Stratigraphic Division And Depositional Environment Analysis Of Late Triassic In Baliu Area In Mojiang County In Yunnan

Stratigraphic division is the integration of stratigraphy theory and practice.Multiple stratigraphic classification theory is the representatives of contemporarystratigraphic classification and concept. In this paper, the studied area is located in thearea of Baliu in Mojiang county in Yunnan province,and the boundary of Jinsha River-Ailao Mountain island arc belt and Changdu-Simao basin. There is not Under toMiddle Triassic strata，but The Upper Triassic strata of the studied area welldeveloped， has clear sequence and abundant fossils in the part of area. Severalsection of Upper Triassic have been measured and described in detail in the studiedarea. On the basis of studying stratigraphic division, according to the characteristics ofthe rock composition, the Upper Triassic is divided into four formal lithostratigraphicunits which are Waigucun Formation, Sanhedong Formation, Waluba Formation andMaichuqing Formation. The characteristics of lithologic association and lateralvariation of all Formations and members are discussed. Based on previous studyabout biostratigraphy, according to the characteristics of fossils association andstratigraphic discuss, biostratigraphic units of Upper Triassic are established. They areIndopecten serraticostus-Plagiostoma deqenense bivalve biological Assemblage inWaigucun Formation； Epigondolella permica-E. slovakensis conodonts Assemblageand Cladophlebis suniana-Danaeopsis fecunda Plant Assemblage in SanhedongFormation； Palaeocardita langnongensis-Weiyuanella rhomboidalis bivalvebiological Assemblage， Hyrcanopteris-Nilssoniopteris Plant Assemblage andDictyophyllidites-Concavisporites sporopollen Assemblage in Waluba Formation；Weiyuanella emeiensis-Unionites trapezoidalis bivalve biological AssemblageandDictyophyllidites-Concavisporites sporopollen Assemblage in MaichuqingFormation.The ownership of chronostratigraphy of each Formation was discussed onthe basises of fossil Assemblage Zone. Combining with the sedimentary background of the studied area, the sedimentary facies and subfacies of measured sections havebeen simply divided,the depositional environment have been simplyanalyzed.Finally，I put forward the The basin evolution model of the study area inLate Triassic.