Changes in the stratigraphic architecture as the response to the Upper Cretaceous tectonic and climatic interplay in the Sanfranciscana Basin, Brazil

Abstract

During the Cretaceous, the Brazilian Intracratonic Sanfranciscana Basin was characterised by fluvial and aeolian deposition, whose facies, palaeosols, and stratigraphic architecture indicate significant changes in tectonics and climate. This work proposes a low-frequency sequence stratigraphic model, using the facies and palaeosols distribution as the stratigraphic proxy for identifying variations in the accommodation space, sediment supply, and their relationship with the tectonic and climatic events. The Unconformity U-0 was generated by the extensional tectonic processes during the Gondwana breakup in the Early Cretaceous and marked the initial continental sedimentation. The Lower Cretaceous Sequence SF1 overlies this unconformity, constituted by fluvial and lacustrine deposits. From south to north, the unconformity U-1 truncates the top of the Lower Cretaceous Sequence SF1 and the Precambrian basement, respectively. Overlaying Unconformity U-1 are the Upper Cretaceous volcanic rocks, fluvial, and aeolian deposits of the Sequence SF2. Because of the vertical and lateral changes, Sequence SF2 is divided into two sequences, SF2A and SF2B, separated by the regional Unconformity U-2, representing climatic and tectonic changes in the basin. During the late stage of sedimentation of Sequence SF1, the ratio between accommodation (A) and sediment supply (S) was positive in the south and negative in the basin's north. The evolution of Sequence SF2A records a negative A/S ratio, followed by an abrupt change to a positive A/S ratio in Sequence SF2B, leading to the genesis of the regional erosive surface of Unconformity U-2. Sequence SF2B also records increased humidity from arid climatic conditions, marked by the 3D regional distribution of facies and palaeosols, linked to the climatic changes detected in South America for the Late Cretaceous.