scholarly journals Relict Late Wisconsinan Dune Fields of the Northern Great Plains, Canada*

2006 ◽  
Vol 58 (2-3) ◽  
pp. 323-336 ◽  
Author(s):  
Stephen A. Wolfe ◽  
David J. Huntley ◽  
Jeff Ollerhead
Keyword(s):  
Boreal Forest ◽  
Great Plains ◽  
Sand Dunes ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Northern Great Plains ◽  
The West ◽  
Air Mass ◽  
Late Wisconsinan ◽  
Dune Activity

Abstract Late Wisconsinan dune activity is investigated within the present-day boreal forest and parkland regions of the northern Great Plains, Canada, to extend the understanding of the spatial and temporal eolian record. Optical ages from stabilized sand dunes document the timing of past activity. Eolian activity ranges from about 16 ka in west-central Alberta to 9 ka in northwestern Saskatchewan. Between about 16 and 13 ka, dune activity in central Alberta occurred in an ice-proximal tundra setting along the margins of the Laurentide and Cordilleran ice sheets. Predominant dune-forming winds were from the west and northwest. Dune activity continued in this area between about 13 and 11 ka within parkland and grassland settings as the Laurentide Ice Sheet retreated to the northeast. Winds continued to blow from the west and northwest, and the climate was likely influenced by an increasingly dominant Pacific air mass. Also beginning at about 13 ka, dune-forming winds along the margins of the retreating Laurentide Ice Sheet were influenced by anticyclonic winds from the southeast that were maintained until about 9 ka. As the Laurentide Ice Sheet retreated, these southeasterly anticyclonic winds were successively replaced by winds from the northwest associated with the Pacific air mass. Dune activity across the region terminated in a time-transgressive manner from the southwest, at about 11 ka, to the northeast, at about 9 ka, with the establishment of boreal forest vegetation and reduced wind strength.

scholarly journals Reconstruction of isostatically-adjusted paleo-strandlines along the southern margin of the Laurentide Ice Sheet in the Great Lakes, Lake Agassiz and Champlain Sea basins

2021 ◽  
Author(s):  
Michael Lewis ◽  
Andy Breckenridge ◽  
James Teller
Keyword(s):  
Great Plains ◽  
Ice Sheet ◽  
Field Measurements ◽  
Google Earth ◽  
Water Bodies ◽  
Laurentide Ice Sheet ◽  
Northern Great Plains ◽  
Published Data ◽  
Southern Margin ◽  
Digital Format

Abstract: Strandlines document the former presence of lakes and a sea in east-central North America along the southern margin of the retreating Laurentide Ice Sheet (LIS). The strandlines of these formerly level water bodies are uplifted to the north and provide evidence of glacial isostatic adjustment (GIA) of the Earth’s crust to the former ice load. We compile published ages and measurements of the present elevation and location of shore features in the strandlines of 8 major paleo-waterbodies from the St. Lawrence Valley to the northern Great Plains in digital format as an aid for the numerical modelling of GIA. Data for eastern water bodies were extracted and digitized from publications during the past 120 years. Digital position co-ordinates were scaled from published maps of survey sites or were determined using Google Earth Pro software. Published data for paleo-lakes Duluth and Agassiz were mainly obtained from field measurements and digital elevation models (DEMs). Two-sigma or 95% probability values are provided for the strandline ages and for isobase (contour) positions representing the deformed water surfaces. Peak strandline gradients reported here were largest at about ca. 13,000 years ago. Lower strandline gradients for older shores may reveal areas closer to the peripheral bulge and areas of thinner ice (lighter crustal loads). Concave upward strandline profiles characterize most paleo-basins whereas a linear uplift profile characterizes the Champlain Sea strandline. Directions of strandline maximum uplift within the former water body basins point towards the thickest part of the LIS near the Québec-Labrador ice dome.

scholarly journals Late Wisconsinan and Holocene History of the Laurentide Ice Sheet*

