Moraines and late-glacial stratigraphy in central Lake Superior

2020 ◽  
Vol 98 ◽  
pp. 19-35
Author(s):  
Steven M. Colman ◽  
Andy Breckenridge ◽  
Lucas K. Zoet ◽  
Nigel J. Wattrus ◽  
Thomas C. Johnson
Keyword(s):  
Seismic Reflection ◽  
Lake Superior ◽  
Late Glacial ◽  
Laurentide Ice Sheet ◽  
Isle Royale ◽  
Lake Agassiz ◽  
Ice Dynamics ◽  
Glacial Sediments ◽  
Western Lake ◽  
Glacial Lake Agassiz

AbstractSeismic-reflection surveys of the Isle Royale sub-basin, central Lake Superior, reveal two large end moraines and associated glacial sediments deposited during the last cycle of the Laurentide Ice Sheet in the basin. The Isle Royale moraines directly overlie bedrock and are cored with dense, acoustically massive till intercalated down-ice with acoustically stratified outwash. Till and outwash are overlain by glacial varves, a lower red unit and an upper gray unit.The maximum extent of late Younger Dryas-age readvance into the western Lake Superior basin is uncertain, but it was probably controlled by both ice dynamics and climate. Our data indicate that during retreat from the maximum, the ice paused just long enough to construct the outer of the two moraines, >100 m high, and then retreated to the inner moraine, during which time most of the lower glacial-lacustrine sequence (red varves) was deposited. Retreat from the inner moraine coincided with a marked flux of icebergs at the calving margin and a change to gray varves. Rapid retreat may be related to both an influx of meltwater from Glacial Lake Agassiz about 10,500 cal yr BP and retreat of the calving margin down an adverse slope into the Isle Royale sub-basin.

Isostatic rebound and its effects on fish colonization and distribution in the western Lake Superior basin

1994 ◽  
Vol 72 (1) ◽  
pp. 78-86
Author(s):  
S. A. Stephenson ◽  
W. T. Momot
Keyword(s):  
Comparative Study ◽  
Lake Superior ◽  
Mountain Lakes ◽  
Isle Royale ◽  
Lake Agassiz ◽  
Western Basin ◽  
Glacial Retreat ◽  
Isostatic Rebound ◽  
Western Lake ◽  
Large Numbers

Ichthyofaunal surveys of the Huron Mountains and Isle Royale, Michigan, and the Sibley Peninsula, Ontario, allow for both a comparative study of colonization events and the effects of sequential isostatic rebound within a large portion of the western Lake Superior basin. The distribution of some fish species in these areas is the result of catastrophic events related to glacial retreat. The highest Huron Mountain lakes were colonized during channel events occurring shortly after the Marquette readvance began its retreat. Some species present on the Sibley Peninsula were likely carried by overflows from Lake Agassiz. Most lakes within these areas, however, were colonized well after 9700 BP, when large numbers of species had gained entrance to Lake Superior, mainly from Mississippi basin refugia. Several species, presumably because of earlier warming periods, had a wider distribution than they exhibit today. Some colonization of Isle Royale was probably through the straying of a few individuals from these populations. Lake Superior remains a formidable barrier to many species, restricting them to favourable areas within the western basin.

Interpretation of seismic reflection and gravity profile data in western Lake Superior

1994 ◽  
Vol 31 (4) ◽  
pp. 652-660 ◽  
Author(s):  
John L. Sexton ◽  
Harvey Henson Jr.
Keyword(s):  
Fault Zone ◽  
Seismic Data ◽  
Seismic Reflection ◽  
Lake Superior ◽  
Rift System ◽  
Isle Royale ◽  
Midcontinent Rift ◽  
Detachment Faults ◽  
Western Lake ◽  
Midcontinent Rift System

