MICROBIALLY INDUCED SEDIMENTARY STRUCTURES—A NEW CATEGORY WITHIN THE CLASSIFICATION OF PRIMARY SEDIMENTARY STRUCTURES

Primary sedimentary structures in siliciclastic depositional areas are synsedimentary formed by physical parameters erosion, deposition and deformation. Cyanobacterial films and mats influence the physical dynamics in various ways. This biotic-physical interference is documented by characteristic 'microbially induced sedimentary structures - MISS' that we placed as own category 'bedding modified by microbial mats and biofilms' into the existing Classification of Primary Sedimentary Structures (Pettijohn & Potter 1964). The structures differ significantly from those we know from carbonate environments.

We distinguish (i) structures induced by microbial leveling of preceedingly existing morphologies of sediment surfaces, e.g. leveled surfaces; (ii) structures induced by biostabilization, e.g. multi-directed ripple marks; (iii) structures induced by baffling, trapping and binding, e.g. biolaminites; (iv) structures induced by imprinting, e.g. sinoidal structures; (v) structures induced by microbial grain separation, e.g. oriented grain textures.

The structures can be recognized also in the fossil record of siliciclastic successions. They permit conclusions on the ancient depositional dynamics, and aid in identification of facies zones. Therefore they provide helpful information for reconstruction of paleoenvironments.