THE XIEJIAN STAGE OF THE CONTINENTAL MIOCENE SERIES IN CHINA

The Xiejian Age was named in 1984, and the Second National Commission on Stratigraphy of China formally recommended in 1999 to establish the corresponding chronostratigraphic unit Xiejian Stage based on the Xiejian Age, which was named after the lithostratigraphic unit Xiejia Formation. In this paper, we propose the Chetougou section, 1 km to the north of the Xiejia village, Tianjiazhai Township, Huangzhong County, Qinghai Province, as the stratotype section of the Xiejian Stage. The Xiejian Stage can be correlated with the marine Aquitanian Stage in the International Stratigraphic Chart, and the lower boundary of both stages is defined at the base of the paleomagnetic Chron C6Cn.2n with an age of 23.0Ma . At the Xiejia section, paleomagnetic data indicate that the lower boundary of the Xiejian Stage is located within the successive deposits of reddish brown massive mudstone in the upper part of the Mahalagou Formation, about 48 m from the base of the overlying Xiejia Formation. Biostratigraphic analyses suggest that the Xiejian Stage includes three Neogene mammal faunal units, NMU 1 to NMU 3. The Xie- jia fauna discovered from the Xiejia section is regarded as NMU 2, and the Suosuoquan fauna from the northern Junggar Basin, Xinjiang, and the Zhangjiaping fauna from the Lanzhou Basin, Gansu correspond to NMU 1 and NMU 3, respectively.