The highest enrichment in light 28Si and oxalate-extractable Siox in Bhs/Bs horizons relative to E/Bh horizons (Fig. 5C; Table 2) highlights that the dissolution of secondary aluminosilicates in E/Bh horizons acts as a Si source for formation of poorly-crystalline aluminosilicates (imogolite-typematerials ITM) in Bhs/Bs horizons