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Sedimentary Evolution of the Lingshui Canyon System in the Qiongdongnan Basin, Northern South China Sea

Abstract

The Lingshui canyon system (LCS), a large axial submarine canyon, developed in late Miocene and located in the south of the Lingshui sag, Qiongdongnan Basin. Its filling forms part of the Huangliu Formation and Yinggehai Formation (Late Miocene- Pliocene age) and was fed by abundant sediments from the west side, northwestern and northern sources. The LSC has very important significance in petroleum geology with good gas discovery. By means of sequence stratigraphic interpretation, seismic multi-attribute and well data analysis, and Mass Transport Deposit(MTD) theoretical model, the evolution of the Canyon system were studied in order to understand the reservoir distribution and guide nature gas exploration. The calcareous nannofossils distributed and the foraminiferal fossils distributed from program of the sidewall core help us to analysis the different eroded-infilling phase. The sedimentary cycle in the Huangliu Formation is distinguished into five subsequences (SSI -SS5), six facies, and divided mainly into two evolution periods from bottom to top. Firstly, canyon infill commenced with debris flows, slumps, and slides, sometimes overlying basal lags, showing messy, incontinuity amplitude reflection in vertical. Secondly, canyon infill show turbidity flow deposits and low sinuosity turbidity channel with a large set of sandstone in packages, which is featured moderate - good continuity, strong amplitude reflection characteristics in the seismic profile. On the top of the SS5 sequence, shingled seismic reflections can be seen at canyon margins. They are interpreted to be associated to continuous lateral migration during channel evolution, resulting in the deposition of accretion packages in the inner side of the channel and erosion at the outer side of the channel. Interbeds of turbidite channel and mass transport deposits occur in the early Pliocene period. Submarine fan sandstones overlay the top of the canyon are mainly reservoirs in late Pliocene.