EARLY DIAGENESIS OF ORGANIC-MATTER AND RELATED SULFUR INCORPORATION IN SURFACE SEDIMENTS OF MEROMICTIC LAKE-CADAGNO IN THE SWISS ALPS

Samples of Recent anoxic sediment (<100 yr BP) from the meromictic Lak e Cadagno (Switzerland) were examined to study sulphur incorporation i nto organic matter at a very early stage of diagenesis. Trace amounts of two organosulphur compounds were identified in the extractable orga nic matter. Desulphurization of the heterocompound and asphaltene frac tions with nickel boride yielded hydrocarbons with a strong dominance of phytane and minor amounts of n-alkanes, steranes and squalane, but may also have converted ester-bound moieties into hydrocarbons as show n by a control experiment with a chloropyll a standard. The amount of sulphur-bound compounds is always higher than the amount of the free p recursors, even in the shallowest sediments. This indicates that the f ormation of organosulphur compounds starts already in the water column or is very effective in the uppermost millimeters of the sediment lay er. Stable carbon isotope data of the sedimentary compounds, and of bi ological material from the water column and from land biota growing ar ound the lake, show that the sulphur-bound phytane in the youngest sam ples is dominated by phytane of bacterial origin. With increasing dept h the amount of phytane of terrestrial origin slightly increases. (C) 1997 Elsevier Science Ltd.