PALYNOLOGICAL CHANGES ACROSS THE CRETACEOUS-PALEOCENE BOUNDARY IN THE NEOTROPICS

The Cretaceous-Paleocene (KP) boundary is recognized as one of the major environmental crisis of earth history. It is associated with a significant extinction of many groups. The palynological record from mid latitudes shows a dramatic and abrupt disappearance of most dominant taxa and nearly all of the Late Cretaceous angiosperms following the KP boundary. An estimated loss of ~30-50% of palynomorph species has been seen throughout the western Interior of North America.

The effect of the KP boundary on the vegetation of tropical latitudes is not known. Were extinction levels of tropical vegetation more intense than in temperate communities? To address this question we have studied 62 palynological samples across the KP boundary of a stratigraphic section in Cesar-Rancheria basin (Northern South America). Several techniques including range through method, rarefaction, per-capita extinction and origination rates, measures of taxonomic diversity, confidence intervals on stratigraphic ranges and Chi Square were used to estimate tropical extinction levels. There is a taxon extinction of 60-70% associated with the boundary and a significant change in the rate of extinction. Origination rates do not seem to be affected. The Paleocene floras are fully dominated by angiosperms, while the Maastrichtian is co-dominated by angiosperms, ferns, and gymnosperms showing that there are important changes in neotropical floras across the KP boundary, far more intense than in temperate regions.