中文摘要：

通过对黄土高原西峰和洛川黄土剖面末次冰期较高分辨率的蜗牛化石组合研究发现，深海氧同位素第3期（MIS3）（59—29kaB．P．）黄土高原的气候变化可分为3个阶段：MIS 3c时期，气候总体相对温暖湿润，但暖湿程度远不及全新世时期，这一阶段出现两次比较温湿的气候波动，西峰最温湿的时期发生在约48—46kaB．P．，其次在约54kaB．P．，洛川较温湿的时期出现在约57kaB．P．；MIS 3b时期，西峰气候比较寒冷，但具有一定的湿度，洛川总体上气候比较冷湿，但较之于西峰无论是温度还是湿度都要高一些；MIS 3a时期，西峰的气候从温凉变得冷干，洛川出现频繁的气候波动。研究认为黄土高原MIS 3c时期较温湿气候状况可能是受控于这一时期地轴倾角控制的太阳辐射梯度的变化，地轴倾角增大，中纬度夏季太阳辐射强度高于低纬度的辐射强度，使得中低纬度之间夏季太阳辐射梯度增加，低纬度海洋向中纬度大陆传输的热量和湿度增加，夏季风加强，从而改善了黄土高原的温湿度状况，喜暖湿的蜗牛种类得以在冰期的环境中生长发育。蜗牛化石的研究结果显示MIS3时期黄土高原不同地区存在明显的区域性差异，与现今气候格局不同的是这一时期黄土高原存在更大的气候环境梯度。

英文摘要：

Marine isotope stage 3 （MIS 3 ）（59 -29kaB. P. ）is a special interval during the last glacial period. It shows a mild climate and can be further divided into three stages, i. e. ,MIS 3a,MIS 3b,and MIS 3c. Among them,MIS 3a and MIS 3c are two relatively warm and humid stages,and the paleoenvironment and forcing mechanism of MIS 3a have been extensively studied. However, the paleoclimate and paleoenviroment during MIS 3c is less well investigated. Moreover, the forcing mechanism of warm-humid climate during this interval remains unclear. Here we present a high-resolution terrestrial mollusk record from the Xifeng（35 °46′N, 107°41′＇E）loess-paleosol sequence, a typical loess-paleosol sequence in the Loess Plateau. A total of 122 mollusk assemblage samples from the Xifeng section have been taken and analyzed with a sampling interval of 10cm in the S0 - L1 （0 - 74kaB. P. ） , and each sample analyzed weighs about 15kg. The result shows that terrestrial mollusk fossil individuals are abundant,and 16 species have been identified. These species can be divided into three groups, namely cold-aridiphilous, thermo- humidiphilous,and oriental groups. Our study, combined with the previously investigated Luochuan land snail record, reveals that the climate in the Loess Plateau during MIS 3 experienced three stages. 1 ） Relatively warm and humid climate prevailed during MIS 3c, but temperature and humidity at this period were lower than that of the Holocene. In Xifeng,the warmest and most humid climate occurred at about 48 -46kaB. P.,and the secondary one at about 54kaB. P., whereas in Luochuan warmer and more humid climate happened at about 57kaB. P. 2）Relatively cold and dry climate appeared during MIS 3b. It was milder in Luochuan than in Xifeng at this period. 3）A relatively warm-humid period during MIS 3a. Climate at this time fluctuated frequently in Luochuan, and changed from warm-cool to cold-dry in Xifeng. Our results reveal that the relatively warm-humid climate during MIS 3c may be resulted