Genesis of topography and regional distribution of the concealed red karst landform in the adjoining area of Hunan–Hubei–Chongqing–Guizhou
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摘要: 红色岩溶为新发现的隐伏型地貌,是埋藏于土下、颜色红艳、形态奇特的岩溶地貌。目前,红色岩溶研究主要集中于定义特征、形成条件、地质成因、演化模式等方面,但其独特的形态的形成机制、塑形过程及隐伏的分布范围尚未深入讨论。文章从物质成分差异、节理裂隙切割及差异溶蚀作用三方面分析红色岩溶地貌形态的形成机制,并讨论了塑形的基本过程及关键地质作用。依据红色岩溶地貌发育的判定条件及地层特征,确定了湘鄂渝黔红色岩溶的分布范围。结果表明:(1)岩层中可溶性物质含量差异及层状韵律层是红色岩溶地貌形态塑形的物质条件。它的动力条件是构造节理裂隙切割与岩体差异溶蚀;(2)红色岩溶地貌形态演化经历四个基本阶段,其中节理裂隙切割、岩土界面溶蚀及节理裂隙面溶蚀是塑形的关键地质作用;(3)湘鄂渝黔四省红色岩溶地貌分布总面积达3 433.83 km2,主要分布于湘北、湘西北、鄂西南、渝东南及黔东北。Abstract:
Red karst is a concealed landform that has been newly discovered and is buried beneath soil, characterized by its red color and unique shapes. It is widely distributed in the area of Wuling mountain of Hunan, Hubei, Chongqing and Guizhou in China. Compared with common karst landforms, red karst landforms have four basic characteristics: red color, stratified convex morphology, landform lithology of argillaceous limestone, and different dissolution causes in soil environment. Because of its bright red color and unique appearance, red karst is very ornamental and has great tourism economic value. The morphological origin of red karst has been discussed from the perspective of macroscopic geological conditions and tectonic forces, but its mechanism of microscopic morphological formation and shaping process have not been deeply analyzed. In addition, as a concealed landform, it is difficult to be found on the surface, so determining its distribution is of great significance for the relevant investigation and research. Therefore, this paper discusses the formation mechanism and shaping process of the concealed red karst landform from the microscopical point of view, and determines the distribution range of the red karst in the adjoining area of Hunan, Hubei, Chongqing and Guizhou. It can provide the basis for the future investigation and development of red karst. Material composition differences, joint fissure cutting and differential dissolution are the key factors in the formation of red karst geomorphology. The main reasons are as follows: (1) The content of soluble matter on the convex surface of red karst landform gradually increases from top to bottom, while the content of soluble matter on the concave surface is the highest and that on the convex surface is the lowest. This shows that the difference of soluble material content is the material basis for the formation of convex and convex forms of red karst landform. (2) The joint fissure is a good transport channel for water required by dissolution, which can greatly improve the weathering and denudation efficiency of karst geomorphic area and lays a prototype for the evolution of geomorphic form. (3) When the content of soluble components in the parent rock is high, the dissolution rate is fast and concave, and on the contrary, it is convex, which causes differential dissolution. During the formation of red karst landform, the difference of material composition horizontally leads to differential dissolution, and the decrease of erosion vertically leads to differential dissolution. Therefore, the difference of soluble material content in rock composition and the layered rhythmic layer are the material conditions that lead to the diversity of red karst geomorphology, and the dynamic conditions are the cleavage of structural joints and the differential dissolution of rock mass. The evolution of red karst morphology