Palynology of the early Miocene Foulden Maar, Otago, New Zealand: Diversity following destruction

Abstract

Foulden Maar crater in Otago, southern New Zealand contains a thick sequence of earliest Miocene (~23Ma) biogenic lacustrine sediments that have preserved a rich terrestrial biota. Diverse spores and pollen recovered from a 183m core through these sediments provide evidence of warm temperate to subtropical environments with high rainfall and cloud cover. Charcoal and burnt and dark-coloured pollen are common in reworked tephra below the lacustrine diatomite. At this early post-eruptive depositional period a diverse regional podocarp/Casuarina/Brassospora lowland forest flora was present, with gleichenaceous ferns suggesting a locally acidic environment, possibly supporting a fire-induced fernland. The regional vegetation soon became dominated by Nothofagus (Brassospora), while a diverse subtropical forest with abundant Mallotus/Macaranga (Euphorbiaceae) developed on fertile volcanic soils around the maar. Evidence from palynomorphs combined with plant macrofossils represented in the lake sediments paints a picture of highly diverse lake margin vegetation that included rare ferns (Davallia), occasional conifers (Podocarpus and Prumnopitys), and a diverse array of monocots including at least one palm, two orchids, and species of Astelia, Cordyline, Freycinetia, Luzuriaga, Ripogonum and Typha. Overall, the vegetation close to the lake was dominated by a wide range of dicots, including Aquifoliaceae (Ilex), Araliaceae, Atherospermataceae (Laurelia), Chloranthaceae, Cunoniaceae, Elaeocarpaceae, Gyrostemonaceae (Gyrostemon), Lauraceae (Beilschmiedia, Cryptocarya, Litsea), Onagraceae (Fuchsia), Meliaceae (Dysoxylum), Monimiaceae (Hedycarya), Myrsinaceae, Myrtaceae, Rutaceae, Santalaceae, Sapindaceae (Cupania), Malvaceae, Strasburgeriaceae, Winteraceae and at least ten Proteaceae. Mistletoes, including several species of Loranthaceae were present. Pollens from bur reeds, bulrushes, flaxes, jointed rushes and sedges suggest that there were some swampy, shallow water edges to the generally steep-sided crater. Pollen evidence from alternate dark and light layers, regarded as being biogenic varves from sedimentology, shows no strong signal for differences in summer and winter pollen deposition. Based on palynology the age of the site is latest uppermost Rhoipites waimumuensis Zone to lower early Proteacidites isopogiformis Zone (New Zealand local stages, late Waitakian–early Otaian, ~23Ma), agreeing with radiometric dates.