Glacial erosional landforms: origins and significance for palaeoglaciology
Glacial erosional landforms: origins and significance for palaeoglaciology
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冰川侵蚀地貌：古冰川学的起源和意义
DOI：
10.1191/0309133304pp401ra
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
M. Bennett
中科院分区：
文献类型：
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作者：
N. Glasser;M. Bennett
大陆规模古冰盖的冰川反演模型现已被认为是古冰川学的重要工具。现有的古冰川学重建对前冰原的尺寸、几何形状和动力学主要基于冰川沉积地貌，而不是冰川侵蚀地貌。造成这种情况的部分原因是缺乏对冰川侵蚀地貌的起源和意义的详细了解。在这里，我们回顾了我们对冰川侵蚀过程和地貌的理解的最新进展，并考虑了它们在古冰川学中的价值。冰川侵蚀涉及通过冰川采石、冰川磨损和冰川融水去除和运输基岩和/或沉积物。这些过程结合起来形成了一系列地貌，这些地貌经常在以前被冰盖和冰川占据的地区观察到，并且可用于古冰川重建。例如，所有冰川侵蚀地貌都为冰下融水的释放和暖基冰的存在提供了证据。当冰盖与其冰床之间形成空洞时，就会形成诸如羊角山、岩石盆地和面冲刷区等冰川采石地貌，因此表明冰床分离所需的有效基础压力较低（0.1-1 MPa）和高滑动速度。基础水压的波动在冰川采石地貌的形成中也发挥着重要作用。冰川磨损的地貌包括流线型基岩特征（“鲸背”）、一些“p 形”、条纹、凹槽、微岩和尾部、基岩凿痕和裂缝。磨损可以通过在基岩上滑动的冰下沉积物体或冰中包含的单个碎屑来实现。尽管磨损模型主要取决于碎屑是否被视为依赖于冰下水压还是独立于冰下水压，但在有效基础压力大于 1 MPa 且滑动速度较低的情况下，似乎有利于磨损。因此，当没有冰床分离时，就会形成以冰川磨损为主的地貌。冰川融水侵蚀地貌包括冰下融水河道和冰缘融水河道。对冰川融水通道与冰下排水系统其他方面（例如冰床接触面积、冰床分离面积和沉淀物填充的洼地）之间关系的研究，可以对以前的冰下水压力与排水关系、有效压力和冰川速度做出推断。融水古速度和古流量也可以通过测量河道形状、河道宽度和在前冰川融水河道内输送的物质尺寸来计算。我们推测，冰川侵蚀地貌可以让我们深入了解古冰川学中地貌和景观尺度上的前冰川条件。暴露年龄测年技术，包括基岩表面的宇宙成因同位素测年，对于增进我们对冰川侵蚀地貌的年龄和年代意义的理解非常重要。我们得出的结论是，冰川侵蚀地貌在冰体重建中具有重要价值，并推测随着暴露年龄测定技术的改进，这些地貌将在古冰川学中获得更大的认可。
Glacial inversion modelling of continental-scale palaeo-ice sheets is now recognized as an important tool in palaeoglaciology. Existing palaeoglaciological reconstructions of the dimensions, geometry and dynamics of former ice sheets are based mainly on glacial depositional, as opposed to glacial erosional, landforms. Part of the reason for this is a lack of detailed understanding of the origin and significance of glacial erosional landforms. Here we review recent developments in our understanding of the processes and landforms of glacial erosion and consider their value in palaeoglaciology. Glacial erosion involves the removal and transport of bedrock and/or sediment by glacial quarrying, glacial abrasion and glacial meltwater. These processes combine to create a suite of landforms that are frequently observed in areas formerly occupied by ice sheets and glaciers, and which can be used in palaeoglaciological reconstructions. For example, all landforms of glacial erosion provide evidence for the release of subglacial meltwater and the existence of warm-based ice. Landforms of glacial quarrying such as roches moutonnées, rock basins and zones of areal scouring are created when cavities form between an ice sheet and its bed and therefore are indicative of low effective basal pressures (0.1-1 MPa) and high sliding velocities that are necessary for ice-bed separation. Fluctuations in basal water pressure also play an important role in the formation of glacially quarried landforms. Landforms of glacial abrasion include streamlined bedrock features (‘whalebacks’), some ‘p-forms’, striae, grooves, micro-crag and tails, bedrock gouges and cracks. Abrasion can be achieved by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. Although abrasion models depend critically on whether clasts are treated as dependent or independent of subglacial water pressure, it appears that abrasion is favoured in situations where effective basal pressures are greater than 1 MPa and where there are low sliding velocities. Consequently, landforms dominated by glacial abrasion are created when there is no ice-bed separation. Landforms of glacial meltwater erosion include both subglacial and ice-marginal meltwater channels. Investigations of the relationship between glacial meltwater channels and other aspects of the subglacial drainage system, such as areas of ice-bed contact, areas of ice-bed separation and precipitate-filled depressions, enable inferences to be made concerning former subglacial water pressure-drainage relationships, effective pressures and glacier velocities. Meltwater palaeovelocity and palaeodischarge can also be calculated from measurements of channel shape, channel width and the size of material transported within former glacial meltwater channels. We surmize that glacial erosional landforms offer insight into former glacio-logical conditions at both the landform- and landscape-scale within palaeoglaciology. Exposure-age dating techniques, including cosmogenic isotope dating of bedrock surfaces, will be important in increasing our understanding of the age and chronological significance of landforms of glacial erosion. We conclude that landforms of glacial erosion are of great value in ice mass reconstruction and speculate that these landforms will achieve greater recognition within palaeoglaciology in line with improvements in exposure-age dating techniques.