A COMPARATIVE STUDY ON DEPOSITIONAL CHARACTERISTICS OF THE COASTAL SAND AND THE CONTINENTAL SHELF SAND OF SOUTHEAST CHINA AND ITS ENVIRONMENTAL SIGNIFICANCE
中国东南部海岸砂与大陆架砂沉积特征比较及其环境意义

The formation and evolution of modem coastal sand and continental shelf sand reflect the dynamic environment characteristics of the land-sea interaction, which have close link with the globe change. Thus, it is a hot spot of the research topics in the area of coastal and ocean sciences. In accordance with the existing disputation on the genesis of the continental shelf sand in China, and according to the basic geological principle, "the present is the key to the past", this paper takes the depositional characteristics of coastal sand of southeast Fujian as the key. It sets up comprehensive environmental indicators for regional coastal sand under the subtropic humid marine monsoon climate. Simultaneously, the author takes the land-sea interaction zone as a unity, for a comparative study on coastal sand and the continental shelf sand. The aim is to find out the responses to Late Pleistocene globe change on the continental shelf sand of the East China Sea, and to expound the characteristics and formation causes of the continental shelf sand. Combined with the analysis of the concept of desertification or desertization, it puts forward a viewpoint that whether the continental shelf of the East China Sea underwent this process or not based on the actual materials. Through the comparative study on the depositional characteristics of the coastal sand and the continental shelf sand, the author recognizes that the coastal sand mainly consists of well sorted, symmetry skewness and find sand, its kurtosis peak is narrow to very narrow. There are abundant impacts of mechanic process on the surfaces of quartz grains. Impacts by river, beach and eolian processes are usually associated with and superimposed one another on the same grain. The triangular marks and V-depressions are the indicating traces of river and beach sand, respectively. The dish-shaped concavities and mechanic pits are the most common surface textures of the coastal eolian sand, but the barchan concavities and curved grain edges are the pilot indicating marks by eolian environment. The heavy mineral assemblages of coastal sand are dominated by relatively high specific gravity which have stable chemical property suggesting the modem high-energy dynamic environments of coast area. It also contains some shell fragments and strong worn foraminiferal tests that are impossibly found in inland desert. The continental shelf sand is with wide range of grain size, and the depositional patterns are quite complicated. It is not well sorted showing typically positive skewness and owns several kurtosis peaks. The various forms of the probability accumulation curves reflect the different transportation ways in diversified environments. The mechanical processes affected on quartz grains are abundant, but impacts by river, beach and eolian processes are also usually associated with and superposed one another on the same grain as the coastal sand. The heavy mineral assemblages of the continental shelf sand sh