Eogenetic karst from the perspective of an equivalent porous medium
Eogenetic karst from the perspective of an equivalent porous medium
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DOI：
10.1007/bf03176484
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发表时间：
2002-09
影响因子：
1.4
通讯作者：
H. Vacher;J. Mylroie
中科院分区：
文献类型：
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作者：
H. Vacher;J. Mylroie
年轻石灰岩在其沉积物附近经历大气成岩作用（自生岩溶），其孔隙主要为双重孔隙，由触洞通道和穿过粒间孔隙基质的优选通道组成。相比之下，灰岩的孔隙度经历陆上侵蚀埋藏成岩作用和隆起（晚期岩溶）主要是一个双重孔隙度的裂缝网络内的管道组成。这两种岩溶之间的鲜明对比可以通过它们在一张图上的位置来说明，该图显示了由直的圆柱形管组成的等效多孔介质的水力特性（n-D空间，其中n是孔隙度，D是管的直径，logn是对logD的作图）。对碳酸盐小岛屿的水文研究表明，水平导水率K在岩溶演化过程中呈数量级增加。早期的岩石学研究表明，在始新世成岩作用期间，石灰岩的总孔隙度几乎没有变化。因此，成岩岩溶的灰岩在空间上沿水平方向移动。相反，从初始沉积物质到晚期岩溶的路径包括在埋藏成岩作用期间随着n的减小而下降，然后在隆起和暴露期间由于裂缝的打开而随着D的增加而侧向移动，最后在沿着裂缝的通道发育期间增加D和n。碳酸盐岩与下层不透水岩石接触处的溪流洞穴（以及由此衍生的碎屑岩成因洞穴）;沿着台地边缘裂缝的垂直洞穴;表层岩溶;沿着地下水位的潜水囊（香蕉洞）;以及在沿海淡水-盐水“界面”形成混合室的侧缘洞穴。相比之下，晚期岩溶的洞穴是一个相互连接的管道系统的一部分，该系统将整个地区排干。碳酸盐岩小岛屿的始新世洞穴，在大多数情况下，没有显着参与岛屿的排水。
The porosity of young limestones experiencing meteoric diagenesis in the vicinity of their deposition (eogenetic karst) is mainly a double porosity consisting of touching-vug channels and preferred passageways lacing through a matrix of interparticle porosity. In contrast, the porosity of limestones experiencing subaerial erosion following burial diagenesis and uplift (telogenetic karst) is mainly a double porosity consisting of conduits within a network of fractures. The stark contrast between these two kinds of karst is illustrated by their position on a graph showing the hydraulic characteristics of an equivalent porous medium consisting of straight, cylindrical tubes (n-Dspace, where n is porosity,Dis the diameter of the tubes, and lognis plotted against logD).Studies of the hydrology of small carbonate islands show that large-scale, horizontal hydraulic conductivity (K) increases by orders of magnitude during the evolution of eogenetic karst. Earlier petrologic studies have shown there is little if any change in the total porosity of the limestone during eogenetic diagenesis. The limestone of eogenetic karst, therefore, tracks horizontally inn-Dspace. In contrast, the path from initial sedimentary material to telogenetic karst comprises a descent on the graph with reduction ofnduring burial diagenesis, then a sideways shift with increasingDdue to opening of fractures during uplift and exposure, and finally an increase inDandnduring development of the conduits along the fractures.Eogenetic caves are mainly limited to boundaries between geologic units and hydrologic zones: stream caves at the contact between carbonates and underlying impermeable rocks (and collapse-origin caves derived therefrom); vertical caves along platform-margin fractures; epikarst; phreatic pockets (banana holes) along the water table; and flank margin caves that form as mixing chambers at the coastal freshwater-saltwater “interface”. In contrast, the caverns of telogenetic karst are part of a system of interconnected conduits that drain an entire region. The eogenetic caves of small carbonate islands are, for the most part, not significantly involved in the drainage of the island.