The ice–substrate interface is an important boundary condition for ice sheet
modelling. The substrate affects the ice sheet by allowing sliding through
sediment deformation and accommodating the storage and drainage of subglacial
water. We present three datasets on a 1 : 5 000 000 scale with different
geological parameters for the region that was covered by the ice sheets in
North America, including Greenland and Iceland. The first dataset includes
the distribution of surficial sediments, which is separated into continuous,
discontinuous and predominantly rock categories. The second dataset includes
sediment grain size properties, which is divided into three classes: clay,
silt and sand, based on the dominant grain size of the fine fraction of the
glacial sediments. The third dataset is the generalized bedrock geology. We
demonstrate the utility of these datasets for governing ice sheet dynamics by
using an ice sheet model with a simulation that extends through the last
glacial cycle. In order to demonstrate the importance of the basal boundary
conditions for ice sheet modelling, we changed the shear friction angle to
account for a weaker substrate and found changes up to 40 % in ice
thickness compared to a reference run. Although incorporation of the ice–bed
boundary remains model dependent, our dataset provides an observational
baseline for improving a critical weakness in current ice sheet modelling
(10.1594/PANGAEA.895889, ).
Introduction
Temperate ice sheets, such as the Laurentide and Eurasian ice
sheets behaved differently depending on whether or not there was thick,
continuous unconsolidated sediments underneath the ice
. These sediments provided a potential pathway for
subglacial water storage and drainage. Areas in which crystalline bedrock is
predominant at the surface tend to have eskers, indicating that subglacial
water drained via large tunnel systems
. The subglacial drainage where the
surface is covered by continuous, unconsolidated sediment tends to be via
linked channel systems . The main cause of these
different drainage regimes is likely related to the roughness of the bed
(i.e. in areas with sediment cover, the surface is smoothed by the glacier,
while in areas with bedrock outcrops will be more irregular). Sediment
deformation in areas with continuous cover is also hypothesized to play a
prominent role in the motion of glaciers
, possibly also including decoupling
with the underlaying, non-deforming surfaces . When
sediments become water saturated, they become mechanically weaker than the
overlying ice. If this happens, it causes a decoupling from the underlying
bed and allows the ice to flow faster than with ice deformation alone.
Whether or not this mechanism could have been spatially and temporally
pervasive is still open to debate .
In North America, there was a distinct difference in ice sheet behaviour
between the sparsely covered Canadian Shield and the sediment-covered
sedimentary basins at the southern and western fringes, and Hudson Bay and
the Foxe Basins in the center and north. The most striking imprint of this in
the geomorphological record is the reduced number of ice streams on much of
the Canadian Shield, while areas covered with continuous sediments have many
. The presence or absence of available unconsolidated
sediment influenced the distribution of ribbed moraine, drumlins and eskers
on the Canadian Shield . Retreat of the Laurentide
Ice Sheet after the Last Glacial Maximum (LGM) also slowed when the ice sheet
became confined to the Canadian Shield . During the advance
of the ice sheet prior to the LGM, the margin remained close to the Canadian
Shield boundary until the ice sheet reached a threshold that allowed it to
advance onto the surrounding plains . The part of the ice
sheet that covered the plains had a low profile relative to the Canadian
Shield, which has been attributed to this contrast in basal conditions
.
Having realistic basal conditions is essential in numerical ice sheet
modelling. Many ice sheet modelling studies of the Laurentide Ice Sheet
used the global sediment thickness map , which was
designed for seismology applications rather than surficial processes. This
dataset reflects the thickness of Phanerozoic sedimentary rock that has not
undergone significant metamorphism. This map does not reflect the actual
distribution of unconsolidated sediments, as many regions of the Canadian
Shield do have continuous sediment cover , and
there are regions of discontinuous unconsolidated sediment cover where there
is sedimentary bedrock . This dataset
also misses Precambrian sedimentary basins that are overlain by
unconsolidated sediments that were modified by ice sheets
. The direct impacts on ice sheet dynamics may only
depend on the uppermost few metres of unconsolidated sediment
, so this map may not be
representative of the sediment properties that affected the ice sheet. More
recently, and used a more
complete parameterization with additional data from the surficial materials
map by . They use a parameter from 0 (no sediments) to 1
(pervasive sediments). Previous modelling studies did not directly account
for variability in the grain size or other properties of the sediments.
In order to gain flexibility in parameterizing sediment parameters for ice
sheet modelling, we present three datasets. These data come from existing
surficial geological maps when possible and are inferred from other studies
where coverage is not complete. (i) The sediment distribution dataset
contains information on the distribution of sediment cover, whether
continuous, veneer, or dominantly bedrock. (ii) The sediment grain size
dataset contains information on the average grain size of the sediments. This
is based on common geological descriptions of sandy, silty and clay-rich
diamicton and glacial sediments. (iii) The bedrock geology dataset contains
the generalized bedrock type, including distinctions between sedimentary,
igneous and metamorphic rock. These data can be used in a variety of ways,
such as by changing the mechanical strength and frictional resistance of the
sediment (such as the shear friction angle), effects of hydrology (porosity
and permeability of the sediments or rock, type of drainage), roughness of
the bed and the erodibility of substrate.
Description of datasetsOverview and construction
In order for a dataset to be usable in ice sheet models, it is necessary for it to
be continuous. Since existing geological map datasets are discontinuous
due to the presence of post-glacial sediments and water bodies
(Fig. ), we had to fill in these gaps. These
datasets include supplementary information from geophysical surveys and
coring studies to compliment existing maps. We also made an inference on
grain size properties in the vast regions without information by using
geological maps. We want to emphasize that these datasets are low-resolution
generalized representations of geological properties. The intended use is for
relatively low-resolution ice sheet simulations (i.e. 5 km or greater) and
are not likely to be appropriate for resolving higher-resolution features.
Illustration showing the relationship between the bedrock, glacial
sediments and postglacial sediments. In glacial times, the ice sheet is in
contact with glacial sediments created by the ice sheet itself and bedrock.
In post-glacial times, the bedrock and glacial sediments can be obscured by
water bodies and post-glacial sediments.
Data coverage (brown areas) derived directly from surficial geology
maps. (a) Sediment distribution and (b) sediment grain size.
With this dataset, the goal is to represent the subglacial sediment
properties for the most recent glaciation, the late Wisconsin glaciation in
North America, for use in paleo-ice sheet modelling and reconstruction. The
late Wisconsin happened between about 31 000 and 34 000 yr BP (years
before present) to about 7000 yr BP . For ice sheet
modelling, using the modern-day distribution and composition of glacial
sediments is likely sufficient to use as a boundary condition for the most
recent glacial period, though further back in time, this assumption may not
be valid . There are great uncertainties in many of
the boundary conditions used in ice sheet modelling, such as uncertainties in
past atmospheric and ocean conditions, but sediment cover likely does not
change that greatly in a single glaciation , so we
do not feel this is a major setback for the use of this dataset. Also, in
areas with crystalline bedrock, it is possible for surfaces to be unmodified
by glacial action . We want to emphasize that the
categories chosen for this dataset are simplified from some of the original
data sources in order to make it easier for ice sheet modellers to manipulate
a limited range of parameters, rather than match specific geological
observations that may only be applicable very small regions. The lack of
sediment grain size information over much of Canada also precludes a large
range of geological parameters. When ice sheet modelling, it is necessary to
have continuous boundary conditions over the whole domain. In areas without
geological information, it is necessary to make inferences on the properties
based on alternative sources of information, such as bedrock geology maps.
The three datasets are largely based on existing surficial and bedrock
geology maps (Table ). Wherever possible, we used the
most up-to-date regional scale (i.e. >1 : 500 000 scale) maps in order
to make it possible to construct the entire dataset in a reasonable amount of
time. For the sediment distribution data, where there was overlap with
the map by , we favoured the more recent dataset. The first
step was to import the existing shapefiles of the maps (or digitizing paper
maps if not available) and break up the units into the classification
schemes that we are using. This involved removing any water bodies and
post-glacial sediment units from the maps and simplifying glacial geological
units that had a more complex scheme than we use. The resulting datasets have
gaps. Figure shows the data coverage purely from surficial
geology maps. To fill in the gaps, we expanded the polygons in a way to
favour the dominant unit in the region, or to extend the trend of elongated
units. The datasets were edited using ArcGIS and QGIS.
Maps used for the creation of the distribution and grain size
dataset.
Map regionDataset usedReferenceCanadadistribution, Canadagrain sizeContinental United States west of the Rocky MountainsdistributionOttawa Quadrangledistribution, grain sizeQuebec Quadrangledistribution, grain sizeBoston Quadrangledistribution, grain sizeHudson River Quadrangledistribution, grain sizeSudbury Quadrangledistribution, grain sizeLake Erie Quadrangledistribution, grain sizeBlue Ridge Quadrangledistribution, grain sizeLake Nipigon Quadrangledistribution, grain sizeLake Superior Quadrangledistribution, grain sizeChicago Quadrangledistribution, grain sizeLouisville Quadrangledistribution, grain sizeLake of the Woods Quadrangledistribution, grain sizeMinneapolis Quadrangledistribution, grain sizeDes Moines Quadrangledistribution, grain sizeOzark Plateau Quadrangledistribution, grain sizeWinnipeg Quadrangledistribution, grain sizeDakotas Quadrangledistribution, grain sizePlatte River Quadrangledistribution, grain sizeWichita Quadrangledistribution, grain sizeRegina Quadrangledistribution, grain sizeMontanadistribution, grain sizeSouthern Cordillera Ice Sheetdistribution, grain sizeNova Scotiagrain sizePrince Edward Islandgrain sizeNew Brunswickgrain sizeNewfoundland and Labradordistribution, grain sizeQuebecgrain sizeNorthern Ontariodistribution, grain sizeSouthern Ontariodistribution, grain sizeManitobadistribution, grain sizeSaskatchewandistributionNorthern Saskatchewangrain sizeAlbertagrain sizeBritish Columbiagrain sizeSouthwestern British Columbiagrain sizeCordillera Ice SheetdistributionYukondistribution, grain sizeYukongrain sizeAlaskadistributionAlaskagrain sizeMainland Northwest Territories, Nunavut and Baffin Islandgrain sizeOffshore Newfoundland and Grand BanksdistributionHudson Straitdistribution, grain sizeGulf of St. Laurencedistribution, grain size, Labrador ShelfdistributionSouthwestern Greenlanddistribution, Central eastern GreenlanddistributionSoutheastern Greenland and IcelanddistributionGreenlanddistributionGreenland and Icelandgrain sizeGreenland Ice Sheetgrain size
There are many areas where late Wisconsin till is buried by glacio-fluvial
and Holocene non-glacial sediments, so the nature or existence of glacial
sediments is uncertain. This is also true for previously glaciated areas
under lakes and the oceans and places currently covered in glaciers, ice caps
and the Greenland Ice Sheet. In these regions, we tried to find published
sediment cores, sedimentary sections and geophysical data that can be used
to estimate the properties of the sediments
(Table ).
