干旱区生态环境知识资源中心

Holocene environment change in the Gobi Desert of Mongolia and northwestern China is of global significance as it is one of the key dust source areas of the world. The Juyanze Basin, located in the central Gobi Desert of southern Mongolian Plateau, is one of the three terminal basins of the Heihe River that flows north from the Qilian Mountain. A series of geomorphic shorelines at different elevations around the basin indicate that large lake levels fluctuated during the past. In this study, we measured the exact elevation of shorelines in the Juyanze Basin using Digital Global Positioning System and found seven shorelines at similar to 37, similar to 36, similar to 34, similar to 30, similar to 28, similar to 24, and similar to 22m above modern basin floor (a.m.b.f.). Optically stimulated luminescence dating was employed to date the deposition of beach sand and gravel sequences at these shorelines. Results indicate a paleolake developed in the basin at similar to 5ka when lake levels reached similar to 26m a.m.b.f.. The lake level then gradually increased to similar to 29m a.m.b.f. at similar to 3.3ka and reached its highest Holocene level of similar to 37m a.m.b.f. at similar to 2.7 ka. The lake environment during 1.1-0.8ka was characterized by frequent lake-level fluctuations at similar to 30m a.m.b.f. The lake disappeared from both East and West Juyanze Basin after similar to 0.6ka. This sequence is out-of-phase with other regional Holocene lake records which indicate Holocene high stands occurred during the early to middle Holocene. We suggest that out-of-phase lake high stands at similar to 5-1ka in the Juyanze Basin are related to geomorphological shifts of the Heihe River channels across its fan/delta, feeding the three sub-basins of the Ejina at different times. Using paleolake shorelines in this region to reconstruct the climate changes needs to be very careful.