THE LAS VEGAS FORMATION

The Las Vegas Formation is a vaguely defined formational name that was established half a century ago to describe distinctive light-colored, fine-grained, fossil-bearing sedimentary deposits exposed in and around the Las Vegas Valley, Nevada (USA). Coeval with that designation, the formation was subdivided into informal units with stratigraphic and chronologic frameworks that have persisted in the literature to the present. Proper usage of the Las Vegas Formational name has been hampered due to the lack of a robust definition and characterization of the entire lithostratigrahic sequence, its geographic distribution, and chronology. In this study, we have comprehensively reevaluated, described, and defined the Las Vegas Formation deposits with detailed stratigraphy, sedimentology, and field relations. A large suite of both radiocarbon and luminescence dates facilitated a complete revision and temporal expansion of the geochronology. We define and characterize 17 mappable 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 within the members. The Las Vegas Formation is now defined as a formal lithostratigraphic unit that 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 and adjacent valleys. The contextual information derived from this new framework is dually noteworthy given that the Las Vegas Formation entombs one of the most significant Pleistocene vertebrate faunas in the American Southwest, the Tule Springs local fauna, and represents a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Stabilizing the nomenclature of these important deposits will facilitate studies of similar deposits associated with desert wetland ecosystems elsewhere in the southwestern U.S.