Tidal range of marsh foraminifera for determining former sea-level heights in New Zealand

Abstract

Quantitative study of live and total foraminiferal faunas in samples from six transects through marsh environments at Kaipara Harbour, Miranda, and Pauatahanui Inlet, New Zealand (two transects each), show the presence of a distinctive high tidal species association that has potential for the recognition of former sea-level heights from late Quaternary deposits. Seven species associations are recognised by R-mode cluster analysis of total (live plus dead) foraminiferal faunal data. Mangrove forest and salt meadow below MHWS (mean high water spring level), in near normal salinity marshes (Kaipara, Miranda), are dominated by an Ammonia association with subsidiary Elphidium excavatum, Haplophragmoides-Miliammina fusca, and Helenina associations. In less saline marshes (Pauatahanui), the salt meadow and rush marsh below MHWS, are dominated by a Haplophragmoides-Miliammina fusca association. In all transects, the narrow zone between MHWS and EHWS (extreme high water spring level) is dominated (>90% relative abundance) by a Trochammina association (T. inflata, T. macrescens, Miliammina obliqua). A palimpsest, Ammonia-dominated, exposed beach fauna on the penultimate chenier interferes with the recognition of this high tidal Trochammina zone in one Miranda transect. Dependent upon their proximity to exposed sea conditions and fast-flowing tidal channels, there are variable numbers of introduced foraminiferal tests (Cornuspira association) in the marshes at all levels. At Pauatahanui, a monospecific fauna of T. macrescens is present just at EHWS (upper 0.1 m of tidal range). This has been recognised previously only in northeast America and may provide the most accurate paleo-sea level marker known. There appear to be no significant tide-related trends in diversity, but in all transects there is a marked abundance peak between MHWS and EHWS levels, which if recognised in fossil faunas could also be useful in determining previous sea-level heights.