Sequence Stratigraphy of Rift Successions - A Conceptual Model

Due to the basins asymmetry and the subsidence controlled by one major fault zone, the accommodation space within a rift basin is variable, and the popular passive-margin-based sequence stratigraphic scheme, where depositional systems tracts develop following a predictable order during a complete cycle of base-level change, is not applicable. For a practical and useful stratigraphic analysis of rift basins, conceptual and methodological adaptations are required. The present paper discusses and exemplifies these adaptations, proposing an integrative sequence stratigraphic conceptual model with two different scenarios (gradual and punctuated subsidence) and defining three tectono-stratigraphic phases: (1) the rift initiation phase, which is characterized by isolated and restricted faults which create incipient half-grabens, infilled with fluvial and deltaic facies; (2) the rift development phase, during which the initial rift faults tend to link and to form a larger and deeper depositional area, recording lacustrine facies with an overall retrogradational trend, and; (3) rift termination phase, when the accommodation decreases, the sedimentation regime is progradational, and the rift basin is filled with fluvio-deltaic and eolian facies. The model is illustrated with examples from two adjacent rift basins from the northeastern region of Brazil, the RecÔncavo and Camamu basins.