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HYPOGENIC CAVE FEATURES
debated. Hill's model (1987, 1996) implies that the gas
migrated updip from the adjacent Delaware Basin from the
Bell Canyon Formation, although this view is not well tied
with paleohydrogeology. DuChene and Cunningham
(2006) suggested the Artesia Group of the Northwest Shelf
as an alternative source of H2S. Another option is H2S
derived from deep source rocks below the Capitan reef
(DuChene, 1986). The resolution of this issue will depend
on a revised paleohydrogeological model, as most of the
gas reached the cave-forming zones in aqueous, not in
gaseous, form (Palmer and Palmer, 2000a). In addition,
results of possible hydrothermal speleogenesis during the
Miocene (Phase 3 caves of Hill, 2000b; 1996) would be
apparently utilized and modified by later processes
invoking sulfuric acid; the effects of these processes are
again difficult to separate. Available radiometric dates for
sulfuric acid footprints (alunite from various caves, 12.3-
3.9 myr; Polyak et al., 1998) certainly post-date the main
phase of cave formation for respective caves and do not
necessarily indicate that it was related to sulfuric acid.
However, the primary problem is that the
paleohydrogeologic environment for speleogenesis of the
Guadalupean caves is not well-discerned. Most works on
speleogenesis in the Guadalupe Mountains have been
focused on geochemistry, mineralogy, and speleothems but
have largely left out in-depth studies of the cave-forming
hydrogeologic environment. The notable exceptions
include the paper by Palmer and Palmer (2000a), which
provides, in addition to a sound hydrochemical
background, a hydrogeological discussion based on
regional morphogenetic analysis of cave patterns and
morphology. DuChene and Cunningham (2006) discussed
paleohydrogeological conditions based on analysis of
tectonic/geomorphologic history.
The principal controversy is about whether the main
cave development occurred under phreatic (bathyphreatic)
conditions or was caused by dissolution at the water table
and/or due to subaerial processes such as condensation
corrosion, involving H2S oxidation in water films and
limestone/gypsum replacement. The only possibile
resolution of this controversy lies in a systematic genetic
analysis of cave patterns and meso-morphology, coupled
with paleohydrogeological and paleogeomorphological
analysis, and proper comparison with the broader context
of hypogenic caves.
Most researchers view caves in the Guadalupe
Mountains as a result of combined bathyphreatic and
water table development. According to the original
model (Davis, 1980; Hill, 1987, 2000a, 2000b),
bathyphreatic (deep-water phreatic, rising flow)
conditions were responsible for the strong vertical
development of these caves, and for the formation of
vertical tubes, fissures and pits; and water table
(shallow-water phreatic) conditions were responsible for
the horizontal development of caves along certain levels
(corresponding to past regional base levels).
Palmer and Palmer (2000a) assigned most cave origins
in the Guadalupe Mountains to bathyphreatic conditions,
due to convergence of oxygenated water with deep-seated
rising flow at depths up to 200 m below the water table or
deeper. They acknowledged that the morphology of
complex 3-D caves, such as Lechuguilla and Carlsbad
Cavern, demonstrate rising flow patterns in both meso- and
mega scales, from major feeders at the lowermost parts of
the systems (such as the Rift and Sulfur Shores areas in
Lechuguilla, and the Nicholson Pit and Lake of Clouds in
Carlsbad Cavern) to highest outlet passages in the
uppermost parts, including present entrances that served as
outlets for rising groundwater (Figure 47). Different levels
of the caves are connected by ascending passages, which
show strong evidence for having been formed by rising
aggressive water. Palmer and Palmer (2000a) further
suggested that ascending complexes were formed in one
stage, although they reserved the view that some chambers
may post-date the systems, being enlarged at discrete
episodes of water table development. An ascending flow
pattern for the Guadalupe caves was also discerned, based
on morphological observations, by Davis (1980).
Observations by the author of this book in various caves of
the region strongly support the views about their ascending
transverse origin. In the meso-scale, the continuous
succession of feeder-outlet and transitional features
(MSRF, see Section 4.4) can be clearly traced throughout
different levels and between them within the whole vertical
range of caves. The sets of photographs illustrating MSRF
components from various hypogenic caves (Plates 1-9, 11)
include many examples from the Guadalupian caves.
Overall, large and complex 3-D caves of the Guadalupe
Mountains give compelling morphological demonstrations
of an ever-ascending flow pattern.
Arguments toward the major role of water table
dissolution and condensation corrosion (e.g. Hose and
Macalady, 2006) are chiefly based on 1) comparison with
active H2S caves elsewhere in the world, 2) references to
horizontal levels in caves, 3) references to gypsum and
sulfuric acid-related minerals, and 4) references to specific
morphologies. In addition, Palmer (2006) shows that the
requirements for very low pH to form alunite found in the
Guadalupe caves can be met only in subaerial conditions.
In apparent contrast to his previously cited view, Palmer
(2006) concluded that much, if not most, of the caves'
volume, including the passages that ascend to entrances,
has been produced subaerially due to sulfuric acid
dissolution through absorption of H2S by water films
condensed on walls and ceilings. The above-mentioned
arguments in favor of the major speleogenetic role of the
water table and vadose development are briefly addressed
below.
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