Abstract

The climate chronology proposed by Broecker and Orr (1958) for the two major Great Basin pluvial lakes has been confirmed and expanded by coupling 80 new radiocarbon measurements with uranium-series isotope measurements. The validity of the ages is evaluated by comparing different materials, chemical fractions of the same material, radiocarbon ages with Th230-U234 ages, and chronology based on geomorphic features with that based on stratigraphic units. The lake-level chronology has been extended to the postpluvial period (<8000 years ago) by radiocarbon measurements and to the preradiocarbon period (>30,000 years ago) by Th230-U234 measurements.

The results suggest that both lakes were relatively high four times during the late Wisconsin: 17,000 years ago; 14,500 years ago; 12,000 years ago; and 9500 years ago. The downcutting of Red Rock Pass probably occurred during the high-water period about 12,000 years ago.

An attempt is made to correlate this chronology with those worked out for the pluviation of the Searles Lake basin, the pollen sequence of Northern Europe, and the glacial oscillations in the North American mid-continent.

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