PROVENANCE OF LOESS MATERIAL AND TRANSPORTATION OF EOLIAN DUST TO THE LOESS PLATEAU AND THE NORTH PACIFIC

Results of a multiple, isotopic, chemical and mineralogical analysis of loess from the three northwestern inland basins (including the Junggar Basin, the Tarim Basin and the Qaidam Basin) and the Loess Plateau region of China are summarized. It is argued that the gobi desert in Mongolia and China, rather than the three inland basins, are the dominant source areas of the Loess Plateau. However, although these gobi and sand deserts are regarded as the main source regions, they serve as dust and silt holding areas rather than dominant producers. The mountain processes (e.g., glacial grinding, frost weathering, salt weathering, tectonic processes) in the Gobi Altay Mts., Hangayn Mts. and the Qilian Mts. have played an important role in producing the vast amounts of loess-sized material for forming the Loess Plateau. Dust entrained from different geomorphological units of China has different contributions to the proximal and distal regions. Dust derived from the Junggar and Qaidam basins is transported by near-surface winds, and thus mainly accumulates on the windward slopes of the local mountains (local dust). For the Tarim Basin, dust can be transported not only by the near-surface winds, but also by the westerlies whenever the dust is entrained to an elevation of > 5000 m asl. In the latter case, dust from the Tarim Basin (the Taklimakan Desert) can be transported out of the basin and ultimately to the remote Pacific (long distance dust). In most cases, dust entrained from the gobi desert in Mongolia and China is transported by near-surface winds, serving as medium distance dust, but occasionally (about 10%), it can be transported by the westerlies to the remote Pacific Ocean and even to the United States (long-distance dust).