2008 ◽  
Vol 41 (2) ◽  
pp. 237-263 ◽  
Author(s):  
Arthur S. Dyke ◽  
Victor K. Prest
Keyword(s):  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Ice Streams ◽  
The West ◽  
Ice Shelves ◽  
Sea Level Oscillations ◽  
History Of ◽  
Ice Retreat ◽  
Late Wisconsinan ◽  
And Migration

AbstractEleven paleogeographic maps and a summary ice retreat map outline the history of advance, retreat, and readvances of the Laurentide Ice Sheet along with associated changes in proglacial drainage and relative sea level oscillations for Late Wisconsinan and Holocene times. The text outlines pertinent chronological control and discusses the paleoglaciology of the ice sheet, with attention to location and migration of ice divides, their attendant domes and saddles, and to ice streams, ice shelves, and mechanisms of déglaciation. At 18 ka the ice sheet consisted of 3 sectors with an interlocked system of ice divides joined at intersector saddles. A throughgoing superdivide is recognized and named the Trans Laurentide Ice Divide. The ice sheet retreated slowly from 18 to 13 ka, mainly along the west and south margins, but still held a near maximum configuration at 13 ka. A regional change in flow pattern over the Prairies just before 14 ka is thought to represent a large reduction in ice volume, but not in extent, and likely was triggered by a switch from nondeforming to deforming bed conditions. Retreat between 13 and 8 ka was vastly more rapid in the west than in the east, which resulted in eastward migration of the divide system of Keewatin Ice but relatively static divides of Labrador and Foxe Ice. By 10 ka the Trans Laurentide Ice Divide had been fragmented as Hudson Ice became increasingly autonomous. By 8 ka Hudson Ice had disappeared, little ice was left in Keewatin, but Foxe Ice still held its near maximum configuration and Labrador Ice was still larger than Foxe Ice. Repeated surging along aquatic margins and calving back of margins thinned by surging probably was the most important mechanism of deglaciation of Keewatin and Hudson Ice. The core of Foxe Ice disintegrated at 7 ka but retreat and readvance of Foxe Ice remnants continued throughout the Holocene.

Absence of Glaciation in Illinois during Marine Isotope Stages 3 through 5

1996 ◽  
Vol 46 (1) ◽  
pp. 19-26 ◽  
Author(s):  
B. Brandon Curry ◽  
Milan J. Pavich
Keyword(s):  
Oxygen Isotope ◽  
Late Stage ◽  
Lake Michigan ◽  
Early Stage ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Argillic Horizon ◽  
Late Wisconsinan ◽  
Lake Michigan Lobe

A10Be inventory and14C ages of material from a core from northernmost Illinois support previous interpretations that this area was ice free from ca. 155,000 to 25,000 yr ago. During much of this period, from about 155,000 to 55,000 yr ago, 10Be accumulated in the argillic horizon of the Sangamon Geosol. Wisconsinan loess, containing inherited 10Be, was deposited above the Sangamon Geosol from ca. 55,000 to 25,000 yr ago and was subsequently buried by late Wisconsinan till deposited by the Lake Michigan Lobe of the Laurentide Ice Sheet. The Sangamonian interglacial stage has been correlated narrowly to marine oxygen isotope substage 5e; our data indicate instead that the Sangamon Geosol developed during late stage 6, all of stages 5 and 4, and early stage 3.

Pleistocene stratigraphy, paleopedology, and paleoecology of a multiple till sequence exposed on the Little Bear River, Western District of Mackenzie, N.W.T., Canada

1993 ◽  
Vol 30 (4) ◽  
pp. 851-866 ◽  
Author(s):  
O. L. Hughes ◽  
C. Tarnocai ◽  
C. E. Schweger
Keyword(s):  
Transition Zone ◽  
Ice Sheet ◽  
Climatic Conditions ◽  
Canadian Shield ◽  
Laurentide Ice Sheet ◽  
Spruce Forest ◽  
River Section ◽  
Valley Glacier ◽  
Bear River ◽  
Late Wisconsinan

