Till characteristics, genesis and transport beneath Antarctic paleo‐ice streams
Till characteristics, genesis and transport beneath Antarctic paleo‐ice streams
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南极古冰流的特征、成因和传输
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发表时间：
2007
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通讯作者：
R. Larter
中科院分区：
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作者：
C. Ó. Cofaigh;J. Evans;J. Dowdeswell;R. Larter
[1] 来自南极大陆架的海洋地球物理数据表明以前存在冰流，这些冰流在最后一个冰川周期期间通过测深槽排出。水流是由细长的冰下河床形态记录的，这些河床形态形成于声学透明的沉积层的上部。该层岩心表明，它是一种脆弱且多孔的冰下耕作区（“软耕区”）。软耕区内的剪切力集中在0.1-0.9 m厚的区域。软耕区是一种“混合”耕种区，由冰下沉积物变形和沉降相结合形成。软耕层的底部以强反射体为标志，代表更密集、更强的“硬耕层”的顶部。该反射体的形式从平坦、连续到深槽、不规则，暗示着沉积物动员和并入软耕层的不同机制的运作。基底反射体的不规则形式与沟槽一致，而平坦、连续的形式更符合沉积物动员，作为与变化相关的冰下牵引地毯。软耕层大规模平流的地球物理证据，结合变形划分为厚度达 0.9 m 的相对较薄层的证据，表明局部剪切带整合在一起，在南极古冰流下方输送了大量沉积物。
[1] Marine geophysical data from the Antarctic continental shelf indicate the former presence of ice streams that drained through bathymetric troughs during the last glacial cycle. Streaming flow is recorded by elongate subglacial bedforms, formed in the upper part of an acoustically transparent sediment layer. Cores from the layer demonstrate that it is a weak and porous subglacial till ("soft till''). Shear within the soft till was concentrated in zones that were 0.1-0.9 m thick. The soft till is a "hybrid'' till, formed by a combination of subglacial sediment deformation and lodgment. The base of the soft till is marked by a strong reflector which represents the top of a denser and stronger "stiff till.'' The form of this reflector ranges from flat and continuous to deeply grooved and irregular, implying the operation of different mechanisms of sediment mobilization and incorporation into the soft till layer. The irregular form of the basal reflector is consistent with grooving, whereas the flat and continuous form is more consistent with sediment mobilization as a subglacial traction carpet related to changes in basal effective stress. Geophysical evidence for large-scale advection of the soft till, combined with evidence for deformation partitioning into relatively thin layers up to 0.9 m thick, indicates that localized shear zones integrated to transport significant volumes of sediment beneath Antarctic paleo-ice streams.