Day 2 : Stop 4

DAY 2 (9/27/2025) - STOP 4

"Bell Canyon Road Cut 2"

COORDINATES: 31.93161° N, 104.73054° W

Fig. 15 Limestone Blocks in Sandstone

    The second Bell Canyon roadcut provided an example of the interaction between the Capitan Reef margin and the deeper portions of the Delaware Basin. The outcrop consisted primarily of light brown sandstone containing numerous large, angular limestone blocks (fig. 15). The angularity of these blocks indicates that they were not transported over long distances; instead, they detached from the reef slope and quickly traveled downslope. Their emplacement into still-unlithified sand suggests a gravity-driven process in which blocks slid or tumbled from higher on the reef front into deeper basin environments.

    After deposition, these limestone blocks became partially embedded within the soft sediment, which later lithified to form sandstone. The sandstone’s light brown coloration reflects the presence of iron minerals, most likely goethite (an iron(II) oxide). This mineral coating on the sand grains indicates oxidizing conditions during or shortly after deposition.

    The limestone blocks are consistent with material derived from the Capitan Reef system, specifically from units such as the Lamar Limestone that shed large fragments downslope into the Bell Canyon Formation. Stratigraphic contrasts are also evident at the site. Some beds display thick, massive sandstone with minimal internal structures, indicating periods of relatively stable sediment supply. In contrast, adjacent exposures show more variation in bed thickness and composition, suggesting fluctuations in depositional conditions, including changes in sediment input, water chemistry, or bottom-current activity. Each bed represents a discrete interval of sediment accumulation under a specific set of environmental conditions. Overall, this exposure records an example of carbonate-slope mass-transport processes interacting with basin-floor siliciclastic sedimentation.