We incorporate sediment data from areas outside of the late Wisconsin limit,
as in an ice sheet simulation, the exact margin of the ice sheet is unlikely
to match the geologically constrained limit and could become more expansive.
For areas south of the Laurentide Ice Sheet limit, there is glacial sediment
from more extensive, older glaciations. These data were taken from the US
quadrangle maps (Table ). In other areas, such as Alaska
and offshore regions, we take the properties from non-glacial sediments and
inferences from bedrock geology maps.
Supplementary resources used for the creation of the distribution
and grain size dataset.
RegionDataset usedNotesReferenceOkanogan Lobe (southernCordillera Ice Sheet)distributionSediment cover is a veneer.(2004)Puget Sound (southernCordillera Ice Sheet)distributionThe Puget Lobe overrode a thick sequence of proglacial sediments.Northern and CentralQuebecdistribution, grain sizeDominantly sandy tills are found, except in regions with sedimentary rock.Ungava Peninsula, Quebecdistribution, grain sizeThick layers of coarse-grained diamicton are found.Hudson Bay Lowlands,Ontariograin sizeGlacial sediments contain roughly equal amounts of clay, silt and sand.Southeastern Manitobagrain sizeGrain size of glacial sediments underneath Lake Agassiz deposits is dependent on the source region, but on average it is silt.Lake Winnipeg, ManitobadistributionGlacial sediments are discontinuous under the entire lake, except where there are end moraines.Alberta Interior Plainsgrain sizeGlacial sediments have a relatively uniform composition that is roughly equal parts clay, silt and sand.British Columbiagrain sizeGlacial sediments generally have similar composition as underlying bedrock, though are more coarse at higher elevations.British Columbia interiorgrain sizeGlacial sediments are silt or sand rich.Mainland Northwest Territories and Nunavutgrain sizeGlacial sediments generally have grain size reflective of bedrock geology.Western Northwest Territoriesgrain sizeAreas overlying the Western Canadian Sedimentary Basin have an unsorted mixture of sand silt and clay.e.g. Hudson BaydistributionMultibeam data collected from Hudson Bay, which were ultimately used in .Eastern Hudson Baydistribution, grain sizeBetcher Islands are relatively barren of unconsolidated sediments; bedrock is Proterozoic sedimentary and volcanic rock.St. Laurence estuarydistributionThick accumulations of glacial sediments only occur where there are bedrock troughs.Offshore Nova ScotiadistributionSeismic and multibeam data indicate significant glacial sediment accumulation., Gulf of Mainedistribution, grain sizeThere is a thick succession of fine-grained sediments; near Cape Cod it is more sandy.Northern NorthwestPassage, Arctic CanadadistributionMultibeam data indicate limited cover by glacial sediments.Gulf of BoothiadistributionMultibeam data indicate a continuous layer of sediments.Coronation and AmundsengulfsdistributionSediment veneer found in the Coronation Gulf and inner Amundsen Gulf is thicker in the outer Amundsen Gulf.Western Lake SuperiordistributionSeismic data indicate that glacial sediment units are not continuous.Western Lake Superior near Thunder Baydistribution, grain sizeThick glacial sediment units were interpreted to be fine grained.Lake Superior and LakeMichigandistribution, grain sizeThick sediment cover with a composition that reflects local geology for Lake Superior, and high clay content for Lake Michigan.Lake OntariodistributionThe core of Lake Ontario has thick glacial sediment cover, but on the margins it is thin and discontinuous., Lake Eriedistribution, grain sizeErie Lobe sediments are clay rich due to reworking of lake sediments.Eastern Great Slave LakedistributionGlacial sediments are thick in some areas, but is not continuous.
Continued.
Regiondataset usednotesreferenceBeaufort SeadistributionSeismic data indicates thick sediment cover.GreenlanddistributionThick glacial sediment cover generally only exists in fjords and high plateaus.GreenlanddistributionSediment cover in areas described by generally completely covers the bedrock., , Offshore GreenlanddistributionAreas with scoured bedrock visible from multibean and seismic data have limited sediment cover, and smooth topography is more continuous., , , Greenland Ice SheetdistributionSeismic evidence indicates the presence of sediments under the ice sheet., Greenland Ice Sheetdistribution, grain sizeMost of Greenland is underlain by Archean and Paleo-proterozoic cratons, which are composed largely of high-grade metamorphic and plutonic rock, and likely has similar characteristics as the Canadian Shield., , Offshore Icelanddistribution, grain sizeSeismic surveys indicate thick sediment cover with relatively fine grain size.Western Icelandgrain sizeOlder glacial sediments have been described as being silt rich and sandy silt., Baffin Islandgrain sizeGrain size reflects bedrock geology.
In the creation of the dataset, existing shapefile compilations were used if
available, which have variable resolution. To simplify the datasets when the
originals were at high resolution, we used the bend simplify tool in
the ARCGIS Cartography/generalization Toolbox, with a tolerance of 5 km and
minimum area of 25 km2. This is visually similar to the generalization
that was used in the surficial materials map by . Any
polygon that had a total area that was less than 2.25 km2 was merged with
the polygon that had the largest shared border to further simplify the
dataset. The final dataset is presented as shapefiles that are compatible
with GIS programs, as well as 5 km resolution NetCDF files.
Sediment distribution dataset
The map of glacial sediment distribution is shown in
Fig. . Data sources for this dataset are shown in
Table . By “glacial sediment” we are referring to
sediment that is produced as a direct result of glacial action. In a generic
sense, it is synonymous with diamicton or till, an unsorted sediment with
grain size ranging from clay to boulder. When possible, we try to determine
the distribution of glacial sediments in extensive areas covered by
post-glacial cover and water bodies (Fig. ; see
Table for sources). Many maps used in this dataset only
give qualitative descriptions of the distribution, and the definition often
varies between mappers. As a result, it is not possible to give an exact
range for sediment thickness or percentage sediment cover. We recommend
that modellers explore a range of values.
Figure shows the relationship between the
three classes with the cover over bedrock. A detailed explanation for the
distribution units, which is based on the scheme found on the Surficial
Materials of Canada map by is as follows.
Sediment distribution. The red line is the glacial limit during the
Last Glacial Maximum, 21 000 yr BP (thousands of years ago). Blanket
regions are where unconsolidated sediments form a continuous surface, veneer
regions have variable amounts of rock outcrops and discontinuous sediment
cover, while rock areas have little or no sediment cover.
Illustration of how the sediment distribution relates to the
underlying bedrock and thickness of the sediments. The rock class has only
isolated patches of sediment, the veneer class has a thin sediment layer with
bedrock outcrops and a visible influence of bedrock topography on the
surface, while with the blanket class, the sediments completely obscure the
bedrock surface.
Rock. Bedrock outcrops are predominant (>75 % of the surface
area is exposed bedrock; ) and extensive glacial sediment
deposits are rare. We include “regolith” areas in the northern Canadian
archipelago, which were not pervasively affected by late Wisconsin glaciation
(even if the upper layer was not well consolidated) and therefore do not
produce glacial sediment deposits.
Veneer. Many maps seem to have a different definition of what
“veneer” means. In general, it means that glacial sediment deposit are
discontinuous (can be zero thickness), but the area covered in glacial
sediment exceeds that of exposed rock. The topography of the underlying
bedrock is usually visible in these areas. In most maps, these areas have
thin cover, with “thin” being defined as anything between less than 1 m
and as much as 10 m. Commonly, the cutoff is set to be 2–3 m, although some
maps (e.g. the Surficial Materials map of Canada by ) do
not explicitly state a value. A recommended thickness value setting for
veneer areas should be less than 3 m to conform to the most common
description of “veneer” provided in maps used in this dataset, though even
a thin layer of glacial sediment might affect the dynamics of an ice sheet
.
Blanket. These regions are defined as regionally continuous glacial
sediment. As with the “veneer” classification, it is not always clear what
thickness or distribution is used as a threshold for defining “blanket”. If
values are given, the threshold is usually greater than 3 m. In
areas with a blanket of sediment, the underlying bedrock topography
is generally not obvious. Glacial sediment units that are described as “hummocky” are
included in this definition. These glacial sediments formed during stagnation
of the ice sheet and are commonly found on elevated regions in western
Canada . The thickness can vary from a few metres to
more than 25 m, but it is assumed here that these deposits are at least
3 m and can be put into the blanket definition.
A scheme similar to this has been used in the studies by
and for use in the modelling
of sediment transport. The difference in our dataset is that we explicitly do
not include post-glacial sediments and instead try to fill these gaps with
supplemental information.
