Surface exposure dating of the Pierre Sublobe of the James Lobe, Laurentide Ice Sheet

2020 ◽  
Vol 97 ◽  
pp. 88-98
Author(s):  
Stephanie L. Heath ◽  
Thomas V. Lowell ◽  
Brenda L. Hall
Keyword(s):  
Late Quaternary ◽  
Ice Sheet ◽  
Age Dating ◽  
Laurentide Ice Sheet ◽  
Des Moines Lobe ◽  
Exposure Dating ◽  
Des Moines ◽  
Contrast Exposure ◽  
Ice Sheet Dynamics ◽  
Exposure Ages

AbstractThe Laurentide Ice Sheet of the last glacial period terminated in several lobes along its southern margin. The timing of maximum extent may have varied among the terminal lobes owing to internal ice sheet dynamics and spatially variable external controls. Some terminal ice lobes, such as the westernmost James Lobe, remain poorly dated. To determine the timing of maximum ice extent in this key location, we have mapped glacial deposits left by the Pierre Sublobe in South Dakota and applied 10Be surface exposure age dating on boulders on moraine ridges associated with three distinct late Quaternary glacial drifts. The oldest and most extensive “Tazewell” drift produced variable 10Be surface exposure ages spanning 20–7 ka; the large range is likely attributable to moraine degradation and subsequent boulder exhumation. The oldest ages of about 20 ka are probably limiting minimum ages for the Tazewell moraine surfaces. By contrast, exposure ages of the youngest “Mankato” drift of the easternmost Pierre Sublobe tightly cluster at about 16 ka. This age for the Pierre Sublobe is consistent with the nearby Des Moines Lobe, suggesting both acted together.

scholarly journals Flow mechanism of the Des Moines lobe of the Laurentide ice sheet

2002 ◽  
Vol 48 (163) ◽  
pp. 575-586 ◽  
Author(s):  
Thomas S. Hooyer ◽  
Neal R. Iverson
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Shear Stresses ◽  
Flow Mechanism ◽  
Des Moines Lobe ◽  
Des Moines ◽  
Rapid Flow ◽  
Basal Shear ◽  
Basal Till

AbstractRapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ∼3 times thicker than in previous reconstructions. Nevertheless, implied basal shear stresses are <15 kPa, so internal ice deformation was not significant. Instead, the lobe likely moved by a combination of sliding, plowing of particles through the bed surface, and bed shear. Consolidation tests on basal till yield preconsolidation stresses of 125–300 kPa, so effective normal stresses on the bed were small. A model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed, resulting in too small a shear traction on the bed to shear it at depth. Consistent with this prediction, measurements of orientations of clasts in basal till yield a weak fabric, implying pervasive bed shear strain less than ∼2, although some stronger fabrics have been reported by others. We infer, tentatively, that movement was principally at the bed surface by plowing.

Cosmogenic Cl-36 surface exposure dating of late Quaternary glacial events in the Cordillera de Talamanca, Costa Rica

2019 ◽  
Vol 92 (1) ◽  
pp. 216-231 ◽  
Author(s):  
Rebecca Potter ◽  
Yingkui Li ◽  
Sally P. Horn ◽  
Kenneth H. Orvis
Keyword(s):  
Costa Rica ◽  
Late Quaternary ◽  
Age Dating ◽  
Complete Disappearance ◽  
Surface Exposure Dating ◽  
Exposure Dating ◽  
Glacial Chronology ◽  
Tropical America ◽  
Exposure Ages ◽  
Cordillera De Talamanca

AbstractGeomorphic evidence of past glaciation, such as U-shaped valleys, aretes, glacial lakes, and moraines, is preserved in the highland surrounding Cerro Chirripó in the Cordillera de Talamanca, Costa Rica. Previous work to establish a glacial chronology has focused on relative age dating of moraines and on radiocarbon dating of basal lake sediments to infer the timing of deglaciation. We used cosmogenic 36Cl surface exposure dating to constrain the ages of moraines within two formerly glaciated valleys, the Morrenas and Talari valleys. Forty-nine boulder samples were processed and measured from four moraine complexes in the Morrenas Valley and two moraine complexes in the Talari Valley. The exposure ages of these samples indicate a major glacial event occurred in this area from ~25 to 23 ka, broadly synchronous with the global last glacial maximum. Our results also indicate periods of glacial retreats and standstills from the deglacial period to the Early Holocene (~16–10 ka) before the complete disappearance of glaciers in this highland. These findings provide important insights into the glacial chronology and paleoclimate of tropical America.

