Study On Sequence And Sedimentary Characteristics Of Triassic Baikouquan Formation On The North Slope Of Mahu Sag,Junggar Basin

The slope area of the Mahu Sag in the northwestern margin of the Junggar Basin is a secondary negative tectonic unit in the Central Sag.It borders the Wu-Xia fault zone(Ma Bei)in the north,reaches the Basong uplift and Xiayan uplift(Ma Dong)in the east,and lies in the Ke-Bai fault zone(Ma Xi)in the west,and the Zhongguao uplift(Ma Nan)in the south.The purpose of the research and discussion in the thesis is the Triassic Baikouquan Formation.According to the current exploration status in the area,a comprehensive systematic sequence stratigraphy study was conducted on the target strata in the study area,and the seismic,well logging and rock feature identification marks of the main sequence interface of the Triassic Baikouquan Formation;Identify and explain 1 long-term datum cycle and 3 mid-term datum cycles.The Baikouquan Formation in the target layer is the Lower Triassic stratum of the Mesozoic Triassic,and the bottom interface.of the Baikouquan Formation coincides with the boundary line(P/T interface)of the Mesozoic and Paleozoic at the same structural sequence interface.It has obvious signs on the characteristics of earthquake,logging and rock,which is easier to identify.On the seismic profile,the underlying Permian strata at the bottom interface of the Baikouquan Formation show different levels of truncation characteristics,which are obviously inconsistent with the overlying strata at an angle.The top interface of the Baikouquan Formation is the lake flooding surface at the end of the deposition of the Baikouquan Formation,showing a relatively continuous in-phase axis.Identify the features and designate this interface as the top interface of Baikouquan Formation.Restricted by the resolution of seismic data in the study area,seismic data cannot be used to identify mid-term datum cycle interfaces.Therefore,it mainly relies on drilling data to identify mid-term datum cycle interfaces.According to the sandstone superimposition pattern and logging profile characteristics,two mid-cycle interfaces can be identified in the Baikouquan Formation.The interface between the lower T1b1 and T1b2 is the boundary between two sets of positive rhythm superimposed sand layers;the interface between the upper T1b2 and T1b3 is the lithological gradient surface of sandy conglomerate and underlying mudstone.The paleo-current analysis shows that the paleo-current direction in wells X 72-Ma 131 and Ma 2 is north-south-west,and the paleo-flow direction in well Ma 6-Ma 18 is north-west-south.The influence of the provenance in the direction of Xiazi Street belongs to the provenance system of Xiazi Street,and the Ma 6-Ma 18 well area is affected by the provenance of Huangyang Spring and belongs to the provenance system of Huangyang Spring.By analyzing core facies,seismic facies,and logging facies,the types of sedimentary facies of the Baikouquan Formation in the study area were divided,and it is believed that the Middle Triassic Baikouquan Formation developed degenerative gravel fan delta deposits.,Mainly including two subfacies of fan delta plain and fan delta front Among them,the subfacies of the fan delta plain are dominated by braided channels at the near end,braided channels at the far end,and floodplain swamps;the subfacies at the front of the fan delta are dominated by underwater distributary channels and interdistributary channels.