Patterns of deformation within a subglacial shear zone: Implications for palaeo-ice stream bed evolution

Narloch, Włodzimierz; Phillips, Emrys; Piotrowski, Jan A.; Ćwiek, Mateusz

doi:10.1016/j.sedgeo.2019.105569

Cited by 13 publications

(7 citation statements)

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“…8), which suggests that cumulative strain was unevenly distributed and probably varied time‐transgressively as the till accreted, or that there was deformation partitioning at the microscale. In general, differences in strain may result from variations in till rheology caused by different clay contents or particle sorting (Underhill and Woodcock, 1987; Hopkins et al, 2019), or porewater pressure variations that would affect the style of deformation (van der Meer et al, 2003; Piotrowski et al, 2006; Menzies et al, 2016; Phillips et al, 2018; Narloch et al, 2020). The different orientations of microshears may also result from rotation of the stress field (Ahlgren, 2001; Shipton and Cowie, 2001) but this is typically associated with pebble‐ or boulder‐sized clasts.…”

Section: Discussionmentioning

confidence: 99%

“…Menzies, 1998; van der Meer and Menzies, 2011). Thus, most of the investigated microstructures comprise: (i) microshears, defined as shear localization fabrics (Tembe et al, 2010) which can also be represented by at least three aligned elongated grains (Larsen et al, 2007; Narloch et al, 2020); (ii) circular structures (also referred to as turbate or rotational structures; Menzies and Reitner, 2016; Menzies et al, 2019; Narloch et al, 2020), which are circular arrangements of grains indicative of ductile deformation (van der Meer, 1993; Menzies and Zaniewski, 2003; Piotrowski et al, 2006); (iii) grain stacks, defined as alignments (bridges) of at least five grains of equal (Iverson et al, 1996; Larsen et al, 2007) or various sizes (Menzies et al, 2016) oriented obliquely to the shear direction (Iverson et al, 1996; Larsen et al, 2007); (iv) crushed grains, which in our thin sections typically are internally fractured grains that probably originate in a non‐ductile environment (Rawling and Goodwin, 2003; Menzies et al, 2016); and (v) till pellets and domains, which are inclusions or zones characterized by uniform textural properties different from the surrounding sediment (van der Meer, 1993; Menzies, 2000b). Other microstructures were noted occasionally, such as shear zones and polygonal structures (sill and dyke structures of Menzies et al, 2016).…”

Section: Methodsmentioning

confidence: 99%

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Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Hermanowski

Piotrowski

Duda

2020

J Quaternary Science

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Deciphering the relationships between streamlined subglacial landforms and deposits therein helps to constrain the dynamics of past ice sheets. Here we present microstructural analyses of till from the largest drumlin field in the North European Lowland generated by a major palaeo-ice stream of the Scandinavian Ice Sheet. Data derived from thin sections and X-ray microtomography (μCT) reveal multiple microstructures including microshears, circular structures, grain stacks and crushed grains. Long axes of micro-clasts measured in thin sections are directionally clustered and have low, down-ice-oriented dip angles. Some samples reveal subordinate clustering oriented at high angles to the main direction. The μCT data show low clustering strengths of clasts and no systematic fabric pattern in the entire set of samples. There is no correspondence between the clast orientations and the directions of drumlin long axes, suggesting that the till is antecedent in relation to the drumlin-shaping process. The observations indicate spatially and temporally variable, shallow-seated brittle and ductile deformation controlled by porewater pressure fluctuations and generated time-transgressively parallel to till accretion. Consistently with previous studies, the data suggest that the Stargard drumlins are erosional remnants of a pre-existing terrain shaped by material removal from the inter-drumlin areas.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Hermanowski

Piotrowski

Duda

2020

J Quaternary Science

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“…The study area underwent glaciotectonic modelling [87][88][89] and a postglacial rebound, glacial isostatic adjustment [90], which undoubtedly modified non-alluvial protrusions, or even formed these structures from the relatively flat preglacial surface (Figure 9). The present state of the art in science is not enough to explain or even understand the origin of the specific geological pattern of river channel flowing atop bedrock protrusion we present in this study.…”

