Stratigraphy and chronology of late Quaternary tephras in Lake Maratoto, Hamilton, New Zealand

Abstract

A 3 m piston core from Lake Maratoto (37°53'S 175°18'E) near Hamilton shows at least 12 thin, well-preserved distal airfall tephras intercalated with humic copropel (dy) deposits. Most of the tephras have been identified by their dominant ferromagnesian mineralogy, their stratigraphic position, and 5 radiocarbon dates. The majority of the tephras are derived from the Taupo and Okataina Volcanic Centres, while others originate from Mayor Island, Tongariro, and possibly Mount Egmont sources. The tephras dated (Libby ages) are: Taupo Pumice (Wk215) 1730 ± 60 years B.P., Tuhua Tephra (Wk214) 6210 ± 70 years B.P., Mangamate Tephra (Wk213) 10 120 ± 100 years B.P., and Rerewhakaaitu Ash (2 dates) (Wk237) 14 700 ± 220 years B.P. and (Wk238) 14 700 ± 180 years B.P. The identification of the tephras in Lake Maratoto extends the previously mapped distribution of North Island post-glacial (Holocene) tephras, and complements studies of soil genesis and weathering in the Waikato region. The core also provides a geochronological basis for further multidisciplinary studies of the paleolimnology, paleoclimate, and sedimentological history of the region.