GEOMORPHOLOGICAL AND ENVIRONMENTAL EVOLUTION IN THE UPPER REACHES OF THE YELLOW-RIVER DURING THE LATE CENOZOIC

Studies of the geomorphology and stratigraphy in the upper reaches of the Yellow River during the late Cenozoic demonstrate that the period of 30-3.4 Ma is characterized by a relatively stable tectonic setting, a persistently hot climate and a wide distribution of inland basins. This long-term stable environment resulted in a planation surface, the main surface on the Qinghai-Xizang (Qingzang) Plateau, on which red e arth crust and karst are formed. Since 3.4 Ma, the Qingzang Plateau wa s uplifted as a whole massif, accompanied by the dissection and disint egration of the main surface, termination of deposition and deformatio n of stratigraphy in red basins, increasing relief and commencing accu mulation of inland molasse formation mainly of conglomerate. Subsequen t strong uplift of the Qingzang Plateau at 2.5 Ma and 1.7-1.66 Ma led to cormation of the basic geomorphological configuration of the Qingza ng Plateau and occurrence of the Yellow River. These three strong upli fts of the Qingzang Plateau between 3.4 Ma and 1.7-1.66 Ma was, theref ore, named the Qingzang movement and divided correspondingly into thre e phases A, B and C. After the appearance of the Yellow River, the Qin gzang Plateau continued uplifting intermittently, resulting in 8 valle y terraces dated to 1.63, 1.5, 1.2, 0.8, 0.6, 0.15, 0.05, and 0.01 Ma, which also recorded the whole process of headward erosion of the Yell ow River.