Dados da Submissão

Título

Pelotas Basin from Cretaceous to Miocene – a provenance study through the time

Texto do resumo

Siliciclastic sediments and sedimentary rocks act as historical recorders, chronicling the evolution of their source areas and significant episodes of paleogeographic history. Based on the identification of source rocks, the tectonic history of the region can be reconstructed, including processes that control sediment erosion and deposition. Developing this study on the South American passive margin can elucidate the processes that controlled basin evolution over time. Pelotas Basin offers invaluable insights into the geological development of the South Atlantic Ocean since the Cretaceous, covering 125 million years of provenance evolution. This study focuses on closing this gap in the provenance history, as only recent deposits from the Holocene and Pleistocene have been studied in the onshore Pelotas Basin. To enhance the understanding, we employed a comprehensive methodology incorporating petrography, whole-rock geochemistry, and U-Pb provenance analysis. Understanding the mineralogy, the composition of the sediments and sedimentary rocks, and the determination of individual zircon grain ages offer crucial information about the source areas of the deposits. All samples analyzed were obtained from core and cutting samples from eight wells in the Pelotas Basin. The age of deposition was determined according to the proposed chronostratigraphic framework based on literature and seismic analyses of the basin. The results obtained until now show, in the Neogene deposits, the presence of zircon grains with ages compatible with the Andean Orogeny, already known for coastal deposits. This presence is even more pronounced in the younger samples. Additionally, there is a widespread occurrence of Brasiliano-aged zircons (500 to 700 Ma peaks), which predominantly consist of granitic sources that could contribute to high-quality reservoirs. In the Paleogene and Upper Cretaceous deposits up to the Coniacian, the provenance reflects different sources identified in the Sul-Rio-Grandense and Uruguayan shields, as supported by whole-rock geochemistry studies. This indicates the presence of various sources, including igneous and metamorphic rocks and the Paraná Basin. Samples from the Turonian, Albian, and Aptian ages exhibit provenance signals that closely resemble those found in the Paraná Basin deposits. This suggests these deposits were likely denuded and eroded after the Gondwana breakup and redeposited in the Pelotas Basin. This finding is particularly relevant for assessing reservoir quality. The identification of various source areas and the implications for reservoir quality underscore the significance of this study in the broader context of South Atlantic geological research.

Palavras Chave

Source-to-sink; Pelotas Basin; South American passive margin.