Analysis and reinterpretation of deformation features in the Rouge River valley, Scarborough, Ontario

2002 ◽  
Vol 39 (9) ◽  
pp. 1373-1391 ◽  
Author(s):  
Laurent Godin ◽  
Richard L Brown ◽  
Aleksis Dreimanis ◽  
Gail M Atkinson ◽  
Derek K Armstrong
Keyword(s):  
Flow Direction ◽  
Normal Fault ◽  
River Valley ◽  
Local Perturbation ◽  
Ice Flow ◽  
Extensive Data ◽  
Deformation Features ◽  
Flow Directions ◽  
Rouge River ◽  
Multiple Episodes

Geometry and timing of deformation affecting Ordovician bedrock and overlying Pleistocene sediments in the Rouge River valley near Scarborough, Ontario, are analysed to evaluate whether or not the structures are a result of glacial action or neotectonic activity. Extensive data on local and regional ice-flow directions are used to evaluate the kinematic compatibility between the observed faults and folds and the local ice-flow directions. Jointing and multiple episodes of faulting affect both the Ordovician bedrock and the overlying Pleistocene sediments. At one site, the bedrock is displaced by a normal fault by a minimum of 1.2 m. Crosscutting relationships constrain the majority of the faulting in the Rouge River valley as being coeval with deposition of the lower Bowmanville till during the Nissouri phase (ca. 23–15 ka), and possibly younger at one locality. The youngest regional ice-flow direction is northwestward; however, local ice-flow directions are highly variable. This can be explained by local perturbation enhanced by the presence of drumlinoid features in the area. Most deformation features are compatible with local and regional ice-flow directions. Glaciotectonic ice-push and ice-thrust deformation affected the Thorncliffe Formation after about 23 ka. Although some faults appear to be kinematically incompatible with ice-flow directions, six boreholes drilled to 52 m depth revealed only minor vertical offsets of bedrock strata in the uppermost 20 m, and an absence of obvious fault offsets deeper, precluding the possibility that the faults observed in the surface exposures were caused by deep-seated neotectonic stresses.

scholarly journals Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data

2007 ◽  
Vol 53 (180) ◽  
pp. 71-83 ◽  
Author(s):  
Jacob Napieralski ◽  
Alun Hubbard ◽  
Yingkui Li ◽  
Jon Harbor ◽  
Arjen P. Stroeven ◽  
...  
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Model Performance ◽  
Initial Step ◽  
Ice Flow ◽  
Flow Models ◽  
Flow Directions ◽  
The Last Glacial Maximum ◽  
Basal Flow ◽  
The Last Glacial

AbstractA major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

Lift-off moraines: markers of last ice-flow directions on the Scotian Shelf

2000 ◽  
Vol 37 (12) ◽  
pp. 1723-1734 ◽  
Author(s):  
Michael R Gipp
Keyword(s):  
High Resolution ◽  
Continental Margin ◽  
Flow Direction ◽  
Seismic Profiles ◽  
Scotian Shelf ◽  
Ice Flow ◽  
Reflection Seismic ◽  
Flow Directions ◽  
Lift Off ◽  
Seismic Lines

Lift-off moraines are acoustically incoherent, subparallel ridges observed on sidescan sonograms and high-resolution reflection seismic profiles on the southeastern continental margin of Canada. They are up to 3 m high, 20–80 m wide, and are commonly overlain by stratified proglacial sediments. Although little is known about them, detailed study of high-resolution seismic profiles from the Emerald Basin and the LaHave Basin, on the Scotian Shelf, show that their height:width ratio varies with the sounder–seabed separation, suggesting that the ridges may be narrower than they appear. Their morphology is similar to DeGeer moraines or cross-valley moraines, which form perpendicular to ice-flow direction. As their orientations can be estimated at the intersection of seismic lines, they can be used to estimate ice-flow directions. Since proglacial sediments are draped directly over top of them, they are assumed to record the direction of last ice flow. This directional data suggests that ice retreated not only northward (to Nova Scotia), but also toward local topographic highs on the continental shelf, which acted as anchoring points for ice rises around both the Emerald and LaHave Basins. This pattern of ice-flow directions suggests that ice flowed from the high ground of banks, converging into basin deeps, suggesting that small moraines within the basins are probably of interlobate origin.

