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
Maximiliano Nicolás Rodriguez, Débora Mical Campetella, Noelia Beatriz Carmona, Juan José Ponce, Martín Nazareno Parada
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引用次数: 0
Abstract
This contribution presents the first study focused on the analysis of microbial mats in the Los Molles Formation (Toarcian – Early Callovian), Neuquén Basin, Argentina. This unit mainly represents 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 microbially 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 and Kinneyia-like wrinkles 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 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. The abundance of the trace fossil Trichichnus sp. throughout the section and the proximity to some Kinneyia-like wrinkle structures 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 for the establishment and development of microbial mats. The extensive levels of microbial mats in the study area suggest that they may have been a source of organic matter for the generation of hydrocarbons from the Los Molles Formation.
期刊介绍:
The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time.
Geobiology invites submission of high-quality articles in the following areas:
Origins and evolution of life
Co-evolution of the atmosphere, hydrosphere and biosphere
The sedimentary rock record and geobiology of critical intervals
Paleobiology and evolutionary ecology
Biogeochemistry and global elemental cycles
Microbe-mineral interactions
Biomarkers
Molecular ecology and phylogenetics.