The last Pluvial Highstand (Late Wisconsin, Tioga Age) in Panamint Valley, Southeast California

A large late Wisconsin age lake has not been previously documented in Panamint Valley which contains a small north basin and a large south basin, both of which could have received overflow from the Owens River system via Searles Lake when the lake exceeded 1700' elevation. A 14C age on gastropod-bearing tufa indicates that the lake's surface elevation was near 512m (1680') at 22,600 ka +/-130 yr. This tufa deposit is about 2-3 meters thick and forms a fringing reef within a bedrock alcove about 1 km north of Water Canyon. The deposit appears to document a water body in the southern basin that would have been about 11 km wide, 52 km long and least 150m (500') deep with a volume around 4000 km3. Tentatively, the highest stand of the Tioga-age glacial lake' could have reached ~1800-1820' based on the marginal-lacustrine gastropod assemblage Helisoma newberryi newberryi, Vorticifex solida (lacustrine indicator), and Stagnicola sp., found in a sandy (beach?) deposit 120' upslope from the 1680' tufa, but probably was not any higher (14C in progress). The lake does not appear to have breached the Wingate Pass spillway at 1977' into Death Valley during the last glacial. Along the lower part of the Shepard Canyon fan, lacustrine silt is exposed at about 415m (1360') in a stream incision overlain by 1.5 to 2.0 meters of alluvial gravel. Tufa underlying the silt yielded a 14C age of 17,130ka +/- 100yr indicating a lake whose shoreline elevation was between 60 to 75 meters above the present valley floor. White chalky silt overlying the tufa at this locality yielded abundant Limnocythere sappaensis, an ostracode that lives within a wide range of total dissolved solids (TDS) in waters that are enriched or dominated by bicarbonate-carbonate and depleted in Ca. Its waters typically have an alk/Ca ratio of 7 or much higher. When this species is abundant and the only ostrocode present, the lake water commonly has a TDS of more than about 20,000 mg/L; in lakes with a much lower TDS other ostracodes are typically present. Thus, the abundance of L. sappaensis, combined with the absence of other ostrocodes, suggests an alkaline-saline lake. A well-developed desert pavement with heavy varnish (Q3a and/or Q2 of Bull, 1999), occurs on the surface above 1.5 to 2.0 m of gravel that overlies the lacustrine silt and tufa dated at 17,130ka +/- 100yr. This pavement apparently postdates the last pluvial maxima and is very latest Pleistocene (or earliest Holocene). However, scattered, well-rounded cobbles that may be beach derived lie on or in Q2 pavement exposed 30-40 meters upslope from the lacustrine sediment outcrop. The main body of the southern lake was nearly dry by 15,050 ka +/-80yr as indicated by the 14C age of root casts found in chalky silt at 357m (1170'), 11m above the present southern playa floor at the lowest part of the Revenue Canyon fan near the axial wash. The drying of Panamint Lake by about 15,050 ka approximately coincides with the time that overflow from Searles Lake is inferred to have ceased. In the northern basin, tufa crops out at about 480m (1570') on the east side of Lake Hill; at the north end of Ash Hill, tufa occurs at about 1650-1700' and higher. The northern basin is isolated by a divide that reaches 1700' west of the Wildrose Horst. The northern lake, about 20 km long, 3-7 km wide, and 35-45 meters above the present valley floor, would have been mainly fed by a large watershed on the Darwin Plateau unless the northern and southern basins were connected.