DOI: 10.1016/j.palaeo.2014.12.003
论文题名: Does porewater or meltwater control tunnel valley genesis? Case studies from the Hirnantian of Morocco
作者: Ravier E. ; Buoncristiani J.-F. ; Menzies J. ; Guiraud M. ; Clerc S. ; Portier E.
刊名: Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN: 0031-0182
出版年: 2015
卷: 418 起始页码: 359
结束页码: 376
语种: 英语
英文关键词: Ice streams
; Meltwater
; Ordovician
; Porewater pressure
; Tunnel valley
英文摘要: Several Ordovician tunnel valleys are exposed in the Moroccan Anti-Atlas Mountains, including the Alnif and the Foum Larjamme tunnel valleys, located 150. km away from each other. Sedimentological and deformational analyses of these two glacial troughs reveal that differing processes lead to their formations.The Alnif tunnel valley contains numerous deformation structures within sediments both below and above the main glacial erosion contact surface. Ball-structures and clastic dykes occur within preglacial sediments down to 35. m below glacial incisions while overlying glacial sediments contain fluted surfaces, clastic dykes, dewatering structures, folds and radial step normal faults. The characteristics of the Alnif tunnel valley can be explained by a porewater pressure-driven model of formation where the localized increase of basal shear stress and porewater pressure underneath subglacial deforming zones lead to the development of a dense hydrofracture network in the preglacial bed. These processes of hydraulic brecciation promoted subglacial remobilization of the preglacial material and contributed to the formation of the tunnel valley.The Foum Larjamme tunnel valley displays undisturbed preglacial sediments and few dewatering structures at the base of the glacial sedimentary infill which suggests relatively low porewater pressures within the tunnel valley during formation. This second type of tunnel valley where porewater pressure remained relatively low appears to have been formed by meltwater erosion. The undulating base of the Foum Larjamme tunnel valley implies progressive erosion by a stable subglacial braided network of Nye-channels, or alternatively by channels migrating laterally during episodic minor subglacial outbursts.These two tunnel valleys highlight the regional variability of processes involved in the formation of tunnel valleys. The distribution of palaeo-ice streams in North Africa illustrate that morphologies and processes involved in the formation of tunnel valleys vary between ice stream and inter-ice stream zones due to variations in meltwater availability, the topography and bed lithological properties. © 2014 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/69066
Appears in Collections: 过去全球变化的重建
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作者单位: Laboratoire Biogeosciences, UMR/CNRS 6282, Université de Bourgogne, 6 Bd Gabriel, Dijon, France; Department of Earth Sciences, Brock University, 500 Glendridge Avenue, St. Catharines, ON, Canada; GDF Suez, Exploration Production International, Faubourg de l'Arche, 1 place Samuel de Champlain, Paris La Défense Cedex, France
Recommended Citation:
Ravier E.,Buoncristiani J.-F.,Menzies J.,et al. Does porewater or meltwater control tunnel valley genesis? Case studies from the Hirnantian of Morocco[J]. Palaeogeography, Palaeoclimatology, Palaeoecology,2015-01-01,418