鄱阳湖湖滨沙山垄状地形的成因
收稿日期: 2009-08-17
修回日期: 2009-12-29
网络出版日期: 2010-03-30
基金资助
国家自然科学基金项目(40771023; 40401006)
Genesis of Ridgelike Landform on Sand Hill on the Shore of the Poyang Lake
Received date: 2009-08-17
Revised date: 2009-12-29
Online published: 2010-03-30
Supported by
National Natural Science Foundation of China, No.40771023; No.40401006
江西星子县沙岭沙山位于鄱阳湖湖滨，临湖一侧发育顺盛行风方向延伸的垄状地形。研究从地貌学、沉积学和年代学的角度分析了垄状地形的成因。按照目前的风场计算出的沙丘走向与合成输沙方向近于垂直，说明这些垄状地形不是纵向沙丘。垄状地形内部发育平行层理，缺少滑动面，则进一步表明垄状地形并非沙丘。对垄状地形之间的沟谷形态观察后发现，这些沟谷与前丘上槽形风蚀坑形态颇为相似，且沙山的环境具备发育槽形风蚀坑的基本条件，所以我们将垄状地形之间的沟谷视为槽形风蚀坑。为确定风蚀坑的形成时代，我们在沙山上风区、下风区边缘选取了6 个剖面，测得的28 个光释光年龄显示，构成垄状地形的沙层堆积于约20 ka BP以前的末次冰期。据此我们推测在冬季风最强的阶段(18-14 ka BP)，沙山由以前的风沙堆积转变为风沙侵蚀，产生了槽形风蚀坑。相邻槽形风蚀坑之间的条状突起就构成了垄状地形，因此星子县沙岭沙山临湖一侧的垄状地形属于风蚀地貌。
韩志勇, 李徐生, 张兆干, 陈英勇, 杨达源, 弋双文, 鹿化煜 . 鄱阳湖湖滨沙山垄状地形的成因[J]. 地理学报, 2010 , 65(3) : 331 -338 . DOI: 10.11821/xb201003008
Sand hills are mainly composed of aeolian sands developed along the north shore of the Poyang Lake. The sand hill at Shaling is situated in Liaohua town of Xingzi county. The relative height of this sand hill is about 100 m and it covers an area of about 10 km2. Ridgslike landform develops on the side facing the Poyang Lake. These ridges trending to merge downwind parallel to the prevailing wind and were assumed to be the sand ridge (longitudinal dune). Although the ridge lines are relatively straight, both the space between contiguous ridges and the length of ridge are different from each other. Based on the wind data measured between 2005-10 and 2006-09, we calculate the bedform trend (132o) with maximum gross normal transport and resultant transport direction (42o) using Trend program. The result demonstrates that only transverse dunes can develop under present wind regime which might be similar to those when ridgelike landform formed because Shaling region is controlled by the funnel effect. Sand mining along the shore expose sections that reveal the sediment structure of the ridgelike landform. Some ridges are composed of two layers, i.e. the surface layer and the interior layer. The surface layer (about several tens of centimeters in thickness) shows massive structure, while the interior layer shows parallel bedding truncated by the former on both sides of the ridge. This structure indicates the slideface is absent within these ridges, and that these ridges are of erosion landform instead of accumulation landform. The erosion postdates the deposition of the interior layer and predates the deposition of the surface layer. Optically Stimulated luminescence (OSL) dating is carried out on 6 sections. 28 OSL ages show that aeolian sand deposited extensively on the sand hill about ~20 ka BP and formed the interior layer. The thicker surface layer in the downwind region only began to deposit at ~0.2 ka BP. Therefore, we conclude that the ridges on the sand hill belong to erosion landform. Since the blowout is a common erosion landform developed in sandy region, the depression between ridges is suggested to be an unusual trough blowout although it exhibits some difference compared with the typical trough blowout developed on foredunes. We think these trough blowouts were shaped during a period of the most strengthened winter monsoon (18-14 ka BP). After that time, trough blowouts were probably modified by both the erosion of the Poyang Lake since ~1 ka BP and the sand hill reactivation initiated by human activity in the past ~0.2 ka BP.
Key words： Poyang Lake; sand hill; ridgelike landform; blowout; OSL
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