A Study On The Devonian Sedimentary Characteristics And Paleogeography In The Xiyi Area,Baoshan City,Western Yunnan Province

Tectonically, the Xiyi region in Baoshan, wesyern Yunnan Province, is located in the Baoshan Block of “Sanjiang” island arc basin of the Tibet-Sanjiang orogenic system. The metallogenetic subdivision of the lead-zinc mining area in the Xiyi Town belongs to the Baoshan-Zhenkang polymetallic metallogenic belt including lead, zinc, copper, and iron. Research in lithology, lithofacies, sedimentary formation and palaeogeographic contributes to further study of the control action of metallogenesis. In this study, this paper studied the characteristics of the strata through describing drilling core section from the lead-zinc mining area in Xiyi Town, and determined the types of sedimentary facies, and further discussed the Devonian paleogeography and sedimentary evolution process.The study area is located in southeastern Baoshan Block, in which the Devonian strata is divided into the Lower Devonian Xiangyangsi Formation, Middle Devonian Heyuanzhai Formation, and Upper Devonian Xiangshan Formtion-Member 1, from bottom to top. It is characterized mainly by carbonate rock in the lithology. The silty limestone, silty dolomite, etc. developed in the bottom of the Xiangyangsi Formation, gray black or grey thin layers of argillaceous siltstone and mudstone and calcareous siltstone, etc developed in the middle part, and limestone and dolomite appeared in the upper part, which was deposited in continental and diamictic continental shelf facies. Heyuanzhai Formation was comprised of dark grey or gray black argillaceous limestone, argillaceous banded limestone, and calcisiltite with dark grey or grey brown nodular limestone and calcirudyte, which was deposited in the the slope and basin facies. Member-1 of the Xiangshan Formation composed mainly of dark or dark grey argillaceous limestone, which was deposited in the basin facies.Based on the research on the Devonian strata, sedimentary characteristics, and sequence stratigraphy in the Lead-Zinc mining area in the Xiyi Town, this paper reshaped the Devonian evolutionary history in the study area. The Xiyi area in Baoshan City overall was in the regressive process in the Early-Middle Devonian. After brief transgression in the Latest Devonian, the Baoshan Block was lack of the Famennian sediments because of the possible uplift. And the parallel unconformity contact between the Devonian and the overlying strata was the result of the erosion of the Latest Devonian.