PHYTANE FROM CHEMOLYTIC ANALYSIS OF MODERN MARINE-SEDIMENTS - A PRODUCT OF DESULFURIZATION OR NOT

A set of modern marine sediments was analyzed to evaluate the role of sulfurization as a mechanism for biomarker preservation during early d iagenesis. The set consisted of sediments accumulating within various oxic to anoxic depositional environments. Raney nickel treatment of th e polar fraction of total extractable lipids (pTEL) from-each sample y ielded 3,7,11,15-tetramethylhexadecane ('phytane') as the dominant pro duct, accompanied in several cases by minor levels of C-27, C-28, and C-29 5 alpha/beta(H)-steranes, n-C-31 alkane, and beta-carotane. Altho ugh others have ascribed such products to a desulfurization reaction, our work reveals significant production of phytane from the action of Raney nickel on the esterified side chain of chlorophyll. Results sugg est that catalytic dehydration/hydrogenation of chlorophyll accounts f or similar to 50 and similar to 4% of the Raney nickel phytane (mPhy) yield measured in suboxic sediments from the Washington shelf and anox ic sediments from Saanich Inlet, respectively. If 8-20% of the pheopig ment detected in the suboxic sediments and all of the pheopigment dete cted in the anoxic sediment exists as pheophytin, the catalytic dehydr ation/hydrogenation process would account for 100 and 50%, respectivel y, of the observed mPhy yield. The collective findings from our work u nderscore the necessity to exercise extreme caution when interpreting the geochemical significance of hydrocarbon products from Raney nickel treatment of pTEL from sediments. Despite the organic chemical fact t hat Raney nickel is a well-known desulfurizing agent, desulfurization cannot be assigned necessarily as the source of hydrocarbons generated by the action of this reagent on complex lipid extracts from sediment s, particularly those from modern environments.