Fast moving palaeo-ice masses within the European Alpine Ice Cap (EAIC) during the Last Glacial M... more Fast moving palaeo-ice masses within the European Alpine Ice Cap (EAIC) during the Last Glacial Maximum within the large valleys of the European Alps are likely comparable in terms of their subglacial conditions to ice streams that drained the larger Quaternary Ice Sheets in Europe and North America. Unlike these continental-style ice sheets, the ice inundating the European Alps, like the Cordilleran Ice Sheet in North America, flowed through confined bedrock valleys that, at close to the glacial maximum, acted in a similar manner to ice streams. Little mention exists as to the extent of soft sediment basal deformation in these deep valleys although increasingly such conditions are known from several parts of the EAIC. The Drau (Drava) ice stream during the Alpine Last Glacial Maximum (= Würmian Pleniglacial, ~ 29 – ~20 ka) as well as small tributary glacier during the early Lateglacial phase of ice decay (~20 – 19 ka) appears as a temperate, fast-moving ice mass that would likely b...
A better understanding of glacial transport and depositional environments has resulted from micro... more A better understanding of glacial transport and depositional environments has resulted from micromorphological studies of glacial sediments over the last several decades. The past-producing Pb-Zn mine at Pine Point, Northwest Territories, has >20 m of continuous diamicton overlying low-relief Paleozoic bedrock, which provides a unique opportunity to further the investigation of micromorphology in the study of glacial sediments, in particular the sustained depositional record versus the erosional records of various ice-flow trajectories and how that information can help document indicator mineral dispersal. Pit-K62 at Pine Point has a ~23 m section of diamicton from which 19 samples were collected and thin sections prepared. This report describes sample collection, thin section production and analysis, and microstructure identification of each of these 19 samples. These results will be combined with glacial stratigraphy and indicator-mineral work previously completed for the area ...
... past several years, Loris Gasparotto and Mike Lozon for their special cartographic skills, to... more ... past several years, Loris Gasparotto and Mike Lozon for their special cartographic skills, to Gail Elliot, Virginia Wagg and Diane Gadoury for word processing and scanning skills, Shara Lee Foster for painstakingly reading through revised chapters and to Rebecca Menzies who ...
Micromorphology and microsedimentology have become invaluable tools in the study of glacial sedim... more Micromorphology and microsedimentology have become invaluable tools in the study of glacial sediments. In the recognition, description and interpretation of microfeatures, and, in particular, microstructures within these sediments, it has become possible to interpret the significance of these microfeatures. These microfeatures are symptomatic of conditions during and following glacial deposition and record the processes of erosion, transport, repeated depositional histories and postdepositional diagenesis. A range of glacial sediments and tills are discussed and examples, typifying these sediment types, presented. New methods of study and innovative ideas on improving our understanding of glacial sediments at the microscale are presented and discussed.
Abstract: The Ross Sea embayment is the outlet for one-third of all Antarctic ice flow, receiving... more Abstract: The Ross Sea embayment is the outlet for one-third of all Antarctic ice flow, receiving input from both East and West Antarctica. Marine-based ice streams, whose stability is susceptible to global sea-level changes, expand and contract across the Ross Sea continental shelf, eroding and deforming the substrate and transporting sediment subglacially. Deposits from the Last Glacial Maximum in the western Ross Sea provide an opportunity to investigate paleo-ice stream processes using sediment cores associated with glacial landforms. This study combines micro-to macro-sedimentological analyses to characterize lithofacies that represent a glacial-interglacial succession. We observe subtle variations in sediment properties within the subglacial unit that suggest till heterogeneity. Physical characteristics that vary both laterally and vertically indicates different sediment response to glacial stress, resulting in non-pervasive deformation within the till. These observations are consistent with the interpretation that a dynamic ice sheet with variable flow regimes existed across the Ross Sea during the Last Glacial Maximum. Further microscopic evidence of dynamic subglacial conditions includes sediment aggregates preserved as discrete grains in the form of soft sediment clasts or till pellets. Till pellet-rich sediment is commonly associated with the transition from a subglacial to proximal glaciomarine environment, although here we demonstrate they are widespread in both facies. Their widespread occurrence downcore and distribution across the continental shelf provides sedimentological evidence of a deformable bed beneath an ice stream during the Last Glacial Maximum. Ultimately, better tools for discriminating between glacial deposits will allow for more detailed reconstructions of ice-sheet history, and thus determine the forcing mechanisms to which the ice is responding.
