Abstract: Based on the study of depositional features, papeoecological features of Paleogene Anjhaihe formation in southem margin of Junggar basin, combining with the characteristics of clay minerals and microelements, it is shown that this formation was dominated by shallow lake environment, with relatively low salinity of lake water in the early stage of deposition; but in the middle stage, the lake was rapidly expanded and deepened, with salinity growing, the halophytic molecules in the biological groups flourished and marine algae fossils occurred; in the late stage the lake basin shrank and was rapidly desalinated. It is inferred that in the middle stage, the deposits of Anjihaihe formnation was once influenced by the seawater of Tethys Sea, forming brackish water environment, with developed halophytic molecules such as Kassinina, Hemicyprideis, etc. of Ostracoda, and marine Dinflagellate appeared. In condition of the highly saline water, it tends to form the lake-bottom anaerobic environment, favorable for preservation and conversion of organic matters, thus most favorable for the shaping of the source rocks.

Key words: Junggar basin, southwestem margin, Anjihaihe formnation, paleoecology, seawater, salinity