Analysis on non-tectonic origin of linear scarps in alluvial-proluvial fan of the west bank of Xidong in Hexi Corridor
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摘要: 构造、侵蚀与人为等多种因素均影响着冲洪积扇线性陡坎的形成和发现。结合无人机高分辨率遥感影像解译、地形地貌剖面分析、探槽开挖、工程地质剖面分析和音频大地电磁探测等多种方法,对河西走廊西洞西滩冲洪积扇发育的线性陡坎地貌由浅及深开展综合对比分析,得到如下结论:地形地貌剖面显示线性陡坎两侧地形高程递变平缓,未见变形现象;探槽揭示了线性陡坎两侧下伏的地层连续,底部地层近水平产出且产状明显小于顶部地层,未见地层错断现象;工程地质剖面表明线性陡坎两侧的Q3冲洪积砂卵砾石层顶面连续,未见地层错动现象;音频大地电磁探测结果显示线性陡坎两侧下伏基岩界面连续完整,未见断层通过迹象。因此,综合认为河西走廊西洞西滩冲洪积扇发育的线性陡坎地貌是由大磁窑河水侧向侵蚀作用形成的,而非构造作用所致。Abstract: The formation and discovery of linear scarps in alluvial-proluvial fan are affected by many factors, such as structure, erosion and human activities. In this paper, combined with the UAV high resolution remote sensing image interpretation, the topographic and the geomorphological profile analysis, the trench excavation, the engineering geological profile analysis and the audio magnetotelluric detection etc., we analyzed comprehensively the landform of the linear scarp developed in the alluvial-proluvial fan of the west bank of Xidong in Hexi Corridor from the shallow layer to the deep layer. The conclusions are as follows: the topographic and geomorphological profile indicates that the terrain elevation on both sides of the linear scarp is turning gradually flat without deformation; The trench reveals that the underlying strata on both sides of the linear scarp are continuous, and the bottom strata are nearly horizontal with the occurrence being significantly less than the top strata and there is no stratigraphic fault; The engineering geological section shows that the top surface of Q3 alluvial-proluvial sandy gravel layer on both sides of the linear scarp is continuous, and there is no formation dislocation; The audio magnetotelluric detection results show that the underlying bedrock interface on both sides of the linear scarp is continuous and complete, with no sign of fault passing. Therefore, it is concluded that the linear scarp landform developed in the alluvial-proluvial fan of the west bank of Xidong in Hexi Corridor is formed by not the tectonic effect rather than the lateral erosion of the Daciyao river.
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表 1 探槽剖面地层描述
Table 1. The description of trench
探槽
编号地层
编号地层特征描述 TC-1 U1 灰褐色砾石与土黄色粉砂混合堆积,厚0.5—0.7 m,偶含砾石,砾石粒径一般为2—10 cm,磨圆和分选较好 U2 粗砂砾石层,厚0.8—1.2 m,砾石磨圆度中等,分选一般,偶见粒径大于5 cm的巨砾,为冲洪积相堆积物 U3 中、细砾石层,偶夹土黄色粉土层,厚0.6—1.2 m,成层性一般,分选和磨圆很差,偶见棱角状砾石 U4 灰褐色砾石层,厚0.3—0.8 m,分选性和磨圆度较差,砾石多呈棱角状,粉砂含量相较于U3层较多,含较多碎石 TC-2 U1 土黄色粉砂层,厚1.5—2 m,成层性较好,偶含棱角状砾石 U2 砾石夹粉砂层,厚1—1.3 m,砾石磨圆一般,多呈棱角状,分选性较差,偶见厚约20 cm的砾石薄层 U3 灰黄色粗砂砾石层,厚1 m,粗砂含量明显多于U2层,砾石多呈次棱角状,分选和磨圆较差 表 2 钻孔岩性描述
Table 2. The description of drilling lithology
钻孔
编号岩性特征描述 1 0—70 m坡洪积碎石土层:主要为泥质粉砂岩,土为粉土;70—110.5 m砂卵砾石层:岩性以泥质粉砂岩为主,局部为花岗岩、砂岩 2 0—32.3 m坡积洪积碎石土层:以泥质粉砂岩为主,土为粉土;32.3—101.5 m冲洪积砂砾石层:泥质粉砂岩为主,局部花岗岩、砂岩 3 0—2.0 m粉土层:土黄色,手搓有砂感,硬塑—坚硬;2.0—100.1 m砂卵砾石层:以泥质粉砂岩、砂岩为主 4 0—52.6 m坡积洪积碎石土层:岩性为泥质粉砂岩,土为粉土;52.6—60 m砂卵砾石层:岩性为砂岩、泥质粉砂岩 5 0—18.5 m坡积洪积碎石土层:岩性为砂岩、泥质粉砂岩,土为粉土;18.5—60 m砂卵砾石层:岩性多呈砂岩,泥质粉砂岩 6 0—2.9 m粉土层:土黄色,干燥、松散;2.9—60 m砂卵砾石层:岩性为砂岩、泥质粉砂岩 -
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