Sequence Stratigraphy of Continental Rift Basins I: A Conceptual Discussion of Discrepant Models

Abstract

Due to the asymmetry of half-grabens and their subsidence controlled by a single major boundary fault, the creation of accommodation space in a rift basin is variable; therefore, the traditional scheme of sequence stratigraphy is not applicable. The present paper discusses this issue, emphasizing the controversy about the initiation of a rift: some authors propose that the onset of a rift is marked by rapid subsidence and the creation of large accommodation, whereas others argue for a slow subsidence regime and consequent low accommodation rates. This paper offers an integrative approach, based on the fact that the initiation of a rift is characterized by isolated and restricted faults that create incipient half-grabens. Towards the phase of rift climax, the initial rift faults tend to link, and form a larger and deeper depositional area, hence developing lacustrine facies with an overall retrogradational trend. Therefore, in some parts of the basin, rift onset is characterized by fluvial sandstone, whereas the basal lacustrine mudstones found in other parts of the rift basin register an already more advanced rift phase. When the rifting ends, the accommodation rate decreases and the sedimentation regime becomes progradational, and the rift basin is filled with fluvial, deltaic, and aeolian facies.