HR: 17:45h
AN: B54C-08    [Abstracts]
TI: Constraining Microbial Cycling of Carbon and Sulfur and Relationships to Macrofaunal Ecology in Cretaceous Cold Seeps
AU: * Lyons, T
EM: timothy.lyons@ucr.edu
AF: Dept. of Earth Sciences, University of California, Riverside, CA 92521, United States
AU: Shapiro, R
EM: rsshapiro@gmail.com
AF: Geological and Environmental Sciences, California State University, Chico, CA 95929, United States
AU: Benjamin, G
EM: bgill003@ucr.edu
AF: Dept. of Earth Sciences, University of California, Riverside, CA 92521, United States
AU: Bates, S
EM: batess@ucr.edu
AF: Dept. of Earth Sciences, University of California, Riverside, CA 92521, United States
AU: Anderson, J
EM: andejuli@isu.edu
AF: Dept. of Geosciences, Idaho State University, Pocatello, ID 83209, United States
AU: Gilhooly, W
EM: williamg@ucr.edu
AF: Dept. of Earth Sciences, University of California, Riverside, CA 92521, United States
AU: Parsons-Hubbard, K
EM: Karla.Hubbard@oberlin.edu
AF: Geology Dept., Oberlin College, Oberlin, OH 44074, United States
AB: The Pierre Shale in Colorado hosts an extensive fault-controlled network of Late Cretaceous fossil-rich carbonate accumulations expressed topographically as the Teepee Buttes. An ancient methane seep origin for these features is clear from carbonate-carbon isotope values that are as light as -50 per mil and from organic biomakers that point to abundant aerobic and anaerobic methanotrophy. A primary goal is to identify the patterns of sulfate reduction linked to anaerobic oxidation of methane (and other possible hydrocarbons) through a detailed isotopic study of sulfur preserved as carbonate-associated sulfate trapped within authigenic and biogenic phases. We are further constraining these patterns by calibrating them against our studies of modern seeps in the Gulf of Mexico. Delineating micro- and macrofaunal symbiotic linkages driven by chemosynthetic (sulfide-oxidizing) bacterial communities is a related goal. Through ongoing analysis of shell material, we hope to fingerprint thiotrophic activity within specific organisms, including lucinid bivalves. Consistent with the abundant benthic macrofauna, C- S-Fe analysis of the host shales indicates that bottom waters were oxygenated at the time of seep activity. Our work expands on previous studies to include a detailed paragenesis of the carbonate fabrics, which is aided by high-resolution C isotope and trace element analysis. Our results show that early-formed carbonates are characterized by depleted C isotope values, comparatively heavy O, low Fe contents, and high Sr and Mg. Late carbonates show isotope and elemental relationships that are generally opposite those of the early precipitates. Botryoidal cements, pelsparites, and yellow calcite dominate the early diagenetic forms. Blocky white sparry cements formed later, and micrite is mostly a product of later micritization of early fabrics and correspondingly shows broad geochemical properties. The overarching focus of all this work is to understand the timing, location (surface vs. subsurface), mechanisms, and specific microbial factors behind carbonate authigenesis and their relationships to macrofaunal ecology.
DE: 0424 Biosignatures and proxies
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0463 Microbe/mineral interactions
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0488 Sulfur cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting