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

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, 2080 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 sounderseabed 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.

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

Journal of Glaciology ◽

10.3189/172756507781833884 ◽

2007 ◽

Vol 53 (180) ◽

pp. 71-83 ◽

Cited By ~ 28

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.

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High resolution shallow reflection seismic profiles, Val Gagne, Ontario Test Site

10.4095/130194 ◽

1987 ◽

Author(s):

R M Gagne ◽

S E Pullan ◽

J A Hunter

Keyword(s):

High Resolution ◽

Test Site ◽

Seismic Profiles ◽

Reflection Seismic

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The application of ambient noise and reflection seismic exploration in an urban active fault survey

Interpretation ◽

10.1190/int-2020-0085.1 ◽

2020 ◽

Vol 8 (4) ◽

pp. SU1-SU10

Author(s):

Xiaoqiong Lei ◽

Jun Zhang ◽

Wenyuan Jin ◽

Chen Han ◽

Xiwei Xu

Keyword(s):

High Resolution ◽

Ambient Noise ◽

Active Fault ◽

Active Faults ◽

Seismic Exploration ◽

Deep Penetration ◽

Seismic Surveys ◽

Reflection Seismic ◽

Active Source ◽

Seismic Lines

As the detection of urban active faults becomes increasingly important, high-resolution detection of urban blind active faults is very important for urban planning, land use, and disaster risk reduction. However, it is difficult to determine the corresponding surface positions in the city environment for noise and building restrictions. The active source reflection seismic technique is considered the best technique to image faults with a high resolution and deep penetration. However, urban geophysical exploration must often consider the complex urban environment, which includes moving vehicles, dense power grids, and irregular buildings. These features make active source reflection seismic exploration difficult for wide application due to its drawbacks of high cost and the necessary use of explosives. In contrast, ambient noise seismic surveys have the advantages of continuous ambient noise sources, low cost, and fast deployment. These advantages are good for urban exploration. Although ambient noise seismic surveys have a lower resolution than active seismic surveys, their ultrahigh-density layout can improve the resolution. We have conducted two active source seismic lines and two ambient noise seismic lines near the Huangzhuang-Gaoliying fault (HGF) in a northern suburb of Beijing. The autocorrelation and crosscorrelation results are consistent with the active source reflection seismic results. They revealed the location of the HGF, which is composed of a set of steep dip faults. The study of the combination of the two techniques demonstrates that ambient noise seismic surveys are effective for urban active fault detection, especially for larger scale area surveys, and active source reflection seismic surveys can be used for detailed surveys. The combination of the two techniques has a higher efficiency and lower costs and can be widely used in blind urban active fault surveys.

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

Canadian Journal of Earth Sciences ◽

10.1139/e85-197 ◽

1985 ◽

Vol 22 (12) ◽

pp. 1864-1871 ◽

Cited By ~ 6

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.

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Stratigraphy of Georges Bank Basin: interpreted from seismic correlation to the western Scotian Shelf

Canadian Journal of Earth Sciences ◽

10.1139/e77-195 ◽

1977 ◽

Vol 14 (10) ◽

pp. 2274-2283 ◽

Cited By ~ 12

Author(s):

John A. Wade

Keyword(s):

Lower Cretaceous ◽

Upper Cretaceous ◽

Georges Bank ◽

Seismic Profiles ◽

Scotian Shelf ◽

Entire Area ◽

Reflection Seismic ◽

Northern Half ◽

Southern Half ◽

Jurassic Rocks

Based on the interpretation of reflection seismic profiles, five major reflecting horizons are correlated from the southwestern Scotian Shelf to Georges Bank. The Mesozoic–Cenozoic stratigraphy of Georges Bank Basin is interpreted to be similar to, but thicker than, the LaHave Platform and consists of 200 m of Tertiary and younger strata, 1000 m of Upper Cretaceous, 600 m of Lower Cretaceous, and 6300 m of Jurassic rocks. The post-Lower Cretaceous facies are interpreted to be clastic across the entire area, while the pre-Upper Cretaceous facies are interpreted to be predominantly clastic in the northern half and predominantly carbonates in the southern half of Georges Bank Basin.

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Active transpression along the Owen oceanic transform fault, India - Somalia plate boundary

10.5194/egusphere-egu21-3285 ◽

2021 ◽

Author(s):

Alexandre Janin ◽

Mathieu Rodriguez ◽

Nicolas Chamot-Rooke ◽

Alain Rabaute ◽

Matthias Delescluse ◽

...

Keyword(s):

