Microbially induced sedimentary structures ( MISS ) in the macrotidal sand flats of the San Antonio Este Bay, Argentina

ABSTRACT This study documents the microbially induced sedimentary structures present in a modern tidal flat in San Antonio Este Bay, Argentina, examining the main factors that control their development within a macrotidal regime. Flooding of the lower supratidal zone during spring tides is not uniform. Perigee and apogee events show different characteristics, with water depths reaching 1.6 m. The lower supratidal zone is aerially exposed for up to 7 days during neap tides, while the upper supratidal zone only becomes inundated during spring tides at perigee or during storm events. This results in exposure periods of over 20 days. Despite high‐energy currents typical of a macrotidal regime, epibenthic microbial mats formed. However, the genesis, distribution and abundance of MISS within the tidal flat depend on the exposure periods and flood current dynamics. Large‐scale microbial folds and roll‐ups were exclusively found in the lower supratidal zone as a result of spring tides at perigee. Storms did not cause these structures. This study on MISS in modern macrotidal flats allows identification of similar scenarios preserved in the fossil record.