New Mexico Bureau of Mines & Mineral Resources Bulletin 117 Geology of Carlsbad Cavern and other caves in the Guadalupe Mountains, New Mexico and Texas

This study attempts to tie together all of the depositional events recorded in Guadalupe caves from Permian time to the present. However, it does so in an overview form rather than in detail, and many problems still remain to be resolved.

Facies—Where exactly are the reef, forereef, backreef, and basinal facies exposed in the caves? What criteria distinguish these facies? Are the Seven Rivers and/or Bell Canyon Formations present in Carlsbad Cavern? Do the sands in the Big Room and New Mexico Room represent intertonguing facies of the Bell Canyon Formation? How has the composition of the limestone and/or dolomite affected the dissolution of the cave passages?

Stability of endellite—How does limestone residue turn to montmorillonite clay and at what acidity does the montmorillonite change to endellite? What processes are involved in the mineral transformation of montmorillonite to endellite and how does the structure exclude contaminant material? What factors cause the different colors of endellite?

Cobble-silt transition—A deeper trench needs to be dug in Lower Cave to see if the cobble-silt interface is a true unconformity. Textural differences of both types of deposits need to be further studied. Floor silt needs to be more thoroughly correlated with amount and kind of silt residue in the surrounding limestone bedrock.

Gypsum textures—How much of the gypsum precipitated from solution and how much of it had a replacement origin? Was replacement via the Queen model, the Egemeier model, or both? Detailed microscopic work needs to be done on the textural features of the gypsum blocks, followed by comparisons with textures in the Castile Formation of the Gypsum Plain.

Chert precipitation—What exactly are the colloidal mechanisms behind the formation of the chert and the color-banded silt in the Big Room? Were the rhythmic bands in the chert formed by a liesegang-ring type mechanism?

Dating of speleothems and silt—More speleothems in key positions need to be dated in order to test the conclusions of this study and to fine-tune geologic events on an absolute time scale. The ESR-dating method needs to be performed on speleothems >350,000 yrs old. More paleomagnetic dating of silts should be done on different levels in Carlsbad Cavern and also in other Guadalupe caves. Since Guadalupe cave passages are believed to range from <600,000 yrs to 3 my in age, a number of paleomagnetic reversals should be distinguishable in the silt deposits. More samples of montmorillonite clay need to be dated by the potassium-argon technique, and problems related to this method need to be resolved.

Sulfur isotopes—More work needs to be done, especially on vertical sequences of gypsum. Why are the sulfur-isotope values of the upper, younger levels of the gypsum blocks in the vertical suite at the Polar Region less depleted in ³²S than the older sections of the block (Table 22)? Also, a sampled gypsum block in the upper Gypsum Passage, Cottonwood Cave, is much less depleted than is sampled sulfur in a block, lower Gypsum Passage. Are these real trends and, if so, what factors caused them?

Chemistry—The sulfur chemistry responsible for the sulfuric-acid dissolution of the caves should be analyzed in detail. The chemical reactions may be multi-step processes involving sulfur bacteria.

Hydrology of cave development—A more elaborate model of the three-dimensional pattern of cave excavation needs to be developed for Carlsbad Cavern and other Guadalupe caves. The geomorphic form of Guadalupe cave passages should be more closely studied in order to gain insight into the hydrologic mechanisms which formed them.

Other Guadalupe caves—The main focus of this study is Carlsbad Cavern. Other caves in the Guadalupe Mountains need to be researched in more detail with respect to the sulfuric-acid model presented herein.