中文摘要：

天山地区黄土磁学特征及古气候意义受到广泛关注。本文以天山北麓乌鲁木齐河T7阶地上覆黄土为研究对象，基于光释光测年建立的时间标尺，通过岩石磁学、沉积学与地球化学等方面的分析，探讨该地区晚更新世古气候特征。光释光测年结果表明，天山北麓乌鲁木齐河T7阶地上覆黄土底界6.8m处的年龄为约41ka，顶部年龄为约14ka；稀土元素分析结果显示该时期黄土物源可能没有发生明显变化；黄土沉积粒度与岩石磁学参数分析结果显示，黄土磁化率、磁颗粒参数（χARM/χlf和χARM/SIRM）等磁学参数与砂粒组分（〉63μm）、中值粒径等粒度参数呈正相关关系，这表明研究区晚更新世黄土磁学性质主要受沉积粒度的控制，符合西北地区黄土磁学增强机制的风动力模式；黄土砂粒组分的变化揭示约41~14ka期间，研究区晚更新世气候呈逐渐干旱化的趋势，但具有不稳定的特点。

英文摘要：

The magnetic characteristics and paleoclimatic implications of Late Pleistocene aeolian sediments in Central Asia have attracted wide attention.The loess on the north piedmont of the Tian Shan Mountain is one of the most important parts of aeolian deposits in Central Asian, and thus this region is an ideal place to study the aridification during the Late Cenozoic in the Asian interior.In this paper, we report the results of chronological, sedimentological, rock magnetic, geochemical and climatic studies of Late Pleistocene loess from the northern Chinese Tian Shan Mountain.The 173 loess samples were collected from the about 8.6m-thick ürümqi River section （URS：43°30＇02.77＂N, 87°19＇26.53＂E; elevation 1673m above sea level） with the vertical interval of 5cm in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland.Our results reveal：（1）Optically stimulated luminescence （OSL）dating constrains the time spans of URS loess sedimentation from ca.50ka to 14ka.（2）The investigation of grain size shows the URS loess grain size distribution is mainly dominated by the silt fraction（2~63μm）, while the contents of clay（〈2μm）and sand（〉63μm） are less.（3）The rock magnetic analysis indicates that medium-coercivity component of the URS loess contributes to the magnetic susceptibility, but the contribution of high-coercivity minerals to the magnetic properties is limited.The further analysis indicates that the pattern of rare earth elements（REEs）of URS is indicative of a possible stable source area of the URS loess deposits, thus change in source area cannot interpret the observed variations of rock magnetic parameters in the URS.Therefore, the sediment particle size composition plays a key role in the variations of magnetism of the URS loess sediments.This is confirmed by correlation analyses between the magnetic parameters（χlf, χARM/χlf, and χARM/SIRM） and the sediment grain size parameters（〉63μm and median particle diameter） respectively, whi