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福建海坛岛北部海岸发育一座覆盖淡灰黄色风成砂层、相对高度达30 m的大沙山,外貌很像风成大沙丘,但同时又具有冲积扇形态。其成因和沉积环境有待考证,而探明大沙山内部沉积构造是判别其成因的主要途径之一。在野外考察的基础上,运用探地雷达(GPR)对大沙山内部沉积构造进行探测,获得约20 m深度范围内的沉积构造图像数据。结果表明:大沙山中上部发育由棱角状砾石或粗砂细砂组成的沉积旋回和沟槽沉积构造,显示出冲积扇上部的沉积构造组合特点;中下部层面中交替呈现弧形沉积构造,大沙山南侧发育有向南倾斜28°~30°的前积层理。结合大沙山西侧冲沟剖面沉积构造、大沙山表面的棱角状砾石特征以及现代风沙地貌分布规律,初步认为大沙山是山前多期沟谷洪流携带的碎屑物沉积形成的冲积扇残余堆积体,沉积间隙受海岸带风沙活动影响。
On the northern coast of Haitan Island, Fujian, there is a Dashashan mountain covering a light-greyish yellow aeolian sand layer with a relative height of 30 m. It looks like a large windy dune and alluvial fan at the same time. Its causes and sedimentary environment have yet to be verified, and the identification of sedimentary structures within Dasha Mountain is one of the main ways to judge its cause. Based on the field investigation, GPR was used to detect the sedimentary structure inside Dasha Mountain, and the sedimentary structural image data within the depth of about 20 m was obtained. The results show that the sedimentary cycles and grooved sedimentary structures consisting of angular gravel or coarse sand and fine sand are developed in the middle and upper part of Dasha Mountain, showing the features of sedimentary assemblage in the upper part of alluvial fan. Sand hill south of the development of the south slope of 28 ° ~ 30 ° before the plot bedding. Based on the sedimentary structure of the gully profile on the west side of Dasashan Mountain, the angular gravel characteristics on the surface of Dasashan Mountain and the distribution pattern of modern sand and sand landform, it is initially believed that Dasha Mountain is the remnant of alluvial fan formed by the detrital sediments carried by the torrent in the piedmont gully Accumulations and sediment gaps are affected by wind and sand activities along the coast.