Sedimentology and paleohydrology of glacial-lake outburst deposits in southeastern Saskatchewan and northwestern North Dakota
Sedimentology and paleohydrology of glacial-lake outburst deposits in southeastern Saskatchewan and northwestern North Dakota
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DOI：
10.1130/0016-7606(1987)99
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发表时间：
1987-05
影响因子：
4.9
通讯作者：
M. Lord;A. Kehew
中科院分区：
文献类型：
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作者：
M. Lord;A. Kehew
在大平原北部，当冰缘湖泊突然干涸时，冰湖爆发，形成了一个相互连接的冰湖溢洪道系统。喷涌具有很强的侵蚀性，因此，这种排放物的沉积物在溢洪道中很少见。在萨斯喀彻温省和北达科他州的Souris、Des Lacs和Moose Mountain溢洪道上的冰川湖泊溃决沉积物具有独特的坝形，并且在内部比那些外溢系统更大块和均匀。本文对突出沉积物进行了描述，并对突出排放物的沉积学和水动力特征进行了解释。粗粒泥沙被侵蚀后，在溢洪道内形成大型沙坝，长达2公里，厚达30米，既可作为悬垂沙坝，也可作为同期滑坡旁凹室中的沙坝。在内部，沙洲由均匀的块状、基质支撑的、分选非常差的卵石砾石组成，其中包含直径达3米的巨石。单个沙坝的最大粒径沿下游和溢洪道方向减小。沙洲的岩性类似于当地的冰川漂移；来自第三纪基岩的物质没有集中在沙洲中，其中溢洪道部分被切割。基于最大粒径数据和shields夹带函数的古水力计算得出了不合理的大值。根据实地观测确定的深度限制进行的补充计算得出了实际值；该方法表明，突出的速度为2.9 ~ 11.7 ms−1，流量为5.8 × 10 4 ~ 8.2 × 10 5 m 3 s−1。溃决期间的沉积物-水浓度，通过将侵蚀的沉积物体积除以源湖体积来估计，平均为重量的20%。根据这一估计，大量的细粒物质被侵蚀，以及突出沉积物的结构，我们推断突出流是高浓度的，在某些地区，沉积物-水的浓度高达40%（重量计）。我们进一步推断，泥沙输运非常有效，大多数颗粒，包括粗砾石，以悬浮形式输运。这种解释与沉积物的沉积学和其他推测证据是一致的。膨胀的剖面导致沉积较粗的沉积物，不论碎屑大小，形成分选不良的块状砾石坝。粒度更细的泥沙，从沙子到粘土的大小，通过溢洪道系统被输送到下游的冰川湖泊。
Glacial-lake outbursts occurred in the northern Great Plains as ice-marginal lakes suddenly drained, forming an interconnected system of glacial-lake spillways. The outbursts were highly erosive, and consequently, deposits from such discharges are rare in the spillways. Glacial-lake–outburst deposits in the Souris, Des Lacs, and Moose Mountain spillways, Saskatchewan and North Dakota, have distinct bar shapes and, internally, are more massive and homogeneous than those of outwash systems. In this paper, the outburst deposits are described, and the sedimentologic and hydrodynamic characteristics of the outburst discharges are interpreted. Coarse-grained sediment eroded from till formed large-scale bars in the spillways, as much as 2 km long and 30 m thick, both as pendant bars and bars in alcoves next to contemporaneous landslides. Internally, the bars consist of homogeneous masses of massive, matrix-supported, very poorly sorted, pebbly cobble gravel, containing boulders as much as 3 m in diameter. The maximum particle sizes in individual bars decrease downstream and toward spillway sides. The lithology of the bars resembles the local glacial drift; material from the Tertiary bedrock, in which the spillways are partially incised, is not concentrated in the bars. Paleohydraulic calculations based on data of maximum particle size and on the Shields9 entrainment function yield unreasonably large values. Supplementary calculations based on depth limits established from field observations yield realistic values; this method indicates that velocities of 2.9 to 11.7 ms −1 and discharges of 5.8 × 10 4 to 8.2 × 10 5 m 3 s −1 were achieved by the outburst. Sediment-water concentrations during the outburst, estimated by dividing the volume of sediment eroded by the source-lake volume, averaged ∼20% by weight. Because of this estimate, the abundant amount of fine-grained material that was eroded, and structure of the outburst deposits, we infer that outburst flows were hyperconcentrated, with sediment-water concentrations being as much as ∼40% by weight in some areas. We further infer that sediment transport was extremely efficient and that most particles, including coarse gravel, were transported in suspension. This interpretation is consistent with the sedimentology of the deposits and other conjectural evidence. Expanding sections caused coarser sediment to be deposited, indiscriminate of clast size, as poorly sorted, massive gravel bars. Finer grained sediment, sand to clay size, was transported through the spillway system into downstream glacial lakes.