Almost all the studied samples proceeding from the Maastrichtian-Danian interval of the Colorado and Punta del Este basins are cuttings, since there are no outcrops of Mesozoic or Palaeogene strata. In the Colorado Basin, we analyzed nine cutting samples from the offshore Cx-1 Well, between 1300 and 1600 metres depth (md) and one core and two cutting samples from the onshore Pedro Luro Borehole, between 1487 and 1550 md (figure 1). Eight cutting samples are derived from the Gaviotín Well, drilled offshore Punta del Este Basin, between 1658 and 1850 md.
The palynological material from the Austral Basin is derived from a surface section at the estancia 25 de Mayo, Southwestern Santa Cruz Province (figure 1). Eleven of the twenty samples processed for palynomorphs contain dinocysts.
The palynological treatment included hydrofluoric and hydrochloric acids, mild oxidation (10% nitric acid for one minute) and a 10% ammonium hydroxide wash for one minute. These procedures were followed by heavy liquid separation of the organic component, differential centrifugation to remove fine particles and screening to concentrate the 10 - 25 and 25-180 µm fractions. The residues from the Cx-1 well were refined, stained with Bismarck C and mounted in Elvacite and Cellosize substitute at the Geological Survey of Canada (Atlantic). The residues from the other sites were mounted in glycerine jelly.
Morphologic studies were made using a Nikon Eclipse 600 microscope at the Universidad Nacional del Sur and specimens were photographed with a Nikon Coolpix 950 digital camera. Coordinates quoted from the Vernier scale of Nikon microscope serial nº 772751 follow the sample and slide number for each specimen illustrated. England Finder (EF) references are provided in the corresponding figure explanations. The types and figured specimens are kept in the Palynological Collection of the Departamento de Geología de la Universidad Nacional del Sur, Bahía Blanca, Argentina. The dinoflagellate cyst nomenclature follows Williams et al . (1998a) and the systematic section uses the classification of Fensome et al . (1993). The geological timescales are from Berggren et al . (1995) and Gradstein et al . (1995).