High Diversity Paleocene Macrofloras From The Salamanca Formation, Central Patagonia, Argentina.

IGLESIAS ARI; WILF PETER; JOHNSON KIRK; ZAMUNER ALBA B.; CÚNEO RUBEN

Bilbao

Congreso; Internacional Meeting of Climate and Biota of the Early Paleogene; 2007

Internacional Meeting of Climate and Biota of the Early Paleogene

Few confirmed Paleocene macrofloras are known from South America, limiting knowledge of plant diversity and composition between the end-Cretaceous event and several extremely diverse Eocene floras. We report new quantitative collections of 2649 identified compression specimens from fluvial sediments of the Salamanca Formation, dated at ~61.7 Ma (Danian-Selandian boundary) from foraminiferal biozones as well as less reliable paleomagnetic interpretation and K-Ar analyses. The samples were collected from two outcrops at the Palacio de los Loros locality, western margin of the San Jorge Basin (southern Chubut Province, Argentina). These samples reveal a considerably greater species richness than was previously known from Paleocene Patagonia, including 36 species of angiosperm leaves as well as angiosperm fruits, flowers, and seeds; ferns, and conifer leaves, cones, and seeds. Based on leaf-area and leaf margin analysis, the woody dicot leaf assemblage indicates a mean annual precipitation of at least 1115 mm and a mean annual temperature of 14.4° ± 2.6 °C. The climate and paleoenvironment are comparable to many similarly collected Paleocene floras from similar paleolatitudes in the USA. Adjusted for sample size using rarefaction, the alpha diversity of angiosperm leaf species at both Palacio de los Loros quarries is more than 50% higher than any of the U.S. Paleocene floras studied, with the exception of environmentally dissimilar tropical rainforest floras from mountain margin habitats in the Denver Basin. Few species from the Salamanca flora are known from other early Paleogene floras in Patagonia; neverless the familial composition is similar including Lauraceae, Sapindaceae, Urticaceae, Rosaceae, Fabaceae, Nothofagaceae, Menispermaceae, Akaniaceae, Arecaceae, Podocarpaceae and Araucariaceae. The richness of dicot leaves in the Salamanca Formation flora is much higher than for comparable Paleocene floras in the Northern Hemisphere and may reflect a less severe end-Cretaceous extinction in Patagonia. The Salamanca flora represents an evolutionary stage leading to the extremely high plant diversity found in Eocene Patagonian floras.