Age and correlation of late quaternary terraces in the Lower Inangahua Valley, West Coast, South Island, New Zealand

Abstract

Three late Quaternary aggradational surfaces are recognised in the Inangahua valley, and are underlain by gravels correlated with the Speargrass, Tophouse, and Manuka Formations of the Upper Buller catchment. The Manuka Formation underlies a high terrace which can be followed down the Buller valley from Murchison to Inangahua, and is thought to have been deposited during the Waimaunga Glaciation (Suggate, 1965). The two younger formations cannot be confidently traced away from the Inangahua valley, and correlation with the Upper Buller formations is indirect. Pollen analyses indicate that both formations were deposited during glacial periods. A radiocarbon date of 20 200 ± 300 years B.P. indicates that the Speargrass Formation is correlated with the Kumara-2₂ advance of the Otira Glaciation. A sample from the Tophouse Formation was beyond the range of dating (> 47500 years B.P.), and this formation is tentatively correlated with the Waimea Glaciation.