Acyclic isoprenoids – molecular indicators of archaeal activity in contemporary and ancient Chinese saline/hypersaline environments

Acyclic isoprenoid hydrocarbons are found to be the predominant components in the organic matter extracted from sedimentary cores and oils of various hypersaline settings, including Tertiary Janghan salt lake basin, Cretaceous Taian salt lake basin, and Triassic, Permian and Cambrian Yangtze evaporitic marine platform. Inland saline lake basins are characterized by tremendous predominance of phytane (iC20) ranging up to 15% of the total extract. While the evaporitic marine sediments are unique for their complete series of super-long-chain acyclic isoprenoids, up to C40. These isoprenoids possess head-to-head, tail-to-tail or regular linkages and generally are indicators of the significant contribution from various archaea (archaebacteria), i.e. halophiles, methanogens and acidothermophiles. According to the great discrepancy of distribution and composition of isoprenoids, these modern and Cenozoic inland salt lake sediments are likely dominated by halophilic archaea, while the studied Mesozoic and Paleozoic evaporitic marine sediments are predominantly distinguished by methanogens and acidothermophiles. Concentration of chlorine salt is more directly proportional to the abundance of phytane than sulfate. Reduced species of sulfur, sulfide, S0 and organic sulfur compounds (OSC), however, may have played a key role in the preservation and formation of the highly abundant phytane observed in the inland salt lake basins.