The interpretation of 1047 km of seismic reflection data collected in western Lake Superior is presented along with reflection traveltime contour maps and gravity models to understand the overall geometry of the Midcontinent Rift System beneath the lake. The Douglas, Isle Royale, and Keweenaw fault zones, clearly imaged on the seismic profiles, are interpreted to be large offset detachment faults associated with initial rifting. These faults have been reactivated as reverse faults with 3–5 km of throw. The Douglas Fault Zone is not directly connected with the Isle Royale Fault Zone. The seismic data has imaged two large basins filled with more than 22 km of middle Keweenawan pre-Portage Lake and Portage Lake volcanic rocks and up to 8 km of upper Keweenawan Oronto and Bayfield sedimentary rocks. These basins persisted throughout Keweenawan time and are separated by a ridge of Archean rocks and a narrow trough bounded by the Keweenaw Fault Zone to the south. Another fault zone, herein named the Ojibwa fault zone, previously interpreted as the northeastern extension of the Douglas Fault Zone, has been reinterpreted as a reverse fault that closely follows the ridge of Archean rocks. Previous researchers have stated that neighboring segments of the rift display alternating polarity of basins associated with large detachment faults. Accommodation zones have been previously interpreted to exist between rift segments; however, the seismic data do not image a clearly identifiable accommodation zone separating the two basins in western Lake Superior. Thus, the seismic profile may lie directly above the pivot of a scissors-type accommodation fault zone, there is no vertical offset associated with the zone, or the zone does not exist. Seismic data interpretations indicate that application of a simple alternating polarity basin – accommodation zone model is an oversimplification of the complex geological structures associated with the Midcontinent Rift System.

An analysis of the late glacial lake levels within the western Lake Superior basin based on digital elevation models

2013 ◽  
Vol 80 (3) ◽  
pp. 383-395 ◽  
Author(s):  
Andy Breckenridge
Keyword(s):  
Lake Michigan ◽  
Digital Elevation Models ◽  
Lake Superior ◽  
Late Glacial ◽  
Glacial Lake ◽  
Lake Levels ◽  
Lake Agassiz ◽  
Western Lake ◽  
Digital Elevation ◽  
Ice Retreat

This study establishes a detailed lake-level history for the Lake Superior basin by mapping strandlines from 10-m and 3-m digital elevation models. There are 24 levels above the mid-Holocene Nipissing level, and elevations increase along a direction of 23.1° due to post-glacial rebound. The highest level, the Epi-Duluth, is steeper than subsequent levels and may pre-date the Lake View ice advance into the western Lake Superior basin at the end of the Younger Dryas stade. The most prominent level is the Duluth, ca. 10,800 cal yr BP. Ice retreat exposed successively lower outlets, routing overflow to the Lake Michigan and Huron basins. By 10,600 cal yr BP, lake levels in the western Superior basin had dropped almost 200 m. This transformative period is complicated by multiple basin-wide events: the influx of glacial Lake Agassiz overflow, the creation of three sub-aqueous moraines, and a red to gray color transition in basin sediments. A later drawdown event has been hypothesized to have initiated the 9300 cal yr BP cooling event, but this flood was much smaller than estimated previously. If freshwater triggered the 9300 cal yr BP event, the source of the water must have been Lake Agassiz, not Lake Superior.

Paleohydrology of the upper Laurentian Great Lakes from the late glacial to early Holocene

2009 ◽  
Vol 71 (3) ◽  
pp. 397-408 ◽  
Author(s):  
Andy Breckenridge ◽  
Thomas C. Johnson
Keyword(s):  
Great Lakes ◽  
Lake Michigan ◽  
Lake Superior ◽  
Late Glacial ◽  
Lake Huron ◽  
Michigan Basin ◽  
Great Lakes Basin ◽  
Lake Agassiz ◽  
Sharp Drop ◽  
Freshwater Fluxes

