We describe the use of a fully volumetric geophysical imaging approach, three-dimensional electrical resistivity (3D ERT), for bedrock detection below mixed sand and gravel deposits typical of fluvial valley-fill terraces. We illustrate the method through an analysis of terrace deposits of the Great Ouse River (UK), where up to 4 m of sand and gravel have filled the valley bottom during the latest Pleistocene. We use an edge detector to identify the steepest gradient in first-derivative resistivity profiles, which yields an estimate of bedrock depth (verified by drilling) to a precision better than 0.2 m (average) and 0.4 m (standard deviation). The 3D ERT method provides a high spatial resolution, which enabled a previously unknown erosional bedrock structure, associated with the change from deeper first terrace to second terrace deposits, to be identified in the Great Ouse valley. The method provides a relatively quick method to quantify terrace fill volume to a greater degree of precision than currently available.
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机译：我们描述了使用全体积地球物理成像方法，三维电阻率（3D ERT），用于在河谷填筑带阶地典型的混合砂砾砾石沉积物下方的基岩检测。我们通过分析大乌斯河（英国）的阶地沉积物来说明该方法，在最近的更新世期间，高达4 m的沙子和砾石填充了谷底。我们使用边缘检测器来识别一阶导数电阻率曲线中最陡的梯度，从而得出基岩深度（通过钻孔验证）的估计值，其精度优于0.2 m（平均值）和0.4 m（标准偏差）。 3D ERT方法提供了很高的空间分辨率，可以在大乌兹河谷中识别出以前未知的侵蚀性基岩结构，以及从较深的第一阶地到第二阶地沉积物的变化。该方法提供了一种相对快速的方法，以比当前可用的方法更高的精确度来量化梯田填充量。
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