HR: 08:15h
AN: PP21A-02    [Abstracts]
TI: Biogeochemistry of Neoproterozoic Snowball Earth and its Aftermath in South China
AU: * Li, C
EM: chaoli@ucr.edu
AF: Department of Earth Sciences, University of California Riverside, 900 University Avenue, Riverside, CA 92521, United States
AU: Love, G
EM: glove@ucr.edu
AF: Department of Earth Sciences, University of California Riverside, 900 University Avenue, Riverside, CA 92521, United States
AU: Sessions, A
EM: als@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E California Boulevard, Pasadena, CA 91125, United States
AU: Lyons, T
EM: timothy.lyons@ucr.edu
AF: Department of Earth Sciences, University of California Riverside, 900 University Avenue, Riverside, CA 92521, United States
AU: Chu, X
EM: xlchu@mail.iggcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, 19 W Tucheng Road, Beijing, 100029, China
AU: Peng, P
EM: pinganp@gig.ac.cn
AF: Guangzhou institute of Geochemistry, Chinese Academy of Sciences, 511 Kehua Street, Guangzhou, 510640, China
AB: Using a combination of lipid biomarkers, inorganic geochemical proxies (Fe speciation and trace element analyses) and stable isotopic abundances (¹³C, ³⁴S, ⁹⁸Mo), we are reconstructing ocean chemistry and aquatic microbial community structure around the Neoproterozoic Sturtian and Marinoan glacial events and later into the Ediacaran in South China. We have sampled outcrop sediment extensively at four locations (Yichang, Shimen, Minle and Zhaoxin), obtaining sedimentary facies ranging from shallow shelf to the deep basin. Our stratigraphic coverage spans from unweathered sediments of the pre-Sturtian Gongdong Formation up to the post-Marinoan Doushantuo Formation. This approach allows us to compile, for the first time, a highly detailed, spatial and temporal record of Neoproterozoic marine biogeochemistry in South China. To assess and augment conventional extractable biomarker hydrocarbon data, we are using the technique of catalytic hydropyrolysis (HyPy) on kerogen residues to release well-preserved kerogen-bound biomarkers that are much less susceptible to contamination since they are covalently bound within an immobile solid matrix deposited synchronously with the host sediment. Interglacial Datangpo and Ediacaran Doushantuo formations that sandwich the Marinoan diamictites are most interesting for detailed organic and inorganic examination and comparison in this study due to their distinct stratigraphic context and unique spatial preservation. A diverse range of normal, branched (2-methyl, 3-methyl and mid-chain monomethylalkanes) and polycyclic alkanes (steranes and hopanes) have been successfully isolated from Doushantuo sediments in Shimen, and a distinct correlation between host-rock lithology and molecular and isotopic characteristics of detected alkane biomarkers was observed, suggesting that the hydrocarbon signals are indigenous and syngenetic with the host rocks. Sediments with appreciable inorganic carbonate content appear to hold most promise for preserving the original biomarker content, since the acidic clay content of black shales may promote maturation and aromatization of the indigenous organic matter. Temporal trends in our geochemical and isotopic records will be discussed.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1055 Organic and biogenic geochemistry
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting