Abstract:
On the western North Island, New Zealand, a Late Quaternary sequence of allophane-dominated cover-bed (Andisol) deposits have accumulated from intermittent accretion and rapid, subsequent weathering of aerially transported detritus of dominantly andesitic provenance. Particle size analyses of Andisol samples were attempted for textural classification and provenance studies. The hydrometer and sedigraph techniques were unsuccessful due to difficulties arising from the flocculation of short-range order clay and organic constituents (SROCO), which prevented complete particle dispersion. Neither acidic (HCl) nor alkaline (NH4OH or NaOH) solutions were effective in completely dispersing samples, so an alternative chemical procedure was devised. This alternative pretreatment involves the selective dissolution of Andisol SROCO constituents by 0.2 mol acid-oxalate reagent (pH 3.0–3.5), and has considerable potential in the determination of particle size, soil textural classification and provenance of allophane-dominated andesitic deposits.
