The Sedimentary System Of Upper Cretaceous In Termit Basin, Niger

The Termit Basin is located in the southeastern Niger and is part of the East Niger Rift Basin in Central and West African Rift System(CWARS).It shows good hydrocarbon exploration prospects due to its oil and gas discoveries in recent years.However,the study area is still in low degree of exploration and has complex geological conditions.Moreover,the well location is unevenly distributed,and the quality of seismic data is poor and lead to the disagreement of provenance and sedimentary system which restricts further exploration of the basin.Based on the theory of sequence stratigraphy and sedimentology,and comprehensive utilize the logging,geochemistry and seismic data,we analyzed the sequence stratigraphic,provenance and sedimentary system of the Upper Cretaceous(Donga and Yogou)in Termit Basin.The Upper Cretaceous(Donga and Yogou)can be divided into 5 third-order sequences,among which Donga Formation could be divided into 2 third-order sequences of DS1~DS2 and Yogou Formation could be divided into 3 third-order sequences of YS1~YS3.We further clarified that the center of Termit Basin is the thickest and the eastern part of study area is thicker than the western.Moreover,the sequence YS3 shows greater differences.We restore the paleogeomorphy of Yogou Formation by eliminating the impacts of the denudation and compaction.The study shows that the paleogeomorphy is very different from the present geomorphy: the original sedimentary thickness of Yogou Formation is thickest in the western part of the basin.By comprehensively utilizing the regional sedimentary background analysis,geochemical analysis(oxidation-reduction conditions and organic matter type)and seismic reflection character,we confirmed that the study area is in the background of the shallow continental shelf during the late Cretaceous.It is further clarified that the source of the Late Cretaceous(Donga and Yogou)sediments in the study area are from the northeast.It indicates that the study area during Late Cretaceous mainly develops delta and shallow continental shelf sedimentary facies.The delta facies can further identify two kinds of sedimentary subfacies(delta front and predelta)and six kinds of sedimentary microfacies(subaqueous distributary channel,distributary mouth bar,distal bar,sheetsand,subaqueous distributary channel mud and predelta mud),which is mainly developed in the eastern part of the study area.The shallow continental shelf can further identify two kinds of sedimentary subfacies(inner continental shelf and outer continental shelf)and four kinds of sedimentary microfacies(storm dunes,storms sheets,inner continental shelf mud and outer continental shelf mud),mainly developing in the middle and west of the study area.On this basis,we established the sedimentary facies model of study area.