The recovery of a lower Miocene palynomorph assemblage in diatomite clasts from RISP Site J/9 sediment cores, gives us a clearer view of the terrestrial vegetation during the early Miocene. This palynomorph assemblage was deposited at a time of minimal glaciation. The assemblage is considerably different from that recovered in the Sirius Group, arguing strongly against the late Oligocene to early Miocene age of the Sirius Group flora suggested by Burckle and Pokras (1991).
A well-preserved, but considerably lower diversity palynomorph assemblage than present in the above samples, occurs with wood and leaf fossils (southern beech, Nothofagus) in the Pliocene Sirius Group of Oliver Bluffs, in the Transantarctic Mountains. No evidence suggests that these palynomorph assemblages are mixed or recycled from older sediment. These palynomorph data enable the reconstruction of Pliocene terrestrial vegetation and help guide discussions of Antarctic glacial history and paleoclimate. These floras may represent the last survivors of the Gondwana vascular paleoflora in Antarctica. Progressive cooling and ice sheet expansion led to local extinction of most flora from the Antarctic continent during the late Pliocene. We are searching for similar records in marine mudstones in DVDP and CIROS drill cores of Southern Victoria Land.
These new palynomorph data from RISP Site J/9 and the Sirius Group provide a clear base, from which we will be able to mark the exit of higher plants from Antarctica. Due to geographic isolation following the break-up of Gondwana continents, the Cenozoic floral record appears to be one of loss (exit) from Antarctica and not of dispersal to Antarctica.