HR: 08:15h
AN: B11B-02    [PDF]
TI: Active Microbial Methane Production and Organic Matter Degradation in a Devonian Black Shale
AU: * Martini, A M
EM: ammartini@amherst.edu
AF: Dept. of Geology, Amherst College, P.O. Box 5000, Amherst, MA 01002 United States
AU: Petsch, S T
EM: spetsch@geo.umass.edu
AF: Dept. of Geosciences, University of Massachusetts-Amherst, 611 N. Pleasant St., Amherst, MA 01003 United States
AU: Nuesslein, K
EM: nusslein@microbio.umass.edu
AF: Dept. of Microbiology, 639 N. Pleasant St., Amherst, MA 01003 United States
AU: McIntosh, J C
EM: jmcintos@j.imap.itd.umich.edu
AF: Dept. of Geological Sciences, University of Michigan, 425 E. University Ave., Ann Arbor, MI 48109 United States
AB: Microorganisms employ many novel strategies to derive energy and obtain nutrients, and in doing so alter the chemistry of their environments in ways that are significant for formation and transformation of geologic materials. One such strategy is natural gas generation in sedimentary basins. Previous research has shown that stable isotopic signatures of CH$_{4}$, CO$_{2}$ and H$_{2}$O in formation waters of gas-producing black shales indicate a microbial origin for several economically viable natural gas reserves. However, these signatures leave several intriguing issues unaddressed, including the identity of the organisms and their metabolic roles and impacts on mineral, isotopic and biomarker signatures. We hypothesize that the extreme reducing conditions required for sedimentary basin methanogenesis are simply the end product of a cascade of microbial processes, initiated by anaerobic respiration of shale organic matter through NO$_{3}$, SO$_{4}$ and/or Fe(III) reduction, secondary processing of anaerobe biomass by fermentative organisms yielding volatile fatty acids and H$_{2}$, and ultimately CO$_{2}$ reduction and/or acetate fermentation to produce CH$_{4}$. This research holds importance for the several aspects of the geochemical carbon cycle. It describes anaerobic hydrocarbon degradation leading to methanogenesis in a sedimentary basin; in many instances this activity has generated economically viable reserves of natural gas. It also provides a benchmark detailing how post-depositional microbial activity in rocks may confound and overprint ancient biosignatures. Interpretation of past environmental conditions depends on molecular and isotopic signatures contained in ancient sedimentary rocks, separated from signatures of metabolically similar modern microbiota living in sedimentary basins. In addition, this research sheds light on an unrecognized and thus unconstrained source of reduced gases to Earth's atmosphere, important for understanding the rates and controls on carbon cycling through geologic time.
DE: 0400 Biogeosciences
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting