Sequence Stratigraphy Of Pliocene-Eopleistocene Epoch And Its Paleoenvironmental Significance In Zanda Basin, Tibet

Zanda basin is one of Cenozoic faulted basin, located in the southwestern of Ali area, Tibetan region, between the Himalayans mountain and Ayilariju mountain.Basin basement is composed of the Mesozoic fold stratum. There is a set of the Pliocene Epoch to the Eopleistocene fluviatile-lacustrine facies sedimentary stratum, the thickness of which is nearly 1,000 meters and is known as one of the most complete and the thickest stratum in Neogene Period sedimentary in Tibetan. On the top is uncomfortably covered with later-Pleistocene Ice accumulation of debris strata.Zanda basin is one of later Cenozoic fore-mountain basin that is formed when the Himalayas collides the interior of the orogenic belt. Therefore, the sedimentary system of Zanda basin and sequence stratigraphic evolution sequence must be inevitably related with the formation and the development of Himalayan formation.The study is centered on field investigation, carried out the sedimentary facies, sedimentary system, sequence stratigraphy, sporopollen and other paleontological fossils, granularity, carbonates, calculations, susceptibility, the easy-to-dissolve rocks and other environmental indicators, palaeomagnetism, ESR and other sedimentary chronology study. The study is centered on the inland basin of the sedimentary strata sequence stratigraphy sequence. Thus understand the basin evolution, discusses the relationship of the basin evolution and Himalaya uplifting and its response to environmental significance. The main conclusion is as follows:1.Zanda Basin can be divided into 4 facies which is composed of alluvial, lacustrine, alluvial-pluvial, ice-lacustrine facies and 7 subfacies. The result is basing on the detailed observation of the Pliocene Epoch to the Eopleistocene outcrop section and systematic working on samples, carrying on sedimentary system characteristics and the analysis of sedimentary facies.2.It discusses the sedimentary sequence stratigraphic control factors. 3-level sequence formed in this district by the tectonic activities, climatic conditions and source of supply, the tectonics of which is the dominant factors.3.The evolvement of the Zanda Basin can be divided into six phases: Initial fault depression phase (Tuolin Group), accelerated fault depression phase (Guge formation 1-3 rock segment ), tensional fault depression phase (Guge formation 4 rock segment ), cut into heart stage (Guge formation 4-5 rock segment), the second initial fault depression phase (Xiangzi formation 1-2 rock segment), accelerated fault depression phase (Xiangzi formation 3 rock segment).4.On the sedimentary characteristics, basin tectonic evolution, climate, source of supply, the analysis of deposit and integrated information of outcrop basis, it is working on sequence stratigraphy division. Zanda basin can be divided 3 3-level sequence, which found on the framework of sequence stratigraphy in the Pliocene Epoch to the Eopleistocene in the basin.5.The preface layer between Sq1 and Sq2 is parallel unconformity which correspond to the Xiangquan movement. The preface layer between Sq2 and Sq3 is angular unconformity which correspond to the Guge movement. The movements which control the preface layer correspond to the Qinghai-Tibet movement. Xiangquan movement (4.40MaB.P.) corresponds to the Qinghai-Tibet Movement A episode. Guge movement (2.68MaB.P.) corresponds to Qinghai-Tibet Movement B episode. Zanda basin topography from the West-high-East-low to current East-high- West-low, this tectonic movement may be counterpart Qinghai-Tibet movement C episode.