9:45 AM - 10:00 AM
[MIS12-14] Development of a new silicate weathering index (RW) and its application to the climate reconstruction
Keywords:Chemical weathering, Major elements, Climate zone, Paleoclimate
Quantifying past weathering intensity is crucial for understanding paleoclimate changes. Given that the chemical composition of sediments reflects the weathering environment in which they were generated, this can provide insights into the intensity and style of weathering during the past. Various weathering indices based on the whole-rock geochemical compositions of sedimentary rocks are widely used, however, these indices have limitations. For example, conventional indices such as CIA, WIP, and W index can only be applied to sediments consisting mainly of silicates, with low concentrations of materials like biogenic calcite. To develop a weathering index applicable to sedimentary rocks formed under various source rocks and environmental conditions, we used multivariate statistics (Independent Component Analysis) to analyze a dataset consisting of igneous rocks (n = 300) and their weathering profiles (n = 273). The chemical variations of the igneous rocks and weathering trends were independently extracted from the dataset, and a new weathering index (the robust weathering index; RW) was proposed. The RW index is independent of SiO2, CaO, and P2O5 contents, which are often greatly influenced by biological and diagenetic processes. We assessed the applicability of the RW index using saprolite profiles, zonal soils, and carbonate-rich paleosols. The RW index is robust even for sediments containing a large amount of non-silicate materials, enabling the comparison of weathering intensity across a wide range of sedimentary rocks. Further, the relationship between the RW index and climatological conditions are investigated. Spatial–temporal reconstructions of paleo-weathering conditions will be improved by applying the RW index to terrestrial and marine sediments.