Study Of The Pingliang Group Algal Reef Development And Sedimentary Microfacies In Yongshou-Longxian Region

This article aims at the algal reef of the late Ordovician Pingliang Group in Yongshou-Longxian region,by field outcrop reconnaissance,drilling core observation of the L well,and testing the samples with carbon and oxygen isotopes and trace element,this paper systematically studied the Reef-related layers and scale and distribution of the algal reef of the research area.And the typical cross-section of algal reefs have been studied in detail,the reef building organisms,the reef attaching organisms and the rock types are defined,combined with the analysis of algal reef layers deposited sedimentary microfacies and tectonic evolution,based on this study,the control factors why the algal reef developed are analyzed and the formative pattern of the reef is summarized.On the basis of field outcrop of Yongshou HaoShihe and Longxian LongMendong reconnaissance and drilling and logging data of the L well collection,the reef building organisms have algae,coral and stromatopora,the reef attaching organisms contain cephalopod,brachiopod,gastropod,crinoid,trilobite and conodontophoridia.the rock types which make up the algal reef consist of algal framestone,algal baffiestone,algal bindstone,bioclastic limestone and algal limestone.The Algal reef sedimentary microfacies mainly is divided into reef base,reef core and reef cover,only Yongshou HaoShihe can be divided into reef flank.Yongshou-Longxian area mainly developed open platform facies,platform margin reef flat facies,platform margin slope facies and deep-water basin facies,platform margin reef flat facies is where the algal reef developed.Factors controlling algal reef development in the study area have tectonic activity,properties of seawater,the relative sea-level change,the ancient latitude,reef building organisms and hydrodynamic conditions,in the end,summed up the formative pattern of the algal reef.