CARBON ISOTOPIC COMPOSITION OF ORGANIC FOSSILS ACROSS ISOTOPIC EXTREMES IN CRYOGENIAN CARBONATES
The morphology of fossil tests suggests a planktonic lifestyle of their precursor organisms. Thus, their isotopic composition should reflect that of the surface waters during the deposition of the Taishir member. Our preliminary results, obtained from the analysis of 8 samples of 15 individual tests by LA-IRMS and 8 samples of 75-125 individual tests by Nano-EA indicate that the carbon isotopic composition of fossil tests do not co-vary with the C isotopic composition of the host carbonate or bulk organic carbon. This implies the presence of isotopically heterogeneous organic matter within the carbonates characterized by large negative δ 13C values. The isotopic heterogeneity will be tested by SIMS analysis of organic-rich material in thin sections and LA-IRMS analyses of bulk organic residues from fossiliferous samples.