EARLY EOCENE PALAEOENVIRONMENTS IN ANTARCTICA: EVIDENCE FROM FOSSIL CONIFERS OF SEYMOUR ISLAND

Exceptionally well-preserved fossil plant material has been collected from a unit within the Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula. This flora was growing on the Antarctic Peninsula during the latest Early Eocene (51-48.5Ma) and is a source of valuable information about Antarctic palaeoclimate and the early stages of cooling from greenhouse to icehouse climate. The plants grew in warm temperate forests on the Antarctic Peninsula, and were subsequently carried into a shallow marine basin where they were preserved within carbonate concretions.

The fossil flora is dominated by plant organs of Araucariaceae conifers. The material includes isolated leaves, cone-scales and conifer branches, preserved intact and in 3D with leaves still attached to the woody stems. Many of the fossils have been permineralised by calcite, which impregnated the tissues and preserved fine internal and external cellular detail. Some fossil impressions and casts are also present. The recently developed Neutron Tomography technique has provided a unique opportunity to study the fossils non-destructively in three dimensions. This novel technique, not previously used on fossils of this type, produced spectacular three-dimensional reconstructions of the Antarctic fossil branches showing leaf arrangement and branch structure.

The coniferous leaves, branches, and cone-scales have been identified as fossil relatives of the extant Araucaria araucana, which is native to montane regions in southern Argentina and Chile. Similar fossil leaves have been found in Palaeogene strata in Patagonia, thus indicating a geographic link between South America and the Antarctic Peninsula during the Eocene.

Angiosperm leaves are present in the flora but are less common. They include Lauraceae, Myricaceae, Myrtaceae, and Proteaceae amongst others, and represent lowland vegetation. Modern equivalent taxa are typically evergreen with thick woody leaves and waxy cuticles.

Palaeoclimatic interpretation of leaf characters and living equivalent plants indicates Antarctica had a temperate moist maritime climate, the lowland regions being warm-temperate while uplands were cooler, probably with winter snow. Oxygen-isotope analysis of associated shells gives cool-temperate values (8.4°C ± 2°C) for shallow marine waters.