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Published July 2021 | Supplemental Material + Accepted Version
Journal Article Open

Biotic community and landscape changes around the Eocene–Oligocene transition at Shapaja, Peruvian Amazonia: Regional or global drivers?


Since 2012, we have investigated a stratigraphic section encompassing the late Eocene–earliest Oligocene interval at Shapaja (Tarapoto area, Peruvian Amazonia, ca. 7°S), through paleontological and geological fieldwork. The measured sedimentary series (120 m-thick [West] plus 90 m-thick [East]), assigned to the upper member of the Pozo Formation, records fluvial micro-conglomeratic lenses intercalated with floodplain and evaporite-rich fine red deposits, estuarine/coastal-plain tidally-influenced fine sandstones, and oxbow lake nodule-rich blue clays. This sedimentary shift coincides locally with the demise of the large Eocene coastal-plain wetland known as Pozo System. The late Eocene–early Oligocene Shapaja section was extensively sampled for chemostratigraphy (δ¹³C on dispersed organic matter and pedogenic carbonate nodules), which in turn allowed for refining the location of the Eocene-Oligocene Transition (EOT) and other climatic events recognized at a global scale (i.e., Oi-1 and Oi-1a). The section has yielded nine fossil localities with plant remains (leaves, wood, charophytes, and palynomorphs), mollusks, decapods, and/or vertebrates (selachians, actinopterygians, lungfishes, amphibians, sauropsids, and mammals), documenting ~130 distinct taxa. Four localities of the upper member of the Pozo Formation at Shapaja predate the EOT, one is clearly within the EOT, while four are earliest/early Oligocene in age. The small leaf impressions found along the Shapaja section could be indicative of dry and/or seasonal conditions for this region throughout and after the EOT. Monkeys, indicative of tropical rainforest environments, are only recorded in a latest Eocene locality (TAR-21). Two biotic turnovers are perceptible in the selachian, metatherian, and rodent communities, well before the EOT [~35–36 Ma] and a few hundred thousand years after the EOT [~33 Ma]. The latter turnover seems to be primarily related to a global sea-level drop (ichthyofauna: marine-littoral elements replaced by obligate freshwater taxa) and/or the onset of a drier and more seasonal climate in early Oligocene times (terrestrial components). Changes in the structure of the Shapaja paleocommunities were mostly driven by the flexural subsidence during the late Eocene, and then globally driven by the earliest Oligocene climatic deterioration.

Additional Information

© 2021 Elsevier. Received 12 December 2020, Revised 22 April 2021, Accepted 7 May 2021, Available online 13 May 2021, Version of Record 19 May 2021. We are indebted to Adriana Albino (Museo de La Plata, Argentina) for her taxonomic assignment of squamate remains. Fieldwork and post-field analyses in Peru were carried out thanks to the support from the National Geographic Society (grant n° 9679-15) and the Campus France program of the French Ministry of Foreign Affairs to POA, from the Doctoral School SIBAGHE/Gaia of the Montpellier University to MB, the Oak Spring Garden Foundation to F. Herrera and from the Institut des Sciences de l'Evolution de Montpellier, and The Leakey Foundation to LM. This work was further supported by an "Investissements d'Avenir" grant managed by the Agence Nationale de la Recherche (CEBA, ANR-10-LABX-25-01) and by the cooperative programs ECOS-FonCyT (A14-U01) and CoopIntEER CNRS-CONICET (n°252540), in the frame of the ongoing cooperation agreement between the Museo de Historia Natural de la Universidad Nacional Mayor San Marcos (Lima, Peru) and the Institut des Sciences de l'Evolution-Université de Montpellier. We are particularly indebted to the invited editor, Carina Hoorn, to Robin M. D. Beck and to an anonymous reviewer for their useful comments and helpful suggestions on a previous version of the manuscript. This is the article ISEM-2021-039 SUD. All authors declare that they do not have any conflict of interest.

Attached Files

Accepted Version - Shapaja_paleocommunities_accepted-merged.pdf

Supplemental Material - 1-s2.0-S0921818121000977-mmc1.xlsx

Supplemental Material - 1-s2.0-S0921818121000977-mmc2.docx


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August 22, 2023
October 24, 2023