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Introduction
Most studies of karst systems are concerned with
shallow, unconfined geologic settings, supposing that the
karstification is ultimately related to the Earth's surface
and that dissolution is driven by downward meteoric
water recharge. Such systems are epigenic (hypergenic).
Concepts and theories developed for unconfined karst
systems overwhelmingly predominate in karst and cave
science, particularly in karst hydrology and
geomorphology, forming a core of the current karst
paradigm. Hypogenic karst, originating from depth and
not related to recharge from the overlying surface,
although becoming more recognized during the last two
decades, remains poorly understood and integrated into
the bulk of karst science.
There are specific reasons for this bias, arising from
the historic paths through which the knowledge of the
karst domain evolved. Epigenic karst systems evolve
when soluble rocks occur in the shallow subsurface or
become exposed, so they inherently express surface
components, readily available for observations and
affecting many aspects of human activity. Epigenic karst
systems form by water infiltrating or in-flowing from
overlying or immediately adjacent recharge surfaces and
develop in genetic relation to landscape. Caves commonly
have a hydrologic connection with the surface and
“genetically inherent” entrances. Karst knowledge in
Western Europe and North America had originally
commenced mainly from exploration and study of such
caves. These factors in combination led to a deeply rooted
belief that epigenic unconfined karst systems
overwhelmingly predominate 1 . Karst features, routinely
1 In contrast, in some regions where karstology as a scientific
discipline preceded cave exploration, and where “covered”
(deep-seated) karst settings are widespread, such as in the
former Soviet Union, deep-seated, hypogene, confined karst and
INTRODUCTION
encountered by wells and mines in soluble rocks at
substantial depths, were (and still are) commonly
regarded as paleokarst features, originally formed in
epigenic settings and subsequently buried under younger
sediments.
Some explored caves, however, display patterns,
morphologies, sediments, and minerals that do not readily
conform to established concepts of epigenic karst
development and speleogenesis. Until recently, they were
(and in many cases still are) explained in terms of
epigenic/unconfined speleogenesis, which led to
numerous more or less obvious misconceptions and
controversies. Over the last 20 years there has been a
rapid increase in the development of speleogenetic ideas
implying a hypogenic and/or confined origin of caves,
with reference to a deep source of acidity or to a confined
flow system. However, in the general context of the
predominant karst paradigm, such caves are still largely
regarded as special, aberrant cases. In his classic work on
cave origin, Palmer (1991) estimated that hypogene cave
systems account for only about 10% of the studied cave
systems, although they include some of the largest ones.
Since then, ongoing re-interpretation of some known
caves has probably increased this percentage. Enhanced
understanding of hypogenic speleogenesis and the
refinement of criteria for their recognition are going to
further increase this figure. More important is the fact that
hypogene/confined karst systems are globally much more
widespread than it is now believed, and the relatively
small fraction of known caves of this type is merely an
exploration bias resulting from their genetic irrelevance to
the surface and inherent lack of accessibility.
some relevant processes have been long recognized, at least in
general terms.
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