A fossil wood flora from the Oligocene of Patagonia, Argentina

PUJANA, ROBERTO ROMÁN; CÉSARI, SILVIA N.; MARENSSI, SERGIO A.

Gramado, Rio Grande do Sul

Simposio; XI Reuniao de Paleobotânicos e Palinólogos (XI Meeting of Paleobotanists and Palynologists); 2004

Fossil woods from the Río Leona Formation, which represents the continental sedimentation during the Oligocene in Southern Patagonia, are analyzed. The age of the Rio Leona Formation is constrained by radiometric absolute dating of the overlying Centinela Formation (late Oligocene-early Miocene) and the underlying Man Aike Formation referred to the Middle to Late Eocene on the basis of marine invertebrates. The first palynological data and preliminar analysis of woods and foliar imprints for this unit were recently presented. Palynological assemblages are dominated by woody angiosperms, mainly Nothofagaceae species accompanied by pollen related to the families Podocarpaceae, Proteaceae, Myrtaceae and possibly Cunoniaceae. Fossil woods were collected in different outcrops of the upper and lower sections of the sequence. The trunks are usually very well preserved as silicifications, that can be compared to extant families. Woods of Podocarpaceae affinity are abundant as well as those of Nothofagaceae. The latter have diffuse porosity and relatively big vessels with simple perforation plates. There are also woods related to Cunoniaceae or Myrtaceae with small vessels and scalariform perforation plates. Some specimens resemble the Proteaceae with simple perforation plates and vessels arranged in tangential and diagonal bands. The studies in progress point out to a considerable diversity in this Oligocene flora.