AbstractBetween 10,500 and 9000 cal yr BP, δ18O values of benthic ostracodes within glaciolacustrine varves from Lake Superior range from − 18 to − 22‰ PDB. In contrast, coeval ostracode and bivalve records from the Lake Huron and Lake Michigan basins are characterized by extreme δ18O variations, ranging from values that reflect a source that is primarily glacial (∼ − 20‰ PDB) to much higher values characteristic of a regional meteoric source (∼ − 5‰ PDB). Re-evaluated age models for the Huron and Michigan records yield a more consistent δ18O stratigraphy. The striking feature of these records is a sharp drop in δ18O values between 9400 and 9000 cal yr BP. In the Huron basin, this low δ18O excursion was ascribed to the late Stanley lowstand, and in the Lake Michigan basin to Lake Agassiz flooding. Catastrophic flooding from Lake Agassiz is likely, but a second possibility is that the low δ18O excursion records the switching of overflow from the Lake Superior basin from an undocumented northern outlet back into the Great Lakes basin. Quantifying freshwater fluxes for this system remains difficult because the benthic ostracodes in the glaciolacustrine varves of Lake Superior and Lake Agassiz may not record the average δ18O value of surface water.

A summary of 19th and early 20th Century researchers of glacial Lake Agassiz, North America: from Noah's Flood to Upham's bathtub and beyond

2014 ◽  
Vol 33 (2) ◽  
pp. 214-226
Author(s):  
Beth Johnson
Keyword(s):  
Laurentide Ice Sheet ◽  
Glacial Lake ◽  
Early 20Th Century ◽  
Ancient Lakes ◽  
Ancient Lake ◽  
Lake Agassiz ◽  
Proglacial Lakes ◽  
Glacial Lake Agassiz ◽  
Lake History ◽  
The U.S

During the last North American deglaciation, meltwater collected along the margins of the Laurentide Ice Sheet in proglacial lakes, the largest of these being glacial Lake Agassiz, which existed for over five thousand years starting ~13,950 cal. years B.P. Lake Agassiz was first described in 1823 by mineralogist William H. Keating of the Long Expedition at a time when diluvianism was often used to explain ancient lakes. Subsequent researchers also recognized the existence of an ancient lake, but the first connections of this lake to a possible glacial source came in 1873. Starting in 1879, Warren Upham spent the next fifteen years researching and publishing on Lake Agassiz, eventually publishing his seminal work, the U.S. Geological Survey's Monograph 25 The Glacial Lake Agassiz. Some of Upham's interpretations were later challenged by William A. Johnston, who favored a more complex lake history.

Sedimentary architecture of the southern basin of Lake of the Woods, Minnesota and its relation to Lake Agassiz history and Holocene environmental change

2018 ◽  
Vol 90 (1) ◽  
pp. 96-109 ◽  
Author(s):  
Devin D. Hougardy ◽  
Steven M. Colman
Keyword(s):  
Seismic Reflection ◽  
Late Holocene ◽  
Lake Basin ◽  
Lake Agassiz ◽  
Southern Basin ◽  
Lake Of The Woods ◽  
Isostatic Uplift ◽  
Sedimentary Architecture ◽  
Glacial Lake Agassiz ◽  
Seismic Reflection Profiles

AbstractLake of the Woods (LOTW) is a large, complex lake basin once occupied by glacial Lake Agassiz. High-resolution seismic-reflection profiles and cores in the shallow, open southern basin of LOTW reveal a sedimentary architecture comprising four lacustrine units separated by three low-stand unconformities. These units represent several phases of Lake Agassiz and its changing configuration. One unconformity marks the Moorhead low phase and another marks the separation of LOTW from Lake Agassiz, perhaps ~10 cal ka BP, as the level of the latter fell, but before final drainage of Agassiz. Initially, the separate Holocene lake in the southern basin was broad and shallow, sometimes marshy or dry. Shortly after 8 cal ka BP, the southern basin dried up completely, despite the progressive rise of the northern outlet of the lake due to differential isostatic uplift. The resulting hiatus is related to the well-documented mid-Holocene arid interval in central North America. A return to wetter conditions in the late Holocene caused the southern basin of LOTW to refill since about 3800 cal yr BP. Late Holocene sediments have accumulated slightly asymmetrically in the basin, possible due to continued southward transgression of the lake as a result of isostatic tilting.

