Assessment of radiocarbon assay and soil stratigraphic techniques for determining the age of gley podzols : Graham's Terrace, North Westland : A thesis submitted in partial fulfilment of the requirements for the degree of Master of Applied Science in the University of Canterbury

Abstract

This study presents field, morphological, and chemical properties of soils, and buried soils formed in a sequence of aeolian coverbeds and interbedded peaty sediments and peats. A thin layer, identified as Kawakawa Tephra is interbedded with these coverbeds and peats and is used as a tephra marker plane. These soils occur on Graham's Terrace, and the coverbeds are underlain by an aggradation surface of Walmean age. The vegetation comprises fern and sedgeland and cutover podocarp-broadleaf-beech forest. Both aggradation gravels and coverbeds are weathered felsic sediments. Coverbeds are thickest and coarsest adjacent to the terrace riser (average 132cm) and thin to 70cm or less with distance (0.5cm- 1 km) away from the terrace margin. Field and laboratory studies have identified two coverbed units, with a buried soil developed on the underlying Waimean outwash gravels. Micromorphological examination of the tephra's glass shard fabric indicates minimal reworking as shards show a preferred orientation. Volcanic glass shards consistently occupy a specific stratigraphic level within the coverbeds, even when not visible in the field. Soil profile features strongly reflect both the effects of gleying and podzolisation, resulting from intense leaching. The present annual rainfall varies from 1500 to 2500mm per annum. The relative mobilities of extractable Fe, Al and Si serve as an indication of the effects of leaching and weathering.