Structure and Fabric on the Burroughs Glacier, South-East Alaska

AbstractThe Burroughs Glacier, south-east Alaska, is a slow-moving remnant (14×3km.) of a much more extensive glacier. It is now entirely below the firn line; ablation has revealed ice structures and fabric once 300 m. or more below the glacier surface.At the present glacier surface three kinds of ice are identified—foliated ice, coarse-grained border ice and very coarse-grained basal ice.Two systems of fine-grained foliation are present. Differential movement in the glacier has caused recrystallization along closely spaced planes. At the glacier surface this produces a steeply dipping longitudinal foliation. A gently dipping foliation, having a regional trough-like structure, may be associated with former stratification planes or with former spoon-shaped shear surfaces.The optic orientation of crystals in the coarser layers of the foliated ice shows three weak maxima, and in the finer layers a single weak maximum, corresponding to one of the coarse layer maxima, and normal to the gently dipping foliation plane. The other maxima in the coarse layers are orientated close to the poles of principal fracture planes.In the coarse ice the fabric shows a pattern with three maxima similar to that obtained in torsion shear experiments. In the glacier the pattern may be formed by shear near the glacier bottom or along gently dipping foliation planes. Grain-size increases towards the glacier terminus, especially in the stagnant ice zone.Structural evidence suggests that in the early stages of the Little Ice Age the ice flow was from west to east. Later it was to east and west from an ice crest in the upper Burroughs Glacier. Structures produced by present movement have been superimposed on older structures.

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Origin of glacial ridges (OIS 6) in the Kaskaskia Sublobe, southwestern Illinois, USA

Quaternary Research ◽

10.1016/j.yqres.2012.06.005 ◽

2012 ◽

Vol 78 (2) ◽

pp. 341-352 ◽

Cited By ~ 3

Author(s):

Nathan D. Webb ◽

David A. Grimley ◽

Andrew C. Phillips ◽

Bruce W. Fouke

Keyword(s):

Debris Flows ◽

Spatial Arrangement ◽

Coarse Grained ◽

Ice Flow ◽

Glacial Ice ◽

Distinctive Features ◽

Fine Grained ◽

The North ◽

Till Fabric ◽

Glacial Landforms

AbstractThe origin of Illinois Episode (OIS 6) glacial ridges (formerly: ‘Ridged Drift’) in the Kaskaskia Basin of southwestern Illinois is controversial despite a century of research. Two studied ridges, containing mostly fluvial sand (OSL ages: ~ 150 ± 19 ka), with associated debris flows and high-angle reverse faults, are interpreted as ice-walled channels. A third studied ridge, containing mostly fine-grained till, is arcuate and morainal. The spatial arrangement of various ridge types can be explained by a glacial sublobe in the Kaskaskia Basin, with mainly fine-grained ridges along the sublobe margins and coarse-grained glaciofluvial ridges in a paleodrainage network within the sublobe interior. Illinois Episode till fabric and striation data demonstrate southwesterly ice flow that may diverge near the sublobe terminus. The sublobe likely formed as glacial ice thinned and receded from its maximum extent. The Kaskaskia Basin contains some of the best-preserved Illinois Episode constructional glacial landforms in the North American midcontinent. Such distinctive features probably result from ice flow and sedimentation into this former lowland, in addition to minimal postglacial erosion. Other similar OIS 6 glacial landforms may exist in association with previously unrecognized sublobes in the midcontinent, where paleo-lowlands might also have focused glacial sedimentation.

