Abstract

The northern Nenana River valley contains evidence for a minimum of five and probably as many as seven distinct glacial episodes that predate the Riley Creek glaciation of late Wisconsin age. The oldest glacial episode, represented in the Nenana Gravel by diamictons and erratic boulders, is late Tertiary in age; the youngest pre-Riley Creek ice advance (the Healy glaciation) is probably early Wisconsin in age. Three new drifts of intermediate age are described and given informal names—Teklanika River, Bear Creek, and Lignite Creek—and use of the preexisting term Browne glaciation is retained. Evidence for the previously described Dry Creek glaciation is not strong enough to justify its designation as a separate major glacial episode.

The glacial record in the northern Nenana River valley is described for three areas that have been physically separated from each other by erosion or by faulting: the outer foothills, the Eight Mile Lake area, and the Nenana canyon. Correlations of drifts between each area, based largely on reconstructed ice gradients and on topographic position within the valley, provide a consistent framework for interpreting the region’s late Cenozoic history. Relative-age criteria based on moraine surface characteristics were found to be of limited value for correlation purposes. However, the overall morphologic expression of moraines, their vertical position in the valley, and their relative extents are useful criteria for regional correlations.