DISCOVERY OF MOUNT MAZAMA CRYPTOTEPHRA IN LAKE SUPERIOR

Tephrochronology is a widely applied method recognized for its exceptional precision in geologic dating and stratigraphic correlation. Tephra from the ~7.6 kyr BP Mount Mazama “climactic eruption”—the caldera collapse that created Crater Lake in Oregon—have been widely identified and applied as stratigraphic isochrons in terrestrial, oceanic, and lacustrine records of northwestern North America, as well as in the Greenland ice core records. Recent findings of a microscopic tephra horizon, or cryptotephra, from Mt. Mazama in Newfoundland indicated that this horizon should also be found in Lake Superior sediments. We present findings that confirm the presence of Mazama ash in two sediment cores from the Lake Superior basin. The discovery of this cryptotephra horizon in Lake Superior sediments indicates its likely presence in the rest of the Laurentian Great Lakes and in terrestrial sediments throughout much of eastern North America. The ubiquity of this stratigraphic horizon should be applicable to a higher resolution evaluation of climatological, ecological, and archaeological events during the early- to mid-Holocene Hypsithermal climate interval throughout much of North America.