1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. Regional Survey of Geology and Mineral Resources, Heilongjiang Province, Harbin 150080, China

This study presents geochemical characteristic analysis of selected samples of the drillcores from zk6 Well, and aims to reconstruct the paleoenvironment of the Chengzihe Formation in Yanxing Basin.It is indicated that Sr/Ba ratios of the lower part of the coal-bearing sections vary from 0.20 to 0.75, with a mean value of 0.41, whereas the Sr/Ba ratios of the upper lacustrine mudstone sections vary from 0.12 to 0.36,with a mean value of 0.21. The above research result indicates that Chengzihe Formation were dominated by freshwater sediment, and the lower coal-bearing section shave higher salinity than the upper lacustrine mudstone sections. Moreover, all of the samples from the Chengzihe Formation display V/(V+Ni)ratios from 0.72 to 0.84, Cu/Zn ratios from 0.10 to 0.55, Th/U ratios from 0.28 to 3.60, ��Eu ratios from 0.4 to 0.84 and Ce_anom values from -0.04 to 0.09, suggesting that the Chengzihe Formation was formed in reduction environment. The lower part of the coal-bearing rock sections show Sr/Cu ratios from 5.87 to 24.12, with a mean value of 11.21, and B content from 232.60×10^-6 to 721.00×10^-6, with a mean value of 425.75×10^-6.The upper lacustrine mudstone sections have Sr/Cu ratios varying from 3.56 to 10.50, with a mean value of 6.00, and have B content varying form 23.69×10^-6 to 119.00×10^-6, with a mean value of 78.36×10^-6. Combination of Rb/Sr radios with sporopollen analysis results suggests that the lower coal-bearing sections were formed in arid climate, whereas upper lacustrine mudstone sections were formed in humid climate. In conclusion, during the deposition of the Chengzihe Formation the climate changed from arid to humid.