Sediment grain size dataset
The map of generalized grain size of glacial sediments is shown in
Fig. . A glacial sediment, diamicton or till (the later
has a definitive glacial origin) is an unsorted material with grain size
ranging from clay to boulder. Glacial sediments generally have a bimodal
grain size distribution, with peaks in the coarse (pebble to boulder) and
fine (clay to sand) fractions . The relative
amount of coarse to fine material is dependent on the distance from the source of the
coarse material, so on glacial geology maps and datasets, glacial sediments
are described in terms of the fine fraction only. To simplify the
classification, we only have three main classification types, based on the
dominant grain size of fine fraction. This classification scheme is based on
the Surficial Materials in the Conterminous United States map
, and we attempted to unify this scheme with maps and
data in Canada. The grain size of the sediments tends to have geographical
dependence. As an example, in the map by , clay-rich
glacial sediment exists in areas around the Great Lakes, where source
material was derived from lake sediments and sandy material in mountainous
regions, where there are extensive rock outcrops. The relative fraction of the
sediment that is coarser than sand cannot be quantified, since most of
the data sources only give qualitative descriptions of the coarse fraction.
Sediment grain size. The red line is the glacial limit during the
Last Glacial Maximum, 21 000 yr BP . The types of sediment
include clay (dominantly fine-grained sediment), silt (an average composition
between sand and clay) and sand (dominantly coarse-grained sediments).
Clay. Glacial sediment has a large clay component (>50 %).
Silt. Intermediate of clay and sand dominant composition. This unit
includes any description called “loamy till”, which is a soil with an
average grain size between sand and silt.
Sand. Sand-rich till with only a minor clay component and more sand
than silt. This includes units that were described as “bouldery till”.
Many maps do not give specific classifications of the grain size of glacial
sediments. The United States quadrangle maps (Table ),
which cover most areas south of about 54∘ north (except in the
Cordillera), fortunately do have this information. The lack of information
north of this is likely due to accessibility issues, where there are few
extensive geology, soil and engineering surveys that would serve as the basis
for such a map. As a result, the sediment type for many of these regions was
derived from bedrock geology maps. In general, glacial sediments in North
America have a composition that similar to the underlying bedrock
, so we assume that the grain size should be related to the
bedrock geology. Since the distribution of clay-rich till appears to
correlate strongly with the location of lakes, it is not included. Our
approach for classifying grain size from geology maps is as follows.
Silt. Fine-grained clastic sedimentary rock (shale, carbonates);
mafic igneous rock; undivided igneous rock; low-grade metamorphic rock (e.g.
greenschist).
Sand. Coarse-grained clastic sedimentary rock (sandstone,
conglomerate); felsic igneous rock; high-grade metamorphic rock (e.g.
gneiss).
Bedrock geology dataset
This dataset (Fig. ) is a simplification of the Geologic Map
of North America . For the area covered
by the Greenland Ice Sheet, we use the map by . The rocks
were divided into the following groups:
Generalized geology. The red line is the glacial limit during the
Last Glacial Maximum, 21 000 yr BP . The rock types are
divided into sedimentary, felsic and mafic, volcanic and plutonic, and
metamorphic categories.
Sedimentary. All units described as being sedimentary.
Felsic plutonic. All rock explicitly described as felsic igneous
(e.g. granite), charnockite, units described as being “felsic and
intermediate” and units that were undivided mafic and felsic rock.
Felsic volcanic. Same as felsic plutonic, but explicitly described
as volcanic (e.g. rhyolite).
Mafic plutonic. All rock explicitly described as mafic igneous (e.g.
gabbro), units described as being “intermediate” and “intermediate and
intermediate”, alkaline and units that were undivided mafic and felsic rock.
Mafic volcanic. Same as plutonic, but explicitly described as
volcanic (e.g. basalt), also includes volcanic deposits that are described as
having interlayered sedimentary layers.
Low-grade metamorphic. Marble, plus units described as being
“undivided crystalline rocks”.
High-grade metamorphic. Units that are highly metamorphosed i.e.
gneiss.
The map has few units that can be confidently placed in the low-grade
metamorphic class, because most of these units are grouped with their
non-metamorphosed source rock class. Therefore it should be assumed that many
of the areas with igneous and sedimentary rock have undergone some level of
metamorphism, particularly on the Canadian Shield. We placed the “undivided
unit” in the low-grade category, as most of these areas are in the
continental shelf where no geophysical surveys or sampling has taken place.
The description given in the original dataset indicates that these rocks
likely contain some amount of metamorphism. It can be assumed that these
rocks along the Atlantic coast were probably subjected to some amount of
metamorphism during the opening of the Atlantic Ocean, or in the case of
Hudson Bay, are likely part of the Precambrian Shield.
Caveats
In this compilation, we tried to incorporate the most recent information on
surficial geology that was available. Unfortunately, there are places where,
due to discrepancies between adjacent maps, there are visible seams. This is
especially evident at the Yukon–Alaska border and the British Columbia–Washington border. Obviously, these areas will be in need of revision when
new mapping information becomes available. There are also discrepancies in
interpretation and classification between maps. A good example is the dataset
we used for Manitoba , which had only two classes for
distribution (blanket and rock). The corresponding map by
divides the regions that are classified as “rock” into veneer and rock.
Since our intention is to use the most up-to-date information, we use the
dataset by , but with the caveat that this also
causes a seam with the adjacent regions in northern Ontario and Saskatchewan
that have a broader classification scheme.
General properties of sediments relating to composition and texture
(see also Eq. 1).
MaterialGrain size (mm)Shear friction angleCohesionPermeabilityDilationClay<0.005<20>10 kPalowappreciableSilt0.05–0.005<30<10 kPavariablevariableSand>0.05>30negligiblehighnoneUsage in ice sheet modelsGeological parameters and impact on ice sheets
Some general properties of sediment grain size types are shown in
Table . Most of these properties are described in more
detail in . These properties are only given in a
qualitative manner because there have been relatively few in situ or
laboratory measurements of these properties over a range of compositions
. Measured permeability values were reported to be
between 1013 and 1016 m2. It is
recommended that, when modelling the behaviour of ice sheets, a range of
values be explored.
The effect of sediment distribution on ice sheet models is less well known.
The patchiness of sediments may result in “sticky spots”, primarily though
bedrock knobs that resist the flow of ice . The lack of
sediment in an otherwise sediment-covered region may increase resistance to
flow as well if sediment deformation is a dominant factor in controlling flow
. The influence of the latter process is likely
controlled by the availability of subglacial water. All of the thickness
categories made in this dataset are derived from existing geological maps.
Because of inconsistencies in classification between maps and vast regions
where there are few direct observations, it is not possible to give a
detailed quantitative estimates of distribution or thickness. These exact
values of the percentage of surface cover and sediment thickness can be set
as a variable in ice sheet models.
The geological map can be used for determining the erosive properties of the
rocks, the source material of glacial sediment (as we did for the grain size
dataset) and drainage of water under the ice into the bedrock aquifer. For
the latter case, the transition from Precambrian rock and sedimentary rock
has been used to explain the relative absence of eskers south of the Canadian
Shield by accommodating the basal meltwater . Modelling
of the effect of bedrock on subglacial water routing has been done by
.
Example of usage of datasets in an ice sheet model
To show the utility of the dataset, we incorporate the information for use
with the ice sheet model PISM 1.0 , with
the addition of an index forcing scheme described in . In
the standard version of PISM, the model for basal sliding has an assumption
that there is a continuous layer of sediment underlying the ice sheet.
Obviously, in areas where sediment coverage is discontinuous, this is not a
valid model. Therefore, the purpose of the following simulations are simply to
demonstrate that, if there is a contrast in the basal conditions based on the
underlying geological parameters, there will be an impact on the resulting
ice sheet simulation. The simulations are not necessarily reflective of the
actual basal conditions of the ice sheet.
In PISM, the basal sediments influence ice sheet dynamics by assuming they
deform as a plastic Mohr–Coulomb material . The
relationship that governs the relationship between the material and the yield
stress, τc, is as follows:
τc=co+Ntan(ϕ).
The sediment parameters include the apparent cohesion, co, and the shear
friction angle, ϕ. The cohesion is generally regarded as insignificant
and set to zero in most ice sheet simulations
. The shear friction angle is the angle that a
material will fracture by given a normal stress above its yield strength. This
is the primary factor used to tune the basal sediment strength in PISM. In
situ and laboratory experimental values of ϕ for glacial sediments have
a large range, between 18 and 40∘. The
parameter N is the difference between the normal stress from the load of
the ice sheet and the water pressure in the sediments. In PISM, this factor
is generally high enough that the sediments will not deform unless they are
saturated. In our simulations, N=0.01 when saturated. For the tests of
these datasets, we only adjust ϕ.
The results shown below are for an ice sheet model that is run for the
whole of the last glacial cycle, the past 122 000 years. A time slice at 21 000 yr BP
is chosen to display the effect of changing the sediment friction angle, as
this was when the North American ice sheets were near their maximum extent
. provide a full description of the
parameters related to other boundary conditions. The shear friction angle
used in their study was a constant 30∘, so to show the effects of
changes in basal geological parameters, this value is lowered. The results
given below are just to show the effects of changing the basal properties. We
make no recommendation of what the values should be. Ultimately, the model
used in PISM is dependent on producing enough water to saturate the
sediment layer . If the water production is too low
(i.e. the basal temperature of the ice is below pressure melting point),
changing the shear friction angle will have no effect on the simulation.
Therefore, in the cases shown in this section, the largest changes occur in
places where there is enough significant ice flow to encourage frictional heating
or that are connected to ocean basins (Fig. ). Efforts to
combine the effects of these datasets with ice sheet hydrology and ice
dynamics are ongoing, and show that this model substantially underestimates
that amount of water that should be available at the base
.
Areas in the default simulation (shown in red) where basal
frictional heating exceeds 0.01 W m-2. The grey region is where there
is grounded ice.
The basal condition model in PISM is based on the assumption that the entire
base of the ice sheet is covered in potentially deformable sediments, the
strength of which is controlled by the sediment shear friction angle. A lower
angle will weaken the ice–bed interface and therefore encourage sliding. The
philosophy of the choice of shear friction angle in these examples is as
follows. Areas with continuous sediment cover should be weak, since sediment
deformation will be the dominant factor in sliding. The angle in
sediment-covered areas are lowered from the reference value to accommodate
this. For the grain size data, finer-grained sediments will be weaker than
coarse-grained sediments, so the angle in areas with finer sediments are
lowered from the reference value. For the geology dataset, we expect that
areas underlain with sedimentary and mafic volcanic rock will be more prone
to erosional effects, therefore are more likely to produce unconsolidated
sediments and should therefore be weaker. The angle in these areas are
reduced from the reference to simulate this effect.
