A PALEOCLIMATE RECORD FROM THE BLACK ROCK DESERT SUBBASIN OF LAKE LAHONTAN: 23,000-12,000 C-14 YR B.P

Three cores were taken from the northeastern--most arm of the Black Rock Desert in NW Nevada in order to determine the paleoclimate through time in this subbasin of Pleistocene Lake Lahontan. A variety of analyses have been performed on the cores including C-14 dating, tephrochronology, preliminary faunal analysis of ostracodes, measurement of paleomagnetic directions and of sediment magnetic parameters. The magnetic parameters include susceptibility, anhysteretic and isothermal remanent magnetizations, the S-parameter, and the anisotropy of magnetic susceptibility. Further analyses currently underway are the measurement of total organic and inorganic carbon, trace element geochemistry using ICP-MS instrumentation, x-ray diffraction work, granulometry and a more detailed ostracode analysis.

C-14 dating, and tephrochronology date the Black Rock Desert record from 23,000-12,000 C-14 yr B.P. Sediment magnetism work shows uniform low coercivity throughout the cores which suggests magnetite or possibly greigite as the primary carrier. The variation in paleomagnetic directions over time can be correlated to the independently dated, paleomagnetic reference record from the Wilson Creek sediments of the Mono Lake region. The resulting chronology for the Black Rock Desert sediments is consistent with that obtained from C-14 ages and tephrochronology.

Magnetic concentrations vary systematically by 50% or more throughout the core, possibly reflecting changes in lake conditions. Sedimentation rates and preliminary ostracode analyses indicate relatively extreme anomalies near the top of the record, which may reflect the large amplitude, high frequency lake-level excursions for Lake Lahontan observed by Benson et al. (1995) between 13,000 and 18,000 C-14 yr B.P. On the other hand, the preliminary ostracode assemblages indicate warm, possibly shallow waters throughout most of the record and the variations observed in the sediment magnetism data were not especially notable in this younger interval.