Developing a South Pacific tephra framework: Initial results from a Samoan Holocene sequence

Abstract

Tephra preserved in sediments form useful isochronous marker layers, linking disparate geological, palaeoenvironmental and archaeological records. The application of tephrochronology is greatly enhanced through the detection of macroscopically invisible tephra (cryptotephra). Here, we identify two discrete cryptotephra in Samoan lake sediments, the first identification of cryptotephra in the region outside of New Zealand. Geochemical data suggest one ash layer is from a local Samoan source, providing the first data on an eruption of this age, adding to knowledge of the local volcanic record. The second has a distinctive rhyolitic glass composition, which matches either that of Raoul Island in the Kermadec Arc (1800 km south of Samoa), or two currently submarine volcanoes in the Tongan Arc, ‘Volcano F’ and Lateiki/Metis Shoal (550 and 700 km south of Samoa, respectively). In all possible source cases, this points to a regionally significant eruption of a Kermadec–Tongan volcano at ca. 10 000 a bp. The study marks the first step in the establishment of a South Pacific tephra framework that can be used to answer questions about the synchronicity of changes in hydroclimate, vegetation and early Polynesian migration patterns, as well as providing more information on the volcanic history of Pacific island volcanoes.