Formation of iron nodules in a Hapludult of central Taiwan

Abstract

This study compared iron nodules with their matrix materials in a Hapludult from central Taiwan. Mineralogy and 14C ages of the iron nodules were compared with their associated matrix materials. The samples were analyzed by X-ray diffraction (XRD) and accelerated mass spectroscopy (AMS). Hydroxy-interlayered vermiculite (HIV) and illite were the major clay minerals in the soil matrix, but illite and kaolinite were dominant in the iron nodules. Clay mineralogy of iron nodules revealed more intense weathering process than the surrounding soil matrix. 14C dates showed that the age of saprolite and iron nodules were similar, and were both much older than those of the soil matrix. It is suggested that iron nodules developed from residuum of the Tertiary shale (saprolite). During pedogenesis, saprolite acted as a nucleus, where Fe coated on its surface was transferred to form iron nodules. Key words: 14C dates, iron nodules, saprolite, soil matrix, Ultisol