Análise Quimioestratigráfica da Formação Salitre e a contribuição da organomineralização nos depósitos microbianos na Chapada Diamantina (BA)

Abstract

The study on the biogenicity of organostructures increasingly relies on the improvement of new techniques to investigate the biosphere-mineral interface, especially regarding geomicrobiology, which feeds the debates on the extent to which microorganisms participate and how biotic processes leave their mark on the fossil record. In view of their excellent exposures, the proterozoic carbonates of the Salitre Formation (Una Group), found in the Chapada Diamantina region, Várzea Nova city (Bahia), were the target of this thesis, which focused on the deepening of the evidences of processes of organomineralization perceptible at various scales of work. For this, a study was carried out in three scales (field, reservoir and detail) aiming: i) a better stratigraphic-structural characterization of the study area; ii) to understand the depositional physicochemical conditions of the Salitre Basin through the study of geochemical proxies (isotopes and trace elements) carried out in core samples from two shallow wells; iii) and to investigate traces of life and their influence on the construction of the organostructures as well as their alterations. In the Neoproterozoic context, this approach makes reference to depositional environment of the diamictites and the overlying carbonates, in other words, if they represent great climatic changes or if they are witness of tectonic processes associated to the opening of a rift system, within the supercontinent Rodinia. From the interpretation of field and chemostatigraphic data obtained in samples of two drilling holes, it is suggested that the diamictites can represent gravitational fluxes in a structural channel reworked in marine environment and that the overlapped carbonates were deposited under conditions of restriction of the basin, hence anoxia, and that in this scenario, possibly a great part of the carbonates may be the result of the influence of a consortium of sulfate reducing bacteria and methanogenic archaeas. These conclusions are made based on the geochemical proxies, on the interpretation of microstructures and also on evidence of trace of life