中国北方新近纪红黏土记录的古气候意义——与动物群化石序列对比

Paleoclimatic characteristic of Neogene Red Clay in Northern China:the correlation of fossil fauna time series

目的研究中国北方新近纪红黏土序列的古气候演化特征。方法对中国北方4个新近纪红黏土剖面沉积物的粒度、磁化率和化石动物群时间序列进行区域对比。结果黄土高原新近纪红黏土沉积以来发生了5次大的气候事件,气候事件的分界线在粒度、磁化率年龄曲线上特征明显,反映的气候特点与化石动物群演替性质完全一致。结论中国北方新近纪红黏土序列古气候演化过程的气候事件均与青藏高原隆升和东亚季风的发展相联系。时间上,南北气候演化事件基本同步;空间上,北部较南部地区变化剧烈。5次气候事件从下到上表现为半湿润、半干旱、湿润、干旱与湿润交替、干旱的气候演化特征;相应动物群生态类型表现为草原-疏林草原、草原为主的疏林草原、森林、草原荒漠与森林交替到草原的演化特点。

Aim To study the paleoclimatic evolutional characteristics of the neogene red clay sequences in Northern China. Methods Make a comparative study on the age-curve of Grain-size, magnetic susceptibility and fauna fossil time series of four different Neogene Red Clay sections in Northern China. Results Five intense climatic incidents had taken place since Neogene Red Clay was depositted in the Loess Plateau. The boundaries of the climatic incidents are obvious on the age-curves of grain-size and magnetic susceptibility, and the climatic characteristics are absolutely consistent with those of fauna fossil. Conclusion The five climatic incidents are all associated with the uplift of Qinghai-Tibet Plateau and the development of the east Asian monsoon. When it comes to time, the climatic incidents are isochronous on the whole from north to south, while regarding to space, the indicators of the climatic in cidents are more acute in the north than those in the south. The sedimentary sequence of red clay can be divided into five segments by the five intense climatic incidents, and from bottom to top the profiles show their paleoclimatic characteristics as subhumid, semiarid, humid, alternation of drought and humidity, and drought, which correspondingly show their regional environment characteristics as sparse forest grassland, sparse forest grassland relying mainly on grassland, forest, alternation of desert steppe and forest, and steppe.