Depositional evidence for marginal oscillations of the Irish Sea ice stream in southeast Ireland during the last glaciation
Depositional evidence for marginal oscillations of the Irish Sea ice stream in southeast Ireland during the last glaciation
复制标题
末次冰期期间爱尔兰东南部爱尔兰海冰流边缘振荡的沉积证据
DOI：
10.1111/j.1502-3885.2003.tb01443.x
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发表时间：
2003
期刊：
影响因子：
2.2
通讯作者：
C. Ó. Cofaigh
中科院分区：
文献类型：
--
作者：
D. Evans;C. Ó. Cofaigh
爱尔兰东南海岸的晚德文世/米德兰代冰川沉积物包含了爱尔兰海冰流（ISIS）边缘的沉积记录。通过屏幕山暴露揭示了一个地层，记录了ISIS（“爱尔兰海丘”）的最初陆上流动，随后是冰流衰退和再进，构建冰川构造脊。冰接触扇（屏风成员）与冰下变形冰碛物和冰上/水下质量流diamicts相关联。在东南部爱尔兰，ISIS在冰前湖沉积物上向岸上移动，这些沉积物被强烈折叠、逆冲和蚕食，产生了一种冰川构造岩，在这种冰川构造岩上沉积了层状和块状的杂岩，形成冰川构造切片。冰边缘衰退和振荡通过以下方式记录：（a）冰近端、水下富二聚岩相;（b）孤立的冰接触冰湖三角洲;（B）冰接触三角洲;（c）冰湖沉积物的同沉积冰川构造扰动和冰接触沉积物的逆冲;（d）近海冰碛脊;（e）改变冰流方向和相变。识别陆上动态（可能是涌动的）冰流边缘的诊断标准包括冲断块冰碛、构造蚀坑冰水沉积和冰川构造岩堆叠序列、变形冰碛和居间层状沉积。此外，水力压裂填充物在沉积物中的广泛发生被ISIS覆盖和局部改造，表明冰川前进期间地下水压力大大升高。位于ISIS陆地边缘周围的冰川沉积物和地貌被解释为陆上冰川流的产物，这些冰川流蚕食和构造叠加了先前存在的海洋和冰川沉积物。冰川前边缘的冰下变形物质的局部构造增厚导致净侵蚀区立即上升-冰下冰碛物净增生的亚边缘区的冰。冰流边缘越稳定，亚边缘沉积堆积就越厚、越复杂。
Late Devensian/Midlandian glacial deposits on the southeast Irish coast contain a record of sedimentation at the margins of the Irish Sea ice stream (ISIS). Exposures through the Screen Hills reveal a stratigraphy that documents the initial onshore flow of the ISIS (‘Irish Sea Till’) followed by ice stream recession and readvances that constructed glacitectonic ridges. Ice‐contact fans (Screen Member) were deposited in association with subglacial deformation tills and supraglacial/subaqueous mass flow diamicts. In SE Ireland, the ISIS moved onshore over proglacial lake sediments which were intensely folded, thrust and cannibalized producing a glacitectonite over which laminated and massive diamictons were deposited as glacitectonic slices. Ice marginal recession and oscillations are documented by: (a) ice‐proximal, subaqueous diamict‐rich facies; (b) isolated ice‐contact glacilacustrine deltas; (c) syn‐depositional glacitectonic disturbance of glacilacustrine sediments and overthrusting of ice‐contact outwash; (d) offshore moraine ridges; and (e) changing ice flow directions and facies transitions. Diagnostic criteria for the identification of dynamic, possibly surging, ice‐stream margins onshore include thrust‐block moraines, tectonized pitted outwash and stacked sequences of glacitectonites, deformation tills and intervening stratified deposits. In addition, the widespread occurrence of hydrofracture fills in sediments overridden and locally reworked by the ISIS indicate that groundwater pressures were considerably elevated during glacier advance. The glacigenic sediments and landforms located around the terrestrial margins of the ISIS are explained as the products of onshore glacier flow that cannibalized and tectonically stacked pre‐existing marine and glacilacustrine sediments. Localized tectonic thickening of subglacially deformed materials at the former margins of glaciers results in zones of net erosion immediately up‐ice of submarginal zones of net accretion of subglacial till. The more stable the ice‐stream margin the thicker and more complex the submarginal sedimentary stack.