THE AGE OF THE BASE OF THE GUSTAV GROUP IN THE JAMES ROSS BASIN, ANTARCTICA

The Lagrelius Point Formation from its type area in north-west James R oss Island, Antarctica has yielded dinoflagellate cysts indicative of an earliest Aptian age. Reworked palynomorphs presumed to be from the Nordenskjold Formation (Kimmeridgian-Berriasian) were also encountered . The Lagrelius Point Formation also contains Early Cretaceous spore-p ollen floras of Austral aspect. The indigenous stratigraphically signi ficant dinoflagellate cysts include Herenaeenia postprojecta, Muderong ia spp., Odontochitina spp. and Ovoidinium cinctum. This assemblage in dicates that the Lagrelius Point Formation, the oldest formation of th e Gustav Group, is Aptian rather than Barremian in age. This in turn m eans that the base of the extensive Cretaceous marine succession in th e James Ross Basin can be dated accurately for the first time. The Lag relius Point Formation is correlated with the Australian Odontochitina operculata dinoflagellate cyst Oppel Zone and the Cyclosporites hughe sii spore-pollen Interval Zone. The extensive record of Aptian marine sedimentation within the James Ross Basin can be correlated directly w ith that of other key localities in the Antarctic Peninsula and Scotia are regions. There is still the possibility of a major stratigraphica l hiatus in the preceding Hauterivian-Barremian stages. (C) 1998 Acade mic Press Limited.