Day 4 : Stop 1

DAY 4 (9/29/2025) - STOP 1

"Carlsbad Caverns (Parking Lot Topography)"

Coordinates: 32.17407° N, 104.44673° W

Fig. 26 Carlsbad Caverns National Park Sign Observed From Parking Lot

    The parking lot (fig. 26) geology at Carlsbad Caverns shows us an outcrop with early diagenetic deformation within shallow-marine carbonate sediments formed in the Tansill Formation. The bedding layers are not fully lithified, as seen from the developed tepee structure (fig. 27). The tepee is a prevalent feature at this site and is a set of originally horizontal carbonate layers that have been pushed upward into a pseudo-anticlinal form. In this case, however, the geometry is misleading because the process is entirely different from true tectonic folding. Instead, the layers were pushed upward while still only partially cemented. The sediments had not yet undergone full diagenesis, such as compaction, lithification, and cementation, which allowed subsurface water pressures to distort them from below.

Fig. 27 Tepee Structure

    This early deformation likely occurred shortly after deposition, when carbonate muds and grain-supported layers remained soft enough to be moved and reshaped. The water responsible for this upward push moved through a narrow conduit in the sediment, focusing pressure into a localized zone that lifted and bent the layers. These conditions produced the recognizable pattern of a tepee structure, where beds diverge upward and then break apart along zones of weakness. At the center of the tepee, there are fragments of broken carbonate that appear trapped in the conduit, forming an intrasedimentary breccia composed of pieces that were snapped from the soft layers and lithified in place as cementation progressed. The outcrop shows subtle evidence of this fragmentation, especially near the hinge area where the beds converge.

    Grain types in the outcrop include ooids, rounded coated grains typical of high-energy, warm, shallow water. These ooids make up part of the limestone framework and indicate deposition along a shallow carbonate platform. Their presence is consistent with the type of sediments that deform into tepee structures, which commonly form in peritidal environments where evaporation, periodic wetting and drying, and groundwater migration intensify early diagenetic processes.

    The geomorphology of the parking lot outcrop we observed showed us a lot about the formation environment in which these structures formed. The outcrop is heavily fractured, with the deformation surfaces now lithified into angular blocks. The yellow to tan coloration and irregular veins cutting across the exposure reflect later stages of cementation and weathering. These fractures do not reflect tectonic stresses but rather the stabilization of once unlithified carbonate layers as pore fluids precipitated calcite along joints and cracks.