Tectonism and sedimentation in the southwestern portion of the Potiguar Rift - onshore Potiguar Basin, Brazil

Abstract

Through an integrated approach, using lithostratigraphic, chronostratigraphic and biostratigraphic data the relative importance of climatic variations and tectonics has been recognized in rift sediments of the onshore Potiguar Basin, Northeast Brazil. Sequence stratigraphy concepts have been applied as a template to integrate sedimentological, geochemical (oxygen isotopes) and biostratigraphic (quantitative palynology) data, as well as backstripping and sedimentary basin modeling techniques to address and recognize the main depositional patterns produced in a rift basin. The main objective is to istinguish the effects of climatic changes and tectonics to the resulting stratigraphic architecture. The studied section includes a Late ValanginianEarly Barremian (Lower Cretaceous) rift interval from the Pendência Formation, located in the southwestern portion of Umbuzeiro Graben in the onshore Potiguar Basin. The depositional setting is interpreted as a progradational fluvial-deltaic system entering a lake through its flexural margin. Seismic stratigraphic and well logs analysis provided an interpretation of two regressive intervals (Green and Yellow sequences), separated by a broad transgressive interval (Orange Sequence), known as the Livramento Shale. The depositional history encompasses three stages: two tectonically active phases, during the deposition of the Green and Yellow sequences, and a tectonically quiescent phase, during the deposition of the Orange Sequence. Paleoclimatic interpretation, based on quantitative palynology and geochemical data (δ18O), suggests a tendency to arid conditions during the tectonically active phases and wet conditions during the tectonically quiescent phase.