Stratigraphy, magnetic susceptibility, and mineralogy of loess-paleosol sequences in southwestern Illinois and eastern Missouri

Magnetic susceptibility (MS) zones, controlled by silt-size magnetite concentrations, have been delineated within oxidized, C horizon Peoria and Loveland Silts along the Illinois and Mississippi Valleys. Lower Peoria and lower Loveland Silts (MS = 55-80 \times 10\sp{-5} SI) and Roxana Silt (MS = 60-90 \times 10\sp{-5}) have high MS probably reflecting greater contributions from Superior Lobe outwash. Middle Peoria and upper Loveland Silts (MS = 20-55 \times 10\sp{-5}) and upper Peoria Silt (MS = 40-60 \times 10\sp{-5}) have low MS, probably reflecting dilution by Lake Michigan Lobe outwash upon maximum advance of glaciers in Illinois. Feldspar/quartz and kaolinite/illite X-ray diffraction peak height ratios also increase in zones of high MS. Bulk and magnetic grain size distributions are generally uniform across MS zones at sections studied. Peoria Silt MS zones are particularly striking in loess proximal to the Illinois (Ancient Mississippi) Valley because of source area shifts caused by Mississippi River diversion at about 20.5 ka. MS zones are less pronounced along the Mississippi Valley south of St. Louis. Alteration of magnetite in gleyed loess can occur but is not thought to cause MS zones observed because minor increases in illite and dolomite in low MS zones are more consistent with a source area hypothesis. Jules and Gardena (interstadial) Geosol occur in upper portions of middle and lower Peoria Silt and are estimated to be 15-16 ka and 20-20.5 ka, respectively. Clay beds, deposited during peak glacial floods (16-20 ka), occur within middle Peoria Silt.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Grimley, David A.

Contributors dc:contributor

• Johnson, W. Hilton

• Geology
• Agriculture, Soil Science

Statement dc:rights

• Copyright 1996 Grimley, David Aaron

Language dc:language

eng

Identifier

AAI9625138
(UMI)AAI9625138

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/19274