MICROBIAL MATS AND THEIR PALAEOENVIRONMENTAL ANALYSIS IN OFFSHORE – SHELF FACIES OF THE LOS MOLLES FORMATION (TOARCIAN – LOWER CALLOVIAN) IN THE CHACAY MELEHUE AREA, NEUQUÉN BASIN, ARGENTINA

RODRÍGUEZ MAXIMILIANO NICOLÁS; CAMPETELLA DEBORA MICAL; CARMONA NOELIA BEATRIZ; JUAN JOSE PONCE; MARTIN NAZARENO PARADA

GEOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2022

1472-4677

This contribution presents the first study focused on the analysis of microbial mats in the Los Molles Formation (Toarcian - Early Callovian), in deposits representing offshore to shelf environments affected by storms and density currents. The Los Molles Formation is one of the oldest source rocks in the Neuquén Basin and constitutes an unconventional shale gas reservoir of great economic importance. The aim of this work was to identify the microbial activity from the description and interpretation of microbial induced sedimentary structures (MISS), to determine the paleoenvironmental and paleoecological conditions under which they formed, and to establish a possible relationship between these structures and the trace fossil Trichichnus. Samples from the levels with MISS were analyzed and described from macroscopic and binocular observations, petrographic microscope thin sections, and SEM samples with EDS analyses. The results showed several levels of microbial mats presenting diverse MISS, including biolaminations, pinnacles and Kinneyia-like wrinkles structures that were described at the macroscopic level. In thin sections, biolaminations, filaments with different degrees of development, oriented grains and pyrite were observed. SEM images and EDS analyses showed different types of filaments, coccoids and EPS with high concentrations of carbon. These results revealed that the studied levels fulfill the established biogenicity criteria, guaranteeing that they have a bacterial origin and a possible link to the organisms that produced the trace fossil Trichichnus that co-occurs in these levels. Furthermore, they revealed that the Los Molles Formation, at the time of its deposition, experienced paleoecological and paleoenvironmental conditions appropriate for the establishment and development of microbial mats.