Carlsbad Caverns is a 30.9 miles long cave underground in the Chihuahuan Desert. It formed by sulfuric acid dissolving limestone resulting in caves of various sizes. About 250 million years ago marine plants and animals built the limestone reef that was dissolved by hydrogen sulfide gas from deep oil and gas deposits mixing with water to result in sulfuric acid. The dissolution of limestone created cavities that would enlarge with further dissolution and time. Then limestone-laden groundwater dripped into the air-filled caverns to produce stalactites and stalagmites (Fig.1). An overview of the various formations in the caverns is shown in figure 2 as well as the chemical equation describing the precipitation of the formations. The Boneyard was formed due to weakly-acidic groundwater permeating cracks and joints in the limestone creating a Swiss cheese like appearance (Fig.3).
Figure 1. Large stalagmite
Figure 2. Image taken at and credited to Carlsbad Caverns National Park.
Figure 3. Boneyard featuring "Swiss cheese" cavities.
Before Carlsbad Caverns, we observed a teepee structure from the Yates and Tansill Formations (Fig.4). Teepee structures form from water injecting from the bottom of the formation resulting in water pressure fracturing the formation. The fractures are filled with calcite and evaporites if shallow or limestone if deep.The outcrop is mainly dolomite limestone with alternating siltstone/shale. Pisolites, being larger than 2mm in diameter, were also present at this stop (Fig.5).
Figure 4. Teepee Structure. Classmate for scale.
Figure 5. Pisolite, pencil is 12cm.
The last stop of the day was to visit a Neptunian dike and sedimentary rocks with algae and sponges (Fig.7&8). Neptunian dikes or a passive fissure fills, form when a fracture or other void is filled with younger sediments (Fig.6).
Figure 6. Neptunian dike that is approximately 3 meters from top to bottom.
Figure 8. Nautilus fossil in boundstone.
Figure 7. Algae fossil.