10Be dating of late Pleistocene megafloods and Cordilleran Ice Sheet retreat in the northwestern United States

Geology ◽  
2017 ◽  
Vol 45 (7) ◽  
pp. 583-586 ◽  
Author(s):  
Andrea M. Balbas ◽  
Aaron M. Barth ◽  
Peter U. Clark ◽  
Jorie Clark ◽  
Marc Caffee ◽  
...  
Keyword(s):  
United States ◽  
Late Pleistocene ◽  
Ice Sheet ◽  
10Be Dating ◽  
Cordilleran Ice Sheet

Reconstructing the Cordilleran Ice Sheet in northern British Columbia during the Late Pleistocene climate reversals

2020 ◽  
Author(s):  
Helen Dulfer ◽  
Martin Margold
Keyword(s):  
British Columbia ◽  
Late Pleistocene ◽  
Regional Scale ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Western Canada ◽  
Alpine Glaciers ◽  
Pleistocene Climate ◽  
Cordilleran Ice Sheet ◽  
Exposure Ages

<p>The Cordilleran Ice Sheet (CIS) repeatedly covered western Canada during the Pleistocene and attained a volume and area similar to that of the present-day Greenland Ice Sheet. Deglaciation of the CIS following the Last Glacial Maximum (LGM) directly affected atmosphere and ocean circulation, eustatic sea level, and human migration from Asia to North America. It has recently been shown that the rapid climate oscillations at the end of the Pleistocene had a dramatic effect on the CIS. Data on glacial isostatic adjustment and cosmogenic nuclide exposure ages indicate that abrupt warming at the onset of the Bølling-Allerød caused significant thinning of the ice sheet, resulting in a fifty percent reduction in mass, while the Younger Dryas cooling caused the expansion of alpine glaciers across the mountains of western Canada. However, the mountainous subglacial terrain makes it challenging to reconstruct the regional-scale deglaciation dynamics of the ice sheet, and its configuration during this period of rapid change remains poorly constrained. </p><p>Here we use the glacial landform record to reconstruct the ice sheet configuration for the central sector of the CIS, over the Cassiar and Omineca Mountains in northern British Columbia, during the Late Pleistocene climate reversals. We present the first regional-scale reconstruction of the CIS following the Bølling-Allerød warming, whereby the ice sheet was reduced to a labyrinth of valley glaciers fed by ice dispersal centres located over the Skeena Mountains in the south and Coast Mountains in the west. Additionally, numerous lateral and terminal late glacial moraines delineate the extent of alpine glaciers, ice caps and ice fields that regrew on mountain peaks above the CIS during the Younger Dryas. Cross-cutting relationships indicate that the valley glaciers of the CIS were slower to respond to the Younger Dryas cooling than the mountain glaciers.</p>

A new set of basaltic tephras from Southeast Alaska represent key stratigraphic markers for the late Pleistocene

2019 ◽  
Vol 92 (1) ◽  
pp. 246-256 ◽  
Author(s):  
Paul S. Wilcox ◽  
Jason Addison ◽  
Sarah J. Fowell ◽  
James F. Baichtal ◽  
Ken Severin ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Late Pleistocene ◽  
Ice Sheet ◽  
Volcanic Field ◽  
Southeast Alaska ◽  
Cordilleran Ice Sheet

AbstractThree new tephras have been identified in Southeast Alaska. An 8-cm-thick black basaltic tephra with nine discrete normally graded beds is present in cores from a lake on Baker Island. The estimated age of the tephra is 13,492 ± 237 cal yr BP. Although similar in age to the MEd tephra from the adjacent Mt. Edgecumbe volcanic field, this tephra is geochemically distinct. Black basaltic tephras recovered from two additional sites in Southeast Alaska, Heceta Island and the Gulf of Esquibel, are also geochemically distinct from the MEd tephra. The age of the tephra from Heceta Island is 14,609 ± 343 cal yr BP. Whereas the tephras recovered from Baker Island/Heceta Island/Gulf of Esquibel are geochemically distinct from each other, similarities in the ages of these tephras and the MEd tephra suggest a shared eruptive trigger, possibly crustal unloading caused by retreat of the Cordilleran Ice Sheet. The submerged Addington volcanic field on the continental shelf, which may have been subaerially exposed during the late Pleistocene, is a possible source for the Southeast Alaska tephras.

Tephrochronologic Constraints on the Late Pleistocene History of the Southern Margin of the Cordilleran Ice Sheet, Western Washington

1997 ◽  
Vol 47 (2) ◽  
pp. 140-146 ◽  
Author(s):  
James E. Begét ◽  
Mary J. Keskinen ◽  
Kenneth P. Severin
Keyword(s):  
Lake Sediments ◽  
Late Pleistocene ◽  
Ice Sheet ◽  
Cascade Range ◽  
Southern Margin ◽  
Ash Layer ◽  
History Of ◽  
Western Washington ◽  
Cordilleran Ice Sheet ◽  
Eastern Washington

An ash layer that appears geochemically correlative with Mt. St. Helens tephra set S occurs in a sequence of Pleistocene lake sediments in the Ohop Valley of the southern Puget Lowland, below Vashon till deposited during the maximum late Pleistocene advance (Fraser Glaciation) of the Puget Lobe of the Cordilleran Ice Sheet. The Puget Lobe reached its maximum southern extent ca. 14,000–14,500 yr B.P., and at least part of set S is evidently somewhat older. Previous radiocarbon and thermoluminescence dates for set S have ranged from 13,000 to 16,000 yr B.P.Geochemically correlative deposits of set S tephra occur in slackwater sediments coeval with the Missoula Floods in eastern Washington, produced by jökulhlaups through the Purcell Trench Lobe of the Cordilleran Ice Sheet. These relationships suggest that advances of glacier lobes on the southern margin of the Cordilleran Ice Sheet were nonsynchronous, as the Pucell Trench lobe east of the Cascade Range advanced to its maximum southern extent prior to the time of the eruption of set S, before the Puget Lobe west of the Cascades reached its maximum southern extent.

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