Section: Resultsmentioning

confidence: 99%

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

Bihałowicz

Wierzbicki

2021

Water

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We study cross-sections on the Detailed Geological Map of Poland (SMGP) to find a geologic and geomorphic pattern under river valleys in Poland. The pattern was found in 20 reaches of the largest Polish rivers (Odra, Warta, Vistula, Narew, and Bug) located in the European Lowland, in the landscape of old (Pleistocene, Saalian) glacial high plains extending between the Last Glacial Maximum (LGM) moraines on the North and the Upland on the South. The Upland was slightly folded and up-faulted during Alpine orogeny together with the thrust of Carpathian nappes and the uplift of Tatra Mts. and Sudetes. The found pattern is an alluvial river with broad Holocene floodplain and the channel developed atop the protrusion of bedrock (Jurassic, Cretaceous limestones, marlstones, sandstones) or non-alluvial, cohesive, overconsolidated sediments resistant to erosion (glacial tills, lacustrine or “ice-dammed lake” clays) of Cenozoic (Paleogene, Neogene, Quaternary—Elsterian). We regard the sub-alluvial protrusion as the limit of river incision and scour. It cannot be determined why the river flows atop these protrusions, in opposition to “differential erosion”, a geomorphology principle. We assume it is evidence of geological flood control. We propose an environmental and geomorphological framework for the hydrotechnical design of instream river training.

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“…As in other locations sediment beneath an ice mass exhibits this form of transport and emplacement mechanism. Once a critical shear stress is reached locally and acts upon the saturated underlying unfrozen sediment, sediment motion can take place (Walter et al, 2014;Phillips et al, 2018;Narloch et al, 2020). Within the sediment, shear zones are likely to form and, at least temporally, effective shear within microscale shear bands (deformation bands) decreases leading to mobilization (Schultz and Siddharthan, 2005;Ballas et al, 2015;Fossen et al, 2017;Brandes et al, 2018;Philit et al, 2018;Carey et al, 2019;Menzies and Reitner, 2019).…”

Section: Discussion Of the Subglacial Conditionsmentioning

confidence: 99%

“…The Alpine glaciers acted close to the glacial maximum in a manner similar to ice streams in the North American Cordilleran Ice Sheet (Dowdeswell and Elverhøi, 2002;Walter et al, 2014;Seguinot et al, 2016Seguinot et al, , 2018Cohen et al, 2018;Stokes, 2018). Understanding subglacial conditions beneath ice streams remains incomplete (Cowan et al, 2012(Cowan et al, , 2014Walter et al, 2014;Davies et al, 2018;Narloch et al, 2020). The geological and rheological environments of ice stream beds play key roles in overall ice sheet dynamics.…”

Section: Introductionmentioning

confidence: 99%

Microsedimentology of tills near Ainet, Austria - were palaeo-ice streams in the European Alps underlain by soft deforming bed zones?

Reitner

Menzies

2020

Austrian Journal of Earth Sciences

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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 be underlain by soft deforming sediment. It is the underlying microsedimentology of parts of the Drau Valley catchment in the Lienz area of Austria that is the focus of this paper. The tills in the Isel Valley at Ainet reveal a detailed depiction of soft sediment deformation processes throughout the basal zones of this ice stream illustrative of temperate basal ice conditions and comparable to those tills of northern Austria under the Inn Ice Stream. The tills exhibit the characteristics of ongoing active soft-sediment deformation. The evidence from Ainet supports the contention that most likely subglacial processes beneath ice streams in the palaeo-EAIC were comparable to those today in Antarctica and in the Quaternary ice streams of the Cordilleran, Laurentide and North European Ice Sheets.

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Patterns of deformation within a subglacial shear zone: Implications for palaeo-ice stream bed evolution

Cited by 13 publications

References 71 publications

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Till kinematics in the Stargard drumlin field, NW Poland constrained by microstructural proxies

Rivers Try Harder. Reversed “Differential Erosion” as Geological Control of Flood in the Large Fluvial Systems in Poland

Microsedimentology of tills near Ainet, Austria - were palaeo-ice streams in the European Alps underlain by soft deforming bed zones?

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