西藏阿里札达盆地上新世-早更新世河湖相地层层序地层分析

根据札达盆地河湖相剖面地层岩性、粒度、沉积构造、古生物等反映的沉积岩相,以及不整合面等沉积特征,可将札达盆地上新世—早更新世河湖相地层,初步划分为两个三级层序(Ⅰ、Ⅱ)。层序Ⅰ代表上新统地层层序,并进一步区分出退积准层序组和进积准层序组。对应上新世湖相沉积由低位体系域—湖泊扩张体系域—湖泊收缩体系域的演化,反映湖泊由源区水系冲积亚相—滨湖三角洲亚相—滨浅湖亚相—半深湖亚相—滨浅湖亚相的湖泊,由扩张到萎缩的一个完整的发展演化旋回。层序II代表下更新统地层层序,反映一个盆地受构造和气候(冰期—间冰期)双重控制的夭折型冰湖形成演化的由冰水冲积相到冰湖沉积相的不完整沉积旋回,为青藏高原新近系上新统与第四系的研究与划分提供了重要依据。

Sequence stratigraphy of the Pliocene-early Pleistocene fluvio-lacustrine facies strata in the Zanda basin,Ali,Tibet

This paper re-evaluates the Pliocene to early Pleistocene sedimentary strata in the Zanda basin, Ali, Tibet. Our study shows that the sediments are primarily lacustrine and fluvial of late Cenozoic age, with subordinate glaciers and glacio-lacustrine components mainly of early Pleistocene age. The sedimentary section can be divided into three formations and eight sedimentary facies. From old to young, the three formations are Tuolin (N1_2t), Guge (N2_2g) and Xiangzi (Qp 1-1x), and eight sedimentary facies are ①alluvial facies, ②shore lake facies, ③shallow lake facies, ④deep lake facies ⑤shallow lake facies, ⑥lakeshore facies, ⑦alluvial-diluvial facies and ⑧ice lake facies. The Tuolin formation contains a single facies (①); the Guge formation contains five (②-⑥); and the Xiangzi formation contains two (⑦-⑧). The Zanda basin fluvio-lacustrine strata can also be divided into two third-level sequences (Ⅰ,Ⅱ), according to strata lithology, granularity, depositional structure and paleobiology. Using this sequence stratigraphy, the evolution of the Zanda basin can be divided into two major stages. Pliocene sequence Ⅰ displays a complete evolution from an expanding to shrinking lacustrine basin as illustrated by the characteristics of alluvial, lakeshore delta, low-lakeshore, and moderately deep lakeshore facies. Sequence Ⅱ, consisting solely of lower Pleistocene strata, reflects evolving sedimentation in an alpine basin controlled by tectonics and climate (glacial-age to interglacial). This study of the Pliocene to early Pleistocene sequence stratigraphy of the Zanda basin will aid an understanding of the late Cenozoic uplifting history of the Qinghai-Tibet plateau, the evolution of its lakes and rivers, climate changes, environmental and paleogeographic evolution, and general Tibetan Neogene to Quaternary stratigraphy.