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

Abstract

The biodiversity and terrestrial ecology of the Late Albian Triton Point Formation (Fossil Bluff Group), Alexander Island, Antarctica is analysed to improve our understanding of polar biomes during the mid-Cretaceous thermal optimum. This formation was deposited on a high-latitude (75°S) floodplain and consists of two facies associations, a lower braided alluvial plain 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) stands 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 forests on mature floodbasin soils, and fern–angiosperm–ginkgo thickets in riparian settings. Growth-ring analysis indicates plants experienced stressful growing conditions on the braidplain characterized by high-frequency flood events, but more favourable growing conditions on the coastal plain. Additional vegetation disturbances were caused by arthropod–fungal attack, frost and wildfire. In terms of structure, composition, ecology and productivity these predominantly evergreen, broad-leafed conifer forests bear similarities to the extant temperate rainforests of New Zealand.

100 Million Years of Antarctic Climate Evolution: Evidence from Fossil Plants

“…The picture also shows the volcanoes on the adjacent arc that were the source of volcaniclastic sediment, much of which was deposited as catastrophic deposits that engulfed standing trees (in the distance in this picture). Paleoclimatic interpretation using fossil plants on Alexander Island is based mainly on comparison with the ecological tolerances of similar living Southern Hemisphere taxa (Falcon-Lang et al, 2001). This indicates that the climate was generally warm and humid to allow the growth of large conifers, with mosses and ferns in the undergrowth.…”

Physiognomic and chemical characters in wood as palaeoclimate proxies

“…Ash and Creber 1992;Falcon-Lang et al 2001;Gregory-Wodzicki 2001). Conclusions drawn from such studies become more rigorous still if associated palaeosols are present and interpreted.…”

Physiognomic and chemical characters in wood as palaeoclimate proxies

“…Where such studies are possible, biologically induced growth cycles can be eliminated and sedimentological evidence can be used to help determine (local) environmental (e.g. Falcon-Lang et al 2001) conditions (Ammons et al 1987) ensuring more rigorous palaeoclimate interpretation. Since in situ material is rare, isolated wood specimens become the focus of attention for palaeoclimate analysis.…”

“…Analysis of these characters in fossil wood, particularly if they originate from localities where there is no modern analogue for comparative analysis such as the high latitudes, is problematic. For example ring width in fossil woods from the southern high latitudes cannot be related to climatic favourability because a continuous light regime would have ensured elevated growth rates during the growing season (Falcon-Lang et al 2001).…”