Subtropical rainforest vegetation from Cosy Dell, Southland: plant fossil evidence for Late Oligocene terrestrial ecosystems

Abstract

A fossil flora from the basal Chatton Formation at Cosy Dell farm near Waimumu, Southland, New Zealand comprises wood, seeds, pollen and spores. A Late Oligocene age (25.4–24.4 Ma) determined from macro- and nannofossils constrains the beginning of marine transgression in this area. The palynoflora comprises more than 100 taxa, in addition to a few spores recycled from underlying Jurassic Murihiku basement. At least 16 ferns are present. Conifers include Araucariaceae and Podocarpaceae (Dacrydium, Dacrycarpus, Lagarostrobos, Microcachrys, Phyllocladus and Podocarpus). The angiosperm palynoflora comprises monocots including Arecaceae, Asparagaceae, Asteliaceae, Pandanaceae and Typhaceae and numerous dicots including Casuarinaceae, Cunoniaceae, Euphorbiaceae, Loranthaceae, Malvaceae, Myrtaceae, Nothofagaceae, Proteaceae and Strasburgeriaceae. The drift flora includes wood and seeds including the tropical legume Entada. Elongate limpets and mangrove snails provide indirect evidence for seagrasses and mangroves. The predominance of rainforest tree pollen and fern spores suggests a regional subtropical coastal forest and high rainfall.