Abstract
Recent studies1–3 of the lipids of marine organisms have revealed numerous novel sterols, many with modified side chains. As yet few of these compounds or their diagenetic products have been recognized in geological materials. However, recent investigations of various marine sediments4–8 have detected, for example, gorgosterol4 (IIo) and several 4-methylstanols7,8 (such as IIIl). Our gas chromatography (GC) and computerized gas chromatography-mass spectrometry (C-GC–MS) investigations of the extractable lipids in Neogene deep-sea sediments from the Japan Trench have revealed highly complex sterol distributions within which 69 different sterols have been characterized9. Several of these sterols9,10 (such as IIm, IIn and IIIo), have been reported as constituents of marine organisms11–13, but not of marine sediments; others are of unknown structure. Here we report the identification of one of these novel sterols, 27-nor-24-methyl-5α-cholestan-3β-ol (Ih) which supports sthe biological demethylation pathways proposed by Kobayashi and Mitsuhashi12. Its diagenetic products would also include 27-nor-24-methylcholestanes which may be unrecognized components of the sterane mass fragmentograms widely used by petroleum geochemists for oil and source rock fingerprinting. Such components might also prove valuable marine markers in the interpretation of palaeoenvironments.
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