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

RODRIGUEZ, MAXIMILIANO NICOLÁS; CAMPETELLA, DÉBORA MICAL; CARMONA, NOELIA BEATRIZ; PONCE, JUAN JOSÉ; PARADA, MARTÍN NAZARENO

GEOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2023

1472-4677

This contribution presents the first study focused on the analysis of microbial matsin the Los Molles Formation (Toarcian – Early Callovian), Neuquén Basin, Argentina.This unit mainly represents offshore-to-shelf environments affected by storms anddensity currents. The Los Molles Formation is one of the oldest source rocks in theNeuquén Basin and constitutes an unconventional shale gas reservoir of great economicimportance. The aim of this work was to identify the microbial activity from thedescription and interpretation of microbially induced sedimentary structures (MISS),to determine the paleoenvironmental and paleoecological conditions under whichthey formed, and to establish a possible relationship between these structures andthe trace fossil Trichichnus. Samples from the levels with MISS were analyzed anddescribed from macroscopic and binocular observations, petrographic microscopethin sections, and SEM samples with EDS analyses. The results showed several levelsof microbial mats presenting diverse MISS, including biolaminations and Kinneyia-likewrinkles structures that were described at the macroscopic level. In thin sections,biolaminations, filament-like microstructures with different degrees of development,oriented grains and pyrite were observed. SEM images and EDS analyses showeddifferent 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. The abundance of the trace fossilTrichichnus sp. throughout the section and the proximity to some Kinneyia-like wrinklestructures levels suggests that the same organisms may have generated them.Furthermore, they revealed that the Los Molles Formation, at the time of its deposition,experienced paleoecological and paleoenvironmental conditions appropriate forthe establishment and development of microbial mats. The extensive levels of microbialmats in the study area suggest that they may have been a source of organic matterfor the generation of hydrocarbons from the Los Molles Formation.