Magnetic mineralogy and fabrics of small-scale glacial flutes, Múlajökull and Breiðamerkurjökull, Iceland

Ives, Libby R.W.

doi:10.31274/etd-180810-4583

Cited by 3 publications

(7 citation statements)

References 111 publications

(345 reference statements)

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“…4). Geomagnetic analyses conducted by Ives (2016) indicate that the magnetic signature of the Múlajökull tills is dominated by pseudosingle-domain and multidomain titanomagnetite, with some titanomaghemite, with grains primarily of silt size (see Appendix A). The AMS of these minerals is controlled by the grain morphology, such that their principal-susceptibility axes align with the morphological axes of the grains (Tarling and Hrouda, 1993).…”

Section: Ams Fabricsmentioning

confidence: 99%

Origin of the active drumlin field at Múlajökull, Iceland: New insights from till shear and consolidation patterns

McCracken

Iverson

Benediktsson

et al. 2016

Quaternary Science Reviews

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Stratigraphic and morphologic data previously collected from the forefield of Múlajökull, Iceland, suggest that its recent surge cycles are responsible for the formation of drumlins there and that their relief reflects both deposition on drumlins and erosion between them. We have tested these ideas and aspects of leading models of drumlin formation by studying past patterns of bed deformation and effective stress in basal tills of the glacier's forefield.Patterns of till strain indicated by the anisotropy of magnetic susceptibility (AMS) of ~2300 intact till samples indicate that till was deposited during shear deformation, with shearing azimuths and planes that conform to the drumlin morphology. Thus, till deposition occurred as drumlins grew, in agreement with LiDAR data indicating that the degree of aggradation of the glacier forefield is largest in areas subjected to the most surges. Previously described unconformities on the drumlin flanks, however, indicate that drumlin relief at Múlajökull has resulted, in part, from erosion. Given that the last surge deposited a till layer both on and between drumlins, a reasonable hypothesis is that erosion between drumlins occurred during normal (quiescent) flow of the glacier between surges. Densities of till samples, analyzed in conjunction with laboratory consolidation tests, indicate that effective stresses on the bed during such periods were on the order of 100 kPa larger between drumlins than within them, an observation consistent with subglacial channels at low water pressure occupying interdrumlin areas. Transport of sediment by turbulent flow in these channels or high effective stress adjacent to them causing enhanced till entrainment in ice or increased depths of bed deformation would promote the sediment flux divergence necessary to erode areas between drumlins. The observation that effective stresses were higher between drumlins than within them is the opposite of that presumed in leading models of drumlin formation. Moreover, the lack of AMS-fabric McCracken et al. 2 evidence of longitudinal compression in drumlin tills does not support some models of drumlin formation that invoke negative till-flux gradients in a deforming bed.

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Section: Ams Fabricsmentioning

confidence: 99%

Origin of the active drumlin field at Múlajökull, Iceland: New insights from till shear and consolidation patterns

McCracken

Iverson

Benediktsson

et al. 2016

Quaternary Science Reviews

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“…If the mineral grains in till become aligned (e.g., during shear), the orientation of the strongest anisotropy will be aligned in the same direction. The Kappabridge was also used to determine the magnetic mineralogy of the Múlajökull till (Ives, 2016), following the method described by . To determine magnetic mineralogy of the Múlajökull till, the Kappabridge measured the temperature at which the sediment lost its magnetic susceptibility, termed the Curie temperature.…”

Section: Ams Fabricsmentioning

confidence: 99%

“…AMS and clast fabrics indicating downglacier simple shear have long been documented in flutes (Eklund and Hart, 1996;Eyles et al, 2014), including those at Múlajökull (Ives, 2016 (Fig. 1.4), makes the crevasse-squeeze hypothesis especially viable.…”

Section: Deformation Of Sedimentsmentioning

confidence: 99%

“…1.1) makes direct correlation impossible, and crevasse patterns during surging likely differed significantly from current ones. A final argument against the flute hypothesis for the flow-parallel ridges is that flutes in the forefield of the glacier, described by Ives (2016) with diagnostic boulders at their heads, are narrower by at least a factor of three than the flow-parallel ridges. (Boulton, 1976;Benn, 1994).…”

Section: Deformation Of Sedimentsmentioning

confidence: 99%

“…This ambiguity indicates the importance of ancillary data in making interpretations. At Múlajökull, the lack of boulders at the heads of flow-parallel ridges and the quite different scale of nearby flutes with boulders at their heads (Ives, 2016) leave little doubt that the ridges are not flutes.…”

Section: Conceptual Model Of Ridge-network Formationmentioning

confidence: 99%

See 2 more Smart Citations

The formation of a rectilinear ridge network, Múlajökull, Iceland

Gadd

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Palaeogeographic reconstruction of the Late Weichselian ice sheet in north‐central Poland based on relief analysis

Teodorski

2023

J Quaternary Science

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North‐central Poland was originally shaped by the Płock lobe of the ice sheet formed during the Weichselian Glaciation. The majority of the studied area comprises the Dobrzyń Lakeland, where numerous terminal moraine hills preserve a record of recession of the ice sheet from the maximum extent of the last glaciation (LGM). Analysis of a digital elevation model enabled the determination of a network of morpholineaments, referring to the formation of linear glacial forms. Recession of the ice sheet from the LGM extent in north‐central Poland was uneven and proceeded in stages. Ice‐sheet recession stages were interspersed with local or regional ice‐sheet advance stages. During these individual periods of ice‐sheet behaviour, ice‐sheet movement changed direction from WNW–ESE to NNW–SSE. Transgression of the ice sheet into the central part of the study area as well as the Kujawy–Dobrzyń subphase may be related to cooling of the climate during 18.5–17.7 ka before ad 2000.

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Magnetic mineralogy and fabrics of small-scale glacial flutes, Múlajökull and Breiðamerkurjökull, Iceland

Cited by 3 publications

References 111 publications

Origin of the active drumlin field at Múlajökull, Iceland: New insights from till shear and consolidation patterns

Origin of the active drumlin field at Múlajökull, Iceland: New insights from till shear and consolidation patterns

The formation of a rectilinear ridge network, Múlajökull, Iceland

Palaeogeographic reconstruction of the Late Weichselian ice sheet in north‐central Poland based on relief analysis

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