A late Miocene subtropical-dry flora from the northern Altiplano, Bolivia

Abstract

A variety of evidence suggests that the Altiplano of the Central Andes, the second highest and largest plateau on earth, underwent significant uplift in the late Miocene–Pliocene. The most important datum supporting recent uplift is a collection of the 10.66±0.06 Ma Jakokkota flora from west-central Bolivia, which implies a paleoelevation no more than 1600±1200 m; today the site has an elevation of almost 4000 m. In order to test the reliability of this estimate, the present study analyzes a new collection of the Jakokkota flora from a lacustrine unit that is 0.2–0.5 Myr younger than the previously analyzed collection from a fluvial unit. Climate estimates based on leaf morphology for the two collections are statistically indistinguishable; the combined flora has a mean annual temperature of 21.5±2.0°C and a mean annual precipitation of 550±180 mm. The similarity of the climate estimates for the two floras suggests that there was not a significant climate change between them, nor a significant bias in the leaf morphology due to differing taphonomic processes. The climate estimate for the combined flora thus presents a representative picture of the late Miocene climate of the northern Altiplano. If one assumes that the climate of the tropics has not changed significantly since the late Miocene, as is suggested by marine isotopic data, then the paleoclimate of the Jakokkota flora implies a paleoelevation of 1160±600 m. Thus, the Jakokkota flora supports the hypothesis of a young age for the Altiplano.