FROM PALAEO-RED TO YELLOW DESERT : EVIDENCE FOR THE EVOLUTION OF ARID ENVIRONMENT IN CENTRAL ASIA

There are many exposures of eolianites distributed near the north and north-eastern fringes of the Tibetan Plateau. The outline of geological evolution of palaeodeserts of China beginning in the Early Cretaceous can be divided into 4 main periods: (a) a red desert period characterized by trade-winds in and before the Earle Cretaceous; (b) a red desert period characterized by planetary west winds from the Late Cretaceous to the Miocene; (c) a transitional period from red desert to yellow desert in the Pliocene; (d) a yellow desert period characterized by winter monsoon and planetary west winds in the Quaternary. In northwest China, the red desert began to wither away and a yellow desert began to develop about 4.6 Ma BP. The red desert died out and the yellow desert was stable from 2.5 Ma BP. Spatially, the red desert in the Tarim Basin of west China, withered earlier than that in the Loess Plateau area. The red desert disappeared completely at 3.4 Ma BP or so in the Tarim Basin at the Yecheng eolianite sections, and at 2.5 Ma BP in the Loess Plateau based on loess and red earth deposits. An indicator for yellow desert motion is change in the position of the desert and loess transitional zone, and for the red desert it is change in the position of the planetary west wind desert and east wind desert transitional zone. While the global climate cooled from the Early Cretaceous to the Cenozoic, the west wind desert and east wind desert transitional zone moved to the south, and the red desert retreated gradually in the pre-Quaternary. Concurrently, the yellow desert and loess transitional zone shifted to the south and developed. The yellow deserts in China developed from the red deserts of the Early Cretaceous following a temperature decline after about 150 Ma BP. So far, we can demonstrate that the history of desert and arid environments in north-western China began at least from the Early Cretaceous. Acknowledgment: the National Natural Science Foundation of China (Granted No: 40272079)