LAUSR

A multi-proxy study, including mineralogy, whole rock geochemistry and palynology analyses, was conducted on 79 samples (64 bulk sediment and 10 pyrite samples) from two sites (ES and DA) located in the Tondè area, Douala sub-basin (Cameroon) to unravel the paleoenvironmental and paleoclimatic conditions prevailing in recent continental deposits. Lithologies of this locality mainly consist of pyriteous claystones (grey and red) and unconsolided sandstones. Encountered pyrite is euhedral (isolated and clusters crystals) and massive with diverse morphologies and sizes. In both sections, major and trace elements show that the clayey materials result from weathering of an intermediate source rock, probably from the surrounding basement (gneiss and micaschist), whereas the sandy materials appear to be recycled. Palynological data consists of a few index species such as Malvaceae and graminaceae which indicate Pleistocene-Holocene age deposits of continental origin (swampy bays of seaside and hinterland). This area was subjected to intense chemical alteration (high CIA values: 97.35–99.43%) as testified by the mineralogical phases, mainly consist of kaolinite, quartz and goethite. Mean annual precipitation (MAP = 221.1e0.0197(CIA-K); ±181 mm.y−1) and mean annual temperature (MAT = 46.9C + 4; ±0.6 °C) are 1575 ±181 mm.y−1 and 25.2 ± 0.6 °C for ES site and then 1566 ± 181 mm.y−1 and 20.3 ± 0.6 °C for DA, thus reflecting a subequatorial to equatorial climate. The pyrite geochemistry is characterized by a weak Al vs. ΣREE positive correlation (r2 = 0.02), a positive Eu anomaly relative to PAAS and a significant negative correlation between ΣREE and the Eu anomaly (r2 = −0.83). These results indicate that pyrite is a late diagenesis product formed by a secondary enrichment and coupled with precipitation under more reducing conditions, linked to the water table fluctuation.