DETAILED CORRELATIONS IN THE NEW ALBANY SHALE OF SOUTHEASTERN INDIANA

Recent work in Tennessee and Kentucky has led to the recognition of laterally extensive erosion surfaces within the Late Devonian Chattanooga Shale, and to a sequence stratigraphic reevaluation of this black shale succession. Detailed study of cores from Indiana indicates that comparable results can be obtained for the laterally equivalent New Albany Shale. Several truncation surfaces have already been positively identified, e.g. at the top of the Blocher, Selmier, Camp Rum, and Clegg Creek Members. Identification was made in core on the basis of visible erosion, abrupt change of lithology, and the presence of lag deposits. Detailed recording of successions deposited above erosion surfaces and correlation of very thin stratal packages from core to core also allows recognition of truncated intervals. In addition, identification of truncated gamma ray log motives helps to track erosion surfaces in areas where no cores are available. Examination of the stratigraphic distribution of resistant organic macerals (Tasmanites cysts) shows intervals of high concentration that may mark flooding surfaces and parasequence boundaries. Through integration with gamma ray logs they provide yet another venue for improved stratigraphic resolution. With this methodology it is possible to demonstrate strong lateral thickness variations and even complete "cut outs" for given shale packages. Failure to recognize the latter is probably the cause for past correlation problems. Because the Cincinnati Arch was a shallow water and intermittently emergent area during Late Devonian times, erosional truncations in the New Albany Shale are most pronounced in its easternmost occurrences. Westward, towards the deeper portions of the Illinois Basin, erosive effects diminish in magnitude or disappear altogether.