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

2016 ◽  
Vol 37 (4) ◽  
pp. 435-456 ◽  
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.

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

1963 ◽  
Vol 4 (36) ◽  
pp. 731-752 ◽  
Author(s):  
Lawrence D. Taylor
Keyword(s):  
Ice Age ◽  
Coarse Grained ◽  
Glacier Surface ◽  
Ice Flow ◽  
Fine Grained ◽  
Glacier Terminus ◽  
Basal Ice ◽  
Differential Movement ◽  
Slow Moving ◽  
Optic Orientation

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.

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

1963 ◽  
Vol 4 (36) ◽  
pp. 731-752
Author(s):  
Lawrence D. Taylor
Keyword(s):  
Ice Age ◽  
Coarse Grained ◽  
Glacier Surface ◽  
Ice Flow ◽  
Fine Grained ◽  
Glacier Terminus ◽  
Basal Ice ◽  
Differential Movement ◽  
Slow Moving ◽  
Optic Orientation

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.

Multi-scale influence of topography on shallow-marine successions associated with long-term transgressions

2021 ◽  
Author(s):  
Miquel Poyatos-Moré ◽  
Ernesto Schwarz ◽  
Salvador Boya ◽  
Luz Elena Gomis-Cartesio ◽  
Ivar Midtkandal
Keyword(s):  
Regional Scale ◽  
Coarse Grained ◽  
Continuous Exposure ◽  
Entire Study ◽  
Shallow Marine ◽  
Sedimentary Characteristics ◽  
Multi Scale ◽  
Depositional Processes ◽  
Mouth Bars

<p>Thick shallow-marine successions associated with long-term transgressions are less well known than their thin, well-sorted counterparts, widely studied due to their potential to form good reservoirs. In these successions, particularly in storm-dominated examples, bioturbation can obliterate primary sedimentary characteristics, making stacking patterns and sequences difficult to define, and challenging our understanding of the main controls in their resulting depositional architecture. This study presents an example from the Jurassic of the Neuquén Basin (Argentina), with the aim to: a) refine the depositional model of a thick, shallow-marine succession associated with a long-term, early post-rift transgression, b) constrain multi-scale controls on stratigraphic architecture and lateral facies variability, and c) discuss their preservation and response to post-depositional processes. To do this, a <300 m-thick succession has been studied along a >10 km continuous exposure, with mapping, sedimentary logging and correlation of stratigraphic units, integrated with subsurface, biostratigraphic and ichnological data. The succession shows an overall retrogradational-aggradational-retrogradational stacking pattern, with several higher frequency regressive units (parasequences and parasequence sets, PSS). The lower part (PSS I) comprises laterally-discontinuous (10's of m) mouth-bars and distributary channel fills, dominated by several m-thick coarsening- and fining-up sandstone packages and m-scale erosive conglomeratic lenses. Above these, the succession (PSS II-IV) is composed by laterally-continuous (>100's of m) storm-dominated lower-shoreface to upper-offshore deposits, dominated by <1m-thick fine-grained and highly bioturbated tabular muddy sandstones and sandy mudstones, with rarely-preserved HCS and bioclastic-rich limestones; their internal characteristics and bed boundaries are diffuse due to pervasive bioturbation, suggesting overall low sedimentation rates and recurrent periods of colonization. The coarse-grained nature and lithology of the mouth bars and channel fills in the lower succession (PSS I) are consistent with a proximal sediment source, associated with erosion of intra-basinal highs. Its variable thickness, lateral distribution and onlap against underlying syn-rift deposits demonstrates partial infill of localized higher-accommodation areas. The well-sorted and finer-grained nature of the shoreface-offshore strata the middle and upper succession (PSS II-IV) indicates a more mature, distal source, with sediment redistributed by longshore currents, and then intensely bioturbated. These deposits display well-defined parasequences internally composed of laterally-continuous bedsets (<5 m-thick). They extend along the entire study area, but show a significant vertical thickness variability. The integration of outcrop and subsurface data mapping (well and seismic) reveals this variability records the stratigraphic response of transgression over a complex, regional-scale ramp-step and underfilled rift topography, which controlled the location of main thickness and facies changes, and promoted areas of favored biogenic reworking. This study offers new insights in how to interpret thick transgressive successions based on primary depositional mechanisms and postdepositional processes, and provides useful tools to understand and predict the nature and potential preservation of these deposits in limited subsurface datasets.</p>

scholarly journals Some Observations on the Behavior of the Liquid and Gas Phases in Temperate Glacier Ice

