关键词: 下蜀黄土, 红外释光测年, 地层年代学, 东亚季风演化, 青藏高原隆升

Abstract: There is some controversy about the chronology of Xiashu loess. The chronology is of drawing special interest as that the beginning age of loess accumulation in this area indicates a threshold in the evolution of East Asia monsoon. This threshold suggests that the uplift of Tibetan reaches a height to be the turning point for the evolution of the East Asia monsoon, and that the south limit of dust accumulation extend from Loess Plateau in Central China to Nanjing area in East China at that time. The Infrared Stimulated Luminescence (IRSL) dating using polymineral fine grain was applied for the first time to the Xiashu loess deposit of Xujiacun profile (32°55' N, 118°56' E) in Nanjing area, East China. There are seven dark red paloesol layers in Xujiacun section. The IRSL age of fisrt paleosol layer bottom is 10.8 ka, indicating that this paleosol was formed during the Holocene. The IRSL age of first loess layer bottom is 71.5 ka, suggesting that this loess layer accumulated during the last glaciation. By correlating the SUS curve of Xiashu loess to that of Luochuan section, together with these IRSL ages and one ESR age (563.6 ka, from the bottom of Xiashu loess of Yanzhiji profile) as the age co ntrol, it can be deduced that the second integrated paleosol layer is identical to the S1 soil of the Loess Plateau formed during the last interglaciation, the third and fourth paleosols together to the S2 soil of the Loess Plateau, the fifth in the Xiash u loess to the S3 soil of the Loess Plateau, and the sixth to S4. By such correlation, the Xiashu loess should be the deposit since the age of L5 of the Loess Plateau (about 500 ka). During the glaciation of L5 of the loess Plateau, the dust reached the N anjing area to form the Xiashu loess due to the intensifying of East Asian monsoon. The ages below L1 become saturated, and are not listed here. Based on the present study, the following conclusions are obtained: The first paleosol layer was formed during the Holocene. The IRSL age of the first loess layer bottom is 71.5 ka, suggesting that it accumulated during the last glaciation. The dust reached the Nanjing area to form the Xiashu loess at about 500 ka, possibly due to the uplift of Tibetan Plateau to a height to be the turning point for the evolution of the East Asia monsoon so as to intensifying the monsoon.

Key words: luminescence dating, Xiashu Loess chronology, East Asia monsoon evolution, uplift of Tibetan Plateau