SEDIMENTARY 24-N-PROPYLCHOLESTANES, MOLECULAR FOSSILS DIAGNOSTIC OF MARINE-ALGAE

Certain C30-steranes have been used for identifying sedimentary rocks and crude oils derived from organic matter deposited in marine environments. Analysis of a C30-sterane from Prudhoe Bay oil indicates that these C30-steranes are 24-n-propylcholestanes that apparently are derived from precursor sterols 24-n-propylidene-cholesterols and 24-n-propylcholesterol. These widely occurring sterols are biochemically synthesized in modern oceans by members of an order (Sarcinochrysidales) of chrysophyte algae. These data thus imply that C30-sterane biomarkers in sedimentary rocks and crude oils have a marine origin. Screening of a few organic-rich sedimentary rocks and oils from throughout the Phanerozoic suggests that these C30-steranes first appeared and, therefore, their source algae evolved between Early Ordovician and Devonian.