Download PDF - Speleogenesis
Download PDF - Speleogenesis
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HYPOGENIC CAVE FEATURES<br />
Amazing Maze Cave (the cave name) is a very densely<br />
packed 3-D network maze with 9 km of passages surveyed<br />
to date. It was originally opened by a road cut in a lowrelief<br />
hill within a broad valley of Edwards Plateau<br />
outliers. Most of the passages lie at a single level but three<br />
or more other levels, connected by outlet/feeder structures,<br />
can be distinguished in the cave within a 22 m thick<br />
stratified section of the Fredericksburg Formation,<br />
Cretaceous Edwards Group (Figure 43; Elliott and Veni,<br />
1994). The cave has no features indicative of downward<br />
percolation, considerable lateral flow or water table action.<br />
Instead, the morphologic suite of rising flow is perfectly<br />
represented in the cave (Plates 4; 9, F and H). Many<br />
passages on the master level contain massive bodies of<br />
microcrystalline gypsum, commonly coated with calcite<br />
crust. This gypsum is similar to the secondary gypsum<br />
known from the Guadalupe Mountains caves, indicative of<br />
a sulfuric acid dissolution mechanism. Gypsum masses in<br />
Amazing Maze Cave have numerous “vents” in them,<br />
which are morphologically continuous with feeders below.<br />
Some of these holes have gypsum blisters at the top.<br />
71<br />
Figure 42. Robber Baron<br />
Cave, Texas, USA, a maze<br />
cave in Cretaceous limestone,<br />
above the confined zone of the<br />
Edwards Aquifer. Survey: San<br />
Antonio Grotto, 1976-77 (from<br />
Veni, 1989).<br />
Gypsum masses do not fill passages from side to side but<br />
occupy central sections, leaving wide gaps between the<br />
gypsum body and walls. They were apparently formed<br />
under water-filled conditions. During our examination of<br />
the cave we found massive occurrences of endellite of<br />
intense purple color in several parts of the cave. In the<br />
main occurrence, endellite rims a feeder in a small passage<br />
at the upper level developed along a diffusely permeable<br />
bed (Plate 4-D). Identification of endellite has been<br />
confirmed by SEM and elemental analysis by M. Spilde<br />
(University of New Mexico). All of these characteristics<br />
strongly suggest the confined transverse origin of Amazing<br />
Maze Cave, in which, at least during some episodes,<br />
dissolution by sulfuric acid had contributed to<br />
speleogenesis through mixing of uprising H2S-bearing<br />
waters with oxygenated waters flowing laterally through<br />
some more transmissive beds. The cave is located above<br />
the White and Backed Oil Field, and a source of sulfates<br />
could be evaporitic beds in the Trinity Group below.<br />
The presence of the massive gypsum and endellite in a<br />
typical stratiform maze cave, which was apparently formed