Magnetic susceptibility and feldspar zonations in the Peoria Loess and Roxana Silt of southwestern Illinois and eastern Missouri: Correlation tools and provenance indicators
- Univ. of Illinois, Urbana, IL (United States). Dept. of Geology
Magnetic susceptibility zonations within the Peoria Loess and Roxana Silt are useful for correlations across several counties in southwestern Illinois and eastern Missouri. The Roxana Silt and lower Peoria Loess (60--80 [times] 10[sup [minus]5] SI units) contain a greater concentration of primary magnetite in all silt fractions than the middle Peoria Loess (40--55 [times] 10[sup [minus]5] SI units). Similarly, feldspar contents (as determined from X-ray diffraction of micronized silts) are 30% to 40% higher in the high susceptibility zones, while the bulk grain size distributions do not vary significantly. Therefore, the origin of these mineralogical zones is best explained by the changing proportion of silt derived from igneous and metamorphic rocks as compared with silt derived from sedimentary rocks. During deposition of the Roxana Silt and lower Peoria Loess, an ice margin in Upper Michigan, Wisconsin, Minnesota, or the Canadian Shield, would be responsible for the erosion of a greater proportion of shield lithologies. During the Wisconsinan glacial maximum, the erosion of Paleozoic sedimentary rocks by the advance of the Lake Michigan Lobe diluted the contribution of shield lithologies to the middle Peoria Loess. Higher magnetite and feldspar contents, present in the upper Peoria Loess when relatively unweathered, coincide with a receding ice margin during the latest Wisconsinan.
- OSTI ID:
- 5025436
- 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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