Subglacial to proglacial depositional environments in an Ordovician glacial tunnel valley, Alnif, Morocco.

• Published in: Palaeogeography, Palaeoclimatology, Palaeoecology
• Main Authors: Clerc, Sylvain, Buoncristiani, Jean-François, Guiraud, Michel, Vennin, Emmanuelle, Desaubliaux, Guy, Portier, Eric
• Other Authors: Biogéosciences UMR 6282 (BGS), Université de Bourgogne (UB)-Centre National de la Recherche Scientifique (CNRS), Exploration Production International, Gaz de France Suez (GDF Suez), Funding of this study from GDF Suez EPI.
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: Tunnel valley; Ordovician ice sheet; Subglacial environment; Proglacial environment; Morocco; [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; Antarctic; The Antarctic; Antarc*; Ice Sheet
• Online Access: https://hal.science/hal-00781624; https://doi.org/10.1016/j.palaeo.2012.12.002

18 pages International audience This paper presents the sedimentary analysis of an exceptional Ordovician glacial tunnel valley in the eastern part of the Anti-Atlas. The valley infill comprises two major glacial erosion surfaces (striated pavements) each overlain by a fining-upward glacial unit. These units are composed of five distinct facies associations, recording the evolution fromsubglacial to proglacial environments, and an additional sixth facies association, overtopping the tunnel valley infill, and associatedwith post-glacial environments. The tunnel valley infill also records a transitional environment between the subglacial and proglacial settings, which is compared with the Antarctic ice-sheet margin. These three environments are defined by the position of the grounding line and the coupling line. The new proposed depositional model also differs from usual Ordovician depositional models in which the main tunnel valley infill is interpreted as essentially proglacial outwash deposits, in a range of glaciomarine to glaciofluvial environments. Overall, a substantial part of the valley infill (~50% of volume) was deposited in a subglacial setting. The sedimentary bodies could form potentially thick and laterally extended, although these were limited by the shape and extent of the subglacial accommodation space. Finally, the sedimentary record, when compared with regional analogues, also provides information for the palaeogeographic reconstruction of the Ordovician ice-sheet in this region.