Multi-scale imaging of the weathering front with geophysical and geochemical techniques

土壤是生命的重要载体，是岩石化学风化和物理侵蚀作用的产物。土壤的范围由构造、气候和植被决定。然而，在不同的气候和生物环境下，人们对风化锋面的程度知之甚少。在这个跨学科的建议中，将结合地球物理和地球化学技术，在智利沿海三个不同的山坡上研究不同的气候环境和不同的植被类型。这样，就可以将劳动密集型和空间受限的风化锋地球化学成像与能够在更大尺度上无创地绘制土壤结构组织和土壤深度的地球物理方法相结合。将使用自上而下的多尺度方法，其中将执行大规模多配置EMI映射，以表征电导率的主要大规模特征。从这些图像中，将选择几个断面，其中将使用更详细的地球物理成像（EMI和GPR）。将采用两个最先进的多配置EMI设备，其探测深度从0.20米到6米不等。此外，几个探地雷达天线将被采用，范围从100到1000兆赫。根据这些地球物理图像，将在几个地点制作螺旋状土壤样品，并分析其质地，pH值，Corg， ECeff和土壤含水量。在选定的样带上挖掘出的土坑将使主元素和微量元素的分析能够破译风化锋面。宇宙成因核素将在关键的土壤坑中破译土壤剥蚀速率和土壤混合深度。所有这些结果将与反演的土坑位置的电磁干扰和探地雷达电参数进行回归，以研究获得的电磁干扰和/或探地雷达层厚度是否与风化厚度相对应，以及获得的低频（电磁干扰）和高频（探地雷达）电导率和介电常数的变化是否与确定的参数相关。我们计划在本分析中也包括在关键土坑进行的其他项目所获得的其他信息。通过这种方式，我们将利用地球物理成像方法从多个深度剖面中提升空间受限的风化锋面知识，以量化不同气候环境和不同植被类型的山坡尺度上的风化锋面。

Soil is an important carrier of life and is produced by chemical weathering and physical erosion of rock. The extent of soil is governed by tectonics, climate, and vegetation. However, little is known about the extent of weathering fronts in different climatic and biotic settings. In this interdisciplinary proposal the weathering front will be investigated on three different hillslope sites along coastal Chile with different climatic settings and different vegetation types by combining geophysical and geochemical techniques. In this way, the labor intensive and spatially restricted geochemical imaging of the weathering front will be used and combined with the geophysical methods that are able to noninvasively map the structural organization of soil and soil depth at larger scales. A top-down multi-scale approach will be used where a large-scale multi-configuration EMI mapping will be performed to characterize the dominant large-scale features in electrical conductivity. From these images, several transects will be selected where a more detailed geophysical imaging (EMI and GPR) will be employed. Two state-of-the-art multi-configuration EMI devices will be employed having a depth of investigation ranging from 0.20 m up to 6m. In addition, several GPR antennas will be employed ranging from 100 up to 1000 MHz. Based on these geophysical images, augered soil samples will be made at several locations and analyzed for texture, pH, Corg, ECeff and soil water content. Excavated soil pits on selected transects will enable the analysis of major and trace elements to decipher weathering fronts. Cosmogenic nuclides to decipher soil denudation rates as well as soil mixing depths will be carried out in the key soil pits. All these results will be regressed with the inverted EMI and GPR electrical parameters at the soil pit locations to investigate whether the obtained EMI and/or GPR layer thicknesses correspond to the weathering thickness and whether changes in the obtained electrical conductivity for low (EMI) and high frequencies (GPR) and permittivity are correlated to the determined parameters. We plan to include also other information obtained by other projects performed at the key soil pits in this analysis.In this way, we will upscale the spatially restricted knowledge of weathering fronts from several depth profiles using geophysical imaging methods to quantify weathering fronts on hillslope scales for different climatic settings and different vegetation types.