Abstract Microsedimentological analyses were used to examine the first 56 m of a 500 m core near ... more Abstract Microsedimentological analyses were used to examine the first 56 m of a 500 m core near Heidelberg, Germany, in the Upper Rhine Valley. This core chronostratigraphically stretches from present day to 450 ka and includes proxy evidence supporting the presence of Wurmian, Eemian and likely components of the Riss and Hoβkirch Stages. The sediment in the core reflects the geomorphic, biotic, pedogenic, and climatic processes. The sediments were deposited in a fluvial environment, at times, within a broad floodplain in the main channel, and also, at other times, some distance from the main river. These upper sediments act as indirect proxy evidence that indicate changes in climate over time illustrative of cool periglacial tundra-like conditions and of milder forested temperate environments from Hoβkirch to present day times. Within the sediments evidence can be found of an interglacial fossil soil followed later by a Holocene temperate climate up to present day. A strong link can be ascertained between macro- and micro-stratigraphic evidence, the latter revealing detailed and invaluable sources of information. This analysis permits the reconstruction of past climate and paleoenvironmental conditions. The application of microsedimentological analyses to the Mannheim Formation reveals a store of data that has been largely hidden when using only macro-sedimentological methods.
Abstract A key aspect of all subglacial tills is the nature and form of microstructures present. ... more Abstract A key aspect of all subglacial tills is the nature and form of microstructures present. Microstructures are symptomatic of repeated deformation phases prior to, during, and after emplacement. Critical to understanding microstructures in subglacial tills are the probable interrelationship that exists between all of these structures. In analyzing subglacial tills a kinematic deformation relationship can be observed existing between all microstructures. Based upon the rheological conditions at the ice basal interface, a close evolving paleo-strain link can be established that relates levels of deformation to all subglacial till microstructures. As subglacial till undergoes strain during transport and emplacement involving fluctuating conditions of porewater content, percentage of clays present, and changing thermal circumstances, a series of microstructures sequentially evolve. Initially, brittle edge-to-edge grain events occur, followed by grains stack development, often allied closely in time, with microshear formation as the sediment deforms, and is consequently followed by the development of ductile rotation structures. Likewise, deformation bands, shear zone formation, and typically “isolated” domains form. As strain and other factors vary over time so many of these microstructures may be obliterated, altered, or re-oriented. Much remains to be understood regarding paleo-strain conditions and subglacial deformation but a first step has been establishing this temporal sequence of microstructure stage development and thus achieving a theory that unifies these disparate microstructures observed in all subglacial tills.
The macro- and micro-sedimentology of a supraglacial melt-out till forming at the Matanuska Glaci... more The macro- and micro-sedimentology of a supraglacial melt-out till forming at the Matanuska Glacier was examined in relationship to the properties of the stratified basal zone ice and debris from which it is originating. In situ melting of the basal ice has produced a laminated to bedded diamicton consisting mainly of silt. Macroscopic properties include: discontinuous laminae and beds; lenses of sand, silt aggregates and open-work gravel; deformed and elongate clasts of clay; widely dispersed pebbles and cobbles, those that are prolate usually with their long axes subparallel to parallel to the bedding. Evidence for deformation is absent except for localized bending of beds over or under rock clasts. Microscopic properties are a unique element of this work and include: discontinuous lineations; silt to granule size laminae; prolate coarse sand and rock fragments commonly with their long axis subparallel to bedding; subangular to subrounded irregular shaped clay clasts often appearing as bands; sorted and unsorted silt to granule size horizons, sometimes disrupted by pore-water pathways. Limited deformation occurs around rock clasts and thicker parts of lamina. This study shows that in situ melting of debris-rich basal ice can produce a laminated and bedded diamicton that inherits and thereby preserves stratified basal ice properties. Production and preservation of supraglacial melt-out till require in situ melting of a stagnant, debris-rich basal ice source with a low relief surface that becomes buried by a thick, stable, insulating cover of ice-marginal sediment. Also required are a slow melt rate and adequate drainage to minimize pore-water pressures in the till and overlying sediment cover to maintain stability and uninterrupted deposition. Many modern and ancient hummocky moraines down glacier of subglacial overdeepenings probably meet these process criteria and their common occurrence suggests that both modern and pre-modern supraglacial melt-out tills may be more common than previously thought.
