Geological Society of America

T317 New Concepts in Glaciation of the Western Cordillera of North America

Wednesday, 25 October 2017
8:00 AM - 12:00 PM
Chelan 2

VARIED MAGNITUDE OF ALPINE GLACIER ADVANCES GREY HUNTER PEAK THEIR CLIMATIC SIGNIFICANCE, YUKON TERRITORY, CANADA

Paper number: T317-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Brent M. Goehring Presenting Author
Tulane University, New Orleans, LA
Brian Menounos
University of Northern British Columbia, Prince George, BC
Gerald Osborn
University of Calgary, Calgary, AB
Adam C. Hawkins
University of Northern British Columbia, Prince George, BC
Brent Ward
Simon Fraser University, Burnaby, BC

Abstract

Resolution of the climatic signal from the positions of former ice sheet margins is confounded by factors such as complex ice dynamics and identification of former ice divides. Alpine glaciers that flow from a single massif, in contrast, produce moraines that are better suited for climate construction, using methods of varying sophistication (e.g. equilibrium line altitude (ELA) reconstruction or coupled mass balance/ice dynamics models). We visited the Grey Hunter region, an alpine massif in Yukon Territory, to better understand the climatic significance of Pleistocene glaciation. Three prominent groups of alpine lateral and end moraines radiate from cirques. Moraines and rock glaciers closest to contemporary ice bodies are 0.5 km from cirque headwalls and interpreted to be Little Ice Age deposits. Fifteen ¹⁰Be ages from boulders associated with the second group of moraines extending about 1.5 - 3 km from the cirques yielded a median age of 18 ka. The outmost moraines terminate 5-7 km down valley from the cirques and are more rounded in form and the moraine boulders more weathered relative to the inner group of moraines. The outermost moraines were previously mapped by others as Marine Isotope Stage (MIS) 2 deposits (McConnell Glaciation). ¹⁰Be ages from eight boulders from these eroded moraines returned a median age of 35 ka. Given the eroded and weathered appearance of both the moraine and moraine boulders, the 35 ka age for these outermost moraines is likely a minimum-limiting age for the deposits; we infer that these deposits are most likely MIS 4 (Gladstone Glaciation). An enigma remains as to factors that caused glaciers to achieve such different extents during MIS 2 and 4. Probable factors for differences in ice extent over the ca. 20 kyr between MIS 4 and 2 include differences in mean climatic conditions between the two marine isotope stages and locally-driven changes in moisture availability due to the varied configurations of the Cordilleran Ice Sheet given that the Cordilleran Ice Sheet existed in differing configurations between the MIS 4 and 2 as well. Another, less likely, possibility is that surface lowering due to basal erosion and deflation of the glacier surface may have redistributed the hyposmetry of the glacier surface, impacting glacier mass balance over longer periods of time.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-301105

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