Stratigraphic Division And Comparison And Sedimentary Facies Analysis Of Early Triassic In Guizhou Dafang Area

Guizhou Dafang Area is opening fold with domes and tectonic basins,which with the general tectonic line of NE or NNE locates in the tectonic deformation zone of Bijie NE trending,The Early Triassic layer is extensively developed in the study area.Through the investigation in Guizhou Dafang area,and based on the stratum section survey data and previous publications,this paper tries to perform multi-stratigraphic subdivision and analysis the sedimentary facies of Early Triassic layer in research area and finally achieves the depositional model map.The study area is inCentral Guizhou district of upper Yangtze subarea,which belongs to Yangtze stratum area,near the transition zone of Central Guizhou district,Northern Guizhou district and Northwest Guizhou district.In this paper we selected 7 typicalmeasured profiles to divide Early Triassic strata reasonably based on the principle and method of the lithostratigraphic division,data analysis of profiles and previous studies.The Early Triassic stratain study area is divided Yelang formation and Jialingjiang formation,Yelang formation consists of Shabaowan section,Huangcunba section and Jiujitan section;Jialingjiang formation consists of one section,two section,three section and four section.Inthis paper we describes the characteristics of lithology,rock combination,stratigraphic thickness,contact relationship andlateral variation in detail.Based on the distribution and combination feature of ancient organisms in th e study area's Early Triassic layer,we set up double shell system: Claraia wa ngicombination zone,Claraia aurita-Claraia stacheicombination zone,Eumorp hotis multiformisacme zone,and Pteria-Entolium discites microtiscombination z one.And we also set up ammonoid:Ophiceras sinensisrange zone,KoninckitesParanoritescombination zone,Owenites-Meeckocerascombination zone,and Tirolit es-Procarnites combination zone.Based on the regional correlationof each bioz one's time limit and horizon,can we assign the stratigraphic attribution of each lithostratic unit.According to the comprehensive analysis of rock mineral properties,rock assemblage,sedimentary structure and sequence,biocompatibility and sedimentation mechanism,this paper mainlyanalyses the section plane of the sedimentary system,and divides Early Triassic layer into the marine depositional system including coastal depositional system and carbonate platformdepositional system through field surveys and indoor studies.Coastal depositional system can also be divided into barrier island coast and no barrier coast.Carbonate platformdepositional system can be divided into beach,openplatform and restricted platform.Based on the study of the lower Triassicsedimentary facies,we set up the depositional model of thelower Triassic strata and summarize the depositional model in Guizhou Dafang area.