Impact of sediment distribution
The basal boundary condition in PISM has an assumption that continuous
sediment cover is over the entire domain . In order to
simulate the differences in sediment distribution, the shear friction angle
is changed depending on the coverage. For continuous areas, it is set to
ϕ=10∘ (weak, deformable bed), for discontinuous areas it is set
to ϕ=20∘, and for rock-dominant areas it is set to
ϕ=30∘ (strong, undeformable bed). Using these values, most of
the Canadian Shield has a shear friction angle of 20∘, while areas
underlain by Phanerozoic sedimentary rock have values of 10∘. The
impact of this is that there are reductions of ice along the east coast of
Canada, the Cordillera, the Great Lakes region, western Arctic Archipelago
and Greenland by up to 40 % (Fig. ). There
is also an increase in ice thickness in the area east of the Cordillera
(5 %–10 % greater), south of the Great Lakes and in Hudson Strait.
The lower resistance to flow likely leads the ice sheet to flow further south
of the Great Lakes relative to the default simulation and is notably thicker
(by several hundred metres). The lack of change in the Canadian Shield,
despite decreasing the shear friction angle, is most likely due to the lack
of meltwater production causing a reduction in basal strength.
Impact of the distribution of sediments on the simulation of North
American ice sheets. (a) Thickness of the ice sheets at
21 000 yr BP (after about 101 000 years of simulation) with the default
shear friction angle, ϕ=30∘. (b) Shear friction angle
adjusted downwards for sediment cover. (c) Ice thickness at
21 000 yr BP using the shear friction angle shown in (b).
(d) Difference in ice thickness between (a) and
(c). The numbers in (d) represent areas mentioned in the
text: (1) eastern Canada, (2) Great Lakes, (3) Cordillera, (4) Hudson Strait,
(5) Arctic Archipelago and (6) Greenland. The green outline shows the exposed
limit of the Canadian Shield.
Impact of sediment grain size
To test the effects of sediment grain size type, the input map from
Fig. was converted to a shear friction angle input by
setting clay to ϕ=10∘, silt to ϕ=20∘ and sand to
ϕ=30∘. This simulates the fact that clay-rich sediments are
mechanically weaker, even though an angle of ϕ=10∘ is below the
low end of measurements of real till . The
difference in ice thickness at 21 000 yr BP is shown in
Fig. . In this case, most of the Canadian Shield,
Greenland and parts of Cordillera have a shear friction angle of
30∘. Some areas south of the Great Lakes are 10∘, while
the rest are 20∘. The end result at 21 000 yr BP is that there is
less change in the simulation compared to the reference. There is a slight
reduction in ice thickness in the Cordillera (10 %–20 %) and east
coast of Canada (5 %–10 %). South of the Great Lakes, where there is
clay-rich till with an angle of 10∘, the ice sheet goes further south
(one grid cell, or 20 km) than the reference simulation.
Impact of the grain size of sediments on the simulation of North
American ice sheets. (a) Thickness of the ice sheets at
21 000 yr BP (after about 101 000 years of simulation) with the default
shear friction angle, ϕ=30∘. (b) Shear friction angle
adjusted downwards for finer-grained sediments. (c) Ice thickness at
21 000 yr BP using the shear friction angle shown in (b).
(d) Difference in ice thickness between (a)
and (c). The numbers in (d) represent areas mentioned in
the text: (1) eastern Canada, (2) Great Lakes, (3) Cordillera, (4) Hudson
Strait, (5) Arctic Archipelago and (6) Greenland. The green outline shows the
exposed limit of the Canadian Shield.
Impact of bedrock geology
The effects of bedrock geology are shown in
Fig. . For this simulation, we adjusted the shear
friction angle downwards for geological types that are more likely erode to
produce deformable sediments. Sedimentary rock is given an angle of
ϕ=10∘ to indicate their relative weakness. Low-grade metamorphic
rock (which include areas where the geology is uncertain) is given an angle
of ϕ=20∘. Volcanic rock is assigned a value of
ϕ=25∘, as it should be more likely to be erodible than plutonic
rock. Plutonic rock and high-grade metamorphic rock retain the default value
of ϕ=30∘. The results show a decrease in ice thickness in the
Cordillera, Canadian Archipelago, eastern Canada and northeastern Greenland
by up to about 30 %. These areas are largely underlain by sedimentary
rock. As with the other simulations south of the Great Lakes region, the ice
sheet goes further south than the reference simulation.
Impact of the geology on the simulation of North American ice
sheets. (a) Thickness of the ice sheets at 21 000 yr BP (after
about 101 000 years of simulation) with the default shear friction angle,
ϕ=30∘. (b) Shear friction angle adjusted downwards
sediments and volcanic rock. (c) Ice thickness at 21 000 yr BP
using the shear friction angle shown in (b). (d) Difference
in ice thickness between (a) and (c). The numbers in
(d) represent areas mentioned in the text: (1) eastern Canada,
(2) Great Lakes, (3) Cordillera, (4) Hudson Strait, (5) Arctic Archipelago
and (6) Greenland. The green outline shows the exposed limit of the Canadian
Shield.
Data availability
Shapefiles and NetCDF files of these datasets are available
on PANGAEA (10.1594/PANGAEA.895889, ).
Conclusions
Our compilation represents the first publicly available
continuous dataset of sediment properties that can be implemented into ice
sheet modelling studies. We have presented three datasets that present
different types of geological data, including sediment distribution, grain
size and bedrock geology for the regions in North America, Greenland and
Iceland that were glaciated during the late Quaternary. The compilation
directly incorporates information from over 50 maps and GIS datasets, plus
additional information from over 40 other sources. These datasets are
intended for use in ice sheet models, where the geological parameters will
have impacts on ice sheet dynamics and hydrology. We demonstrated that
changing the basal conditions in an ice sheet model on the basis of these
datasets does impact the modelled thickness of the ice. In our simple
experiments where we changed the shear friction angle to account for changes
in geological properties based on inferred weakness of the ice–bed
interface, there were changes of ice thickness by up to 40 %. With these
datasets, we hope that improvements can be made to ice sheet models to
incorporate this geological data and create a more realistic representation
of basal conditions. Examples of such application include changing the shear
friction angle in a Mohr–Coulomb plastic basal sliding model, or changing
water routing properties in a basal hydrology model. These properties are key
to explaining observed ice sheet dynamics, notably the rapid advance and
retreat of the Laurentide Ice Sheet, during the last glacial cycle.
Author contributions
EJG compiled the datasets and was the main author of the text.
LN designed the ice sheet model simulation. All authors contributed to the
text and design of the study.
Competing interests
The authors declare that they have no conflict of
interest.
Acknowledgements
This work was funded by the Helmholtz Climate Initiative REKLIM (Regional
Climate Change), a joint research project at the Helmholtz Association of
German research centres (HGF). This study was also supported by the PACES-II
program at the Alfred Wegener Institute and the Bundesministerium für
Bildung und Forschung funded project, PalMod. The development of PISM is
supported by NASA grant NNX17AG65G and NSF grants PLR-1603799 and
PLR-1644277. Figures in this paper were plotted with the aid of Generic
Mapping Tools . We want to thank Jeremy Ely and an
anonymous reviewer for their review, which led to improvements in the dataset
and manuscript. We would like to thank Thompson Davis for notifying us of
several errors in the references.
Edited by: Reinhard Drews
Reviewed by: Jeremy Ely and one anonymous referee
References
Abe-Ouchi, A., Saito, F., Kawamura, K., Raymo, M. E., Okuno, J., Takahashi,
K.,
and Blatter, H.: Insolation-driven 100,000-year glacial cycles and hysteresis
of ice-sheet volume, Nature, 500, 190–193, 2013.Alley, R. B.: In search of ice-stream sticky spots, J. Glaciol., 39,
447–454, 10.3189/S0022143000016336, 1993.Aylsworth, J. M. and Shilts, W. W.: Bedforms of the Keewatin ice sheet,
Canada, Sediment. Geol., 62, 407–428,
10.1016/0037-0738(89)90129-2, 1989.Batchelor, C. L., Dowdeswell, J. A., and Pietras, J. T.: Seismic
stratigraphy,
sedimentary architecture and palaeo-glaciology of the Mackenzie Trough:
evidence for two Quaternary ice advances and limited fan development on the
western Canadian Beaufort Sea margin, Quaternary Sci. Rev., 65,
73–87, 10.1016/j.quascirev.2013.01.021, 2013.Booth, D. B.: Glaciofluvial infilling and scour of the Puget Lowland,
Washington, during ice-sheet glaciation, Geology, 22, 695–698,
10.1130/0091-7613(1994)022<0695:GIASOT>2.3.CO;2, 1994.Borns Jr., N. R., Gadd, P. L., Martineau, G., Chauvin, L., Fullerton, D. S.,
Fulton, R. J., Chapman, W. F., Wagner, W. P., and Grant, D. R.: Quaternary
geologic map of the Quebec 4∘×6∘ quadrangle, United
States and Canada, Miscellaneous Investigations Series MAP I-1420 (NL-19),
edited by: Richmond, G. M. and Fullerton, D. S., U.S. Geological Survey,
scale 1:1,000,000, 1987.Bouchard, M. A.: Subglacial landforms and deposits in central and northern
Quebec, Canada, with emphasis on Rogen moraines, Sediment. Geol., 62,
293–308, 10.1016/0037-0738(89)90120-6, 1989.Boulton, G. S., Dobbie, K. E., and Zatsepin, S.: Sediment deformation beneath
glaciers and its coupling to the subglacial hydraulic system, Quaternary
Int., 86, 3–28, 10.1016/S1040-6182(01)00048-9, 2001.Bueler, E. and Brown, J.: Shallow shelf approximation as a “sliding law” in
a thermodynamically-coupled ice sheet model, J. Geophys. Res., 114, F03008,
10.1029/2008JF001179, 2009.Calov, R., Ganopolski, A., Petoukhov, V., Claussen, M., and Greve, R.:
Large-scale instabilities of the Laurentide ice sheet simulated in a fully
coupled climate-system model, Geophys. Res. Lett., 29, 69-1–69-4,
10.1029/2002GL016078, 2002.Carlson, A. E., Jenson, J. W., and Clark, P. U.: Modeling the subglacial
hydrology of the James Lobe of the Laurentide Ice Sheet, Quaternary Sci.
