HR: 1340h
AN: B23D-1587    [Abstracts]
TI: Stable Carbon and Oxygen Isotope Composition of Soil and Shell from an Archeological Site in Kimble County, Texas
AU: * Salazar, K K
EM: ksalazar1@satx.rr.com
AF: University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States
AU: Paul, D
EM: debajyoti.paul@utsa.edu
AF: University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States
AU: Skrzypek, G
EM: Grzegorz.Skrzypek@utsa.edu
AF: University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States
AU: Tomka, S A
EM: steve.tomka@utsa.edu
AF: University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States
AB: We report stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopic composition of inorganic carbonates, soil organic matter (SOM), and terrestrial gastropod shells present in a 130cm soil profile (radiocarbon date of 2340-2120 B.P) recovered from archeological site 41KM69, Kimble County, Texas. Prior to soil carbonate and SOM analyses, samples were treated with 5% sodium hypochlorite to remove organic matter and treated with 4% HCl to remove inorganic carbonate, respectively. Isotopic compositions of samples were obtained utilizing a Gasbench II (for carbonate-acid reaction technique) and a CHNS Elemental Analyzer (for SOM) coupled with a Delta^Plus XP Isotope Ratio Mass Spectrometer in continuous-flow. δ¹³C of carbonates in the soil profile varies in the range -2.15 to -4.63 ‰. δ¹⁸O of carbonates (ranging from -3.22 to -3.92‰) show little variation within the profile. δ¹³C of SOM (-25.61‰ to -22.83‰) suggests that C3 plants were predominant in the study area. There is ~3‰ enrichment in ¹³C of SOM at the bottom of profile relative to the top. Previous studies have shown that δ¹³C of modern soil carbonates are higher by 14-16‰ than SOM, whereas our results show about 20‰ difference. δ¹³C of land snail shells ( Rabdotus, Polygyra, Helicina) recovered from the soil show strong linear correlation with depth (R²= 0.88): -9.46‰ at 60cm to -5.4‰ at 112cm. δ¹⁸O of shells show no correlation with depth and range from - 3.34‰ to 0.62‰. Excluding one shell analysis, δ¹³C of shells and SOM exhibit good correlation (R²= 0.80). Previous studies of variation in δ¹³C in land snail shell document that carbon isotopic composition in shell are primarily a function of snail diet. Balakrishnan et al. (2005) have shown that δ¹³C of shells in C3 vegetation regimes range from -10.0‰ to -8.8‰, which is consistent with our results. Although, the interpretation of δ¹⁸O values in land snails is not straightforward, values are probably related to several different climate signals including temperature, rainfall, and relative humidity and may be used for potential markers of local climate conditions.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0486 Soils/pedology (1865)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4870 Stable isotopes (0454, 1041)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting