Weathering patterns in high‐latitude regolith

Large areas distributed on the Earth's surface are covered by regolith, an unconsolidated heterogeneous material overlying bedrock. In high‐latitude areas, most of the land surface has been reworked and eroded by both glacial and fluvial processes, leaving only remnants of formerly extensive regolith covers. In an effort to further the understanding of weathering patterns and processes in old regolith covers, a comprehensive study of localities spread across Norway was carried out. On the basis of the distribution of minerals and elements within regolith, as well as its internal structure and geomorphologic setting, we ascertained that it was formed in situ and originated in pre‐Quaternary times. There are similarities between the study sites with respect to regolith thickness, zonation, and composition. The Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP) suggests that the degree of chemical weathering in the regolith is advanced compared to the parental bedrock with a maximum change of over 80%, which indicates a substantial increase in the proportion of secondary versus primary minerals. Mineral analysis identified kaolinite and gibbsite, which are considered indicative of advanced weathering and therefore support this observation. On the basis of statistical relationships between different grain size fractions (<125 μ m), we observed a consistent pattern, which revealed that physical weathering becomes progressively less important in the production of grains smaller than 32 μ m. On the basis of this finding, we infer that chemical weathering progressively dominates the production of fine silt, very fine silt, and clay, whereas physical weathering primarily controls the production of grain size fractions larger than 32 μ m. This particular pattern is suggested to be an intrinsic feature in the formation of weathered high‐latitude regolith.