Slope instability on a shallow contourite-dominated continental margin, southeastern Grand Banks, eastern Canada
Slope instability on a shallow contourite-dominated continental margin, southeastern Grand Banks, eastern Canada
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DOI：
10.1016/j.margeo.2017.01.001
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发表时间：
2017-01
期刊：
影响因子：
2.9
通讯作者：
H. Rashid;K. Mackillop;J. Sherwin;D. Piper;B. Marche;M. Vermooten
中科院分区：
文献类型：
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作者：
H. Rashid;K. Mackillop;J. Sherwin;D. Piper;B. Marche;M. Vermooten
海底沉积物破坏和相关的大块搬运沉积（MTDs）在加拿大东部大陆斜坡环境中广泛存在，通常与冰盖穿过外大陆架有关。在过去的105年里，大浅滩的东南部边缘没有被冰川覆盖，有一个很深的冰架断裂。因此，上大陆坡主要由拉布拉多海流从北方运来的沉积物组成。高分辨率地震剖面和10米长的活塞岩心显示，在水深500至1000米的灰泥等长岩漂移中，沉积物破坏和MTDs广泛存在。这项研究记录了过去4.8万年的地层学和沉积物破坏事件的记录。海因里希层H1至H5具有独特的岩石学、物理性质和整体地球化学特征，并受到大量14c - ams日期的限制。岩土力学分析表明，第四纪沉积剖面为轻度欠固结，可能与深部流体的泄漏增强了高沉积速率（高达0.5 m/ka）有关。然而，使用Su/ p0计算的安全系数和三轴试验的摩擦角表明，边坡在9°的梯度下是静态稳定的。粉质轮廓岩沉积物的阿特伯格极限测量表明，在循环荷载作用下易液化。有证据表明，在数十公里长的斜坡上发生了明显的同步破坏，可能是罕见的被动边缘地震的结果。这些浅水轮廓岩沉积物具有较高的砂和粗粉质含量，生物物质少得多，沉积物和岩土特性的变化更快，所有这些都使它们更容易受到沉积物破坏的影响。
Submarine sediment failures and related mass-transport deposits (MTDs) are widespread on the eastern Canadian continental slope settings and in general, have been related to ice sheets crossing the outer shelf. The southeastern Grand Banks margin was not glaciated in the last 105years and has a deep shelf break. As a result, the upper continental slope consists principally of sediment transported from the north by the Labrador Current. High-resolution seismic profiles and 10-m long piston cores show widespread sediment failure and MTDs in a plastered contourite drift from 500 to 1000 m water depth. This study documents the stratigraphy of the past 48,000 years and the record of sediment failure events. Heinrich layers H1 to H5 have been recognized from distinctive petrology, physical properties, and bulk geochemistry and are constrained by numerous14C-AMS dates. The geotechnical analysis shows that the latest Quaternary sediment section is mildly underconsolidated, perhaps related to high sedimentation rates (up to 0.5 m/ka) enhanced by some leakage of deep fluids. Nevertheless, factor of safety calculations using Su/P0and friction angles from triaxial testing suggest the slope is statically stable up to gradients of 9°. Atterberg limit measurements of silty contourite sediments indicate susceptibility to liquefaction under cyclic loading. There is evidence that apparently synchronous failure occurred over many tens of kilometres of the slope, probably as a result of rare passive margin earthquakes. These shallow water contourite deposits have a higher sand and coarse silt content, much less biogenic material, and more rapid variations in sediment and geotechnical properties than those of the deep-water equivalents, all of which make them more susceptible to sediment failure.