Structure of the Salina-Forest City interbasin boundary from seismic studies

Abstract

As petroleum-exploration efforts in the midcontinent become directed toward smaller fields and the search for minerals is extended into new areas, the edges of the Salina and Forest City basins will become of increased interest to industry. The principal boundary feature between the two basins is the Nemaha Ridge, a linear feature that extends from near Omaha, Nebraska, to near Oklahoma City, Oklahoma. Recent seismic studies at the Kansas Geological Survey have revealed a complex array of faulted and folded structures in the vicinity of the Humboldt fault zone (the eastern flank of the Nemaha Ridge). Faulting of both normal and reverse types is present, including horsts and grabens. Although some Permian-age faulting is present, most of the Permian deformation occurred as monoclinal draping at the flanks of theNemahaRidge. Recent microearthquake activity suggests that some of the faults are slightly active along a zone 400 km (240 mi) long (north-south) and 50 km (30 mi) wide (east-west) coincident with the NemahaRidge from southeastern Nebraska to north-central Oklahoma. Seismic-reflection evidence suggests that either uplift along the Nemaha occurred contemporaneously with Pennsylvanian deposition or uplift and peneplantation occurred during a period of exposure between the deposition of Mississippian sediments and Pennsylvanian sediments. Analyses of boundary structures and intrabasin structures are not complete without knowledge of basement rock history and basement structure. Microearthquake-arrival and deep-reflection data recently obtained from the Consortium for Continental Reflection Profiling (COCORP) in Kansas reveal intrabasement structures in the 10-35-km (6-21-mi) depth range. Data from aeromagnetic studies and basement drilling reveal block-faulting patterns and several episodes of Precambrian intrusive and/or extrusive vulcanism. Much of the data presented in this paper is not yet fully analyzed, but preliminary results suggest that the integrated assistance is expanding the scientific knowledge of the earth's crust and upper mantle in the midcontinent. Specifically, it is hypothesized that petroleum deposits are related to localized heating in the upper crust and are associated with igneous intrusions and ascension of mantle fluids into the crust probably during Cretaceous time. This hypothesis is consistent with the existence of known deposits of petroleum.