Dust accumulation in the New Zealand region since the last glacial maximum

Abstract

Loess is widespread in New Zealand; deposits > 1 m thick cover 10% of the land area. It has mainly been derived from dust deflated from river floodplains during the last glacial maximum (LGM). Dust accumulation continues today downwind of major river floodplains. Most loess is quartzofeldspathic, having its origins in Mesozoic and Neogene rocks of the axial ranges and hill country. In the central North Island there are deposits of volcanic loess derived from aeolian reworking of tephras. Loess morphology and properties vary greatly due to diverse parent materials, post-depositional climates and drainage conditions. The widespread 26,170 cal. yr Kawakawa Tephra provides a datum for calculating mass accumulation rates (MARs). Rates are mostly within the range 70-150 g m-2yr-1, but enhanced deposition at one site gave a rate of 360 g m-2yr1-. Contemporary MARs of 40-100 g m-2yr-1 were determined for distances of 1.75-0.4 km downwind of the Rakaia River. LGM MARs of quartz for two marine cores (P69 & Q858) drilled 100-300 km east of New Zealand are 40-70 g m -2yr-1. The MAR of the aeolian component of P69 is estimated to be ca 15 g m12yr-1