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Science 5 October 2001:
Vol. 294. no. 5540, pp. 145 - 148
DOI: 10.1126/science.1062363
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Reports

Organic Carbon Composition of Marine Sediments: Effect of Oxygen Exposure on Oil Generation Potential

Yves Gélinas,1*dagger Jeffrey A. Baldock,2 John I. Hedges1

Anaerobic sedimentary conditions have traditionally been linked to the generation of the source rocks for petroleum formation. However, the influence of sedimentary redox conditions on the composition of freshly deposited organic matter (OM) is not clear. We assessed the effect of in situ exposure time to oxic conditions on the composition of OM accumulating in different coastal and deep-sea sediments using solid-state 13C nuclear magnetic resonance (NMR). 13C NMR spectra were resolved into mixtures of model components to distinguish between alkyl carbon present in protein and nonprotein structures. There is an inverse relation between the length of exposure to oxic conditions and the relative abundance of nonprotein alkyl (alkylNP) carbon, whose concentration is two orders of magnitude higher in coastal sediments with short exposure times than in deep-sea sediments with long exposure times. All alkylNP-rich samples contain a physically separate polymethylene component similar in composition to algaenans and kerogens in type I oil shales. The duration of exposure to oxic conditions appears to directly influence the quality and oil generation potential of OM in marine shales.

1 School of Oceanography, Box 357940, University of Washington, Seattle, WA 98195-7940, USA.
2 Commonwealth Scientific and Industrial Research Organization (CSIRO) Land and Water, Personal Mail Box 2, Glen Osmond, South Australia 5064, Australia.
*   To whom correspondence should be addressed.

dagger    Present address: Department of Chemistry and Biochemistry, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Quebec, Canada, H3G 1M8. E-mail: ygelinas{at}alcor.concordia.ca

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