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.