绿洲的发生类型及时空演变

ON THE OASES GENEIS TYPES AND EVOLUTION IN TIME AND SPACE

本文阐述了对绿洲定义的理解，并就绿洲的发生类型、形成机制、时空变迁及开发建设转化条件诸方面较详细的发表了见解。

The formation mechanism,genesis types and evolution regularities in time and space of the oases are briefly summed up.According to their geographic situations and climaticconditions,the oases can be classified into two types,those of the subtropic zone and thoseof the temperate zone. Oases llre located on different landrorms such as alluvial fan,alluvialplain and delta. Since Holocene,the evolution of the oasis in Northwestern China’s arid area has gonethrough four evolution stages. The first one is primitive ollsis,the second is palaeo-oasis,the third is old oasis,and the last is neo-oasis. In sum,those factors,such as climatic change,channel migration of rivers,expansionof sandy desert,salinization of soil,destraction of war and population increase, etc. causedthe dlscard of oasis. There are two kinds of regularities for the oasis change. One is changing from lowerreaches of a river to its upper reaches,namely,headward migrating;the other is developingacross a river in pace with downcutting and terrace formation.