HR: 17:00h
AN: U24C-05    [Abstracts]
TI: Biomarker evidence for shallow water marine euxinia through the PTB in the Panthalassic Ocean (Peace River Basin Embayment, Canada)
AU: * Hays, L E
EM: lhays@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Beatty, T
EM: tbeatty@ucalgary.ca
AF: University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada
AU: Henderson, C M
EM: charles.henderson@ucalgary.ca
AF: University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada
AU: Summons, R E
EM: rsummons@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Love, G D
EM: glove@ucr.edu
AF: University of California at Riverside, 900 University Ave., Riverside, CA 92521, United States
AB: Protracted euxinic conditions in the late Paleozoic and early Mesozoic oceans may have been an important paleoenvironmental factor in the Permian-Triassic Boundary (PTB) extinction. Release of hydrogen sulfide during upwelling or transgressive events from such an ocean (Kump et al. 2005; Riccardi et al. 2006) may have been a driver of the extinction in both marine and terrestrial environments. Worldwide marine PTB sections show evidence for a stratified water column and the presence of sulfidic deep water, at least episodically (Isozaki 1997; Grice et al. 2005). Taxa that are particularly characteristic of such an environment are the green sulfur bacteria, or Chlorobiaceae. These anoxygenic phototrophic bacteria utilize sulfide as an electron donor for photosynthesis and live in modern stratified water columns where euxinia extends into the photic zone. Indeed, biomarkers derived from these organisms have been identified at a number of the PTB sections. The Peace River embayment in western Canada has been identified as a section that spans the PTB based on conodont biostratigraphy (Henderson 1997). Samples from five drill cores in this section provide new insight into the state of the Panthalassic Ocean during this time of unprecedented turnover in Earth's biota. Using standard biomarker protocols, we identified aromatic hydrocarbons that are diagentic products of the carotenoids isorenieratene and chlorobactene, which are diagnostic for the brown and green strains, respectively, of the Chlorobiaceae. The occurrence of chlorobactane is especially notable since the green-pigmented varieties of the Chlorobiaceae require higher light intensities than the brown-pigmented forms and, in modern environments where they have been found, occur between 13 and 30 m of the surface. This is the first time that chlorobactane has been reported from a PTB section and it suggests a particularly shallow chemocline periodically at this location. The δ13C values for the aryl isoprenoids are 13C-enriched relative to the signatures for n-alkanes and other compounds produced by the dominant phototrophic primary producers in surface waters, a feature distinctive for Chlorobiaceae. These analyses, combined with other biomarker data from these samples also indicate that there was a marked disruption to the community structure of phytoplankton at this location at the end of the Paleozoic. Grice, K., et al. (2005). Science 307: 706-709. Henderson, C. M. (1997). Bulletin of Canadian Petroleum Geology 45: 693-707. Isozaki, Y. (1997). Science 276: 235-238. Kump, L. R., et al. (2005). Geology 33: 397–400. Riccardi, A. L., et al. (2006). Geochimica et Cosmochimica Acta 70: 5740-5752.
DE: 1600 GLOBAL CHANGE
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 9615 Permian
SC: Union [U]
MN: 2007 Fall Meeting