HR: 1340h
AN: GP13A-0019    [Abstracts]
TI: Isolating the Alteration By-products From the Detrital Component in Alaskan Loess by Chemical Extraction: a Feasibility Study for Paleoclimate Reconstruction
AU: * Lagroix, F
EM: lagroix@ipgp.jussieu.fr
AF: IPGP, Laboratoire de Paléomagnétisme, Paris, 75252 France
AU: Banerjee, S K
EM: banerjee@umn.edu
AF: Institute for Rock Magnetism, 100 Union St. SE, Minneapolis, MN 55455 United States
AU: Banerjee, S K
EM: banerjee@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN 55455 United States
AU: Berquo, T S
EM: berqu013@umn.edu
AF: Institute for Rock Magnetism, 100 Union St. SE, Minneapolis, MN 55455 United States
AB: In this study, we observe and quantify the effects of sodium citrate-sodium bicarbonate-sodium dithionite (CBD) treatments on loess and paleosol from Central Alaska. Four type zones are identified corresponding to the modern soil (Type 1), the visibly altered parent loess material (Type 2), the `unaltered' parent loess material (Type 3), and the paleosol (Type 4). The type zones differ in magnetic mineral assemblages, concentration and/or grain size. A representative sample from each type zone at two Central Alaskan loess deposits and their sub-samples having undergone 1, 2, 3, or 4 CBD treatments (for a 2 g sample, one treatment = 0.5 g of dithionite, 15 min, 80°C) were investigated. Our results show that all type zones, including those of the `unaltered' loess, have at least one CBD extractable component. Superparamagnetic particles in Type 1 and 4 are dissolved as well as a low coercivity of remanence (~20 mT) population, which together represent the alteration by-product of pedogenesis. The dominant remanence carrying population dissolved in Types 2 and 3 is characterized by a higher coercivity of remanence (~150 mT). A similar component was observed by Deng et al. [JGR, v.110, B03103, 2005] in Chinese loess from Jiaodao and attributed to low-temperature oxidation of MD magnetite. The coercivity of remanence of the non-extractable component is similar in all four Types (~40 to 50 mT). We conclude that magnetic proxies of wind strength can be represented by concentration parameters such as χ and M_S and magnetic granulometry parameters such as M_RM_S and RTSIRM lost upon low-temperature cycling of only the CBD non-extractable component, in all sample types. Understanding how Alaskan loess has archived past climate conditions such as precipitation is dependent on more precise characterization of the mineralogy of the CBD extractable components. The mineralogical interpretation presented will be based on M"{o}ssbauer spectra being measured at 300 K and 4.2 K.
DE: 1512 Environmental magnetism
DE: 1540 Rock and mineral magnetism
DE: 3617 Alteration and weathering processes (1039)
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005