Subdivisions and Depositional Environments Of New Albany Shale (Devonian-Mississippian) in Indiana

Abstract

The New Albany Shale in Indiana is dominantly brownish-black, carbon-rich, quartzose, dolomitic, pyritic shale that was deposited during late Middle Devonian, Late Devonian, and Early Mississippian times. Greenish-gray carbon-poor shale, dolomite, and sandstone also are present and permit stratigraphic subdivision of the formation. In descending order, the Clegg Creek Member, Camp Run Member, Morgan Trail Member, Selmier Member, and Blocher Member are named and described in this report in the southern Indiana outcrop area. The lower two members are widely traceable in the subsurface, but the upper three members are not differentiated in the subsurface. The Antrim Shale, Ellsworth Shale, and Sunbury Shale, together equivalent to the New Albany, are recognized in the Michig n basin part of northern Indiana. The Ellsworth Shale can be traced into the northern part of the Illinois basin in Indiana, where it is recognized as a member of the New Albany Shale. The New Albany Shale was deposited in a widespread inland sea. The sea was characterized by quiet water that probably was deep in places. The organic matter was derived from a floating mat of algae and accumulated under reducing bottom conditions that were inimical to benthonic faunas. Breaks in the algal mat or its periodic disruption allowed carbon-poor greenish-gray shale, with benthonic faunas, to be deposited. The algae also may have induced the formation of dolomite by changing the hydrogen-ion concentration of the water.