Quaternary integrative stratigraphy,biotas,and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

The Quaternary strata on the Qinghai-Tibet Plateau contain rich information about the paleoclimate and environmental evolution,record the evolution process of the Quaternary regional tectonics,paleogeography,and geomorphology of the plateau,and are extremely important areas for studying the Quaternary geological events and regional environmental evolution.According to a comprehensive analysis of the regional stratigraphic data and the development and evolution characteristics of the biota,based on the differences in the lithostratigraphic units,sedimentary characteristics,landforms,and drainage systems,the Quaternary strata on the Qinghai-Tibet Plateau and its surrounding areas are divided into five stratigraphic regions:the Tarim region,Loess Plateau region,Qinghai-Tibet Plateau region,Yunnan-Guizhou Plateau region,and India-Ganges region.The Qinghai-Tibet Plateau stratigraphic region is divided into seven stratigraphic sub-regions:the West Kunlun-Karakorum,AltunQilian Mountains,Qaidam-Hehuang,East Kunlun-Bayan Har,Qiangtang,East Xizang-West Yunnan-West Sichuan,and Gangdise-Himalayan sub-regions.This paper briefly describes the lithostratigraphic units of the seven stratigraphic sub-regions of the Qinghai-Tibet Plateau.According to the lithostratigraphic sequence and its sedimentary characteristics,stratigraphic contact relationship,formation age,and evolution of the biota in each stratigraphic sub-region,the Quaternary tectonic paleogeographic evolution of the Qinghai-Tibet Plateau is divided into four stages.(1)The inherited differential uplift stage since the Pliocene(2.6-1.8/1.5 Ma):the regional sedimentary differences were significant,and the stratigraphic distribution was limited,the alluvial-proluvial sandy conglomerate was widely developed along the piedmont,and fluvial and lacustrine deposits were developed in the low-lying areas between the mountains.(2)The mountain range flattening stage(1.8/1.5-1.2/0.8 Ma):the erosion unconformity surfaces around the plateau were widely distributed,large rivers were formed,and lake sediments developed in the intermountain basins and the hinterland of the plateau.(3)1.2/0.8-0.128 Ma:the plateau continued to rise in a large range,with significant topographic differences and intensified mountain erosion.At about 0.8 Ma,the plateau uplifted above the snow line and entered the cryosphere,mountain glaciers developed,and the alpine arid environment gradually formed.(4)0.128 Ma-:the mountains rose and erosion intensified,and intermountain basins and lakes were widely distributed.There were significant differences in the regional sedimentary characteristics,and the sedimentary types developed toward diversification.The modern plateau landform pattern was basically formed.

Geochronology and Mineral Composition of the Pleistocene Sediments in Xitaijinair Salt Lake Region,Qaidam Basin:Preliminary Results

Xitaijinair （XT） Salt Lake, located in the western Qaidam Basin, is significant for recon- structing the evolution of inland drying climate. However, the chronological and mineralogical records from this lake are rare. This study investigated the chronology （accelerator mass spectrometry （AMS） 14C ages and optically stimulated luminescence （OSL） ages） and mineral compositions of sediment in the 240-cm-deep XT Section of the Xitaijinair Salt Lake region. The conclusions are drawn as follows： （1） Nine AMS 14C ages, ranging between 33 and 40 cal ka BP, are obviously younger than the two OSL ages （57.9 and 69.1 ka）. The 14C ages probably reflect contamination with modern carbon. （2） Both 14C and OSL ages indicate that the surface of Xitaijinair Salt Lake region has suffered erosion. （3） The se- diments of XT Section are composed of silicates （quartz, muscovite, clinochlore and albite）, carbonates （calcite, dolomite, and ankertie）, halite and gypsum.

Sr-Nd-Pb Isotopic Compositions of the Neogene Eolian Deposits in the Xining Basin and Implications for Their Dust Sources

The Neogene eolian deposits in the Xining Basin are valuable archive for studying the evolution of the Asian monsoon system and geomorphic processes of Northwest China. The Neogene eolian deposits that paleomagnetically dated at about 14 Ma probably were sourced from the middle and west Qinghai-Tibetan Plateau（QTP） as indicated by elemental compositions and magnetic properties. This study provides the Sr-Nd-Pb isotopic ratios of different sediments（gravels from the river terraces, Neogene eolian deposits and Quaternary loess） in the Xining Basin. The results show that：（1） Sr-Nd isotopic compositions of terrace gravels are different from those of the Neogene and Quaternary eolian deposits, although the Nd isotope ratios of gravel on the 10 th terrace（T10） and eolian deposits are similar.（2） Pb isotopic compositions of river gravels are obviously different from the eolian deposits in the Xining Basin. However, Pb isotopic compositions of eolian deposits in the basin are similar to those of eolian deposits in the central Chinese Loess Plateau.（3） Sr-Nd-Pb isotope results indicate that the Neogene eolian deposits in the Xining Basin were probably sourced from remote areas outside of the basin by long-distance transportation. The Qaidam Basin is probably an important source area for the eolian deposits in the Xining Basin.