© KGS, 2006 - Transactions of the 1999 AAPG Midcontinent Section Meeting (Geoscience for the 21st Century), 1999 Study of Sequences in New Albany Shale of Southeastern Illinois Basin 21 1 A Regional Study of Sequences in the New Albany Shale of the Southeastern Illinois Basin (Indiana) with Gamma-Ray Logs and Well Cores

Priyanka Johri and Juergen Schieber Department of Geology, The University of Texas at Arlington, Texas

The New Albany Shale of southern Indiana is a middle to late Devonian black shale unit that constitutes an impor- tant hydrocarbon source rock in the Illinois Basin. Going from east to west, the New Albany Shale thickens and changes its lithologic characteristics. These changes reflect the gradual deepening from the shallow water regions on the Cincin- nati Arch to the deeper water regions of the Illinois Basin. In outcrop studies from Tennessee and central Kentucky, recognition of widespread erosion surfaces allowed a sequence-stratigraphic subdivision of this black-shale succession. Gamma-ray logs from southern Indiana show that these subdivisions can be carried into the subsurface west of the New Albany outcrop belt. Systematic tracing of these sequences through the Illinois Basin may in the future allow substantial refinement in the understanding of the deposi- tional history of these rocks, The observed variability between adjacent gamma-ray logs is attributed to the erosional truncation at the top of individual shale packages. Additional variability is introduced because some shale packages that are present in western Indiana have been lost completely to erosion in eastern Indiana and Kentucky. The transgressive base of individual sequences typically coincides with an increase in gamma-ray intensity. Future study of these shales will be the basis of making a better connection between the conformable sequences of the Illinois Basin interior and the discordant sequences of the Cincinnati Arch region.

Geoscience for the 21st Centuly Edited by D. F. Merriain: Transactions of the Am. Assoc. Petroleum Geologists Midcontinent Section Meeting (Wichita, KS), 1999

American Association of Petroleum Geologists, 1999 Midcontinent Section, Transactions, Geoscience for the 21st Centuq