CORRELATION, DISPERSAL, AND PRESENTATION OF THE KAWAKAWA TEPHRA AND OTHER LATE QUATERNARY TEPHRA LAYERS IN THE SOUTHWEST PACIFIC-OCEAN

Voluminous rhyolitic eruptions and prevailing westerly winds have disp ersed late Quaternary ash from the Taupo Volcanic Zone (TVZ) of the No rth Island, New Zealand, across the Southwest Pacific Ocean. We identi fy the Taupo (1850 C-14 years), Waimihia (3280 yr), Rerewhakaaitu (14 700 yr), and Kawakawa (22 590 yr) Tephra layers in deep ocean cores, m ainly on the basis of their stratigraphic position, radiometric age, a nd glass shard chemistry. Approximately 25 km(3) of Taupo Tephra were dispersed ENE at least 650 km from the TVZ whereas c. 22 km(3) of Waim ihia Tephra and c. 14 km(3) of Rerewhakaaitu Tephra travelled over 500 km to the east. In contrast, at least 400 km(3) of Kawakawa Tephra oc cur out to 1400 km southeast of the TVZ. Such widespread dispersal is not only a function of the size of the Kawakawa eruption, but is also influenced by the strong wind regime during the last glaciation as man ifest by high aeolian quartz contents of sediments encasing the tephra . More ash appears to have deposited offshore than is predicted by exp onential thinning models. Taupo Tephra, in particular, has a conspicuo us second thickness maximum, 660 km from the eruption centre. Dispersa l has extended over different depositional settings that have affected the tephra layers. The best preserved deposits are in zones of high s edimentation including channel levees, submarine fans, and boundary cu rrent drifts. In contrast, preservation is poor in regions of active c urrents including the continental shelf, the crest of Chatham Rise, an d the foot of Chatham Rise - Hikurangi Plateau where a deep western bo undary current is intensified. Primary tephra deposits are also at ris k in regions of frequent gravitational mass movement such as offshore Hawke Bay and eastern Bay of Plenty. Further postdepositional modifica tion is by bioturbation, especially where tephra are c. < 1 cm thick; thicker deposits tend to survive, which implies a smothering of the be nthic fauna.