TIDAL EROSION OF MICROBIALLY INDUCED SEDIMENTARY STRUCTUES IN AN INNER FUNNEL-SHAPED ESTUARY

PAN, J; MAISANO, L.; CUADRADO, D.G.

PUERTO MADRYN

Conferencia; 9th International Conference on Tidal Sedimentolog; 2015

Some of the most important processes in estuarine environments involve tidal currents, whichare responsible for sediment deposition and erosion. Therefore, tidal sedimentology has focused in recent years in finding signatures in the stratigraphic record that help recognize ancient tidal processes. In addition, Schieber (2004) emphasized that the preservation of sedimentary structures in this setting may be promoted by the presence of microbial mats, which provide cohesion and cementation. A thorough explanation of the influence of tidal cycles in sedimentation patterns was presented by Kvale et al. (1995) and Kvale (2006, 2012), who considered the combined gravitational attraction of the sun and the moon. Spring tides result in stronger than average tidal currents, whereas neap tides result in weaker than average tidal-current velocities. The purpose of this study is to relate tidal energy to some of the microbially-induced sedimentary structures (MISS) present in the supratidal zone. The structures consist of a shrinkage crack and a flipped-over biofilm. The energy reaching the supratidal zone was quantified following tidal records and wind-driven storm events, while the recognition and evolution of MISS was described under the prevailing conditions. The study was performed on the supratidal zone of Puerto Cuatreros, in the internal Bahía Blanca estuary (38º53?52?S; 62º22?59?W) where the supratidal flats are colonized by microbial mats (Figure 1). The supratidal zone occupies that part of a coastal area above the mean high-tide level, and is inundated by the sea only during the highest (spring) tides, certain prevailing wind patterns and storm events. Puerto Cuatreros supratidal flat is located >4.4 m in relation to a tidal gage at Puerto Ingeniero White (8 km towards the mouth of the estuary). The zone is also of utmost importance, in that it contributes tidal signatures in sediments, allowing recognition of tidal influence.