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的产物。土壤的范围受地质构造、气候和植被的影响。然而，人们对不同气候和生物背景下风化锋的程度知之甚少。 在这一跨学科的建议，风化锋将调查三个不同的山坡网站沿着智利沿海不同的气候环境和不同的植被类型相结合的地球物理和地球化学技术。通过这种方式，将使用劳动密集型和空间受限的风化锋地球化学成像，并与能够在更大尺度上非侵入性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，其中将执行大尺度多配置EMI映射以表征电导率中的主导大尺度特征。从这些图像中，将选择几个断面，其中将采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，其调查深度从0.20 m到6 m不等。此外，还将采用100至1000 MHz的多个GPR天线。根据这些地球物理图像，将在几个地点采集螺旋钻土壤样本，并分析质地、pH值、Corg、ECeff和土壤含水量。在选定的样带上挖掘土坑，将能够分析主要和微量元素，以破译风化锋。将在关键土坑中进行宇宙成因核素测试，以破译土壤剥蚀率和土壤混合深度。所有这些结果将回归与反EMI和GPR电参数在土壤坑的位置，以调查是否获得的EMI和/或GPR层的厚度对应于风化厚度，以及是否在获得的低（EMI）和高频率（GPR）的电导率和介电常数的变化与确定的参数。我们还计划将其他项目在主要土壤坑中获得的其他信息纳入分析，通过这种方式，我们将使用地球物理成像方法从几个深度剖面中提升空间限制的风化锋知识，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。

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.