近年来中国第四纪研究与全球变化

RECENT PROGRESS OF QUATERNARY RESEARCH OF CHINA AND GLOBAL CHANGES

多种多样的第四纪沉积物广泛分布于中国的陆地和海洋，黄土、沙漠、红土、湖泊、岩溶、冰川以及悠久的历史文化，有着丰富的气候环境演变信息，全球在第四纪时期发生的各种变化，出现的各种事件几乎都可以在中国找到记录。青藏高原的隆升对周边乃至全球的环境演变有着重要影响。中国是进行全球变化研究的重要地区。

Extensive environmental changes took place during Quaternary. It is in this period that the regime of modern geomorphology of China was set up. With its vast territory covering the north temperate to the subtropical and the tropical zone,the country is diverse in geomorphological features, biotas, geological and tectonic backgrounds and Quaternary deposits. Almost all events of global environmental change can be found in the country.Quaternary sediments are useful materials to reconstruct the Quaternary environmental history. Among them, loess is in all senses the most important carrier of the environmental information in China. Characterized by its tremendous thickness and almost complete sequence, loess occupies an area of 450 000 km2, mainly concentrated in the Loess Plateau. Paleomagnetic dating revealed that the Gauss/Matuyama boundary is just near the bottom boundary of loess[4]. It strongly support the suggestion of setting the bottom boundary of Quaternary at about 2.5 Ma B.P. Alternations of loess and paleosol reflect climatic changes.Thirty-seven alternations of loess and paleosol were recognized since 2.5Ma B.P.and indicate the same numbers of climate cycles. Each cycle start& from a cold and dry episode to accumulate loess and ends with a warm and wet episode to produce paleosol[2,3].Paleosol S0 now to Paleosol S26 at 1.8Ma B.P. in typical loess sections can clearly be found their correspondences after Stage 61 of the deep sea isotopic curve[6]. In addition, a depth-age conversion curve obtained from the Weinan loess section[7] is roughly correlatable to the SPECMAP curve[8].The distribution of loess is closely related to that of desert. The loess-desert transition belt is fragile and sensitive to environmental changes. The expansion and reduction of desert are dependent upon environments.Lakes are other reservoirs of information of envilronmental changes.There are a great number of lakes in China: fresh water lakes are mainly distributed in East China and the Yunnan-Guizhou Plateau, while closed inland salt water lakes are distributed in Northwest China and the Qinghai-Xizang (Tibet) Plateau.The elevation of these salt water lakes varies from-155m to 4 900m. In the Qarhan salt lakes there are two thick salt beds: one brine salt bed formed at 25 000a B.P.and another potash salt bed formed at 15 000a B.P. These two salt beds represent two salt-forming episodes and hence two relatively .dry stages in Northwest China[12].The fluctuation of the lake-water level is another indicator of climate change.Higher lake-water levels and the desalination of salt lake water usually correspond to moderate climate and higher precipitation.China is one of countries with well-developed karst in the world. There has been karst from Proterozoic to Quaternary and from subtropical South China to arid-semiarid North China[15]. Both climate changes and tectonic subsidence and uplift influence the development of karst. Especially in Southwest China, a variety of karst landscapes formed during Quaternary provide abundant materials for reconstructing the tectonic and climatic change history[16].China has a vast sea area and a long coast line, which provide favorable conditions for studying eustatic movements and climate fluctuations. There are seven warm epochs and six cold epochs to be recognized from marine and coastal sediments.The Quaternary environment changes of China have been strongly influenced by the neotectonic movement, especially in the Qinghai-Xizang Plateau. The uplift of the plateau during Quaternary is estimated to be about 3 000 meters or more with an average rate of 1-1.5mm/a[18]. Moreover, repeated precise geodetic leveling surveys carried out recently show that the uplift is still going on now. The long-time and large-scale rise of the Qinghai-Xizang Plateau is not a negligible factor not only for studying China's Quaternary environments but also for studying global changes.A lot of palaeoanthropological relics have been discovered in China, including representative fossils of almost every development stage of ma