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.

摘要

年代学在新西兰至关重要，那里的古气候研究使用火山灰层的年龄作为年代标记。奥克兰火山区 (AVF) 中的玛尔湖以长时间（>10,000 年）的连续沉积物积累为特征，为古气候研究提供了出色的档案，其中还包含来自远端的已知年龄流纹岩、安山岩和当地的玄武岩火山灰。对来自Ōrākei 盆地（约130,000 年）的沉积物序列使用多方法年龄模型，结合放射性碳测年、地质年代学、发光测年和相对磁性古强度的调整，我们呈现新年龄，并测试和改进现有火山灰的可靠性14 个玄武岩、18 个安山岩和 8 个流纹岩火山灰层的年龄。

我们的结果显示与先前公布的年龄总体上非常一致（除了为 Okareka tephra 推导出的新年龄，这里报告为 23,525 cal yr BP）但减少了误差范围。与以前公布的年龄相比，火山灰年龄的更大差异主要发生在放射性碳测年限制之外。修订后的年龄有涉及tephrochronology研究的潜在影响（狭义），在AVF并在新西兰北部观测到的气候变化，如可能较冷的海洋同位素阶段（MIS）5B比MIS4时机火山喷发的复发率.