Day 2 : Stop 3

DAY 2 (9/27/2025) - STOP 3

"Bell Canyon Road Cut"

COORDINATES: 31.91463° N, 104.75889° W

Fig. 14 Quartz Aerenite & Quartz Wackes

    At this roadcut, we examined rocks belonging to the Bell Canyon area, located across from the wall of Capitan Limestone. The outcrop is made of very fine-grained sandstone that is mostly quartz, with some layers containing a bit more muddy material. The upper portion of the outcrop forms thick, blocky beds of quartz arenite, well-cemented sandstone made almost entirely of quartz grains (fig.14). Just beneath it, the rock shifts into thinner, more fragile layers of quartz wacke, where fine mud is mixed with the sand, giving the rock a darker appearance. Seeing the two stacked directly on top of one another demonstrated the shifting conditions on the basin floor. Periods of stronger, sand-rich currents produced the arenite beds, while quieter periods allowed finer sediment to settle and form the wackes. Some of these beds bend slightly instead of lying perfectly flat. Together, the interbedded arenites and wackes record the last sediment entering the Delaware Basin before sand deposition came to an end.

    These rocks were originally deposited in the deeper part of the ancient Delaware Basin, which once bordered the large Capitan Reef. As parts of the reef broke off and slid down the slope, limestone clasts moved into this softer, still-loose sand. Over time, all of it hardened together as the sand was buried, squeezed, and cemented into rock. The sandstone itself would have formed from fine material carried out into deeper water by currents that periodically swept through the basin, dropping thin layers of sand during energetic events and allowing calmer periods to settle in between.

    The reef once stood tall in shallow water, while this sandstone formed far below it, collecting debris that tumbled down the slope. What we see now is the final sandstone unit deposited in the basin before conditions changed again, recording the transition from an active reef environment to a quieter and deeper water setting.