Stratigraphic and sedimentological models of rift basins

Abstract

This chapter reviews models for the stratigraphic and sedimentological evolution of rift basins at the basin scale and at the half-graben or facies model scale. Different models have been presented for the geotec- tonic evolution of rifts (pure shear, simple shear, heterogeneous stretching and volcanic- or plume-related rifts) and these are reviewed. The different stratigraphic signatures of each of these geotectonic models are discussed in terms of the nature and the occurrence of pre-rift strata, syn-rift unconformity, syn-rift strata, post-rift unconformity and post-rift strata. This simple stratigraphic analysis reveals that each geotectonic model should have a unique stratigraphic signature that has not been previously documented. The stratigraphic signatures of the Gulf of Suez, Red Sea and Gulf of Aden are reviewed and compared with the geotectonic models previously proposed for these basins. It is concluded that the pure shear model is applicable to all basins and that the southern Red Sea is modified by plume-related volcanism.

Rift basins are reviewed at the half-graben or facies model scale where recent advances in structural and sedimentary geology have revealed a complex and evolving three-dimensional template for erosion, sediment production, sediment transport and deposition. New facies models for the tectono-sedimentological evolution of rift basins are proposed in the light of the three-dimensional structural models. Recent work ap plying sequence stratigraphic concepts to rift basins is reviewed which illustrates that the recognition and nature of depositional sequences at a variety of scales gives important information on the tectono-sedimentary evolution of rift basins. These include the timing and style of fault movement, the complexity of relative sea- level changes on rotating fault blocks and transfer zones, and the temporal and spatial isolation of clastic and carbonate facies associations in depositional sequences.