Investigação da origem microbial em rochas da formação Irati por meio de análise petrográfica

Abstract

Black shales represent an important moment of lack of oxygen on the seabed and, because of this, have great economic relevance, since they are the main sources of oil and gas. Although several studies indicate that these types of deposits have complex characteristics about their genesis, the controlling factors of shale generation are quite detailed. However, studies from the descriptive point of view of the interactions between microorganisms and the substrate are still few. Given this importance, this study sought to understand the microbial action in the genesis of black shales of the Irati Formation in the South of the Paraná Basin, during the lower Permian (Cisuraline). The Irati Formation constitutes thick layers of shaleded in an epicontinental sea with fluctuations in salinity and oxygenation of the substrate. From the qualitative petrographic analysis of 16 slides, it was possible to identify and characterize the microbial features and their forms of interaction with sedimentary particles. The main features found were load behavior structure, wavy-crinkly growth structure, trapping plots – baffing and trapping, roll-up structures, and fenestral lamination. The analysis of these structures provides better assimilation of the relationship between microbial mats and geological conditions related to the history of their depositional environment.