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.

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>

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

New Dates on Late Pleistocene Dacitic Tephra from the Mount Edgecumbe Volcanic Field, Southeastern Alaska

1998 ◽  
Vol 49 (1) ◽  
pp. 123-125 ◽  
Author(s):  
James E. Begét ◽  
Roman J. Motyka
Keyword(s):  
Late Pleistocene ◽  
Volcanic Field ◽  
Tephra Layer ◽  
Southeast Alaska ◽  
Radiocarbon Dates

New radiocarbon dates on charcoal incorporated in proximal airfall deposits indicate the largest late Pleistocene eruption from the Mt. Edgecumbe volcanic field in Southeast Alaska occurred ca. 11,250 ± 50 14C yr B.P. The more precise dating of the principal Edgecumbe tephra layer greatly improves its utility as a tephrochronologic marker horizon in southeastern Alaska.

scholarly journals A cosmogenic nuclide chronology of Cordilleran Ice Sheet configuration during the Last Glacial Maximum in the northern Alexander Archipelago, Alaska

2021 ◽  
Author(s):  
Caleb K. Walcott ◽  
Jason P. Briner ◽  
James F. Baichtal ◽  
Alia J. Lesnek ◽  
Joseph M. Licciardi
Keyword(s):  
Continental Shelf ◽  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Glacial Refugia ◽  
Glacial Maximum ◽  
Human Migration ◽  
Last Glacial ◽  
The North ◽  
Cordilleran Ice Sheet ◽  
Alexander Archipelago

Abstract. The late-Pleistocene history of the coastal Cordilleran Ice Sheet (CIS) remains relatively unstudied compared to chronologies of the Laurentide Ice Sheet. Yet accurate reconstructions of CIS extent and timing of ice retreat along the Pacific Coast are essential for a variety of reasons including paleoclimate modeling, assessing meltwater contribution to the North Pacific, and determining the availability of ice-free land along the coastal CIS margin for human migration from Beringia into the Americas. To improve the chronology of CIS history in the Alexander Archipelago, Alaska, we applied 10Be and 36Cl dating to boulders and glacially sculpted bedrock outcrops in areas previously hypothesized to have remained ice-free throughout the local Last Glacial Maximum (lLGM; 20–17 ka). Results indicate that these sites, and more generally the coastal northern Alexander Archipelago, became ice-free by 15.1 ± 0.9 ka (n = 12 boulders; 1 SD). We also provide further age constraints on deglaciation along the southern Alexander Archipelago and combine our new ages with data from two previous studies. We determine that ice retreated from the outer coast of the southern Alexander Archipelago at 16.3 ± 0.8 ka (n = 14 boulders; 1 SD). These results collectively indicate that areas above modern sea level that were previously mapped as glacial refugia were covered by ice during the lLGM until between ~16.3 and 15.1 ka. As no evidence was found for ice-free land during the lLGM, our results suggest that previous ice-sheet reconstructions underestimate the regional maximum CIS extent, and that all ice likely terminated on the continental shelf. Future work should investigate whether presently submerged areas of the continental shelf were ice-free.

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.

New constraints on the last deglaciation of the Cordilleran Ice Sheet in coastal Southeast Alaska

2020 ◽  
Vol 96 ◽  
pp. 140-160 ◽  
Author(s):  
Alia J. Lesnek ◽  
Jason P. Briner ◽  
James F. Baichtal ◽  
Alex S. Lyles
Keyword(s):  
Ice Sheet ◽  
Last Deglaciation ◽  
Rapid Phase ◽  
Southeast Alaska ◽  
Alpine Glaciers ◽  
Air Temperatures ◽  
The Last Deglaciation ◽  
Cordilleran Ice Sheet ◽  
Exposure Ages ◽  
Outer Coast

AbstractUnderstanding marine-terminating ice sheet response to past climate transitions provides valuable long-term context for observations of modern ice sheet change. Here, we reconstruct the last deglaciation of marine-terminating Cordilleran Ice Sheet (CIS) margins in Southeast Alaska and explore potential forcings of western CIS retreat. We combine 27 new cosmogenic 10Be exposure ages, 13 recently published 10Be ages, and 25 new 14C ages from raised marine sediments to constrain CIS recession. Retreat from the outer coast was underway by 17 ka, and the inner fjords and sounds were ice-free by 15 ka. After 15 ka, the western margin of the CIS became primarily land-terminating and alpine glaciers disappeared from the outer coast. Isolated alpine glaciers may have persisted in high inland peaks until the early Holocene. Our results suggest that the most rapid phase of CIS retreat along the Pacific coast occurred between ~17 and 15 ka. This retreat was likely driven by processes operating at the ice-ocean interface, including sea level rise and ocean warming. CIS recession after ~15 ka occurred during a time of climatic amelioration in this region, when both ocean and air temperatures increased. These data highlight the sensitivity of marine-terminating CIS regions to deglacial climate change.

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