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Aspects of the steroid geochemistry of a recent diatomaceous sediment from the namibian shelf

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  • Chemistry
  • Earth Science


Aspects of the steroid geochemistry of a recent diatomaceous sediment from the Namibian Shelf OCEANOLOGICA ACTA 1982 -VOL. 5 - No 3 ~ --------'----~- Aspects . of the steroid geochemistry of a recent diatomaceous Steroids - Recent sediments Diagenesis Organic geochemistry Stéroïdes Sédiments récents Dia genèse Géochimie organique sediment from the N ami bian Shelf ABSTRACT RÉSUMÉ O. J. Smith •, G. Eglinton •, R. J. Morris b, E. L. Poutanen b • Organic Geochemistry Unit, School of Chemistry, Bristol University, Bristol, UK. b Institute of Oceanographie Sciences, Wormley, Godalming, Surrey, UK. Received 26/10/81, in revised fonn 7/1/82, accepted 22/1/82. Five consecutive 2 cm thick sections, from a core taken on the South-West African shelf, have been analysed for various classes of steroidal compounds. Fifty-two different sterols were identifted, ranging from C26-C30, in concentrations up to 38 J.lg/g dry weight of sediment. Steroidal ketones (sterones) and alkenes (sterenes) were also present, in concentrations up to 8.6 J.lg/g and 1.8 J.lg/g dry weight of sediment respectively. Many of the sterols can be related to the known large input of diatoms, but there is also evidence for a contribution from coccolithophorids and coelenterates. The major sterol in all sections was 4 ex, 23, 24-trimethyl-5 a-cholest-22-en-313-ol ( dinosterol) which, together with several other 4-methyl-sterols, might be expected to be explained by a dinoflagellate input. However, no recognisable dinoflagellate remains were observed under the light microscope and a major, as yet uncharacterised, phytoplankton source is postulated. Nuclear saturated stanols with both 5 a- and 513 (H)-conftgurations were abundant, comprising 43-77% of the total 4-desmethyl sterols. A depth proftle of the stanolfstenol ratio suggests that reduction of the A5- double bond of stenols is occurring in the sediment. The presence of suites of stanones corresponding to all the major stenols and

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