Loess, soil stratigraphy and Aokautere Ash on late Pleistocene surfaces in south Westland, New Zealand: Interpretation and correlation with the glacial stratigraphy

The detailed stratigraphy and chronology for Late Pleistocene glaciations in north Westland have not previously been applied to glacial deposits and landforms of south Westland, in part because of lack of exposure. A stratigraphy for loess coverbeds offers the potential for discriminating and correlating landforms in this region. This study, in Saltwater Forest and surrounding areas in south Westland, confirms the presence of loess and of the incorporated 22,600 BP (radiocarbon years) Aokautere Ash beneath Late Pleistocene moraine and terrace surfaces. Loess sheets are thin (ca. 40 cm thick) and accretion rates have been low (ca. 30 mm ka(-1) during the last stadial of the last glaciation). Boundaries between loess sheets were placed at the surface of buried soils (paleosols) identified from their morphology. Criteria for recognition of buried soils differ between the moderately well drained moraine sites and poorly to extremely poorly drained terrace sites. Five loess sheets have been recognised and correlated to the oxygen isotope record on the basis of the position of maximum counts of glass shards of Aokautere Ash, pollen analysis, and radiocarbon dates. Loess sheets 1 and 2 are of Last (Otira) Glacial age; loess sheet 3 accumulated during the Last (Kaihinu) Interglacial; and, loess sheet 4 accumulated during the penultimate (Waimea) glaciation. Loess sheet 5 is of at least Waimean age. Copyright (C) 1996 INQUA/Elsevier Science Ltd