Gold Run tephra: a Middle Pleistocene stratigraphic and paleoenvironmental marker across west-central Yukon Territory, Canada

Abstract

Gold Run tephra has been found at Thistle Creek, Sixtymile River, and the Klondike goldfields of west-central Yukon, Canada. It is a hornblende-bearing rhyolitic tephra with thicknesses of up to 10 cm at each site, suggesting a widespread distribution across interior Alaska and the Yukon Territory, given the long distance to the nearest volcanic centre. Old Crow, Flat Creek, and TA tephra beds are stratigraphically associated with Gold Run tephra at our study sites and have distinctive compositions. Gold Run tephra is not accommodated by the current classification scheme for late Cenozoic distal tephra beds in Alaska and the Yukon Territory — a scheme based on the physical and chemical attributes — so that its provenance is unknown. An early-Middle Pleistocene age is supported by a glass fission-track age of 0.74 ± 0.06 Ma, a normal remanent magnetic polarity for the enclosing loess, and the presence of a late Irvingtonian faunal assemblage in the associated organic-rich silts at Thistle Creek. Hence, Gold Run tephra was deposited during the very early part of the Brunhes Chron, at which time a shrub tundra environment prevailed across west-central Yukon.