Palynology, age and environmental significance of some peat beds in the upper Pleistocene Hinuera formation, South Auckland, New Zealand

Abstract

The first period of Hinuera Fonnation deposition (Hinuera-l) probably began before 40 000 yr BP, but after 65 000 yr BP, and ceased by 20 000 yr BP. The most active phase of the second period (Hinuera-2) occurred between 20 000 and 17 000 yr BP. Sedimentation slowed dramatically after 18000-17 000 and ceased between 14 000 and 12000 yr BP. After 14 000-12 000 yr BP the Waikato River stopped migrating across its aggrading floodplain, began downcutting, and assumed its present entrenched, meandering course. Extensive, raised peat bogs, characteristic of the present landscape, began to develop. Pollen analysis of thin peat layers within Hinuera-2 sediments enables some conclusions to be made about vegetation and climate between 20 000-18000 yr BP. Scrub, grassland and swamp were the dominant vegetation types in the Middle Waikato Basin. The little forest that existed probably consisted of small areas of Nothofagus (menziesii and fusca group) and Libocedrus. A cool, possibly dry and/or drought-prone climate, which was, however, also characterised by high intensity rainstonns, would explain the nature of both sediments and vegetation. Phormium tenax (New Zealand flax) leaf and rootstock fossils, found in a 20 000 yr BP peat at the base of Hinuera-2 sediments, were incorrectly ascribed in a previous paper to Rhopalostylis sapida (nikau palm).