Strain patterns in glacitectonically thrusted sediments and conditions during thrusting

Warbritton, Matthew J.; Iverson, Neal R.; Schomacker, Anders

doi:10.1016/j.jsg.2020.104064

Cited by 5 publications

(6 citation statements)

References 56 publications

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“…Deformation associated with transport is focused along thin, water-lubricated zones, often allowing thrust blocks of non-or weakly lithified and unfrozen sediment to move with only limited internal deformation [29,54]. Thrust stacks record repeated events of thrusting, hydrofracturing, and water-escape [58]. The initial detachment of soft sediment blocks in ice marginal zones took place in response to ice-push and gravity-spreading at the margins of retreating glaciers in Iceland [56], Denmark [58], and Sweden [59].…”

Section: Glacial Ripping and Rubble Till Formation In Other Sedimentary Rocksmentioning

confidence: 99%

“…Thrust stacks record repeated events of thrusting, hydrofracturing, and water-escape [58]. The initial detachment of soft sediment blocks in ice marginal zones took place in response to ice-push and gravity-spreading at the margins of retreating glaciers in Iceland [56], Denmark [58], and Sweden [59]. Beneath the retreating ice margin at Loch Eriboll, glaciological conditions were broadly similar, with high meltwater fluxes, episodically high groundwater pressure, and thin ice cover.…”

Section: Glacial Ripping and Rubble Till Formation In Other Sedimentary Rocksmentioning

confidence: 99%

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Glacial Ripping in Sedimentary Rocks: Loch Eriboll, NW Scotland

2021

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Glacial ripping is a newly recognized process sequence in which subglacial erosion is triggered by groundwater overpressure. Investigations in gneiss terrain in lowland Sweden indicate that ripping involves three stages of (i) hydraulic jacking, (ii) rock disruption under subglacial traction, and (iii) glacial transport of rock blocks. Evidence for each stage includes, respectively, dilated fractures with sediment fills, disintegrated roches moutonnées, and boulder spreads. Here, we ask: can glacial ripping also occur in sedimentary rocks, and, if so, what are its effects? The case study area is in hard, thinly bedded, gently dipping Cambrian quartz-arenites at Loch Eriboll, NW Scotland. Field surveys reveal dilated, sediment filled, bedding-parallel fractures, open joints, and brecciated zones, interpreted as markers for pervasive, shallow penetration of the quartz-arenite by water at overpressure. Other features, including disintegrated rock surfaces, boulder spreads, and monomict rubble tills, indicate glacial disruption and short distance subglacial transport. The field results together with cosmogenic isotope ages indicate that glacial ripping operated with high impact close to the former ice margin at Loch Eriboll at 17.6–16.5 ka. Glacial ripping thus can operate effectively in bedded, hard sedimentary rocks, and the accompanying brecciation is significant—if not dominant—in till formation. Candidate markers for glacial ripping are identified in other sedimentary terrains in former glaciated areas of the Northern Hemisphere.

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Section: Glacial Ripping and Rubble Till Formation In Other Sedimentary Rocksmentioning

confidence: 99%

Section: Glacial Ripping and Rubble Till Formation In Other Sedimentary Rocksmentioning

confidence: 99%

Glacial Ripping in Sedimentary Rocks: Loch Eriboll, NW Scotland

2021

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“…Deformation associated with transport is focused along thin, water-lubricated zones, often allowing thrust blocks of non-or weakly lithified and unfrozen sediment to move with only limited internal deformation [55] [30]. Thrust stacks record repeated events of thrusting, hydrofracturing and water-escape [59]. The initial detachment of soft sediment blocks in ice marginal zones took place in response of ice-push and gravity-spreading at the margins of retreating glaciers in Iceland [57], Denmark [59] and Sweden [60].…”

Section: Glacial Ripping and Rubble Till Formation In Other Sedimentary Rocksmentioning

confidence: 99%

“…Thrust stacks record repeated events of thrusting, hydrofracturing and water-escape [59]. The initial detachment of soft sediment blocks in ice marginal zones took place in response of ice-push and gravity-spreading at the margins of retreating glaciers in Iceland [57], Denmark [59] and Sweden [60]. Beneath the retreating ice margin at Loch Eriboll, glaciological conditions were broadly similar, with high meltwater fluxes, episodically high groundwater pressure and thin ice cover.…”

