Abstract: Xiejian Stage is a regional chronostratigraphic unit of Chinese Neogene, with its lower boundary being roughly correlative to that of the international Aquitanian Stage. This boundary coincides with the lower boundaries of the Miocene and Neogene. Although Xiejian Stage has been formally recognized and widely used (NCSC , 2002) , its lower boundary has not been well defined and the boundary stratotype has not been established. Based on field and lab work on the Tertiary beds and faunas in the northem Junggar area ( Fig. 1 ) during the last few years , we present an analysis of the Tieersihabahe section and recommend it as a candidate for the stratotype of the lower boundary of Xiejian Stage. The Tieersihabahe section is northwest to the Dure village in the northern rim of the Junggar Basin, Xinjiang (Fig. 1) ; it consists of four units, ranging from bottom up: Tieersihabahe , Suosuoquan, Halamagai and Kekemaideng formations ( Figs. 2 —3). The sequence is 194.5 m thick and the lower two formations are continuous, with no stmctural disturbance, and contains Late Oligocene and Early Miocene mammals ( Figs. 2 —4). In the measured section (02Tr) , the lower limit of Suosuoquan Formation is at the level of 33 m ( Fig. 4) . The lithology of these rock units has been reported elsewhere (Ye et al., 2001 a; 2003) .