Cosmogenic nuclide data sets from the Sierra Nevada, California, for assessment of nuclide production models: I. Late Pleistocene glacial chronology

Abstract

Abstract The Cosmic-Ray prOduced NUclide Systematics on Earth Project (CRONUS-Earth Project) has reused a limited number of ‘legacy’ 10 Be and 36 Cl samples from late Pleistocene moraines in the Sierra Nevada for the testing and evaluation of cosmogenic nuclide production rates derived by the CRONUS-Earth Project. A secure glacial chronology for the range is necessary for this purpose. Evidence for the timing of glacial fluctuations is provided by direct radiocarbon ages marking glacial termini at various times and by chronologies on lacustrine cores, marine cores, and speleothem records. Evaluation of these records yields a relatively consistent picture. Tioga 3 glaciers were close to their maximum extent from >20 to about 17 ka. Close to 17 ka they retreated rapidly, then began to readvance at ∼16.8 ka. The Tioga 4 readvance culminated at about 16.2 ka and rapid retreat ensued, with the equilibrium line altitude rising by 400 m by 15.7 ka and the range probably virtually ice-free by a short time thereafter. There is no evidence of ice readvance until the Recess Peak glaciation. Dating of this readavance is inconsistent, with direct dates on glacial features and some lacustrine and speleothem records placing it between 14.0 and 13.0 ka, but many regional records are more consistent with an advance during the interval 13.0 to 12.6 ka. After consideration of all the evidence I have assigned ages of 15.75 ± 0.5 ka for Tioga 4 retreat and 13.3 ± 0.25 for the maximum extent of the Recess Peak glaciation.