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Micromorphology of modern tills in southwestern Spitsbergen – insights into depositional and post-depositional processes

Polish Polar Research ◽

10.1515/popore-2016-0023 ◽

2016 ◽

Vol 37 (4) ◽

pp. 435-456 ◽

Cited By ~ 5

Author(s):

Katarzyna Skolasińska ◽

Grzegorz Rachlewicz ◽

Witold Szczuciński

Keyword(s):

Textural Properties ◽

Coarse Grained ◽

Glacial Deposits ◽

Glacier Surface ◽

Depositional Processes ◽

Basal Ice ◽

Mass Flows ◽

Characteristic Features ◽

Marginal Zones ◽

Layer Deformation

AbstractTextural properties and microstructures are commonly used properties in the analysis of Pleistocene and older glacial deposits. However, contemporary glacial deposits are seldom studied, particularly in the context of post-depositional changes. This paper presents the results of a micromorphological study of recently deposited tills in the marginal zones of Hansbreen and Torellbreen, glaciers in southwestern Spitsbergen. The main objectives of this study were to compare modern tills deposited in subglacial and supraglacial conditions, as well as tills that were freshly released from ice with those laid down several decades ago. The investigated tills are primarily composed of large clasts of metamorphic rocks and represent coarse-grained, matrix-supported diamictons. The tills reveal several characteristic features for ductile (e.g.turbate structures) and brittle (e.g.lineations, microshears) deformations, which have been considered to be indicative of subglacial conditions. In supraglacial tills, the same structures are common as in the subglacial deposits, which points to the preservation of the primary features, though the sediment was transferred up to the glacier surface due to basal ice layer deformation and redeposited as slumps, or to formation of similar structures due to short-distance sediment re-deposition by mass flows. This study revealed that it might not be possible to distinguish subglacial and supraglacial tills on the basis of micromorphology if the latter are derived from a subglacial position. The only noted difference was the presence of iron oxide cementation zones and carbonate dissolution features in supraglacial tills. These features were found in tills that were deposited at least a few years ago and are interpreted to be induced by early post-depositional processes involving porewater/sediment interactions.

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Identifying fast ice flow from landform assemblages in the geological record: a discussion

Annals of Glaciology ◽

10.3189/172756499781821887 ◽

1999 ◽

Vol 28 ◽

pp. 59-66 ◽

Cited By ~ 60

Author(s):

Jane K. Hart

Keyword(s):

Ice Sheet ◽

Sediment Supply ◽

Coarse Grained ◽

Ice Streams ◽

Ice Flow ◽

Land Form ◽

Tidewater Glaciers ◽

Fine Grained ◽

Fast Ice ◽

Fast Flow

AbstractDifferent types of fast ice flow (both spatial and temporal) in valley glaciers (surging glaciers, tidewater glaciers and deforming-bed glaciers) and ice sheets (ice streams and deforming-bed ice-sheet flow) are discussed briefly. Although there are unlikely to be any specific individual landforms associated with fast ice flow, there may be landform assemblages.At valley glacier scale, it is suggested that there are two landform assemblages: (1) an ice-thrust type, dominated by bulldozed push moraines and hummocky moraines (associated with glaciers with a high supraglacial sediment supply, a coarse-grained substrate and a coarse-grained proglacial sediment wedge); and (2) a bed-flow type dominated by “squeeze” push moraines, flutes and drumlins (associated with glaciers with a low supra- glacial sediment supply and fine-grained substrate). The ice-thrust type alone is only associated with discontinuous fast flow (on both rigid and deforming beds); whilst the bed-flow type is associated with both continuous and discontinuous fast flow.It is suggested that these two landform assemblages may also be indicative of fast ice flow at ice-sheet scale, in particular the bed-flow style. If that is the case, then discontinuous fast ice flow may be indicated by the ice-thrust landform assemblage and the bed-flow style where drumlins are present.It is also suggested that specific evidence for ice streams includes the distinctive land-form assemblages within valley or fan-like locations, and a predictable pattern of velocity reflected by drumlin elongation ratios.

