![]() ![]() (1998) when using ACs as the monitor in argon age determinations. It is suggested that this 40Ar/39Ar age replace that of Renne, et al. We propose a new 40Ar/39Ar age for the Quaternary mineral dating standard ACs that reflects the astronomical calibration of FCs and age of the Cobb Mountain polarity event. Although this geomagnetic event is not part of the most recent geologic timescale, refined ages on short-lived excursions could hold importance to understanding time scales for the wavering nature of Earth’s magnetic field. SinglecrystalĪstronomically relative 40Ar/39Ar ages for the Huckleberry Ridge Tuff are indistinguishable from previously determined ages, and provide a degree of confidence in the astronomical calibration. Multi-crystal sanidine experiments of the Bishop Tuff provide an astronomically relative 40Ar/39Ar age for the eruption and associated Matuyama/Brunhes magnetic polarity transition. Two other ash flows in the American west were analyzed: the Bishop and the Huckleberry Ridge Tuffs. Moreover, this new ACs age is consistent with the astronomical age of the Cobb Mountain event, independently determined through correlation of oxygen isotopes in a piston core (Horng, et al. Precision nearing the ambitious 0.1% goal of the EARTHTIME project. New single-crystal analyses, performed on a Noblesse multi-collector noble gas mass spectrometer, suggest a refined 40Ar/39Ar age for ACs, with Of particular interest, the Quaternary mineral dating standard Alder Creek sandine (ACs) is the type locality for the Cobb Mountain geomagnetic event. Using an astronomically calibrated age for the monitor mineral Fish Canyon sanidine (FCs 28.201 ± 0.046 Ma, Kuiper, et al., 2008), ages of Pleistocene geomagnetic polarity events are reexamined. ![]() American west tephras offer a prime opportunity to integrate these two independent timescales with the geomagnetic
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