Rev., 26, 1384–1397, 10.1016/j.quascirev.2007.02.002, 2007.Christoffersen, P., Tulaczyk, S., Wattrus, N. J., Peterson, J.,
Quintana-Krupinski, N., Clark, C. D., and Sjunneskog, C.: Large subglacial
lake beneath the Laurentide Ice Sheet inferred from sedimentary sequences,
Geology, 36, 563–566, 10.1130/G24628A.1, 2008.
Clague, J. J.: Quaternary geology of the Canadian Cordillera, in:
Quaternary
Geology of Canada and Greenland, in: Geology of
Canada, edited by: Fulton, R. J., chap. 1, 17–96, Geological Survey of Canada, 1989.Clague, J. J., Fulton, R. J., and Ryder, J. M.: Surficial geology, Vancouver
Island and adjacent mainland, British Columbia, map, Open File 837,
Geological Survey of Canada, Ottawa, Canada, scale 1:1,000,000,
10.4095/129736, 1982.
Clark, P. U. and Pollard, D.: Origin of the middle Pleistocene transition by
ice sheet erosion of regolith, Paleoceanography, 13, 1–9, 1998.Clark, P. U. and Walder, J. S.: Subglacial drainage, eskers, and deforming
beds
beneath the Laurentide and Eurasian ice sheets, Geol. Soc.
Am. Bull., 106, 304–314,
10.1130/0016-7606(1994)106<0304:SDEADB>2.3.CO;2, 1994.
Cofaigh, C. Ó., Stokes, C. R., Lian, O. B., Clark, C. D., and Tulacyzk,
S.:
Formation of mega-scale glacial lineations on the Dubawnt Lake Ice Stream
bed: 2. Sedimentology and stratigraphy, Quaternary Sci. Rev., 77,
210–227, 2013.Corbett, L. B., Bierman, P. R., Lasher, G. E., and Rood, D. H.: Landscape
chronology and glacial history in Thule, northwest Greenland, Quaternary
Sci. Rev., 109, 57–67, 10.1016/j.quascirev.2014.11.019, 2015.Corbett, L. B., Bierman, P. R., and Davis, P. T.: Glacial history and
landscape evolution of southern Cumberland Peninsula, Baffin Island, Canada,
constrained by cosmogenic 10Be and 26Al, Bulletin, 128,
1173–1192, 10.1130/B31402.1, 2016.
Cuffey, K. M. and Paterson, W. S. B.: The physics of glaciers, Elsevier,
Burlington, MA, USA, 2010.
Dawes, P. R.: The bedrock geology under the Inland Ice: the next major
challenge for Greenland mapping, Geol. Surv. Den. Greenl., 17, 57–60, 2009.Denne, J. E., Luza, K. V., Richmond, G. M., Jensen, K. M., Fishman, W. D.,
and Wermund Jr., E. G.: Quaternary Geologic Map of the Wichita
4∘× 6∘ Quadrangle, United States, Miscellaneous
Investigations Series Map I-1420 (NJ-14), edited by: Richmond, G. M. and
Christiansen, A. C., U.S. Geological Survey, scale 1:1000000, 1993.Dowdeswell, J. A., Evans, J., and Cofaigh, C. Ó.: Submarine landforms
and
shallow acoustic stratigraphy of a 400 km-long fjord-shelf-slope transect,
Kangerlussuaq margin, East Greenland, Quaternary Sci. Rev., 29,
3359–3369, 10.1016/j.quascirev.2010.06.006, 2010.
Dreimanis, A. and Vagners, U. J.: Bimodal distribution of rock and mineral
fragments in basal tills, in: Till, a symposium, edited by: Goldthwait, R. P.,
237–250, Ohio State University Press, Columbus, Ohio, 1971.Duchesne, M. J., Pinet, N., Bédard, K., St-Onge, G., Lajeunesse, P.,
Campbell, D. C., and Bolduc, A.: Role of the bedrock topography in the
Quaternary filling of a giant estuarine basin: the Lower St. Lawrence
Estuary, Eastern Canada, Basin Res., 22, 933–951,
10.1111/j.1365-2117.2009.00457.x, 2010.
Duk-Rodkin, A. and Hughes, O. L.: Surficial Geology, Upper Ramparts River,
District of Mackenzie, Northwest Territories, Map 1783A, scale 1 : 250 000, Geological Survey
of Canada, 1993.Dyke, A. S.: An outline of North American deglaciation with emphasis on
central and northern Canada, in: Quaternary Glaciations–Extent and
Chronology – Part II: North America, edited by: Ehlers, J., Gibbard, P. L.,
and Hughes, P. D., Developments in Quaternary Science, 373–424,
Elsevier, 10.1016/S1571-0866(04)80209-4, 2004.Dyke, A. S., Andrews, J. T., Clark, P. U., England, J. H., Miller, G. H.,
Shaw,
J., and Villette, J. J.: The Laurentide and Innuitian ice sheets during the
Last Glacial Maximum, Quaternary Sci. Rev., 21, 9–31,
10.1016/S0277-3791(01)00095-6, 2002.Evans, D. J. A., Phillips, E. R., Hiemstra, J. F., and Auton, C. A.:
Subglacial
till: formation, sedimentary characteristics and classification,
Earth-Sci. Rev., 78, 115–176, 10.1016/j.earscirev.2006.04.001,
2006.Eyles, N., Boyce, J. I., and Barendregt, R. W.: Hummocky moraine:
sedimentary
record of stagnant Laurentide Ice Sheet lobes resting on soft beds,
Sediment. Geol., 123, 163–174, 10.1016/S0037-0738(98)00129-8,
1999.Eyles, N., Moreno, L. A., and Sookhan, S.: Ice streams of the Late Wisconsin
Cordilleran Ice Sheet in western North America, Quaternary Sci. Rev.,
179, 87–122, 10.1016/j.quascirev.2017.10.027, 2018.Farrand, W. R., Mickelson, D. M., Cowan, W. R., and Goebel, J. E.: Quaternary
geologic map of the Lake Superior 4∘× 6∘
quadrangle, United States and Canada, Miscellaneous Investigations Series Map
I-1420 (NL-16), edited by: Richmond, G. M. and Fullerton, D. S., U.S.
Geological Survey, scale 1:1000000, 1984.
Fisher, D., Reeh, N., and Langley, K.: Objective reconstructions of the Late
Wisconsinan Laurentide Ice Sheet and the significance of deformable beds,
Geogr. Phys. Quatern., 39, 229–238, 1985.Freire, F., Gyllencreutz, R., Greenwood, S. L., Mayer, L., Egilsson, A.,
Thorsteinsson, T., and Jakobsson, M.: High resolution mapping of offshore
and onshore glaciogenic features in metamorphic bedrock terrain, Melville
Bay, northwestern Greenland, Geomorphology, 250, 29–40,
10.1016/j.geomorph.2015.08.011, 2015.Fullerton, D. S., Cowan, W. R., Sevon, W. D., Goldthwait, R. P., Farrand, W.
R., Muller, E. H., Behling, R. E., and Stravers, J. A.: Quaternary geologic
map of the Lake Erie 4∘× 6∘ quadrangle, United
States and Canada, Miscellaneous Investigations Series Map I-1420 (NK-17),
edited by: Fullerton, D. S. and Richmond, G. M., U.S. Geological Survey,
scale 1:1,000,000, 1991.Fullerton, D. S., Sevon, W. D., Muller, E. H., Judson, S., Black, R. F.,
Wagner, P. W., Hartshorn, J. H., Chapman, W. F., and Cowan, W. D.: Quaternary
geologic map of the Hudson River 4∘× 6∘ quadrangle,
United States and Canada, Miscellaneous Investigations Series Map I-1420
(NK-18), edited by: Fullerton, D.S., U.S. Geological Survey, scale
1:1,000,000, 1992.Fullerton, D. S., Bluemle, J. P., Clayton, L., Steece, F. V., Tipton, M. J.,
Bretz, R., and Goebel, J. E.: Quaternary geologic map of the Dakotas
4∘× 6∘ quadrangle, United States, Miscellaneous
Investigations Series Map I-1420 (NL-14), edited by: Fullerton, D. S., U.S.
Geological Survey, scale 1:1,000,000, 1995.Fullerton, D. S., Ringrose, S. M., Clayton, L., Schreiner, B. T., and Goebel,
J. E.: Quaternary geologic map of the Winnipeg
4∘× 6∘ quadrangle, United States and Canada,
Miscellaneous Investigations Series Map I-1420 (NM-14), edited by: Fullerton,
D. S., U.S. Geological Survey, scale 1:1,000,000, 2000.
Fullerton, D. S., Colton, R. B., Bush, C. A., and Straub, A. W.: Map showing
spatial and temporal relations of mountain and continental glaciations on the
northern plains, primarily in northern Montana and northwestern North
Dakota, Scientific Investigations Map 2843, United States Geological Survey,
2004.Fullerton, D. S., Christiansen, E. A., Schreiner, B. T., Colton, R. B., and
Clayton, L.: Quaternary Geologic Map of the Regina
4∘× 6∘ quadrangle, United States and Canada,
Miscellaneous Investigations Series Map I-1420 (NM-13), edited by: Fullerton,
D. S. and Bush, C. A., U.S. Geological Survey, scale 1:1,000,000, 2007.Fullerton, D. S., Colton, R. B., and Bush, C. A.: Quaternary geologic map of
the Glasgow 1∘× 2∘ quadrangle, Montana, Open-File Report
2012-1217, scale 1 : 250 000, U.S. Geological Survey, 2012.Fullerton, D. S., Colton, R. B., and Bush, C. A.: Quaternary geologic map of
the Shelby 1∘× 2∘ quadrangle, Montana, Open-File Report
2012-1170, scale 1 : 250 000, U.S. Geological Survey, 2013.Fullerton, D. S., Colton, R. B., and Bush, C. A.: Quaternary geologic map of
the Wolf Point 1∘× 2∘ quadrangle, Montana and North
Dakota, Open-File Report 2016-1142, scale 1 : 250 000, U.S. Geological Survey,
10.3133/ofr20161142, 2016.Fulton, R. J.: Quaternary Geology of Canada and Greenland, Vol. 1 of Geology
of Canada, Geological Survey of Canada, Ottawa, Canada, 5 pp.,
10.4095/127905, 1989.Fulton, R. J.: Surficial materials of Canada, Map 1880A, scale
1 : 5 000 000, Geological Survey of
Canada, 10.4095/205040, 1995.
