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

Deformed microbial mat structures in a semiarid temperate coastal setting

“…The mat chips, not rounded and resembling mudclasts, are found not far from the coastline of the tidal channel and are related to erosional events by high energy tidal currents. These type I microbial structures are similar to those found in the supratidal zone of estuarine environments, as the temperate Bahía Blanca estuary (Cuadrado et al, , 2014Pan et al, 2013b) and in different estuarine areas of the world (e.g., Mellum Island, thoroughly described by Noffke et al, 2001a), lake environments (e.g., the Egyptian coast studied by Taher and Abdel-Motelib, 2014), and coastal sabkhas (e.g., the Tunisian coast researched by Noffke et al, 2001b). Eriksson et al (2007) named these structures as mat-destruction features and found them in sandstones in the rock record.…”

“…12). This hydraulic pressure is raised after rainfalls and unusual high spring tide incoming from the east, and therefore there is an uplift force with the potential to detach the microbial mats from the underlying sediments Cuadrado et al, 2014). Under such conditions, the liquefied sand below the microbial mat acts as a slippery surface, and the high flexibility on wet mats affected by strong tidal current shear stress sets the scenario for the formation of mat folds, buckles, and roll-ups.…”

“…The first ones entangle particles, and most of the motile benthic microorganisms present in the surface are embedded in highly adhesive mucilages, collectively known as EPS (extracellular polymeric substances, Decho, 1990). Consequently, the characteristics of sediments are altered, thus increasing the erosive critical threshold in aquatic environments under unidirectional currents (Hagadorn and McDowell, 2012); tidal currents (Noffke, 2010), and even wave-shear stress (Cuadrado et al, 2014).…”

Early Triassic environmental dynamics and microbial development during the Smithian–Spathian transition (Lower Weber Canyon, Utah, USA)

“…The preservation of F2 at the top and at the base of some megaripples suggests that they were deposited in the same environment as F1, where desiccation cracks mark periods of subaerial exposure in the intertidal zone (Burchette and Wright, 1992;Flügel, 2004). In modern environments, microbial features are commonly associated with megaripples of mid ramp, but are also particularly well-preserved in the inner peritidal domain where they contribute to the biostabilization of the siliciclastic substrate (Gerdes et al, 2000;Cuadrado et al, 2011Cuadrado et al, , 2014Noffke and Awramik, 2013). The preserved planar, undulated, wavy and bulbous laminae of F2a and F2b suggest that filament-dominated microbial mats acted on the preservation of sedimentary structures (Schieber, 1999;Werhmann et al, 2012).…”

“…This points toward a zonation of MISS morphologies in a proximal-distal transect along the ramp. Actualistic investigations highlight thatwhether precipitating (microbialites/stromatolites) or not (MISS)microbial mats better grow during quiet periods with low erosion or in environments with low hydrodynamism (Gerdes et al, 2000;Noffke et al, 2003;Cuadrado et al, 2014). Hydrodynamic conditions along the Smithian ramp in LWC seem to be moderate and relatively constant during the period of dolosilisiclastic sedimentation, likely corresponding to an "ecological window" sensu Noffke et al (2002), where hydraulic reworking is moderate.…”