The Eau Claire Formation in Iowa, an Upper Cambrian, inner shelf, cratonic clastic wedge
- Iowa Dept. of Natural Resources, Iowa City, IA (United States). Geological Survey Bureau
The Eau Claire Formation has been defined, in its outcrop belt in west-central Wisconsin, as an argillaceous, fine-grained sandstone and shale interval sandwiched between coarser sandstone units of the older Mt. Simon Fm and the younger Wonewoc Fm. This stratigraphic arrangement continues into the subsurface of eastern iowa, but undergoes substantial variation throughout the rest of the state. Terrigenous clastic-dominated facies of the Eau Claire in northern and eastern Iowa are laterally transitional to mixed terrigenous clastic/carbonate facies in southern and western iowa. These lithofacies transitions are independently correlatable through trilobite and brachiopod biostratigraphy. Carbonate dominated facies (dolomite and limestone) contain a diverse suite of rock types including bioturbated skeletal wackestones/packstones, skeletal grainstones and cryptalgal/microbial boundstones. Locally, pyritic and glauconitic encrusted hardgrounds occur. Maximum carbonate facies development within terrigenous clastic dominated sections is interpreted to have occurred under the conditions of transgression and maximum coastal onlap during Crepicephalus zone time. The establishment of carbonate production facies tracts was possible due to clastic sediment entrapment up the depositional slope, resulting in clearer-water sedimentary environments in southern Iowa. The development of dominant carbonate production facies tracts in western Iowa were enhanced by their distal position along the northeasterly sourced (present latitudinal coordinates) clastic sediment dispersal path. The Eau Claire was probably never deposited in far southwest Iowa and adjacent southeast Nebraska due to the presence of paleohighlands, but this land area appears to have been only a minor source area for terrigenous clastic sediment supply.
- OSTI ID:
- 7069733
- Report Number(s):
- CONF-9303210-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:3; Conference: 27. annual Geological Society of America (GSA) North-Central Section meeting, Rolla, MO (United States), 29-30 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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