Effect of sampling interval on the resolution of oxygen isotopic paleotemperature trends—an example from the New Zealand Early Miocene

Abstract

Oxygen isotopic analyses of closely spaced (~35000 year) samples of the planktic foraminifera Globigerina (G.) woodi Jenkins from a 15 m section of massive mudstone within the Early Miocene Taumatamaire Formation, South Auckland, reveal a significant cyclical fluctuation in their isotopie composition of 0.8%c in about 300000 years, as well as possible superimposed smaller oscillations of 0.3%c in about 80000 years. If the isotopie values are primarily temperature related, then these short-term oscillations correspond to temperature changes of 3.5°C and 1.5°C respectively and are of as great a magnitude as the single isotopie temperature fluctuation previously reported for the entire 11 m.y. period covering the Waitakian to Altonian (latest Oligocene to Early Miocene inclusive) Stages in New Zealand. Successful definition of such short-term, cyclical isotopie fluctuations requires a sampling interval of considerably less than 100000 years.