[7][8][9][10] However, the formation also witnessed a former system of petroleum which showed major amounts of uranium associated with organic matter.

[10] During burial of the formation, its multiple black shales were heated and in doing so expelled hydrocarbons that migrated into underlying sandstones, with the first episode of the oil migration being synchronous along with a silicification event that derived into a hot and low salinity fluid which is proven by fluid inclusions trapped in overgrowths of quartz.

In the third and final episode of oil migration within the Francevillian B formation, oil-to-gas conversion generated overly-pressured gas trapped with uraniferous bitumen nodules in pores.

Changes in the stress regime probably favoured radial hydrofracturing around the bitumen nodules as well as the subsequent development of a somewhat pervasive micro-fracture network.

[10] The formation has been proposed to have preserved microfossils,[11] as well as flattened disk-like macrofossils, the latter dubbed the "Francevillian biota".