Modern microbial mats in siliciclastic tidal flats: Evolution, structure and the role of hydrodynamics

Abstract

Microbial mats in coastal environments play an important role in both stabilizing the sediment and preserving sedimentary structures. They represent the first biological systems that appeared on Earth, even forming large fossils in carbonate settings known as stromatolites. However, microbial mats have also been recognized for siliciclastic environments as sandy mat structures. In particular, mats are the primary element of the so-called Microbially-Induced Sedimentary Structures (MISS) and their various types represent very useful proxies for the interpretation of the environmental conditions in which they were formed. The objectives of this paper are twofold. The first is to provide a general background review of microbial mats in tidal flats, including their evolution, structure, and morphology. The second objective is to provide amodern case study inwhich we examine the role of storms relative to day-to-day tidal currents. Although tidal currents could be an important eroding factor, we demonstrate that waves, no matter their magnitude, play a significant role in developing different types of MISS such as wrinkle structures and eroding mats into flipped-over fragments. Furthermore, we also show the significance of wave-induced pressure onto groundwater in forming other types of MISS as Kinneya structures and petee ridges. Knowing the environmental conditions to which presentdaymicrobial mats are subject and howthey evolve upon drastic changes in those conditions (i.e., stormevents), represent an important basis for the interpretation of fossil MISS.