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Lacking absolute age constraints for the Vazante Group sedimentary rocks, we conducted a study of Re-Os systematics in the three shale levels that are the primary focus of the PRF funded biomarker study. Our new Re-Os isochron ages for organic-rich shale and geological observations reveal that the upper half of the glaciogenic Vazante Group in Brazil is late Mesoproterozoic in age, extending the known record of low latitude Precambrian ice ages into a time traditionally believed to be ice free. Biomarker, sulfur isotope, and iron speciation analyses support the presence of a strongly stratified ocean during post-glacial sea level rise and deposition of the bituminous shale horizons. The radiometric constraints broadly link profound climate change to the tectonic and biological upheavals of the late Mesoproterozoic Era, supporting the view that extreme and prolonged environmental change fostered the evolution of higher life forms. If the new Re-Os age constraints are correct, the new biomarker studies of the Vazante Group become even more important as an earlier report identified the presence of 24-IPC, which is a known biomarker for demosponges, in a sample of the Morro do Calcario shale. Verification of the biomarker results would suggest a pre-1.1 Ga origin for Earth's earliest animals. Sixty-one biomarker samples from three different levels in the Vazante Group were collected by Kristen Miller in 2007 from a basin wide distribution of exploration cores. Miller presented her biomarker results at the 2009 annual GSA meeting. Powdered samples were characterized by Rock Eval analysis at the University of Aachen, Germany, and the powders were also analyzed for TOC, %S, and δ³⁴S compositions. An initial set of samples from the Morro do Calcario shale were extracted using an ASE at the College of William and Mary's Virginia Institute of Marine Science. Other samples were extracted by repeated sonication in dichloromethane. The organic extracts were then separated into saturated, aromatic, and polar fractions using column chromatography. An internal standard, 3-methylheneicosane, was added to the saturated fraction and analyses of the saturated fractions were performed at the Geophysical Laboratories of the Carnegie Institution for Science using a Hewlett Packard 6890N gas chromatograph coupled to a Hewlett Packard 5973 Mass Selective detector. The samples were run in full scan and selected ion monitoring (SIM) modes. N-alkanes, pristane, phytane, hopanes and steranes were observed in most samples, and compounds were identified by their elution time and mass spectra. Relative abundances of hopane and sterane compounds and absolute abundances of n-alkanes, pristane and phytane were calculated from the 191, 217, and 85 SIM ion chromatograms respectively. Peak areas of each compound were manually integrated using Hewlett Packard MS ChemStation software. The n -alkane distributions differ between cores and range from unimodal low molecular weight to slightly bimodal or higher molecular weight distributions. Pristane and phytane, which are the C₁₉ and C₂₀ isoprenoid products of phytol, were present in all of the samples, indicating active photosynthesis. Insofar as phytol is either reduced to phytane or oxidized to pristane under different environmental conditions, their ratio can be used to estimate the redox conditions during deposition. The pristane/phytane (Pr/Ph) ratios from these data suggest anoxic and potentially hypersaline conditions. Hopanes originate mainly from prokaryote microorganisms and were detected in all of the samples. Under reducing conditions, the amount of the C₃₅ homohopanes relative to the total C₃₁-C₃₅ homohopanes (C₃₅ % total) is >5%. The C₃₅ % total ranges from 4.4 to 14%. The C₃₅/C₃₄ and %C₃₅ ratios directly correlate with each other and inversely correlate with Pr/Ph. A %C₃₅ above 5% indicates reducing conditions. Most of the samples however are near or greater than 5 % which may indicate reducing conditions. Additionally, the ratio of C₃₁22R/C₃₀ hopanes is near or greater than 0.25 indicating a marine source. The Gammacerane index monitors the relative amount of gammacerane, which is believed to reflect redox stratified water columns. Our samples (10xGamma/(Gamma+C₃₀) range from 0.52-1.4 and correlate directly with %C₃₅ and C₃₅/C₃₄ and inversely with Pr/Ph, so that all redox indicators are consistent with each other. Hopane and sterane biomarker ratios indicate that the samples are mature and that they are in the peak oil generating stages. C27 through C₂₉ regular steranes and diasteranes, which are usually attributed to eukaryotic inputs, were identified in each sample. The samples are all grouped together on the ternary diagram indicating that they had a similar source. Compound specific isotope analyses were performed at the University of Maryland using an Agilent 6890 Gas Chromatograph coupled to a GV IsoPrime Continuous Flow Mass Spectrometer. CSIA is a technique used to determine the carbon isotopic composition of individual compounds and is an important tool for evaluating biomarker sources and syngeneity because compounds that originate from the same biological source should have similar isotopic compositions. Average isotopic compositions of the n-alkanes are slightly depleted relative to bulk organic carbon. Additionally, phytane was isotopically depleted relative to the n-alkanes and bulk organic carbon. Lipids from both autotrophs and heterotrophs are depleted relative to average biomass therefore, the depletion of n-alkanes and phytane relative to bulk organic carbon suggests that the extracted organic matter is related to the kerogen and may be syngenetic. Furthermore, the enrichment of the n-alkanes relative to phytane is typical of Proterozoic units and may indicate intense heterotrophic reworking of organic matter under anoxic conditions. Taken together, the structural identification and carbon isotopic signature of the biomarkers analyzed thus far are suggestive of organic matter that was deposited under reducing conditions. This may indicate a stratified water column with oxygenated surface water overlying anoxic deep water. This is supported by carbon and sulfur isotopic as well as iron speciation analyses of the Morro do Calcario shale, which indicate high rates of primary production and a small, isotopically enriched sulfate pool. If metazoans were present during the Mesoproterozoic in the Vazante basin, it is most-likely that they would have been restricted to the oxic zone. The search for 24-IPC and other biologically significant biomarkers will continue in the next year through GC-MS-MS analyses.