Download PDF - Speleogenesis
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76<br />
NCKRI Special Paper No. 1<br />
Figure 47. Projected vertical profiles through part of Lechuguilla<br />
Cave, showing the nearly independent flow systems through the<br />
entrance series and through the Sulfur Shores – Underground<br />
Atlanta systems (from Palmer and Palmer, 2000a).<br />
1) The situation with reference to active H2S caves that<br />
are currently at the water table stage is similar to the<br />
interpretation of maze caves of non-sulfuric acid origin<br />
(see Section 4.3); it is tempting to extrapolate present<br />
locally observed processes to more general interpretations<br />
of cave genesis. Commonly-cited examples include Kane<br />
Caves (Wyoming, USA), caves of Frasassi Gorge (central<br />
Italy) and Cueva de Villa Luz (Tabasco, Mexico). They do<br />
demonstrate quite aggressive subaerial dissolution by<br />
sulfuric acid (through H2S oxidation by atmospheric<br />
oxygen), both in flowing water and in condensed water<br />
films, which certainly contributes to the morphology of<br />
these caves. This is insufficient, however, to generalize<br />
this as a major speleogenetic mechanism, responsible for<br />
the origin of a wide category of hypogenic caves. Mass<br />
balance considerations and the requirement for removal of<br />
dissolved matter (not met in many occasions, especially in<br />
extensive maze caves with diffuse outflow) make such<br />
generalizations unfeasible. Other caves in the same regions<br />
(or inactive parts of the same caves) include situations that<br />
are a poor fit to the water table/subaerial speleogenesis<br />
model (e.g. see the above description of hypogenic caves<br />
in central Italy).<br />
2) References to horizontal levels in caves often<br />
include stories that are only somewhat horizontal (see<br />
Figure 23 and description above for Frasassi Gorge caves).<br />
Such stories do not correlate throughout adjacent caves and<br />
even between different areas of the same caves, which<br />
would be expected for true water table levels. They are<br />
commonly conterminous either vertically or laterally with<br />
clearly inclined stories within the same cave or in other<br />
caves of the same areas. In most cases, such stories are<br />
controlled by the distribution of initial porosity structures,<br />
either stratigraphically concordant (in most cases) or<br />
discordant to bedding. More discussion of “horizontality”<br />
is given below with regard to the Guadalupe Mountains<br />
caves.<br />
3) Buck et al. (1994) described five types of gypsum<br />
in Guadalupe caves, two of which are basic and most<br />
relevant to the issue under discussion: (a) massive<br />
subaqueous gypsum sediment that forms large bodies in<br />
passages and rooms, and (b) subaerial gypsum crusts that<br />
replace bedrock by sulfuric acid reaction. Thin<br />
replacement gypsum crusts definitely form above the water<br />
table, but these are volumetrically insufficient to account<br />
for the caves' development. Massive gypsum sediments are<br />
found in many caves that show no signs or possibility of<br />
water table development, such as Monte Cucco caves in<br />
central Italy, Amazing Maze Cave in Texas, and Yellow<br />
Jacket, Spider, Dry, and Endless caves in the Guadalupe<br />
Mountains. This gypsum is apparently formed in waterfilled<br />
passages. As to sulfuric-acid related minerals, these<br />
obviously reflect water table conditions due to the low pH<br />
requirement (Palmer, 2006), but this does not support a<br />
high relative significance of this environment in overall<br />
speleogenesis.<br />
4) Some morphologies of the active H2S caves are<br />
commonly referred to as being specific to sulfuric acid<br />
caves of water table/subaerial origin. Such references<br />
include maze patterns, abrupt changes in morphology,<br />
numerous dead-ends, ceiling cupolas, etc. However, these<br />
morphologies are specific neither to the water table<br />
situation nor to sulfuric acid speleogenesis. Instead, these<br />
features are characteristic of a wide class of ascending<br />
transverse caves, as argued throughout this book using<br />
both theoretical reasoning and references to caves, for<br />
which water table development and sulfuric acid<br />
dissolution are definitely ruled out.<br />
The author's contention is that caves in the Guadalupe<br />
Mountains were mainly formed by rising transverse<br />
speleogenesis, possibly by both hydrothermal dissolution<br />
and sulfuric acid dissolution, with water table development<br />
playing secondary, modifying roles. Previous<br />
bathyphreatic hypotheses (Hill, 1987, 2000a, 2000b;<br />
Palmer and Palmer, 2000a) operated with the notion of an<br />
unconfined aquifer in the Capitan platform when<br />
discussing rising flow, i.e. an aquifer in which the water<br />
table under atmospheric pressure forms the upper<br />
boundary. However, speleogenesis in the Capitan platform<br />
prior to its exhumation and erosional lowering of the<br />
adjacent basin surface occurred under confined conditions.<br />
It is assumed by many workers that Salado evaporites and<br />
younger sediments spread across the shelf regions<br />
(Crysdale, 1987; Garber et al., 1989; Ulmer-Scholle et al.,<br />
1993; Scholle et al., 2004; DuChene and Cunningham,<br />
2006), so that they provided a confining cover over the<br />
carbonate platform before they were removed during