Revised tephrochronology for key tephras in the 130-ka Ōrākei Basin maar core, Auckland Volcanic Field, New Zealand: implications for the timing of climatic changes

Abstract

Tephrochronology is of paramount importance in New Zealand where paleoclimate studies use ages of volcanic ash layers as chronological makers. Maar lakes in the Auckland Volcanic Field (AVF) are characterised by continuous sediment accumulation over extended periods of time (>10,000 years) providing outstanding archives for paleoclimate studies also containing distally-sourced known-age rhyolitic, andesitic and locally-sourced basaltic tephra. Using a multi-method age model for the sediment sequence from Ōrākei Basin (ca. 130,000 years) combining radiocarbon dating, tephrochronology, luminescence dating, and tuning of relative magnetic paleointensity, we present new ages, and test and refine the reliability of existing tephra ages for 14 basaltic, 18 andesitic and eight rhyolitic tephra horizons. Our results show overall strong agreement with previously published ages (except the new age derived for the Okareka tephra, here reported as 23,525 cal yr BP) but reduce the error ranges. Larger differences in tephra ages compared to previously published ages occur predominantly beyond the radiocarbon dating limit. The revised ages have potential implications for studies involving tephrochronology (sensu stricto), for volcanic eruption recurrence rates in the AVF and for the timing of climatic changes observed in northern New Zealand, such as a possibly cooler marine isotope stage (MIS) 5b than MIS4.