HIGH DIVERSITY PALEOCENE MACROFLORAS FROM THE SAN JORGE BASIN, (CHUBUT, ARGENTINA): IMPLICATIONS FOR PLANT DIVERSITY DURING THE EARLY PALEOGENE

IGLESIAS WILF LABANDEIRA JOHNSON ZAMUNER CÚNEO

Bahía Blanca

Simposio; XII Simposio Argentino de Paleobotánica y Palinología; 2006

Universidad nacional Del Sur

Few confirmed Paleocene macrofloras are known from South America, limiting knowledge of South American plant diversity after the end-Cretaceous event and before the high plant diversity of the Eocene. We report new quantitative collections of 2649 identified compression specimens from the Paleocene Salamanca Formation, found at two outcrops in the Palacio de los Loros locality, western San Jorge Basin. These samples reveal considerably greater species richness than was previously known from the Paleocene in Patagonia, including 36 species of angiosperm leaves as well as fruits, flowers, and seeds of angiosperms, ferns and diverse conifers. 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 morphotypes at both Palacio de los Loros quarries is >50% higher than for any of the U.S. Paleocene floras studied, with the exception of one environmentally dissimilar in the Denver Basin. Also, we assessed the diversity of foliar damage from insect herbivory, and found a particularly high richness. The richness of leaves and insect damage in the Palacio de los Loros flora is much higher than for comparable floras in the Northern Hemisphere and may reflect a less severe end-Cretaceous extinction in Patagonia. This may have set the evolutionary stage for the extremely high plant diversity found in Eocene Patagonian floras.