1975 ◽  
Vol 14 (71) ◽  
pp. 213-233 ◽  
Author(s):  
C. F. Raymond ◽  
W. D. Harrison
Keyword(s):  
Large Scale ◽  
Water Flux ◽  
Coarse Grained ◽  
Glacier Surface ◽  
Cross Sectional ◽  
Gas Phases ◽  
Upper Limit ◽  
Melt Water ◽  
Glacier Ice ◽  
Typical Summer

Microscopic and textural observations were made on ice samples cored from Blue Glacier slightly below the equilibrium line to depths of 60 m. Observations were started within a few minutes after collection Water was found in veins along three-grain intersections, in lenses on grain boundaries and in irregular shapes. Gas was found in bubbles in the interior of crystals, in bubbles touching veins and locally in veins Vein sizes showed some spread; average cross-sectional area was about 74 × 10−4mm2with no discernible, trend with texture or depth except within 7 m of the surface. Before the samples were examined they could have experienced a complex relaxation which could have changed them significantly As a result it is not possible to determine thein situsize of veins, but an upper limit can be determined. Also it is not possible to predict intergranular water flux per unit area, but 1 × 10−1m a−1represents an upper limit. In coarse-grained ice the water flux density is likely to be even smaller, because of a low density of veins and blocking by bubbles. This indicates that only a very small fraction of the melt-water production on a typical summer day can penetrate into the glacier on an intergranular scale except possibly near the surface. The existence of conduit-like features in several cores suggests that much melt water ran nevertheless penetrate the ice locally without large-scale lateral movements along the glacier surface. The observed profile of ice temperature indicates that the intergranular water flux may be much smaller than the upper limit determined from the core samples.

scholarly journals Some Observations on the Behavior of the Liquid and Gas Phases in Temperate Glacier Ice

1975 ◽  
Vol 14 (71) ◽  
pp. 213-233 ◽  
Author(s):  
C. F. Raymond ◽  
W. D. Harrison
Keyword(s):  
Large Scale ◽  
Water Flux ◽  
Coarse Grained ◽  
Glacier Surface ◽  
Cross Sectional ◽  
Gas Phases ◽  
Upper Limit ◽  
Melt Water ◽  
Glacier Ice ◽  
Typical Summer

Microscopic and textural observations were made on ice samples cored from Blue Glacier slightly below the equilibrium line to depths of 60 m. Observations were started within a few minutes after collection. Water was found in veins along three-grain intersections, in lenses on grain boundaries and in irregular shapes. Gas was found in bubbles in the interior of crystals, in bubbles touching veins, and locally in veins. Vein sizes showed some spread; average cross-sectional area was about 7 × 10−4 mm2 with no discernible, trend with texture or depth except within 7 m of the surface. Before the samples were examined they could have experienced a complex relaxation which could have changed them significantly. As a result it is not possible to determine the in situ size of veins, but an upper limit can be determined. Also it is not possible to predict intergranular water flux per unit area, but 1 × 10−1 m a−1 represents an upper limit. In coarse-grained ice the water flux density is likely to be even smaller, because of a low density of veins, and blocking by bubbles. This indicates that only a very small fraction of the melt-water production on a typical summer day can penetrate into the glacier on an intergranular scale except possibly near the surface. The existence of conduit-like features in several cores suggests that much melt water can nevertheless penetrate the ice locally without large-scale lateral movements along the glacier surface. The observed profile of ice temperature indicates that the intergranular water flux may be much smaller than the upper limit determined from the core samples.

scholarly journals Formation of band ogives and associated structures at Bas Glacier d’Arolla, Valais, Switzerland

