Aeolian Activity And Climatic Changes In The Gonghe Basin Since The Last Glacial Maximum

The Gonghe Basin, located in the northeastern Qinghai-Tibetan Plateau, is an intermountain fault basin. The basin is about210km long from east to west and60km wide from north to south, with a total area of about13800km2. The elevation of most parts of the basin is between2600and3400m. In the basin, average annual temperature is2.0～3.3℃, average annual precipitation is311.1～402.1mm and average annual potential evaporation is1528～1937mm. Due to its unique geographical location, the basin is sensitive to the climatic and environmental changes, and is an ideal site for the researches into the pattern of climatic changes during the Holocene. In this paper, four aeolian deposition sections in the Gonghe Basin were studied. Based on the optically stimulated luminescence (OSL) dating and the sedimentary stratigraphic sequences of the aeolian deposits, the history of aeolian activity and climatic changes in the Gonghe Basin since the last glacial maximum were reconstructed, in combination with climatic proxies, such as grain size, element content, magnetic susceptibility and loss on ignition. Meanwhile, the results were compared with climatic changes recorded by the aeolian depositions and lake sediments in the northeastern Qinghai-Tibetan Plateau. The major conclusions are reached as follows:1. For aeolian deposits in the hinterland of the Gonghe Basin, the chemical weathering is primary. Alternation of the pedogenesis on particle size is not significant. Coarse particles in the deposits can be used to indicate aeolian activity. Compared to the Al, the major elements in the profile have no obvious migration and enrichment and basically represent the pristine signals of dust depositions.2. According to the stratigraphic changes, the>63μm particle content, the genetically sensitive components and the SiO2/TiO2ratio, four periods of the intense aeolian activity were identified in the Gonghe Basin since the last glacial maximum, namely,20～18,12～11,9.4～7.8and6-5ka BP. After4.5ka BP, paleosols widely developed in the basin. The aeolian activity was intensive in the early to middle Holocene, whereas it became weak during the late Holocene.3. Changes in grain size, CIA and magnetic susceptibility of the TGM, MGTA and MGTB sections in the hinterland of the basin are different from those of the GMY section, which is located in the southeastern margin of the Gonghe Basin, close to the pedimonts. The difference suggests that moist and thermal redistributions due to elevation and topography across the basin can lead to distinctly different environments, which has an important influence on dust emission and its chemical alternation after deposition.4. Dust emission is mainly affected by the wind strength and vegetation cover. In this study, surface soil humidity is likely to be the major controlling factor for aeolian activity. In the Qinghai Lake Basin and the Gonghe Basin, the aeolian activity was intensive during the early-middle Holocene and appeared to weaken during the late Holocene. However, a large number of climatic records from lake sediments in the northeastern Qinghai-Tibetan Plateau show an opposite climate change pattern:warm and humid during the early to middle Holocene, cold and dry during the late Holocene. Actually, this difference could be ascribed to the different responses of aeolian deposits and lake sediments to climatic changes. Water-level fluctuations in the marginal area affected by the Asian summer monsoon may be mainly in response to regional precipitation, whereas aeolian activity intensity may be controlled by the regional effective moisture, most likely in response to temperature changes regulated by the solar radiation.