Funder, S.: Quaternary Geology of the Ice-Free areas and Adjacent Shelves of
Greenland, in: Quaternary Geology of Canada and Greenland, edited by: Fulton,
R. J., Geological Survey of Canada, Geology of Canada, no. 1 in chap. 13,
743–792, 1989.Funder, S. and Klüver, B. G.: Quaternary Map of Greenland Scoresby
Sund, Map Sheet 12, scale 1:500,000, The Geological Survey of
Greenland, 1988.Gadd, N. R., Veillette, J. J., Fullerton, D. S. (Ed.), Wagner, P. W., and
Chapman, W. F.: Quaternary geologic map of the Ottawa 4∘×6∘ quadrangle, United States and Canada, Miscellaneous
Investigations Series Map I-1420 (NL-18), scale 1:1,000,000, U.S.
Geological Survey, 1993.Garrity, C. P. and Soller, D. R.: Database of the Geologic Map of North
America, adapted from the map by J. C. Reed, Jr. and others (2005), U.S.
Geological Survey Data Series 424, U.S. Geological Survey,
available at: https://pubs.usgs.gov/ds/424/ (last access: 17 August
2017), 2009.Geological Survey of Canada: Surficial geology of Canada, Map Canadian
Geoscience Map 195 (preliminary, surficial data model v. 2.0 conversion of
Map 1880A), scale
1:5000000, Geological Survey of Canada, 10.4095/295462, 2014.Goebel, J. E., Mickelson, D. M., Farrand, W. R., Clayton, L., Knox, J. C.,
Cahow, A. C., Hobbs, H., and Walton Jr., M. S.: Quaternary geologic map of
the Minneapolis 4∘×6∘ quadrangle, United States,
Miscellaneous Investigations Series Map I-1420 (NL-15), edited by: Richmond,
G. M. and Fullerton, D. S., U.S. Geological Survey, scale 1:1,000,000,
1983.
Government of Newfoundland and Labrador: Geoscience atlas, Tech. rep.,
Geological Survey Division of the Department of Natural Resources, St.
John's, NL, Canada, version: 3, Build: 1, Build Date: 22 October 2013.
Gowan, E., Niu, L., Knorr, G., Lohmann, G., and Hinck, S.: Investigating the
role of subglacial geology on ice sheet dynamics, Geophys. Res. Abstr.,
EGU2018-721, EGU General Assembly 2018, Vienna, Austria, 2018a.Gowan, E. J., Niu, L., Knorr, G., and Lohmann, G.: Geology datasets in North
America, Greenland and surrounding areas for use with ice sheet models,
PANGAEA, 10.1594/PANGAEA.895889, 2018b.Gowan, E. J., Tregoning, P., Purcell, A., Montillet, J.-P., and McClusky, S.:
A model of the western Laurentide Ice Sheet, using observations of glacial
isostatic adjustment, Quaternary Sci. Rev., 139, 1–16,
10.1016/j.quascirev.2016.03.003, 2016.Grasby, S. E. and Chen, Z.: Subglacial recharge into the Western Canada
Sedimentary Basin – Impact of Pleistocene glaciation on basin
hydrodynamics, Geol. Soc. Am. Bull., 117, 500–514,
10.1130/B25571.1, 2005.Gray, H. H., Bleuer, N. K., Lineback, J. A., Swadley, W. C., Richmond, G. M.,
Miller, R. A., Goldthwait, R. P., and Ward, R. A.: Quaternary geologic map of
the Louisville 4∘×6∘ quadrangle, United States,
Miscellaneous Investigations Series MAP I-1420 (NJ-16), edited by: Richmond,
G. M. and Fullerton, D. S., U.S. Geological Survey, scale 1:1000000,
1991.Gray, J. T. and Lauriol, B.: Dynamics of the late Wisconsin ice sheet in the
Ungava Peninsula interpreted from geomorphological evidence, Arctic
Alpine Res., 17, 289–310, 10.2307/1551019, 1985.Gregoire, L. J., Payne, A. J., and Valdes, P. J.: Deglacial rapid sea level
rises caused by ice-sheet saddle collapses, Nature, 487, 219–222,
10.1038/nature11257, 2012.
Gustafson, D. J.: A Geophysical Investigation of Dewatering Structures in
Western Lake Superior, Master's thesis, University of Minnesota, 2012.Håkansson, L., Alexanderson, H., Hjort, C., Möller, P., Briner,
J. P.,
Aldahan, A., and Possnert, G.: Late Pleistocene glacial history of Jameson
Land, central East Greenland, derived from cosmogenic 10Be and 26Al exposure
dating, Boreas, 38, 244–260, 2009.Hallberg, G. R., Lineback, J. A., Mickelson, D. M., Knox, J. C., Goebel, J.
E., Hobbs, H. C., Whitfield, J. W., Ward, R. A., Boellstorf, J. D.,
Swinehart, J. B., and Dreeszen, V. H.: Quaternary Geologic Map of the Des
Moines 4∘×6∘ Quadrangle, United States, Miscellaneous
Investigations Series Map I-1420 (NK-15), edited by: Richmond, G. M.,
Fullerton, D. S., and Christiansen, A. C., U.S. Geological Survey, scale
1:1,000,000, 1994.Harrison, J. C., St-Onge, M. R., Petrov, O. V., Strelnikov, S. I., Lopatin,
B. G., Wilson, F. H., Tella, S., Paul, D., Lynds, T., Shokalsky, S. P.,
Hults, C. K., Bergman, S., Jepsen, H. F., and Solli, A.: Geological map of
the Arctic, Map 2159A, Geological Survey of Canada, Ottawa, Canada, scale
1:5,000,000, 2011.Hartshorn, W. B., Thompson, W. F., Chapman, R. F., Black, R. F., Richmond, G.
M., Grant, D. R., and Fullerton, D. S.: Quaternary geologic map of the Boston
4∘×6∘ quadrangle, United States and Canada,
Miscellaneous Investigations Series Map I-1420 (NK-19), edited by: Richmond,
G. M. and Fullerton, D. S., U.S. Geological Survey, scale 1:1,000,000,
1991.
Henriksen, N., Higgins, A. K., Kalsbeek, F., and Pulvertaft, T. C. R.:
Greenland from Archaean to Quaternary, Geol. Surv. Den. Greenl., 18, 1–126,
2009.Hildes, D. H., Clarke, G. K., Flowers, G. E., and Marshall, S. J.: Subglacial
erosion and englacial sediment transport modelled for North American ice
sheets, Quaternary Sci. Rev., 23, 409–430,
10.1016/j.quascirev.2003.06.005, 2004.
Hjort, C., Ingólfsson, Ó., and Norðdahl, H.: Late Quaternary
geology and glacial history of Hornstrandir, northwest Iceland: a
reconnaissance study, Jökull, 35, 9–29, 1985.Howard, A. D., Behling, R. E., Wheeler, W. H., Daniels, R. B., Swadley, W.
C., Richmond, G. M., Goldthwait, R. P., Fullerton, D. S., Sevon, W. D., and
Miller, R. A.: Quaternary geologic map of the Blue Ridge 4∘×6∘ quadrangle, United States, Miscellaneous Investigations Series
Map I-1420 (NJ-17), edited by: Richmond, G. M., Fullerton, D. S., and
Christiansen, A. C., U.S. Geological Survey, scale 1:1,000,000, 1991.
Hutchinson, D. R., Lewis, C. F., and Hund, G. E.: Regional stratigraphic
framework of surficial sediments and bedrock beneath Lake Ontario,
Geogr. Phys. Quatern., 47, 337–352, 1993.
Ingólfsson, Ó.: Late Weichselian glacial geology of the lower
Borgarfjördur region, western Iceland: a preliminary report, Arctic, 38,
210–213, 1985.Iverson, N. R. and Zoet, L. K.: Experiments on the dynamics and sedimentary
products of glacier slip, Geomorphology, 244, 121–134,
10.1016/j.geomorph.2015.03.027, 2015.Jackson, G. D.: Geology, Belcher Islands, Nunavut, Open File 4923, scale
1 : 125 000, Geological
Survey of Canada, 10.4095/292434, 2012.Josenhans, H. and Lehman, S.: Late glacial stratigraphy and history of the
Gulf of St. Lawrence, Canada, Can. J. Earth Sci., 36,
1327–1345, 10.1139/e99-030, 1999.Josenhans, H. W. and Zevenhuizen, J.: Dynamics of the Laurentide ice sheet
in
Hudson Bay, Canada, Mar. Geol., 92, 1–26,
10.1016/0025-3227(90)90024-E, 1990.
Karlstrom, T. N. V.: Surficial geology of Alaska, USGS Numbered Series IMAP
357, scale 1 : 584 000, U.S. Geological Survey, 1964.
