A catena of soils on Bealey Spur, Canterbury, New Zealand

Abstract

The soils of a catena an Bealey Spur, an ice-truncated spur in the upper Waimakariri River valley, Canterbury, New Zealand, were studied with the primary objective of locating, isolating, and characterising poorly ordered aluminosilicates resembling allophane. Other aspects relating to the general pedology and crystalline clay mineralogy of the soils were also studied in some depth.

The soils of the site chosen for study showed profile and distribution characteristics related to slope, drainage, podzolisation , and windthrow. A repeating sequence of soil profile classes, extending from hill crest to basin floor, was identified as the Bealey Catena.

The chemical and physical properties of five profiles chosen for examination were characteristic of acid, podzolised soils in catenas. Soils in the lower slope positions were poorly-drained, had finer textures, and contained more organic matter. They also showed accumulations of phosphorus and aluminium.

Poorly-ordered aluminosilicates had accumulated in the Bs and Cs horizons of four of the five profiles. Relatively pure samples of these complexes were isolated from the C horizon of the Lower Footslope profile, and established, using a range of chemical and instrumental techniques, to be proto-imogolite allophane.

E horizons in the five profiles contained varying proportions oi the expanding clay minerals vermiculite and beidellite. The structural formula of beidellite was determined and its relationship to vermiculite in transformation processes during weathering discussed. It was concluded that beidellite is a transformation product of muscovite, that vermiculite is an intermediate in the transformation process in podzol E horizons, and that the vermiculite → beidellite transformation is not reversible.