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.