海岸、内陆沙漠与大陆架砂质沉积石英颗粒表面结构的对比研究

A CRITICAL EVALUATION OF THE HYPOTHESIS OF CHINESE CONTINENTAL SHELF DESERTIFICATION

东海大陆架砂质沉积石英颗粒表面结构与东海现代海岸沉积具相似性，而与内陆沙漠具明显的差异性。末次冰期时东海大陆架属河口－海岸环境，部分地区发育有海岸风成堆积，但未见大陆架发生过大规模沙漠化的迹象。

Wince 1991, some researchers have proposed a hypothesis claiming that the continental shelves of China were once a desert environment during the low sea level period of the last glacial maxima in late Pleistocene. This hypothesis has been used to interpret the origin and formation of the remaining deposits in the shelf regions. The hypothesis' main evidence includes the disintegration of the integrated marine stratum, extensive mixed deposits, endless erosional surface texture of repose angle, buried dune groups and ventifacts, etc.. We argue that although it is logical to use such evidence for large scale analysis of the geological environment of China's continental shelves during the late glacial maxima, it is inadequate to prove the validity of the hypothesis. Moreover, the hypothesis does not consider the impact of the post glacial marine transgression on the aeolian san which might have been on the continental shelves. The paper explores four specific issues. (1) Lacking biological evidence, the criteria used to analyze aeolian sand facies (ancient sand dunes) and desert environment (ancient desert) should be comprehensive and based on multiple indices. The selected indices should be able to diagnose the processes and environmental features. However, the hypothesis' indices such as the “buried sand dune groups” are mostly multiorigin indices that are not unique to desert environment. (2) Although ventifacts (aeolian gravel) are an indicator of intensive aeolian process, they do not surely represent arid desert environment. A comparison of the characteristics of the egometry and surface textures of the gravel indicates that the gravel from the seabed of the South Huanghai Sea differ significantly from the typical ventifacts of the modern desert environment. Hence they should not be regarded as one and the same thing. (3) Under the dry and cold climate conditions during the glacial period, aeolian sands (dunes )were difficult to be cemented and diagenized, and they may be easily destructed or regormed by post glacial marine transgression. Therefore, such sediment structures as “texture of repose angle” and such sand dune morphologies as the “buried sand groups” are not likely to be preserved extensively. In conclusion, the remaining deposits on the continental shelves of China should not be regarded as ancient desert deposition.