Premium
Iron Concretions in a Typic Dystrochrept in Taiwan
Author(s) -
King H. B.,
Torrance J. K.,
Bowen L. H.,
Wang C.
Publication year - 1990
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1990.03615995005400020029x
Subject(s) - goethite , weathering , saprolite , pedogenesis , hematite , geology , mineralogy , soil horizon , matrix (chemical analysis) , evergreen , quartz , geochemistry , chemistry , soil water , soil science , botany , paleontology , organic chemistry , adsorption , chromatography , biology
Prominent Fe concretions, singly and in clusters up to 30 cm across, occur in a Typic Dystrochrept pedon developed under evergreen mixed hardwood, on 60% slopes, by in situ weathering of Tertiary shales. The round to subangular polygonal structures contain a gray matrix (N 5) surrounded by two Fe‐rich layers. The inner layer is dark reddish brown (5YR 3/3) and is composed of 60% Fe 2 O 3 , almost equally as hematite and goethite. Energy‐dispersive x‐ray analysis indicates higher concentrations of Fe, Mn, Ca, and some trace elements than in the soil matrix. The outer reddish‐yellow (7.5YR 6/6) layer is goethite rich: only Fe and Zn are consistently in greater abundance than in the soil matrix. Thin‐section studies and chemical evidence suggest that the concretions commence their formation during the weathering of saprolite, are most prominently developed between 50‐ and 100‐cm depth, and remain mainly as fragments above 30 cm. The Fe forming these concretions appears to be cycled downward during their disintegration, to become involved again in the process. A life cycle for the concretions, based on the balance of erosion, Fe mobilization, and reprecipitation at the site, is proposed.