Reconstruction of the Green Bay, Lake Michigan and DesMoines Lobes, 21-11,000 B.P.: Ice Surfaces Profiles, Landform- Sediment Associations & Deglaciation Chronolog

只有少数研究考察了大型冰川裂片的动力学，尽管它们控制着劳伦泰德冰盖的质量平衡。通过分析冰面剖面、地貌-沉积物关联和进退年代学，研究了21 ~ 11000 BP脱冰期南劳伦泰德冰川裂片在不同时期的关系。冰川重建、地貌沉积物关联和年代学这三条独立的证据线的整合，应该会增加对这些裂片的动态历史的理解，以及它们是否对劳伦泰德冰盖的崩塌做出了重大贡献。地貌证据表明，这些裂片有时经历过浪涌型或流流状态。也有证据表明冰边缘停滞和迅速退缩。在特定地点或时间的流动状况取决于目前的河床条件和影响物质平衡的气候因素。该项目将记录这些流动状态的变化，并从现场对床况的证据估计中得出结论。最终的结果将是一个改进的概念模型，说明在最后一次冰川消退期间，大型冰川叶是如何对变化的条件做出反应的。这将导致对气候、冰盖和沉积记录之间关系的更有信心的解释。迄今为止，已经对劳伦泰德南部冰原的两个裂片在消冰的几个早期阶段进行了重建。重建的冰川剖面显示，在消冰过程中，基底剪应力在25 ~ 5 kPa之间变化，以浪涌型流和稳定片状流为主。关于南劳伦特裂片的一个悬而未决的主要问题是，退缩是以-40至100米/年的速率渐进发生，还是以-500至1000米/年的速率灾难性地发生。这个问题的答案对于理解南劳伦泰德冰缘的行为以及解释这些裂片的消冰年代学至关重要。格陵兰冰芯的快速变暖和气候变化是否导致了冰芯的快速崩塌？冰川沉积物表明两者之间可能存在联系，但地表暴露日期（10be、25Al和36Cl）必须从年代不确定的陆地记录中获得，才能对现有的年代学提供独立的检验。地貌-沉积物关系将被研究，以确定它们与古冰川条件重建的关系。将描述沉积物结构、沉积结构和基底接触，以确定在13000 BP前后的推进过程中，冰川床搬运类型是否存在重大差异。低轮廓浪涌型叶片与细粒湖泊沉积物和湖盆的关系将被调查和记录。在可以记录冰面坡度明显不同的地方，对相关沉积物的仔细检查应该将湿变形床与冰床界面处的水浓度区分开来。因此，研究人员使用了三种不同的数据集来记录劳伦泰德冰盖南缘退缩期间的冰川状况：冰面剖面、地貌-沉积物关联和年代学。

Mickelson 9627798 Only a few studies have examined the dynamics of large glacier lobes, even though they controlled the mass balance of the Laurentide ice sheet. By analyzing ice-surface profiles, landform-sediment associations, and advance-retreat chronologies, this research process relationships of three southern Laurentide glacier lobes, at various time during deglaciation 21-11,000 BP. This integration of three separate lines of evidence: glacier reconstructions, landform sediment associations, and chronology should increase understanding of the dynamic history of these lobes and whether or not they contributed significantly to the collapse of the Laurentide ice sheet. Geomorphic evidence suggests that these lobes at times experienced surge type or streaming flow regimes. There is also evidence suggesting ice marginal stagnation and rapid retreat. Flow regime at a specific site or time depended on bed conditions present and climatic factors influencing mass balance. This project will document these changes in flow regime and derive from field evidence estimates of bed conditions. The final result will be an improved conceptual model of how large glacier lobes responded to changing conditions during the last deglaciation. This will lead to more confident interpretations of the relationships between climate, ice sheets, and the sedimentary record. Reconstructions of two lobes of the southern Laurentide ice sheet during several early phases of deglaciation have been produced so far. Reconstructed glacier profiles indicate that basal shear stresses varied from 25 kPa to 5 kPa during deglaciation and that surge-type flow and steady sheet-type flow were common. A major unanswered question about southern Laurentide lobes is whether retreat occurred progressively at rates of -40 to 100 m/y or catastrophically with rates of -500 to 1000 m/y. The answer to this question is fundamental to understanding the behavior of the southern Laurentide ice margin as well as in interpreting the deglaciation chronologies of these lobes. Was there a rapid collapse corresponding to a rapid warming and climate change seen in Greenland ice cores? Glacial deposits suggest there could be a relationship, but surface exposure dates (10be, 25Al, and 36Cl) must be obtained from the poorly dated terrestrial record to provide an independent test of existing chronologies. Landform-sediment associations will be investigated to determine their relationship to reconstructions of paleoglacier conditions. Sediment fabric, sedimentary structures, and basal contacts will be described to determine whether there are major differences in the type of glacier bed transport between pre- and post- 13,000 BP advances. The association of low profile surge-type lobes with fine-grained lake sediments and lake basins will be investigated and documented. Where a clear difference in ice surface slope can be documented, careful examination of the associated sediment should distinguish a wet deforming bed from concentration of water at the ice-bed interface. Thus, three different data sets are used to document glacier conditions during retreat along the southern margin of the Laurentide ice sheet: ice surface profiles, landform-sediment associations, and chronology.