HR: 0800h
AN: B11A-1013    [Abstracts]
TI: Triple-Oxygen Isotope Analyses of Sulfate Occluded in Caliches
AU: * Howell, K J
EM: khowell@geol.lsu.edu
AF: Louisiana State University, E235 Howe-Russell, Baton Rouge, LA 70803 United States
AU: Bao, H
EM: bao@lsu.edu
AF: Louisiana State University, E235 Howe-Russell, Baton Rouge, LA 70803 United States
AB: Sulfate is the ultimate sink of atmospheric sulfur compounds and can provide important information about atmospheric compositions and processes. For example, ozone signatures are readily recorded in sulfate of atmospheric origin; however, atmospheric sulfate is rarely preserved in geologic records because it is extremely soluble and easily carried away by surface water. The only known cases of preserved atmospheric sulfate are in old, hyperarid desert surfaces like the Atacama Desert and the Antarctic Dry Valleys. Caliches, pedogenically formed calcite-rich layers or nodules in semi-arid to arid environments, could be potential reservoirs for preserving atmospheric sulfate because of the relatively dry climate in the regions where caliche forms. Here, two types of caliche are examined: modern caliche formed on limestones, basalts, and rhyolites in western Texas and New Mexico and fossil caliche formed on late-Cenozoic volcaniclastic deposits in western Nebraska. Analysis of the modern samples shows generally high caliche-associated sulfate (CAS) concentrations ranging from ~100 to 2000 ppm, with caliche developed on limestone having some of the highest concentrations and those formed on basalts and rhyolites having some of the lowest. Triple-oxygen stable isotope measurements show that the CAS has Δ ¹⁷O values (i.e., ¹⁷O-anomaly) ranging from -0.1 to 0.7 ‰ with higher ¹⁷O anomalies associated with igneous parent materials. Analysis of the fossil caliches from western Nebraska reveals CAS concentrations ranging from ~10 to 300 ppm and Δ ¹⁷O values ranging from 0.5 to 2.3 ‰. These data suggest atmospheric sulfate has survived the soil processes unaltered before being incorporated into solid caliche formation. Further confirmation of atmospheric sulfate records in much older caliches may lead to a new proxy for probing ancient atmospheric compositions and chemical processes.
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: 3322 Land/atmosphere interactions (1218, 1631, 1843)
SC: Biogeosciences [B]
MN: Fall Meeting 2005