Assessing AMS 14C ages of detrital organics from Holocene and late-Pleistocene moraines, east-central Sierra Nevada, California, USA

Abstract

Obtaining age estimates of moraines which have insufficient carbon for conventional 14C dating may be possible by AMS 14C dating of detrital organic material in the till matrix. Sufficient detrital carbon was available in the till matrix of Holocene and late-Pleistocene moraines of upper Laurel Creek Canyon, east-central Sierra Nevada, California, for AMS 14C measurements. Radiocarbon analysis of till matrix organics from the moraine closest to the headwall, M1, reveals an age of 2875 ± 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 13 600 ± 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 context, other palaeoecologic records in the Sierra Nevada, and palaeolake records in the western United States.