BIOMARKERS IN THE NEOPROTEROZOIC UINTA MOUNTAIN GROUP, COMPARISONS AND INFERENCES ABOUT BIOLOGICAL INPUT

The Uinta Mountain Group of eastern Utah occurs in an east west trending belt of quartz arenite, arkose and minor shale. Shale samples were collected for biomarker analysis from the Mt. Watson formation, Hades Pass formation, the Red Pine Shale in the western part of the basin. In addition, one sample of the undivided Uinta Moutain Group in the eastern part of the basin was found to have sufficient organic carbon for biomarker analysis. Biomarkers are branched and cyclic organic molecules found in shale, carbonate and other organic rich rocks. Information about diagenesis, depositional environment and biological input is embedded in the molecular structure and relative abundance of these hydrocarbon compounds. Many Precambrian rocks have passed the thermal window during which significant oil deposits can form, and/or their organic constituency has been altered by bacterial degradation. In the case of well preserved, organic rich rocks, however, such as the Red Pine Shale of the Uinta Mountain group, or shale deposits from the Lena and Aldan River section of the Siberian platform, some of the more resistant biomarkers can survive. These include low molecular weight normal and branched alkanes that are associated with cyanobacterial mats, and certain forms of algae. Pentacyclic and tricyclic compounds are also present in the Siberian samples indicating input from various algal and bacterial sources. This preliminary report on Uinta Mountain Group and Siberian samples adds to a growing body of data that catalogues the biological input to Neoproterozoic units such as the Chuar Group of the Grand Canyon Supergroup (Summons and Walter, 1990), and the lower Ungoolya Group of the Officer Basin (Arouri et al. 2000) among others.