| Aeolian sand depositions have been attributed to a drought and windy climate, representing dune-field expansion and/or dune buildup, whereas paleosols represent stabilization of dunes. Therefore, sequences of aeolian sand, loess and/or paleosols can reliably reflect the history of aeolian activity and climate changes. The Gonghe Basin, located in the northeastern Qinghai-Tibetan plateau, is an intermountain fault basin. The basin is influenced by the Asian monsoon and the westerlies, which is highly sensitive to climatic changes due to its high altitude and marginal position. In addition, aeolian deposits, widely distributed in this region, mainly distributed in valley area, loess hilly-gully region and beach areas, are excellent records of aeolian activity and climate changes, especially "Mugetan Formation", as described by Dong (1993).In this study, aeolian deposits at four sites in the Gonghe Basin were dated by Optically Stimulated luminescence (OSL) dating, in order to reconstruct the history of aeolian activity over the late Quaternary, in combination with climatic proxies, such as grain size, elemental compositions, magnetic susceptibility and loss on ignition (LOI). The major conclusions are reached as follows:According to the lithostratigraphic changes, three periods of intense aeolian activities were identified in the Gonghe Basin since the late Quaternary, namely,31.3～28.3ka in section ML,17.17～15.6ka in section TX,16.9ka in section QJ,10.21～9.88ka and7.22ka in section SG. However, aeolian activities became weak during the late Holocene, and paleosols widely developed across the whole basin.There were significant spatial differences for aeolian activity in the Gonghe basin. The aeolian activity was intensive in the study area during the last glacial maximum (LGM). During the early to mid Holocene, the aeolian activity was intensive, especially in the hinterland of the basin, such as sections SG, TGM, MTGA and MGTB. However, the aeolian activity was weak in the piedmonts, such as sections ML, TX, QJ and GMY. In the late Holocene, the aeolian activity was restrained, to a great extent.Based on a large number of OSL dating for aeolian deposition samples in the semi-arid zones of China, the relationships among OSL ages, latitudes and elevations were established. The aeolian activity was intensive during the LGM. From the late glacial to the early Holocene, aeolian activity was intensive on the northeastern Qinghai-Tibetan plateau and in the central deserts, whereas it was weak in the northeastern deserts. During the mid Holocene, aeolian activity was, to a certain degree, restrained in the northeastern Qinghai-Tibetan plateau and the northeastern deserts. As for the late Holocene, paleosols widely developed in the northeastern Qinghai-Tibetan plateau, but aeolian activity was intensive in the northeastern and central deserts, where human activity may have played a significant role by overly collecting firewood, grazing, and reclaiming farmlands.Aeolian activity can be regarded as a function of vegetation cover, wind strength, and supply of sand-sized particles, of which vegetation cover is most important, which is in turn controlled by effective moisture. During the early Holocene, the occurrence of aeolian sand probably represents a low level of effective moisture, as an integrative result of higher temperature, redistribution of meteoric water and variations in elevation, rather than regional aridity. As for the late Holocene, enhanced effective moisture does not necessarily require an increase in regional precipitation, but may result from moisture balance between lower precipitation and lower evaporation due to decreased temperature. For this reason, the paleoclimatic changes inferred from aeolian deposits have to be interpreted cautiously as wet or dry climates. |
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