CHARACTERIZATION OF MODEL EVAPORITIC ENVIRONMENTS THROUGH THE STUDY OF LIPID COMPONENTS

A saline circuit has been studied as a model of coastal evaporite systems. The lipid composition of diverse salt ponds encompassing calcite, gypsum and halite domains has been determined. Most of the lipid material has been found in the carbonate samples and is related to algal/cyanobacterial debris. Lipids in the gypsum domain are of heterotrophic microbial origin and extreme halophilic bacteria constitute the main lipid contribution in the halite samples. n-Alkane distributions with high predominance of n-docosane constitute a previously described feature of sedimentary evaporitic conditions that is characteristic of the intermediate calcite/gypsum samples. In the calcite domain, the presence of C20 highly branched isoprenoid olephines, tetrahymanol and the large amounts of phytol constitute likely precursors of lipids usually found in evaporitic environments (i.e. C20 highly branched isoprenoid alkanes, gammacerane and high phytane/pristane ratios). Their occurrence point to dehydration and hydrogenation as two main diagenetic processes leading to the formation of "evaporitic molecular markers".