Biodiversity and terrestrial ecology of a mid-Cretaceous, high-latitude floodplain, Alexander Island, Antarctica

The biodiversity and terrestrial ecology of the Late Albian Triton Point Fo rmation (Fossil Bluff Group), Alexander Island, Antarctica is analysed to i mprove our understanding of polar biomes during the mid-Cretaceous thermal optimum. This formation was deposited on a high-latitude (75 degreesS) floo dplain and consists of two facies associations, a lower braided alluvial pl ain unit and an upper coastal meander-belt unit. Analysis of fossil plants in well exposed palaeosols reveals the existence of spatially complex plant communities. Braidplains supported patchy, low-density (91 trees/ha) stand s of podocarp and taxodioid conifers on floodbasin substrates, and conifer- cycadophyte-fern-angiosperm thickets in riparian settings. Coastal meander- belts supported medium density (568 trees/ha) podocarp-araucarian conifer f orests on mature floodbasin soils, and fern-angiosperm-ginkgo thickets in r iparian settings. Growth-ring analysis indicates plants experienced stressf ul growing conditions on the braidplain characterized by high-frequency flo od events, but more favourable growing conditions on the coastal plain. Add itional vegetation disturbances were caused by arthropod-fungal attack, fro st and wildfire. In terms of structure, composition, ecology and productivi ty these predominantly evergreen, broad-leafed conifer forests bear similar ities to the extant temperate rainforests of New Zealand.