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Steranes are minor hydrocarbon components of crude oil which are derived from the sterols of living systems and provide a vehicle for the study of the origin and chemical development of petroleum. Sterols, the precursors of steranes, were found in a number of freshwater and marine sedimentary environments exhibiting a range of redox conditions. Up to 10 ppm of the plant sterols beta-sitosterol, stigmasterol, cholesterol, and campesterol were found in the sediments by using gas chromatography and mass spectrometry. Steranols, which are intermediate between the oxygenated unsaturated plant sterols and the reduced crude-oil steranes, were found in modern Arctic marine sediments, as were hydrocarbon steranes similar in structure to those of petroleum. Steranols were about hal as abundant as the corresponding sterols. The steranes totaled about 0.1 ppm. The presence of steranols and steranes in such recent sediments indicates that some processes which are necessary for the formation of petroleum constituents--in this case reduction--occur very early in the diagenetic conversion of organic debris to crude oil.
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