Englacial Deltaic Sediments as Evidence for Basal Freezing and Marginal Shearing, Leirbreen, Southern Norway

• Published in: Journal of Glaciology
• Main Authors: Harris, Charles, Bothamley, Keith
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1984
• Subjects: glacier; Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s0022143000008455; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000008455

Abstract A frozen englacial band of current-bedded silts, sands, and gravels were observed close to the snout of the temperate glacier Leirbreen. Little-disturbed sedimentary structures indicated a deltaic origin, the lack of disturbance showing that the sediments were frozen prior to their incorporation by the glacier and did not suffer shearing during glacial transport. It was concluded that they accumulated originally in a subglacial pool when the glacier was more extensive than today. Subsequent thinning of the glacier during recession allowed penetration of winter cooling to the base and freezing of subglacial sediments. The resulting layer of frozen sediment was protected from summer thawing by the overlying glacier and might therefore have been subject to further increase in thickness during successive winters. Incorporation of the frozen sediment band into the glacier resulted from compressive flow against the marginal zone of cold-based ice, leading to the development of thrust planes which penetrated through the glacier and into the frozen subglacial material. Shearing along such a thrust plane immediately below the frozen sediment layer, brought it through the glacier to the surface in a relatively undisturbed state.