PODZOLISATION MECHANISMS AND THE SYNTHESIS OF IMOGOLITE IN NORTHERN SCANDINAVIA

The nature of the short-range ordered Al and Fe minerals of the spodic B horizons of northern Scandinavia was studied by selective dissoluti on, transmission electron microscopy, infrared absorption and sulphate adsorption experiments. Imogolite-type materials (proto-imogolite all ophane and well-developed imogolite) were the predominant oxalate-extr actable Al minerals. Minor amounts of gibbsite and kaolinite were also found. The Fe oxides were less abundant and relatively well crystalli zed. Imogolite-type materials were the predominant source of positive charge, as evidenced by the amount of sulphate adsorbed. The Fe:Al rat io of the pyrophosphate extracts was positively correlated with the ra tio of pyrophosphate-C to oxalate-extractable Al - this observation pr ovides field evidence that imogolite-type materials were particularly unstable in the presence of organic substances. It is hypothesized tha t most accumulated Al and Fe originated from the congruent dissolution of primary minerals followed by the downward migration and degradatio n of metal-organic complexes, but incongruent weathering within the B horizon might have made additional contributions to the precipitation of the short-range ordered minerals. Historical climatic change might, to some extent, explain why metal-organic complexes were almost absen t in many B horizons.