Geomorphic Evolution of a Continental Slope in a Delta Reformed Passive Continental Margin Basin:A case study of a deep-water zone in the Niger Delta Basin
[Objective]Continental slopes have become a major focus in petroleum exploration because of their enor-mous sediment and hydrocarbon potential. Research on the geomorphic evolution of continental slopes contributes to deep-water sedimentology and petroleum exploration. This paper focused on the abundant terrigenous supply of a con-tinental slope in a delta reformed passive continental margin basin. A new methodology for the restoration of ancient slope geomorphic evolution based on the principle of depositional architecture was discussed.[Methods]Taking a study area on a continental slope in Niger Delta Basin as an example,seismic,logging,and core data were compre-hensively applied to reveal the geomorphic evolution characteristics of the continental slope based on the spatio-temporal evolution of depositional architecture in 13 sequences.[Results]The geomorphic evolution of the study area can be divided into 2 stages. In stage 1,study area transformed from an abyssal plain to continental slope,and the landform was unrestricted. The geomorphic evolution in this stage was driven by the progradation of large deltas. The geomorphic evolution in stage 2 included 3 periods dominated by thrust faults,mud-diapirs,and sedimentation. The landform evolved gradually from restricted to semi-restricted and then to the present non-restricted type. The geo-morphic evolution in stage 2 was controlled by gravity sliding. During the thrust faulting,the activity intensity of the underlying flowing mudstone was limited,and the landform was controlled by thrust faults. The study area was located in the remote thrust province of a gravity sliding system. During the mud-diapir period,the intensity of diaper activity increased significantly and was able to change the geomorphic characteristics independently. As a result,the topogra-phy of study area began to transform from a thrust to mud-diapir province.[Conclusions]The gravity sliding structur-al system was driven by sedimentary processes,and its spatial combination and evolution characteristics were similar to sedimentary facies. The adjacent extensional,mud-diapir and thrust province were closely related in genesis,which was similar to a sequential sedimentary facies. Therefore,the vertical superposition relationship of different structural activities indicated the macro trend of the continental slope advancing seaward contemporaneously. In conclusion,the spatio-temporal evolution characteristics of the gravity flow depositional architecture in the typical deep-water study area can provide important evidence for the restoration of paleogeomorphic evolution of a deep-water continental slope.
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