Study On Sedimentary Characteristics And Lithofacies Palaeogeography Of The Silurian In Beishan

This paper mainly focuses on the basic geology of Sedimentology in Beishan area.Under the basis of fully studying and absorbing the geological data and the previous research of Beishan,using basic theory of petrology,sedimentology,paleontology and tectonic geology as practical guidance,combining major technologies of field geologic survey about outcrops,profile,route and laboratory analysis,this paper does systematically analyzed stratigraphic characteristics and Sedimentary facies,restored the Silurian paleogeographic pattern in the stratigraphic framework,and to explore its deposition-tectonic response mode.First of all,based on the field investigation and verification of the Silurian residual strata in Beishan,it does simplely reunificated and supplemented the definition of individual stratigraphic units and explored its age,and then compared and anynasised the characteristics of Silurian Stratigraphy and biostratigraphic characteristics.Secondly,through the petrology,sedimentary structure,paleontology and other important facies marks Identified shallow sea,shallow sea shelf,semi-deep sea-deep sea and shallow ocean volcanic-sedimentary facies,and anynasised its sedimentary characteristics,sedimentary environment of Silurian Beishan,showing that Beishan is a residual oceanic basin sedimentary system which mianly develop marine sediments and volcanism under a unsteady tectonic setting In the Silurian period.And then,it based on previous studies on the evolution of the tectonic background,the magma event in the area and the study of Silurian strata,sedimentary facies and sedimentary characteristics,combining Source area,Seawater changes and so on,restored the Silurian ancient paleogeography by the method of "Advantage Phase" and "Univariate Analysis Comprehensive Mapping",and drawn up the lithofacies palaeogeography map of the major Silurian period.Last,according to the result of the restoration of paleogeography and the study of evolution of sedimentary-tectonics,the significant conclusions are as follows: Beishan has displayed a paleogeographic pattern that separated by sea troughs and continents in Silurian,the lands gragually had been expanding and the Hongliuhe-Niuquanzi-Xichangjing basin had been shrinking,and seawater gradually withdraw;Gongpoquan group volcanic rocks are widely developed with a representative character of the "ditch-arc-pot" system,which indicates Mid-late Silurian is the most critical stage of plate subduction and reduction;From the perspective of sedimentation,Beishan shows the tectonic setting of the plate assembling and compressing each other In the Silurian period.