New Insights into Precambrian Seismic Stratigraphy, South-Central Indiana

Abstract

Analyzing Precambrian geology in intracratonic basins is restricted, almost exclusively, to geophysical investigations. We present and interpret three 2-D seismic reflection profiles in south-central Indiana and interpret two distinct pre-Mt. Simon seismic reflection sequences in the context of regional geology. These seismic profiles were donated by CountryMark, Inc. and were previously discussed by Walker and Hinks (2015). The two distinct seismic units are observed below the typical succession of well-stratified Paleozoic rocks and are comprised of an acoustically transparent zone of sporadic and discontinuous internal reflections overlying a highly reflective and well-layered interval that persists to at least 2.0 s TWTT. Marked westward thinning of this transparent unit occurs in east-west profiles accompanied by a thickening of the basal layered sequence.

Fitting our seismic data to a geologic model, we interpret the regional existence of a Precambrian clastic sedimentary unit overlying rocks of the Eastern Granite-Rhyolite Province (EGRP). Shrake (1990) and Drahovzal et al. (1997) discuss the occurrence of the Middle Run Formation in southwest Ohio as poorly reflective and underlain by a reflective, layered sequence. Recently, Freiburg (2015) described the existence of the pre-Mt. Simon Argenta Formation from core in central Illinois. A deep well in Lawrence County, Indiana, recovered basaltic rocks from below the Mt. Simon, which is consistent with the occurrence of mafic flows or sills within the Middle Run of northern Kentucky (Drahovzal et al., 1997). The deeper well-layered unit observed in these profiles resembles that described on COCORP data across Illinois where it was termed the Centralia Sequence and part of the EGRP (Pratt et al. 1989). The pattern of poorly reflective clastic rocks overlying strongly layered sequence of the EGRP may be a consistent pattern seen in seismic data across the region.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016