Descrição de localidades fossilíferas e distribuição estratigráfica de macro e microfósseis no cretáceo da bacia sanfranciscana a leste do Rio São Francisco

Abstract

The Sanfranciscana Basin comprises one of Brazil's most extensive sedimentary deposits, mainly encompassing glacial rocks from the Carboniferous-Permian period and Cretaceous strata formed in various fluvial, lacustrine, desert, and volcanic contexts. Its location within the São Francisco Craton and its age make it an important window for understanding the evolution of environments and their biotas during the Mesozoic Era in the central portions of Western Gondwana. This relevance has attained global significance, primarily due to recent paleontological discoveries, such as a rich fauna of crustaceans, annelids, fish, lizards, and dinosaurs. While the outcrops of the Sanfranciscana Basin in the central-west region of the State of Minas Gerais have been studied in detail over the last fifty years, the exposures occurring east of the São Francisco River in the northern part of the state remain poorly known. In this regard, this dissertation aims to describe two fossiliferous localities in the municipality of Lagoa dos Patos, which have been the subject of preliminary studies regarding their paleontological potential, reporting the occurrence of fossils and providing such data for lithostratigraphic and biostratigraphic correlations. By means of field surveys and the construction of geological profiles, the localities were analyzed concerning their sedimentary facies, revealing the occurrence of different depositional environments, such as low-energy lakes, ephemeral rivers in arid settings, and fluvio-deltaic environments under aeolic influenced. These environmental changes are fundamental to understanding the geological evolution of the region and its interactions with climatic factors. The faciological characteristics are similar to those of the Quiricó Formation in the southwestern portion of the Sanfranciscana Basin (Mata da Corda Plateau region), although the fossil record is different. A significant amount of ostracods was collected with strict stratigraphic control, allowing the recognition of at least one yet undescribed genus for the Sanfranciscana Basin. Charophyte algae, Skolithos ichnofossils, lepisosteid fish scales, dinosaur teeth, and bones were also recovered and positioned in the geological column of the localities. The association of ostracods and charophytes allows the recognition of an oligohaline environment, possibly paralic. Furthermore, the Ilyocypris-Fossocytheridea ostracod association suggests that the stratigraphic horizons of the region are more recent than those of the Quiricó Formation cropping out in the Mata da Corda Plateau, as also suggested for the occurrence of vertebrates. As discussed, the obtained results have important implications not only for the studied region but also for the understanding of geological and biological processes throughout the Sanfranciscana Basin.