Bioestratigrafia e interpretação paleoambiental da formação Tremembé – Bacia de Taubaté/SP

Abstract

Rock samples of outcrops from the mining companies Extrativa Santa Fé Ltda and Aligra - Indústria e Comércio de Argila Ltda provided the base material for this investigation into palynological, palynofaciological and organic geochemistry analyses of the Taubaté Basin, São Paulo State. The sediments belong to the Tremembé Formation and comprise microclastic rocks. The Tremembé Formation is known for its rich fossil record and clay mineral content, widely used as raw material for various industrial processes. The generating potential of the sediments was evaluated through qualitative and quantitative analyses of organic content, percentage of total organic carbon (TOC), and Rock-Eval pyrolysis. Furthermore, using transmitted light optical microscopy, observation of the palynological content allowed the identification of characteristic species in terms of age and thermal maturation through the Spore Color Index (SCI) and depositional paleoenvironment. Palynofacies were individualized via reflected light optical microscopy, and together with Rock-Eval pyrolysis data, the quality and type of kerogen were determined. The organic content of the two mining companies shows a predominance of amorphous, globose, and dispersed organic matter of lacustrine origin. Moreover, it is composed mainly of the genera Botryococcus and Pediastrum algae. Palynological associations allowed the section to be temporally positioned in the Oligocene. The abundance of bisaccate pollen grains attributable to conifers, represented mainly by the species Podocarpidites marwickii and Dacrydiumites florinii, combined with the presence of spores, suggests a temperate paleoclimate with humid niche conditions. The pyrolysis results and microscopic observation of the organic content in fluorescence mode show that deposition occurred under anoxic conditions, allowing better preservation of organic matter with high potential for generating hydrocarbons. The clay minerals analyzed using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques with an EDS coupled device, characterized as detrital, originating from the leptinitic gneiss of Paraíba, gave rise to mixed clays with montmorillonite-kaolinite constitution. The result of this combination of clay minerals defines a climatic event with alternating rainy and warmer periods, characterized by well-defined seasons, typical of a temperate climate. Furthermore, it is believed that the erosion caused by the steep relief existing in the area was more pronounced due to these specific climatic conditions. Therefore, the combination of palynological, palynofaciological, organic geochemical and mineralogical data clearly demarcates the paleoenvironment and paleoclimate of the studied sections.