Download PDF - Speleogenesis

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NCKRI Special Paper No.1
Figure 1. Epigenic and hypogenic karst in the context of basinal groundwater flow. Adopted and modified from Tóth (1999). The figure
shows mainly gravity-driven flow in an idealized homogenous basin. In reality, most sedimentary sequences are highly heterogeneous,
and gravity-driven flow interacts with other flow mechanisms.
As speleogenesis is a dynamic process capable of
considerably changing primary porosity and permeability,
it can itself create zones of high permeability along
initially insignificant (in terms of regional or intermediate
groundwater flow systems) cross-formational flow paths,
or even without any initially guiding disruptions. In
soluble beds (which originally commonly serve as
confining beds; see Section 3.2) this goes through one of
the mechanisms of ascending transverse speleogenesis,
and in overlying insoluble beds permeability
enhancement occurs via fracturing and brecciation above
cave porosity zones. Thus, hypogenic speleogenesis may
give rise to new discharge zones and contribute to
segmenting laterally extensive “throughflow” regions.
The classification of regional hydrogeologic
structures, introduced at the beginning of this section, can
be presented as an evolutionary succession: artesian
basins - disrupted basins - layered massifs -
hydrogeologic massifs. This corresponds to the successive
stages in the general tectonic and geomorphic evolution
of sedimentary basins. Similarly, this evolutionary trend
provides a framework to classify karst types and
speleogenetic environments based on the evolutionary
history of a soluble-rock aquifer (Klimchouk, 1996a;
Klimchouk and Ford, 2000; Figure 2): from deposition
and early emergence above sea level (syngenetic
/eogenetic karst) through deep burial and re-emergence
(the group of intrastratal karst types: deep-seated karst,
subjacent karst, entrenched karst) to complete exposure
(denuded karst). If karst bypasses burial, or if the soluble
rock is exposed after burial without having experienced
any significant karstification during burial, it represents
the open karst type. Different types of karst, which
concurrently represent the stages of karst development,
are marked by distinct combinations of the structural
prerequisites for groundwater flow and speleogenesis,
flow regimes, recharge/discharge configurations,
groundwater chemistry, and degree of inheritance from
earlier conditions.
Although this classification does not directly specify
the origin of caves, it characterizes dominant
speleogenetic environments and their evolutionary
changes. Karst types are viewed as stages of
hydrogeologic/geomorphic evolution, between which the