摘要
在禹门口南山西省河津、万荣县境内黄河阶地上发育了一些固定、半固定沙丘，注入黄河的汾河将这些沙丘分成了南北两部分。北部的沙丘多在海拔４００ｍ左右，高出现代黄河约３５ｍ，位于黄河的第二级阶地上，由两条南北向的沙垄和两垄之间分布的抛物线形沙丘构成特殊的景观。这些抛物线形沙丘一般高度约７～８ｍ，背风面突出，迎风坡坡度一般为１５°～２０°，背风坡坡度一般大于４０°。风沙堆积下伏的河流堆积物的１４Ｃ年龄为２６．４０±０．８ｋａＢＰ，表明沙丘形成于距今２６ｋａ以来。南部沙丘海拔高度近５００ｍ，高出现代黄河水面１５０ｍ，覆盖于黄河第三级阶地之上。一个天然剖面揭示，第三阶地的底部为黄色中粗砂与灰绿色粉砂粘土互层，中部为灰黄色黄土，顶部为黄色风沙层。在黄土地层中可以识别出Ｓ１古土壤和位于风沙堆积下面的可能为Ｌ１ＳＳ１的弱成土层。由此推断风沙堆积于距今３万ａ以来。黄河阶地上的沙丘是在特殊的地区和特定的时期；强大的风力、丰富的沙源和气候变干条件下形成的。虽然东岸沙丘已是固定、半固定沙丘，但沙化仍然是该地区的一个问题。由于３～４ａ前开始在丘前洼地栽种苹果树，破坏了下风向沙丘迎风面的植被，造成了原来已固定沙丘的活化，在沙丘顶部生成了新?
To the south of Yumenkou, there are some fixed and semi fixed sand dunes dist ributed on terraces of the Yellow River in the Hejin and Wanrong counties of Sha nxi Province. The Fen river divided the dunes into two parts. The dunes in the n orth part, about 400 meters above the sea level and 35 meters above the present table of the Yellow River, are on the second terrace. They are composed of two sand ridges trending N-S and parabolic dunes between ridges. The parabolic dune s are 7￣8 meters high and have convex downwind, their stoss slopes are 15°￣20 °, downwind slopes are around 40°. The alluvial sediments of the second terrac e was dated to be 26 40±0 8 ka BP by the 14 C method, which indicate that the dunes were formed since 26 ka BP. The dunes in the south part, about 500 m above the sea level and around 150 m above the water surface , are on the third terrace of the Yellow River. A natural profile shows t hat the third terrace is composed of interbedded yellow coarse medium sand and siltclay grey green layers in the lower part, grey yellow loess (silts) in the middle part, and aeolian sands on the top. In the loess, the S 1 paleosol and a weaker paleosol, properly the L 1SS 1 and just below the aeolian sands, can be distinguished. It suggested that the aeolian sands were formed since 30 ka BP . The dunes on the terraces of the Yellow River are formed under strong wind, ri ch sand supply, and arid climate in this special area and during the special per iod. Though the aeolian sands are existed in forms of fixed or semi fixed dune s, the desertification is still a problem in this area. Some fixed dunes in the north part reactived because vegetation at inter dunes low lands were replace d by apple tre es 3￣4 years ago. New parabolic dunes over 1 m high formed on the top of the older dunes. Exposed tree roots indicate that the surface soil a nd sand have been eroded about 0 3 m. The wind erosion is also very strong in the south part. For example, roots of persimmon trees to the north of Xifan vil lage in Wanrong County have been uncovered about 1.2 m.
出处
《中国沙漠》
CSCD
北大核心
1999年第2期184-186,共3页
Journal of Desert Research
基金
山西省自然科学项目
国家自然科学基金
关键词
沙丘
局部环境
气候变化
人类活动
黄河
Dunes\ Local environments\ Climatic change\ Human activi ty\ The Yellow River
