Microbial mats in the Río Mayer Formation (Lower Cretaceous), Austral Basin, Argentina: Paleoenvironmental and paleoceanographic significance

ABSTRACT This contribution focuses on studying microbial mats in the Lower Cretaceous marine succession of the Río Mayer Formation, at Estancia Cristina locality, Austral Basin, Argentina. This formation has been the subject of increasing study in recent years due to its potential as an unconventional reservoir and ongoing exploration efforts. The main purpose of this work was to identify the occurrence of microbial activity from the characterisation and interpretation of microbially induced sedimentary structures (MISS), and to integrate this information with sedimentological and ichnological data to determine the paleoenvironmental and paleoecological conditions under which they formed. Macro‐and microscopic studies done in the field and in the laboratory allowed us to identify different MISS, such as biolaminations, wrinkle structures, microbial remnants, layers with pyrite enrichment and sponge pore fabric. In SEM images, it was also possible to identify filaments and levels with fossilised extracellular polymeric substances (EPS). Four main facies associations (FA1–FA4), representing upper to lower offshore, inner shelf, inner shelf to upper offshore, and lower offshore, respectively, have been recognised in this section. Combined sedimentological, ichnological and geobiological analysis allowed us to infer that upwelling processes acted in the Austral Basin during the deposition of this formation. In addition, it is also discussed that the extensive occurrence of microbial mats in the basin may have helped preserve and provide, at least partially, the organic matter that led to the generation of hydrocarbons in the Río Mayer Formation.