Recent studies have shown the important influence of pore-water movement and the subglacial therm... more Recent studies have shown the important influence of pore-water movement and the subglacial thermal regime on processes of erosion and deposition at the subglacial interface. the influence of migrating freezing fronts within subglacial material has been largely ignored. the phenomena of ice-water interface processes will be examined and their relevance to subglacial processes illustrated. four case studies are presented that deal with the various effects that freezing-front movement may have on pore water, consolidation, shear strength, and likely diagenetic characteristics of subglacial deposits. the influence upon erosional and depositional processes will be outlined, and a mechanism related to potential surge-like conditions within the subglacial zone postulated.
Most drumlins are composed of till that appears similar in all characteristics to non-drumlin til... more Most drumlins are composed of till that appears similar in all characteristics to non-drumlin till. Evidence, however, in the form of till layer sequences and from palaeomagnetic Koenigsberger ratios indicate that drumlin till may have a slightly higher pore-water content at the time of lodgement than nondrumlin till. In order that deposited till remains at the ice-glacier-bed interface to initiate drumlin formation, it must undergo rapid geotechnical changes whereby its pore-water content is dissipated thereby increasing the shear strength of the till. Two mechanisms of pore-water removal are possible. Firstly, pore water may be removed from localized patches within a mobile layer of till at the ice-glacier-bed interface, thus creating nuclei of higher-strength till around which deforming till may adhere. Secondly, removal of water initially from the thin water film at the base of a glacier may result in increased pressure melting of the ice leading to till melt-out and subsequent ...
Fast moving palaeo-ice masses within the European Alpine Ice Cap (EAIC) during the Last Glacial M... more Fast moving palaeo-ice masses within the European Alpine Ice Cap (EAIC) during the Last Glacial Maximum within the large valleys of the European Alps are likely comparable in terms of their subglacial conditions to ice streams that drained the larger Quaternary Ice Sheets in Europe and North America. Unlike these continental-style ice sheets, the ice inundating the European Alps, like the Cordilleran Ice Sheet in North America, flowed through confined bedrock valleys that, at close to the glacial maximum, acted in a similar manner to ice streams. Little mention exists as to the extent of soft sediment basal deformation in these deep valleys although increasingly such conditions are known from several parts of the EAIC. The Drau (Drava) ice stream during the Alpine Last Glacial Maximum (= Würmian Pleniglacial, ~ 29 – ~20 ka) as well as small tributary glacier during the early Lateglacial phase of ice decay (~20 – 19 ka) appears as a temperate, fast-moving ice mass that would likely b...
A better understanding of glacial transport and depositional environments has resulted from micro... more A better understanding of glacial transport and depositional environments has resulted from micromorphological studies of glacial sediments over the last several decades. The past-producing Pb-Zn mine at Pine Point, Northwest Territories, has >20 m of continuous diamicton overlying low-relief Paleozoic bedrock, which provides a unique opportunity to further the investigation of micromorphology in the study of glacial sediments, in particular the sustained depositional record versus the erosional records of various ice-flow trajectories and how that information can help document indicator mineral dispersal. Pit-K62 at Pine Point has a ~23 m section of diamicton from which 19 samples were collected and thin sections prepared. This report describes sample collection, thin section production and analysis, and microstructure identification of each of these 19 samples. These results will be combined with glacial stratigraphy and indicator-mineral work previously completed for the area ...
... past several years, Loris Gasparotto and Mike Lozon for their special cartographic skills, to... more ... past several years, Loris Gasparotto and Mike Lozon for their special cartographic skills, to Gail Elliot, Virginia Wagg and Diane Gadoury for word processing and scanning skills, Shara Lee Foster for painstakingly reading through revised chapters and to Rebecca Menzies who ...
