Marine terraces of the Waitutu district and their relation to the late Cenozoic tectonics of the southern Fiordland region, New Zealand

Abstract

At least 13 marine terraces or their remnants, with maximum shoreline altitudes of c. 3 m, 60, 90, 140, 230, 320, 370, 460, 580, 660, 780, 870 and 1040 m, are preserved in the Waitutu district of southeast Fiordland. Alluvial terraces related to glaciation of the immediate hinterland cross the marine terraces and allow the terraces to be confidently matched to the glacial/interglacial sequence. Three well-preserved marine terraces of the Last Interglacial separate fluvioglacial terraces of the Last and Penultimate Glaciations. An uplift rate of 1.1 mm/yr, derived from the altitude of the fourth youngest terrace inferred to represent oxygen isotope stage 5e, is used to estimate the ages of the older marine terraces by linear extrapolation, up to > 900,000 years. The Waitutu marine terraces traced into southwestern Fiordland decrease markedly in height, to levels corresponding to an uplift rate of 0.6 mm/yr. The higher peaks of Fiordland conform to a summit-level surface which is interpreted to be, in effect, a marine terrace of very early Pleistocene age. The surface is broadly domed in a pattern matching the marine terraces of the south coast. Many of the strong structural features in the vicinity of southern Fiordland, associated with the convergent boundary between the Indo-Australian and Pacific plates, are of late Miocene age and belie the simple deformation pattern of essentially epeirogenic uplift the area has undergone in the Quaternary.