How Two Western Grand Canyon Early Miocene Paleo-Water-Tables Tie Into Grand Canyon Incision Models

The geomorphic history of Grand Canyon, and especially Western Grand Canyon, remains unsettled. Groundwater speleothems, in particular cave mammillaries, in and around Grand Canyon that denote paleo-water-tables are among other dateable materials such as basalts and travertines that produce incision histories of the canyon. Due to their preservation in caves and their U-Pb dating relevance, cave mammillaries yield the existence of paleo-water-tables and thus incision rate results at higher elevations above the Colorado River compared to other materials. Near-water-table speleothemic material such as cave mammillary is likely common within the canyon region and it is not restricted to caves or carbonate rocks. Here we report two paleo-water-tables on the Hualapai Plateau that have ages of 21.51 ± 0.83 Ma and 18.57 ± 0.43 Ma using the isotope dilution U-Pb method, and 20.87 ± 0.55 Ma and 18.34 ± 0.93 Ma using the laser ablation U-Pb method. The timing of these Hualapai Plateau paleo-water-tables complements other age evidence on the plateau and introduces important constraints for discussing both the “young” and “old” Western Grand Canyon arguments.