OSL DATING FOR HOLOCENE LOESS-PALEOSOL PROFILE AND ITS RECORDED SOIL EROSION EVENTS IN THE EASTERN WEIHE RIVER BASIN

Fifteen loess samples were collected from Laoguantai (LGT) Holocene loess-paleosol profile in the eastern Guanzhong basin, and then optically stimulated luminescence (OSL) dating for polymineral fine grains of these samples were made by application of single-aliquot regenerative-dose (SAR) protocol. The measured results show that OSL ages estimated from[post-IR] OSL signals are maximums, and that ages estimated from IRSL signals are minimum or consistent with those estimated from BLSL signals. The generally younger OSL ages estimated from IRSL and BLSL signals may originate from abnormal decay of feldspar within polymineral fine grains. There is no such problem in the[-post-IR] OSL signals, so the OSL ages estimated from the[-post-IR] OSL signals have more credibility. Based on the[-post-IR] OSL ages and the measured magnetic susceptibility and grain-size of the profile, the study has discovered two soil erosion periods due to increased sheetwash. The first stage of soil erosion event took place about 9.34-12.40 ka, in which the climate became warmer to the Holocene Megathermal in this area. The second stage of soil erosion event took place about 3.76-4.60 ka, in which the Holocene Megathermal would soon be ended and the worsening of climate was beginning in this area, which provides scientific evidence for exploring the Flood Event and its climate background took place in the early Xia Dynasty of China. The two soil erosion events discovered in this area indicate that the East Asian monsoon was not stable during the Holocene, showing rapid fluctuations on millennial to sub-millennial timescales.