Early Paleocene Macrofloras of Patagonia and their Significance for Austral Biogeography and Biodiversity

ARI IGLESIAS; WILF PETER; JOHNSON KIRK; RUDY SLINGERLAND

San Carlos de Bariloche

Congreso; Southern Connection Congress; 2010

Universidad del Comahue

We report on new and rediscovered macrofloras from southern Chubut Province, Patagonia, Argentinathat represent the first stratigraphically controlled and quantitatively collected Paleocene macroflorasfrom southern South America. The floras provide critical information about floristic diversity andcomposition following the Cretaceous-Paleogene boundary (K-T) and prior to the extremely high plantdiversity in Patagonia by the warm early Eocene. The collections, from several sites in the estuarineSalamanca Formation and the overlying, fluvial Peñas Coloradas Fm., date from ca. 61.7 Ma, about ~463 / 150 m.y. after the K-T boundary. The floras represent varied paleocommunities preserving more than 50species of angiosperm leaves as well as flowers, fruits and seeds, ferns, and conifer leaves andreproductive structures. Among the lineages identified are: Akaniaceae, probable Nothofagaceae, andNageia-like and other Podocarpaceae leaves, as well as Lygodium, Araucariaceae, Palmae, Fabaceae,Menispermaceae, Rosaceae, Lauraceae, Salicaceae, Sapindaceae, Malvaceae, Urticaceae, and aBrassicales flower. Although the biogeographic signature of the flora is clearly gondwanic, there appearsto be greater compositional distinctiveness from coeval Australian floras than is seen in PatagonianEocene floras, suggesting some degree of endemism after the K-T followed by increased interchangeacross Antarctica with Eocene warming.