Oligocene Age of the Classic Belen Fruit and Seed Assemblage of North Coastal Peru based on Diatom Biostratigraphy

The Belen flora, in north coastal Peru, is the most diverse fruit and seed assemblage yet known from the Paleogene of South America. Little original paleobotanical work has been performed on this assemblage since the pioneering treatments published by E. W. Berry in the 1920s, and the precise age has not been determined. Nevertheless, the flora has been regarded as a focal point in understanding the vegetational, orogenic, and climatic history of northern South America, and in recent literature it has been assumed to be early Eocene. In order to tighten this age assignment, which has varied from early Eocene to early Oligocene in the opinions of different authors, we revisited the Belen site, measured the stratigraphic section, and processed the fruit-and seed-containing sediment for age-diagnostic microfossils. Although pollen and foraminifera were not recovered, the sediment is rich in diatoms. The diatom assemblage includes Lisitzinia ornata and Rocella vigilans, among others, indicating a latest early Oligocene age (similar to 30-28.5 Ma) for these deeper marine sediments, which we infer to have been subsequently reworked into the Belen environment. We also reevaluate the botanical identifications, which are based on the original museum specimens supplemented by more recently collected specimens. The Belen flora provides a window into extinct forests in South America that were present before the rising of the Andes in western Peru.