西藏佩枯错盆地帮荣组沉积环境演化特征

Variation characteristics of the depositional environment in the Peiku Co Basin,Tibet

笔者通过西藏佩枯错盆地帮荣组剖面的野外地质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ESR法和U系测年资料,分析了晚更新世帮荣组沉积环境演化特征。分析结果表明,127～15kaB.P.的晚更新世时,佩枯错盆地进入强烈断陷阶段,佩枯错古湖经历了初始浅湖期,发展深湖期和萎缩浅湖期一个完整的湖泊演化过程。127～56kaB.P.,气候温暖湿润,湖水增加,古湖发育进入浅湖期;56～31kaB.P.,湖水波动上升,古湖进入发展深湖期;31～15kaB.P.,湖泊步入萎缩浅湖期,15kaB.P.左右出现的冻融褶皱,可能指示该区进入冰缘期。

Based on field geological survey and an analysis of such environmental indicators as grain sizes, magnetic susceptibility and carbonate content as well as ESR and U-series ages, this paper discusses the variation of the depositional environment in the Bangrong Formation during late Pleistocene. The analytical results show that the Peiku Co paleolake underwent a whole process of lake evolution：the initial shallow lake period and the development of the deep lake and the shrinkage into the shallow lake. During 127-15 ka B.P. in Late Pleistocene, the basin evolved into the strong rift stage. Being warm and humid, the water table of the lake rose, and the paleolake evolved into the shallow lake stage during 127-56 ka B.P. The paleolake went into the deep lake stage with the surface of paleolake wave rising during 56-31ka B.P. The paleolake shrank into the shallow lake stage during 31-15 ka B.P. The emergence of freeze-thaw fold may suggest that this region went into the ice-border period.