Section: Glacial Ripping and Rubble Till Formation In Other Sedimentary Rocksmentioning

confidence: 99%

Glacial Ripping in Sedimentary Rocks: Loch Eriboll, NW Scotland

Hall¹,

Mathers²,

Krabbendam³

2021

Preprint

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Glacial ripping is a newly recognized process sequence in which subglacial erosion is triggered by groundwater overpressure. Investigations in gneiss terrain in lowland Sweden indicate that ripping involves three stages of (i) hydraulic jacking, (ii) rock disruption under subglacial traction and (iii) glacial transport of rock blocks. Evidence for each stage includes, respectively, dilated fractures with sediment fills, disintegrated roches moutonnées and boulder spreads. Here we ask: can glacial ripping also occur in sedimentary rocks, and, if so, what are its effects? The case study area is in hard, thinly bedded, gently dipping Cambrian quartz-arenites at Loch Eriboll, NW Scotland. Field surveys reveal dilated, sediment filled, bedding-parallel fractures, open joints and brecciated zones, interpreted as markers for pervasive, shallow penetration of the quartz-arenite by water at over-pressure. Other features, including disintegrated rock surfaces, boulder spreads and monomict rubble tills, indicate glacial disruption and short distance subglacial transport. The field results, together with published cosmogenic isotope ages, indicate that glacial ripping operated with high impact close to the former ice margin at Loch Eriboll at 17.6-16.5 ka. Glacial ripping thus can operate effectively in bedded, hard sedimentary rocks and the accompanying brecciation is significant – if not dominant - in till formation. Candidate markers for glacial ripping are identified in other sedimentary terrains in former glaciated areas of the Northern Hemisphere.

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“…Using compressive strength tests on ice from Taylor Glacier Lawson (1996) showed that the addition of 10% debris by volume resulted in increases and decreases in ice viscosity. Although some studies have concluded that the addition of debris has no impact on the strength of the ice (Cuffey et al., 2000; Jacka et al., 2003; Moore, 2014), the general view is that ice containing sediment is expected to be stronger than adjacent ice and less susceptible to ductile deformation well below the freezing point (Moore, 2014; Warbritton et al., 2020). In an extensive review of the behavior of frozen debris Moore (2014) concluded that ice‐debris mixtures are more resistant to deformation at low temperatures than pure ice but that at temperatures closer to melting the growth of an interfacial water film can lead to profound weakening.…”

Section: Introductionmentioning

confidence: 99%

Deformation, Strength and Tectonic Evolution of Basal Ice in Taylor Glacier, Antarctica

Fitzsimons,

Samyn,

Lorrain

2024

JGR Earth Surface

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Observation and measurements of ice structure and deformation made in tunnels excavated into the margin of Taylor Glacier, a polythermal glacier in the McMurdo Dry Valleys of Antarctica, reveal a complex, rapidly deforming basal ice sequence. Displacement measurements in the basal ice, which is at a temperature of −18°C, together with the occurrence of cavities and slickenslides, suggest that sliding or rapid deformation in thin zones of high shear occurs at structural discontinuities within the basal zone. Strain measurements show that the highest strain rates occur in ice with average debris concentrations of 26% followed by ice with debris concentrations of around 12%. The lowest strain rates occur in clean bubbly ice that has very low debris concentrations (<0.02%). Deformation within the basal ice sequence is dominated by simple shear but disrupted by folding which results in shortening of the debris‐bearing ice followed by attenuation of the folds due to progressive simple shear which generates predominantly laminar basal ice structures. About 60% of glacier surface velocity can be attributed to deformation within the 4.5 m thick sequence of basal ice that was monitored for this study, and 15% of motion can be attributed to sliding or very localized shear. The combination of high debris concentrations and high strain rates in the debris‐bearing ice results in high rates of abrasion and the production of striated and facetted clasts typical of temperate glaciers, even though the basal ice is at a temperature of −18°C.

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Strain patterns in glacitectonically thrusted sediments and conditions during thrusting

Cited by 5 publications

References 56 publications

Glacial Ripping in Sedimentary Rocks: Loch Eriboll, NW Scotland

Glacial Ripping in Sedimentary Rocks: Loch Eriboll, NW Scotland

Glacial Ripping in Sedimentary Rocks: Loch Eriboll, NW Scotland

Deformation, Strength and Tectonic Evolution of Basal Ice in Taylor Glacier, Antarctica

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