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NCKRI Special Paper No. 1
confining beds, but also on the tectonic regime of a region.
The uplift trend and the neotectonic activity favor crossformational
communications between aquifers.
Cross-formational hydraulic communication is one of
the most important factors determining the resources and
chemical composition of groundwaters in the upper
hydrogeodynamic stories of sedimentary basins. It has
been largely overlooked in karst hydrogeology and
speleogenetic studies. It obviously has an immense
importance, and provides a broad perspective for
implications to hypogenic speleogenesis. The above
described regularities of basinal hydraulics determine
locations of zones particularly favorable for speleogenesis.
The place of hypogenic speleogenesis within a basinal
flow domain is shown in Figure 1. It is commonly
associated with discharge segments of regional or
intermediate flow systems. But arguments throughout this
book, supported by numerous field examples worldwide,
strongly suggest that this association is largely because
hypogenic transverse speleogenesis creates these discharge
segments, making them recognizable at the regional scale,
by greatly enhancing initially available cross-formational
permeability structures or even by creating new efficient
ones. The profound effect of a high permeability rock unit
on the regional flow pattern was demonstrated
theoretically by Freeze and Witherspoon (1967) and
validated by many regional hydrogeologic studies. In
basins containing soluble formations, the primary result of
speleogenesis is converging groundwater flow to zones
where ascending cross-formational communication is
greatly enhanced by speleogenesis.
3.2 Hydrostratigraphic conversion of soluble
formations
The hydrostratigraphy of a sedimentary succession is
determined mainly by the relative permeabilities of the
rock units. Aquifers are separated from each other and
from the upper unconfined aquifer by low-permeability
beds. Initial matrix permeabilities of common porous
aquifers (e.g. many medium- to coarse-grained clastic
sediments) are normally several orders of magnitude
greater then that of soluble rocks such as massive
limestones or sulfates prior to speleogenesis. Soluble
formations are commonly vertically conterminous with
formations with initially higher permeability and serve as
intervening beds (aquitards) in a multiple-aquifer system.
However, they change their hydrostratigraphic role to
karstic aquifers in the course of speleogenetic evolution.
As tectonism and uplift impose fracture permeability,
intervening soluble units increasingly transmit
groundwater between (non-karstic) aquifers in zones of
sufficient head gradients. According to Girinsky's (1947)
premise, flow in separating beds is predominantly vertical,
so speleogenesis evolves in transverse communication
paths across the soluble formation. When conduit systems
are developed within soluble formations, conventional
karst wisdom views the situation as a karst aquifer
sandwiched between relative aquitards, without
appreciating that the initial conditions were quite the
opposite (Figure 6). Failure to recognize the proper
relationships commonly causes reverse misconceptions in
hydrostratigraphic interpretations of layered systems:
soluble units, particularly evaporites, may be treated as
impervious beds (aquitards) in a system, or they may be
regarded “by definition” as karstified media.
Switching of hydrogeological functions of different
beds in a sequence during the speleogenetic evolution of
the soluble ones is quite common in confined settings
(Klimchouk, 1990, 1992, 1994, 1996b, 2000a; Lowe,
1992). This is because changes in permeability of soluble
units through time are much more dynamic and drastic
than changes in non-soluble beds. However, it is important
to recognize that hydraulic properties of karst aquifers
evolved in response to hypogenic transverse speleogenesis,
and are characteristically different from epigenic karst
aquifers, the aspects further discussed in the next three
sections.
Figure 6. Conversion of the hydrogeological function of a soluble
bed in a multiple-aquifer system in the course of speleogenesis
(from Klimchouk, 1996b).
3.3 The concept of transverse speleogenesis
In unconfined settings, early conduit development
occurs by lateral flow through an aquifer, from the input
boundary to the output boundary. Furthermore, it was
commonly implied that water flows along the long
dimension of fractures, which are commonly arranged
laterally relative to bedding (Figure 7), or along pathways
that combine long dimensions of several laterally
connected fissures. Long flow lengths and therefore low
discharge/length ratios (sensu Palmer, 1991) are inferred in
such a configuration, which is commonly used in modeling
of early conduit development. Similarly, the parameter of
passage length, or cave development, derived from
speleological mapping, tacitly implies the meaning of the