Palynology, age, and paleoenvironments of carbonaceous facies in the Kaihu Group (Late Pliocene-Pleistocene), northern North Island

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Mildenhall, D.C.; Stokes, S.; Nelson, C.S. 1992 Palynology, age, and paleoenvironments of carbonaceous facies in the Kaihu Group (Late Pliocene-Pleistocene), northern North Island. Lower Hutt: DSIR Geology & Geophysics. Record / New Zealand Geological Survey 46 41 p.

Abstract: The Kaihu Group of northern North Island consists of poorly consolidated sand, silt, and scarce lignite and gravel overlying more consolidated rocks of late Pliocene or older age. The lensoid and highly variable lignites and carbonaceous beds volumetrically form about 5% of the group. Their field characteristics are used to classify them as either (a) dune paleosols and interdune deposits, (b) dune-impounded lake and stream delta deposits, or (c) back-barrier valley and floodplain deposits. The palynology of the lignites and carbonaceous sands suggests deposition of the group in several coastal, well-watered interglacial environments, with spores and pollen generally representing deposition from lowland coastal forest and swampland situations. The surrounding non-fossiliferous or poorly fossiliferous sediments, dominantly eolian sand, represent less favourable conditions for plant growth and subsequent fossilsation. Previous palynological analyses of the Kaihu Group are reviewed and reinterpreted, supplemented by new data from 48 samples from lignitic horizons at 5 new localities. For palynological results for the Kaihu Group are presented for the first time. The Ohuka Formation is regarded as the basal unit of the Kaihu Group and is dated as Hautawan, although it could be as old as uppermost Mangapanian, The age range of the Kaihu Group sensu stricto, excluding the Kaawa Formation on lithological grounds, is regarded as Hautawan to Holocene. The formations within the group include from the base the Ohuka, Awhitu (Hautawan-Mamhauan), Pareotaunga and Nihinihi (Mamhauan-Castlecliffian), Shelly Beach and Hood (Haweran), and Waioneke and Mitiwai (latest Haweran). (auths)

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