The Little Bear River section lies in a transition zone between Mackenzie Lowland and Canyon Ranges of Mackenzie Mountains. Within the transition zone, the maximum extent of the Laurentide ice sheet overlaps the former extent of montane glaciers that emanated from the higher parts of Canyon Ranges or from the still higher Backbone Ranges to the southwest. Five montane tills, each with a paleosol developed in its upper part, indicate five separate glaciations during each of which a valley glacier emanating from the headwaters of Little Bear River extended eastward into the transition zone. The uppermost of the montane tills is overlain by boulder gravel containing rocks of Canadian Shield origin deposited by the Laurentide ice sheet.Solum and B horizon depths, red colours, and lack of leaching and cryoturbation indicate that although each successive interglacial interval was cooler than the preceding one, even the last of the intervals was warmer than the Holocene. Climatic conditions during one of the intervals inferred from the paleobotanic data, particularly spruce forest development, are consistent with conditions inferred from the associated paleosol.The uppermost of the montane tills is thought to correlate with till of Reid (Illinoian) age in central Yukon. The paleosol developed on that till is, accordingly, thought to correlate with the Diversion Creek paleosol developed on drift of Reid age. The Laurentide boulder gravel is assigned to a stade of Hungry Creek Glaciation of Late Wisconsinan age. The Laurentide ice sheet reached its apparent all-time western limit during the Hungry Creek Glaciation maximum.

scholarly journals Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

2007 ◽  
Vol 39 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D. A. Fisher ◽  
N. Reeh ◽  
K. Langley
Keyword(s):  
Yield Stress ◽  
Flow Direction ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Surface Slopes ◽  
Late Wisconsinan

ABSTRACT A three dimensional steady state plastic ice model; the present surface topography (on a 50 km grid); a recent concensus of the Late Wisconsinan maximum margin (PREST, 1984); and a simple map of ice yield stress are used to model the Laurentide Ice Sheet. A multi-domed, asymmetric reconstruction is computed without prior assumptions about flow lines. The effects of possible deforming beds are modelled by using the very low yield stress values suggested by MATHEWS (1974). Because of low yield stress (deforming beds) the model generates thin ice on the Prairies, Great Lakes area and, in one case, over Hudson Bay. Introduction of low yield stress (deformabie) regions also produces low surface slopes and abrupt ice flow direction changes. In certain circumstances large ice streams are generated along the boundaries between normal yield stress (non-deformable beds) and low yield stress ice (deformabie beds). Computer models are discussed in reference to the geologically-based reconstructions of SHILTS (1980) and DYKE ef al. (1982).

Genesis of carbonate till in the lee sides of Precambrian Shield uplands, Hemlo area, Ontario

1987 ◽  
Vol 24 (10) ◽  
pp. 2004-2015 ◽  
Author(s):  
Stephen R. Hicock
Keyword(s):  
Ice Sheet ◽  
Glacial Maximum ◽  
Laurentide Ice Sheet ◽  
The South ◽  
Precambrian Shield ◽  
Basal Zone ◽  
Compressive Flow ◽  
Late Wisconsinan ◽  
Basal Till

Near Hemlo, Ontario, highly calcareous till is confined to areas located downglacier from Precambrian uplands, at least 150 km from the Paleozoic–Precambrian boundary. It comprises subglacial meltout till between lodgment tills, and the calcareous package overlies noncalcareous basal till (not studied) and underlies noncalcareous supraglacial meltout till. The tills can be distinguished by textural, carbonate, and clast compositions. Glaciotectonic deformations, stone fabrics and striae, and stone provenance from the tills, as well as erosional and depositional landforms, indicate that ice advanced to the south–southwest across bedrock contacts and over Precambrian uplands.Deposition of all five tills can be explained with one glacial event. As the Late Wisconsinan margin of the Laurentide ice sheet advanced against uplands about 20 km northeast of Hemlo it experienced compressive flow while depositing the non calcareous basal till. Upshearing of stoss-side local debris high into the ice also occurred as englacial ice overrode the slowed basal zone. Once over the upland, englacial ice assumed extending flow, and downshearing of distal debris, which was deposited as calcareous lodgment till on the lee sides of uplands. After the glacial maximum, the glacier ceased internal movement and subglacial meltout till was laid down. A late reactivation of the ice deposited the upper lodgment till and final stagnation formed the supraglacial meltout till.

