DEVELOPMENT AND EVOLUTION OF HORQIN SANDY LAND AND ANCIENT HYDROLOGICAL NETWORKS
科尔沁沙地及其古水文网的演化变迁

In Horqin region,the formation and development of sandy land was closely related to the change and evolution of ancient rivers.In the paper,the macroscopic features of sandy land and drainage network were carefully analyzed according to remotely sensed images and field investigations.It was found that there were five identifiable stages of drainage network,codes as paleochannel-Ⅰ to -Ⅴ.The distribution characteristics of each drainage network stage were different from other's.There were at least four activation stages of desert.The paleochannel-Ⅴ might develop before the desert-Ⅱ and -Ⅲ and might form before the last glacial period,or an earlier period,such as midPleistocene.In the stage,rivers in Horqin areas flowed into the paleo-Songliao lake.The paleochannel-Ⅳ formed when the desert-Ⅱ and/or-Ⅲ developed.In the stage that might be the last glacial period,rivers in Horbin and the paleo-Songliao lake shrank and the rivers disappeared in deserts and did not flow into the paleo-Songliao lake.The paleochannel-Ⅲ developed after the desert-Ⅱ and -Ⅲ when may be the last deglaciation period.In the stage,temperature-rising result in a large amount of snow and ice melt-water to flow into rivers and overflow into lowlands between sand ridges to connect the ancient-Xilamulun river,the ancient-Laoha river and the ancient-Jiaolai river.The paleochannel-Ⅱ might form during the Holocene Optimal period.In the stage corresponding to the desert-Ⅰ stage,the uniform west-Liao river formed and there were several times of desert activation and dormancy.The river-Ⅰ developed at present and belong to the desert-Ⅰ stage.Most active deserts distributed in the Wengniute area.