Hypogene Speleogenesis

Recognition of the wide occurrence, significance, and specific characteristics of hypogene speleogenesis during last two decades signifies a major paradigm shift in karst science, previously overwhelmingly dominated by epigene concepts and models. Hypogene karst is one of the fundamental categories of karst, at least of equal importance with more familiar epigenic karst. Hypogene and epigenic karst systems are regularly associated with different types, patterns, and segments of flow systems, which are characterized by distinct hydrokinetic, chemical, and thermal conditions. Hypogene speleogenesis is the formation of solution-enlarged permeability structures by water that recharges the cavernous zone from below, independent of recharge from the overlying or immediately adjacent surface. It develops mainly in leaky confined conditions, although it may continue through unconfined ones. Hydraulic communication along cross-formational flowpaths, across lithological boundaries, different porosity systems, and flow regimes allows deeper groundwaters in regional or intermediate flow systems to interact with shallower and more local systems, permitting a variety of dissolution mechanisms to operate. A specific hydrogeologic mechanism acting in hypogenic transverse speleogenesis (restricted input/output) suppresses the positive flow-dissolution feedback and speleogenetic competition seen in the epigenic development. Hypogenic caves occur in different soluble rocks in a wide range of geological and tectonic settings, basinal through orogenic. Overall patterns of cave systems are strongly guided by the spatial distribution of the initial (prespeleogenetic) permeability features and hydrostratigraphic barriers and interfaces within the soluble and adjacent units, by the mode of water input to, and output from, cave-forming zones and by the overall recharge–discharge configuration in the multiple aquifer system. Because of their transverse nature, hypogene caves have a clustered distribution in plan view, although initial clu