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

• Published in: The Journal of geology 2012-07, Vol.120 (4), p.467-476
• Main Authors: Manchester, Steven R., Herrera, Fabiany, Fourtanier, Elisabeth, Barron, John, Martinez, Jean-Noël
• Format: Article
• Language: English
• Subjects: Algae; Bacillariophyceae; Berries; Diatoms; Flora; Fossils; Fruits; Geological time; Invertebrates; Outcrops; Paleobotany; Plants; Sandstones; Seeds; Stratigraphy; Taxa
• ISSN: 0022-1376; 1537-5269
• DOI: 10.1086/665797

The Belén 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 Belén 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 includesLisitzinia ornataandRocella vigilans, among others, indicating a latest early Oligocene age (∼30–28.5 Ma) for these deeper marine sediments, which we infer to have been subsequently reworked into the Belén environment. We also reevaluate the botanical identifications, which are based on the original museum specimens supplemented by more recently collected specimens. The Belén flora provides a window into extinct forests in South America that were present before the rising of the Andes in western Peru.