AGE OF THE JIAWA FORMATION AND ENVIRONMENTAL EVOLUTION OF LITANG COUNTY,SICHUAN PROVINCE

The Jiawa Formation in the Jiawa Basin, Litang County, Sichuan Province, is a sequence of loose fluvio-lacustrine deposits about 300m deep.According to the magnetostratigraphic, the B M boundary is located at 157.0m depth in the middle part of the section and the Olduvai normal polarity chron is recorded at the bottom.According to Cande and Kent's polarity time scale, it can be inferred that the deposition of the Jiawa Formation stared at about 2.10 Ma BP and ended at about 0.10 Ma BP. On the basis of sporopollen analysis, the vegetation changed from subalpine conifer forest to alpine meadow, and the sedimentary environment varied from fluvial-lacustrine facies to alluvial facies.