ISOTOPICALLY HEAVY CARBON IN THE C-21 TO C-25 REGULAR ISOPRENOIDS IN HALITE-RICH DEPOSITS FROM THE SDOM FORMATION, DEAD-SEA BASIN, ISRAEL

A series of Miocene/Pliocene halite deposits (with extremely low organ ic carbon contents) from the Sdom Formation (Dead Sea Basin, Israel) h ave been studied. Distributions and delta(13)C contents of biomarkers have been determined using GC-MS and irm-GCMS analyses, respectively. The hydrocarbon fractions consist mainly of pristane, phytane and C-21 to C-25 regular isoprenoids. The predominance of C21+ regular isopren oids in the Dead Sea halites and other hypersaline deposits indicate t hat these components could be derived from ether-bound membrane lipids of halophilic archaea. The lack of intact ether-bound lipids in the p olar fractions indirectly infers that such components have already bee n released at early stages of diagenesis. Their delta(13)C contents ar e enriched in C-13, by UP to 7 parts per thousand, compared to the bio markers of presumed phytoplanktonic origin (i.e. steranes and hopanes) within the same sediment sample, in agreement with a source other tha n algae and cyanobacteria, thus, tentatively assigned as halophilic ar chaea. Based on biomarker distributions, delta(13)C contents and miner al compositions, these sediments appear to have been deposited in a sa linity stratified water body with a bottom water brine. Continual evap oration and deposition of the higher salts (i.e. carnallites) are favo urable conditions for the growth of halophilic archaeal communities. ( C) 1998 Elsevier Science Ltd. All rights reserved.