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Iceberg calving rates from northern Ellesmere Island ice caps, Canadian Arctic, 1999–2003

Journal of Glaciology ◽

10.3189/002214308785837048 ◽

2008 ◽

Vol 54 (186) ◽

pp. 391-400 ◽

Cited By ~ 29

Author(s):

Scott Williamson ◽

Martin Sharp ◽

Julian Dowdeswell ◽

Toby Benham

Keyword(s):

Glacier Surface ◽

Ice Flow ◽

Ice Caps ◽

Ice Cap ◽

Glacier Terminus ◽

Devon Ice Cap ◽

Order Of Magnitude ◽

Iceberg Calving ◽

Flow Through ◽

Calving Rate

AbstractOptical satellite imagery was used to estimate glacier surface velocities and iceberg calving rates from Agassiz and western Grant Ice Caps, Nunavut, Canada, between 1999 and 2003. The largest mean annual surface velocities ranged from ∼400 to 700 m a−1, but velocities in the ∼100–200 m a−1 range were common. Summer velocities were up to an order of magnitude larger than annually averaged velocities. The highest velocity (∼1530 m a−1) was measured on the floating tongue of Lake Tuborg Glacier between 19 July and 19 August 2001. Calving rates from individual glaciers varied by up to a factor of two between successive years. Summer calving rates were ∼2–8 times larger than annual average rates. The average ratio of the calving flux due to terminus-volume change to that due to ice flow through the glacier terminus was ∼0.81 for the annual rates and ∼1.71 for summer rates. The estimated mean annual calving rate from Agassiz Ice Cap in the period 1999–2002 was 0.67 ± 0.15 km3 a−1, of which ∼54% emanated from Eugenie Glacier alone. This total rate is similar to a previously estimated calving rate from Devon Ice Cap.

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Fabric and texture at Siple Dome, Antarctica

Journal of Glaciology ◽

10.3189/172756505781829359 ◽

2005 ◽

Vol 51 (173) ◽

pp. 281-290 ◽

Cited By ~ 32

Author(s):

C.L. Diprinzio ◽

L.A. Wilen ◽

R.B. Alley ◽

J.J. Fitzpatrick ◽

M.K. Spencer ◽

...

Keyword(s):

Ice Core ◽

Ice Age ◽

West Antarctica ◽

Ice Flow ◽

Thin Sections ◽

Fine Grained ◽

Additional Information ◽

Siple Dome ◽

History Of ◽

Last Ice Age

AbstractPreferred c-axis orientations are present in the firn at Siple Dome, West Antarctica, and recrystallization begins as shallow as 200 m depth in ice below –20°C, based on digital analysis of c-axis fabrics, grain-sizes and other characteristics of 52 vertical thin sections prepared in the field from the kilometer-long Siple Dome ice core. The shallowest section analyzed, from 22 m, shows clustering of c axes toward the vertical. By 200 m depth, girdle fabric and other features of recrystallized ice are evident in layers (or regions), separated by layers (regions) of typically finer-grained ice lacking evidence of recrystallization. Ice from about 700–780m depth, which was deposited during the last ice age, is especially fine-grained, with strongly vertical c axes, but deeper ice shows much larger crystals and strong evidence of recrystallization. Azimuthal asymmetry of some c-axis fabrics, trends in grain-size, and other indicators reveal additional information on processes and history of ice flow at Siple Dome.

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Geometry of Former Subglacial Water Channels and Cavities

Journal of Glaciology ◽

10.3189/s0022143000029944 ◽

1979 ◽

Vol 23 (89) ◽

pp. 335-346 ◽

Cited By ~ 32

Author(s):

Joseph Walder ◽

Bernard Hallet

Keyword(s):

Flow Direction ◽

Water Film ◽

List Type ◽

Ice Flow ◽

Glacier Terminus ◽

Basal Ice ◽

Limestone Bedrock ◽

Rock Interface ◽

Active Processes ◽

Nearly Continuous

AbstractThe spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions: 1.A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.2.At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.3.Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-flow direction, perhaps as a result of locally enhanced sheet flow of subglacial water.