Reply to the discussion by N. Eyles and A. Mohajer on "Analysis and reinterpretation of deformation features in the Rouge River valley, Scarborough, Ontario"

2003 ◽  
Vol 40 (9) ◽  
pp. 1303-1305 ◽  
Author(s):  
Laurent Godin ◽  
Richard L Brown ◽  
Aleksis Dreimanis ◽  
Gail M Atkinson ◽  
Derek K Armstrong
Keyword(s):  
River Valley ◽  
Deformation Features ◽  
Rouge River

A note on the glacial geology and postglacial emergence of the Lake Harbour region, Baffin Island, N.W.T.

1985 ◽  
Vol 22 (12) ◽  
pp. 1864-1871 ◽  
Author(s):  
Peter Clark
Keyword(s):  
Large Scale ◽  
Flow Direction ◽  
Baffin Island ◽  
Ice Streams ◽  
Ice Flow ◽  
The North ◽  
West Antarctic ◽  
Ice Stream ◽  
Flow Directions ◽  
Late Wisconsinan

Ice-flow indicators in the Lake Harbour region of northern Hudson Strait define two flow directions affecting this area during the late Wisconsinan glaciation. A pronounced southward flow direction indicated by medium- and large-scale erosional and depositional features represents ice flow from an ice dome centered to the north, perhaps Foxe Basin and (or) Amadjuak Lake. Carbonate-rich till and striations represent eastward–southeastward ice flow down the axis of Hudson Strait. Convergence of ice-sheet flow with a rapidly moving ice stream has been observed and modelled for West Antarctic ice streams and involves sharp bending of flow lines at the point of convergence. A similar scenario is proposed for the Lake Harbour region to explain the two contrasting ice-flow patterns. Impingement of an ice stream in Hudson Strait onto the southern coast of Baffin Island suggests the influence of northerly flowing ice, perhaps from the Ungava plateau.Radiocarbon dates on marine shells and archeological samples are used to reconstruct the postglacial emergence of the Lake Harbour region. The marine limit (90 m aht) and deglaciation are dated by extrapolation at ca. 8300 years BP. Postglacial emergence is characterized by an initial uplift rate of 4.4 m/100 years, which decreased to 0.2 m/100 years over the last 3900 years. The initial rate (4.4 m/100 years) is nearly 50% lower than rates calculated elsewhere in the Hudson Strait region and is interpreted to reflect the influence of an ice load centered over Amadjuak Lake directly north of the Lake Harbour region.

Discussion of "Analysis and reinterpretation of deformation features in the Rouge River valley, Scarborough, Ontario"

2003 ◽  
Vol 40 (9) ◽  
pp. 1299-1301 ◽  
Author(s):  
N Eyles ◽  
A Mohajer
Keyword(s):  
River Valley ◽  
Deformation Features ◽  
Rouge River

scholarly journals Weichselian sedimentary record and ice-flow patterns in the Sodankylä area, central Finnish Lapland

2020 ◽  
Vol 92 (2) ◽  
pp. 77-98
Author(s):  
Annika Katarina Åberg ◽  
◽  
Seija Kultti ◽  
Anu Kaakinen ◽  
Kari O. Eskola ◽  
...  
Keyword(s):  
Flow Direction ◽  
Flow Patterns ◽  
Ice Flow ◽  
Fluvial Deposits ◽  
Finnish Lapland ◽  
Aeolian Deposits ◽  
Scandinavian Ice Sheet ◽  
Lidar Dem ◽  
Flow Directions ◽  
Late Weichselian

Three different till units separated by interstadial fluvial deposits were observed in the Sodankylä area in the River Kitinen valley, northern Finland. The interbedded glaciofluvial sediments and palaeosol were dated by OSL to the Early (79±12 to 67±13 ka) and Middle (41±9 ka) Weichselian. A LiDAR DEM, glacial lineations, the flow direction of till fabrics, esker chains and striations were applied to investigate the glacial flow patterns of the Sodankylä, Kittilä and Salla areas. The analysis revealed that the youngest movement of the Scandinavian Ice Sheet is not visible as DEM lineations within the studied areas. The modern morphology in Kittilä and Salla shows streamlined landforms of various dimensions mainly oriented from the NW and NNW, respectively, corresponding to the Early/Middle Weichselian ice-flow directions inferred from till fabrics. The Late Weichselian ice flow has produced an insignificant imprint on the landforms. This study suggests a northern location for the ice-divide zone during the Early/Middle Weichselian, and a more western–southwestern position during the Late Weichselian. The OSL ages of 14±3.3 ka from the aeolian deposits may indicate ice-free areas during the Bølling–Allerod warm period in the vicinity of the River Kitinen.

