The Controlling Of Slope Belt On Sediment And Lithological And Stratigraphic Traps In Large-scale Down Warped Lacustrine Basins, A Case Study In The South Of Songliao Basin

Through the study of sequence stratigraphy and the geomorphology of slope belt, the dissertation aims to establish the stacking patterns and the evolvement of facies in the south of the Songliao basin and to analyze the controls of slope geomorphology on sedimentology and sequences. The study has shown that incisions and valleys of mutli-grade slopes govern the sedimentary systems. Slope belt have apparent controls on the development of low-stand system tracks. Low-stand slope belt govern the development of bottom-lacustrine fans, and high-stand and transgressive slope belt co-govern the development of delta front. The distribution of thick sands that fill in the channels are largely controlled by the ravines and valleys formed during high-stand systems. Based on accurate and thorough analysis of sandstones in the key area, the critical angle that could form gravity flows under slope belt conditions is established. An attempt was made to establish the model of sedimentary response to different geomorphologies. With a comprehensive study of the change in strata thickness, revision of compaction and reestablishing of paleo water depth, the study proved that debris flow could form under a critical grade of 6m/km. These, coupled with physical simulation, have further proven that mutual compensation exits in the course of forming debris flows: low angle and gradient needs larger height, high angle and gradient needs smaller height. Sedimentary models under low-gradient environment are established based on analysis of drilling, logging and seismic data, and further study proved that the occurrence, scale and distribution of debris flows and the shape of incised valleys all have obvious difference under long and short distance of low gradient slopes. All of these, coupled with exploration fruits and distribution of lithological and stratigraphic traps in the Haituozi area, a model for the developing of different traps under slope belt background is established. Slopes and toe of slopes of low-stand slope belt are the favorable sites for the developing of bottom-lacustrine fans and channel-filling related lithological traps, stratigraphic onlapping traps and fault-lithology composite traps. Regions that develop high-stand and transgressive distributary channel and mouth bars are favorable sites that could form potential high-saturated lothology-fault composite and structure straps. The upside of low-stand slope belt is favorable region where transgressive onlapping stratigraphic traps could develop. These roles provided valuable references for the forecasting of lithological and stratigraphic traps under slope belt backgrounds in down warped lacustrine basins.