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

绿湾、密歇根湖和得梅因波瓣的重建，距今 21-11,000 年：冰面剖面、地貌-沉积物关联

• 批准号: 9627798
• 负责人: David Mickelson
• 金额: $ 14.47万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-08-01 至 1999-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9627798&HistoricalAwards=false
• 关键词: Reconstruction; Green; Bay; Lake; Michigan

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.

米克尔森9627798 只有少数研究研究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、地形-沉积物组合和进退年表，研究了21- 11，000 BP冰消期不同时期劳伦蒂德南部三个冰川裂片的关系。 这三个独立的证据线的整合：冰川重建，地形沉积物协会，和年代学应该增加了解这些裂片的动态历史，以及它们是否对劳伦泰德冰盖的崩溃做出了重大贡献。 地貌证据表明，这些叶片有时经历浪涌型或流态。 也有证据表明冰边缘停滞和快速撤退。 特定地点或时间的流态取决于当前的床条件和影响质量平衡的气候因素。 本项目将记录这些水流状态的变化，并从河床条件的现场证据估计中得出。 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，大型冰川裂片如何应对不断变化的条件。 这将导致对气候、冰盖和沉积记录之间关系的更有把握的解释。 到目前为止，已经制作了在冰川消退的几个早期阶段南部劳伦泰德冰盖的两个裂片的重建。 重建的冰川剖面表明，基底剪切应力变化从25千帕至5千帕，在冰消期和浪涌型流和稳定片型流是常见的。 关于劳伦蒂德南部的一个主要的未解问题是，退缩是以-40至100米/年的速度逐渐发生的，还是以-500至1000米/年的速度灾难性地发生的。 这个问题的答案是根本的了解南部劳伦蒂德冰缘的行为，以及在解释这些裂片的冰川消退年表。 格陵兰冰芯中是否存在与快速变暖和气候变化相对应的快速崩溃？ 冰川沉积物表明可能存在某种关系，但必须从日期不佳的陆地记录中获得表面暴露日期（10 be，25 Al和36 Cl），以提供对现有年表的独立测试。 将调查地貌沉积物协会，以确定它们与古冰川条件重建的关系。 沉积物组构，沉积结构和基底接触将被描述，以确定是否有重大差异的类型之间的冰川床运输前和后13,000 BP的进步。 将调查和记录低剖面涌浪型凸起与细粒湖泊沉积物和湖盆的关系。 在冰面坡度有明显差异的地方，仔细检查相关沉积物，应能区分湿变形床和冰床界面处的水浓度。 因此，三个不同的数据集被用来记录冰川退缩期间沿着南部边缘的Laurentide冰盖的条件：冰面剖面，地貌沉积物协会，和年表。