Palynology of core 80/20 and its implications for understanding Holocene sea level changes in the Firth of Thames, New Zealand

Abstract

Peat recovered in core 80/20 from below marine sediments and in 35 m of water in the Firth of Thames has been examined for palynological evidence of the paleoenvironment in which it was deposited. Radiocarbon ages of 11,900 and 14,000 years BP for the uppermost and lowermost layers of peat were obtained.Palynofloras from 10 samples indicate a stable vegetation community during the 2 000 year period represented by the core. The community consisted of a lowland swamp vegetated by Restionaceae, Leptospermum, sphagnum moss, and Gleichenia, merging on the coastal side with mangrove (Avicennia), and surrounded inland and on promontories by rainforest dominated by conifers, beech, and tree ferns. Several samples contain mangrove, glasswort (Salicornia), and dinoflagellate cysts, which testify to the local marginal marine/saltmarsh environment and provide a good estimation of sea level at the time of peat accumulation.Core 80/20 provides the earliest confirmed record of mangrove in the Quaternary of New Zealand.According to generally accepted data, sea level between 14,000 and 11,900 years BP was at around -55 to -70 m. Our data indicate a stillstand at c. -35m in the Firth of Thames at about that time. The difference may be evidence for a rapidly rising sea level, although it is more likely to reflect local tectonic uplift.

Holocene vegetation and volcanic activity, Auckland Isthmus, New Zealand

“…These features are also consistent with pollen spectra reported by Pocknall et a/. (1989) from the Firth of Thames (Fig.…”

Holocene vegetation, climate and history of a raised bog complex, northern New Zealand based on palynology, plant macrofossils and tephrochronology

“…From these regional comparisons, it would seem that the basal radiocarbon date (Wk-1025) is spuriously young and that the uppermost muds may be c. 10 000 years older than the basal peats. Further confirmation of this explanation comes from a pollen site in the Firth of Thames, 70 km north of the Kopouatai core site and in the same sedimentary basin (Figure 1), where peat dated as between 14 000 and 11900 yr BP yielded dryland pollen spectra indicating northern warmtemperate rainforest and a climate similar to that of today (Pocknall et al, 1989). This palynostratigraphical anomaly might be explained by a <5% contamination by much younger carbon of Wk-1025 (e.g., Polach, 1976), which would make the basal Kopouatai muds much older, perhaps dating to the last stadial of the last (Otiran) glacial.…”

Early to Mid Holocene pollen samples containing mangrove pollen from Sponge Bay, East Coast, North Island, New Zealand

“…(Macphail and McQueen (1983) regard Avicennia pollen as well-to over-represented in Pleistocene and Recent deposits, but do not give reasons for this conclusion). Therefore, sparsely fossiliferous samples such as these are inadequate for determining whether A vicennia pollen should be present or not; it has not formed more than 9% of total pollen in any East Coast sample, and in the Firth of Thames only 20% mangrove pollen recovery was reported by Pocknall et al (1989) from samples that must have been almost beneath the living trees. The modern infill sediments are too young to contain Avicennia.…”