Karrow, P. F.: Quaternary Geology of the Great Lakes Subregion, in:
Quaternary Geology of Canada and Greenland, edited by: Fulton, R. J., Vol. 1,
chap. 4, 326–350, Geological Survey of Canada, 1989.King, E. L.: Quaternary unconsolidated sediment thickness on the Grand Banks
of Newfoundland and northeast Newfoundland Shelf; a GIS database, Open File
7513, scale 1 : 500 000, Geological Survey of Canada, 10.4095/295113,
2014.Kjær, K. H., Larsen, E., van der Meer, J., Ingólfsson, Ó.,
Krüger, J., Benediktsson, Í. Ö., Knudsen, C. G., and Schomacker,
A.: Subglacial decoupling at the sediment/bedrock interface: a new mechanism
for rapid flowing ice, Quaternary Sci. Rev., 25, 2704–2712,
10.1016/j.quascirev.2006.06.010, 2006.
Klassen, R.: Quaternary geology of the Southern Canadian Interior Plains,
chap. 2, 138–166, Geological Survey of Canada, 1989.Kovanen, D. J. and Slaymaker, O.: Glacial imprints of the Okanogan Lobe,
southern margin of the Cordilleran Ice Sheet, J. Quaternary Sci.,
19, 547–565, 10.1002/jqs.855, 2004.Kulessa, B., Hubbard, A. L., Booth, A. D., Bougamont, M., Dow, C. F., Doyle,
S. H., Christoffersen, P., Lindbäck, K., Pettersson, R., Fitzpatrick, A.
A. W., and Jones, G. A.: Seismic evidence for complex sedimentary control of
Greenland Ice Sheet flow, Science Advances, 3, e1603071,
10.1126/sciadv.1603071, 2017.
Larsen, N. K., Kjær, K. H., Funder, S., Möller, P., van der Meer,
J. J., Schomacker, A., Linge, H., and Darby, D. A.: Late Quaternary
glaciation history of northernmost Greenland–Evidence of shelf-based ice,
Quaternary Sci. Rev., 29, 3399–3414, 2010.
Laske, G. and Masters, G.: A Global Digital Map of Sediment Thickness, EOS T.
Am. Geophys. Un., 78, F483, 1997.
Lewis, C. F. M., Cameron, G. D. M., King, E. L., Todd, B. J., and Blasco, S.
M.: Structural contour, isopach and feature maps of Quaternary sediments in
western Lake Ontario, Report INFO-0555, Atomic Energy Control Board, Ottawa,
Canada, 1995.Licciardi, J., Clark, P., Jenson, J., and Macayeal, D.: Deglaciation of a
soft-bedded Laurentide Ice Sheet, Quaternary Sci. Rev., 17, 427–448,
10.1016/S0277-3791(97)00044-9, 1998.Lineback, J. A., Dell, C. I., and Gross, D. L.: Glacial and postglacial
sediments in Lakes Superior and Michigan, Geol. Soc. Am.
Bull., 90, 781–791, 10.1130/0016-7606(1979)90<781:GAPSIL>2.0.CO;2,
1979.Lineback, J. A., Bleuer, N. K., Mickelson, D. M., Farrand, W. R., and
Goldthwait, R. P.: Quaternary geologic map of the Chicago 4∘×6∘ quadrangle, United States, Miscellaneous Investigations Series
Map I-1420 (NK-16), edited by: Richmond, G. M. and Fullerton, D. S., U.S.
Geological Survey, scale 1:1000000, 1983.
Lipovsky, P. S. and Bond, J. D.: Yukon digital surficial geology compilation,
digital release 1, Yukon Geological Survey, release date: 8 April 2014.
Loring, D. H. and Nota, D. J. G.: Morphology and sediments of the Gulf of St.
Lawrence, Bulletin of the Fisheries Research Board of Canada 182, Fisheries
Research Board of Canada, 147 pp., 1973.MacLean, B.: Marine geology of Hudson Strait and Ungava Bay, Eastern Arctic
Canada: Late Quaternary sediments, depositional environments, and late
glacial-deglacial history derived from marine and terrestrial studies,
Geological Survey of Canada Bulletin, 566, 200 pp., 10.4095/212180,
2001.MacLean, B., Blasco, S., Bennett, R., England, J., Rainey, W., Hughes-Clarke,
J., and Beaudoin, J.: Ice keel seabed features in marine channels of the
central Canadian Arctic Archipelago: evidence for former ice streams and
iceberg scouring, Quaternary Sci. Rev., 29, 2280–2301,
10.1016/j.quascirev.2010.05.032, 2010.MacLean, B., Blasco, S., Bennett, R., Lakeman, T., Hughes-Clarke, J., Kuus,
P.,
and Patton, E.: New marine evidence for a Late Wisconsinan ice stream in
Amundsen Gulf, Arctic Canada, Quaternary Sci. Rev., 114, 149–166,
10.1016/j.quascirev.2015.02.003, 2015.
Margold, M., Stokes, C. R., and Clark, C. D.: Ice streams in the Laurentide
Ice Sheet: Identification, characteristics and comparison to modern ice
sheets, Earth-Sci. Rev., 143, 117–146, 2015.Massey, N. W. D., MacIntyre, D. G., Desjardins, P. J., and Cooney, R. T.:
Digital map of British Columbia: whole province, GeoFile 2005-1, B.C.
Ministry of Energy and Mines, Victoria, BC, Canada, scale 1:1,000,000,
2005.Matile, G. L. D. and Keller, G. R.: Surficial Geology Compilation Map Series,
Tech. rep., Manitoba Science, Technology, Energy and Mines, Manitoba
Geological Survey, scale 1:1,000,000, available at:
https://www.manitoba.ca/iem/geo/gis/geoscience.html (last access:
13 October 2017), 2006.
McMartin, I., Dredge, L. A., Ford, K. L., and Kjarsgaard, I. M.: Till
composition, provenance and stratigraphy beneath the Keewatin Ice Divide,
Schultz Lake area (NTS 66A), mainland Nunavut, Open File 5312, Geological
Survey of Canada, 2006.Melanson, A., Bell, T., and Tarasov, L.: Numerical modelling of subglacial
erosion and sediment transport and its application to the North American ice
sheets over the Last Glacial cycle, Quaternary Sci. Rev., 68, 154–174,
10.1016/j.quascirev.2013.02.017, 2013.Morlighem, M., Williams, C. N., Rignot, E., An, L., Arndt, J. E., Bamber, J.
L., Catania, G., Chauché, N., Dowdeswell, J. A., Dorschel, B., Fenty, I.,
Hogan, K., Howat, I., Hubbard, A., Jakobsson, M., Jordan, T. M., Kjeldsen, K.
K., Millan, R., Mayer, L., Mouginot, J., Noël, B. P. Y., O'Cofaigh, C.,
Palmer, S., Rysgaard, S., Seroussi, H., Siegert, M. J., Slabon, P., Straneo,
F., van den Broeke, M. R., Weinrebe, W., Wood, M., and Zinglersen, K. B.:
BedMachine v3: Complete bed topography and ocean bathymetry mapping of
Greenland from multibeam echo sounding combined with mass conservation,
Geophys. Res. Lett., 44, 11051–11061, 10.1002/2017GL074954, 2017.
Niessen, F., Matthiessen, J., and Stein, R.: Sedimentary environment and
glacial history of the Northwest Passage (Canadian Arctic Archipelago)
reconstructed from high-resolution acoustic data, Polarforschung, 79,
65–80, 2010.Niu, L., Lohmann, G., Hinck, S., and Gowan, E. J.: Sensitivity of atmospheric
forcing on Northern Hemisphere ice sheets during the last
glacial-interglacial cycle using output from PMIP3, Clim. Past Discuss.,
10.5194/cp-2017-105, 2017.
Ontario Geological Survey: Quaternary Geology of Ontario, Tech. Rep.
Dataset 14, scale
1 : 1 000 000, digital map, 1997.
Ontario Geological Survey: Surficial geology of southern Ontario,
Miscellaneous Release Data 128, revised 2010, 2003.Piotrowski, J. A., Mickelson, D. M., Tulaczyk, S., Krzyszkowski, D., and
Junge,
F. W.: Were deforming subglacial beds beneath past ice sheets really
widespread?, Quaternary Int., 86, 139–150,
10.1016/S1040-6182(01)00056-8, 2001.Piotrowski, J. A., Larsen, N. K., and Junge, F. W.: Reflections on soft
subglacial beds as a mosaic of deforming and stable spots, Quaternary Sci.
Rev., 23, 993–1000, 10.1016/j.quascirev.2004.01.006, 2004.
Piper, D. J. W., Mudie, P. J., Fader, G. B., Josenhans, H. W., MacLean, B.,
and
Vilks, G.: Quaternary geology of the southwestern Canadian Shield, in:
Geology of the Continental Margin of Eastern Canada, edited by: Keen, M. J.
and Williams, G. L., Geology of Canada Series 2, chap. 10, 475–607,
Geological Survey of Canada, 1990.PISM authors: PISM, a Parallel Ice Sheet Model, available at:
http://www.pism-docs.org, last access: 19 October 2017.Plouffe, A.: Quaternary geology of the Fort Fraser and Manson River map
areas, central British Columbia, Bulletin 554, scale 1 : 250 000,
Geological Survey of Canada, 10.4095/211641, 2000.Prest, V. K.: Surficial Deposits of Prince Edward Island, Map 1366A, scale
1 : 126 720,
Geological Survey of Canada, 10.4095/108971, 1973.Principato, S. M., Jennings, A. E., Kristjánsdóttir, G. B., and
Andrews, J. T.: Glacial-marine or subglacial origin of diamicton units from
the southwest and north Iceland shelf: implications for the glacial history
of Iceland, J. Sediment. Res., 75, 968–983,
10.2110/jsr.2005.073, 2005.
Rampton, V. N.: Quaternary geology of the Tuktoyaktuk coastlands,
Northwest
Territories, Memoir 423, Energy, Mines and Resources Canada, 1988.
