2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 4
Presentation Time: 8:45 AM


VOGEL, Marilyn B., Exobiology Branch, NASA Ames Research Center, Bldg. N239-4, Moffett Field, CA 94035, MOLDOWAN, J. Michael, Geological and Environmental Sciences, Stanford University, Stanford, CA 94305 -2115, JAHNKE, Linda L., Exobiology Branch, NASA Ames Rsch Ctr, M/S 239-4, Moffett Field, CA 94035, DES MARAIS, David J., Exobiology Branch, NASA-Ames Rsch Ctr, Mail Stop 239-4, Moffett Field, CA 94035 and DEHLER, Carol M., Department of Geology, Utah State Univ, 4505 Old Main Hill, Logan, UT 84322, mvogel@mail.arc.nasa.gov

Organic matter from the Red Pine Shale of the Neoproterozoic Uinta Mountain Group have branched chain and polycyclic biomarkers indicating input from phototrophic and chemotrophic microbial sources. A diaryl isoprenoid and alkylbenzenes detected in aromatic moieties from several samples may derive from green sulfur bacteria indicating photic zone anoxia (Summons and Powell, 1988; Koopmans et al., 1996). Sterane patterns are characterized by enrichment in C27 sterane, suggesting restricted eukaryotic diversity at the site of deposition. Monomethyl-alkanes and 2-methyl-hopanes are evidence of significant input from cyanobacterial sources. Samples contain diverse suites of gem-dialkyl-, and cycloalkyl- alkanes, analogous to the suites of so called “BAQCs” reported by Kenig et al., 2003, 2005. Logan et al., (1999) and Greenwood et al., (2004) interpret BAQCs to reflect prokaryotic input enhanced by redox gradients and/or euxinic conditions in Precambrian environments based on associations between microbial mat fabrics, d13C values of organic matter, and d34S values of coexisting pyrite. In Phanerozoic organic matter BAQCs are found in association with isotopic and stratigraphic evidence of euxinic conditions and/or active redox boundaries (Kenig and others, 2005; Zinniker, 2005). The specific assemblages reported here are similar to suites of cycloalkylalkanes and BAQCs from Permian – Triassic boundary carbonates (Schwab and Spangenberg, 2004). In all cases BAQCs and cycloalkylalkanes occur in sediments associated with major climate perturbations (e.g. glaciation or ocean anoxic events) or at redox boundaries established by geochemical cycles (e.g. sulfur, carbon, Fe, Mn).