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.

Keywords:

• Hauraki Gulf
• Firth of Thames
• marine sediment cores
• peat
• palynology
• ¹⁴C dating
• Oturian
• Holocene
• late Quaternary
• Avicennia
• sea level