VOLCANOGENIC KARSTIFICATION AT ZACATON - A HYPOGENE PROCESS EXPOSED AT THE EARTH'S SURFACE

Volcanogenic karstification – hypogene processes interacting with the shallow surface created Sistema Zacatón in Tamaulipas, Mexico, which hosts one of the world’s most unique karst systems and developed as a result of hypogenic processes associated with Pleistocene volcanism. We infer from a range of geochemical, thermal, isotopic, and geomorphic data that the aggressiveness of the waters is a result of shallow igneous activity. The result is the deposition of immense hot spring Quaternary travertines and large phreatic cenotes (pozas) created by dissolution and collapse. One of the pozas, El Zacatón, is one of the deepest phreatic sinkholes (~317 meters below the water table as mapped using a suite of sonar transducers, inertial navigation, and a Doppler velocity meter to navigate, map, and sample the physical underwater environment simultaneously). “Lids” of calcium carbonate,been detected by electrical resistivity, have isolated large underlying water-filled voids. Waters in the deepest sinkholes are reducing and warm with elevated levels of carbon dioxide and methane and are anoxic throughout the entire water column. These systems host a diverse microbial habitat that may contain new kingdoms of archea and bacteria identified by DNA sequencing, and it is possible that unique microorganisms may have evolved in the sealed sinkholes. The recognition of analogous systems in Turkey (Obruks) implies that volcanogenic (hypogene) karstification may be more common than usually inferred because we have only examined those that have broken through to the surface. Long-term models of deep karstic systems may have to extend wider and deeper than is common.