mainly goes through four basic stages: the formation stage of material conditions for morphological development, the emergence stage of dissolved rock layers, the formation stage of erosive groundwater in weathered soil, and the stage of differential dissolution in soil. The formation of red karst mainly goes through three key geological processes: (1) joint fissure cutting; this effect has mainly shaped the outlines of trapezoids and cylinders. (2) rock and soil interface corrosion; due to the undulating rock surface, the rock and soil interface corrosion makes erosive groundwater with fast dissolution rate accumulate in the low concave of the surface, often forming a conical or sharp rock mass. (3) dissolution of joint fissure surface; vertically, due to the continuous consumption of erosive H+ ions, both the dissolution ability and dissolution rate decrease, with the increase of depth, forming an approximate V-shaped grike; at the same time, the erosive groundwater dissolves the rock wall on both sides of the joint fissure surface in the transverse direction, and is controlled by the difference of soluble material composition, forming the concave-convex interlayer. According to the definition of red karst geomorphology and the field investigation by the research team, five factors such as color, morphology, lithology, exposure and geomorphology conditions are selected as the criteria for determining red karst geomorphology. The rock composition of the red karst geomorphology in Hunan, Hubei, Chongqing and Guizhou is more dependent on the stable distribution of purplish red nodular limestone and argillaceous limestone in Dawan Formation, supplemented by the purplish red carbonate rock in Guniutan Formation or the Cross Pu Formation, in which the outcrop area of Dawan Formation is the key development area. According to 1∶200,000 geological map, the potential distribution area of concealed red karst geomorphology in the adjoining area of Hunan–Hubei–Chongqing–Guizhou covers 3,433.83 km2, and it is distributed in a narrow strip or partially distributed in a patch in SW–NE direction. -
表 1 碳酸盐岩溶蚀试验结果
Table 1. Results of the test for carbonate karst dissolution
编号 粉末量/g 溶蚀残余量/g 溶蚀量/g 溶蚀百分量/% Y1 13.589 2.481 11.108 81.74 Y2 7.786 1.306 6.480 83.23 Y3 11.501 2.388 9.113 79.24 Y4 11.315 2.565 8.750 77.33 Y5 11.710 3.231 8.479 72.41 Y6 15.602 5.210 10.392 66.61 表 2 红色岩溶界定标准(修改自姜伏伟等[2])
Table 2. Definition standard of red karst (modified from Jiang Fuwei, et al[2])
依据内容 特点标准 颜色 红色系,包含紫红色、深红色、鲜红色、浅红色、粉红色等。 形态 层面互层凹凸,凹凸层数大于10层,凹凸程度大于10 cm。 岩性 奥陶系中下统的泥质灰岩、泥灰岩、灰岩-泥岩互层等含一定泥质的可溶岩。 裸露情况 岩体整体/局部裸露。 地貌条件 山顶出露,沟谷出露,斜坡出露。 表 3 奥陶系大湾组、牯牛潭组和十字铺组分布区域
Table 3. Distribution area of the Ordovician Dawan Formation, Guniutan Formation and Cross Pu Formation
地层 地区 湖北省 湖南省 贵州省-重庆市 恩施-
黄石区通山-
崇阳区郧西-
随州区湘西北区 湘中小区 鄂西南 渝黔 扬子-华南
过渡区八面山
小区武陵山
小区秀山-江
口小区城口-巫
溪小区湄潭
小区三都
小区奥陶系中统 庙坡组 大田坝组 胡乐组 两岔口组 牯牛潭组 舍人湾组 烟溪组 风洞岗组 庙坡组及
牯牛潭十字铺组 十字铺组 奥陶系下统 牯牛潭组 宁国组 吊麻沟组 大湾组 大湾组 九溪组 桥亭子组 紫台组 湄潭组 同高组 表 4 湘鄂渝黔红色岩溶地貌潜在分布面积统计
Table 4. Statistics of the potential distribution area of red karst geomorphic landform in the adjoining area of Hunan–Hubei–Chongqing–Guizhou
序号 图幅名称 分布面积/km2 分布区个数 1 大庸幅 46.38 23 2 恩施 215.89 12 3 黔江 279.45 31 4 桑植 132.22 20 5 石门 215.31 7 6 湄潭 209.60 98 7 瓮安 193.30 46 8 咸丰 244.43 24 9 永顺 377.76 75 10 酉阳 511.36 31 11 吉首 429.26 19 12 镇远 92.81 22 13 芷江 16.81 5 14 沿河 155.81 18 15 江口 116.61 73 16 都匀 196.83 72 合计 3 433.83 576 -
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