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GSA Annual Meeting, November 5-8, 2001

Paper No. 0
Presentation Time: 1:30 PM-5:30 PM

MAGNETIC SUSCEPTIBILITY AS AN INDICATOR OF TEXTURAL, MINERALOGICAL, AND CHEMICAL PROPERTIES OF LOWER MISSISSIPPI VALLEY SEDIMENTS


EVANS, Frank B.1, AUTIN, Whitney J.1, TAHAR, M. Z.2 and ASLAN, Andres3, (1)Department of the Earth Sciences, SUNY College at Brockport, Brockport, NY 14420, (2)Department of Physics, SUNY College at Brockport, Brockport, NY 14420, (3)Department of Physical and Environmental Sciences, Mesa State College, Grand Junction, CO 81501, dirtguy@esc.brockport.edu

A core on the Macon Ridge in northeast Louisiana has been collected for detailed analysis of magnetic, textural, mineralogical, and chemical properties of sediments in the Lower Mississippi Valley. This site represents a well-drained, oxidized landscape on a Wisconsin-age terrace with a relatively simple post depositional pedogenic history. Approximately 1 m of Peoria Loess covers sandy fluvial deposits, and the surface soil profile is characterized by argillic horizon development, soil rubification, and pedogenic mixing (Dexter Series, Ultic Hapludalfs).

Volume magnetic susceptibility (k) measurements using a Bartington MS2F field probe suggest a correlation to grain size and mineral magnetic composition (possibly detrital magnetite and/or pedogenic iron oxides). The profile of k versus depth varies with sediment texture, but also appears to be magnetically enriched due to iron oxide accumulation.

Mass dependent magnetic susceptibility (c) measurements indicate significant post depositional alteration in an oxidizing soil forming environment. Measurements at 465 Hz and 4.65 kHz allow for calculation of frequency dependent changes in susceptibility (cfd%). Down profile values of cfd% range from about 6 - 26 %, indicating that neoformation of hematite, magnetite and/or maghemite is a possible contributor to k.

Measuring cfd% helps to infer magnetic domains that are influenced by depositional processes (no superparamagnetic grains) or alterations of iron bearing minerals due to chemical weathering (significant superparamagnetic contribution). No change in cfd between low and high frequencies corresponds to an absence of superparamagnetic grains, an intermediate change of <10% in cfd implies a mixture of magnetic domains, and larger changes in cfd imply dominance of superparamagnetic grains.

Lower Mississippi Valley deposits of different relative ages and landscape settings are under investigation, and we hypothesize that the general susceptibility signal has characteristic patterns associated with lithofacies and post depositional alterations imprinted on the volume magnetic susceptibility signal.

Session No. 30--Booth# 18

Stratigraphy (Posters) I: Silisiclastic
Monday, 5 November 2001: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 33, No. 6, October 2001, p.430
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