Revised chronology of northwest Laurentide ice-sheet deglaciation from beryllium-10 exposure-dated erratics on the western Canadian Shield

2020 ◽  
Author(s):  
Alberto Reyes ◽  
Anders Carlson ◽  
Jesse Reimink
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Canadian Shield ◽  
Laurentide Ice Sheet ◽  
Exposure Dating ◽  
Poor Region ◽  
A Site ◽  
Exposure Ages

&lt;p&gt;The timing of northwest Laurentide ice-sheet deglaciation is important for understanding how ice-sheet retreat, and associated meltwater discharge, may have been involved in abrupt climate change and rapid sea-level rise at the end of the last glaciation. However, the deglacial chronology across the western Canadian Shield is poorly understood, with only a handful of minimum-limiting &lt;sup&gt;14&lt;/sup&gt;C dates and sparse cosmogenic nuclide exposure dates constraining the timing and pattern of northwest Laurentide ice-sheet retreat across &gt;1000 km of ice-sheet retreat to the marine limit west of Hudson Bay. We present cosmogenic &lt;sup&gt;10&lt;/sup&gt;Be surface exposure dating of glacial erratics at two sites, within a ~160,000 km&lt;sup&gt;2&lt;/sup&gt; region with no reliable temporal constraints on ice-margin retreat, to directly date the timing of northwest Laurentide ice-sheet deglaciation. Six erratics perched directly on bedrock at a site on the western edge of the Slave Craton have exposure ages between 12.8&amp;#177;0.6 and 12.2&amp;#177;0.6 thousand years ago (ka;&amp;#160;&amp;#177;1sigma). Five erratics on bedrock, sampled at a site 115 km up-ice to the east, yielded exposure ages between 10.8&amp;#177;0.5 and 11.6&amp;#177;0.5 ka. When corrected for decreased atmospheric depth due to isostatic uplift since deglaciation, the error-weighted mean ages for the two sites indicate that the Laurentide ice sheet retreated through this region of the western Canadian Shield between 13.3&amp;#177;0.2 and 11.8&amp;#177;0.2 ka, or at least 1 kyr earlier than inferred from the canonical compilation of minimum-limiting &lt;sup&gt;14&lt;/sup&gt;C dates for deglaciation and paleo-glaciological models. We tentatively infer a preliminary ice-margin retreat rate of ~0.1 m kyr&lt;sup&gt;-1&amp;#160;&lt;/sup&gt;over this interval spanning much of the Younger Dryas which, compared to earlier estimates, implies a substantially lower volume of meltwater flux from the retreating northwest Laurentide ice sheet at this time. &amp;#160;Additional exposure ages on glacial erratics across this data-poor region are needed for validation of existing deglacial ice-sheet models, which can in turn contribute to comprehensive testing of hypotheses related to northwest Laurentide ice-sheet retreat rate, abrupt deglacial sea-level rise, and potential forcing of associated climate change events.&lt;/p&gt;

Late Tertiary to late Quaternary record in the Mackenzie Mountains, Northwest Territories, Canada: stratigraphy, paleosols, paleomagnetism, and chlorine - 36

1996 ◽  
Vol 33 (6) ◽  
pp. 875-895 ◽  
Author(s):  
A. Duk-Rodkin ◽  
R. W. Barendregt ◽  
C. Tarnocai ◽  
F. M. Phillips
Keyword(s):  
Late Quaternary ◽  
Ice Sheet ◽  
Climatic Conditions ◽  
Unconsolidated Sediments ◽  
Laurentide Ice Sheet ◽  
Stratigraphic Sequence ◽  
Late Tertiary ◽  
Mackenzie Mountains ◽  
Late Wisconsinan ◽  
Stratigraphic Succession

