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A catalogue of microbial structural signatures is presented, based upon the coupling of fundamental biogeochemical–microbial processes and local morphogenetic determinants. It summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones (temperate humid: Mellum Island, southern North Sea; subtropical arid: coast of southern Tunisia). Textural geometries reveal a high structural diversity, but their determinants are primarily based upon six major parameters: (1) intrinsic biofactors: structural diversification of sedimentary microbial films and mats inherent in the organisms, i.e. their construction morphology, growth, taxis and behaviour, and local abundance of specific morphotypes. Most prominent are the ensheathed filamentous cyanobacteria Microcoleus chthonoplastes and Lyngbya aestuarii, and the sheathless filamentous cyanobacterium Oscillatoria limosa. (2) Biological response to physical disturbances: sediment supply, erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats. (3) Trapping/binding effects: physicobiological processes give rise to grain orientations and wavy to lenticular lamina, lamina‐specific grain arrangements and ‘sucrose’ calcium carbonate accumulations. (4) Secondary physical deformation of biogenic build‐ups: mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures. (5) Post‐burial processes: textural fabrics that evolve from mechanical effects of gas formation from decaying mats, and features related to the formation of authigenic minerals (calcium carbonates, calcium sulphates, pyrite). (6) Bioturbation and grazing: post‐depositional structures, such as Skolithos‐type dwellings, traces of burrowing insects, gastropod grazing traces and faecal pellets. In synopsis, the catalogue firstly comprises a sound set of ubiquitous signatures. This uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings. The catalogue secondly documents signatures that are extremely sensitive to tidal position, hydrodynamic regime and overall climatic conditions. These kinds of signature indicate narrow facies zones, which often coincide with the activity or dominance zones of certain organisms. An overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings.

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Extensive tidal areas of the Recent coast of southern Tunisia are overgrown by microbial mats. Different mal types of which each are dominated by distinct and ,,veil adapted cyanobacterial species develop. Ecological rcsponse of the mat-forming microorganisms to climatological, hydrological and sedimentological factors produce characteristic sedimentary structures (= microbially induced sedimentary structures).A succession of Pleistocene rocks crops out near the lagoon El Bibane, southern Tunisia. The stratigraphic section comprises structures that we regard as fossil equivalents to those microbially induced structures we observe in the Recent coastal area. Preservation of the structures ix result of lithification of the microbial mats. This we conclude from fossil filaments of cyanobacteria visible within the rock matrix.The Recent microbially induced sedimentary structures indicate facies zones within the modern tidal environment. Comparison of the Recent structures with the fossil analogues recorded in the stratigraphic section aids to identify the same distinct facies zones within the Pleistocene coastal environment also.Erosion by water currents forms step-like cliffs, and the microbial mat is undermined and ripped off piece by piece. Shallows within the supratidal area are overgrown by copious microbial mats comprising structures like biolaminites and -varvites, as well as polygons of cracks. The features originate from effects triggered by seasonal variations of climate. Tufts and reticulate pattern of bulges indicate supernatant water films covering the mat surfaces. Morpholo,L,ically higher parts of the Recent tidal area are overgrown bv single-layered mats forming petecs, induced by microbial mat growth and evaporitive pumping.The study demonstrates that microbially induced sedimentary structures can be used to reconstruct small-scaled facies zones within coastal environments. They also include hints on palcoclimatological, hydrological and scdimentological conditions.