SOME OPINIONS ABOUT THE TRIASSiC STRATIGRAPHYIN THE BAYAN HARA AREA

The upper ,middle and lower series may be recognized in the Triassic System in the BayanHara area distributed along the Hoh Xil ,Bayan Hara ,Daxue and Qionglai mountains. Formerlythey were called the Xikang Group and Bayan Hara Group ,Which were subdivided into forma-tions and subformations ,but their regional strategraphic correlation and devision are quite in-consistent. On the basis of the basin analysis ,this paper fut forward opinions about the strati-graphic system and nomenclature. For the Lower Triassic , lying on the Yangtze oldland, theeastern and southeastern parts of the sedimentary basin have a stable basement and the rockstherein consist mainly of slate with sandstone and limestone,about 200m thick. Forrnerly thisseries was named the Pochigou Formation,and it is advisable to continue to use this name. Thecentral and western parts rest on the basement of the Variscan folal ,so are rather active ,with asedimentary thickness as much as 3000- 6000m. It is advisable to name the lower series therethe Changmahe Formation. The Mlddle Teiassic is characterized by occurrcnce of sandstonebeds and its thickness increases from 600m in the southeastern part to 2000 3b00m in thenorthwestern part.It is advisabe to name it the Zhagunao Formation. The Upper "Triassic iscomposed of two contineuous rock formations in the whole area. For the lower part ias sanus-tone bdes occur repeatedly ,the original stratigraphic unit has many names , which are difficult tocorrelate. The author considers that it is right to use the Xindu Formation as the representativename for the upper series there. The upper part may be named the Sandstone formation for thetime being as it is less studed.