Sedimentary System In The Sequence Framework Of The Upper Ordovician Lianglitage Formation In Northern Tazhong Area

This paper mainly studies the sequence division of the Lianglitage Formation in the northern part of the central part of Tarim Basin,as well as the types of internal sedimentary facies and the law of horizontal and vertical distribution.It also analyzes the controlling factors and finally establishes the sedimentary model of the stratum.The Upper Ordovician Lianglitage Formation in the Tazhong is in a transgressive secondary sequence deepened by upward bodies of water.Based on the interpretation of the key interfaces of the seismic profiles,the author summarizes the sequence divisions of the strata of the predecessors,with a variety of The analysis of the sedimentation and rotation characteristics of logging data,combined with core description and lithology,divided the Lianglitage formation into two three-order sequences and five four-order sequences,and established the Lianglitage Formation high-precision sequence stratigraphic framework.The lithology of the Lianglitage Formation is mainly grey-white mudstone,light-gray bright crystal-lime-grained limestone,bioclastic limestone,containing some algal limestone,argillaceous limestone,etc.The bottom part is mainly composed of gray mudstone.Limestone dominates,with high grain content in the middle,many species of organisms,and abundance of species.There are usually stucco mounds and reefs,and the upper part is gray muddy limestone with a thin layer of dark grey muddy and argillaceous stripes.In the Lianglitage Formation,two major phases of the open platform and the platform margin are mainly developed.In the open platform,there are mainly sand swarfs,bioclasts,reefs,and intertidal sea subfacies within the pedestal,and stucco mounds develop in some areas.The platform margin develops a marginal beach and inter-ocean subfacies.The facies belt extends from the open platform northwards to the platform margin.The fringe facies of the sq1 fourth-order sequence platform mainly develops high-density granit beach deposits,a small amount of stony mounds and intertidal sea deposits,and a large-scale beach develops in the middle of the open platform.There are contiguous or sporadic shoals developed in some parts of the sea and associated with the mud mounds;the size of the sq2 sequence sedimentary facies belts within the open platform and the platform margins have been reduced;the size of the sq3 sequenced tidal flats with an increase,the beach body in the platform margin is not obvious;the size of the beach in the sq4 sequence platform has been further expanded,and part of the beach between the sea area has formed a beach body.The size of the sprawling beach has been further expanded or combined,and the platform margin has increased.The size of the beach between the beach and the inner bay is reduced;the scale of the sq5 sequence platform marginal beach continues to decrease,and the size of the beach between the beaches increases,the size of the beach inside the platform becomes smaller,and a denuded area is formed near the Zhong-1 well.The paleo-geomorphological features are mainly low in the south,high in the north,high in the east and low in the west,and the overall thickness varies greatly.Most of them are in the range of 180-350 m.The overall thickness of the platform margin is greater than the open platform.The influence of tectonism on the distribution of the facies belts,paleo-geomorphology,sedimentary facies,sedimentary thickness,and unconformity and denudation have great influence on sedimentation.By analyzing the differences in sedimentary facies,sedimentary thickness,and differential erosion patterns in different regions of the study area,the tower was established.The depositional pattern of the open platform-tableland edge-slopes from the south to the north of the Upper Ordovician Lianglitage Formation in the northern part of the Central Tarim Basin was established.