Soil-Age Relationships on Late Quaternary Moraines, Arrowsmith Range, Southern Alps, New Zealand

Abstract

Loess on Holocene moraines has accumulated steadily since moraine deposition resulting in soils that generally lack buried horizons and have a degree of development which closely reflects the age of the underlying till. The progressive development of two field indices and five laboratory properties of these soils are best described by logarithmic functions. Indices of pedogenic iron and rubification yield the highest correlation with age of deposit. Rates of soil development are faster than those reported for other parts of the eastern Southern Alps and curves of most soil properties flatten within ca. 10 ka.

In contrast, the use of soils to date pre-Holocene moraines is greatly hindered by loess redistribution which commonly results in eroded and/or buried soils. Radiocarbon dates from charcoal within loess on pre-Holocene moraines suggest that loess reworking has been episodic, resulting in soils that are far younger than underlying tills. Holocene reworking of loess on upland sites in response to fires, frost action, and high winds may serve as an analog for large-scale late Pleistocene loess reworking on the Canterbury Plains.