Title: Signature
of magnetic enhancement in a loessic soil in Nebraska, United States of
America
Author(s): Geiss
CE, Zanner CW, Banerjee SK, Joanna M
Source: EARTH
AND PLANETARY SCIENCE LETTERS 228 (3-4): 355-367 DEC 15 2004
Document Type: Article
Language: English
Abstract: Our
study of a loessic soil profile from east-central Nebraska shows that
the A horizons of the modem soil are characterized by higher
concentrations of fine-grained (<0.1mum) magnetic minerals. This
pedogenic magnetic component lead, to higher, values of
concentration-dependent parameters, such as magnetic susceptibility (%)
isothermal remanent magnetization (IRM) and anhysteretic remanent
magnetization (ARM), combined with increases in fi-equency-dependent
susceptibility (/fd) and ARM/IRM ratios. Hysteresis properties are
relatively insensitive towards the presence of this pedogenic magnetic
component.
The magnetic properties of the soil profile are dominated by
ferrimagnetic magnetite or maghemite. Analyses of "soft" HUM (sIRM) and
"hard" IRM (hIRM), however, do show that approximately 80-90% of the
remanence carrying magnetic component exists in the form of hematite or
goethite and that the magnetically enhanced horizons are enriched in
both ferri- and antiferromagnetic minerals.
The pedogenic magnetic component is most likely caused by the
conversion of paramagnetic. iron-bearing minerals to ferri- and
antiferromagnetic minerals. Soil compaction, lessivage or
decalcification cannot explain the observed magnetic soil properties.
Magnetic analyses of loess-paleosol sequences from the midwestern
United States may yield valuable information about regional variability
of paleoclimate. Based on the fine-grained nature of the pedogenic.
magnetic component. we expect grain-size-dependent proxies (ARM,
ARM/IRM, %(fd)) to yield better paleoclimatic information than
low-field magnetic susceptibility used in previous analyses. (C) 2004
Elsevier B.V. All rights reserved.
Author Keywords: environmental
magnetism; loess; soil; Holocene; Nebraska; climate reconstruction
KeyWords Plus: CHINESE
LOESS; GRAIN-SIZE; PALEOCLIMATIC SIGNIFICANCE; SUSCEPTIBILITY SIGNAL;
HYSTERESIS PROPERTIES; CENTRAL ALASKA; RECORD; DEPENDENCE; PALEOSOLS;
SEDIMENTS
Addresses: Geiss
CE (reprint author), Trinity Coll, Dept Phys, McCook Hall 105,300
Summit St, Hartford, CT 06106 USA
Trinity Coll, Dept Phys, Hartford, CT 06106 USA
Univ Nebraska, Sch Nat Sci, Lincoln, NE 68583 USA
Univ Minnesota, Newton Horace Winchell Sch Earth Sci, Minneapolis, MN
55455 USA
Mt Holyoke Coll, S Hadley, MA 01075 USA
Publisher: ELSEVIER
SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS
Subject Category: GEOCHEMISTRY
& GEOPHYSICS
IDS Number: 882JV
ISSN: 0012-821X