Abstract:

The Termit basin, which is located in the southeastern Niger and belongs to the northern part of West African rift system, is a Mesozoic-Cenozoic rift basin developed on the Precambrian-Jurassic basement. It is characterized by a great transgression and superimposition of two phases rifting. Its tectonic evolution experiences rifting, sag, rifting, with sedimentary evolution showing nonmarine facies, marine facies, nonmarine facies in the Early Cretaceous, Late Cretaceous and Paleogene, respectively. The sequence stratigraphic architecture of the Lower Cretaceous rifting of Termit basin is analyzed based on tectonic controls on strata development. The evolution of rifting can be divided into three phases that are rift initiation, rift climax and rift recession. Each phase is characterized by unique sequence stratigraphic architecture in response to difference of fault movement. The small increment of fault movement in rift initiation sequence causes a small subsidence, and the fault scarp has not been eroded. Aggradational to retrogradational longitudinal fluvial or delta will respond in footwall, and aggradational fluvial or delta will deposit in hangingwall. Rift climax sequence is characterized by strong fault movement. The footwall is deposited by retrogradational subaqueous fan, and the hangingwall is dominated by retrogradational delta due to the more subsidence and less sediment supply. Fault movement becomes weak and trends to cease in rift recession sequence. Progradational fan delta is developed in the footwall, and progradational delta is deposited in the hangingwall. This study indicates that sequence stratigraphic architecture of rift basin is greatly controlled by rifting. The sequence stratigraphic analyses based on the tectonic evolution of rift basin can predict distribution of depositional systems effectively.

Key words: rift basin, rifting phase, sequence stratigraphic architecture, Termit basin, West African rift system, sediments