Late pliocene and quaternary glaciations of New Zealand

Abstract

Evidence of Late Pliocene glaciations is fragmentary. The Ross Glaciation in northwest South Island is correlated with the first marine faunal evidence of marked cooling in the Wanganui Basin in southern North Island; it is inferred to be in the 2.6-2.4 Ma age range. The Porika Glaciation, in a separate area of northwest South Island, is younger, judged by palynology, and is correlated with a cooling 2.2-2.1 Ma BP inferred from stratigraphic evidence of lowered sea level in the Wanganui Basin: A gap of >1.5 Ma in the record of glaciations is largely filled by Wanganui Basin marine sediments, although an unconformity cuts out the record between ca. 1.45 and 1.0 Ma BP; since then, the many sedimentary cycles caused by sea level changes are presumed to be glacio-eustatic in origin. Uplifted interglacial marine terraces, back to marine Oxygen Isotope Stage 17, and river terraces formed by cold-climate aggradation, are linked into the cyclic sequence through loess and tephra in their cover beds. East of the South Island, cores from the DSDP Site 594 in the southwest Pacific record the earliest glaciation and, higher in the core, nine periods of South Island glaciation in the last 0.7 Ma. Onshore, because of uplift and erosion, only the last four glaciations, assigned to Oxygen Isotope Stages 10, 8, 6, and 4+2, are identified, being named Nemona, Waimaunga, Waimea and Otira Glaciations. They are best known in north Westland (northwest South Island) where the relations of glacial outwash and interglacial shoreline deposits are displayed. The late Otira Glaciation (Stage 2) is radiocarbon dated as beginning somewhat before 22.3 ka BP, culminating ca. 18 ka BP, and ending at ca. 14 ka BP, when rapid deglaciation began. A relatively small advance at ca. 12 ka BP may have been followed by little change until after 8.6 ka BP. Recession was then followed by a period of advance from ca. 5 ka BP until recent centuries and a subsequent recession that still continues.