Study On Stratigraphic And Sedimentary Environment Of Xiangyangsi Formation Of Lower Devonian In Wandianba Area, Western Yunnan

The study area in tectonic units is between Gondwana and Lao Ya continental teti-Himalayan tectonic zone(domain).The central region is western margin of Yangtze Block—arc basin system ofmélange belt, Lanping—Simao foreland basin is adjacent to the east, west region isthe estern Baoshan Basin. It is an ideal research sites for plate kinematics, dynamics and plate boundaries orogenic and diagenetic mineralization of southwest China.It is Excellent prospecting.Wandianba area exposed to the Xiangyangsi formation is part of Baoshan-Zhenkang Basin with the west side of chang ning- Meng Lian Belt, the stratum exposure is good, is to study the early devonian sedimentary environment of good vehicle.This article is in yunnan baoshan-longling area such as Wandianba, Mengtong street five regional geology and mineral resources survey, on the basis of field work, through collecting predecessors’ research in this area and adjacent area data and lower devonian in this study area exposed to the Xiangyangsi formation completed after the data analysis and research.Based on the predecessors’ research results, the bay dam area of the east and the west Xiangyangsi formation of lower devonian strata contrast analysis and the study of sedimentary basin tectonic evolution, mainly in the following:(1) Find out the lower devonian Wandianba area the Xiangyangsi formation of the Xiaoxin stockade village and the Bailang village were built for clastic rocks and siliceous rocks and clastic rocks and carbonate rocks.(2) According to the principle of base level cycle, the dam region will bay the Xiangyangsi formation of Bailang village is divided into 2 long-term base-level cycle sequence and 6 med-term base level cycle sequence, the Xiangyangsi formation of Xiaoxin stockade village is divided into 2 long-term base-level cycle sequence and 6 mid-term base-level cycle sequence.(3)Through the Xiangyangsi formation sedimentary facies marks of comprehensive study, think that the Xiangyangsi formation of Xiaoxin stockade village for shallow sea shelf deposit, can further identify the shallow shelf sedimentary, deep water and land peng; the Xiangyangsi formation of Bailang village for shallow sea shelf deposit and carbonate open platform deposits, to further identify the intertidal zone and subtidal zone and shallow shelf, deep water and land peng, and other sedimentary units.(4) Through the Xiangyangsi formation contrast research, think the Xiangyangsi formation of Xiaoxin stockade village and the Xiangyangsi formation of Bailang village belongs to with the same name, different depth of the water environment of deposition.(5) Comprehensive east-west Xiangyangsi formation sedimentary environment comparative analysis research, and combined with the feature of regional geological and tectonic background, think the early devonian period, wan dam region in the stage of transgression, coastline continue to promote land, and reveal the palaeogeographic features that is closer to the ocean in the east. As of late early Paleozoic to early late Precambrian pangaea, Paleozoic period of the baoshan block as the original tethys and ancient tethys ocean development and long-term development of edge in a passive state, caused the lower devonian the palaeogeographic pattern of the Xiangyangsi formation.