Micromorphology and microsedimentology have become invaluable tools in the study of glacial sedim... more Micromorphology and microsedimentology have become invaluable tools in the study of glacial sediments. In the recognition, description and interpretation of microfeatures, and, in particular, microstructures within these sediments, it has become possible to interpret the significance of these microfeatures. These microfeatures are symptomatic of conditions during and following glacial deposition and record the processes of erosion, transport, repeated depositional histories and postdepositional diagenesis. A range of glacial sediments and tills are discussed and examples, typifying these sediment types, presented. New methods of study and innovative ideas on improving our understanding of glacial sediments at the microscale are presented and discussed.
Abstract: The Ross Sea embayment is the outlet for one-third of all Antarctic ice flow, receiving... more Abstract: The Ross Sea embayment is the outlet for one-third of all Antarctic ice flow, receiving input from both East and West Antarctica. Marine-based ice streams, whose stability is susceptible to global sea-level changes, expand and contract across the Ross Sea continental shelf, eroding and deforming the substrate and transporting sediment subglacially. Deposits from the Last Glacial Maximum in the western Ross Sea provide an opportunity to investigate paleo-ice stream processes using sediment cores associated with glacial landforms. This study combines micro-to macro-sedimentological analyses to characterize lithofacies that represent a glacial-interglacial succession. We observe subtle variations in sediment properties within the subglacial unit that suggest till heterogeneity. Physical characteristics that vary both laterally and vertically indicates different sediment response to glacial stress, resulting in non-pervasive deformation within the till. These observations are consistent with the interpretation that a dynamic ice sheet with variable flow regimes existed across the Ross Sea during the Last Glacial Maximum. Further microscopic evidence of dynamic subglacial conditions includes sediment aggregates preserved as discrete grains in the form of soft sediment clasts or till pellets. Till pellet-rich sediment is commonly associated with the transition from a subglacial to proximal glaciomarine environment, although here we demonstrate they are widespread in both facies. Their widespread occurrence downcore and distribution across the continental shelf provides sedimentological evidence of a deformable bed beneath an ice stream during the Last Glacial Maximum. Ultimately, better tools for discriminating between glacial deposits will allow for more detailed reconstructions of ice-sheet history, and thus determine the forcing mechanisms to which the ice is responding.
Abstract Microsedimentological analyses were used to examine the first 56 m of a 500 m core near ... more Abstract Microsedimentological analyses were used to examine the first 56 m of a 500 m core near Heidelberg, Germany, in the Upper Rhine Valley. This core chronostratigraphically stretches from present day to 450 ka and includes proxy evidence supporting the presence of Wurmian, Eemian and likely components of the Riss and Hoβkirch Stages. The sediment in the core reflects the geomorphic, biotic, pedogenic, and climatic processes. The sediments were deposited in a fluvial environment, at times, within a broad floodplain in the main channel, and also, at other times, some distance from the main river. These upper sediments act as indirect proxy evidence that indicate changes in climate over time illustrative of cool periglacial tundra-like conditions and of milder forested temperate environments from Hoβkirch to present day times. Within the sediments evidence can be found of an interglacial fossil soil followed later by a Holocene temperate climate up to present day. A strong link can be ascertained between macro- and micro-stratigraphic evidence, the latter revealing detailed and invaluable sources of information. This analysis permits the reconstruction of past climate and paleoenvironmental conditions. The application of microsedimentological analyses to the Mannheim Formation reveals a store of data that has been largely hidden when using only macro-sedimentological methods.
