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Understanding geologic mechanisms that form karst is of global interest . An estimated 25 % of the world's population obtains water from karst aquifers and numerous major petroleum reserves are found in paleokarst reservoirs , so characterization and classification of specific types of karst is essential for resource management . Sistema Zacatón , which includes the second deepest underwater cave in the world , is hypothesized to have formed from volcanogenic karstification , defined as a process that relies on four components to initiate and develop deep , subsurface voids : a carbonate matrix , preferential groundwater flowpaths (fractures ) , volcanic activity that increases groundwater acidity , and groundwater flux through the system . Phases of karstification creating this modern hydrogeological environment are defined using numerous methods : field mapping , 3 -D imaging of surface and aqueous environments , geophysical investigations , physical and chemical hydrogeologic characterization , and microbial analysis . Interpretation of the results yields a multi -phased speleogenetic model of the karst , with most phases occurring in the late Pleistocene . The surface rocks are carbonate travertine with Pleistocene mammoth fossils found within the rock matrix , and are interpreted as a hydrothermal travertine terrace formed as nearby volcanic activity peaked , thus representing the end member of a carbonate mass transfer system originating deep in the subsurface . The modern karst system includes a dynamic set of deep , phreatic sinkholes , also called cenotes , which propagated up through the travertine , eventually exposing hydrothermal water supersaturated with carbon dioxide to the atmosphere . In some cases these cenotes have precipitated seals of a second stage of travertine as CO₂ degassed , capping the sinkhole with a hydrologic barrier of travertine . Evidence of these barriers is observed in aqueous physical and geochemical characteristics of the cenotes , as some have high hydrologic gradients and contrasting geochemistry to those of neighboring cenotes . Investigations of electrical resistivity geophysics and underwater sonar mapping support the hypothesis of the barriers and define the morphology in intermediate and final phases of sinkhole sealing . Volcanogenic karstification is not limited to Sistema Zacatón , although the localized nature coupled with rapid and extreme degrees of karstification makes it an ideal modern analogue for classifying other karst systems as volcanogenic . |
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