Micromorphological characteristics of glacimarine sediments: implications for distinguishing genetic processes of massive diamicts
Micromorphological characteristics of glacimarine sediments: implications for distinguishing genetic processes of massive diamicts
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DOI：
10.1007/s00367-009-0160-8
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发表时间：
2010-04
影响因子：
2.1
通讯作者：
A. Kilfeather;C. Ó Cofaigh;J. Dowdeswell;J. Meer;D. Evans
中科院分区：
文献类型：
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作者：
A. Kilfeather;C. Ó Cofaigh;J. Dowdeswell;J. Meer;D. Evans
Glacimarine diamict 是通过不同的过程产生的，仅使用宏观沉积学标准通常会出现遗传分化问题。微形态学为此类研究提供了一个潜在有用的工具。准备了来自极地北大西洋、南极洲和北爱尔兰海的已知冰蓝宝石起源的宏观大量硬岩样品，用于微形态分析，以（1）识别不同沉积模式所特有的微观结构，（2）解释这些结构的遗传过程。这些样本包括泥石流、冰山湍流和悬浮沉降沉积物，这些沉积物来自第四纪晚期冰川影响的海洋环境：潮水冰川、冰下或前冰架以及冰流终点前的大陆坡。结果显示了泥石流沉积物的两个显着特征：近水平和垂直颗粒的双峰颗粒结构，以及沙子和卵石颗粒上的层状粘土和淤泥涂层。涂层最适合在具有较细粒度分布的沉积物和泥石流沉积物中形成，这些沉积物在槽口扇上具有相对较长的运行距离，这表明颗粒在浮力、湍流的水环境中持续旋转。这很重要，因为它阻止了塞流输送泥石流。冰山鼻甲的微观形态以前从未被描述过。它包含与耕地中描述的结构相似的结构，因此仅根据微形态标准似乎不太可能明确识别这些沉积物。悬浮沉积物的范围从含有微化石的细粒块状沉积物到以突然的结构变化为特征的更异质的粗沉积物，分别来自冰远端和近冰冰川环境。靠近冰的沉积物包含细小的垂直线，标记了落石穿过湿基质的轨迹。这些落石痕迹在之前的研究中尚未报道过。
Glacimarine diamicts are produced by diverse processes, and genetic differentiation is often problematic using macro-sedimentological criteria alone. Micromorphology offers a potentially helpful tool in such investigations. Macroscopically massive diamict samples of known glacimarine origin, from the Polar North Atlantic, Antarctica and north Irish Sea, were prepared for micromorphological analysis to (1) identify microstructures unique to different modes of sedimentation and (2) interpret genetic processes from those structures. The samples comprised examples of debris-flow, iceberg-turbate and suspension settling deposits from late Quaternary glacier-influenced marine environments: tidewater glacier, sub- or pro-ice shelf and continental slopes in front of ice stream termini. Results show two significant features of debris-flow sediments: a bimodal grain fabric of near-horizontal and -vertical grains, and laminated clay and silt coatings on sand and pebble grains. Coatings are best developed in sediments with finer grain-size distributions and in debris-flow sediments which have had relatively long run-out distances on trough-mouth fans, suggesting continuous rotation of grains in a buoyant, turbulent aqueous environment. This is significant because it precludes debris-flow delivery by plug flow. The micromorphology of iceberg turbate has not been described previously. It contains structures similar to those described in tills, so that unambiguous identification of these sediments seems unlikely based on micromorphological criteria alone. Suspension sediments range from fine-grained massive diamicts containing microfossils to more heterogeneous coarser sediments characterised by abrupt textural variations, from ice-distal and ice-proximal glacimarine environments respectively. The ice-proximal sediments contain fine vertical lineations marking the trajectories of dropstones through wet matrix. These dropstone tracks have not been reported in previous studies.