HR: 13:40h
AN: PP53A-01    [Abstracts]
TI: Clumped-isotope thermometry of modern
pedogenic carbonates
AU: * Da\"eron, M
EM: daeron@gps.caltech.edu
AF: California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States
AU: Quade, J
EM: quadej@email.arizona.edu
AF: University of Arizona, Department of Geosciences, Tucson, AZ 85721, United States
AU: Elier, J
EM: eiler@gps.caltech.edu
AF: California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States
AB: The carbonate "clumped-isotope" thermometer (Ghosh et al., 2006a) constrains the crystallization temperatures of carbonate minerals by comparing the abundance of ¹³C¹⁸O bonds in these minerals to a stochastic abundance derived from the bulk isotopic composition of C and O atoms. Unlike previous ¹⁸O-based carbonate paleo-thermometers, this method does not require knowledge of the parent water's composition. It was calibrated using synthetic carbonates, and has subsequently been applied to paleo- pedogenic rhizoliths of Miocene age (Ghosh et al., 2006b). In order to test the technique's applicability to the study of soils and paleosols, we measured temperatures recorded by "modern" (Late Holocene) pedogenic carbonates from several sites in Arizona. At each site, clasts exhibiting stage-I carbonate coating were sampled at different depths. The carbonate was then processed using the protocol described by Ghosh et al.\ (2006a). Coating extracts from one or more clasts sampled at the same depth exhibit the same "clumped-isotope" temperature within instrumental precision limits. These temperatures vary as a function of depth in a pattern which fits the profile predicted by a simple heat diffusion model for the months of July and August, which together account for most of the yearly rainfall at these sites. Our results thus support using "clumped-isotope" measurements as an indicator of precipitation temperatures in soils and paleosols, and highlight the technique's sensitivity to the seasonality of precipitation. Many potential applications in pedologic, climatic and tectonic studies stand to benefit from further investigation of the signal recorded by modern soils. \ Ghosh, P. et al., 2006a. C-13-O-18 bonds in carbonate minerals: a new kind of paleothermometer. Geochimica et Cosmochimica Acta 70(6):1439--1456. Ghosh, P. et al., 2006b. Rapid uplift of the Altiplano revealed through C-13-O-18 bonds in paleosol carbonates. Science, 311(5760):511--515.
DE: 0486 Soils/pedology (1865)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting