Flank margin caves can connect to regionally extensive touching vug networks before burial: Implications for cave formation and fluid flow
Flank margin caves can connect to regionally extensive touching vug networks before burial: Implications for cave formation and fluid flow
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侧翼边缘洞穴在埋葬前可以连接到区域广泛的接触孔洞网络：对洞穴形成和流体流动的影响
DOI：
10.1002/esp.5114
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发表时间：
2021
影响因子：
3.3
通讯作者：
Mejia, Jessica Z.
中科院分区：
文献类型：
--
作者：
Breithaupt, Charles I.;Gulley, Jason D.;Moore, Paul J.;Fullmer, Shawn M.;Kerans, Charles;Mejia, Jessica Z.
侧翼边缘洞穴是洞穴孔隙的极端端元，其形成是由于成岩作用驱动较小的溶解孔隙空间的逐步聚结。由于在形成过程中的形态隔离，普遍的假设是，流体流入和流出侧翼边缘洞穴发生通过基质渗透性和相邻的腔室只有通过非基质孔隙在埋藏，坍塌和压裂水力连接。然而，据我们所知，没有研究评估如何侧翼边缘洞穴连接到现代碳酸盐岩台地的区域流动系统。在这项研究中，我们评估的连通性威尔斯，钻孔，蓝洞，并在日益老化的基岩上圣萨尔瓦多岛，巴哈马，潮汐衰减分析侧翼边缘洞穴。在全新世基岩中未报告潜水岩溶特征，来自威尔斯井的渗透率大小表明全新世沉积物沿沿着基质主导的流动路径与海洋相连。威尔斯、钻孔周围基岩的渗透率大小以及海洋同位素子阶段（MIS）5e期间沉积的岩溶特征表明，通过基质和接触洞穴孔隙度与海洋相连。钻孔，蓝洞，和侧面边缘洞穴在前MIS5基岩连接到海洋通过触摸溶洞。我们认为，在圣萨尔瓦多逐渐变老的基岩中观察到的基岩渗透性、洞穴数量和洞穴大小的增加是连续海平面静止带上淡水透镜体累积数量的函数。我们认为，两个最大的洞穴的形态是一致的溶解在多个透镜占据较低的海拔，崩溃导致突破圆顶，并在随后的高位叠印的崩溃室。因此，一些洞穴可能不反映周围的主要商会基岩的连通性，但可能反映在较低的海拔地区，其前身商会形成的成岩成熟基岩的连通性。
Flank margin caves are extreme endmembers of vuggy porosity that form as diagenesis drives the progressive coalescence of smaller solutional pore spaces. Due to their morphological isolation during formation, the prevailing hypothesis has been that fluid flow in and out of flank margin caves occurs via the matrix permeability and that adjacent chambers only become hydraulically connected through nonmatrix porosity during burial, collapse, and fracturing. To our knowledge, however, no studies have evaluated how flank margin caves are connected to regional flow systems in modern carbonate platforms. In this study, we evaluate the connectivity of wells, boreholes, blue holes, and flank margin caves in increasingly older bedrock on San Salvador Island, Bahamas, using tidal attenuation analysis. Phreatic karst features are not reported in Holocene bedrock, and permeability magnitudes from wells suggest Holocene deposits connect to the ocean along matrix‐dominated flow paths. Permeability magnitudes in bedrock surrounding wells, boreholes, and karst features deposited during Marine Isotope Substage (MIS) 5e suggest connection to the ocean through matrix and touching vug porosity. Boreholes, blue holes, and flank margin caves in pre‐MIS5 bedrock connect to the ocean via touching vugs. We suggest that increasing bedrock permeability, cave number, and cave size observed within progressively older bedrock on San Salvador is a function of the cumulative number of freshwater lenses emplaced over successive sea‐level stillstands. We suggest that the morphologies of the two largest caves are consistent with dissolution in multiple lenses occupying lower elevations, collapse resulting in breakout domes, and overprinting of collapse chambers during subsequent highstands. As a result, some caves may not reflect connectivity of the bedrock surrounding the main chambers but may reflect connectivity of more diagenetically mature bedrock at lower elevations where their antecedent chambers formed.
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