Dinoflagellate Taxonomy and Biostratigraphy of the Mid- to Late Eocene and Early Oligocene of New Zealand

Abstract

<p>This document presents results from a study of the Mid- to Late Eocene and earliest Oligocene marine palynomorphs from on-shore and near-shore New Zealand. Eighty samples of appropriate age from across mainland New Zealand were examined for fossil dinoflagellates. Acritarchs encountered in the study are described, also, and the phenetic taxonomy of the Acritarcha provides an interesting contrast to the present 'mixed' state of dinoflagellate taxonomy: phylogenetic above the genus rank, and arguably below it, but predominantly phenetic at the genus rank. Extensive single mount collections were harvested from a number of samples which were found to be especially rich, well preserved, or which contained new taxa. The outcome has included descriptions of 25 new species, in addition to two (Corrudinium regulare and Corrudinium otagoense) published in an earlier paper (Clowes & Wilson 2006), namely: Achilleodinium echinatum, Achilleodinium improcerum, ?Areoligera hampdenensis, Batiacasphaera perforata, Chlamydophorella neopilata, Chlamydophorella pilata, Corrudinium bujakii, Deflandrea totara, Disphaerogena morgansii, Graptodinium inconditum, Graptodinium reticulatum, Nummus inornatus, Operculodinium crouchii, Operculodinium schioleri, Operculodinium pulcher, Operculodinium vulgare, Phthanoperidinium aculeatum, Phthanoperidinium australe, Phthanoperidinium dentatum, Phthanoperidinium granulatum, Phthanoperidinium spumosum, Phthanoperidinium tenuimurum, Pyxidinopsis mundus, Pyxidinopsis teuriensis, Samlandia tenuis. Although there remain some difficulties where the adopted suprageneric phylogeny meets the traditionally phenetic generic constructs, adopting an explicitly phylogenetic approach to dinoflagellate taxonomy was found to be a fruitful approach. Investigation into some of the new taxa described herein was first prompted by geographic or temporal occurrence criteria which hinted that relationships might be other than those immediately suggested by gross morphology. Only upon closer inspection were subtler morphological distinctions noticed. To adopt a wholly phylogenetic approach almost certainly requires the abandonment of taxa, particularly genera, which are uniquely defined by mutually exclusive morphological criteria. Other clues to phylogeny, such as stratigraphic and regional occurrence data, may also have to be recognised. Notwithstanding, all taxa described herein are, in fact, defined by means of conventional morphological distinctions. This study does not take the bold step to suggest a new taxon based wholly on geographical and temporal criteria. Doing so, however, is clearly a rational extension to the ideas presented herein, and is thought worthy of further investigation. A subordinate goal of this study was to further refine the younger part of Wilson's dinoflagellate biozonation for New Zealand (Wilson 1984d, 1987, 1988; Morgans et al. 2004), to: improve resolution, if possible; clarify an ambiguous boundary remaining in the literature, between the Wetzeliella hampdenensis and Wilsonidium tabulatum zones; incorporate more common taxa, which are not restricted to particular ecological settings. This has been progressed by a number of measures, including adopting a consistent approach to defining zone boundaries; replacement of the Wilsonidium echinosuturatum and Wilsonidium lineidentatum Zones with three new zones, Deflandrea convexa (early Porangan - late Porangan), Graptodinium inconditum (late Porangan - early Bortonian), and Impagidinium elegans (early Bortonian - late Bortonian); and the establishment of an additional new zone, the Stoveracysta kakanuiensis Zone, straddling the Eocene-Oligocene boundary.</p>