Caracterização palinológica, palinofaciológica e de geoquímica orgânica da formação urucutuca - cretáceo superior da bacia de Almada, NE - Brasil

Abstract

The main objective of this thesis was to conduct an integrated study on palynology, palynofacies, and organic geochemistry (TOC and Rock-Eval Pyrolysis) of the section corresponding to the Neocretaceous portion of the Urucutuca Formation. Regionally, it corresponds to the transgressive marine stage in the tectono-sedimentary evolution of the basins on the Brazilian eastern margin. Due to its broad temporal distribution, its characterization is of great importance, which was developed for the Almada Basin through the analysis of 56 samples from two continuous core wells (SST-02 and SST-03), drilled in the onshore portion of the basin. From the analysis of the palynofloristic association, 11 species of pollen grains, 8 species of spores, 12 species of dinoflagellates, 2 genera of freshwater algae, and 1 genus of marine algae were identified. The quantitative evaluation of the palynomorphs showed the predominance of elements of continental origin. Results from the palynological analysis allowed the recognition of the palynozone Tricornites elongatus through the occurrence of species Palaeocystodinium lidiae, Dinogymnium acuminatum, Tricornites elongatus, Cricotriporites almadensis, and Crassitricolporites brasiliensis. It is noteworthy that this biochronological unit is part of the zonation in the other basins along the Brazilian eastern coast. The palynological association enabled the placement of the two cores in the Upper Maastrichtian interval. Through the characterization of organic matter using palynofacies analyses combined with organic geochemical data, it was possible to differentiate 2 types of palynofacies, quite similar between the two cores. Palynofacies 1 is characterized by the predominant presence of the phytoclast group – 67% and 73%; followed by amorphous organic matter (AOM) with 28% and 25%, and the palynomorphs comprising only 5% and 2% on average in the SST-02 and SST-03 wells, respectively. Palynofacies 2 shows AOM as the main constituent group (64% and 67%); phytoclasts occupy the second most abundant group (31% and 30%), and palynomorphs reach 5% and 3% on average for SST-02 and SST-03, respectively. TOC values ranged from poor to good for both wells, with values between 0.32% and 1.42% for SST-02 and 0.11% and 1.37% for SST-03. Rock-Eval pyrolysis data indicated poor generating potential and Type IV organic matter. A migratory trend was interpreted in the depositional paleoenvironment of the sediments, from a dysoxic-anoxic marginal basin transitioning to a suboxic-anoxic/restricted marine distal basin. The base of the sections is predominantly composed of terrigenous elements, while the top is mainly formed by amorphous organic matter. This study, with the extensive palynological analysis integrated with palynofacies and organic geochemistry, contributes to the expansion and clarification of the bioestratigraphic framework and depositional paleoenvironment of the Almada Basin, providing an interaction and debate between the results obtained and the data already published.