乍得Doseo盆地东部坳陷下白垩统Kedeni组层序地层格架与沉积体系分布OA北大核心CSTPCD

A significant breakthrough has been made in hydrocarbon exploration in the Kedeni For-mation of the Doseo Basin in the Central African Rift System.However,the stratigraphy and sedimentary infill of this dominant formation are still unclear,which has become a key constraint for the next step of hydrocarbon exploration.In this study,the Kedeni Formation in the Eastern Depression of Doseo Basin is taken as the research object.Based on the theory of seismic stratigraphy and sedimentology,combined with the core,logging and seismic data,the sequence stratigraphic framework and sedimentary system distribution of Kedeni Formation are clarified.The research results demonstrate that the Kedeni Formation exhibits three identifiable sequence interfaces,dividing into two third-order sequences(SQ Ⅰ and SQ Ⅱ),in response to two'transgressive-regressive'cycles.The sediments of Kedeni Formation mainly came from four directions,and six types of sedimentary facies were developed.Distribution of sedimentary facies was characterized by east-west differentiation and features of vertical inheritance.Normal delta were distributed in the southeastern gentle slope zone and the central low uplift zone,whereas the braided river delta were primarily distributed in the long axis direction of the northeast and the southern steep slope zone.The fan delta and the nearshore subaqueous fan developed in the downthrown side of the boundary fault in the northern steep slope zone.The sublacustrine fan were mainly distributed in the deep lake area of the western sag.Vertically,the framework sandstone scale of the SQ Ⅰ was larger than that of the SQ Ⅱ,and in each third-order sequence,the delta-subaqueous fan was more developed in the lower unit composed of a lowstand system tract and a transgressive system tract.The sequence and sedimentary evolution of the Kedeni Formation were primarily controlled by factors such as the structural activity of major faults,differ-ential sediment supply from the south to the north,and shifts in climate from semi-arid to humid condi-tions.Under the guidance of sequence-sedimentary model,it is considered that the small-scale fan delta front-nearshore subaqueous fan sandstone in the northern steep-slope zone,the large-scale normal delta front and braided river delta front sandstone in the south and northeast,and the sublacustrine fan sand-stone in the deep lake area of the western sag can be regarded as favorable exploration targets within the re-gion.