Plio-Pleistocene paleoclimate in the Southwest Pacific as reflected in clay mineralogy and particle size at ODP Site 1119, SE New Zealand

Abstract

Clay mineralogical and particle size data from Ocean Drilling Program (ODP) Site 1119 reflect processes associated with the deposition of the Canterbury Drifts and the evolution of the New Zealand south-eastern shelf, and are strongly correlated with Pliocene–Pleistocene climatic and oceanographic fluctuations. Elevated smectite contents at the base of Site 1119 (latest Early Pliocene ∼3.9–3.5 Ma) also occur regionally in the Southern Ocean and point towards an alternative sediment source other than nearby New Zealand terranes. The abrupt reduction in smectite content at ∼3.5 Ma and replacement by dominant chlorite–illite assemblages corresponds to the onset of Late Pliocene cooling climate conditions and more intense onland physical weathering. High illite contents in Late Pliocene–Early Pleistocene (∼3.0–1.7 Ma) sediments suggest a more southern terrane (e.g. Haast Schist) source influence and widened shelf conditions. An upward increase in clay content reflects an increased supply of glacier-derived detrital sediment, concurrent with global climate deterioration during the Late Pliocene–Pleistocene. Grainsize fining of the background mean sortable silt (mss) signal indicates reduced Southland Current flow, consistent with its forced seaward migration across Site 1119 over time due to continual eastward shelf progradation. Clay mineralogy and particle size data at ODP Site 1119 exhibit a relationship with both global climatic conditions and with Southwest Pacific paleoceanographic and paleoclimatic regimes.