Reed, J. C., Wheeler, J. O., and Tucholke, B. E.: Geologic Map of North
America: Decade of North American Geology, Map 001, scale 1 : 500 000,
Geological Society of America, 2004.Sado, E. V., Fullerton, D. S., Baker, C. L., and Farrand, W. R.: Quaternary
Geologic Map of the Sudbury 4∘×6∘ quadrangle, United
States and Canada, Miscellaneous Investigations Series Map I-1420 (NL-17),
edited by: Fullerton, D. S., U.S. Geological Survey, scale 1:1 000 000, 1993.Sado, E. V., Fullerton, D. S., and Farrand, W. R.: Quaternary Geologic Map of
the Lake Nipigon 4∘×6∘ quadrangle, United States and
Canada, Miscellaneous Investigations Series Map I-1420 (NM-16), edited by:
Fullerton, D. S., U.S. Geological Survey, scale 1:1000000, 1994.Sado, E. V., Fullerton, D. S., Goebel, J. E., and Ringrose, S. M.: Quaternary
Geologic Map of the Lake of the Woods 4∘×6∘
quadrangle, United States and Canada, Miscellaneous Investigations Series Map
I-1420 (NM-15), edited by: Fullerton, D. S., U.S. Geological Survey, scale
1:1000000, 1995.
Scholz, C. A.: Late and Post-glacial Lacustrine Sediment Distribution in
western Lake Superior From Seismic Reflection Profiles, in: Thirtieth Annual
Institute On Lake Superior Geology, Wausau, Wisconsin, United States, 61–62,
1984.Schreiner, B. T.: Quaternary geology of the Precambrian Shield,
Saskatchewan, Report 221, scale: 1:1000000, Saskatchewan Energy
and Mines, Saskatchewan Geological Survey, 1984.
Simpson, M. A.: Surficial Geology Map of Saskatchewan, Map, scale
1 : 1 000 000, Environment Branch, Saskatchewan Research Council, from
surficial geology maps at 1 : 250 000 scale by Campbell, J. E. and
Simpson, M. A., and 1 : 1 000 000 scale by Schreiner, B. T., 1997.Soller, D. R. and Garrity, C. P.: Quaternary sediment thickness and bedrock
topography of the glaciated United States east of the Rocky Mountains,
Scientific Investigations Map 3392, scale 1 : 5 000 000, U.S. Geological Survey,
10.3133/sim3392, 2018.Soller, D. R. and Reheis, M. C.: Surficial Materials in the Conterminous
United States, U.S. Geological Survey Open File Report OFR-03-275, U.S.
Geological Survey, scale 1:5,000,000, available at:
https://pubs.er.usgs.gov/publication/ofr2003275 (last access: 5 August
2016), 2004.Soller, D. R., Reheis, M. C., Garrity, C. P., and Van Sistine, D. R.: Map
Database for Surficial Materials in the Conterminous United States, U.S.
Geological Survey Data Series 425, U.S. Geological Survey, available at:
http://pubs.usgs.gov/ds/425, scale 1:5,000,000 (last access: 5 August
2016), 2009.Stea, R. R., Conley, H., and Brown, Y.: Surficial geology of the province of
Nova Scotia, Map 92-3, Nova Scotia Department of Natural Resources, Mines and
Energy Branchs, Halifax, Nova Scotia, Canada, scale 1:500000, 1992.Stokes, C. R., Clark, C. D., Lian, O. B., and Tulaczyk, S.: Ice stream sticky
spots: a review of their identification and influence beneath contemporary
and palaeo-ice streams, Earth-Sci. Rev., 81, 217–249,
10.1016/j.earscirev.2007.01.002, 2007.Stokes, C. R., Tarasov, L., and Dyke, A. S.: Dynamics of the North American
Ice Sheet Complex during its inception and build-up to the Last Glacial
Maximum, Quaternary Sci. Rev., 50, 86–104,
10.1016/j.quascirev.2012.07.009, 2012.St-Onge, M. R., Van Gool, J. A., Garde, A. A., and Scott, D. J.:
Correlation
of Archaean and Palaeoproterozoic units between northeastern Canada and
western Greenland: constraining the pre-collisional upper plate accretionary
history of the Trans-Hudson orogen, Geol. Soc. Spec.
Publ., 318, 193–235, 10.1144/SP318.7, 2009.Storrar, R. D., Stokes, C. R., and Evans, D. J.: Morphometry and pattern of a
large sample (>20 000) of Canadian eskers and implications for subglacial
drainage beneath ice sheets, Quaternary Sci. Rev., 105, 1–25,
10.1016/j.quascirev.2014.09.013, 2014.
Sugden, D.: Landscapes of glacial erosion in Greenland and their relationship
to ice, topographic and bedrock conditions, in: Progress in geomorphology:
Papers in honour of David L. Linton, Institute of British Geographers,
London, UK, Special publication, no. 7, 177–195, 1974.Swinehart, J. B., Dreeszen, V. H., Richmond, G. M., Tipton, M. J., Bretz, R.,
Steece, F. V., Hallberg, G. R., and Goebel, J. E.: Quaternary geologic map of
the Platte River 4∘×6∘ quadrangle, United States,
Miscellaneous Investigations Series Map I-1420 (NK-14), edited by: Richmond,
G. M., U.S. Geological Survey, scale 1:1000000, 1994.Tarasov, L. and Peltier, W.: A geophysically constrained large ensemble
analysis of the deglacial history of the North American ice-sheet complex,
Quaternary Sci. Rev., 23, 359–388,
10.1016/j.quascirev.2003.08.004, 2004.Tarasov, L., Dyke, A. S., Neal, R. M., and Peltier, W.: A data-calibrated
distribution of deglacial chronologies for the North American ice complex
from glaciological modeling, Earth Planetary Sc. Lett., 315–316,
30–40, 10.1016/j.epsl.2011.09.010, 2012.Teller, J. T. and Fenton, M. M.: Late Wisconsinan glacial stratigraphy and
history of southeastern Manitoba, Can. J. Earth Sci., 17,
19–35, 10.1139/e80-002, 1980.
Thériault, R., Beauséjour, S., and Tremblay, A.: Geological map of
Quebec, QERPUB – Publication du M.E.R. DV2012-07, scale 1 : 2 000 000, Ministère des
Resources naturelles, Québec, 2012.Thorleifson, L. H., Wyatt, P. H., Shilts, W., and Nielsen, E.: Hudson Bay
lowland Quaternary stratigraphy: evidence for early Wisconsinan glaciation
centered in Quebec, in: The Last Interglacial–Glacial Transition in North
America, edited by: Clark, P. U. and Lea, P. D., Vol. 270 of Special
Paper, 207–221, Geological Society of America,
10.1130/SPE270-p207, 1992.Todd, B., Lewis, C., Nielsen, E., Thorleifson, L., Bezys, R., and Weber, W.:
Lake Winnipeg: geological setting and sediment seismostratigraphy, J. Paleolimnol., 19, 215–243, 10.1023/A:1007997024412, 1998.Todd, B. J. and Shaw, J.: Laurentide Ice Sheet dynamics in the Bay of Fundy,
Canada, revealed through multibeam sonar mapping of glacial landsystems,
Quaternary Sci. Rev., 58, 83–103,
10.1016/j.quascirev.2012.10.016, 2012.Todd, B. J., Fader, G. B., Courtney, R. C., and Pickrill, R. A.: Quaternary
geology and surficial sediment processes, Browns Bank, Scotian Shelf, based
on multibeam bathymetry, Mar. Geol., 162, 165–214,
10.1016/S0025-3227(99)00092-4, 1999.
Tulaczyk, S., Kamb, W. B., and Engelhardt, H. F.: Basal mechanics of Ice
Stream B, West Antarctica: 2. Undrained plastic bed model, J.
Geophys. Res.-Sol. Ea., 105, 483–494, 10.1029/1999JB900328,
2000.Uchupi, E. and Bolmer, S.: Geologic evolution of the Gulf of Maine region,
Earth-Sci. Rev., 91, 27–76, 10.1016/j.earscirev.2008.09.002,
2008.Voges, A.: International Quaternary Map of Europe, Map IQuaME2500,
Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover, Germany,
scale 1:2,500,000, 1995.Walter, F., Chaput, J., and Lüthi, M. P.: Thick sediments beneath
Greenland's ablation zone and their potential role in future ice sheet
dynamics, Geology, 42, 487–490, 10.1130/G35492.1, 2014.
Weidick, A. and Christoffersen, M.: Quaternary Map of Greenland Søndre
Strømfjord – Nûgssuaq, Map Sheet 3, scale 1 : 500 000, The
Geological Survey of
Greenland, 1974.
Weidick, A. and Christoffersen, M.: Quaternary Map of Greenland
Frederikshåbs Isblink – Søndre Strømfjord, Map Sheet 2, scale
1 : 500 000, The Geological Survey of Greenland, 1978.
Weidick, A. and Klüver, B. G.: Quaternary Map of Greenland
SydgrønSund, Map Sheet 1, scale
1 : 500 000, The Geological Survey of Greenland, 1987.Wessel, P., Smith, W. H., Scharroo, R., Luis, J., and Wobbe, F.: Generic
mapping tools: improved version released, EOS T. Am.
Geophys. Un., 94, 409–410, 10.1002/2013EO450001, 2013.Wheeler, J. O., Hoffman, P. F., Card, K. D., Davidson, A., Sanford, B. V.,
Okulitch, A. V., and Roest, W. R.: Geological Map of Canada, Map 1860A, scale 1 : 5 000 000,
Geological Survey of Canada, 10.4095/208175, 1996.Whitfield, J. W., Ward, R. A., Denne, J. E., Holbrook, D. F., Bush, W. V.,
Lineback, J. A., Luza, K. V., Jensen, K. M., and Fishman, W. D.: Quaternary
geologic map of the Ozark Plateau 4∘×6∘ quadrangle,
United States, Miscellaneous Investigations Series Map I-1420 (NJ-15), edited
by: Richmond, G. M. and Weide, D. L., U.S. Geological Survey, scale
1:1,000,000, 1993.Wilson, F. H., Hults, C. P., Mull, C. G., and Karl, S. M.: Geologic map of
Alaska, Scientific Investigations Map 3340, scale 1 : 1 584 000, United States Geological Survey,
10.3133/sim3340, pamphlet 196, 2015.Yukon Geological Survey: Yukon Digital Bedrock Geology, Tech. rep.,
available at:
http://www.geology.gov.yk.ca/update_yukon_bedrock_geology_map.html,
last access: 2 September 2016.