MODELING CONTROLS ON LUNETTE FORMATION: IMPLICATIONS FOR INFERRING LATE QUATERNARY PALEOCLIMATE FROM PLAYA-LUNETTE SYSTEMS ON THE HIGH PLAINS

Lunettes—fixed, low-relief, isolated crescentic dunes emplaced on the leeward margins of internally drained playa basins—are disproportionately associated with larger and deeper playas on the High Plains of western Kansas, northwest Texas, and eastern New Mexico. This relationship has been attributed to the cementation of lunettes by re-precipitated lacustrine carbonate derived from ephemeral lakes and wetlands formed in large, deep playas that intersect the water table. Though interacting hydrologic and sedimentary processes influence lunette accretion by modulating the unit sediment supply (i.e., the sediment supply per unit playa area), we propose that lunette formation is predominantly dependent on total sediment supply, which is proportional to the playa area and also correlated with playa depth. We employ a cellular-automaton-based source-to-sink model adapted from Werner’s (1995) dune algorithm to simulate how playa area influences the presence/absence of lunettes. Our results indicate that lunette formation is associated with a threshold ratio of sediment supply, which is directly proportional to playa area, given a constant sediment transport capacity. Playa-lunette systems are highly sensitive to hydroclimate fluctuations and, concomitantly, represent unique terrestrial archives of late Quaternary paleoclimate. Increased understanding of the controls on lunette formation is critical to inferring changes in the relative influence of interacting geomorphic, pedogenic, hydrologic, sedimentary, and biologic processes on the evolution of playa-lunette systems in response to late Quaternary climate change. Further, given the significant correlation between playa and lunette morphometries, our results may have implications for resolving the enigmatic origin of playas, which provide focused groundwater recharge, surface-water storage, wetland habitat, and promote particulate retention and the preservation of archaeological sites.