Seismic-reflection surveys of the Isle Royale sub-basin, central Lake Superior, reveal two large end moraines and associated glacial sediments deposited during the last cycle of the Laurentide Ice Sheet in the basin. The Isle Royale moraines directly overlie bedrock and are cored with dense, acoustically massive till intercalated down-ice with acoustically stratified outwash. Till and outwash are overlain by glacial varves, a lower red unit and an upper gray unit.The maximum extent of late Younger Dryas-age readvance into the western Lake Superior basin is uncertain, but it was probably controlled by both ice dynamics and climate. Our data indicate that during retreat from the maximum, the ice paused just long enough to construct the outer of the two moraines, >100 m high, and then retreated to the inner moraine, during which time most of the lower glacial-lacustrine sequence (red varves) was deposited. Retreat from the inner moraine coincided with a marked flux of icebergs at the calving margin and a change to gray varves. Rapid retreat may be related to both an influx of meltwater from Glacial Lake Agassiz about 10,500 cal yr BP and retreat of the calving margin down an adverse slope into the Isle Royale sub-basin.

中文翻译：

---

苏必利尔湖中部的冰碛和晚冰期地层学

苏必利尔湖中部的皇家岛次盆地的地震反射调查揭示了在该盆地的劳伦泰德冰盖的最后一个周期中沉积的两个大型端部冰碛和相关的冰川沉积物。皇家岛冰碛直接覆盖在基岩之上，其核心是密集的声学大块冰，直到插入下冰，并具有声学分层外流。冰盖和外冲覆盖着冰川、下部的红色单元和上部的灰色单元。晚期新仙女木时代重新推进到苏必利尔湖盆地西部的最大程度尚不确定，但它可能受到冰动力和气候的控制。我们的数据表明，在从最大值撤退期间，冰暂停了足够长的时间以构建两个冰碛的外部，> 100 m 高，然后退回到内部冰碛，在此期间，大部分较低的冰川 - 湖泊序列（红色varves）沉积。从内部冰碛撤退恰逢产犊边缘冰山的显着流动和灰色的变化。快速退缩可能与大约 10,500 cal yr BP 冰川湖 Agassiz 的融水流入以及产犊边缘沿逆坡后退到 Isle Royale 次盆地有关。