Structure and morphology of the top of Precambrian crystalline rocks in the Illinois Basin region
- Illinois State Geological Survey, Champaign, IL (United States)
- Indiana Geological Survey, Bloomington, IN (United States)
- Kentucky Geological Survey, Lexington, KY (United States)
New basement tests and seismic-reflection profiles in the Rough Creek Graben, Wabash Valley Fault System, and other parts of the Illinois Basin have significantly advanced the authors understanding of basement morphology and tectonics. Few details of the paleotopographic component of basement morphology are known, but 100 m or more of local paleotopographic relief is documented in a few places and more than 300 m of relief is known in the western part of the basin. Based on fewer than 50 wells in the Illinois Basin that penetrate Precambrian crystalline basement, it is composed principally of granite and rhyolite porphyry with small amounts of basalt/diabase or andesite. Most of the regional morphology must be projected from structure maps of key Paleozoic horizons, including the top of Middle Ordovician Trenton (Galena), the top of Middle Devonian carbonate (base of New Albany Shale), and other horizons where data are available. The shallowest Precambrian crystalline basement within the Illinois Basin occurs in north-central Illinois where it is [minus]1,000 m MSL. Paleozoic sedimentary fill thickens southward to over 7,000 m in deeper parts of the Rough Creek Graben where crystalline basement has been depressed tectonically and by sediment loading to below [minus]7,000 m MSL. Although trends in Paleozoic strata show continued thickening in the area of the Mississippi Embayment, maximum sediment fill is preserved in the Rough Creek Graben. The general shape of the basin at the level of Precambrian crystalline basement is largely inferred from structure mapped on Paleozoic strata. Half-grabens and other block-faulted features in basement rocks are manifest in small-scale structures near the surface or have no expression in younger strata.
- OSTI ID:
- 5725545
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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