δ^(13)C values and hydrogen index records in sediment organic matter of RH core of Zoige Basin,eastern Qing-Zang(Tibet)Plateau and their environmental significance

Total organic carbon （TOC） content correlates very well with hydrogen index （HI） in the sedi-ments of RH core in the Zoig Basin.And the δ13C values of TOC become more positive while both TOCcontent and HI decline,indicating the subaerial exposure or the lake sedimonts approaching to the water lev-el.On the basis of the above,RH core sediments are divided into 23 climatic fluctuation stages,including 12 warm-humid stages and 11 dry-cold stages,which can he compared with oceanic oxygen isotopestages,loess profile and polar ice-core records.

Glacial-interglacial cycles recorded in clay minerals from the eastern Tibetan Plateau over the last 800 ka and their indications

Clay mineral proxies have been widely used to reconstruct changes in provenance and the paleoclimate.However,high-altitude clay mineral indications and long-term and orbital variations have not been fully explored.Herein,we present an800-ka clay-mineral record from a lacustrine sediment core(ZB13-C2)from the Zoige Basin on the eastern Tibetan Plateau(TP).X-ray diffraction and scanning electron microscopy were used to identify the clay mineral assemblages and their micromorphological characteristics of core ZB13-C2.The results revealed that the clay minerals in core ZB13-C2 are mainly illite,with small amounts of chlorite,kaolinite,and smectite(including irregular mixed-layers of illite-smectite(I/S)and chloritesmectite(C/S)).The clay mineral assemblages and proxies exhibit three stages of change,which are mainly controlled by the Zoige watershed range under different climate conditions.The watershed was limited to the southeastern region with altitudes ranging from~3500 to~4200 meters above sea level(m a.s.l.),and glacial-interglacial hydraulic erosion controlled the input of bedrock debris during 800-621 ka BP.It expanded to higher altitudes(~4200 to~4700 m a.s.l.)due to stronger seasonal freezethaw weathering without significant glacial-interglacial variations under a cooling and drying climate during 621-100 ka BP.Finally,it expanded to its highest altitudes of~4700 to~5200 m a.s.l.northwest of the watershed after 100 ka BP,and hydraulic erosion increased obviously under a warm climate of the interstadial MIS 3 on the TP.The watershed underwent two major expansions under different climatic conditions at~621 ka and 100 ka BP,with the wet/dry alternation became strong at~621 ka BP.These results reveal that long-term temperature changes and the wet/dry alternation at high altitudes controlled the watershed range and degree of the physical erosion,and that the indications of clay minerals should be carefully clarified before they are used as climate indicators,especially on the TP.