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Architecture and sedimentation of outwash fans in front of the Myrdalsjokull ice cap, Iceland

Kjaer, Kurt LU ; Sultan, L; Kruger, J and Schomacker, Anders LU (2004) In Sedimentary Geology 172(1-2). p.139-163
Abstract
In this study, we introduce the architecture and style of sedimentation of two outwash fans in front of the Myrdalsjokull ice cap, central south Iceland, that broaden different types of ice-marginal sedimentation. At Kotlujokull, a southeastern outlet of the ice cap, fan formation was monitored from the late 1970s to 2002; thus, the style of sedimentation is well understood and the relationship to the depositional architecture easily established. In front of Slettjokull, a northern lobate extension of the ice cap, a fan from the 10th century AD is capped by neoglacial till sheets. At both sites, the fan surfaces were reconstructed in three dimensions. Ground Penetrating Radar (GPR) provided the thickness and internal structure of sediment... (More)
In this study, we introduce the architecture and style of sedimentation of two outwash fans in front of the Myrdalsjokull ice cap, central south Iceland, that broaden different types of ice-marginal sedimentation. At Kotlujokull, a southeastern outlet of the ice cap, fan formation was monitored from the late 1970s to 2002; thus, the style of sedimentation is well understood and the relationship to the depositional architecture easily established. In front of Slettjokull, a northern lobate extension of the ice cap, a fan from the 10th century AD is capped by neoglacial till sheets. At both sites, the fan surfaces were reconstructed in three dimensions. Ground Penetrating Radar (GPR) provided the thickness and internal structure of sediment bodies. Geological exposures and excavations were used for detailed sedimentological documentation of the outwash deposits in proximal-to-distal transects. The outwash deposits at both Kotlujokull and Slettjokull are considered to be alluvial fans of the hochsander type, i.e., supraglacially fed, as they show all the architectural characteristics of alluvial fans with a semiconical shape, a restricted radial length of ca. 0.5-1.5 km, a plano-convex cross-profile and a slope gradient ranging between 1 and 5. Fan deposits are dominated by planar or low-angle cross-bedded sand facies interbedded with thin laminae of fine gravel occasionally draped by mud. Sedimentation occurs during upper flow regime sheetflows associated with antidune migration within an aggrading, shallow braided-stream network. Hochsanders are intimately linked to advancing or stationary glaciers with steep ice-cored frontal slopes that favor supraglacial over subglacial drainage. Most important, hochsander fans lack any proximal-to-distal transition in the grain-size distribution, sediment facies or facies associations. Because much classification of glacial outwash sediments is based on proximal-to-distal distinctions, it is crucial to consider the depositional model for hochsanders. This study also indicates a strong dependence between the altitudes of the buried fan surface and the present-day terrain in the forefield of Slettjokull, illustrating that subsequent to fan formation, subglacial landforms merely mask many of the pre-existing morphological features. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
sediment architecture, hochsander, outwash fans, supraglacial, Iceland, Myrdalsjokull
in
Sedimentary Geology
volume
172
issue
1-2
pages
139 - 163
publisher
Elsevier
external identifiers
  • wos:000225346400008
  • scopus:7544225097
ISSN
0037-0738
DOI
10.1016/j.sedgeo.2004.08.002
language
English
LU publication?
yes
id
cd394d84-2926-4bd8-834d-1e3349f915fa (old id 259802)
date added to LUP
2007-08-02 16:27:28
date last changed
2017-11-19 04:12:58
@article{cd394d84-2926-4bd8-834d-1e3349f915fa,
  abstract     = {In this study, we introduce the architecture and style of sedimentation of two outwash fans in front of the Myrdalsjokull ice cap, central south Iceland, that broaden different types of ice-marginal sedimentation. At Kotlujokull, a southeastern outlet of the ice cap, fan formation was monitored from the late 1970s to 2002; thus, the style of sedimentation is well understood and the relationship to the depositional architecture easily established. In front of Slettjokull, a northern lobate extension of the ice cap, a fan from the 10th century AD is capped by neoglacial till sheets. At both sites, the fan surfaces were reconstructed in three dimensions. Ground Penetrating Radar (GPR) provided the thickness and internal structure of sediment bodies. Geological exposures and excavations were used for detailed sedimentological documentation of the outwash deposits in proximal-to-distal transects. The outwash deposits at both Kotlujokull and Slettjokull are considered to be alluvial fans of the hochsander type, i.e., supraglacially fed, as they show all the architectural characteristics of alluvial fans with a semiconical shape, a restricted radial length of ca. 0.5-1.5 km, a plano-convex cross-profile and a slope gradient ranging between 1 and 5. Fan deposits are dominated by planar or low-angle cross-bedded sand facies interbedded with thin laminae of fine gravel occasionally draped by mud. Sedimentation occurs during upper flow regime sheetflows associated with antidune migration within an aggrading, shallow braided-stream network. Hochsanders are intimately linked to advancing or stationary glaciers with steep ice-cored frontal slopes that favor supraglacial over subglacial drainage. Most important, hochsander fans lack any proximal-to-distal transition in the grain-size distribution, sediment facies or facies associations. Because much classification of glacial outwash sediments is based on proximal-to-distal distinctions, it is crucial to consider the depositional model for hochsanders. This study also indicates a strong dependence between the altitudes of the buried fan surface and the present-day terrain in the forefield of Slettjokull, illustrating that subsequent to fan formation, subglacial landforms merely mask many of the pre-existing morphological features.},
  author       = {Kjaer, Kurt and Sultan, L and Kruger, J and Schomacker, Anders},
  issn         = {0037-0738},
  keyword      = {sediment architecture,hochsander,outwash fans,supraglacial,Iceland,Myrdalsjokull},
  language     = {eng},
  number       = {1-2},
  pages        = {139--163},
  publisher    = {Elsevier},
  series       = {Sedimentary Geology},
  title        = {Architecture and sedimentation of outwash fans in front of the Myrdalsjokull ice cap, Iceland},
  url          = {http://dx.doi.org/10.1016/j.sedgeo.2004.08.002},
  volume       = {172},
  year         = {2004},
}