부산대학교 도서관

The chemical and physical properties, clay mineralogy, and [sup.14]C radiocarbon age of iron nodules found in a Ultisol located on a low elevation terrace of Taiwan were investigated. The results indicated that the amount and size of iron nodules increase with soil depth. Free iron contents in nodules were markedly higher than in the surrounding soil matrix. [Fe.sub.o]/[Fe.sub.d] ratio was low in all iron nodules, indicating that the predominant form of free iron was crystalline. Al-substituted goethite was found as the predominant oxide mineral and Al substitution ranged from 16 to 24% mole. Illite and hydroxy-interlayered vermiculite and kaolinite were the dominant clay minerals in the iron nodules. X-ray fluorescence (XRF) analysis of the iron nodules are composed primarily of Fe, Si, and Al, and minor amounts of Mn. Based on the similarity of clay mineralogical compositions and radiocarbon dating ages, it is suggested that the major driving force promoting the formation of iron nodules was in situ weathering of saprolite by the frequent wetting/drying cycles. We speculate that illuviated iron played only a minor role in their formation. Additional keywords: clay mineralogy, [sup.14]C radiocarbon, goethite, iron nodules, saprolites, soil matrix.
Introduction Nodules typically occur in hydromorphic soils of humid temperate climates. Compared with concretions, nodules do not occur commonly in soils. Sherman and Kanehiro (1954) and Folster (1968) reported that [...]