2002 ◽  
Vol 48 (161) ◽  
pp. 287-300 ◽  
Author(s):  
Becky Goodsell ◽  
Michael J. Hambrey ◽  
Neil F. Glasser
Keyword(s):  
Ground Penetrating Radar ◽  
Three Dimensional ◽  
Shear Zones ◽  
Glacier Surface ◽  
Glacier Tongue ◽  
Basal Ice ◽  
Planar Structures ◽  
Geophysical Techniques ◽  
Reverse Faulting ◽  
Ground Penetrating

AbstractStructural glaciological, sedimentological and geophysical techniques are used to provide new insight concerning the formation of band ogives and associated structures at Bas Glacier d’Arolla, Switzerland. Sedimentary stratification, crevasse traces and transverse foliation are identified as planar structures in the lower icefall and glacier tongue. Stratification and crevasse traces are progressively deformed into, and enhance, the transverse foliation found in the glacier tongue. Three-dimensional geometry has been defined using ground-penetrating radar, which portrays four main characteristics: (i) deep reflectors interpreted as the ice/bed interface, (ii) alternating reflection-rich and reflection-poor zones interpreted as ogives, (iii) up-glacier-dipping reflectors, interpreted as planar structures, and (iv) down-glacier-dipping reflectors of uncertain origin. At the glacier surface, each band ogive consists of a light and dark band. The dark bands contain more intense foliation which, on differential weathering, traps fine debris. Clasts and clear ice of basal character within dark ogive bands suggest that basal ice has been raised to the glacier surface. The most applicable model for the formation of band ogives at Bas Glacier d’Arolla is a refinement of Posamentier’s (1978) “reverse faulting” hypothesis. In this context, multiple shear zones are formed, through which basal ice is uplifted to the glacier surface to produce the dark, foliated ogive bands. This model fits observations reported from other glaciers with band ogives.

scholarly journals Thermal conditions at the bed of the Laurentide ice sheet in Maine during deglaciation: implications for esker formation

2007 ◽  
Vol 53 (183) ◽  
pp. 646-658 ◽  
Author(s):  
Roger LeB. Hooke ◽  
James Fastook
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Thermal Conditions ◽  
Temperature Gradients ◽  
Laurentide Ice Sheet ◽  
Glacier Surface ◽  
Basal Ice ◽  
Viscous Heat ◽  
Additional Water ◽  
The University

The University of Maine Ice Sheet Model was used to study basal conditions during retreat of the Laurentide ice sheet in Maine. Within 150 km of the margin, basal melt rates average ∼5 mm a−1 during retreat. They decline over the next 100 km, so areas of frozen bed develop in northern Maine during retreat. By integrating the melt rate over the drainage area typically subtended by an esker, we obtained a discharge at the margin of ~1.2 m3 s-1. While such a discharge could have moved the material in the Katahdin esker, it was likely too low to build the esker in the time available. Additional water from the glacier surface was required. Temperature gradients in the basal ice increase rapidly with distance from the margin. By conducting upward into the ice all of the additional viscous heat produced by any perturbation that increases the depth of flow in a flat conduit in a distributed drainage system, these gradients inhibit the formation of sharply arched conduits in which an esker can form. This may explain why eskers commonly seem to form near the margin and are typically segmented, with later segments overlapping onto earlier ones.

scholarly journals Devising a procedure for assessing the subgrade compaction degree based on the propagation rate of elastic waves

2021 ◽  
Vol 1 (5 (109)) ◽  
pp. 6-15
Author(s):  
Vitalii Kovalchuk ◽  
Ivan Kravets ◽  
Olga Nabochenko ◽  
Arthur Onyshchenko ◽  
Olexander Fedorenko ◽  
...  
Keyword(s):  
Elastic Waves ◽  
Propagation Rate ◽  
Coarse Sand ◽  
Technical Condition ◽  
The Body ◽  
Coarse Grained ◽  
Subgrade Soils ◽  
Subgrade Soil ◽  
Study Results ◽  
Characteristic Features

