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 fades, 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 rnsequence 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 foot wall, 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.%Termit盆地位于尼日尔东南部,属于西非裂谷系的北延部分,是发育于前寒武系-侏罗系基底之上的中、新生代裂谷盆地.该盆地早白垩世-古近纪经历了“裂谷-坳陷-裂谷”的构造演化过程及“陆相-海相-陆相”的沉积演化过程,表现为晚白垩世大规模海侵、早白垩世和古近纪两期裂谷叠置的特点.基于构造作用影响裂谷盆地层序发育的观点,分析了Termit盆地下白垩统裂谷阶段内的层序地层充填样式.根据裂谷作用的强弱,将早白垩世裂谷阶段划分为裂谷初始期、裂谷深陷期及裂谷萎缩期3个阶段.裂谷初始期层序断裂活动弱,构造沉降小,长轴物源体系较为发育,陡坡带为加积至退积型河流或三角洲沉积,缓坡带发育加积型河流或三角洲体系.裂谷深陷期层序断裂活动强烈,构造沉降大,陡坡带形成退积型水下扇或滑塌扇沉积,缓坡带发育退积型三角洲体系,盆地中心为泥岩充填.裂谷萎缩期层序断裂活动减弱并趋于停止,陡坡带为进积型扇三角洲沉积,缓坡带发育进积型三角洲体系.研究表明:裂谷作用对层序地层充填样式具有明显的控制作用,以构造作用为主线的裂谷盆地层序地层分析方法,能有效预测沉积体系和储层分布.
展开▼
