CONTRIBUTION OF CARBONATE PRECIPITATION TO THE PRESERVATION OF RIPPLES IN SILICICLASTIC SEDIMENTS COLONIZED BY MICROORGANISMS

QUIJADA EMMA I.; GOMEZ, E. A.; PERILLO, V. L.; MAISANO, L.; RANIOLO, LUÍS ARIÉL

latin american journal of sedimentology

Asociación Argentina de Sedimentología

Lugar: La Plata; Año: 2021 vol. 28 p. 119 - 130

1669-7316

The present study documents the biostabilization and early lithification of ripplemarks created during high-energy hydrodynamic events in a coastal environmentcolonized by microbial mats. The presence of microorganisms and theircharacteristic secretion of exopolymeric substances (EPS) are biological factorsthat diminish the sediment permeability, a first step to maintain seawater over thesediment. Subsequently, seawater is evaporated causing an increase in salinitythat leads to the precipitation of calcite and gypsum. The calcite precipitationcovering the microbial mat and ripple marks is documented in detail. The studywas conducted in Paso Seco (40°38’40’’S; 62°12’22’’W), a modern coastal flat withinan elongated semi-closed basin colonized by microbial mats frequently inundated.Salinity was measured in different ponds in the flat with different degrees ofevaporation, and in a tidal creek. Water samples were analysed to determineCa2+, CO32- and SO42- concentrations. Seawater level fluctuations relative to thetidal flat were measured through a 10-month period in 2018 using a HOBO waterlevel logger. Ripple field formation over the tidal flat was documented after theoccurrence of a severe storm and was monitored throughout three field trips. Sixmonths after the formation of the ripples, a sedimentary block containing theirvertical section was taken to perform petrographic studies. A laterally continuousdense micritic calcite layer, 100–200 μm in thickness, was identified coveringripple structures, improving the immobilization of these bedforms, and promotingtheir early lithification. Our observations of modern sedimentary structures andthe in situ study of their evolution and early lithification may be potentially usefulto be taken into account for the interpretation of similar sedimentary structures inthe geological record.