Tephrochronology is a widely applied method recognized for its exceptional precision in geologic dating and stratigraphic correlation. Tephra from the ca. 7.6 ka Mount Mazama caldera-forming (climactic) eruption has been widely identified and applied as stratigraphic isochron sediments of northwestern North America, as well as in the Greenland ice core records. Recent findings of a microscopic tephra accumulation, or cryptotephra, from Mount Mazama in Newfoundland indicated that this horizon should also be found in Lake Superior sediments. We present findings that confirm the presence of Mount Mazama ash in two sediment cores from the Lake Superior basin, indicating its likely presence in the rest of the Laurentian Great Lakes and in deposits throughout much of eastern North America and beyond. The ubiquity of this stratigraphic horizon should be applicable to a higher resolution evaluation of climatological and ecological events and archaeological sites during the early to mid-Holocene thermal maximum throughout much of North America.

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