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ASCENDING HYPOGENIC SPELEOGENESIS
The above general pattern is commonly complicated
by faults, fault-cored anticlines, structural domes,
stratigraphic “windows,” karstified zones, etc. These
features create additional preferential paths for focused
cross-formational communication, which sometimes
considerably complicate the regional hydrogeologic
pattern. The overall importance of cross-formational flow
can be illustrated by the following estimates for the
Dnieper-Donetsk basin (eastern Ukraine), where the flow
in aquifers is supported largely by vertical water exchange
(up to 88-100%) rather than by lateral communication with
marginal recharge areas. In the central parts of the basin,
lateral inflow from the adjacent areas comprises only 10 to
32% of the total groundwater flux (Shestopalov, 1989).
Hitchon provided an excellent study of basin-wide
distribution of hydraulic heads in the Western Canada
Sedimentary Basin, particularly illustrative for both
topographic (1969a) and geologic (1969b) effects. Both
major and minor topographic features are shown to exert
an important control on the distribution of recharge and
discharge areas and on the regional and local flow systems.
However, the variations of geology, particularly the
presence of highly permeable beds, even quite local
laterally, result in significant changes in the regional
topography-induced flow system. It was demonstrated in
Hitchon (1969b) that a pattern of low fluid potential areas
is largely related to distribution of the Upper Devonian and
Carboniferous carbonate and evaporite rocks, particularly
of carbonate reef complexes. However, the fluid potential
lows and highs are recognized within the carbonate rocks
themselves, indicating laterally uneven permeability
distributions. Even lithofacies changes within a major
soluble formation, such as variations in proportions of
anhydrite in carbonate rocks or changes from dolomite to
limestone, are often reflected at the basinal scale in the
hydraulic head maps for a given formation and juxtaposed
sequences. Some reef complexes are known to lack good,
high permeability continuity in an updip direction but have
excellent hydraulic continuity between the vertically
adjacent reef complexes. Drawdown imposed in some of
the low-fluid-potential areas is reflected through up to 900
m of strata, across several stratigraphic units and a major
unconformity. Clearly, many geology-induced variations
of hydraulic head distribution within the basin, as
described by Hitchon (1969b), could be best interpreted in
terms of, and shown to illustrate the role in the basinal
hydrogeology, of hypogenic transverse speleogenesis as it
is treated in this book. See Figure 5 for a case from
Alberta, which can be conceptually translated to the buried
Capitan reef complex in the eastern Delaware Basin of the
USA, with associated transverse karstification in both the
reef and the overlying evaporite strata (Figure 59). The
model speleogenetic reference for both situations could be
the known hypogenic caves in the presently exhumed part
of the Capitan reef complex in the Guadalupe Mountains.
Figure 5. Hydraulic head distribution in the Upper Devonian
Wabamun Group of central and southern Alberta (from Hitchon,
1969b). As described in that paper, the north-trending trough on
the potentiometric surface in the subscrop of this group, shown on
the figure, is reflected in a corresponding trough on the
potentiometric surface of the overlying Manville Group.
A corresponding trough can be seen in the underlying Winterburn
Group, which in turn overlies the low fluid potential drain formed by
the Crossmont reef complex, a hydraulic extension of the low fluid
potential system of the Rimbey-Meadowbrook reef chain.
Another important generalization from basin-wide
studies is that rates of cross-formational exchange in a
multiple-aquifer system depend not only on permeabilities,
thicknesses, continuity, and number of intervening
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