西藏札达盆地上新世—早更新世气候变迁与湖泊演化

摘要

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.%通过孢粉组合分析,结合河湖相地层岩性特征和古地磁及电子自旋共振(ESR)法年龄测定结果,探讨了西藏札达盆地上新世—早更新世的古气候变迁与札达古湖泊演化的关系.研究表明,札达盆地古湖泊演化可划分为早(湖泊形成期)、中(稳定发展期)、晚(湖泊消亡期)三期.早期(距今5.41 ～4.40 Ma),札达盆地为温凉而干旱的疏林草原植被气候,随后转变为温暖稍湿的森林草原植被气候,最后转变为温暖潮湿的亚热带针阔叶混交林气候,这一时期古湖开始形成；中期(距今4.40～2.57 Ma),古气候进入寒温期,古植被表现为先由暖温带针阔叶混交林带向山地寒温带暗针叶林带过渡,再由山地暖温带针阔叶混交林→山地寒温带暗针叶林交替出现的过程,古湖泊进入发育期；晚期(距今2.57～1.36 Ma),湖区古气候环境进入寒冷期,古植被为山地寒温带暗针叶林→山地暗针叶林向低矮灌木→干冷草原的变化,古湖泊进入消亡阶段.古湖泊演化与古植被、古气候演变有很好的相关性,高原隆升控制了古气候环境的变化,进而影响湖泊水量的变化.