Devils Hole

Perhaps one of the most widely cited 5 0caicite records is that of the Devils Hole vein calcite (Winograd et al. 1992) which records glacial-interglacial shifts in 1 to 2%o from... 

Szabo BJ, Kolesar PT, Riggs AC, Winograd H, Lndwig KR (1994) Paleochmatic iirferences from a 120,000-year calcite record of water-table fluctuations in Browns Room of Devils Hole, Nevada. Qnat Res 41 59-69... 

Winograd IJ, Coplen, TB, Landwehr JM, Riggs AC, Ludwig KR, Szabo BJ, Kolesar PT, Revesz KM (1992) Continuous 500,000-year chmate record from vein calcite in Devils Hole, Nevada. Science 258 255-260... 

Ludwig, K.R., Simmons, K.R., Szabo, B.J., Winograd, I.J., Landwehr, J.M., Riggs, A.C. and Hoffman, R.J. (1992) Mass-spectrometric 230Th-234U-238U dating of the Devils Hole calcite vein. Science 258, 284 -287. 

Figure 13. Oxygen and Carbon isotope ratios from underwater flowstone in Devils Hole, Nevada. From Coplan et al. (1994).

Coplen, T. B., Winograd, I. J., Landwehr, J. M., and Riggs, A. C., 1994, 500,000-year stable carbon isotope record from Devils Hole, Nevada, Science. 263 361-365. 

INFLUENCE OF DEPOSITIONAL ENVIRONMENT ON DEVILS HOLE CALCITE MORPHOLOGY... 

Devils Hole, a steeply dipping (-80°) tectonically fonned planar fissure >165 m deep (Riggs et al., 1994), has been accumulating calcite speleothems that contain at least two different paleoclimate records. Below water table deposits contain a 560,000 year paleo-climate isotopic record (Winograd et al., 1992), while above water table deposits record 120,000 years of changing water table elevation (Szabo et al., 1994). The different depositional environments in Devils Hole control the form of the speleothems. 

Devils Hole is in the arid southern Great Basin, approximately 90 km west-northwest of Las Vegas, Nevada (Fig. 1). Average annual precipitation in Pahrump, NV, about 65 km... 

Figure 1. Location of Devils Hole and salient features in its vicinity. Dashed-dotted line marks approximate boundary of the Ash Meadows groundwater system. Dashed line marks approximate boundary of highly transmissive aquifer. They also coincide with approximate position of the Spotted Range-Mine Mountain structural zone. Arrows indicate the inferred direction of groundwater flow. Shaded areas are approximate recharge areas. Adapted from Winograd et al. (1992).

Surface water temperature is approximately 32°C throughout the year. Water temperature is 34.25°C at a depth of 51 meters (R.J. Hoffman, U.S. Geological Survey, 1990, personal communication). Water in Devils Hole is slightly supersaturated with respect to calcite (saturation index averages about 0.18) with calculated Pco2 values from 0.0123 to 0.0141 atm (Plummer et al., 2000). The water has been supersaturated with calcite for at least 500,000 years. 

Browns Room (Fig. 3), an air-filled chamber, is accessible only by diving to a depth of about 25 meters in Devils Hole and ascending a different branch of the fissure back to the water table (Hoffman, 1988, p. 6 Riggs et al., 1994). Browns Room has a blocky shape that results from breakdown blocks falling from between splays of the fault (Riggs et al., 1994). The room extends approximately 9 meters above the present water table. An 8 m by 7 m pool of warm Ash Meadows groimdwater occupies the southwest end of Browns Room. Millers... 

Figure 2. View northeast into Devils Hole. The left side of the opening is the footwall of the fault. The width of the opening at the water table is about 2 to 2.5 meters.

Figure 3. Map of Devils Hole. BR is Browns Room, and M is Millers Chamber. Mammillary calcite is the only speleothem morph below the water table. Rafts currently form on the surface on the main chamber and in Browns Room. Folia only form in Browns Room, and popcorn forms in both Millers Chamber and Browns Room.

Devils Hole contains five distinct morphologies of speleothems that are readily discriminated by the naked eye. Their form is mainly a consequence of the carbonate precipitation environment, that is, whether the carbonate precipitated above, at, or on the water table in humid air, or below the water table. As a result, once we learn to recognize the different speleothem morphologies, and relate them to their precipitation environments, we can quickly begin to reconstruct the progression of environmental conditions at a site from the arrangement of speleothem morphologies deposited there. 

Figure 4. Mammillary calcite coating the walls of Devils Hole about 23 m below water table. Note the gently rounded protuberances that characterize the coating. A core of mammillary calcite about 42 cm thick was recovered from approximately 30 meters below the water table. Photograph courtesy of Ray J. Hoffinan.

Mammillary calcite on the hanging wall of Devils Hole is white, translucent, and unbanded. Footwall mammillary calcite, on the other hand, is strongly banded because silt and clay debris that settled on the up-facing surfaces were incorporated into the mammillary coating by continuing calcite precipitation. Well-developed bands on cross sections of up-facing mammillary calcite surfaces disappear abruptly wherever the depositional surface rolls over to vertical or overhanging. 

Figure 8. Accumulation of rafts (arrows) at a depth of about 28 meters below Browns Room in Devils Hole. Rafts have been cemented in place by continued precipitation of mammillary calcite. Thickness of bedrock block left of the arrow is about 15 cm.

While rafts make up an insignificant volume of the precipitated material in Devils Hole, their presence does have a an impact on underwater exploration of Devils Hole. Because rafts only form on a free water surface, and because they sink to the bottom whenever the surface tension of that free surface is disturbed, presence of rafts on the footwall in Devils Hole tells us that there is an air-filled chamber above. 

---