Characteristics Of Sedimentary Facies Of Huaitoutala Formation Of Carboniferous In North Margin Of Qaidam Basin

The Huaitoutala Formation of Carboniferous in the northern margin of Qaidam Basin has great potential for oil and gas development.A detailed study of its sedimentary facies characteristics and distribution is of great significance for guiding oil and gas exploration in the northern margin of Qaidam Basin.In order to understand the petroleum geologic characteristics of Huaitoutala Formation of Carboniferous in the northern margin of Qaidam Basin,this paper,based on previous studies,combines field outcrop observation,typical profile measurement,fine observation description under sample slice microscopy and geochemical analysis in sample chamber,applies sedimentology,petroleum geology,reservoir geology and petroleum geochemistry to study.The sedimentary characteristics and distribution of Huaitoutala Formation in the northern margin of Qaidam Basin are comprehensively studied,so as to reveal the sedimentary facies types and plane distribution of the Carboniferous Huaitoutala Formation in the northern margin of Qaidam Basin,and establish the sedimentary model of the Carboniferous Huaitoutala Formation in the northern margin of Qaidam Basin.In the Early Huaitoutala Formation of the Carboniferous in the study area,clastic rocks with positive-spinning conglomerate,sandstone,siltstone and mudstone were developed,of which conglomerate and sandstone were the main,followed by mudstone.The conglomerate is mainly gray,medium-thick layered,with complex gravel composition,mainly composed of sedimentary rocks,quartzite,granite,etc.The sandstone types are mainly feldspar quartz sandstone,feldspar lithic sandstone and siltstone.The marine carbonate rocks are mainly developed in the middle and late stages of the Huaitoutala Formation,including bioclastic limestone and internal clastic limestone,followed by sorghum limestone.According to the analysis of the environmental parameters of the trace and rare earth elements of the Huaitoutala Formation of the Carboniferous in the study area,the trace element analysis shows that the sedimentary period of the Huaitoutala Formation in the study area is climate dry heat,seawater is salted-strongly salted-The process of salinization evolution consists of anoxic reduction-strong reduction-reduction environment change process;rare earth element analysis shows that the light-rare earth element enrichment of the Carboniferous Huaitoutala Formation in the study area is relatively low,and the ?Eu has a negative anomaly.The La/Yb-?REE discriminant diagram indicates that the Huaitoutala Formation carbonate rocks are mainly derived from shale and calcium in the water bodies of the basin.Based on the in-depth analysis of the petrological characteristics,sedimentary tectonic features,sedimentary facies markers and geochemical characteristics of the Huaitoutala Formation of the Carboniferous in the study area,the development of the Huaitoutala Formation in the Wanggaxiu area of the North Qaidam Basin is summarized.There are four types of sedimentary facies and 12 sedimentary subfacies of fan delta,shore,restricted platform and open platform.In the early stage of the Huaitoutala Formation,with the intrusion of seawater,the interbedded coal line of dark gray conglomerate,gray sandstone and dark mudstone was developed;in the mid-sedimentary stage of the Huaitoutala Formation,the medium-thick layer of muddy bioclastic limestone was developed.Containing bioclastic limestone with thin layer of dark mudstone;in the late stage of the Huaitoutala Formation,the development of bright-grained bioclastic limestone,brilliant-grained limestone,gravel-bearing,sandstone and limestone,the whole process gradually Deeper.The sedimentary facies of the Huaitoutala Formation evolved from the fan delta and the coastal phase developed in the early part of the Huaitoutala Formation to the limited mesophase and open platform facies deposited in the middle and late stages of the Huaitoutala Formation.On this basis,a fan delta-shore-limited land-opening platform deposition model was established.