A late Miocene plant fossil assemblage from the Whitianga Group, Coromandel, New Zealand

Kennedy, E.M.; Hayward, B.W.; Reichgelt, T; Gregersen, R.; Ngadi, N.; Clowes, C.D. 2024 A late Miocene plant fossil assemblage from the Whitianga Group, Coromandel, New Zealand: Composition and climate estimates. Lower Hutt, NZ: GNS Science. GNS Science report 2022/42. 57 p.; doi: 10.21420/R54A-RA03

Abstract

An outcrop of late Miocene lacustrine mudstone from the c.11 Ma Carina Rock Ignimbrite Formation, Whitianga Group, yielded an angiosperm-dominated leaf flora, here calledthe Kaimarama flora. Thirty-one dicot broadleaved angiosperm leaf morphotypes were differentiated from collections made from this flora, and leaf morphology-based methodsof paleoclimate analysis were applied. In addition, the Kaimarama flora includes monocot angiosperm leaf fragments, Phyllocladus, other podocarps, Araucariaceae leaves, leaflets of a likely Cupressaceae, fern fragments, seeds and fruits. Associated faunal remains are rare and currently only amount to one insect wing impression, a partial freshwater bivalve impression and insect damage on some of the leaves. A moderately diverse palynoflora in the associated sediments supports the presence of fern-dominated vegetation, perhaps a proximal wetland/open land environment and a mixed conifer- and Nothofagaceae-dominated forest. Myrtaceae-like remains are also common in the macrofossil assemblage but rare in the palynology assemblage. Despite attempts, identifiable cuticle has not yet been extractedfrom the leaves, so leaf-based taxonomic inferences are based only on macromorphology and are therefore tentative.Leaf morphology-based paleoclimate analysis of the Kaimarama flora (using the CLAMP [Climate Leaf Analysis Multivariate Program] method) produced temperature estimates consistent with a seasonal temperate climate. Both CLAMP and Bioclimatic Analysis, a nearest-living-relative-based approach, produced estimates of mean annual temperature (MAT) similar to, or a little cooler than, the ~14°C MAT of Kaimarama today, with rainfall in the order of 150 cm during the growing season. Several other late Miocene floras are known from both North and South Island but only two have previously been analysed using leaf morphology-based methods of climate analysis, both from near Dunedin, the Kaikorai flora and the Double Hill flora. Paleoclimate estimates from the Kaimarama flora are broadly consistent with the temperate climate estimates derived from the Kaikorai flora. (auths)