HR: 09:45h
AN: B31E-08    [Abstracts]
TI: Molecular Evidence for Radical Changes in Ocean Chemistry Across the Permian Triassic Boundary at Meishan in South China
AU: * Love, G D
EM: glove@mit.edu
AF: Dept Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Cao, C
EM: changquncao@hotmail.com
AF: Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, 210008 China
AU: Jin, Y
EM: jinyugan@yahoo.com
AF: Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, 210008 China
AU: Summons, R E
EM: rsummons@mit.edu
AF: Dept Earth, Atmospheric and Planetary Sciences Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AB: Samples from outcrop and from a new core drilled through the Permian Triassic Boundary at the type section at Meishan have been examined for biomarker and isotopic evidence of biotic and associated environmental change. Late Permian sediments from Meishan Beds 22-27 are characterized by indicators of anoxia including low Pr/Ph ratios and abundant aryl isoprenoids and isoreneieratane derived from the precursor carotenoid isorenieratene. The latter compounds are biomarkers for green sulfur bacteria (Chlorobiaceae) and are considered reliable indicators of euxinic water columns where sulfide extends to the photic zone. The peak of Chlorobiaceae biomarker abundance coincides with a rapid and synchronous drop in the ŸO13C and ŸO15N values of kerogen. On passing up into the Early Triassic, the biomarker signal for Chlorobiaceae wanes and is almost absent by Bed 30 where it is replaced by one for cyanobacteria including abundant hopanes and 2-methylhopanes and accompanying methyl and dimethyl alkanes. A very high value for the hopane/sterane ratio from Beds 30-38 indicates continuing dominant cyanobacterial productivity and only minor inputs from an algal plankton. The prevalence of aryl isoprenoids in P-Tr sediments at the Meishan section of South China is also recorded in a recently cored borehole, Hovea-3, of the Perth Basin, Western Australia. This suggests similar paleoenvironmental conditions prevailed across the Tethys Ocean during and immediately after the P-Tr Boundary. In particular, the presence of biomarkers for Chlorobiaceae at two separate locations indicates that water column euxinia was pervasive during the extinction event and suggests that sulfide may have been a key toxic agent.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting