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 Cretaceousmarine succession of the Rıo Mayer Formation, at Estancia Cristinalocality, Austral Basin, Argentina. This formation has been the subject ofincreasing study in recent years due to its potential as an unconventionalreservoir and ongoing exploration efforts. The main purpose of this workwas to identify the occurrence of microbial activity from the characterisationand interpretation of microbially induced sedimentary structures (MISS),and to integrate this information with sedimentological and ichnologicaldata to determine the paleoenvironmental and paleoecological conditionsunder which they formed. Macro-and microscopic studies done in the fieldand in the laboratory allowed us to identify different MISS, such as biolaminations,wrinkle structures, microbial remnants, layers with pyrite enrichmentand sponge pore fabric. In SEM images, it was also possible to identifyfilaments 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 upwellingprocesses acted in the Austral Basin during the deposition of this formation.In addition, it is also discussed that the extensive occurrence of microbialmats in the basin may have helped preserve and provide, at least partially,the organic matter that led to the generation of hydrocarbons in the RıoMayer Formation.