Sterenes in surface sediments from the southwest African shelf and slope

Surface sediment samples collected from the southwest African (Namibian) shelf and slope have been analyzed for their hydrocarbon content. In the surface samples a class of olefinic isoprenoid hydrocarbons, the Sterenes, have been found to represent 20–40% of the total hydrocarbons. To the best of our knowledge Sterenes have not been reported in surface marine sediments in such high concentrations.Cholest-2-ene, cholestadiene, cholestatriene, 24-methylcholest-2-ene, 24-methylcholestadiene, 24-ethylcholest-2-ene and 24-ethylcholestadiene were found in the sediments and identified by high resolution glass capillary gas chromatography-mass spectrometry.The formation of Sterenes from sterols via microbiological processes or chemical auto-oxidation, followed by subsequent dehydration mechanisms and double bond isomerizations. is postulated.It appears that there are highly unique environments in the upwelled area off southwest Africa providing the microbiological and chemical conditions for rapid diagenesis of the sterols within a time scale of 100 yr or less.