关键词: 鄱阳湖, 沙山, 垄状地形, 风蚀坑, 光释光

Abstract:

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