CHANGE OF THE PALEOCLIMATE AND EVOLUTION OF THE LAKE DURING PLIOCENE-EARLY PLEISTOCENE IN ZANDA BASIN, TIBET

According to the pollen combination analysis, paleomagnetic chronology, electron spin resonance (ESR) age of fluviolacustrine facies deposition and lithology characteristics, this paper discussed the relationship between paleoclimate and the evolution of Zanda paleolake during Pliocene-early Pleistocene in anda basin, Tibet. Study shows that the Zanda paleolake has went through three phases: early marsh period, the medium-term developing period and late dying out of lake period. The Zanda paleolake began to take shape in early period(5.41~4.40 Ma). The paleoclimate of Zanda basin firstly was woodland and grassland vegetation in arid climate with less warm, then into a warm and slightly wet climate of the forest-steppe vegetation, and finally into a warm and humid subtropical mixed forest climate. The Zanda paleolake was developing in the medium-term (4.40~2.57 Ma).The paleoclimate was into the cold period, reflected by the paleovegetation firstly from warm temperate zone of coniferous-broad leaf forests to mountain cool temperature zone of dark coniferous boreal forest, and then from mountain warm temperate zone of coniferous-broad leaf forests alternating process. The Zanda paleolake was disappearing in late period (2.57 ~ 1.36 Ma). Paleoclimate and paleoenvironment was into the cold period, with the paleovegetation alternating change from mountain dark coniferous forest and mountain dark coniferous forest to the low-shrub steppe and dry and cold grassland. Evolution of the Zanda paleolake has good relationship with the change of the paleovegetation and paleoclimate. Uplift of the plateau has controlled the paleoclimate and paleoenvironment changes, thereby affected the quantity of the lake changes.