High Resolution ◽

Plate Boundary ◽

Linear Structure ◽

Historical Seismicity ◽

Transform Fault ◽

Seismic Profiles ◽

Time Calibration ◽

Carlsberg Ridge ◽

Regional Tectonic ◽

Seismic Lines

The Owen oceanic transform fault is a 300-km long linear structure connecting the Carlsberg and Sheba spreading centers in the northwest Indian Ocean. It presently forms with the Carlsberg ridge the active plate boundary between India and Somalia. The Owen transform fault accommodates the left-lateral strike-slip motion between India and Somalia at a rate of about 23 mm/yr. &#160;Firstly identified by Tuzo Wilson in the 60s, this oceanic transform remains poorly described. The fault was recently surveyed in the Spring of 2019 during the VARUNA and CARLMAG cruises (https://doi.org/10.17600/18001108, https://doi.org/10.17600/18000872) along its entire length aboard BHO Beautemps-Beaupr&#233;, an oceanographic ship operated by the French Naval Hydrographic and Oceanographic Services (SHOM) and the French Navy.During these missions a set of high-resolution seismic lines (>5000 km) were acquired together with high resolution multibeam bathymetry. The data cover both the active and fossil traces of the transform fault between 9&#176;N and 15&#176;N, at a place where continuous deposition of the distal Indus turbiditic sediments offers a unique high-resolution stratigraphic record of past regional tectonic events.The new bathymetric mapping reveals two remarkable transpressive ridges on the active fault trace. A precise stratigraphic work using seismic profiles and drilling data of the ODP leg 117 allows the time calibration of the new seismic lines as far south as the Carlsberg ridge.We show that a major compressive event occurred on the Owen Oceanic Transform Fault recently between 1.5 Ma and 2.4 Ma. Compression is still active today as evidenced by Sub-bottom profiler data (3.5 kHz) and two compressive focal mechanisms found in the historical seismicity records. At the intersection with the Carlsberg ridge, the southern transpressive ridge bends and stands ~1200 m above the seafloor at its apex, suggesting a maximum surrection rate near 800 m/Ma.&#160; These new geophysical dataset combined with previous cruises offers an unprecedented window on the recent evolution of the India-Somalia plate boundary.

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

Bulletin of the Geological Society of Finland ◽

10.17741/bgsf/92.2.001 ◽

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.

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SEISMIC CHARACTERISTICS AND SEDIMENTARY DISTRIBUTION ON THE SOUTH SHETLAND ISLANDS CONTINENTAL MARGIN, ANTARCTICA

Brazilian Journal of Geophysics ◽

10.22564/rbgf.v32i3.509 ◽

2014 ◽

Vol 32 (3) ◽

pp. 549 ◽

Cited By ~ 1

Author(s):

Fabio José Guedes Magrani ◽

Arthur Ayres Neto

Keyword(s):

High Resolution ◽

Continental Margin ◽

South Shetland Islands ◽

Geological Samples ◽

The South ◽

Seismic Profiles ◽

Shetland Islands ◽

Bransfield Strait ◽

Sandy Silt ◽

Seismic Amplitudes

ABSTRACT. This work consists in characterizing the sedimentary distribution of the South Shetland Islands continental margin, Bransfield Strait, Antarctica, throughthe interpretation and correlation of high-resolution seismic profiles and geological samples. The analysis of echo-characters, seismic amplitudes and their correlationwith the collected samples, revealed five different echo types. Echo types I and II have good seismic resolution and are characterized by continuous sharp bottom echoeswith subparallel reflections. Echoes III and IV are characterized by diffuse and very prolonged bottom echoes with no subbottom reflectors. Echo V is associated withglacial deposits on the upper slope in response to deglaciation and transport of coarse grains in a muddy matrix and is characterized by diffraction hyperbolae. Theecho-characters showed good correlation with geological samples collected along the Bransfield Strait and bays of the King George Island, but the correlation with theseismic amplitude map was not as obvious. Echo I shows medium-high amplitudes and samples within its area of occurrence (AM-02 and AM-14) indicate silty sandand sandy silt, respectively. Echo II presents the lowest seismic amplitudes and the sample collected within its area (AM-17) shows approximately 90% mud content.Echoes III and IV, located on the shallowest portions of South Shetland’s continental margin, demonstrate medium-low amplitude values, and are related to samplesAM-01 and AM-04, both classified as sandy silt with approximately 35%sand.Keywords: Bransfield Strait, echo-characters, high-resolution seismic, sedimentary analysis. RESUMO. O presente trabalho consiste na interpretação integrada da sísmica de alta resolução e da amostragem geológica, a fim de caracterizar a geologia de fundona região da margem continental das Ilhas Shetland do Sul, Estreito de Bransfield, Antártica. A caracterização geológica foi realizada através da análise de ecocaráteres, mapas de amplitude sísmica e sua correlação com os sedimentos coletados. Cinco diferentes ecocaráteres foram identificados e classificados. Ecos I e II demonstramboa resolução e são caracterizados por ecos contínuos e nítidos com reflexões subparalelas. Ecos III e IV são caracterizados por ecos difusos, muito prolongados ecom ausência de refletores subparalelos. O Eco V está associado a depósitos glaciais no talude superior, em respostas ao degelo, e ao transporte de grãos grossos em uma matriz mais fina. Além disso, é caracterizado pela presença de hipérboles de difração. Os ecocaráteres mostraram boa correlação com os testemunhos geológicos coletados no Estreito de Bransfield e nas baías da Ilha Rei George, mas não apresentaram uma relação óbvia com o mapa de amplitudes. O Eco I possui amplitudes médio-altas e as amostras contidas em sua área (AM-02 e AM-14) indicam, respectivamente, um conteúdo de areia siltosa e silte arenoso. O Eco II apresenta os menores valores de amplitude com conteúdo de lama (argila + silte) de aproximadamente 90%, conforme a amostra AM-17. Os Ecos III e IV, localizados nas porções mais rasasda margem continental das Shetland do Sul, demonstram valores médio-baixos de amplitude e se relacionam às amostras AM-01 e AM-04, ambas siltes-arenosos com conteúdo de areia de aproximadamente 35%.Palavras-chave: Estreito de Bransfield, ecocaráteres, sísmica de alta resolução, análise sedimentar.

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

Canadian Journal of Earth Sciences ◽

10.1139/e02-059 ◽

2002 ◽

Vol 39 (9) ◽

pp. 1373-1391 ◽

Cited By ~ 11

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. 2315 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.

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