MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
New insights into the Eocene Western Antarctic forests: fossil woods from La Meseta Formation
Autor/es:
PUJANA, ROBERTO ROMÁN; SANTILLANA, SERGIO; MARENSSI, SERGIO A.
Lugar:
Tokyo
Reunión:
Congreso; IX Internacional Organization of Paleobotany Conference; 2012
Institución organizadora:
Chuo University
Resumen:
The La Meseta Formation outcrops in Marambio (Seymour) Island, in west Antarctica and is well known for the abundance of fossils (including vertebrates, invertebrates, woods, leaves, pollen and a flower). The age of the unit was constrained to the Eocene using palaeontological and isotopic data. A collection of 120 samples of fossil woods from the Early and Midle Eocene allomembers of the formation was analyzed. On most of the woods the best anatomical descriptions were obtained observing small fragments under MEB rather than acetate peels and thin cuts under light microscopes. Almost 70 % of the observed samples were identified as gymnosperms. Among them, Phyllocladoxylon of the Podocarpaceae is the most common, followed by Araucariaceae and Cupressaceae. Phyllocladoxylon fossil woods have an affinity to the Prumnopityoid clade plus Microcachrys and Microstrobos of the Podocarpaceae, characterized by one or rarely two large pits in the cross-fields. Some variation on the fossils assigned to Phyllocladoxylon was observed, indicating that least two taxa may be represented. Araucariaceae have the typical alternate pitting and Cupressaceae are characterized by the small cross-field pits and axial parenchyma. On the other hand, angiosperms are dominated by the Nothofagaceae. The results of our palaeoxylological data indicate that the Early-Middle Eocene forest canopy in the Marambio (Seymour) Island area was dominated by gymnosperms, mainly Podocarpaceae, in contrast with the Nothofagaceae dominance observed in slightly younger (close to the Eocene-Oligocene boundary) units of West Antarctica. Growth ring analysis indicates seasonality based on the well marked growth ring boundaries and stable annual conditions based on the mean sensitivity values. Both, the growth rings and the present taxa suggest temperate climates.