EXTRACTION OF BOUND PORPHYRINS FROM SULFUR-RICH SEDIMENTS AND THEIR USE FOR RECONSTRUCTION OF PALEOENVIRONMENTS

PORPHYRINS, which are present in most sediments and crude oils, repres ent the 'molecular fossils' of compounds such as chlorophylls, bacteri ochlorophylls and haems in the organisms from which the organic materi al is derived1-4. They have the potential to provide information about palaeoenvironmental conditions at the time of deposition5-9. Porphyri ns derived from degradation of chlorophylls are of particular interest because of the possibility of relating palaeoproductivity estimates f rom sediments to chlorophyll-based measurements of present-day product ivity determined by remote sensing. But standard analytical methods do not detect all of the porphyrins present in a geological sample - a s ubstantial fraction of the porphyrins may be bound to kerogen10,11 or to solvent-extractable macromolecules, or may be degraded by the oxida tive extraction procedures. It has been shown recently12-16 that sulph ur may play a crucial part in binding 'biomarker' molecules at an earl y stage of sediment diagenesis, and that desulphurization using Raney nickel may liberate small molecules bound to sulphur-containing specie s. Here we show that this approach releases large amounts of porphyrin s from the total organic extract of a sulphur-rich marl. Liberating bo und porphyrins in this way may greatly enhance the amount of informati on on palaeoenvironments that can be extracted from geochemical analys is of sediments.