Analysis Of Sedimentary Facies Of Shaqiaomu Formation In Southern Rongma Town, Nima County, Tibet

This paper mainly studies the sedimentary microfacies and sedimentary facies of the Shaqiaomu Formation in southern Rongma Town,Nima County,Tibet.Through field observations,it was found that the Shaqiaomu Formation is not a typical clear carbonate platform plateau facies deposit,in which a large amount of land-derived clastic inclusions are developed,with obvious mixed sedimentary characteristics.Although previous researchers have studied the sedimentary facies of this formation,they have not studied the sedimentary microfacies in detail.Based on field surveys and indoor rock slice identification analysis,this paper studied the main rock types of the Shaqiaomu Formation and classified them into three major categories:(1)Terrestrial clastic rock,mainly consisting of fine sandstone,siltstone,Silty mudstone,muddy siltstone,pebbly coarse sandstone,etc.;(2)Carbonate rocks,mainly muddy limestone,bioclastic limestone,bright-grained antimony limestone,etc.;(3)mixed sedimentary rock,Mixed sedimentary rocks formed by doping of terrigenous debris and carbonate rocks,including muddy mudstones,sandy muddy limestones,gray sandstones,internal clastic mudstones,calcareous siltstones,and terrestrial fragments Crushed bio-clastic mudstone and so on.Based on the relationship between terrigenous debris and carbonates,four types of mixed sedimentary strata were identified in the Shaqiaomu Formation:(1)Carbonate and terrigenous interbedded layers,with medium-thin layer bioclastics The muddy limestone is composed of thin siltstone and silty mudstone.(2)Carbonate rock and mixed sedimentary rock are interbedded or interbeded with mutual sedimentation: mainly thin and medium argillaceous limestone and bioclastic mud.Interbedded layer of crystal limestone;(3)Interbedded layer of mixed sedimentary rock and terrigenous clastic rock,mainly composed of medium-thick argillaceous limestone with thin silty mudstone,medium-thin siltstone with calcareous siltstone,and calcareous powder.Sandstone and fine sandstone are interbedded;(4)Different types of mixed sedimentary rocks are interbedded or interbedded by mutual sedimentation: mainly thin-bedded muddy micrite intercalated with thin calcium fine sandstone,middle thin layer containing silt Chip muddy limestone with thin layer of calcium fine sandstone.Based on the combination of lithologic and lithologic features,sedimentary structures,and fossil characteristics of shale lithology,two sedimentary facies,three sedimentary facies,and several types of sedimentary facies were identified in the Shaqiao Formation.Foreshore subphase and Linbin subphase;the mixed shelf phase includes only inland shed subfacies.