The last deglaciation of Alaska

Abstract

ABSTRACT. We review available chronologies that constrain the timing of glacier

Pace and Process of Active Folding and Fluvial Incision Across the Kantishna Hills Anticline, Central Alaska

“…A single sand horizon near the top of the ~12‐m‐thick gravel of Qt1 yields an OSL age of 22 ± 3 ka. Within uncertainty, all terrace ages except the youngest (which we replicate at three locations) broadly agree with cosmogenic (Dortch et al, ) and calibrated radiocarbon ages (Briner et al, ) of upstream moraines that mark glacial maxima at 20.8–22.3, 16.7–17.6, and 14.0–15.1 ka. This agreement suggests climatic modulation of terrace formation (e.g., Pan et al, ) and supports our assumption of terrace isochrony along the ~15‐km length of Eagle Gorge.…”

“…New ages of strath terraces that flank the McKinley River across the Kantishna Hills anticline place quantitative bounds on rates of shortening (~1.2 m/kyr) and differential rock uplift and incision (≤1.4 m/kyr) since ~22 ka. Close agreement between the new terrace ages and dates of regional glacial maxima (e.g., Briner et al, ) imply a climatic origin for the McKinley River terraces. Across the anticline crest, where rock uplift rates approach local maxima, an approximately threefold reduction in McKinley River channel width implies an average fivefold increase in unit stream power with minimal concomitant increases in slope.…”

“…We report new ages of the McKinley River terrace deposits (~22, ~18, and ~14–9 ka) that closely match the timing of local glacial maxima (e.g., Briner et al, ). This temporal agreement implies that climatic conditions favorable to glacial advances also perturbed the McKinley River discharge to sediment load ratio, forcing aggradation of the 6–12‐m‐thick channel deposits that now cap the terraces superimposed on the growing fold (cf., Pan et al, ).…”

Late Quaternary Vegetation Development Following Deglaciation of Northwestern Alexander Archipelago, Alaska

“…Reviews of glacial history of southeastern Alaska (Mann, 1986;Mann and Hamilton, 1995) emphasize how little was known about the region's glacial record as of the mid-1980s and mid-1990s. Since then, progress in interpreting the onshore history of the LGI has been limited (e.g., Briner et al, 2017;Lyles et al, 2017). Important new information derived from cosmogenic dating of erratic boulders and glacially scoured bedrock surfaces indicate that LGI glacial ice was somewhat more extensive in southwestern Alexander Archipelago than was depicted in maps by Carrara et al (2003Carrara et al ( , 2007 and Kaufman and Manley (2004).…”

“…Along the western margins of the archipelago, and farther south in the area of Haida Gwaii in B.C., crustal adjustments included forebulge development caused by westward lateral movement of upper mantle material from under the Coast Mountains that had subsided under the weight of thick glacial ice. The forebulge elevated coastal areas of the western archipelago and raised large areas of the inner continental shelf well beyond the areas that were exposed by at least -125 m of eustatic sea level lowering alone (Clague, 1983;Hetherington et al, 2004;Briner et al, 2017).…”