Abstract
The late Mesoproterozoic to early Neoproterozoic Middle Run Formation contains vital information about the crustal evolution of the North American Craton. Four reprocessed seismic reflection lines in the vicinity of the AK Steel facility in Middletown, Ohio, provide new insights into the structural and depositional setting of the Middle Run Formation in this region. A residual statics solution improved the resolution and coherency of reflections in these profiles that underlie the Cambrian Mount Simon Sandstone. Reprocessing revealed gently inclined, west-southwest-dipping reflectors and the occurrence of an angular unconformity between the Middle Run Formation and the overlying Paleozoic strata. The weak and discontinuous seismic reflection character of the Middle Run Formation in these seismic lines overlies a sequence of stronger parallel reflections that are like those observed on the eastward ODNR-1-88 seismic line located near core hole DGS 2627, the stratotype of the Middle Run Formation. This inferred thickness indicates that the basin in which the Middle Run Formation was deposited ranges from at least 670 to 1,128 m (2,200 to 3,700 ft) deep at the AK Steel area and dips gently west-southwest, which is in contrast with the moderate easterly dip observed on the ODNR-1-88 seismic line to the northeast. Correlation of these features across the 10 km (approximately 6 mi) cross-strike gap between the AK Steel lines and the ODNR-1-88 seismic line suggests the presence of a reverse fault with approximately 792 m (2,600 ft) of estimated vertical displacement. A regional cross section—including the WSU 1990 seismic line eastward of the ODNR-1-88 line—exhibits a faulted west-verging asymmetric syncline in near proximity to the Grenville Front. This cross section also shows that deformation of the Middle Run Formation and the underlying layered sequence exhibits a consistent tectonic style of reverse faulting and folding that developed in response to Grenville Front tectonism.
Highlights
Purpose of StudyIn 1991, four seismic reflection lines were acquired in the vicinity of the AK Steel plant near Middletown, Ohio (Fig. 1A)
The seismic units below the base of the Mount Simon Sandstone on the AK Steel seismic lines exhibit a pattern similar to that observed on the ODNR-1-88 seismic line (Shrake 1991), the latter located northeast of the AK Steel area (Fig. 1B)
The Middle Run Formation reflections within the AK Steel and ODNR-1-88 seismic lines are characterized by weak and more discontinuous seismic reflections
Summary
Purpose of StudyIn 1991, four seismic reflection lines were acquired in the vicinity of the AK Steel plant (formerly ARMCO Steel) near Middletown, Ohio (Fig. 1A). The lines were required by the Ohio Environmental Protection Agency (OEPA) as a condition for permitting 2, Class I injection wells into the Cambrian Mount Simon Sandstone. These 4 lines were originally intended to examine the structural character of the subsurface rocks in and near the proposed injection wells and target horizon. The purpose of the current study is to (1) reprocess the AK Steel seismic lines with emphasis on better understanding the seismic reflections below the Paleozoic sedimentary cover of the region, and (2) examine the relationship between the 1991 AK Steel lines and 2 previously acquired seismic lines, ODNR-1-88 and Wright State University 1990 (WSU 1990), located eastward of the AK Steel plant (Fig. 1B). Interpretation of the reprocessing results, combined with recently published age dates for the Precambrian Middle Run Formation and timing of regional tectonic events, allow analyses of structural and sedimentological elements in the area—plus plausible explanations for the sedimentary provenance, age of deposition, and timing of deformational events associated with the Middle Run Formation in southwest Ohio
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