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ASCENDING HYPOGENIC SPELEOGENESIS
length of flow that formed a passage. These views
represent what can be called lateral (or longitudinal)
speleogenesis, a concept that is generally adequate when
applied to unconfined settings. It is deeply rooted in the
speleogenetic literature and was commonly translated to
speleogenesis in confined settings within the older
simplistic artesian flow concept, resulting in misleading
implications.
As shown above, ascending hydraulic communication
across compact soluble beds is predominant in leaky
confined multiple-aquifer systems. However, the
conventional concept of lateral speleogenesis does not
adequately reflect the arrangement of flowpaths and the
flow pattern in this case. Klimchouk (2000a; 2003a)
suggested a concept of transverse speleogenesis to
describe ascending conduit development in a soluble
formation recharged from below.
Figure 7. A diagram illustrating general concepts of lateral (A)
versus ascending transverse (B) flow through a single fracture and
a fissure network encased in a soluble bed (from Klimchouk,
2003a). See also Figure 8.
Where upward flow occurs through a fractured soluble
bed that functions as a leaky aquitard, flow actually
follows the fracture height (Figures 7 and 8-A), or along a
sequence of heights of the vertically connected fractures
(Figure 8-B). Flow distances through a soluble rock are
rather short, commonly on the order of meters or a few
tens of meters, thus allowing rather high discharge/length
ratios. Where laterally continuous fracture networks are
present within certain intervals, flow and speleogenesis
may include a lateral component within the generally
transverse flow pattern. Maps of caves formed in this way
may display tens or even a few hundred kilometers of
integrated passages, spread over hundreds of meters of
straight lateral distance, but these figures have nothing to
do with the actual flow pattern and flow length through the
soluble formation in the case of transverse speleogenesis in
confined settings.
Transverse speleogenesis denotes conduit
development driven by the vertical gradients in hydraulic
head or density across a soluble formation so that flow is
generally directed transversely relative to bedding and
stratiform fracture networks, often arranged in several
superimposed stories (Figure 8-B). The pattern of
transverse speleogenesis may include some lateral
components within laterally extensive and connected
permeability structures, but the overall cave-forming flow
system remains transverse relative to the soluble
formation, linking together its vertically arranged input and
output boundaries.
It is interesting to note that speleogenesis in the vadose
zone is also predominantly transverse in the sense
described above. However, the main regularities and
patterns of speleogenesis are strikingly different in the case
of descending free-flow through the vadose zone than in
the case of ascending flow through a confined system.
Figure 8. A = Transverse flow through a fracture network in a
single level, with fractures crossing a bed for the whole thickness;
B = transverse flow through fracture networks in multiple levels.
Litho- and hydrostratigraphy depicted corresponds to the case of
the western Ukraine, however such multi-level arrangement of
fracture networks is common for stratified carbonate and sulfate
sequences (from Klimchouk, 2003a).
In describing the concept of ascending transverse
speleogenesis, reference to bedding implies “idealized”
settings of sub-horizontal stratification predominant in
most basins. However, it can be misleading in the case of
intensely folded formations, sub-vertical bedding common
in folded regions, and ancient structural stories of many
basins that experienced a long and complex evolution. See
Osborne (2001a) for a case of ascending speleogenesis in
steeply-dipping rocks. In such situations, the concept
should be better taken with reference to sequence
boundaries or simply to the approximate horizontal datum.
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