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First investigations of fine-grained cryogenic cave carbonates from a High-Arctic permafrost karst system in Greenland

10.5194/egusphere-egu21-14642 ◽

2021 ◽

Author(s):

Anika Donner ◽

Christoph Spötl ◽

Paul Töchterle ◽

Irka Hajdas ◽

Gina E. Moseley

Keyword(s):

Sampling Site ◽

Water Film ◽

High Arctic ◽

Water Infiltration ◽

Ice Age ◽

Coarse Grained ◽

Lower Latitude ◽

Published Data ◽

Climate Conditions ◽

Fine Grained

In recent years, cryogenic cave carbonates (CCC) have become the focus of studies tracking past climate change in periglacial environments. Two types of these speleothems occur, fine-grained CCC (CCCfine), which form due to the rapid freezing of a thin water film on ice, and coarse-grained CCC whose origin is related to the slow freezing of water pockets inside cave ice. Here, we report for the first time the occurrence of CCCfine from a cave in northeast Greenland, presently situated in continuous permafrost.Eqik Qaarusussuaq (Cove Cave), located at 80.2&#176; N, is a 103 m long, gently-dipping phreatic passage that was discovered during the 2019 Greenland Caves Project Expedition (www.greenlandcavesproject.org). CCCfine were found in a dry chamber 65 m behind the entrance. The cave air temperature at the CCC site of -14.7 &#176;C contrasts with outside air temperatures of up to +18.0 &#176;C in July 2019. This, together with current dry conditions at the sampling site, indicates that water infiltration, necessary for CCC formation, is not possible under present-day climate conditions. This is further supported by a lack of ice found within the cave.Stable isotope analyses of CCC show &#948;18O values ranging from -21.9 to -16.0 &#8240; and &#948;13C values between 8.4 and 11.7 &#8240; VPDB. While the &#948;13C values are consistent with published data of CCCfine from caves at lower latitudes, the &#948;18O values are significantly lower and plot in the field of CCCcoarse (cf. &#381;&#225;k et al., 2018). This shift reflects the much lower &#948;18O values of meteoric precipitation in northeast Greenland compared to lower latitude sites.Exploratory radiocarbon dating suggests that CCCfine formed in this High Arctic cave as recent as during the end of the Little Ice Age.&#160;Reference&#381;&#225;k, K., Onac, B.P., Kadebskaya, O.I., Filippi, M., Dublyansky, Y., Luetscher, M., 2018. Cryogenic mineral formation in caves. In: Per&#351;oiu, A., Lauritzen, S.-E. (Eds.), Ice caves. Elsevier, Amsterdam, Netherlands, pp.&#160;123&#8211;162.

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Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation

Geological Society of America Bulletin ◽

10.1130/b35590.1 ◽

2020 ◽

Vol 133 (1-2) ◽

pp. 379-392 ◽

Cited By ~ 2

Author(s):

Lily S. Pfeifer ◽

Gerilyn S. Soreghan ◽

Stéphane Pochat ◽

Jean Van Den Driessche

Keyword(s):

Chemical Weathering ◽

Ice Age ◽

Coarse Grained ◽

Mean Annual Temperature ◽

Fine Grained ◽

Chemical Index ◽

Low Degree ◽

Low Latitudes ◽

Chemical Index Of Alteration ◽

Unique Distribution

Abstract Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation.

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Geometry of Former Subglacial Water Channels and Cavities

Journal of Glaciology ◽

10.1017/s0022143000029944 ◽

1979 ◽

Vol 23 (89) ◽

pp. 335-346 ◽

Cited By ~ 75

Author(s):

Joseph Walder ◽

Bernard Hallet

Keyword(s):

Flow Direction ◽

Water Film ◽

List Type ◽

Ice Flow ◽

Glacier Terminus ◽

Basal Ice ◽

Limestone Bedrock ◽

Rock Interface ◽

Active Processes ◽

Nearly Continuous

AbstractThe spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions:1.A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.2.At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.3.Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-flow direction, perhaps as a result of locally enhanced sheet flow of subglacial water.

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