A stratigraphic sequence of unconsolidated sediments ranging in age from Late Pliocene to Late Pleistocene is recorded in the Canyon Ranges of the Mackenzie Mountains. Three of the sections (Katherine Creek, Little Bear River, and Inlin Brook) expose bedrock and Tertiary gravel overlain by colluvium and a multiple till sequence of montane origin, separated by paleosols and capped by a till of Laurentide origin. The sections are correlated on the basis of lithology, paleosol development, paleomagnetism, and chlorine dating of surface boulder erratics. A formal stratigraphic nomenclature is proposed for the deposits of this region. The sequence of glacial tills separated by paleosols reflects a long record of glacial–interglacial cycles. Soil properties from the oldest paleosol to modern soil show a general decrease in the degree of soil development, suggesting a progressive deterioration of interglacial climatic conditions. A normal–reverse–normal sequence of remanent magnetization was determined within the stratigraphic succession and assigned to the Gauss–Matuyama–Brunhes chrons, respectively. A Gauss age was assigned to the basal colluvium, an early Matuyama age (including Olduvai) to the first two tills, and a Brunhes age to the last three tills. Laurentide deposits are of Late Wisconsinan age and are restricted to the uppermost part of the stratigraphic succession. Chlorine dates for surface boulders place the all-time limit of the Laurentide Ice Sheet at about 30 ka. The Late Wisconsinan Laurentide Ice Sheet was the only continental ice to reach the Mackenzie and Richardson mountains of the northern Cordillera.

Age of the Berlin moraine complex, New Hampshire, USA, and implications for ice sheet dynamics and climate during Termination 1

2019 ◽  
Vol 94 ◽  
pp. 80-93
Author(s):  
Gordon R.M. Bromley ◽  
Brenda L. Hall ◽  
Woodrow B. Thompson ◽  
Thomas V. Lowell
Keyword(s):  
New England ◽  
New Hampshire ◽  
Global Climate ◽  
Ice Sheet ◽  
Atmospheric Temperature ◽  
Laurentide Ice Sheet ◽  
White Mountains ◽  
Southern New England ◽  
Ice Sheet Dynamics ◽  
St Lawrence River

AbstractAt its late Pleistocene maximum, the Laurentide Ice Sheet was the largest ice mass on Earth and a key player in the modulation of global climate and sea level. At the same time, this temperate ice sheet was itself sensitive to climate, and high-magnitude fluctuations in ice extent, reconstructed from relict glacial deposits, reflect past changes in atmospheric temperature. Here, we present a cosmogenic 10Be surface-exposure chronology for the Berlin moraines in the White Mountains of northern New Hampshire, USA, which supports the model that deglaciation of New England was interrupted by a pronounced advance of ice during the Bølling-Allerød. Together with recalculated 10Be ages from the southern New England coast, the expanded White Mountains moraine chronology also brackets the timing of ice sheet retreat in this sector of the Laurentide. In conjunction with existing chronological data, the moraine ages presented here suggest that deglaciation was widespread during Heinrich Stadial 1 event (~18–14.7 ka) despite apparently cold marine conditions in the adjacent North Atlantic. As part of the White Mountains moraine system, the Berlin chronology also places a new terrestrial constraint on the former glacial configuration during the marine incursion of the St. Lawrence River valley north of the White Mountains.