Abstract A key aspect of all subglacial tills is the nature and form of microstructures present. ... more Abstract A key aspect of all subglacial tills is the nature and form of microstructures present. Microstructures are symptomatic of repeated deformation phases prior to, during, and after emplacement. Critical to understanding microstructures in subglacial tills are the probable interrelationship that exists between all of these structures. In analyzing subglacial tills a kinematic deformation relationship can be observed existing between all microstructures. Based upon the rheological conditions at the ice basal interface, a close evolving paleo-strain link can be established that relates levels of deformation to all subglacial till microstructures. As subglacial till undergoes strain during transport and emplacement involving fluctuating conditions of porewater content, percentage of clays present, and changing thermal circumstances, a series of microstructures sequentially evolve. Initially, brittle edge-to-edge grain events occur, followed by grains stack development, often allied closely in time, with microshear formation as the sediment deforms, and is consequently followed by the development of ductile rotation structures. Likewise, deformation bands, shear zone formation, and typically “isolated” domains form. As strain and other factors vary over time so many of these microstructures may be obliterated, altered, or re-oriented. Much remains to be understood regarding paleo-strain conditions and subglacial deformation but a first step has been establishing this temporal sequence of microstructure stage development and thus achieving a theory that unifies these disparate microstructures observed in all subglacial tills.
The macro- and micro-sedimentology of a supraglacial melt-out till forming at the Matanuska Glaci... more The macro- and micro-sedimentology of a supraglacial melt-out till forming at the Matanuska Glacier was examined in relationship to the properties of the stratified basal zone ice and debris from which it is originating. In situ melting of the basal ice has produced a laminated to bedded diamicton consisting mainly of silt. Macroscopic properties include: discontinuous laminae and beds; lenses of sand, silt aggregates and open-work gravel; deformed and elongate clasts of clay; widely dispersed pebbles and cobbles, those that are prolate usually with their long axes subparallel to parallel to the bedding. Evidence for deformation is absent except for localized bending of beds over or under rock clasts. Microscopic properties are a unique element of this work and include: discontinuous lineations; silt to granule size laminae; prolate coarse sand and rock fragments commonly with their long axis subparallel to bedding; subangular to subrounded irregular shaped clay clasts often appearing as bands; sorted and unsorted silt to granule size horizons, sometimes disrupted by pore-water pathways. Limited deformation occurs around rock clasts and thicker parts of lamina. This study shows that in situ melting of debris-rich basal ice can produce a laminated and bedded diamicton that inherits and thereby preserves stratified basal ice properties. Production and preservation of supraglacial melt-out till require in situ melting of a stagnant, debris-rich basal ice source with a low relief surface that becomes buried by a thick, stable, insulating cover of ice-marginal sediment. Also required are a slow melt rate and adequate drainage to minimize pore-water pressures in the till and overlying sediment cover to maintain stability and uninterrupted deposition. Many modern and ancient hummocky moraines down glacier of subglacial overdeepenings probably meet these process criteria and their common occurrence suggests that both modern and pre-modern supraglacial melt-out tills may be more common than previously thought.
Recent studies have shown the important influence of pore-water movement and the subglacial therm... more Recent studies have shown the important influence of pore-water movement and the subglacial thermal regime on processes of erosion and deposition at the subglacial interface. the influence of migrating freezing fronts within subglacial material has been largely ignored. the phenomena of ice-water interface processes will be examined and their relevance to subglacial processes illustrated. four case studies are presented that deal with the various effects that freezing-front movement may have on pore water, consolidation, shear strength, and likely diagenetic characteristics of subglacial deposits. the influence upon erosional and depositional processes will be outlined, and a mechanism related to potential surge-like conditions within the subglacial zone postulated.
Most drumlins are composed of till that appears similar in all characteristics to non-drumlin til... more Most drumlins are composed of till that appears similar in all characteristics to non-drumlin till. Evidence, however, in the form of till layer sequences and from palaeomagnetic Koenigsberger ratios indicate that drumlin till may have a slightly higher pore-water content at the time of lodgement than nondrumlin till. In order that deposited till remains at the ice-glacier-bed interface to initiate drumlin formation, it must undergo rapid geotechnical changes whereby its pore-water content is dissipated thereby increasing the shear strength of the till. Two mechanisms of pore-water removal are possible. Firstly, pore water may be removed from localized patches within a mobile layer of till at the ice-glacier-bed interface, thus creating nuclei of higher-strength till around which deforming till may adhere. Secondly, removal of water initially from the thin water film at the base of a glacier may result in increased pressure melting of the ice leading to till melt-out and subsequent ...
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