EVIDENCE FROM THE CENTRAL GREAT BASIN FOR AN EXTENDED DRY PERIOD BETWEEN 3000 AND 2000 CAL YR BP AND ITS POTENTIAL GEOGRAPHIC EXTENT

We present new data from sediment cores in the Spring Valley of eastern Nevada that contribute to our understanding of Great Basin paleoclimate and build upon the legacy of work produced by Larry Benson. A 7600 year-old 7 m sediment core obtained from Stonehouse Spring provides a relatively long, high-resolution record from a valley location (elev. 1914 m) in the central Great Basin. We present LOI pollen, and mollusk data to evaluate past hydrology and climate. Evaluating the hydrologic and climate history of this area is important because 40,000 to 60,000 acre-feet of groundwater could potentially be pumped from Spring Valley by the Southern Nevada Water Authority, the owner of Stonehouse Spring.

LOI and pollen data indicate that basin was dry at 7600 cal yr BP, a period noted by Benson as one of extreme drought across the Great Basin. Recharge began sometime after 7500 cal yr BP. Wet sedge meadow was present by 5700 cal yr BP and persisted until ~3000 cal yr BP at which point it appears to have largely disappeared, turning into a dry grassy meadow with shrubs more common than trees. This dry phase persisted until ~2000 cal yr BP, at which time a wet meadow again returns until the present time. Mollusks consist predominantly of terrestrial species and are only present during dry phases. We hypothesize that acidified water dissolved mollusks when spring discharge was high.

An extended dry phase from 3000 to 2000 cal yr BP is found in other paleohydrologic records in the central and western Great Basin, including sites worked on by Benson and collaborators. This dry period is not widely discussed in the literature, but appears to have regional coherence throughout central Nevada. Our paper reviews the geographic extent of this drought and its implications for Great Basin paleoclimatology.