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ABSTRACT: Age Correlation of Petroleum of Unknown Source Using Biological Markers

J. M. Moldowan, S. R. Jacobson, B. J. Huizinga, C. Y. Lee

Determination of age constraints on petroleums from unknown sources provides a means of choosing among possible source rock candidates, predicting migration scenarios for oil, and determining the timing of its emplacement in the reservoir. A number of parameters used to assign such age constraints to petroleum have been suggested by geochemists. However, any constraining marker, regardless of age, may not be found in a particular facies because the parent organisms are absent in those sediments. Thus, the presence of a specific age correlation marker may be significant whereas its absence may not.

We have investigated two markers for their age-correlation significance. Oleanane, a marker related to pentacyclic triterpanes in flowering plants (angiosperms) occurs in many Late Cretaceous or younger rocks and oils, even though angiosperm fossils are known in older rocks. A survey of a sequence of middle to upper Cretaceous rocks from Wyoming provides an example of a Late Cretaceous age for the onset of oleanane. However, a level of uncertainty exists for older Cretaceous rocks where a trace component with many similarities to oleanane (which could in fact be oleanane) can occur.

C30-steranes (24-n-propylcholestanes) have been used as a widely occurring marker for marine organic input to petroleum. A recent report postulates the origin of C30-sterances from marine Sarcinochrysidales order of Chrysophycase (golden brown algae). Although the fossil record of these algae has not been recorded, our sample base indicates that C30-steranes, and therefore their parent organisms, originate in the Middle Ordovician.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990