MICROBIALLY INDUCED SEDIMENTARY STRUCTURES (MISS) - BIOSIGNATURES IN SANDS AND SANDSTONES

In order to facilitate the detection of life on other planets, astrobiologists investigate Earthly analogues of extraterrestrial environments. Main focus is to study, how microorganisms interact with physical and chemical parameters, and which sedimentary structures or biosignatures rise from this interaction. The studies are conducted in both modern and ancient settings.

The most valuable information has been from the study of stromatolites, bacterial cell fossils, or sparsely distributed biomarker molecules and isotopes in fresh or consolidated deposits. These are found in chemical environments, where mineral precipitation and cementation, and fossil preservation are common. However, a large volume of terrestrial and extraterrestrial deposits consists of sands or sandstones. This contribution discusses the significance of those deposits as archives of biosignatures.

The benthic microorganismsthat form microbial mats in shallow-marine and tidal settings are mainly composed of bacteria and cyanobacteria. The benthic microorganisms create characteristic sedimentary structures of mm to m scales by interacting with the physical sedimentary dynamics caused by water motion. Because of the great morphological variety and the different modes of formations, those sedimentary structures are classified into a separate category ‘ microbially induced sedimentary structures – MISS'. The MISS have a high preservation potential, and are found in siliciclastic deposits of early Archean age to present day.

This contribution demonstrates, how remote sensing techniques can detect ‘multidirected ripple marks', ‘erosional remnants and pockets', and other structures. Thin-sections reveal typical laminated pattern and textures that are typically related to microbial activities. The chemical composition of filaments and presence of organic carbon supports the biogeneicity of fossil features. In the search for biosignatures, the distribution of microbial mats (and MISS) in their (paleo)environments has to be taken into account.