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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Lateral plucking as a mechanism for elongate erosional glacial bedforms: Explaining megagrooves in Britain and Canada
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Lateral plucking as a mechanism for elongate erosional glacial bedforms: Explaining megagrooves in Britain and Canada

机译：横向拔毛是延长侵蚀性冰河床形的一种机制：解释英国和加拿大的大槽

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Megagrooves are kilometre-scale linear topographic lows carved in bedrock, separated by ridges, typically in areas of largely devoid of till. They have been reported from several areas covered by Pleistocene glaciations, such as Canadian Northwest (NW) Territories, Michigan and NW Scotland. Here we report two previously undocumented megagroove fields from Ungava, Canada, and northern England, and present new analyses of the megagrooves from NW Scotland. This paper seeks to determine the nature of the lithological and structural controls on the occurrence and formation of megagrooves. Analysis of both geomorphological and bedrock properties shows that megagrooves are generally: confined to well stratified or layered bedrock, such as (meta)sedimentary rocks with closely spaced joints, and tend not to occur on massive rocks such as gneiss or granite, or thick-bedded sedimentary rocks; subparallel to palaeo-ice flow and the strike of the strata; and tend not to occur where palaeo-ice flow is at high angles to the strike of strata; produced by significant glacial erosion by sustained unidirectional ice flow. Detailed analysis of megagrooves in NW Scotland shows that neither glacio-fluvial erosion, nor differential abrasion was the dominant mechanism of formation. A mechanism, here termed 'lateral plucking', is suggested that involves block plucking on rock steps parallel to ice flow. Removal of joint-bounded blocks from such rock steps involves a component of rotation along a vertical axis. Block removal may be enhanced by a direct component of shear stress onto the vertical stoss sides. The lateral plucking mechanism results in horizontal erosion at right angles to the ice flow, and enhances the groove/ridge topography. Megagrooves are potentially useful as palaeo-ice flow indicators in areas devoid of till, and can thus complement the palaeo-ice stream datasets which are presently largely based on soft-sediment landform studies. British Geological Survey
机译：巨型槽是刻在基岩中，由山脊隔开的千米级线性地形低点，通常在基本上没有耕作的地区。在更新世冰川覆盖的多个地区（例如加拿大西北（NW）地区，密歇根州和苏格兰西北地区）已报告了它们。在这里，我们报告了加拿大Ungava和英格兰北部两个以前未记录的巨型槽场，并提供了来自西北苏格兰的巨型槽的新分析。本文力求确定巨型槽的形成和形成的岩性和构造控制的性质。对地貌和基岩性质的分析表明，大槽一般为：局限于层状或分层良好的基岩中，例如节距较近的沉积（成因）沉积岩，而在片麻岩或花岗岩或厚厚的岩石中则不会出现层状沉积岩;与古冰流和地层走向亚平行;在古冰流与地层走向成大角度的情况下往往不会发生;由持续的单向冰流引起的重大冰河侵蚀产生。对苏格兰西北部大型槽的详细分析表明，冰川-河流冲刷和差异磨蚀都不是形成的主要机制。建议采用一种称为“横向拔除”的机制，该方法涉及在平行于冰流的岩石台阶上进行块拔除。从这种岩石台阶上移开节理界的块体涉及沿垂直轴的旋转分量。可以通过将剪切应力的直接分量施加到垂直的槽口侧面来增强砌块的去除。横向拔除机制导致与冰流成直角的水平侵蚀，并增强了凹槽/山脊的形貌。 Megagrooves可能在没有耕地的地区用作古冰流指示剂，因此可以补充目前主要基于软沉积地貌研究的古冰流数据集。英国地质调查局

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