干旱区绿洲的成因类型及演变

Formation causes and evolution of oases in arid areas

绿洲是伴随干旱区荒漠环境的形成而形成的。天然绿洲形成与水、土条件关系密切,人工绿洲形成则与水土及矿产资源开发有关。荒漠区绿洲受水、土条件的限制,具有沿河流冲积平原呈带状,在河流出山口呈扇状或点状分布的特点。绿洲分布模式主要有沿河道线状分布、沿河谷阶地层状分布、沿山麓平原片状分布、沿断层或洼地泉水出露地点零星点状分布等4种。基于绿洲形成与水、土关系密切,而地貌及其过程对水、土条件有制约作用的事实,考虑绿洲成因类型及其演变过程,以绿洲“状态成因”为分类原则,选取(1)绿洲的地名;(2)绿洲形成的地貌形态成因类型;(3)天然植被类型与人工绿洲形成结果等为指标,进行绿洲成因类型的划分。各绿洲成因类型的特点不同。在人为与自然因素的综合作用下,绿洲类型常发生由天然绿洲→人工绿洲、绿洲→荒漠或荒漠→人工绿洲演变,其演变模式主要有6种。

Oases form under desert environment in arid areas. Because of the limitation of water and soil conditions, the formation of natural oases is closely related to water and soil conditions, whereas the formation of artificial oases is related to water, soil and mineral resources. Oases in desert regions are generally distributed in belts in the alluvial plains but in fans or spots in the debouchures. There are 4 oasis distribution patterns, i.e., the belt-shaped distribution along watercourses, step-shaped distribution along valley terraces, area-shaped distribution in piedmont plains, and spot-shaped distribution along faults or in depressions with springs. As the formation of oases is closely related to the water and soll conditions and the water and soil conditions are strongly affected by landforms and their processes, the formation causes of oases are classified based on considering the oasis types and oasis evolution by selecting the oasis names, formation causes of landforms affecting oasis formation, and natural vegetation types and artificial oasis formation as the indexes. The features are different from different oases. Under the joint effects of artificial and natural factors, the oasis evolution patterns are generally as＂ natural oasis→artificial oasis, and oasis→desert or sand desert →artificial oasis. There are 6 oasis evolution modes in Xinjiang.