HR: 17:45h
AN: B44A-08 INVITED     [Abstracts]
TI: Episodic Cyanobacterial Expansions During Permian-Triassic Biotic Crisis at Meishan in South China
AU: * Xie, S
EM: xiecug@163.com
AF: State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: * Xie, S
EM: xiecug@163.com
AF: Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS United Kingdom
AU: Pancost, R
EM: r.d.pancost@bristol.ac.uk
AF: Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS United Kingdom
AU: Huang, X
EM: xyhuang00@sina.com.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Jiao, D
EM: jiaodan-1216@163.com
AF: State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Lu, L
EM: lqlu@cug.edu.cn
AF: Faculty of Material and Chemical Engineering, China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Huang, J
EM: jhhuang@cug.edu.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Wang, H
EM: hmwang@cug.edu.cn
AF: School of Environmental Studies, China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Yang, F
EM: wyang@public.wh.hb.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Yin, H
EM: hfyin@cug.edu.cn
AF: State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences, 388 Lumo Rd, Wuhan, 430074 China
AU: Evershed, R
EM: r.p.evershed@bristol.ac.uk
AF: Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS United Kingdom
AB: The Permian-Triassic (P-Tr) mass extinction was the most severe biotic crisis in the Phanerozoic, eliminating over 90% of all marine species and 70% of terrestrial vertebrate families. The pattern of the marine mass extinction near the P-Tr boundary is still debated. A stepwise multi-phase biotic extinction proposed on the basis of several southern China sections has recently been challenged by a proposal of a main sudden biotic crisis. Reconciling this debate is necessary in order to estimate the duration (abruptness) of the extinction and to evaluate proposed mechanisms. In contrast with the previous investigations focusing on faunal fossil records, we have conducted a survey of microbial biomarkers (molecular fossils) in sedimentary rocks spanning the P-Tr boundary at Meishan sections in South China where the GSSP was defined. By using the powerful techniques of gas chromatography-mass spectrometry (GC-MS) and GC-combustion-isotope ratio MS, we are able to identify a series of biomarkers and measure the compound-specific carbon isotope composition. In the saturated hydrocarbon fraction of solvent extracts of the sedimentary rocks, a series of 2α-methylhopanes (2-MHP) derived from cyanobacterial 2-methyl-bacteriohopanepolyols precursors are present. The ratio of 2-MHP to hopanes (2-MHP index) reflects the abundance of cyanobacterial component relative to the general bacterial population. The striking aspect of the Meishan 2-MHP profile is the presence of two distinct maxima (beds 26 and 29) within the investigated intervals. Significantly, the 2-MHP indices are stratigraphically coupled with the faunal extinction probability; minima in 2-MHP indices coincide with, or slightly precede, the times of maximum faunal extinction (beds 25 and 28), while maxima in 2-MHP indices clearly lag extinction. It appears that faunal and microbial turnover was closely related, probably reflecting their ecological coupling and/or distinct but coincidental responses to external environmental forcings. The large changes in cyanobacterial population abundances, coupled with faunal mass extinction, likely signify a stepwise multi-phase environmental perturbation. In addition, the two cyanobacterial expansions are characterised by two strong negative shifts (about 9 per mil in δ¹³C values of n-C19 n-alkanes, likely derived from phytoplankton and/or bacteria. In contrast, positive excursions are observed in association with the two horizons of faunal mass extinction. The large fluctuation of n-alkane δ¹³C signature clearly suggests major, episodic changes in either micro-organism inputs or sedimentary environmental conditions during the P-Tr biotic crisis.
DE: 0420 Biomolecular and chemical tracers
DE: 0424 Biosignatures and proxies
DE: 0448 Geomicrobiology
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: Fall Meeting 2005