THE LAST GLACIAL MAXIMUM IN CENTRAL AND SOUTHERN NORTH ISLAND, NEW-ZEALAND - A PALEOENVIRONMENTAL RECONSTRUCTION USING THE KAWAKAWA TEPHRA FORMATION AS A CHRONOSTRATIGRAPHIC MARKER

Kawakawa Tephra Formation, comprising Oruanui Ignimbrite flow member a nd Aokautere Ash airfall member, represents the products of an excepti onally large and widespread volcanic eruption from Taupo Volcanic Cent re in the North Island of New Zealand. The eruption occurred during th e Last Glacial Maximum, and is radiocarbon dated at c. 22.6 ka B.P. Th ermoluminescence ages are in broad agreement with the radiocarbon age. The presence of Aokautere Ash in loess deposits, in alluvial gully-fi lls, on river terraces, and its absence from unstable sites, permits a detailed assessment of geomorphic activity during the Last Glacial Ma ximum. Widespread erosion of regolith, aggradation of river valleys, a nd deposition of loess, particularly in the period following eruption of the Kawakawa, point to a cold, dry, variable climate. A collation o f pollen data for sediments containing Aokautere Ash, and those C-14 d ated in the range 17-23 ka, shows that tall forest was highly restrict ed in the central and southern parts of the North Island. An apparentl y subalpine grassland/shrubland was present at sites from present sea level to over 800 m elevation, suggesting that factors other than lowe r temperatures, such as exposure to wind and frost, fire and reduced r ainfall, were important in controlling vegetation patterns. We conclud e that the interval 23-13 ka B.P., broadly equivalent to oxygen isotop e stage 2, represents the period of greatest environmental change in t he North Island.