New age model for Onepoto maar, Auckland, New Zealand, based on a revised tephrochronology of the lake sediment sequence

Abstract

Tephrochronology has proven to be a reliable dating tool in the context of northern New Zealand lakes due to the numerous volcanic centres on the North Island that have repeatedly erupted during the late Quaternary. The widely-distributed tephras often have distinctive geochemical compositions with many of these tephra layers preserved in the sediments that infill maar lakes in the Auckland Volcanic Field (AVF). Here, we present a revised age model for the Onepoto Maar lake sediment sequence, using 14 rhyolitic, seven basaltic, and two andesitic tephra layers with assigned ages as markers. These were integrated with bulk organic matter and pollen-derived radiocarbon ages to establish the new age-depth model. Improvement of the age model for the pre-45 ka section of the Onepoto record was based on the usage of tephras with refined ages: Eg2, Eg4, and Eg10 (Taranaki Maunga-sourced) and AVF D, AVF C, AVF B, and 90 AVF (AVF-sourced). The correlation of the Onepoto tephra horizons to the recently refined, multi-method derived, age model of the Ōrākei maar tephra sequence has improved the robustness of the new Onepoto age model. Consequently, this approach has enabled development of reliable age assignations for tephra layers contained in the Onepoto sediments beyond the limit of ¹⁴C dating. Accurate chronologies for lake sediment sequences, such as the one presented here, are vital for paleoenvironmental research. Thus, the revised Onepoto age model improves upon previous models for our study site, offering more robust age control for regional paleoclimate studies covering the last two glacial cycles. It will also allow the extension of the existing high-resolution paleoenvironmental and paleoclimatic records developed from the AVF maar lakes beyond MIS 5e to at least late MIS 7.