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

Petroleums and bitumens from Early Proterozoic (almost-equal-to 1800 Ma) to Miocene (almost-equal-to 15 Ma) age marine strata contain 24-isopropylcholestanes, a novel group of C30 steroids. The abundance of these compounds, relative to 24-n-propylcholestanes, varies with source rock age. Late Proterozoic (Vendian) and Early Cambrian oils and/or bitumens from Siberia, the Urals, Oman, Australia, and India have a high ratio of 24-isopropylcholestanes to 24-n -propylcholestanes (greater-than-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 reflect the relative abundance of certain Porifera (sponges) and certain marine algae through time. Geochemical indicators such as this, which can constrain the source rock age of a migrated oil, are useful in source rock identification during petroleum exploration.