The time-dependent physics of ice sublimation through thin layers of till is considered, to determine whether sublimation could be sufficiently slow to permit the preservation of ice for 8 Ma in the Dry Valleys, Antarctica. This could only happen if the ice had been very thick, but other evidence (crystal size, dating of other ice-cored moraines) is not consistent with this possibility. Steady-state models suggest that sublimation is rate-controlled by vapor transport. A time-dependent model coupling vapor concentration, air pressure, temperature and ice concentration is formulated, and the resulting equations solved non-linearly. No transient coupling between vapor concentration, air temperature and pressure that substantially slows down sublimation was found in the numerical experiments. This means either that vapor transport is being slowed down by some unconsidered physical process or that the ice is much younger than 8 Ma.

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Criteria to distinguish between sediments that have been subglacially deformed and those that are undeformed, or deformed by other mechanisms, are sparse. In this paper we develop structural criteria to reconstruct the deformation history of glacial sediments that can be readily applied in the field as well as to analyses of thin sections of tills and related materials.Progressive simple shear is the simplest model to describe the deformation history of subglacially deformed sediments. It includes most of their characteristic structural aspects and provides tools for the kinematic analysis of subglacially deformed sediments. Progressive simple shear generates asymmetric structures, in which the principal direction of finite extension is subparallel to the direction of shearing. This is the simple shear fabric's most distinctive characteristic, and that which most reliably defines the palaeo-ice flow direction.

Till and moraine emplacement in a deforiting bed surge -an example from a marine environment Boulton, G.S.; van der Meer, J.J.M.; Hart, J.; Beets, D.; Ruegg, G.H.J.; Wateren, F.M.; Jarvis, J. Published in:Quaternary Science Reviews DOI:10.1016/0277-3791(95) Link to publication Citation for published version (APA):Boulton, G. S., van der Meer, J. J. M., Hart, J., Beets, D., Ruegg, G. H. J., Wateren, F. M., & Jarvis, J. (1996). Till and moraine emplacement in a deforiting bed surge -an example from a marine environment. Quaternary Science Reviews, 15, 961-987. DOI: 10.1016/0277-3791(95)00091-7 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 10 May 2018Quaternary Science Reviews, Vol. 15, pp. 961-987, 1996. PergamonCopyright © 1996 Elsevier Science Ltd. Printed in Great Britain. All rights reserved. 0277-3791(95) Abstract --The glacier Sefstrombreen in Spitsbergen surged across an arm of the sea between QSR 1882 and 1886 and rode up onto the island Coraholmen. Marine and terrestrial geological observations and archive records show that the glacier advanced on a deforming carpet of marine mud which was eroded from its original location, transported, and smeared over the sea bed and ~ Coraholmen as a deformation till. The glacier emplaced about 210Sm ~ (0.2 km 3) of drift in the terminal 2 km of its advance in a maximum of 14 years, leaving a thickness of up to 20 m on Coraholmen, which was doubled in size as a result.~ ~ During the surge, subglacial muds were characterised by high water pressures, low effective pressures and low frictional resistance to glacier movement. Original sedimentary inhomogenities permit fold structures to be identified, but repeated refolding and progressive remoulding produce mixing and homogenisation of deformation tills.The surge was probably shortlived, and as the heavily crevassed glacier stagnated, underlying water saturated muds were intruded into crevasses and then extruded on the glacier surface. Reticulate "crevasse-intrusion" ridges on Coraholmen and the sea floor reflect the orientation of surge generated crevasses. Water and sediment was also extruded beyond the glacier at its maximum extent, to form extensive flows producing "till tongues" both on Coraholmen and the sea floor extending over 1.3 km from the glac...