A Study Of Plant Fossils From Landslip Hill Silcrete

Abstract

The Miocene Landslip Hill silcrete from Southland, southern New Zealand is a fluvial deposit consisting of quartz sand cemented by amorphous silica, in which numerous randomly oriented three-dimensional plant fossils are preserved as moulds. Leaf fossils include one fern, at least three conifer morphotypes, one monocot and about 30 distinct angiosperm leaf morphotypes with dicotyledonous or magnoliid affinities. Additionally, eight different fruit or seed types are recognised. Some morphotypes have affinities with Araucariaceae, Podocarpaceae, Nothofagaceae, Casuarinaceae, Elaeocarpaceae and Lauraceae. Quantitative paleoclimate estimates for temperature and precipitation variables were obtained by cross-correlating physiognomic variation of dicotyledonous and magnoliid leaf morphotypes with two pre-existing modern leaf assemblage calibration datasets using the Climate Leaf Analysis Multivariate Program (CLAMP). Monthly temperature and precipitation values resemble modern Auckland, New Zealand, with average temperatures of warmest months of 21°C versus a modern 19°C, cold month averages of 11°C versus 10°C and an annual average of 16°C versus modern 15°C. Paleo-precipitation estimates are similar, as the three wettest months average 146 mm per month versus a modern 130 mm and the average of three driest months is 60 mm versus 80 mm per month. An inferred mean annual precipitation of 1300 mm versus 1210 mm in modern Auckland is also indicated. The Miocene Landslip Hill silcrete contains a diverse floral assemblage which is inferred to have grown in a much warmer and more humid climate than occurs in present day Southland, New Zealand. Prevailing conditions would have been a relatively moderate average annual precipitation with relatively little seasonal variation and a more or less year-round growing season.