Vegetational and climatic history during oxygen isotope stage 7 and early stage 6, Taranaki, New Zealand

Abstract

A detailed palynological record from terrestrial cover beds of the Brunswick Marine Terrace (c 310 000 yr) is described from the Ararata Gully Site near Hawera, south Taranaki, New Zealand Lignite 3 m thick contains compressed wood, thin andesitic and rhyohtic tephra, and abundant fossil pollen Following cutting of the marine terrace during interglacial oxygen isotope stage 9, podocarp‐hardwood forest with abundant Prumnopitys taxifolia grew in the area during interstadial substage 7c This was succeeded by podocarp‐beech forest and grass‐shrubland during stadial substage 7b Podocarp‐hardwood forest, characterised by pollen assemblages similar to those of the early‐mid Holocene for this area, then grew regionally during interglacial substage 7a Dacrydium cupressinum and Ascarma lucida were prominent during the interglacial peak Later, during the cooling period leading into glacial stage 6, Metrosideros, Leptospermum‐type, and Acacia‐type expanded in vegetation surrounding the site These Myrtaceae‐dominated assemblages have no modern analogue in New Zealand, but appear to have more affinity with Australian sclerophyll vegetation Grass‐shrubland and Nothofagus forest expanded regionally as temperatures continued to fall in early glacial stage 6 The Ararata Gully pollen sequence is interpreted to represent almost all of oxygen isotope stage 7 and early stage 6 ‐ a period from c 240 000 to c 180 000 years ago This is the most complete record of vegetation and climate covering this period so far obtained in New Zealand The results are compared with those from other sites in central‐western North Island. Oxygen isotope substages 7a and 7c are shown to have been of substantially different climatic character Only substage 7a was a fully interglacial period with vegetation and climate which was, for a time, equivalent to that of the early‐mid Holocene climate optimum Substage 7c should be considered an interstadial period. Interglacial vegetation communities of apparently similar composition have been able to repeatedly re‐occupy the south Taranaki lowlands during the warmest, wettest, and mildest periods of the late Quaternary Many taxa making up these communities were restricted in distribution to protective inland environments during the long glacial, stadial, and interstadial periods, but were able to expand in response to climatic amelioration that culminated in relatively brief interglacials, such as the present Other species may have been filtered out by this cyclical process if they were unable to respond to such rapid climatic changes This plasticity of the New Zealand vegetation has resulted in a lack of distinctive vegetation types that might distinguish any one interglacial period from another in the middle and late Quaternary, at least in south Taranaki. A rhyohtic tephra bed, informally named Ararata Gully tephra, is described and correlated with the oxygen isotope sub‐stage 7c and 7b boundary (c 235 000 yr). © 1997 Taylor and Francis Group, LLC.