Quaternary stratigraphy and soil of part of the Waimarino block (Pipiriki) Wanganui River

Abstract

The study area lies 50km north of Wanganui city, on the Whanganui River near the settlement of Pipiriki. This is an area of dissected hill country in which three major soil types are recognised: three steepland soils and two soils on lowland areas, one associated with waterlogged areas and the other associated with river overbank deposits. The yellow brown earths develop on most slopes but loams and the intergrades (both of which contain allophane) also occur and their distribution is controlled by topography and soil parent material. Waterlogged soils are also controlled by topography. The time in which all these soils have developed and the climate during their formation can be estimated due to the presence of the Kawakawa Tephra (dated at 22,600 yrs B.P). Micromorphology has been used to detemine the pedogenesis of the soil types, with a major emphasis on structure and how it changes with soil type and the type of topography. The micromorphology has shown that the soil types exhibit similar characteristics when under stress. All soil types in the field area are prone to slipping although the loams and the intergrades due to the presence of allophane appear to be more prone.