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

E-mail Addresses: christoph.geiss@trincoll.edu, czanner@unlnotes.unl.edu, banerjee@umn.edu, jminott@hotmail.com

Publisher: ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS

Subject Category: GEOCHEMISTRY & GEOPHYSICS

IDS Number: 882JV