中文摘要：

泥河湾盆地油房遗址是中国北方重要的旧石器时代中、晚期遗址，它蕴含丰富的古人类活动遗存。该遗址剖面（1270cm）以风成沉积为主，沉积较为连续，遗址年代大致为56～27ka B.P.（1290～20cm），跨越旧石器时代中期和晚期及深海氧同位素第3阶段（MIS 3），可以为研究泥河湾地区旧石器文化演变与气候变化提供重要依据。本文利用粒度、烧失量，通过端元分析模型，结合关键地层花粉含量及炭屑探讨了泥河湾盆地旧石器中期到晚期文化过渡的环境背景，结果表明：56.0～48.1ka B.P.的旧石器时代中期晚段，沉积物平均粒径较粗，有机质含量较低，细砂含量较高，有流水作用影响，植被以草原为主；48.1～35.2ka B.P.可能是文化过渡时期，该段沉积物粒径和粗颗粒物含量为整个剖面最低值，粘土和有机质含量则为全剖面最高值，环境状况总体较为良好，植被仍以草原为主，但周围山地可能有森林，相对于旧石器中期晚段，其有效湿度增大；35.2～27.4ka B.P.为旧石器晚期文化，该段粒径逐渐变粗，有机质含量逐渐变低，植被覆盖度降低，气候变干；27.4～27.2ka B.P.平均粒径和细砂含量达到整个剖面最大值，粘土和有机质含量为整个剖面最小值，植被盖度最低，气候最为冷干，可能进入寒冷的MIS 2阶段。旧石器中晚过渡期晚段，由于气候环境由温湿向凉干/冷干的转化，可能与H4降温事件有关，泥河湾地区生态环境变差，食物资源短缺，迫使古人改变生产工具-细石器，提高生产力。

英文摘要：

The Nihewan Basin is located in the transitional zone of the North China Plain and the Mongolian Plateau. It is about 80km from east to west and 15～20km from north to south. The Sanggan River flows from west to east. The Nihewan Basin is one of the largest and most concentrated and most abundant areas in Paleolithic of China. Youfang site（40°13＇52″N, 114°41＇02″E; 921m a.s.l.）is located in Nihewan Basin, and is one of the few places across the middle and late Paleolithic, containing both North China small stone relics and microlithic relics. The site profile（depth 1270cm）is mainly composed of wind deposition, and the deposition is continuous. The whole section（1290～20cm）is sampled continuously at intervals of 5cm. A amount of small stones were unearthed in the stratum of 1290～1150cm（56～52ka B.P.）and many fine stone products were unearthed in the layer of 870～20cm（45.3～27.2ka B.P.）. Dating in this section is about 56～27ka B.P. （1290～20cm）dated by the OSL acrossing the MIS 3. The Youfang site can be used for the study Nihewan Paleolithic culture evolution, and provide an important basis for climate change. Based on grain size, ignition loss, combined with pollen and charcoal in the key stratum, the environmental background of transitional period between the mid and late Paleolithic is reconstructed in this paper. The result shows that （1） the average grain size（42μm）is coarse, the clay（12%）and organic matter（3%）content is lower, which is influenced by water flow, and all above shows that the typical grassland environment was the main type during the late period of mid-Paleolithic（56.0～48.1ka B.P.）; （2）the average grain size（27.8μm）and coarse particle content（〉63μm） are the lowest（13.3%）and clay as well as organic matter content（3.6%）are highest in the whole profile in the transitional culture layer（48.1～35.2ka B.P.）, showing good climate and grassland environment and tree pollen concentration is high in the early