Pleistocene Freshwater Mollusks on the Floor of Owens Lake Playa, Eastern California

Abstract

Patches of shelly sediments on the floor of Owens Lake playa contain a freshwater molluscan fauna dominated by two planorbid snails, Helisoma newberryi (Lea) and Vorticifex effusa (Lea). Other less common species include the valvatid snails, Valvata utahensis Call and Valvata humeralis Say; the planorbid, Gyraulus parvus (Say); and a sphaeriid clam, Pisidium sp. The assemblage is indicative of a fully developed pluvial lake. Other studies have demonstrated that the late Pleistocene (probably early Wisconsinan) source beds for these mollusks are folded and faulted in the vicinity of Point Bartlett, with the shells having been eroded and reworked during late Wisconsinan and Holocene lake level highstands. A trench excavated in this area confirms this complex pattern of reworking from truncated limbs of folded Pleistocene lake beds. In this way, older Pleistocene mollusks have "leaked" into younger Pleistocene and Holocene depositional environments, potentially mixing fossils from different pluvial cycles.