Variation in Soil-Catena Characteristics of Moraines with Time and Climate, South Island, New Zealand

Abstract

AbstractSoil catenas on three moraines in each of two areas with different climate were studied to determine (a) downcatena soil differentiation with climate and time and (b) their usefulness in estimating the relative ages of the underlying deposits. In the dry area (mean annual precipitation (MAP), ca. 0.5 m) all soils have A/Bw/C profiles formed in loess/till. Their similarity in morphology and in most chemical characteristics with catena position and age suggests that the low MAP does not result in much redistribution of water, elements, or sediment downcatena. This similarity also suggests ages close to each other and correlation with the Otiran Glaciation (oxygen-isotope stages 2 and 4). In the wet area (MAP ca. 3 m) the soils also formed in loess/till and with time (a) soil morphology progresses from A/Bw/C to A/E/B/C, (h) reduced properties intensify, especially in the downcatena profiles, (c) citrate-bicarbonate-dithionite-extractable Fe displays accumulation in the youngest catena followed by loss in the older catenas, and (d) downcatena trends in total chemical data display marked losses of the more mobile elements. These data demonstrate that although catena development is rapid in a wet climate, the downcatena contrast can be muted with time due to a change from processes dominated by oxidation to those dominated by reduction. Soil catena properties in the wet area are sufficiently different to not refute age estimations suggested by Suggate (1990): youngest moraine, oxygen-isotope stage 2; intermediate moraine, isotope stage 4; and oldest moraine, isotope stage 10. An unresolved problem in both areas is the possibility of soil erosion to foul soil-age relations.