MICROBIALLY INDUCED SEDIMENTARY STRUCTURES (MISS) AS PALEOCLIMATE INDICATORS

Tidal systems are significant objects of geoscientific studies, because the depositional surfaces represent interfaces between sediment and water or atmosphere, where a multitude of interfering physical, chemical, and biological processes take place. The proccesses reflect environmental and climate conditions. In the consolidated rocks, the processes are recorded by sedimentary structures or mineral formings that permit conclusions on conditions in the past. My contribution shows with modern and ancient peritidal environments that ‘Microbially Induced Sedimentary Structures (MISS)’ serve as excellent paleoclimate indicators. Peritidal sedimentary environments are widely colonized by benthic cyanobacteria that form biofilms and microbial mats. The bacterial communities interfere with the prevailing sedimentary dynamics, and form ‘Microbially Induced Sedimentary Structures’. The structures are defined as the 5th category within the existing Classification of Primary Sedimentary Structures, and are regarded as counterparts to stromatolites. We distinguish tidal sedimentary environments in arid-(sub)tropical climate zones, where evaporation and in situ carbonate production takes place, from those of moderate climate zones, where no or minor mineral precipitation can be observed. In evaporitic environments of arid-(sub)tropical climate zones, the microbenthos experiences periodical desiccation, or evaporation of crystals within the sedimentary surface. The interaction between chemical parameters and microbes originates MISS like e.g., petees, or polygonal patterns of cracks. In thin-sections, carbonate particles like ooids can be detected. Siliciclastic tidal systems represent moderate climate zones, and are governed by physical sedimentary dynamics. The benthic cyanobacteria influence the sedimentary processes in various ways, e.g., by biostabilization; microbial pushing of grains; or baffling, trapping, and binding. By these activities, the microbes form MISS like ‘erosional remnants and pockets’ or ‘oriented grains’. Comparative actualistic and non-actualistic studies on MISS provide worthy information for the reconstruction of paleoclimates on Earth, and other planets.