COLLABORATIVE RESEARCH: Subglacial Deforming Beds as Erosive and Sedimentary Agents: An Experimental Study of Particle Comminution and Rock Erosion

冰下沉积物变形作为一种新的、独特的、甚至可能是主要的快速冰流和冰流形成机制，越来越被人们所接受。通过这种机制，可以产生广泛的土层，以快速的速度移动，并完全沉积在冰川下。目前，在冰流和土生成的变形床模型中，有两个基本假设：(1)这些快速变形的床有效地侵蚀下垫基岩，足以维持所需的高泥沙通量；(2)它们可以产生通常在收银机中观察到的碎片粉碎的证据。对南极西部冰流b下面的冰的观测和实验研究结果表明，这些假设大大改变了目前对变形床的现有认识。然而，尚不清楚冰流B的观测结果是否还可以外推到其他冰下环境。本文提出了一系列的试验来研究剪切土体对颗粒的粉碎速率和基岩的侵蚀速率。在这些实验中，将使用现有的环剪装置，在适用于变形床模型（6 kPa N 100 kPa）的有效法向应力下，将6种不同类型的土体剪切到大应变（~100,000）。剪切前和剪切后粒度的比较、粘土粒度的组成以及砂粒的形状和微观形貌将决定颗粒的粉碎程度。岩石侵蚀的速率将在安装在环形剪切装置上的常见岩性的岩石板上测量。结果将用于检验假设(1)和(2)的一般有效性。收集到的数据将为侵蚀和粉碎的定量公式提供实验基础，可用于未来变形床的建模。最后，这些实验有可能产生可靠的沉积学标准，用于测试某一特定的农田是否完全由冰下变形产生。

9819346TulaczykSubglacial sediment deformation is becoming increasingly accepted as the new, distinct, and perhaps even predominant mechanism of fast ice flow and till generation. By this mechanism, extensive layers of till may be generated, transported at fast rates, and deposited entirely subglacially. At present, two fundamental assumptions are made in the deforming-bed models of ice flow and till generation: (1) that these rapidly deforming beds erode underlying bedrock efficiently enough to sustain the required high sediment fluxes; and (2) that they can produce the evidence of debris comminution which is commonly observed in tills. Results of observational and experimental investigations of the till from beneath Ice Stream B. West Antarctica suggest that these assumptions changes significantly the presently existing understanding of deforming beds. However, it is not clear whether the observations from Ice Stream B till can be extrapolated to other subglacial environments. A series of experiments is proposed here to study the rates of particle comminution and bedrock erosion by shearing till. In these experiments, an existing ring shear device will be used to shear six different types of till to large strains (~100,000) under effective normal stresses which are applicable to the deforming-bed model (6 kPa N 100 kPa). Comparison of pre-shear and post-shear granulometry, composition of clay-size fraction, as well as sand grain shape and micromorphology will determine the extent of particle comminution. The rate of rock erosion will be measured on rock plates of common lithologies mounted in the ring shear device. The results will be used to test the general validity of the assumptions (1) and (2). The collected data will provide an experimental basis for quantitative formulations of erosion and comminution that can be used in future modeling of deforming beds. Finally, these experiments have the potential to yield solid sedimentological criteria for testing whether a given till may or many not have been generated fully by subglacial deformation.