This paper reports the analysis of the methods for estimating the technical condition of the subgrade underneath a constructed railroad track or road during its operation. The study results have proven that the issue related to monitoring and controlling high-quality compaction of a heterogeneous subgrade remains relevant and requires the construction of reliable experimental methods for assessing the subgrade degree of compaction. A procedure for determining the compaction of subgrade in the laboratory has been devised, based on inertial microcomputer technologies, which makes it possible to assess the degree of compaction of subgrade soils depending on the propagation rate of an impact's elastic waves. An experimental study has been performed into the propagation rate of elastic waves across a homogeneous subgrade made of coarse-grained sand and a heterogeneous subgrade made of coarse sand with a layer of clay in the middle of the prism. The study results established that the propagation rate of an elastic wave in a heterogeneous subgrade accepts a lower value than the rate of wave propagation in a homogeneous subgrade. Through the dynamic interpretation, by using a discriminant statistical analysis, the characteristic features have been defined in the distribution of accelerations in the body of the homogeneous and heterogeneous subgrade, depending on the degree of compaction, which would make it possible to monitor the state of the subgrade during operation. As the degree of the subgrade soil compaction affects the technical condition of roads

scholarly journals Characteristics of Striae and Clast Shape in Glacial and Non-Glacial Environments

2021 ◽  
Author(s):  
◽  
Clifford Barrie Atkins
Keyword(s):  
Mass Movement ◽  
Coarse Grained ◽  
Significant Advance ◽  
Tectonic Deformation ◽  
Glacial Origin ◽  
Wide Range ◽  
Glacial Environments ◽  
Glacial Processes ◽  
Characteristic Features ◽  
Different Origins

<p>Linear abrasion features on rock surfaces are produced by interacting rock particles in relative motion. The most common examples are striae produced by temperate glaciers, and as a consequence, striae have long been used as a means of identifying the passage of past glaciers. However, there are many non-glacial processes that can produce striae. These have been sporadically documented in the geological literature but have failed to make a lasting impression on the wider Earth Sciences community. These non-glacial processes include tectonic deformation, meltwater flow, non-glacial ice, wind action, volcanic blasting, mass movements of rock debris, among many others. Many produce coarse-grained deposits similar in character to glacial tills and there are several instances where non-glacial deposits and striae have been misinterpreted as glacial in origin. This thesis examines linear abrasion features (mostly striae) from five different environments, three glacial (temperate, polythermal and cold) and two non-glacial environments (mass movement and tectonic) to characterise the striae from different origins. The aim was to assess if there are readily observable and measurable differences in striae character between environments and to develop field-based criteria that allow a sound judgement of their origin in the geological record. Over 760 measurements of individual striae were made (orientation and size) on around 20 representative clasts and characteristic features of about 50 striated clasts from the various environments are illustrated in an "Atlas of linear abrasion features". In addition clast shape and striae occurrence were measured on 1260 clasts from deposits and about 100 bedrock linear abrasions from a cold-based glacier were recorded. The results show that some striae are diagnostic of certain environments but a combination of clast shape and striae characteristics is the most reliable method of correctly interpreting coarse-grained deposits with striated clasts. Results also highlight the wide range of striae characteristics within each environment and the importance of lithology in striae generation. This is evident even within the well-known temperate glacial environment where there is a marked contrast between striae formed within a thick debris layer and those formed in thin debris-rich basal ice. There appears to be little difference in striae formed by temperate and polyhermal glaciers, but glacial striae are readily distinguishable from striae found in various mass movement deposits or tectonically deformed conglomerates. Glacial striae tend to be sub-parallel to the clast long axes and show a high density on individual surfaces, whereas those in non-glacial origin typically show a lower density of slightly shorter, wider striae and show either no preferred orientation or weak grouping. The survivability of glacial abrasion features of clasts once they have entered a fluvial system has been assessed in a small South Island glacier fed river. This has provided a basis for estimating the proximity of a glaciofluvial deposit to the glacier front. Striae are found to survive only 1 to 2 km and glacial facets are mostly removed within 6 km. The study has also documented previously undescribed linear abrasion features from a cold-based glacier in Antarctica. This discovery is a significant advance in understanding cold glacial processes, and has provided new criteria for recognising the passage of cold-based glaciers in polar areas or regions where cold-based ice may have existed in the past.</p>

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