The Research Of Storm Deposits In The Lower Devonian Of Ganxi,Beichuan,Sichuan And Its Geological Significance

This paper is based on the actual measurement data of the storm deposits sections in the Lower Devonian of Beichuan,Sichuan,through the study of sections structures and sedimentary evolution of Ganxi Formation Xiejiawan Formation andYangmaba Formation,establish storm deposits sequences and distribution models of Ganxi Formation Xiejiawan Formation andYangmaba Formation.And combine the experiment results of tempestite casting thin sections to analyze the geological significance of tempestite preliminarily.Storm deposits are widely developed in the Lower Devonian Ganxi Formation Xiejiawan Formation andYangmaba Formation of Beichuan,Sichuan,multiphase storm deposits are vertical superimposition.The characteristics of storm deposits are obvious,like the erosion surface,gutter casts,shell lag deposits,parallel bedding,hummocky cross-stratification,biological genesis structures and other storm sedimentary structures that are developed.In Ganxi Formation Xiejiawan Formation and Yangmaba Formation,7 types of storm deposits sequences and 3 types of storm deposits are developed: proximal sandy storm deposits,proximal diamictic storm deposits and distal sandy storm deposits,Among them,the Ganxi Formation,the lower paragraph of Xiejiawan Formation development of proximal storm deposits,the top of upper paragraph of Xiejiawan Formation and Yangmaba Formation development proximal mixed storm deposit,while the upper paragraph of Xiejiawan Formation development of distal sandy storm deposits.the relatively complete storm sequence consists of the erosion surface and gutter casts(Sa),shell lag deposits(Sb),parallel bedding(Sc),hummocky cross-stratification(Sd)and biological genesis structures(Se).The lithology of tempestite in the Lower Devonian Ganxi Formation Xiejiawan Formation andYangmaba Formation of Beichuan includes: siltstone,muddy siltstone,clastizoic muddy siltstone and sandy bioclastic limestone.In these rocks,the matrix content of siltstone is low and its sorting and roundness are preferable,indicating the storm has constructive effects on sediment transformation.The geological Significance of Storm deposits research includes the same time implication,the meaning,the implication of latitude,the palaeogeographic significance,after the discussion to determine the lower Devonian of Ganxi Formation,it was in a tropical subtropical region of low latitudes,the sedimentary environment was neritic shelf.