SEDIMENTARY FACIES AND PALEOCLIMATE OF NANHUA SYSTEM IN HUIZE AREA, NORTHEASTERN YUNNAN PROVINCE: Evidence from Element Geochemistry

The sedimentary environment and paleoclimate of Chengjiang Formation and Nantuo Formation of Nanhua System in Huize area of northeast Yunnan Province are studied through data collection, section survey, rock-mineral identification, major and trace elements analysis, correlation of characteristic index parameters and comprehensive modeling of sedimentary facies. The Chengjiang Formation and Nantuo Formation, occurred from bottom to top, both belong to terrigenous clastic rock series, showing a parallel unconformity contact. The Chengjiang Formation consists of mainly silty mudstone, siltstone, fine sandstone, fine-grained quartz gritstone and lithic sandstone. The Nantuo Formation is mainly a set of grayish yellow medium-thick polymictic moraine conglomerate. Sedimentary cycles are developed in Chengjiang Formation, with sedimentary structures such as small trough cross-bedding, oblique bedding, parallel bedding and horizontal bedding. The analysis results of major and trace element characteristic indexes including SD, CV, CIA, CIW, PIA, ICV, Na/K, Al/Ca, Ru/Sr, V/Cr, U/Th and Ni/Co of fine clastic rocks from Chengjiang Formation all indicate the sedimentary environment of oxidation or weak oxidation. It is considered that Chengjiang Formation is of lake facies, including shore-lake and shallow-lake subfacies, with a warm and humid climate; while Nantuo Formation is glacial facies, including moraine and glacial lake subfacies, with a cold and dry climate.