case there is no evidence of wholesale tilting or deformation of the underlying shale package. Whereas beds in the lower portion of package 1 are horizontal and conformable over a basal unconformity on Ordovician carbonates, beds in the upper portion of package 1 may form folds (wavelength 10’s of meters), complex contortions, and collapse features (e.g. ball and pillow structures). In thin section we see complex microfolds and microfaulting that have been associated with shock-induced soft sediment deformation in other studies. These macroscopic and microscopic features suggest widespread soft sediment deformation due to cataclysmic forces. Conodont data suggest that these strata predate the early Frasnian Flynn Creek crater in central Tennessee. The 3.6 km diameter of the crater suggests that impact shock was insufficient to cause disturbance across such a large area. Yet, whether a shallow water wet impact could have generated enough of a surge to cause destabilization of watery muds in localities as much as 200 km’s distant deserves further study. Alternatively, if the Flynn Creek impact can be related (via further conodont studies) to the Alamo breccia in Nevada, a powerful surge from the much larger Alamo impact may explain the observed sediment disturbance.