STUDY OF HOLOCENE AND LATEST PLEISTOCENE GLACIAL HISTORY IN THE NORTH AMERICAN CORDILLERA: A LOOK INWARD AT DEBATES AND DILEMMAS

The study of Holocene and latest Pleistocene glacial history in North America began in the early 20^th century with consideration of young moraines in the Sierra Nevada. Considerable progress in the ensuing decades has been punctuated by debates and as-yet unresolved dilemmas. Herein I look not at results, but at some aspects of the enterprise.

Historical debates include semantic ones involving the meanings of “Little Ice Age” and “Neoglacial”. There is still confusion arising from the original meaning of LIA as a glacial advance and its later adoption by some as a climatic interval. Past substantive debates are illustrated by arguments in Colorado and Wyoming whether moraines in front of LIA moraines are Neoglacial or late-glacial in age. Ongoing debates include (a) the utility of lichenometry as a dating technique and (b) whether or not there was a significant early Holocene advance, particularly in the Cascades.

Interpretation problems in the past have resulted from excessive faith in relative dating techniques and then by loose interpretation of contexts of 14C ages. The latter include association of “outwash” sediment ages with moraine ages and assumptions that bog-bottom ages provide absolute, rather than minimum, ages of underlying sediments. Current interpretation problems arise from inconsistent considerations of denudation in moraine dating, particularly TCN dating.

Current dilemmas include distinguishing climate signals from noise, interpretation of inconsistencies in an area (reality? noise? dating errors?) and deciding when to exclude “outliers” , size/extent and distribution of Younger Dryas moraines, number of late-glacial advances, reconciliation of information from lateral-moraine stratigraphy and end-moraine ages, distinguishing glacial signals in lake sediments from other influences on sediment input, radiocarbon plateaus, how to know when OSL dating works and doesn’t work, and whether to regard TCN ages as maxima or minima.

This science, being field-based rather than experimental, lacks the repeatability potential and culture found in, say, chemistry. Nevertheless the science would benefit if individuals more often examined each other’s field interpretations, and were less irked by subsequent researchers entering their field areas for some fresh scrutiny.