陕西榆林风沙滩区全新世气候和环境变迁

榆林长城沿线处于环境变化敏感带，其风沙滩区沉积剖面的磁化率和粒度分析结果显示，该区全新世早期11500～10000aBP随着全球气候的逐渐转暖，磁化率、黏粒和粉沙含量逐渐增高；全新世中期的10000～45003BP气候相对比较湿润，植被覆盖度增大，风沙活动减弱，地表沉积物当-中粉沙和黏土成分含量显著增大，风化成壤作用增强，地表发育沙质弱古土壤；全新世中期后段的4500～3000aBP期间，气候以比较温和湿润为主，但在4200～4000aBP出现一个气候干旱事件，风沙活动强烈；近3000a以来，气候显著干旱化，波动频繁，地表风沙沉积物显著变粗，表现出有5次沙漠扩张。该区生态环境演化、人文历史变迁基本上是自然因素与人为活动综合作用的结果，以自然演化为主，近代人为因素对环境变化起着加强和放大作用。

Holocene Climate and Environmental Changes in the Eolian Sand Section of Yulin, Shaanxi Province

The eolian-sand section along the Great Wall in Yulin, Shaanxi province, is sensitive to climate and environmental changes. The magnetic susceptibility and particle-size analysis in Dabaodang profile showed that the early Holocene（11 500～10 000 a BP）, was a transition during the change in eolian regime and dust source because of the weakened northwesterly monsoon along with the global climatic amelioration; the middle Holocene （10 000～4 500 a BP） was relatively humid, while vegetation coverage increased, aeolian activities weakened, silt and clay compositions were significantly increased, weathering pedogenesis was enhanced, and sandy weak paleosols were developed; the late stage of the middle Holocene（4 500～3 000 a BP） was mild and humid in general, but at 4 200～4 000 a BP an arid climate event occurred, with intensive eolian sand activities; the climate was droughty and fluctuating frequently in recent 3 000 a, while eolian sand was significantly coarser, which showing 5 times desert expansions. Natural factors played an important role in the environmental changes in this area, and human activities greatly strengthened and amplified the changes at the modern times.