Radiocarbon and luminescence dating of overbank deposits in outwash sediments of the Last Glacial Maximum in North Westland, New Zealand

Abstract

In the Grey River valley, North Westland, New Zealand, extensive terraces of outwash sediments assigned to the Otira glaciation form outstanding geomorphologic features. Four layers of organic sediments subdivide stratified outwash gravels of the major terrace. The age of the fine-grained sediments is constrained by 55 radiocarbon (14C) ages and 8 optically stimulated luminescence (OSL) ages. The calibrated radiocarbon ages cover the age range between 21 350 and 23 890 cal yr BP. The ages for each different layer are consistent and are in stratigraphic order with mean ages of 22 350 cal yr BP (layer A), 22 470 cal yr BP (layer B), 22 930 cal yr BP (layer C), and 22 960 cal yr BP (layer D). OSL dating of the silty overbank deposits alternating with the organic beds imply a deposition at 21 700 ± 2600 yr. The use of different organic compounds for radiocarbon dating (separated organic residues, humic acids, terrestrial seeds) and the consistency with the luminescence dating support the reliability of the results. We use the informal name Raupo complex for the overbank deposits and consider it to reflect a moderate climate oscillation between two glacial advances during Oxygen Isotope Stage 2. © 2003 Taylor & Francis Group, LLC.