Ohariu tephra and associated pollen-bearing sediments near Wellington, New Zealand

Abstract

A rhyolitic tephra found at two localities in Ohariu Valley near Wellington is intercalated in carbonaceous silts which are overlain by gravels, loesses, and paleosols. The tephra is informally named Ohariu tephra. It consists mainly of glass shards, associated with quartz, sodic plagioclase, hypersthene, hornblende, biotite, and rare zircon. The glass shards have been dated by the fission-track method as 0.22 ± 0.03 m.y. b.p. Pollen analysis indicates that climatic conditions in Ohariu Valley at that time were subalpine. The pollen assemblages and loess units are correlated with pollen assemblages and palynologically determined cold phases recorded from a drillhole at Petone, and indicate that the period was the first of at least the four latest cold phases to affect the Wellington area.