FIELD OBSERVATIONS ON THE EVOLUTION OF RETICULATE PATTERNS IN MICROBIAL MATS IN A MODERN SILICICLASTIC COASTAL ENVIRONMENT

PAN, JERÓNIMO; CUADRADO, DIANA G.

JOURNAL OF SEDIMENTARY RESEARCH - (Print)

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Tulsa, OK; Año: 2018 vol. 88 p. 24 - 37

1527-1404

Reticulate patterns often found in siliciclastic rocks may have been associated with or the product of biological activity. They are also present in modern environments, and laboratory experiments have elucidated the role of filamentous cyanobacteria in their formation, thus considering these microbes putatively as ecosystem engineers. The present study traces the evolution of reticulate structures in situ in a modern siliciclastic coastal sedimentary basin for over a year, under different hydrodynamic conditions. The results give new insights on the parameters involved in the formation and preservation of these microbial structures. Field-observations documented the development of millimeter-size microbial reticulate structures with specific geometries. They were found in temporary ponds starting from 2-dimensional submerged laminated cyanobacterial mats, and ultimately creating 3-dimensional protruding tufts and pinnacles in junctional positions after their desiccation. Microbial reticulates were formed 4 days after a storm flooding and 2 days after seawater vacated the area under calm conditions, by virtue of the motility of filamentous cyanobacteria. Through their subsequent consolidation they can be maintained in the form of reticulate structures and tufts for extended periods (months). These structures were found sharing an area with deformation sedimentary structures such as folds, roll-ups and ripped microbial mats, formed under high energy. Therefore, calm settings such as those created by a shallow water lamina seem to be a requisite for the formation of microbial reticulates, but once they become established, they can withstand high-energy hydrodynamic regimes. Our observations of modern structures and the sequential in situ study of their evolution provide linking references to laboratory and rock-record microbial reticulates aiding in paleoenvironmental reconstruction.