Paleoclimate and Paleoenvironment of Gonghe Basin, Qinghai-Tibet Plateau, During the Lastdeglacial: Weathering, Erosion and Vegetation Cover Affect Clay Mineral Formation

With the analysis of the sources and formation mechanism of the clay minerals in the sediment core from the Dalianhai lake in the Gonghe Basin, northeastern Tibet-Qinghai Plateau, clay mineral composition proxies, grain-size and carbonate contents have been employed for high-resolution study in order to reconstruct East Asian Summer Monsoon (EASM) over the northeastern Tibet-Qinghai Plateau during the lastdeglacial. The study also extended to establish a relationship between vegetation cover changes and erosion during the last 14.5 ka with pollen record and clay mineral proxies. Smectite/kaolinite and smectite/(illite+chlorite) ratios allow us to assess hydrolysis conditions in lowlands and/or physical erosion process in highlands of the Gonghe Basin. Before 12.9 Cal ka BP, both mineralogical ratios show low values indicative of strong physical erosion in the basin with a dominant cold and dry phase. After 12.9 Cal ka BP, an increase in both mineralogical ratios indicates enhanced chemical weathering in the basin associated with a warm and humid climate. The beginning of Holocene is characterized by high smectite/(illite+chlorite) and smectite/kaolinite ratios that is synchronous as with deposition of many peat laminae, implying the best warm and humid conditions specifically between 8.0 to 5.5 Cal ka BP. The time interval after 5.0 Cal ka BP is characterized by a return to high physical erosion and low chemical weathering with dry climate conditions in the basin. Comparing variations of clay mineral assemblages with previous pollen results, we observe a rapid response in terms of chemical weathering and physical erosion intensity to a modification of the vegetation cover in the basin.