中文摘要：

长江中下游第四纪砂沉积的成因仍然存在争论。通过对江西南昌横岗＂砂山＂剖面石英颗粒表面形态特征的研究,分析探讨＂砂山＂的成因。结果表明：石英颗粒大多呈次棱角状到次圆状,表面具有碟形坑、新月形坑、麻坑等风成特征,还存在贝壳状断口、V形坑、水下磨光面等水成特征,SiO_2溶蚀和沉淀也显著发育。综合分析,横岗剖面是河床砂经风力近距离搬运堆积而成的,是长江中下游第四纪风成砂的一部分。横岗剖面由下而上黄色砂层与褐红色砂层交替出现,褐红色砂层石英砂磨圆度较黄色砂层略好,黄色砂层石英砂表面较为洁净,外动力在石英颗粒表面留下的机械作用痕迹较为清晰,褐红色砂层石英砂表面SiO_2溶蚀和沉淀作用显著发育,部分颗粒表面机械作用痕迹被SiO_2溶蚀和沉淀所遮蔽或改造,颗粒表面凹凸不平,横岗剖面颜色和石英颗粒表面形态的变化记录了该地区由干到湿气候环境的周期性波动。

英文摘要：

The origin of Quaternary sand deposition in the middle and lower reaches of the Yangtze River is still controversial. Preliminary study was made on the surface morphology of quartz grains from the subtropical ＂sand dune＂ section at Henggang, Nanchang County, Jiangxi Province,south China. Scanning electron microscopy （SEM） analysis demonstrations that of the quartz grains are mostly subangular or subrounded, with dish-shaped pits, cres- cent-shaped pits and pockmarked pits that are characteristics of aeolian origin. Conchoidal fracture, V-shaped pits and underwater polished surface, which indicate aqueous origin, are observed. Dissolution and deposition of SiO2 is notable. Some aqueous features were masked or reworked by later aeolian superimposition. Chemical overprint on aqueous and aeolian features was also traced, this reveals the underwater features were formed originally, then the aeolian process contributed, and finally the reworking of post-depositional chemical action occurred. Comprehensive analysis suggests that the sand deposit in Henggang section was formed by aeolian short range transport and accumu- lation of riverbed sands, being part of the Quaternary ＂sand dunes＂ in middle and lower reaches of the Yangtze Riv- er. The alternation of yellow sands and maroon sands in the section reflects the wet-dry variation in the depositional environment. The quartz grains in the yellow sands are often angular or subangular, with clean surface imprinted by mechanical action and displaying clear dish-shaped pits, conchoidal fracture and V-shaped pits, implying a rela- tively arid and wind strength dominated depositional environment. The quartz grains in the maroon sands are more rounded, with many directed dissolution pits, irregular dissolution gouges, siliceous sphernles and siliceous scales. The mechanical action was masked by the later deposition of SiO2. The surfaces of the quartz grains are uneven, or even covered by siliceous films. It gives an indication of post-deposition pedogenesis in the m