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HYPOGENIC CAVE FEATURES<br />

in the Segovia (Fort Lancaster) Formation of the<br />

Cretaceous Edwards Group (Kastning, 1983; Onac et al.,<br />

2001). The lower stories lie within massive dolomitic<br />

marly units and have generally larger dimensions than the<br />

upper stories. The upper stories with denser maze<br />

development lie within more porous beds separated by a<br />

marly unit. Cupolas at the uppermost story open up into a<br />

distinct bed of touching-vugs type porosity (“burrowed<br />

bed”), which probably served as a “receiving aquifer”<br />

during the ascending formation of the cave (Figure 9).<br />

Most of the cave lies beneath that vuggy bed, which is<br />

overlain by the thick unit of massive limestone that<br />

provides a caprock. Another maze cave in the vicinity,<br />

Felton Cave (2.05 km), is in many respects similar to<br />

Caverns of Sonora but has more diverse trends of passages<br />

(Kastning, 1983).<br />

Figure 44. Map of Caverns of Sonora (by G. Veni and P. Sprouse;<br />

adapted from Elliott and Veni, 1994).<br />

The cave perfectly displays the morphologic suite of<br />

rising flow (Plates 4-G, 6-B and 9 A, C and G). Passages at<br />

different stories are often co-planar, with rift-like or oval<br />

connections between stories. Smaller connections are<br />

domepits from the perspective of a lower story. Where<br />

passages at different stories are not co-planar, they are<br />

connected by steep passages with a rising sequence of<br />

dome-like forms. Ceilings, especially at upper levels,<br />

demonstrate complex half-tube/pendant morphology. The<br />

morphology of Caverns of Sonora bears strong imprints of<br />

dissolution by multiple buoyant currents and shows no<br />

appreciable modification by a water table or epigenic<br />

recharge.<br />

<strong>Speleogenesis</strong> of Caverns of Sonora had been<br />

interpreted by Kastning (1983) in terms of a classic<br />

epigenic concept, assuming passage development by<br />

lateral flow recharged from above, with progressive<br />

shifting from upper levels to lower levels, in response to<br />

lowering of base levels. The ascending hypogenic origin<br />

of the Caverns of Sonora, besides morphological and<br />

hydrostratigraphic considerations, is strongly corroborated<br />

by the recent finding of metatyuyamunite, a uraniumvanadium<br />

mineral diagnostic of sulfuric acid dissolution<br />

(Onac et al., 2001). The cave was formed under confined<br />

conditions in the mixing zone between deep-seated H2Sbearing<br />

warm fluids and an oxygenated shallow flow<br />

system.<br />

The origin of the major caves in the Guadalupe<br />

Mountains, New Mexico, USA, including some of the<br />

largest caves in the United States such as Carlsbad Cavern<br />

(43.2 km long, 315 m deep) and Lechuguilla Cave (193.4<br />

km long, 490 m deep), is firmly attributed to sulfuric acid<br />

speleogenesis (e.g., among others, Davis, 1980; Hill, 1987,<br />

2000a, 2000b; Palmer and Palmer, 2000a; Palmer, 2006).<br />

The caves are formed in carbonate reef and backreef<br />

formations of Permian age, exhumed during several<br />

episodes of uplift (of which the Cenozoic is believed to be<br />

the main one) from beneath largely evaporitic sediments of<br />

the adjacent Delaware Basin (Figure 45). Most of these<br />

caves are developed near the reef-forereef contact in the<br />

largely massive Capitan Formation and the reef-backreef<br />

contact between the Capitan and prominently bedded<br />

Seven Rivers and Yates Formations (DuChene and<br />

Martinez, 2000), but some caves or parts of caves lie<br />

within the backreef succession. Caves are scattered along<br />

the mountain ridge, which plunges from southwest (from<br />

elevations up to 2767 m) to northeast (to elevations of<br />

about 1000 m) for about 70 km. Many of these caves have<br />

stratigraphically-conformable multi-story maze patterns,<br />

network or spongework, or both, but some caves display<br />

complex vertically extended 3-D structures that include<br />

maze and chamber elements at many loosely defined<br />

stories, and sub-vertical conduits connecting them (Figures<br />

16, 17, and 46). The caves show no genetic relationships<br />

with the surface and fit most other criteria for ascending<br />

transverse caves (Section 4.1). It is apparent that<br />

Guadalupian caves, or their segments, utilized various<br />

kinds of original porosity available throughout different<br />

members of the rock succession, including syndepositional<br />

faults and fractures (Koša and Hunt, 2006), other<br />

syndepositional features such as teepees (Plate 16),<br />

paleokarstic cavities and zones, uplift-related<br />

discontinuities, and vuggy porosity. Depending on their<br />

nature and position within the geological structure, various<br />

porosity systems (and hence respective cave elements) can<br />

be distributed conformably within the stratigraphy or be<br />

discordant to the bedrock structure.<br />

Although caves in the region have received much<br />

scientific attention during the last 30 years, speleogenesis<br />

in the Guadalupe Mountains still has many controversial<br />

aspects. A comprehensive overview of speleogenesis in the<br />

Guadalupe Mountains and discussion of relevant issues is<br />

clearly beyond the scope of this book. But this case is<br />

treated here more extensively compared to other entries in<br />

this section because the Guadalupes are a prime reference<br />

region of hypogenic speleogenesis, and interpretations of<br />

their speleogenesis are highly important in illustrating<br />

hypogenic processes.<br />

73

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