Diagenetic transformations from dioctahedral to trioctahedral smectite and berthierine to various mixed-layered minerals (I-Sm, C-Sm, B-C) are suggested.

Acid volcanoclasts served as a feedstock for eogenetic formation of smectite and berthierine.

Trace element whole-rock and EDS glass chemistry are both indicative for the rhyodacite to trachyandesite volcanic character and its repetitive nature in an active geotectonic development of Gabon basin.

Burial conditions largely controlled smectite diagenesis but parameters like the initial smectite composition and sediment porosity were also important.