Physical modeling of ice-sheet-induced salt movements using the example of northern Germany

IF 2.8 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Earth Surface Dynamics Pub Date : 2024-04-26 DOI:10.5194/esurf-12-559-2024
Jacob Hardt, Tim P. Dooley, Michael R. Hudec
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Abstract

Abstract. Salt structures and their surroundings can play an important role in the energy transition related to a number of storage and energy applications. Thus, it is important to assess the current and future stability of salt bodies in their specific geological settings. We investigate the influence of ice sheet loading and unloading on subsurface salt structures using physical models based on the geological setting of northern Germany, which was repeatedly glaciated by the Scandinavian Ice Sheet during the Pleistocene. Apparent spatial correlations between subsurface salt structures in northern Germany and Weichselian ice marginal positions have been observed before, and the topic is a matter of ongoing debate. Recently described geomorphological features – termed surface cracks – have been interpreted as a direct result of ice-sheet-induced salt movement resulting in surface expansion. The spatial clustering and orientation of these surface cracks has not been well understood so far, owing to only a limited number of available studies dealing with the related salt tectonic processes. Thus, we use four increasingly complex physical models to test the basic loading and unloading principle, to analyze flow patterns within the salt source layer and within salt structures, and to examine the influence of the shape and orientation of the salt structures with respect to a lobate ice margin in a three-dimensional laboratory environment. Three salt structures of the northern German basin were selected as examples that were replicated in the laboratory. Salt structures were initially grown by differential loading and buried before loading. The ice load was simulated by a weight that was temporarily placed on a portion of the surface of the models. The replicated salt structures were either completely covered by the load, partly covered by the load, or situated outside the load extent. In all scenarios, a dynamic response of the system to the load could be observed; while the load was applied, the structures outside the load margin started to rise, with a decreasing tendency with distance from the load margin, and, at the same time, the structures under the load subsided. After the load was removed, a flow reversal set in, and previously loaded structures started to rise, whereas the structures outside the former load margin began to subside. The vertical displacements during the unloading stage were not as strong as during the load stage, and thus the system did not return to its pre-glaciation status. Modeled salt domes that were located at distance from the load margin showed a comparably weak reaction. A more extreme response was shown by modeled salt pillows whose margins varied from sub-parallel to sub-perpendicular to the load margin and were partly covered by the load. Under these conditions, the structures showed a strong reaction in terms of strain and vertical displacement. The observed strain patterns at the surface were influenced by the shape of the load margin and the shape of the salt structure at depth, resulting in complex deformation patterns. These physical modeling results provide more evidence for a possible interplay between ice sheets and subsurface salt structures, highlighting the significance of three-dimensional effects in dynamic geological settings. Our results lead to a better understanding of spatial patterns of the surface cracks that were mapped at the surface above salt structures and offer further room for interpretation of the influence of salt movements on the present-day landscape.
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以德国北部为例,建立冰盖诱发盐分移动的物理模型
摘要盐体结构及其周围环境可在能源转型过程中发挥重要作用,这与许多存储和能源应用有关。因此,评估盐体在其特定地质环境中当前和未来的稳定性非常重要。德国北部在更新世期间曾多次遭受斯堪的纳维亚冰盖的冰川作用,我们根据德国北部的地质环境,利用物理模型研究了冰盖加载和卸载对地下盐结构的影响。德国北部地表下盐层结构与魏希塞尔冰缘位置之间存在明显的空间相关性,这个问题一直存在争议。最近描述的地貌特征(称为地表裂缝)被解释为冰盖引起的盐运动导致地表扩张的直接结果。迄今为止,由于对相关盐构造过程的研究数量有限,人们对这些地表裂缝的空间集群和走向还不甚了解。因此,我们使用四个日益复杂的物理模型来测试基本的加载和卸载原理,分析盐源层和盐结构内部的流动模式,并在三维实验室环境中研究盐结构的形状和方向对叶状冰缘的影响。我们选取了德国北部盆地的三个盐结构作为示例,在实验室中进行了复制。盐结构最初通过差动加载生长,并在加载前埋入地下。冰载荷是通过临时放置在模型部分表面的砝码来模拟的。复制的盐结构要么完全被荷载覆盖,要么部分被荷载覆盖,要么位于荷载范围之外。在所有情况下,都可以观察到系统对荷载的动态响应;在施加荷载时,荷载范围外的结构开始上升,并随着与荷载范围距离的增加而呈下降趋势,与此同时,荷载范围内的结构开始下沉。移除荷载后,荷载流发生逆转,之前的荷载结构开始上升,而之前荷载边缘外的结构开始下沉。卸载阶段的垂直位移不如加载阶段强烈,因此系统没有恢复到冰川期之前的状态。距离荷载边缘较远的盐穹顶模型的反应同样微弱。模拟盐枕的反应更为极端,其边缘从与荷载边缘次平行到次垂直不等,并且部分被荷载覆盖。在这些条件下,结构在应变和垂直位移方面表现出强烈的反应。地表观测到的应变模式受到荷载边缘形状和深层盐结构形状的影响,从而产生了复杂的变形模式。这些物理建模结果为冰盖与地下盐结构之间可能存在的相互作用提供了更多证据,凸显了三维效应在动态地质环境中的重要性。我们的研究结果使人们更好地理解了在盐结构上方地表绘制的地表裂缝的空间模式,并为解释盐运动对当今地貌的影响提供了进一步的空间。
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来源期刊
Earth Surface Dynamics
Earth Surface Dynamics GEOGRAPHY, PHYSICALGEOSCIENCES, MULTIDISCI-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
5.40
自引率
5.90%
发文量
56
审稿时长
20 weeks
期刊介绍: Earth Surface Dynamics (ESurf) is an international scientific journal dedicated to the publication and discussion of high-quality research on the physical, chemical, and biological processes shaping Earth''s surface and their interactions on all scales.
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