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12<br />
NCKRI Special Paper No.1<br />
3. Ascending hypogenic speleogenesis<br />
In karst and cave science, three major problems can be<br />
traced that hindered proper understanding of hypogenic<br />
speleogenesis. First, caves formed in hypogenic and<br />
confined domains are accessible for exploration and study<br />
largely when they are brought into the unconfined realm<br />
due to uplift and denudation, hence when they become<br />
relict, decoupled from their formational environment and<br />
often partly overprinted by unconfined speleogenesis.<br />
They were commonly interpreted, despite now apparent<br />
contradictions, in the context of contemporary epigenic<br />
conditions. Classical examples are the works of Davis<br />
(1930) and Bretz (1942) who, in their theorizing of<br />
unconfined speleogenetic conditions, included many caves<br />
now known to have an ascending water origin (Ford,<br />
2006). Although some of the most remarkable “atypical”<br />
caves are now recognized to be of hypogenic origin (e.g.<br />
Wind and Jewel caves of the Black Hills, South Dakota,<br />
USA; Carlsbad Cavern, Lechuguilla Cave, and other caves<br />
of the Guadalupe Mountains, USA; giant gypsum mazes of<br />
western Ukraine), many other caves await reevaluation.<br />
Another example is the former interpretation of the<br />
western Ukrainian giant mazes as being formed by lateral<br />
flow through the gypsum bed between entrenching subparallel<br />
river valleys (Dublyansky and Smol'nikov, 1969;<br />
Dublyansky and Lomaev, 1980). Second, even where a<br />
hypogenic origin was assumed, speleogenetic regularities<br />
and models devised for unconfined conditions were often<br />
simply taken to be equally applicable to the largely<br />
confined realm. And third, in earlier attempts to interpret<br />
some caves (particularly network mazes) in terms of<br />
artesian origin, old simplistic views of artesian flow were<br />
commonly implied, which again led to apparent unresolved<br />
contradictions.<br />
Most stratified sedimentary basins are characterized by<br />
considerable heterogeneity and large contrasts in vertical<br />
permeability, which is, along with basin geometry<br />
conditions, the main cause of the wide occurrence of<br />
multiple-aquifer confined systems. The terms “confined”<br />
and “artesian” refer to hydrodynamic conditions and imply<br />
that groundwater is under pressure in a bed or stratum<br />
confined above and below by units of distinctly lower<br />
permeability. The potentiometric surface in such aquifers<br />
lies above the bottom of the upper confining bed. These<br />
terms are commonly used as synonymous and this usage is<br />
adopted here, although “artesian” was originally applied to<br />
aquifers in which the potentiometric surface lies above<br />
ground level.<br />
Confusion often arises when the terms “artesian”,<br />
(“confined”) and “phreatic” are misleadingly understood as<br />
being equivalent, especially where bathyphreatic<br />
conditions are concerned. The term “phreatic” refers to<br />
conditions where water saturates all voids in a rock or<br />
sediment, in contrast to vadose conditions, above the water<br />
table, where voids are water-filled only temporarily, if<br />
ever. In this sense, phreatic unconfined and confined<br />
conditions are alike. Moreover, water in phreatic conduits<br />
is always confined by the host rock and possesses some<br />
hydraulic head above the conduit ceiling. For example,<br />
Glennie (1954) termed water rising from such deep<br />
phreatic paths “artesian.” Jennings (1971, p.97) noted that<br />
such usage is in a strict sense incorrect, but it serves as a<br />
reminder that consolidated rock can act virtually as its own<br />
aquiclude.<br />
Klimchouk (2000a; 2003a) suggested limiting use of<br />
the term “artesian” (“confined”) to prevailing flow<br />
conditions in an aquifer or a multiple-aquifer system,<br />
rather then to flow conditions within a single conduit. Use<br />
of the term “phreatic” should be restricted to the lower<br />
zone in unconfined aquifers, limited above by a water table<br />
that is free to rise and fall. The distinction between<br />
phreatic and confined conditions is important in the<br />
context of speleogenesis (see Section 3.7).