Bio-sedimentary structures evolving from the interaction of microbial mats, burrowing beetles and the physical environment of Tunisian coastal sabkhas

Abstract

Microbial mats are widespread biotic systems in Tunisian coastal sabkhas. In these environments, staphilinid beetles are important bioturbators, making vertical burrows and depositing characteristic hillocks of excavation pellets on the mat surface. The intimate interplay between microbial and beetle activities results in a structured sedimentary surface. Small photosynthetic domes or bulges develop which in turn become microbially overgrown and gypsum-encrusted. Other examples are mat expansion domes above vertical burrows, and excavation pellets overgrown by biofilms trapping aeolian sand grains. In many cases the structures are too complex to explain clearly their formation. Since modern microbial mat-related surface structures form the base for interpretation of fossil record, it is essential to decipher what is contributed by the different structuie-forming factors.