11万年来河西走廊东部黄土沉积记录的百年分辨率东亚冬季风变化  

CENTENNIAL-RESOLUTION EAST ASIAN WINTER MONSOON VARIATIONS RECORDED BY LOESS DEPOSITS IN THE EASTERN HEXI CORRIDOR OVER THE LAST 110 KA

作　　者：易施钰 盛美[1] 李宗耀 王喜生[1] YI Shiyu;SHENG Mei;LI Zongyao;WANG Xisheng(Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081)

机构地区：[1]自然资源部古地磁与古构造重建重点实验室,中国地质科学院地质力学研究所,北京100081

出　　处：《第四纪研究》2022年第6期1517-1528,共12页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:42074078、42104080和41672178);中国地质科学院地质力学研究所基本科研业务费项目(批准号:DZLXJK202008)共同资助。

摘　　要：在河西走廊东段的祁连山北麓与腾格里沙漠交接地带发育的较大范围的黄土堆积为探讨东亚夏季风西北缘的古季风演化提供了不可多得的天然素材。本研究利用甘肃武威沙沟剖面32.2 m的黄土-古土壤序列作为研究对象,开展了光释光测年和高分辨率的岩石磁学、环境磁学和全岩粒度分析,重建了该地区11万年来的古季风演化历史,并探讨了其驱动机制。结果表明:1)该剖面11万年来连续沉积的黄土-古土壤序列与邻近古浪剖面同期地层的全岩粒度表现出完全的可比性,二者的沉积速率均达30 cm/ka以上,记录了东亚夏季风西北缘千百年分辨率的气候快速变化特征;2)磁粒度参数M_(rs)/M_(s)和H_(cr)/H_(c)与中值粒径间良好的线性相关表明,研究区黄土磁学特征主要受控于冬季风强度主导的“wind vigor”模式;3)全岩粒度和磁粒度参数均记录了完整的Dansgaard-Oeschger旋回和Heinrich事件,表明北半球高纬气候对黄土高原西北边缘气候的深远影响和中-高纬北半球气候显著的遥相关过程,而由北大西洋经向翻转环流强弱所引起的北极海冰变化可能是导致东亚冬季风强度变化的最直接原因。The thick Quaternary eolian deposits in the eastern Hexi corridor, located at the transitional zone between the northern foothills of the Qilian Mountains and the southern margin the Tengger Desert, are ideal archives for retrieving high-resolution paleomonsoon history in the northwestern margin of the East Asian summer monsoon(EASM). By using optical stimulated luminescence(OSL)dating and high-resolution(2-cm resolution)rock magnetic and bulk grain size analyses, we chose the upper 32.2-m loess-paleosol sequences from the Shagou section(37° 33′ 07″ N, 102° 48′ 29″ E)in the Wuwei County, Gansu Province to reconstruct monsoon evolutionary history of the region over the past 110 ka and explore possible driving mechanisms. All age control points are selected to match the Dansgaard-Oeschger(D-O)cycles and Heinrich(H)events to reconstruct this chronosequence since 110 ka. High-resolution magnetic and bulk grain size results for the interval S_(0)~S_(1) reveal evident magnetic enhancement but decrease in grain size for two sub-paleosol layers of S_(1)SS_(1) and S_(1)SS_(2). During the last glacial, the magnetic concentration parameter of anhysteretic remanent magnetization(ARM)and magnetic granulometry parameters of ARM/SIRM and ARM_(rs)/M_(s)are all sensitive to SD magnetic particles, and show generally low-amplitude variations, indicating very weak pedogenesis. Compared with low-amplitude fluctuations both of ARM and ARM-based ratios during the last glacial, the two depth levels with high values of saturation isothermal remanent magnetization(SIRM)during the last glacial may correspond to marine isotope stages of 2 and 4(MIS 2 and MIS 4), respectively. Moreover, SIRMs show generally high values in the studied sequence, which may reflect the sensitivity of SIRM to a broader range of ferrimagnetic particle sizes(both finer SD and coarser PSD-MD magnetic particles). The magnetic concentration parameter of saturation magnetization(M)also exhibits consistent fluctuations with that of SIRM during the last glacial

关 键 词：季风边缘区 磁粒度 D-O旋回 HEINRICH事件 腾格里沙漠南缘 气候快速变化 

分 类 号：P534.63[天文地球—第四纪地质学] P941.73[天文地球—古生物学与地层学]