Studies in New Zealand Oligocene and Miocene Plant Macrofossils

Abstract

Assemblages of fossil leaves ranging in age from Upper Oligocene to Upper Miocene or Lower Pliocene have been examined from localities in Southland, Central Otago, the Dunedin area, the Buller region and Great Barrier Island. Nearly 200 form taxa have been recognized so far; of these 52 are figured and described and the remainder are included in an illustrated catalogue. Conifers, Casuarinaceae and Nothofagus spp. are discussed in detail. Thirteen new species are named and described: Gleichenia southlandica, Hypolepis maruiensis, Blechnum maruiense, Dacrydium (Lagarostrobos) franklinoides, Microcachrys imbricata, Phyllocladus strictus, Libocedrus compressa, Nothofagus southlandica, Gymnostoma stellata, Gymnostoma crassa, Casuarina avenacea, Metrosideros diffusoides and ? Eucalyptus roxburghiensis. Six new species are described but not named as more detailed study is still proceeding. A further ten new form taxa are identified to genus level only. The fossil flora from the Kaikorai Valley, Dunedin, originally described by Oliver (1936) is revised and Blechnum proceroides, Nothofagus pinnata, N. australis, N. kaikoraiensis and Ripogonum latipetiolatum are new names arising from this revision. The fossil assemblages from Southland and Central Otago are derived from heath, swamp and forest communities developed on an early to mid Tertiary peneplain. In contrast the fossil floras of the Buller region reflect predominantly forest vegetation developed on young soils of a prograding coastal floodplain backed by rapidly rising fault block ranges, while the fossil floras of Dunedin and Great Barrier Island reflect vegetation periodically affected by volcanic activity. Late Oligocene and Miocene climates throughout New Zealand appear to have been humid and at least as warn as Auckland today, although conditions on the east coast of the South Island may have been cooler and drier than on the west. The sediment containing the Landslip Hill fossil flora is interpreted as a silcrete and resembles similar deposits in Australia. The uncompressed state of the fossils and the preservation of turgid cell structures indicates early silica cementation in a surface or near-surface environment, probably as a result of direct precipitation of silica from ground water. The present-day New Zealand flora appears to be derived in part from the late Cretaceous flora of coastal eastern Gondwanaland. Other south-west Pacific floras may stare a similar origin, and may also have contributed to the New Zealand flora following fragmentation of the continental margin. The distribution of New Zealand Tertiary plants, as far as it is known, is consistent with my inferred paleogeography.