西藏札达盆地古格组剖面沉积环境演化特征

Features of the change in Pliocene depositional environment at the Guge Formation section in the Zanda basin, Tibet

通过对西藏札达盆地古格组剖面的实际调查以及沉积物粒度、磁化率、碳酸盐等环境指标的分析,结合古地磁和ESR法测年资料,探讨了古格组4.4-2.74Ma的沉积环境变化。分析结果表明4.4Ma象泉运动以后,札达盆地沉积环境发生了显著变化,沉积环境由前期河流相沉积向湖相沉积转变。形成了厚度达500余米的古格组沉积,反映札达古湖沉积由滨湖-浅湖-半深湖-滨浅湖阶段的变化,即湖泊产生-发展-消亡的全过程。其发育过程与晚新生代以来高原隆升以及气候、环境变化密切相关。

Based on a field survey and analysis of environmental proxies （magnetic susceptibility, grain size, carbonate content, ESR ages etc.）, the paper discusses the change of the depositional environment at the Guge Formation section in the Zanda basin, Tibet, at 4.40-2.74 Ma. The analytical data show that remarkable changes in depositional environment took place in the Zanda basin after the Xiangquan movement at 4.4 Ma： the depositional environment changed from the fluvial facies in the early stage to the lacustrine facies in the late stage, forming a thickness of more than 500 m of sediments of the Guge Formation. It reflects the changes of the sediments in the Zanda paleolake from the lakeshore→shallow lake→semi-deep lake→lakeshore-shallow lake, i.e. the entire process from the emergence→development→extinction of the paleolake. Its growth process is closely related to the plateau uplift and climatic and environmental changes since the late Cenozoic.