The impact of benthic microbial communities in sediment dispersion and bedform preservation : a view from the oldest microbially induced sedimentary structures in South America.

Abstract

The influence of microbial communities upon sedimentary dynamics is an issue of increasing significance. Over the last decades, studies have

revealed a particular class of sedimentary structures and textures produced by the interaction among distinct flows, marine substrate, and ben- thic microbial communities. We present evidence of the oldest record of microbially-induced sedimentary structures (MISS) in South Amer- ica, as recorded in low-grade metasedimentary rocks of the Early Mesoproterozoic (~1536 ± 33 Ma) Tiradentes Formation, state of Minas

Gerais, SW Brazil. Types 1, 2, and 3 correspond to wrinkle, pustular, and dome structures related to flat or rippled bed surfaces, preserved in

metasandstone deposited in shallow marine settings. Evidence supporting the microbial origin of these structures includes delicate morphol- ogy, degree of alignment, presence of original mat cover, and orientation of quartz grains indicating biostabilization. The presence of distinct

MISS associated with well-preserved ripple marks, wrinkled surfaces, and flatbeds suggests deposition under varied energy conditions with different potentials for the preservation of surficial structures. Vertical growth of microbial communities influences sediment cohesion and stability. This reduces substrate roughness and, as a consequence, wave and current shear, thereby increasing the preservation potential of bedforms and delicate features of their bedding surfaces.