The seafloor geomorphology of the Windmill Islands, Wilkes Land, East Antarctica: implications for regional ice-sheet evolution

High-resolution marine sonar swath mapping, covering an area of ca. 33 km2 in the vicinity of the Windmill Islands (67° S, 110° E), Wilkes Land, east Antarctica, permits visualisation and description of the near-shore geomorphology of the seafloor environment in unprecedented detail and provides invaluable insight into the ice-sheet history of the region. Mesoproterozoic metamorphic basement exhibits prominent sets of parallel northwest-trending linear fault sets that probably formed during fragmentation of eastern Gondwana during the Mesozoic. The fault systems appear to control regional coastal physiographic features and have, in places, been preferentially eroded and exploited by subsequent glacial activity. Possibly the earliest formed glacially-derived geomorphological elements are networks of sub-glacial meltwater channels which are preserved on bedrock platforms and ridges. Subtle glacial lineations and streamlined landforms record evidence of the westward expansion of the grounded, Law Dome ice sheet margin, probably during the late Pleistocene Last Glacial Maximum, the direction of which coincides with glacial striae on onshore crystalline bedrock outcrops. The most striking glacial geomorphological features are sets of arcuate ridges confined mostly within glacially excavated `U-shaped valleys, exploiting and developed along bedrock fault sets. These ridge sets are interpreted as `push moraines or grounding zone features, formed during episodic retreat of highly channelised, topographically controlled ice-streams following ice surging, possibly in response to local environmental forcing during the mid-late Holocene. Minor post-glacial marine sedimentation is preserved in several small (1 km2) `isolated marine basins with shallow seaward sills.

高分辨率海洋声呐条带测绘（high-resolution marine sonar swath mapping）覆盖了南极东部威尔克斯地风车群岛（Windmill Islands，67°S，110°E）周边约33平方千米的海域，首次以前所未有的精细程度实现了近岸海底地貌的可视化与描述，同时为该区域的冰盖历史研究提供了极为宝贵的见解。中元古代（Mesoproterozoic）变质基底（metamorphic basement）发育多组显著的北西向平行线性断裂构造，这些构造大概率形成于中生代（Mesozoic）东冈瓦纳大陆裂解时期。该断裂体系似乎控制了区域海岸地貌特征，且在部分区域被后续冰川活动优先侵蚀改造。区域内最早形成的冰川成因地貌要素，可能是保存在基岩台地与山脊之上的冰下融水水道网络。微弱的冰川线理与流线型地貌记录了接地的劳穹冰盖（Law Dome ice sheet）边缘向西扩张的证据，此次扩张大概率发生在晚更新世末次冰盛期（Last Glacial Maximum），其扩张方向与陆上结晶基岩露头处的冰川擦痕（glacial striae）方向一致。最引人注目的冰川地貌为多组弧形山脊，这些山脊大多分布在冰川侵蚀形成的"U型谷"内，沿基岩断裂带发育并受其改造。此类弧形山脊被解释为"推积碛（push moraines）"或冰盖接地带构造，形成于冰涌之后受地形约束的高河道化冰流的阶段性退缩过程，此次退缩可能响应了中晚全新世（Holocene）的局地环境驱动作用。少量冰后海洋沉积保存在数个面积约1平方千米的"孤立海盆"中，这些海盆均带有较浅的向海海槛（sill）。