Cenozoic dinoflagellate cytests from the Colorado basin, Argentina

Cenozoic sediments from the well Cx-l of offshore Colorado Basin were studied. The dinoflagellate cysts assemblages are diverse and well preserved praviding stratigraphic control for the section. Selected dinoflagellate cyst last occurrences or abundance events suggest seven age intervals: Maastrichtian, Paleocene, Late Eocene to Early Oligocene, Late Oligocene to Early Miocene, Mid Miocene, Late Miocene and Late Miocene to Early Pliocene. These results are compared with previous studies, carried out by other authors exhibiting a consistent succession of events throughout the basin. Qualitative and quantitative dinoflagellate cyst data allow the recognition of apparent sea level changes. Sediments ranging frorn Maastrichtian to Selandian in age show a gradual rise in sea leve!. These assemblages bear both gonyaulacacean and peridiniacean dinoflagellate cysts suggesting open marine conditions with a marked fall in sea level at the top of this interval. Sediments interpreted as Late Eocene to Early Oligocene in age were deposited in a more open marine environment. At the Early Oligocene/Late Oligocene boundary a second low see level episode occurred.Throughout the Late Oligocene to Early Miocene and Mid to Late Miocene intervals high dinocyst abundances and the presence of oceanic species suggest a sea level highstand. Upwards the dominance of terrestrially derived palynomorphs as well as the scarcity of dinoflagellate cysts indicate nearshore depositional environments at the end of the Miocene-Early PlioceneFil: Guerstein, Gladys Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Junciel, Gabriela. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Universidad Nacional del Sur; Argentin

Diconodinium lurense sp. nov., a late Maastrichtian to Danian dinoflagellate cyst from Southwest Atlantic basins

Los depósitos del Cretácico Superior y Cenozoico de las cuencas del Colorado y Austral, Argentina y Cuenca Punta del Este, Uruguay son portadores de asociaciones de quistes de dinoflagelados diversas. Diconodinium lurense sp. nov. es un elemento común en las asociaciones provenientes del Maastrichtiano tardío-Daniano en las distintas cuencas. Esta nueva especie se caracteriza por presentar un autofragma densamente cubierto por espinas cortas, cuernos apical y antapical relativamente largos y por un arqueopilo variable Ia-IPa. Nuestras evidencias indican que el rango estratigráfico de Diconodinium lurense sp. nov. se extiende desde al Maastrichtiano tardío hasta el Daniano, constituyendo un importante marcador bioestratigráfico para la transición Cretácico-Paleógeno en las cuencas del Atlántico Sudoccidental.Upper Cretaceous and Cenozoic deposits from the Colorado and Austral basins, Argentina and the Punta del Este Basin, Uruguay contain diverse organic-walled dinoflagellate cysts, including Diconodinium lurense sp. nov. which occurs in the late Maastrichtian and Danian throughout the basins. The new species is characterized by an autophragm that is densely covered by short spines and by relatively long apical and antapical horns, and by a variable Ia to IPa archeopyle. On our evidence, the stratigraphical range of Diconodinium lurense sp. nov. is latest Maastrichtian to Danian, and is thus a useful biostratigraphical marker for the Cretaceous-Palaeogene transition in the southwest Atlantic basins.Fil: Guerstein, Gladys Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Junciel, Gabriela. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Guler, Maria Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Daners, Gloria. Universidad de la República. Facultad de Ciencias; Urugua