The Paleocene-Eocene transition in the Gulf of Guinea: Evidence of the PETM in the Douala basin, Cameroon

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) was identified for the first time in two sections (Bongue and Dibamba) from the Douala sub-basin located in the Gulf of Guinea, Cameroon. This discovery was based on a multi-disciplinary approach including biostratigraphy and occurrence of benthic and planktic foraminifera and ostracods, major and trace element contents, mercury, organic carbon isotope (δ13Corg values), total organic carbon (TOC), whole-rock and clay mineralogy. A combination of lithology, microfossil assemblage, and carbon isotope data indicate zone P5 and the top of the Paleocene enabling the definition of the Paleocene-Eocene boundary (PEB). A negative carbon-isotope excursion (CIE) spanning from the uppermost Paleocene deposits to the earliest Eocene sediments (PETM interval) shows a shift in δ13Corg values of 1.5‰ in Bongue and 3.0‰ in Dibamba. In both sections, this interval is affected by widespread acidification, as revealed by carbonate dissolution and microfossil preservation (i.e., species are dwarfed, broken, thin shelled, and with holes). The very low carbonate content and the scarcity of microfauna indicate the severity of acidification during the PETM, especially in the early Eocene where only one species was identified (Igorina broedermanni). Mercury anomalies, TOC contents, and trace element concentration ratios, point to volcanic activity linked to the Cameroon Volcanic Line (CVL) intrusive magma, and a decrease in productivity prior to the PETM. In addition to climate change, our geochemical and mineralogical data support the hypothesis that other environmental perturbations such as an increase in productivity and detrital input, as well as a decrease in bottom water oxygenation occurred during the PETM in the Douala sub-basin.