Processes of MISS-formation in a modern siliciclastic tidal flat, Patagonia (Argentina)

Abstract

The study focus on the description of several MISS as erosional pockets and remnants, flipped-over edges, and large microbial deformation structures as roll-ups, folds and gas domes, in the context of sediment composition, hydraulics, and geomorphology. The aim of the paper is to recognize the mechanisms of formation of MISS by analyses on hydrodynamics under the influence of the geomorphology. The study was conducted in an elongated inactive tidal channel colonized by microbial mats (2.5 × 0.3 km) in a progradation environment. To continuously record the water-level fluctuations, a HOBO water level logger was placed 40 cm below the flat surface for two years. The sea water enters several times a year, during storms, where the flood currents were characterized by faster velocity than ebb currents, reaching a water depth up to 0.70 m over the tidal flat. That coastal process creates MISS over the tidal flat. The most conspicuous microbial structures are the huge deformation roll-ups several m-scale, associated to elongated rip-off mats, folds and flipped over mats. The process of fluidization was postulated to explain the sand-infilling of gas domes and folds we observed. This process would result from the wave action on the water column that produces a temporal fluid behavior of the underlying sand.