Isotopically heavy carbon in the C21 to C25 regular isoprenoids in halite-rich deposits from the Sdom Formation, Dead Sea Basin, Israel

A series of Miocene/Pliocene halite deposits (with extremely low organic carbon contents) from the Sdom Formation (Dead Sea Basin, Israel) have 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 isoprenoids in the Dead Sea halites and other hypersaline deposits indicate that these components could be derived from ether-bound membrane lipids of halophilic archaea. The lack of intact ether-bound lipids in the polar fractions indirectly infers that such components have already been released at early stages of diagenesis. Their delta(13)C contents are enriched in C-13, by UP to 7 parts per thousand, compared to the biomarkers of presumed phytoplanktonic origin (i.e. steranes and hopanes) within the same sediment sample, in agreement with a source other than algae and cyanobacteria, thus, tentatively assigned as halophilic archaea. Based on biomarker distributions, delta(13)C contents and mineral compositions, these sediments appear to have been deposited in a salinity stratified water body with a bottom water brine. Continual evaporation and deposition of the higher salts (i.e. carnallites) are favourable conditions for the growth of halophilic archaeal communities. (C) 1998 Elsevier Science Ltd. All rights reserved.