The late Quaternary palynology of Pohehe Swamp, Eketahuna district, N.W. Wairarapa

Abstract

Pohehe Swamp at Atea, near Eketahuna and adjacent to the eastern edge of the Northern Tararua Range, contains grey silty clays, 4.3 m thick, which probably derived from loess deposited in water. To describe the sediments the informal Pohehe Formation is proposed. The formation overlies alluvial gravel correlated with Eketahuna Terrace Gravel representing the First Stadial of the Last Glaciation. Dated horizons are the present day surface, the Aokautere Ash Member of the Kawakawa Tephra (20.5 +/-0.5 ka BP) 2 m below the ground surface, and at 3.7 m below the ground surface a layer with a radio carbon age of >/= 36 ka BP. Assuming a constant sedimentation rate of 0.1 m per ka the base is 42 ka old. Palynomorphs have been recovered from the entire sequence, though they tend to be sparse in the 1.6 m - 1.2 m depth above the Aokutere Ash Member. The palynology shows that from 43 ka to 23.5 ka BP the climate was cool and the regional vegetation was silver beech (Nothofagus menziesii) forest with grassland in exposed areas. The timber line was at 500 m. From 23.5 ka to 13 ka BP the climate was colder and grassland was the dominant vegetation type. About 13 ka BP the climate warmed rapidly and podocarp-dicotylous forest became dominant. Silver beech(Nothofagus menziesii) forest is now absent from the area; it seems to have gradually decreased in area after 23.5 ka BP and to have disappeared by 18 ka BP for reasons unknown.