Paleoenvironmental and vegetation evolution during the PETM in the Gulf of Guinea: A study based on integrated palynological and chemostratigraphic analysis of the Miang section in the Douala Basin, Cameroon

• The PEB recorded through swamp to back swamp coastal deposits in Miang. • Late Paleocene and early Eocene periods identified by palynomorphs and δ 13 C org shift. • Pre-PETM and PETM indicate weathered and dysoxic setting under warm, humid climate. • Angiosperm-rich Lowland Rainforest/Open Forest dominated Gulf of Guinea. The Paleocene–Eocene environment and vegetation evolution is widely documented worldwide. While a few similar studies have been undertaken in the Gulf of Guinea and the continental interior, they remain very limited, and provide no evidence of the Paleocene–Eocene thermal maximum (PETM). To address this gap, we conducted a comprehensive new sedimentological, palynological, mineralogical, and geochemical analysis of the Miang outcrop in the Douala Basin that encompasses silty-clayey deposits typical for swamp to back swamp coastal settings. The analysis of pollen and spore taxa, including Proxapertites operculatus, Proxapertites cursus, Echitriporites trianguliformis, Psilamonocolpites sp., Crototricolpites protoannemariae, Echitricolpites communis, Psilastephanocolporites sp., and Echimonocolpites rarispinosus and allowed the delineation of the pantropical Proxapertites operculatus Zone, corresponding to the Paleocene–Eocene transition, as well as Cameroon Spathiphyllum vanegensis (ZpI) and Retibrevitricolpites triangulatus (ZpII) zones, which indicate the late Paleocene and early Eocene epochs, respectively. This, combined with the organic carbon-isotope excursion (CIE: ∼-6.4‰), contributed to accurately determining the Paleocene–Eocene boundary (PEB). Geochemical and clay mineralogical data indicate that the paleoenvironment experienced intrusive volcanism linked with the Cameroon Volcanic Line (CVL), and enhanced primary productivity, both of which show marked decline prior to the PEB. Additionally, significant chemical alteration (CIA values: 85–94) occurred under warm and humid conditions (kaolinite: 70–88% and smectite: 10–23%), with sediments being reworked and deposited in a dysoxic setting conducive to organic matter preservation, especially from the pre-PETM period onwards. From the pre-PETM to early PETM, the Gulf of Guinea was probably covered by an extensive Lowland Rainforest/Open Forest ecosystem with a diverse flora, mostly angiosperms, that thrived in warm and humid conditions. From the mid-Lower Eocene onwards, Lowland Rainforest/Open Forest and Freshwater Swamp Forest species began to coexist with certain Mangrove-Coastal Swamp species, indicating proximity to the sea.