Glaciological reconstruction of the Laurentide Ice Sheet: physical processes and modelling challenges

2000 ◽  
Vol 37 (5) ◽  
pp. 769-793 ◽  
Author(s):  
Shawn J Marshall ◽  
Lev Tarasov ◽  
Garry K.C Clarke ◽  
W Richard Peltier
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Late Glacial ◽  
Laurentide Ice Sheet ◽  
Glacial Cycle ◽  
Physical Processes ◽  
Ice Dynamics ◽  
Geologic Record ◽  
Basal Flow

Current understanding of Pleistocene ice-sheet history is based on collective inferences from three separate avenues of study: (1) the geologic and paleoceanographic records, (2) the isostatic record, and (3) the behaviour of contemporary glaciers and ice sheets. The geologic record provides good constraint on the areal extent of former ice sheets, while isostatic deflection patterns provide important information about late-glacial ice-sheet thickness. The picture emerging from geologic and isostatic deductions is suggestive of a thin and mobile Laurentide Ice Sheet relative to present-day Greenland and Antarctica. We model Laurentide Ice Sheet evolution through a glacial cycle to explore the glaciological mechanisms that are required to replicate the geologic and isostatic evidence. A number of glaciological processes important to the ice-sheet evolution are not fully understood, including marine-based ice dynamics, iceberg calving, rheologic properties of ice, and basal flow dynamics. We present a spectrum of glacial cycle simulations with different treatments of poorly constrained physical processes. We conclude that glaciological model reconstructions can only be reconciled with the late-glacial geologic record of a thin, low-sloping Laurentide Ice Sheet by invoking (1) extremely deformable ice, (2) widespread basal flow, or (3) paleoclimate-ice-sheet fluctuations which give last glacial maximum ice sheets that are far from equilibrium.

Retreat of the Laurentide Ice Sheet from 14,000 to 9000 Years Ago

1971 ◽  
Vol 1 (3) ◽  
pp. 316-330 ◽  
Author(s):  
H. E. Wright
Keyword(s):  
Great Lakes ◽  
Lake Michigan ◽  
Lake Superior ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Great Lakes Region ◽  
Forward Movement ◽  
Western Lake ◽  
Basal Sliding ◽  
Lake Michigan Lobe

The intricate pattern of moraines of the Laurentide ice sheet in the Great Lakes region reflects the marked lobation of the ice margin in late Wisconsin time, and this in turn reflects the distribution of steam-cut lowlands etched in preglacial times in the weak-rock belts of gentle Paleozoic fold structures. It is difficult to trace and correlate moraines from lobe to lobe and to evaluate the magnitude of recession before readvance, but three breaks stand out in the sequence, with readvances at about 14,500, 13,000, and 11,500 years ago. The first, corresponding to the Cary advance of the Lake Michigan lobe, is represented to the west by distant advance of the Des Moines lobe in Iowa, and to the east by the overriding of lake beds by the Erie lobe. The 13,000-year advance is best represented by the Port Huron moraine of the Lake Michigan and Huron lobes, but by relatively little action to west and east. The 11,500-year advance is based on the Valders till of the Lake Michigan lobe, but presumed correlations to east and west prove to be generally older, and the question is raised that these and some other ice advances in the Great Lakes region may represent surges of the ice rather than regional climatic change. Surging may involve the buildup of subglacial meltwater, which can provide the basal sliding necessary for rapid forward movement. It would be most favored by the conditions in the western Lake Superior basin, where the Superior lobe had a suitable form and thermal regime, as estimated from geomorphic and paleoclimatic criteria. The Valders advance of the Lake Michigan and Green Bay lobes may also have resulted from a surge: the eastern part of the Lake Superior basin, whence the ice advanced, has a pattern of deep gorges that resemble subglacial tunnel valleys, which imply great quantities of subglacial water that may have produced glacial surges before the water became channeled.

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