Soil patterns in weathering, clay translocation and podzolisation on hilly and steep land at port underwood, Marlborough Sounds, New Zealand: Classification and relation to landform and altitude

Abstract

Six soil profiles ranging in altitude from 30 m to 580 m at Port Underwood in the Marlborough Sounds, New Zealand, are described, classified and discussed in terms of their morphology, chemistry and mineralogy. The soils are formed from greywacke on hilly and steep land under a climate ranging from mild and humid at lower elevations to cool and superhumid at the highest elevation. The profiles show distinct altitudinal patterns in weathering, clay translocation, leaching and podzolisation. Differences in weathering are related mainly to geomorphic history, whereas differences in leaching and podzolisation are attributed mainly to the effects of climate. Weathering has been strongest at altitudes below about 200 m where the soils are dominated by kaolinitic clay minerals. Parent materials were probably inherited from Late Pleistocene interglacial or interstadial weathering. At higher altitudes less weathered soils containing mainly vermiculite clays are formed from parent materials exposed by widespread periglacial erosion and deposition during the last glaciation, and from periodic erosion and deposition during the Holocene. Clay translocation, as evidenced by the presence of argillic horizons, has been most active at lower altitudes where the soils are older and the climate is drier than at higher elevations. Field and laboratory data show that the 2 profiles at the highest elevation are podzolised. They have substantial accumulations of illuvial amorphous minerals and mineral-organic complexes in subsoils, and one profile also has morphological eluvial features with an underlying placic horizon. Neither the New Zealand Genetic Classification nor Soil Taxonomy satisfactory classifies the podzolised soils. We think that they would be better classified as Spodosols or as spodic subgroups of Inceptisols.