Silicon fractionation of fragipan and non-fragipan horizons in the Central United States

Mineralogical differences between seam and prism material in loess‐derived fragipans in western Kentucky

“…Furthermore, Fe d and Al d were correlated with one another, suggesting an association between these elements. These findings confirm our past results that free iron oxide minerals such as goethite and/or hematite might be present in the fragipan and contribute to the binding of Si and dense nature of these horizons (Matocha et al., 2018; Shepard et al., 2023). In order to provide greater insight on these possible associations, we followed the wet chemical results with more direct mineralogical techniques to separate mineralogical characteristics from the prism and seam materials.…”

“…Further, it was suggested that the aluminum (Al) associated with the dithionite extraction that isolates Fe oxides was not coordinated with the silica but was more likely substituted into the Fe oxides (Duncan & Franzmeier, 1999; Marsan & Torrent, 1989). Past work from loess‐derived fragipans in Kentucky has documented patterns in dithionite‐extractable Si, Al, and Fe, which would suggest the presence of Al‐substituted goethite and its possible role in binding Si (Matocha et al., 2018; Shepard et al., 2023). There is some debate about the importance of this mechanism in light of more recent studies demonstrating that fragipan formation was favored by low goethite and elevated kaolinite concentrations in fragipan soils from Brazil (Ramos et al., 2015).…”