Vegetation and climate from two Oligocene glacioeustatic sedimentary cycles (31 and 24 Ma) cored by the Cape Roberts Project, Victoria Land Basin, Antarctica

Abstract The Cape Roberts Project recovered over 1500 m of coastal glaciomarine sediments of Oligocene and Early Miocene age off the Ross Sea margin of Antarctica. The strata are characterised by cyclic repetition of facies in a glaciomarine setting, and are interpreted to be a record of glacial-interglacial episodes involving significant changes in eustatic sea level on Milankovitch frequencies. We have undertaken a detailed study of pollen and spores (miospores) from an Early Oligocene (31 Ma), and a Late Oligocene (24 Ma) cycle. Although miospores are sparse in the core, averaging only ∼1 grain per gram of sediment processed, over 1200 Cenozoic miospores were recovered for this study. Previous studies of miospores from Ross Sea sediments have encountered problems differentiating between reworked and in situ palynomorphs. Here, only samples containing a low relative abundance of an Eocene dinoflagellate cyst assemblage (the Transantarctic Flora) have been used to infer the contemporaneous Oligocene miospore flora. The flora of the Early Oligocene cycle is dominated by three species of Nothofagidites , and four types of Podocarpidites . The assemblage from the Upper Oligocene cycle is also dominated by Nothofagidites and Podocarpidites , but with the addition of two distinctive taxa, an angiosperm pollen and a bryophyte spore. Notwithstanding these additions, there is a slight decrease in floral diversity between the two cycles. While this study confirms that some floristic changes did occur between Early and Late Oligocene time on the Victoria Land coast, the present data suggest that the changes were not extensive. It is likely that the vegetation of both cycles was a low diversity scrub of low stature, consisting of mainly Nothofagus , podocarps, and bryophytes. Modern analogues suggest that this vegetation was growing in a climate significantly warmer (Mean Summer Monthly Temperature 4–12 °C) than is found on the present day Victoria Land (MSMT − 5 °C), although colder that the temperate climate suggested by the diverse flora found in Ross Sea sediments of Eocene age.