PALEOENVIRONMENTAL IMPLICATIONS OF NOVEL C-30 STERANES IN PRECAMBRIANTO CENOZOIC AGE PETROLEUM AND BITUMEN

Petroleums and bitumens from Early Proterozoic (almost-equal-to 1800 M a) to Miocene (almost-equal-to 15 Ma) age marine strata contain 24-iso propylcholestanes, a novel group of C30 steroids. The abundance of the se compounds, relative to 24-n-propylcholestanes, varies with source r ock age. Late Proterozoic (Vendian) and Early Cambrian oils and/or bit umens from Siberia, the Urals, Oman, Australia, and India have a high ratio of 24-isopropylcholestanes to 24-n -propylcholestanes (greater-t han-or-equal-to 1), while younger and older samples have a lower ratio (less-than-or-equal-to 0.4). Temporal changes in this parameter may r eflect the relative abundance of certain Porifera (sponges) and certai n marine algae through time. Geochemical indicators such as this, whic h can constrain the source rock age of a migrated oil, are useful in s ource rock identification during petroleum exploration.