scholarly journals LGM Summer Climate on the Southern Margin of the Laurentide Ice Sheet: Wet or Dry?*

2005 ◽  
Vol 18 (16) ◽  
pp. 3317-3338 ◽  
Author(s):  
David H. Bromwich ◽  
E. Richard Toracinta ◽  
Robert J. Oglesby ◽  
James L. Fastook ◽  
Terence J. Hughes
Keyword(s):  
Boundary Conditions ◽  
Great Plains ◽  
Land Surface ◽  
Thermal Gradient ◽  
Mesoscale Model ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Low Level ◽  
Summer Climate ◽  
Southern Margin

Abstract Regional climate simulations are conducted using the Polar fifth-generation Pennsylvania State University (PSU)–NCAR Mesoscale Model (MM5) with a 60-km horizontal resolution domain over North America to explore the summer climate of the Last Glacial Maximum (LGM: 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level. The simulated LGM summer climate is characterized by a pronounced low-level thermal gradient along the southern margin of the LIS resulting from the juxtaposition of the cold ice sheet and adjacent warm ice-free land surface. This sharp thermal gradient anchors the midtropospheric jet stream and facilitates the development of synoptic cyclones that track over the ice sheet, some of which produce copious liquid precipitation along and south of the LIS terminus. Precipitation on the southern margin is orographically enhanced as moist southerly low-level flow (resembling a contemporary Great Plains low-level jet configuration) in advance of the cyclone is drawn up the ice sheet slope. Composites of wet and dry periods on the LIS southern margin illustrate two distinctly different atmospheric flow regimes. Given the episodic nature of the summer rain events, it may be possible to reconcile the model depiction of wet conditions on the LIS southern margin during the LGM summer with the widely accepted interpretation of aridity across the Great Plains based on geological proxy evidence.

Holocene dune activity and environmental change in the prairie parki and and boreal forest, central Saskatchewan, Canada

The Holocene ◽  
2006 ◽  
Vol 16 (1) ◽  
pp. 17-29 ◽  
Author(s):  
Stephen A. Wolfe ◽  
Jeff Ollerhead ◽  
David J. Huntley ◽  
Olav B. Lian
Keyword(s):  
Environmental Change ◽  
Boreal Forest ◽  
Great Plains ◽  
Late Holocene ◽  
Early Holocene ◽  
Aeolian Activity ◽  
Landscape Response ◽  
Response To Environmental Change ◽  
Holocene Activity ◽  
Dune Activity

Past aeolian activity was reconstructed at four dunefields in the prairie parkland and boreal forest of central Saskatchewan to elucidate landscape response to environmental change. Optical ages from stabilized dunes in the boreal transition ecoregion indicate two episodes of activity. The first, at about 11 ka, corresponds to a period of early-Holocene parkland and grassland cover following deglaciation and drainage after about 13.0 ka, and brief establishment of boreal forest. The second, between about 7.5 and 5 ka, corresponds to a period of mid-Holocene parkland-grassland cover. Optical ages from dunefields in the prairie parkland primarily record mid-Holocene activity, between about 7.5 and 4.7 ka, corresponding to a period of grassland cover, with some reworking continuing into the late Holocene. Although this area was deglaciated by about 13.5 ka, there is no evidence of early-Holocene dune activity, suggesting that mid-Holocene activity may have reworked earlier deposits here. Consequently, much of the morphology and stratigraphy observed in these dunefields are associated with mid-Holocene activity, likely associated with increased aridity and reduced vegetation cover at that time. This study provides the most northerly evidence of mid-Holocene dune reactivation on the Great Plains, lending support to the assertion that aeolian activity was widespread at that time.

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.

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