Tephrostratigraphy and geochronology of a ca. 120 ka terrestrial record at Lake Poukawa, North Island, New Zealand

A 198-m-long core was obtained from Lake Poukawa, Hawkes Bay, New Zealand for paleoclimatic analysis. A chronology extending back to ca. 120 ka has been developed using a combination of tephrostratigraphy, radiocarbon, optical, and U–Th disequilbrium dating. The core contains a new record of tephra beds, including temporal intervals poorly recorded elsewhere, and revises the dispersal for some known events. Thirty macroscopic tephra beds were identified, comprising 20 rhyolites with compositions consistent with previously studied tephra from Taupo and Okataina calderas, and 10 andesites–dacites compositionally similar to Tongariro and Egmont centre eruptions. Electron microprobe data provides evidence for a total of 24 rhyolite eruptions amongst the 20 macroscopic beds. Four widespread rhyolitic marker beds: Whakatane (4.6 ka), Kawakawa (22.6 ka), Tahuna (ca. 43 ka), and Rotoehu (ca. 50 ka) provide temporal constraints for the upper 40 m of the core. The occurrence of Opepe (9 ka) and Okaia (23 ka) tephra beds in this core extends their known dispersal to southern North Island. A previously unrecognised and chemically distinct rhyolite tephra (ca. 35 ka) was also found in the sequence. Twelve rhyolitic tephra occur in the interval 50–120 ka, a period in which the timing and nature of volcanic events is poorly understood at proximal sites of the Taupo Volcanic Zone.The Lake Poukawa core provides evidence for widely dispersed tephra-producing eruptions from Egmont volcano and Tongariro centre back to about 120 ka. The tephra are glassy, unlike many proximal deposits, and can be geochemically fingerprinted, thus providing an opportunity to develop a framework for eruptions not assessable in proximal localities. The pre-50 ka, high-K Egmont tephra are compositionally similar to younger (post-30 ka) proximal pyroclastics, but differ from contemporaneous low- and medium-K rocks that characterise the proximal ring-plain of the volcano. An average Holocene peat accumulate rate of 1.5 m/ka and an average post-50 ka sedimentation rate of 0.78 m/ka are implied from the ages of interbedded tephra. However, the depositional history of the core is complex because tephra at a depth of 40 m, and optical and U–Th disequilbrium ages at ca. 103 m are the same age within analytical uncertainties. This implies either rapid alluvial sedimentation or unrecognised problems in the dating methods. U–Th disequilbrium ages, together with paleoecological information, suggest that a peat interval at 143–146 m depth formed during the last interglacial maximum (oxygen isotope substage 5e).