Late Pleistocene palynology of terrestrial cover beds at the type section of the Rapanui Terrace, Wanganui, New Zealand

Abstract

This study investigates the vegetational and climatic history recorded by fossil pollen preserved in terrestrial cover beds at the type section of the Rapanui Marine Terrace, Wanganui, New Zealand. At this section, laterally extensive Rapanui Lignite and Rapanui Dunesand overlie marine sands of the Rapanui Formation, which were deposited after the cutting of the Rapanui marine platform during the last interglacial sensu stricto. The lowermost sample, below Rapanui Lignite proper, contains a pollen assemblage derived from podocarp-hardwood forest, indicating a palaeoenvironment similar to, or cooler and drier than, the present. The Rapanui Lignite contains pollen assemblages derived from a low forest/shrubland with prominent Myrtaceae, and including a now-extinct Acacia-type. These assemblages are derived from vegetation lacking a modern analogue in New Zealand, and they are considered to indicate a palaeoclimate which was also cooler and possibly drier and windier than at present. The presence of Libocedrus and Acacia-type on the Wanganui lowlands during the period of deposition of Rapanui Lignite indicates important late Pleistocene biogeographic differences for these taxa, compared with the present. Since the Rapanui Formation marine sands are estimated to be c. 120,000 years old, and the overlying terrestrial sediment appears to be more or less conformable, the lowermost pollen sample probably represents the end of the last interglacial (oxygen isotope substage 5e) or the transition period to the following stadial. The Rapanui Lignite is correlated with stadial oxygen isotope substage 5d, and is estimated to date to c. 110,000 years ago.