The reasons for the inheritance of the composition and properties of red-colored soils of the modern weathering crust within the western part of the Sichuan Basin of China

In this work, we conducted an experimental evaluation and analysis of the characteristics and makeup of red-colored rocks from four representative Cretaceous and Jurassic sedimentary sequences in the western Sichuan Basin of China, as well as their weathering products. To determine the direction of weathering processes and the cause-and-effect link between the characteristics and composition of the parent rocks and the excess chemical components in the weathered soils, the chemical index of alteration was calculated. The findings demonstrated that, with regard to features like color, density of solid component, organic carbon content, granulometric composition, pH, mineral composition, and content of main chemical elements, all samples of weathered (dispersed) soils are quite comparable to the parent rocks. All samples of weathered soils and parent rocks exhibit similar chemical weathering characteristics and an index, according to the results of the CIAcorr calculation and the examination of the A–CN–K triangle diagrams. Furthermore, all of them have attained a moderate level of chemical weathering, with samples from Jurassic rocks (J3p, J3s, and J2s) having far lower weathering intensities than those from Cretaceous rocks (K1c). The red-colored rocks are characterized by weak chemical weathering and rapid development of physical weathering. This weathering characteristic can be attributed to the parent rock’s uniform texture and mostly clayey composition, which break down readily in environments with high humidity and plenty of heat. The low level of chemical weathering is due to the fact that the parent rock itself has undergone a significant change in chemical composition during sedimentation and subsequent diagenesis, and has acquired a high degree of resistance to subsequent transformation under modern conditions. Therefore, the characteristics and makeup of purple soil are mostly determined by the parent rock.