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Abstract
The stratigraphic and chronologic relationships of Hinemaiaia Tephra and Whakatane Ash are examined using distal tephras preserved in organic-rich deposits at five sites in eastern and northern North Island, New Zealand. A c. 10 mm thick, unnamed white rhyolitic ash layer described at two of the sites (Tiniroto and Poukawa), and previously of disputed stratigraphie significance, also occurs at the other three sites (Kaipo, Rotomanuka, and Okoroire) as a primary airfall tephra. The tephra is derived from the Taupo Volcanic Centre and is correlated with Hinemaiaia Tephra (definition of Froggatt) using similarity of stratigraphie position, composition (ferromagnesian mineralogy and glass chemistry), and radiocarbon age. It stratigraphically overlies Whakatane Ash. The tephra underlying Whakatane Ash, and previously identified as Hinemaiaia Ash (definition of Vucetich & Pullar), is probably Motutere Tephra.
Hinemaiaia Tephra has a mean age of (old T½) c. 4500 years, Whakatane Ash c. 4800 years. New 14C dates, obtained on peat or gyttja adjacent to these tephras, are (old T½, years B.P.): 4220 ± 60 (NZ3160A), 4490 ± 70 (Wk541) (above Hinemaiaia Tephra); 4470 ± 70 (Wk542) (below Hinemaiaia Tephra); 4800 ± 50 (NZ3161A), 4490 ± 60 (Wk496), 4530 ± 60 (Wk497), 4260 ± 140 (Wk662) (below Hinemaiaia Tephra and above Whakatane Ash); 5210 ± 80 (NZ3162A), 4860 ± 70 (Wk501), 4850 ± 80 (Wk660) (below Whakatane Ash).
Based on the distal occurrences described here, the Hinemaiaia Tephra has a much more widespread distribution than previously demonstrated, and may have been emplaced by a very powerful “above average” plinian eruption.