Evaporite Microbial Sediments

Abstract

Signatures of microbial life in shallow evaporite systems are discussed using examples from modern coastal hypersaline settings. Organisms contributing to microbial sediments are assigned to moderate halophiles (e.g. cyanobacteria, other phototrophic bacteria, diatoms, non-phototrophic eubacteria) and extremely halophilic taxa (e.g. green algae and halobacteria). Primary production creates the organic base upon which biogeochemical cycles are based that produce a variety of authigenic minerals found in deposits of hypersaline settings. Characteristic microbial sediments include stromatolitic laminae, biolaminoid facies and sedimentary augen structures. Communities dominated by stenotopic major taxa often contribute with less unambiguous laminated structures, e.g. flocculent organics, to the sedimentary record. Based on the criteria of brine depth and salinity, a biofacies classification of marine derived microbial sediments is proposed.