浑善达克沙地新生代以来古气候环境变迁

PALAEOCLIMATE CHANGE OF OTINDAG SANDY LAND SINCE CENOZOIC

在干旱-半干旱区，地表强烈地侵蚀和堆积过程不仅影响着区域人类生产活动，而且还通过粉尘传输影响北半球甚至更大空间尺度的气候和环境，因此干旱-半干旱区气候变化研究受到国际社会的普遍关注。浑善达克沙地地处东亚季风的尾闾地带，生态环境脆弱，对气候变化响应敏感，是研究我国乃至北半球干旱-半干旱区气候环境变化的理想场所。该区新生代以来发生多期火山活动，广泛发育玄武岩与沙层、泥页岩、砂岩等互层。文章通过野外实地考察，基于前人在浑善达克沙地火山年代学研究，利用该区已有的玄武岩K-Ar年龄，结合古地磁和释光测年数据约束沉积相年代，建立地层年代框架，通过分析沉积相特征和气候替代指标，发现浑善达克沙地地区气候在晚古新世-早始新世温暖湿润，中始新世和晚始新世相对干旱，渐新世相对湿润；在中新世经历早期暖干到中期暖湿转变，后期又逐渐变得干冷，上新世时相对湿润，一直持续到中更新世，晚更新世变得相对干旱；全新世以来频繁冷暖干湿波动。新生代早期和中期浑善达克沙地气候变化主要受全球气候冷暖干湿变化和青藏高原生长的影响，晚新生代以来全球冰量变化叠加青藏高原隆升共同作用于沙区气候演变过程。

The significant dust source of the Northern Hemisphere is the result of arid and semiarid climate change in northern China. It has already attached increasing attentions of the international community as it can affect the ecological environment of the Northern Hemisphere. Otindag sandy land is located in the arid and semiarid region of Inner Mongolia plateau in northern China, where is the boundary of the East Asian monsoon. The ecological environment in this sand land area is fragile and sensitive to climate change. However, the previous studies on paleoclimate change in this area are mainly concentrated on period less than 20 ka B.P., and the research before 20 ka B.P. have rarely been reported. The volcanic area of Otindag sandy land is an important part of the Cenozoic volcanic region in China. Basalt interbeded with sand layer, mud shale, sandstone and conglomerate formed by multiple volcanic activities is widely developed in this region. In this study, the dating data of K-Ar for basalt, paleomagnetism for clastic rock sediments in fluvial and lacustrine facies and optically stimulated luminescence（OSL） for aeolian sediments are summarized based on the chronology of predecessors in Otindag sandy land. In addition, the corresponding chronological framework of sedimentary strata is established using these age data. Compared with sedimentary facies and climatic proxies, climate in Otindag sandy land was relatively warm and moist from Late Paleocene to Early Eocene. During the Middle Eocene and Late Eocene, climate was relatively arid, and it was warm and humid in the Oligocene. The climate experienced an transition from warm and arid in the Early Miocene to warm and humid in the Middle Miocene, then became dry and cold in the Late Miocene. It was relatively humid during Pliocene and lasted until the Middle Pleistocene. Climate in the study area became relatively arid in the Late Pleistocene. The climate has fluctuated frequently in cold, warm, dry and wet after Holocene. The uplift of the Tibetan Plateau has a great influence on climatic change since Cenozoic in Otindag sandy land. Climate changes corresponded to the global warm and cold events during the Early and Middle Cenozoic. Climatic variations of Otindag sandy land since the Late Cenozoic are interpreted as the teleconnection to the global ice volume change, and the uplift of the Tibetan Plateau which reinforce the East Asian Monsoon.