Last Interglacial age of the Eva Forest Bed, Central Alaska, from thermoluminescence dating of bracketing loess

Abstract

The Eva Forest Bed in the Yukon-Tanana Upland of east-central Alaska represents a frozen, buried, boreal forest. This bed consists of well-preserved peat lenses, sticks, roots, logs, as well as rooted and unrooted stumps of trees. Where preserved, the Eva Forest Bed is overlain by the Goldstream Formation and underlain by Gold Hill Loess. Almost all exposures have a prominent unconformity at the top of the Gold Hill Loess, even where the forest bed is not preserved. Attempts have been made over the last 50 yr to determine the age of this bed numerically. We report here details of thermoluminescence (TL) dating of 14 samples of loess from above and below this unconformity in the Fairbanks area. Together with knowledge about the climatic indicators from the Eva Forest Bed, these TL age estimates: (1) indicate that the most probable age of the Eva Forest Bed is ∼125 ka, the time of the warmest part of oxygen isotope stage 5; and (2) confirm stratigraphic inferences from tephra beds in the upper Gold Hill Loess that erosion has removed variable thicknesses of the original loess complex “just prior” to the development of the Eva Forest Bed.