Radiocarbon and cation-ratio ages for rock varnish on Tioga and Tahoe morainal boulders of Pine Creek, earstern Sierra Nevada, California, and their paleoclimatic implications

TitleRadiocarbon and cation-ratio ages for rock varnish on Tioga and Tahoe morainal boulders of Pine Creek, earstern Sierra Nevada, California, and their paleoclimatic implications
Publication TypeJournal Article
Year of Publication1987
AuthorsDorn RI, Donahue DJ, Turrin BD, Jull AJT, Linick TW
JournalQuaternary Research
Volume28
Pagination36-49
KeywordsSierra Nevada
Abstract

Accelerator mass spectrometry 14C analyses of organic matter extracted from rock varnishes on morainal boulders yield limiting minimum ages for three crests of the Tioga glaciation. At Pine Creek in the eastern Sierra Nevada, varnish started to form on boulders of the outermost Tioga moraine before 19,000 yr B.P., and varnish originated on the innermost Tioga moraine before 13,200 yr B.P. Comparisons with lake-level, paleohydrological, paleoecological, colluvial, and rock varnish micromorphological data indicate that central-eastern California and western Nevada experienced a moisture-effective period during the late Pleistocene but after the Tioga maximum, and perhaps as Tioga glaciers receded from the mouth of Pine Creek canyon. Varnishes on Tahoeage morainal boulders at Pine Creek have cation-ratio ages of about 143,000–156,000 yr B.P., suggesting that the Tahoe glaciation should not be correlated with oxygen-isotope stage 4 in the early Wisconsin, but rather with stage 6. Varnishes on morainal boulders of an older glaciation at Pine Creek are dated by cation ratio at about 182,000–187,000 yr B.P.