Glaciotribology of drumlins and megascale glacial lineations: an enigma solved?
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    Abstract:

    Ice streams are fast- flowing (up to 10 km/a) arterial corridors as much as 1000 km long and 200 km wide, inset within ice sheets that leave low relief longitudinally- corrugated beds consisting of highly- elongated flow- parallel ridges and grooves (megascale glacial lineations). These are spatially and genetically related to larger less elongate drumlins whose origin(s) remain enigmatic despite more than 150 years of investigation. This uncertainty is largely because of the wide variability of the geology of their cores and the difficulties of observing their formation below modern ice sheets. New high resolution (0. 5 m) LiDAR- based mapping and geological studies of the well- exposed beds of Pleistocene paleo ice streams shows that drumlins and megascale glacial lineations are a bedform continuum composed entirely of bedrock, or partial rock and older antecedent sediment favouring an erosional origin proposed by many workers. Here we highlight analogous elliptically- streamlined and grooved surfaces produced by abrasion of substrates below granular debris undergoing confined shear in a wide range of non- glacial geologic settings, both here on Earth and on Mars. Large detachment faults in metamorphic core complexes and the surfaces of subduction zone megathrusts show grooved surfaces that are directly analogous in form and scale to megascale glacial lineations. 3- D profiling of fault traces below gouge show progressive elimination of drumlin- like ‘elliptical bumps’ to form grooved slicken sided surfaces that reduce drag and allow continued slip. Distinct ‘streaking’ of subglacial earthquakes recorded below modern ice streams is consistent with localized erosion and shear of substrate materials within grooves strengthening the link to fault kinematics. More widely, the basal surfaces of ejecta blankets surrounding meteorite impact craters, pyroclastic flows from volcanoes and at the base of landslides and mass transport deposits are also grooved as a result of erosion below basal granular debris that segregates into distinct longitudinal ‘sub- streams’. Elliptical bumps and grooved surfaces cut by granular ‘wear debris’ (defined as a ‘third layer’) are also seen on the surfaces of man- made and biological materials in frictional contact. Correspondingly, we propose that drumlins and megascale glacial lineations are kinematically related components of a glaciodynamic hierarchy of what can be called ‘wear tracks’ or ‘longitudinal shear marks’ cut at different ice velocities by coarse- grained deforming till (a subglacial ‘third layer’) being dragged over the substrate, whether composed of sediment, or rock (or any combination). The drumlin- MSGL enigma that has been the focus of more than 150 years of research is now closer to being resolved.

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Zhou Weiwei, Nick Eyles, Shane Sookhan, Niko Putkinen.2021. Glaciotribology of drumlins and megascale glacial lineations: an enigma solved?[J]. Acta Geologica Sinica,95(8):2306-2317

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History
  • Received:December 05,2020
  • Revised:April 07,2021
  • Adopted:April 08,2021
  • Online: April 16,2021
  • Published: