P203-TU TEMPORAL AND FACIES CONTROLS ON THE DISTRIBUTIONS OF UNCOMMON STERANES FROM NEOPROTEROZOIC SEDIMENTS AND OILS Amy E. KELLY 1 , Gordon D. LOVE 2 , Emmanuelle GROSJEAN 3 , John E. ZUMBERGE 4 and Roger E. SUMMONS 1 1. EAPS Dept., Massachusetts Institute of Technology, 42-44 Carleton St, E34, Cambridge, MA 02142, USA 2. Dept. of Earth Sciences, University of California, Riverside, Geology Building, Riverside, CA, 92521, USA 3. Geoscience Australia, Canberra, ACT 2601, Australia 4. GeoMark Research, Ltd., 9748 Whithorn Drive, Houston, TX 77095, USA Molecular fossils provide a means to evaluate paleoenvironmental redox conditions and broad-scale aspects of carbon cycling. This information can be used to study the changing environmental conditions over the Neoproterozoic-Cambrian boundary during the radiation of multicellular organisms. We are analyzing Neoproterozoic sedimentary rocks and oils from Australia, Siberia, and Oman to determine how the distributions of steranes change as a function of age, lithology, maturity, and paleoredox conditions. The origins of uncommon steranes of interest including C 19 norsteranes, 21-norsteranes, 27-norcholestanes, and 24-isopropylcholestanes are also being investigated (Figure 1). 21-norsteranes 27-norchol estane 24-isopropyl cholestane A- norsterane 19-norsterane C 19 norsteranes Figure 1. Chemical structures of the compounds of interest, including possible structures for the C 19 norsteranes. In recent studies of late Neoproterozoic source rocks and oils from Oman, a series of C 19 steranes with three isomers, referred to as A, B, and C, were identified (Grosjean et al., 2005). The relative abundance of compound C increases with the salinity of the depositional environment in these samples, implying that compound C has the potential to be a salinity indicator. 21-norsteranes have been known to exist as 21-norcholestanes, and recently their 24- methyl and 24-ethyl homologues have been identified in saline depositional environments (Bao & Li, 2001; Grosjean et al., 2005). These are valuable salinity indicators in immature