Ribbed bedforms, markers of palaeo-ice stream margins, basal meltwater drainage and ice flow dynamic

2021 ◽  
Author(s):  
Jean Vérité ◽  
Édouard Ravier ◽  
Olivier Bourgeois ◽  
Stéphane Pochat ◽  
Thomas Lelandais ◽  
...  
Keyword(s):  
Flow Direction ◽  
Local Stress ◽  
Sediment Surface ◽  
Shear Stresses ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Physical Experiments ◽  
Stream Beds ◽  
Ice Water

<p>Over the three last decades, great efforts have been undertaken by the glaciological community to characterize the behaviour of ice streams and better constrain the dynamics of ice sheets. Studies of modern ice stream beds reveal crucial information on ice-meltwater-till-bedrock interactions, but are restricted to punctual observations limiting the understanding of ice stream dynamics as a whole. Consequently, theoretical ice stream landsystems derived from geomorphological and sedimentological observations were developed to provide wider constraints on those interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of subglacial periodic bedforms transverse to the ice flow direction – ribbed bedforms – remain unclear. The purpose of this study is (i) to explore the conditions under which these ribbed bedforms develop and (ii) to constrain their spatial organisation along ice stream beds.  </p><p>We performed physical experiments with silicon putty (to simulate the ice), water (to simulate the meltwater) and sand (to simulate a soft sedimentary bed) to model the dynamics of ice streams and produce analog subglacial landsystems. We compare the results of these experiments with the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. Based on this comparison, we can draw several conclusions regarding the significance of ribbed bedforms in ice stream contexts:</p><ul><li>Ribbed bedforms tend to form where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. Where the ribs initiate, we hypothesize that high driving stresses generate high basal shear stresses, accommodated through bed deformation of the active uppermost part of the bed.</li> <li>Ribbed bedforms can develop subglacially from a flat sediment surface beneath shear margins (i.e., lateral ribbed bedforms) and stagnant lobes (i.e., submarginal ribbed bedforms) of ice streams, while they do not develop beneath surging lobes.</li> <li>The orientation of ribbed bedforms reflects the local stress state along the ice-bed interface, with transverse bedforms formed by compression beneath ice lobes and oblique bedforms formed by transgression below lateral shear margins.</li> <li>The development of ribbed bedforms where the ice-bed interface is unlubricated reveals distinctive types of discontinuous basal drainage systems below shear and lobe margins: linked-cavities and efficient meltwater channels respectively.</li> </ul><p>Ribbed bedforms could thus constitute convenient geomorphic markers for the reconstruction of palaeo-ice stream margins, palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.</p>

scholarly journals Deformation in Rutford Ice Stream, West Antarctica: measuring shear-wave anisotropy from icequakes

2013 ◽  
Vol 54 (64) ◽  
pp. 105-114 ◽  
Author(s):  
S.R. Harland ◽  
J.-M. Kendall ◽  
G.W. Stuart ◽  
G.E. Lloyd ◽  
A.F. Baird ◽  
...  
Keyword(s):  
Shear Wave ◽  
Flow Direction ◽  
Transversely Isotropic ◽  
Shear Wave Splitting ◽  
Ice Crystal ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Wave Splitting

Abstract Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produce elastic and rheological anisotropy, which informs ice-flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in Rutford Ice Stream, West Antarctica, using observations of shear-wave splitting from three-component icequake seismograms to characterize ice deformation via crystal-preferred orientation. Over 110 high-quality measurements are made on 41 events recorded at five stations deployed temporarily near the ice-stream grounding line. To the best of our knowledge, this is the first well-documented observation of shear-wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2 to 80 ms and suggests a maximum of 6% shear-wave splitting. The fast shear-wave polarization direction is roughly perpendicular to ice-flow direction. We consider three mechanisms for ice anisotropy: a cluster model (vertical transversely isotropic (VTI) model); a girdle model (horizontal transversely isotropic (HTI) model); and crack-induced anisotropy (HTI model). Based on the data, we can rule out a VTI mechanism as the sole cause of anisotropy – an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice films in the plane perpendicular to the flow direction. The results suggest a combination of mechanisms may be at play, which represent vertical variations in the symmetry of ice crystal anisotropy in an ice stream, as predicted by ice fabric models.

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

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

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

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