~8Ma以来中国东部半湿润区构造与轨道尺度的季风演化及其全球变化信号

Monsoon dominates the climatic change of the East Asia area. After the eastern Asian monsoon occurred, several important environmental events took place associated with the strengthen of inland aridification. The events were assumed to be related to the uplift of the Tibet Plateau. However, the signals that were related to the uplift of the Tibet Plateau, the inner system fluctuations of the Asian monsoon, and global climate respectively may be different and should be indentidied from various records. Thus, a record of the eastern Asian monsoon that was not influenced directly by the uplift of the Tibet Plateau is important to analyze the properties of the climatic change events and evaluate and their influence. In the study, a long core of the Cenozoic sediments from the Huaihe basin was chosen because the basin is the inland basin in the most of the Cenozoic period and sedimentary materials from the Tibet Plateau began to deposit in the basin only in the late Quaternary. The evolution sequence of the Eastern Asian monsoon that represented the climatic characteristics of the semi-humid region will be gotten from the core record. The occurrence time of the winter monsoon and the sedimentary facies related to glacial-interglacial cycles in the semi-humid region will be investigated. The coupling manner and the evolution events of winter and summer monsoons during the Cenozoic period will be studied in order to reveal the relationship among the uplift of the Tibet Plateau, the development of the Asian monsoon and the global climatic fluctuations.

东亚季风主导着东亚地区的气候变化，自第三纪形成以来发生了多次伴随着内陆干旱化加强的重大变动，被认为与青藏高原隆升存在密切联系，然而各种记录中分别与高原隆升、季风演变和全球冰量变化有关的信号还有待区分，尤其是需要有东亚季风不受青藏高原直接影响的独立演化信号作对比，才能更好解读气候环境事件的性质和影响范围。本项目拟利用淮北平原新生代沉积长岩芯记录，建立一条晚新生代以来能反映构造和轨道尺度气候波动、不受青藏高原抬升直接影响、代表中国东部半湿润区的季风气候演化序列，从中提取东亚季风的独立演化信号，查明中国东部半湿润区的粉尘沉积起始时间、冰期间冰期旋回在半湿润区沉积相的表现方式，揭示半湿润区冬、夏季风的耦合方式和演化规律，辨别分别与青藏高原、东亚季风系统、和全球气候波动有关的气候环境事件和过程，探讨东亚季风对高原隆升的响应、以及与全球气候波动的关系。

获得一条晚新生代以来能反映构造和轨道尺度气候波动、代表中国东部半湿润区的季风气候演化记录是本课题的主要科学目标，目的是为了查明东部半湿润区粉尘大规模沉积起始时间、半湿润区冬夏季风耦合方式，并分辨高原隆升、季风演化和全球冰量变化的信号。.课题获得了以下主要成果（1）针对淮河盆地481m岩芯开展了古地磁绝对年龄时间标尺的建立工作，利用对应淮河流域东部三次第四纪火山喷发的三层高磁化率值火山灰层作为绝对年龄控制，参考附近已有岩芯的古生物化石群落深度资料（78.9-82.85 m处早更新世中-晚期东方剑齿象和46.2 m处中更新世晚期葛氏斑鹿和水鹿），最后获得了淮南地区的层序地层岩性柱和8Ma以来的绝对年龄时间标尺，确认淮河盆地自大约8Ma以来开始下降接受沉积。（2）发现在上新世60万年周期、冰期间冰期、全新世等不同时间尺度上，淮河半湿润区与北方半干旱区湿度变化都存在反向波动趋势，即，认为淮河流域这种异于北方干旱半干旱区的气候特征是由于印度季风减弱、西太平洋副高西伸增强造成江淮地区梅雨加强、同时淮河地区冬季风减弱致使梅雨带北移的共同作用所造成的。（3）找到了地质时期黄河入淮的证据，确认了发生在距今大约13000年前的一次黄河入淮事件，这是目前已知最早的黄河入淮事件。（4）发现1.7Ma大规模干旱化开始向东扩展到淮河流域。发现从大约1.7Ma起，岩芯开始转变为以原生和次生黄土为主要岩性，并频繁出现钙质结核，因此可以确认1.7Ma以后淮河流域开始成为亚洲内陆干旱化直接影响地区，是亚洲内陆干旱化的一个重要扩张事件。（5）确认了8Ma以来的东部半湿润区几个主要构造尺度古气候事件，发现淮河半湿润区与全球构造尺度上重大气候事件一致，8Ma盆地拉张形成、6.5 Ma亚洲干旱化加强、3.6-2.7Ma季风加强、2.6 Ma亚洲季风开始稳定波动和0.95 Ma中更新世革命等事件。（6）获得了淮河流域全新世人类活动的黑碳记录，发现人口的增加与黑碳浓度的增加密切相关，识别出~7.5kaBP、~3.5kaBP和1.5kaBP以后三个强烈人类活动造成的多火阶段。