地文期与地文期研究

PHYSIOGRAPHIC STAGES AND THEIR RESEARCH IN CHINA

在20世纪初期至中期,地文期研究帮助解决了中国新生代地形发育和地层划分的相对时序难题。由于W.M.Davis侵蚀循环学说适用于追溯作整体抬升的高原的“构造运动、过程和阶段”发育特征,所以,如今地文期研究对取得青藏高原隆起历史证据、寻求云贵高原喀斯特发育历史与高原地文发育各阶段间的对应关系,以及重建新生代早期中国地理环境等重要理论与实践问题都具有重要意义。随着地球科学的发展与科学技术的进步,侵蚀循环在理论和方法上应当作些相应补充和修正:侵蚀期所对应的堆积物———初始冲积、断块抬升区边缘的相关沉积,以及年代学问题等,均需要作进一步的研究。

The meaning of physiography was restricted within the category of geomorphology by A. Penck in 1887 from a broad definition of physical geography by B. Varanius. In 1899, W. M. Davis established his theory of erosional cycle or the geographical cycle with terms of tectonics, agencies and time. Davis used stages or periods to summarize different features of landform development on the same landmass when the Crest was relatively steady after uplifting. The research of physiographic stages around the world has been an application of the Davisian theory. The research of physiographic stages in China was first carried out by an American geologist B. Willis in 1903. After that, many Chinese and foreign geologists and geographers had studied physiographic stages of most parts of China before 1950s. They had made great contributions to the preliminary understanding and establishing of the frame of the Cenozoic stratigraphy and regional tectonic history in China. During the 1950s and later on, research on physiographic stages in China was stagnated owing to the influence of the pre-Soviet geo-science thoughts and the emphasis on application research. However, physiographic record is an important part of palaeo-environment information and the methods of physiographic research are mainly based on macro section analysis. It has practical significance for modem geomorphology, Quaternary geology and Cenozoic geography. That is why many scholars, such as Yang Zhongjian （Young C C）, Liu Dongsheng （Liu Tungsheng）, Zhou Tingm （ Chow T Z） , Luo Laixing et al. , emphasized the fundamentality of carrying out profound research of physiographic stages during the 1970s. The Qing-Zang （Tibet） Plateau was formed in an interrupted uplifting way as a whole, whereas the Himalayas was formed as a folding product. The plateau began to rise around a time between the Early and Late Cretaceous （Liu Xun et al. 1985）. But the Himalayan Sea lasted until the Neogene （Chu Xuchun, 1985）. Thus, the orogenetic movement of the Himalayas must have been later than that. As the plateau is an uplifted integer with interruption, the research of physiographic stages on it will accord with the principles of the Davisian theory. But the physiographic record about the plateau uplifting has not been studied in detail at present. The lack of physiographic research makes it difficult to have a better understanding of the background and processes of the formation of the modem pattern of geographic environment in China and the history and processes of eolian deposits in China. The Yun-Gui Plateau is also a place where more physiographic studies are needed. This region has the most typical surface and underground karst landforms with the widest distribution and most diverse types in the world. The relationship between the karstification history and the stages of physiographic evolution still remains an issue which waits for the researchers of phisigraphic stages to tackle. The theory and methodology of physiographic stage research should be modified and enriched with the progress of sedimentology, geomorphology, chronology and other relating disciplines and the development of science and technology. For instance, it should be realized that firstly, there are primary alluviums deposited along river valleys in mountainous regions during an erosion stage and graded alluviums and aggradational alluviums are two kinds of sediments formed in a depositional stage under different conditions; secondly, the research of denudation areas should be integrated with the study of accumulation areas using the roles of correlative sediments ; thirdly, the chronological research will be helpful to raise the precision of the results of physiographic stage research and the chronological study of the regolith on planation surfaces is one of the keys to confirm erosion stages. To sum up, the research of physiographic stages in China still has its theoretic and practical significances.