Late Holocene cryptotephra from Cascade Lake, Alaska: supporting data for a 21,000-year multi-chronometer Bayesian age model

Multiple chronometers can be employed for dating Holocene palaeoenvironmental records, each with its own inherent strengths and weaknesses. Radiocarbon dating is one of the most widely used techniques for producing chronologies, but its application at high-latitude sites can be problematic. Here, cryptotephra identified in the Late Holocene portion of a core from Cascade Lake, Arctic Alaska, resolve a divergence identified between radiocarbon and paleomagnetic secular variation (PSV) data in the top 1.5 m of the sediment sequence. Identifiable geochemical populations of cryptotephra are shown to be present in detectable concentrations in sediment from the north flank of the Brooks Range for the first time. Major element glass geochemical correlations are demonstrated between ultra-distal cryptotephra and reference samples from the Late Holocene caldera forming eruption of Opala, Kamchatka, as well as three eruptions in North America: the White River Ash (northern lobe), Ruppert tephra and the Late Holocene caldera forming eruption of Aniakchak. The correlated ages of these cryptotephra support the PSV ages reported in Steen et al. (this volume) and provide evidence for an old-carbon effect in Cascade Lake. Chronological data from the Cascade Lake were then combined using a Bayesian approach to generate an age-depth model that extends back to 21,000 cal yr BP.