Subglacial overdeepenings are common elements of mountain forelands and have considerable implications for human infrastructure. Yet, the processes of overdeepening by subglacial erosion and especially the role of bedrock geology are poorly understood. We present a case study of the Gebenstorf-Stilli Trough in northern Switzerland, a foreland overdeepening with a regionally unique, complex underlying bedrock geology: in contrast to other Swiss foreland overdeepenings, it is incised not only into Cenozoic Molasse deposits, but also into the underlying Mesozoic bedrock. In order to constrain the trough morphology in 3D, it was targeted with scientific boreholes as well as with seismic measurements acquired through analysis of surface waves. Our results reveal an unexpectedly complex trough morphology that appears to be closely related to the bedrock geology. Two sub-basins are incised into calcareous marls and Molasse deposits, and are separated by a distinct ridge of Jurassic limestones, indicating strong lithological control on erosional efficiency. We infer generally relatively low glacial erosion efficiency sensu stricto (i.e. quarrying and abrasion) and suggest that the glacier's basal drainage system may have been the main driver of subglacial erosion of the Gebenstorf-Stilli Trough.

冰下过度加深是山地前地的常见元素，对人类基础设施有相当大的影响。然而，人们对冰下侵蚀过度加深的过程，尤其是基岩地质的作用知之甚少。我们介绍了瑞士北部 Gebenstorf-Stilli 海槽的案例研究，该前陆过深具有区域独特、复杂的下伏基岩地质：与其他瑞士前陆过深过深不同，它不仅被切入新生代磨拉石矿床，而且被切入到下伏中生代基岩。为了限制 3D 中的槽形貌，它以科学钻孔以及通过分析表面波获得的地震测量为目标。我们的结果揭示了一个出乎意料地复杂的槽形态，它似乎与基岩地质密切相关。两个子盆地被切割成钙质泥灰岩和磨拉石沉积物，并被明显的侏罗纪石灰岩脊隔开，表明对侵蚀效率的强烈岩性控制。我们推断严格意义上的冰川侵蚀效率通常相对较低（即采石和磨损），并认为冰川的基底排水系统可能是 Gebenstorf-Stilli 海槽冰下侵蚀的主要驱动因素。