THE LAS VEGAS FORMATION

The Las Vegas Formation was established half a century ago to designate the distinctive, light-colored, fine-grained, fossil-bearing sedimentary deposits exposed in and around the Las Vegas Valley, Nevada (USA). Coeval with that designation, the sediments were subdivided into informal units with stratigraphic and chronologic frameworks that have persisted in the literature to the present. Usage of the Las Vegas Formation name has been hampered due to the lack of a robust definition and characterization of the entire lithostratigraphic sequence, its geographic distribution, and chronology. In this study, we have reevaluated and described deposits attributed to the Las Vegas Formation with detailed stratigraphy, sedimentology, and field relations. A large suite of both radiocarbon and luminescence ages facilitates revision and temporal expansion of the geochronology. In all, we characterize 17 informal geologic units within the formation, each dating to a unique period of geologic time, with stratigraphically ascending members X, A, B, D, and E and attendant beds in members B, D, and E. The age of the Las Vegas Formation spans at least the middle Pleistocene to early Holocene (~573 ka–8.53 ka) and is related to past groundwater discharge in the Las Vegas Valley. The contextual information derived from this new framework is dually noteworthy, given that the sediments entomb one of the most significant Pleistocene vertebrate faunas in the American Southwest, the Tule Springs local fauna, and represent a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Characterizing the nature of these important deposits will facilitate studies of similar deposits associated with desert wetland ecosystems elsewhere in the southwestern U.S.