Late Neogene unconformity-bounded tuffaceous sequences: northwestern Chatham Rise, New Zealand

Unconformity-bounded, late Miocene to Recent sedimentary sequences produced by fluctuating paleoceanographic conditions on the northwestern Chatham Rise have been sampled in a series of piston-cores from exposures at wide, mid-bathyal, oblique to slope, current-scour channels and from submarine canyons at the head of the adjacent Hikurangi Trough. The biostratigraphic framework for these mostly hemipelagic sequences is based on foraminiferan and nannofossil dating of the cores. Volcanic glass-rich horizons (tephra), with glass shards of calc-alkaline rhyolitic composition, occur commonly in late Opoitian to Haweran (late Pliocene - late Pleistocene) sediments. Although the physical oceanography and sedimentary processes of the region are unfavourable for preserving megascopic tephra, five chemically and stratigraphically distinct tuffaceous horizons are recorded in Pleistocene cores, implying at least five discrete eruptions. Two late Pleistocene tuffaceous horizons are correlated tentatively with Layer E (c. 0.27 Ma) and Layer D (= Mt Curl Tephra; c. 0.35 Ma) in several southwestern Pacific deep-sea cores. Other tuffaceous horizons contain two or more chemical populations of glass shards that have been mixed and reworked by extensive bioturbation and current winnowing, during periods of very slow sedimentation. Distances of 460-600 km between the core sites and source vents in the Coromandel Volcanic Zone (early Pliocene) and Taupo Volcanic Zone (Pleistocene) imply very explosive eruptions.