Transport Direction of Peoria Loess in Nebraska and Implications for Loess Sources on the Central Great Plains

2001 ◽  
Vol 56 (1) ◽  
pp. 79-86 ◽  
Author(s):  
Joseph A. Mason
Keyword(s):  
Climatic Change ◽  
Great Plains ◽  
Source Region ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Secondary Sources ◽  
River Floodplains ◽  
Transport Direction ◽  
Loess Deposition ◽  
Ice Sheet Dynamics

AbstractIn the midwestern United States, large rivers draining the Laurentide Ice Sheet (LIS) were the most important sources of Peoria Loess, deposited during the last glaciation. Loess deposition near those rivers may have responded primarily to ice-sheet dynamics rather than direct effects of climatic change. In contrast, it has been proposed that thick Peoria Loess on the central Great Plains was derived mainly from unglaciated landscapes northwest of the main loess deposits. In this study, transport directions inferred from more than 600 measurements of Peoria Loess thickness in Nebraska are used to test the hypothesis that much of the Peoria Loess on the Great Plains is nonglaciogenic. A strong northwest to southeast thickness trend indicates that most Peoria Loess in Nebraska was transported from one or more unglaciated northwestern source areas rather than from glacially influenced river floodplains. The Missouri River (draining the LIS), the Platte River (draining alpine glaciers), and the Elkhorn River (unglaciated basin) were secondary sources. Their contribution is not detectable beyond a distance of 40–60 km. Peoria Loess deposition on the central Great Plains was largely a direct response to climatic change in the unglaciated source region.

Improved reconstruction of the southeastern Laurentide Ice Sheet deglaciation: constraining ice thinning using in-situ cosmogenic 10Be and 14C and critically evaluating different retreat rate chronometers

2020 ◽  
Author(s):  
Christopher Halsted ◽  
Jeremy Shakun ◽  
Lee Corbett ◽  
Paul Bierman ◽  
P. Thompson Davis ◽  
...  
Keyword(s):  
United States ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Ice Thickness ◽  
Northeastern United States ◽  
Terminal Moraine ◽  
Ice Volume ◽  
Ice Retreat ◽  
Exposure Ages

&lt;p&gt;In the northeastern United States, there are extensive geochronologic and geomorphic constraints on the deglaciation of the southeastern Laurentide Ice Sheet; thus, it is an ideal area for large-scale ice volume reconstructions and comparison between different ice retreat chronometers. Varve chronologies, lake and bog-bottom radiocarbon ages, and cosmogenic nuclide exposure ages constrain the timing of ice retreat, but the inferred ages exhibit considerable noise and sometimes disagree. Additionally, there are few empirical constraints on ice thinning, forcing ice volume reconstructions to rely on geophysically-based ice thickness models. Here, we aim to improve the understanding of the southeastern Laurentide Ice Sheet recession by (1) adding extensive ice thickness constraints and (2) compiling all available deglacial chronology data in the region to investigate discrepancies between different chronometers.&lt;/p&gt;&lt;p&gt;To provide insight about ice sheet thinning history, we collected 120 samples for in-situ &lt;sup&gt;10&lt;/sup&gt;Be and 10 samples for in-situ &lt;sup&gt;14&lt;/sup&gt;C cosmogenic exposure dating from various elevations at 13 mountains in the northeastern United States. By calculating ages of exposure at different elevations across this region, we reconstruct paleo-ice surface lowering of the southeastern Laurentide Ice Sheet during deglaciation. Where we suspect that &lt;sup&gt;10&lt;/sup&gt;Be remains from pre-Last Glacial Maximum periods of exposure, in-situ &lt;sup&gt;14&lt;/sup&gt;C is used to infer the erosional history and minimum exposure age of samples.&lt;/p&gt;&lt;p&gt;Presently, we have measured &lt;sup&gt;10&lt;/sup&gt;Be in 73 samples. Mountain-top exposure ages located within 150 km of the southeastern Laurentide Ice Sheet terminal moraine indicate that near-margin thinning began early in the deglacial period (~19.5 to 17.5 ka), coincident with the slow initial margin retreat indicated by varve records. Exposure ages from several mountains further inland (&gt;400 km north of terminal moraine) collected over ~1000 m of elevation range record rapid ice thinning between 14.5 and 13 ka. Ages within each of these vertical transects are similar within 1&amp;#963; internal uncertainty, indicating that ice thinned quickly, less than a few hundred years at most. This rapid thinning occurred at about the same time that varve records indicate accelerated ice margin retreat (14.6&amp;#8211;12.9 ka), providing evidence of substantial ice volume loss during the B&amp;#248;lling-Aller&amp;#248;d warm period.&lt;/p&gt;&lt;p&gt;Our critical evaluation of deglacial chronometers, including valley-bottom &lt;sup&gt;10&lt;/sup&gt;Be ages from this project, is intended to constrain ice margin retreat rates and timing in the region. Ultimately, we will integrate our ice thickness over time constraints with the existing network of deglacial ages to create a probabilistic reconstructions of the southeastern Laurentide Ice Sheet volume during its recession through the northeastern United States.&lt;/p&gt;

