A Coherent and Genetically-Based Stratigraphic Framework for the New Albany Shale Succession: Methods and Results

Ovidiu Remus Lazar and Juergen Schieber
Indiana University, Bloomington, IN

Considerable stratigraphic variability and the use of synonymous names in different parts of Indiana, Illinois, and Kentucky have led to a complex and rather confused stratigraphic terminology for the Middle-Late Devonian New Albany Shale of the Illinois Basin. Following a sequence stratigraphic approach developed in outcrop sections, drill cores located hundreds of kilometers apart and spanning the full depth range of the Illinois Basin were examined for the presence of sequence boundaries (erosion surfaces) and their correlative conformities.

Erosion surfaces in the New Albany Shale are typically associated with lag deposits. Common lag components are sand to silt size quartz and pyrite grains (rounded to sub-rounded), conodonts, Tentaculites, Lingula shell fragments, and Tasmanites cysts. The common presence of lag deposits together with knife-sharp contacts at the base of shale packages supports the concept of intermittent sea level drop and erosion within the shale succession. The erosion surfaces and their associated features show that the New Albany Shale does not represent a continuous depositional succession. Instead, it consists of at least five major stacked shale packages that are bounded by regional erosion surfaces that connect to adjacent basins. Identification and tracing of these erosion surfaces and their intervening shale packages is augmented by the presence of the biostratigarphic marker Foerstia (Protosalvinia), UV maxima that mark maximum flooding surfaces, and truncation of gamma ray log motives. In conjunction, these observations allow the establishment of a coherent and genetically based stratigraphic framework for the New Albany Shale succession.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005