Significant uncertainties remain regarding the temporal evolution of natural vegetation during the Quaternary, and drivers of past vegetation change, on the Chinese Loess Plateau(CLP). This study presents analyses of total organic carbon isotopic composition(TOC) and n-alkane ratios(C31/C27) from the Lingtai loess-palaeosol sequence on the central CLP over the last 450 kyr. The results demonstrate that the vegetation in this region comprised a mix of C_3 and C_4 plants of herb and woody growth-form. C_3 plants dominated for most of the last 450 kyr, but this did not lead to extensive forest. C_3 woody plants were more abundant in MIS9(S3 period) and MIS5(S1 period) during warm and humid climate conditions. Herbs increased in the region since 130 kyr, possibly as a result of increased aridity. On the orbital timescales, there was a reduction of C_3 herbal plants in MIS11(S4) than in MIS12(L5), and in Holocene than in the last glacial period. Our isotope and n-alkane proxy records are in agreement with Artemisia pollen changes in the region, which is/was the dominant species in this area and varying due to different heat and water conditions between glacial and interglacial periods. Though the climate in MIS1(S0) was similar to that in MIS11(S4), a significant increase in woody plants during the Holocene suggests the impact of human activities and ecological effects of changes in fire activity.
ZHOU BinWALI GuzalnurFrancien PETERSEMichael I BIRD
Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits(the Xiashu loess)in the lower reaches of the Yangtze River.Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau(CLP)have been proposed.Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique.This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess.The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior.Instead,the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River,indicating the dominance of proximal dust source.Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China,possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.
Deciphering the eolian sources is critical to understand the paleo-significance of the Quaternary eolian deposits(the Xiashu loess)in the lower reaches of the Yangtze River.Both a local source from the fluvial sediments of the Yangtze River and a distal source from the northern deserts similar to that of the loess on the Chinese Loess Plateau(CLP)have been proposed.Recent researches show great advantages of detrital zircon ages as a source tracer for Asian dust based on the laser ablation U-Pb isotopic dating technique.This work presents the U-Pb ages of zircon grains extracted from the Xiashu loess.The results indicate that the Xiashu loess has a very different age distribution of zircon grains from that of the loess on the CLP as well as the materials in the arid lands of the Asian Interior.Instead,the zircon ages of the Xiashu loess are indistinguishable from the fluvial sediments of the Yangtze River,indicating the dominance of proximal dust source.Proximal source of the Xiashu loess implies that extensive eolian processes might have existed in the currently wet South China,possibly in response to the full glacial conditions after the middle Pleistocene transition of global climate.
