ASSESSING AMS C-14 AGES OF DETRITAL ORGANICS FROM HOLOCENE AND LATE-PLEISTOCENE MORAINES, EAST-CENTRAL SIERRA-NEVADA, CALIFORNIA, USA

Obtaining age estimates of moraines which have insufficient carbon for conventional C-14 dating may be possible by AMS C-14 dating of detrit al organic material in the till matrix. Sufficient detrital carbon was available in the till matrix of Holocene and late-Pleistocene moraine s of upper Laurel Creek Canyon, east-central Sierra Nevada, California , for AMS C-14 measurements. Radiocarbon analysis of till matrix organ ics from the moraine closest to the headwall, M1, reveals an age of 28 75+/-60 BP (ETH 13550). The next oldest moraine, M2, yields 4450+/-60 BP (ETH 12810). M3, the oldest moraine in the Bloody Mountain Cirque, yielded organics with a radiocarbon age of 13600+/-120 BP (ETH 12812). While results are preliminary, these ages are among the first on till matrix in the Sierra Nevada and are consistent with geomorphic contex t, other palaeoecologic records in the Sierra Nevada, and palaeolake r ecords in the western United States.