Fluid-pressure controlled soft-bed deformation sequence beneath the surging Breiðamerkurjökull (Iceland, Little Ice Age).

• Published in: Sedimentary Geology
• Main Authors: Denis, Michaël, Buoncristiani, Jean-François, Guiraud, Michel
• Other Authors: Biogéosciences UMR 6282 (BGS), Université de Bourgogne (UB)-Centre National de la Recherche Scientifique (CNRS), Study funded by a research allocation from the Ministère de l'Education Nationale, de la Recherche et de la Technologie, and by a research contract (“Région Bourgogne – UMR 5561 Biogéosciences – TOTAL n° 05 516 AA 013 S29, Interactions déglaciations, déformation et enregistrement stratigraphique”).
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2009
• Subjects: Subglacial deformation; Fluid pressure; Breiðamerkurjökull; Iceland; Clast-fabric analysis; [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy; [SDE.MCG]Environmental Sciences/Global Changes; glacier
• Online Access: https://hal.science/hal-00423389; https://doi.org/10.1016/j.sedgeo.2009.07.013

16 pages International audience The general subject of this paper is subglacial deformation beneath Breiðamerkurjökull, a surging Icelandic glacier. More specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation. During Little Ice Age maximum, the two outcrops studied, North Jökulsarlon (N-Jk) and Brennhola-Alda (BA), were located at 2550 m and 550 m respectively from the front of the Breiðamerkurjökull. Sedimentological analysis at the forefield of the glacier shows thick, coarse glaciofluvial deposits interbedded with thin, fine-grained shallow lacustrine/swamp deposits, overlain by a deformed till unit at N-Jk. BA outcrop shows fine-grained shallow lacustrine/swamp deposits overlain by a deformed till unit. The sequence of deformation events from one outcrop to the other is similar. First, major thrust planes, which were rooted in shallow lacustrine/swamp deposits developed by glacially induced simple shear. Next, the thrusts were folded, indicating the deformation of hydroplastic sediment assisted by moderate fluid pressure. Then clastic dyke swarms crosscut the sedimentary succession, proving that fluid overpressure caused hydrofracturing associated with fluidisation. Finally, as water escaped from the glacier bed, fluid pressure dropped, and normal faulting occurred in brittle-state subglacial sediments. Fluidpressure variations are related to glacier dynamics. They control the deformation sequence by modifying subglacial rheological behaviour and the nature of the subglacial tectonism.