Sedimentary Characteristics And Tectonic Setting Of Middle Triassic Clastic Rocks In Guichao Area, Funing, Yunnan Province

Baifeng Formation in Middle-Trassic is a set of relatively special clastic sediment in the area of Guichao in Funing of Yunna province,which is sandwiched between the northern and southern arc volcanic.Comformably contacting with Intermittently exposedarc volcanic on the north side, under the volcanic rock was Luolou group in Lower-Trassic. It is in fault contact with the arc volcanicon thesouth side and Napo forearc basin is located south of the southern arc volcanic.Few work on basin structural attributes in Middle-Lower Trassic had been carried out in the area of Guicao before. By analysising the geological sections in the field, the thesis systematicallyanalyzed the sediment sequences and filling characteristics,sedimentary facies, microfacies and provenance of the Middle-Trassic,and the tectonic setting of the middle three sedimentary sedimentary environment is determined.There are several understandings as follow.The Middle-Trassic deposition in the area of Guichao is a shallow marine to batheyal sediment, filled withfan delta facies, the turbidite fan facies and the deep-water basin sediments. Thefeatures of the Fan delta facies are well-developed conglomeratechannel,tabular cross bedding,sandstonesheet with ripple lamination,ine grained clastic rocks, thin bedded sandstone,silty sandstone and mud. The turbidity fan facies is character with the development of Bouma Sequence,including climbing ripple lamination,convolute lamination, normal-graded bedding and so on.The deep-water basin facies is composed of dark-grey or black-beaten mudstone, filled with thin fine sandstone banded. Paleocurrent flow suggests material is transported to northwest and northeast.Detrital composition analysis under the microscope show that the Middle-Trassic stone is feldspathic lithic greywacke, which is characterized by many pyroclastic,whichshow the lithogenous material are from arc volcanic and experienced recycled orogeny.Our result suggests that the Middle-Lower Trassic in Guichao area is an intra-arc sediment.