Eocene and Oligocene Sedimentary Cycles in New Zealand

Abstract

Abstract Neritic deposits of Eocene and Oligocene age, partly underlain by coal measures, occur over large areas of south-west Auckland, west Nelson and north Westland, and north-east Otago (Waitaki). The well described deposits of south-west Auckland and Waitaki consist of sedimentary units bounded by unconformities and each containing distinctive fossils. Each sedimentary unit reflects an increase, each unconformity a decrease, in depth of sea, and the successions represent cycles of deposition and non-deposition or erosion. The succession of cycles in Waitaki matches that in south-west Auckland. The early Tertiary of Nelson and Westland has not been fully described but seems to contain comparable sedimentary cycles. The changes in sea depth could have been caused either by essentially uniform vertical tectonic oscillations of virtually the whole of New Zealand, or by eustatic sea-level fluctuations. If eustatic sea-level fluctuations occurred they should have affected strata of the same age and facies throughout the world. Eocene and Oligocene cycles have been described in Western Europe and in the Gulf Coast area of North America, and formations of the same age described in Victoria, Australia, can be interpreted as sedimentary cycles. Correlations by planktonic Foraminifera, as yet imperfect, suggest that the sequences of cycles in Europe, North America, and Australia can be matched with the sequence in New Zealand.