Late-Pleistocene geomorphological and geochronological history of the former Patagonian Ice Sheet in north-eastern Patagonia (43°S)

2020 ◽  
Author(s):  
Tancrede P.M Leger ◽  
Andrew S. Hein ◽  
Angel Rodes ◽  
Robert G. Bingham ◽  
Derek Fabel
Keyword(s):  
Late Pleistocene ◽  
Late Quaternary ◽  
Ice Sheet ◽  
Glacial History ◽  
Climatic Fluctuations ◽  
Eastern Sector ◽  
North Eastern ◽  
Westerly Winds ◽  
Proglacial Lake ◽  
Exposure Ages

&lt;p&gt;The former Patagonian Ice Sheet was the most extensive Quaternary ice sheet of the southern hemisphere outside of Antarctica. Against a background of Northern Hemisphere-dominated ice volumes, it is essential to document how the Patagonian Ice Sheet and its outlet glaciers &amp;#64258;uctuated throughout the Quaternary. This information can help us investigate the climate forcing mechanisms responsible for ice sheet &amp;#64258;uctuations and provide insight on the causes of Quaternary glacial cycles at the southern mid-latitudes. Moreover, Patagonia is part of the only continental landmass that fully intersects the precipitation-bearing southern westerly winds and is thus uniquely positioned to study past climatic fluctuations in the southern mid-latitudes. While Patagonian palaeoglaciological investigations have increased, there remains few published studies investigating glacial deposits from the north-eastern sector of the former ice sheet, between latitudes 41&amp;#176;S and 46&amp;#176;S. Palaeoglaciological reconstructions from this region are required to understand the timing of late-Pleistocene glacial expansion and retreat, and to understand the causes behind potential latitudinal asynchronies in the glacial records throughout Patagonia. Here, we reconstruct the glacial history and chronology of a previously unstudied region of north-eastern Patagonia that formerly hosted the Rio Huemul and Rio Corcovado (43&amp;#176;S, 71&amp;#176;W) palaeo ice-lobes. We present the first detailed glacial geomorphological map of the valley enabling interpretations of the region&amp;#8217;s late Quaternary glacial history. Moreover, we present new cosmogenic 10Be exposure ages from moraine boulders, palaeolake shoreline surface cobbles and ice-moulded bedrock. This new dataset establishes a high-resolution reconstruction of the local LGM through robust dating of five distinct moraines limits of the Rio Corcovado palaeo-glacier. Our results demonstrate that, in its north-eastern sector, the Patagonian Ice Sheet reached its last maximum extent during MIS 2, thus contrasting with the MIS 3 maxima found for the southern parts of the ice sheet. We also present geomorphological evidence along with chronological data for the formation of two ice-dammed proglacial lake phases in the valley caused by LGM ice-extent fluctuations and final glacial recession. Furthermore, this dataset allows us to determine the timing and onset of glacial termination 1 in the region. Finally, our findings include the reconstruction of a proglacial lake drainage and Atlantic/Pacific drainage reversal event caused by ice sheet break-up in western Patagonia. Such findings have significant implications for climate fluctuations at the southern mid-latitudes, former Southern Westerly Winds behaviour and interhemispheric climate linkages during and following the local LGM. They provide further evidence supporting the proposed latitudinal asynchrony in the timing of expansion of the Patagonian Ice Sheet during the last glacial cycle and enable glacio-geomorphological interpretations for the studied region.&lt;/p&gt;

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