The formation comprises a succession of lenticular bodies showing two main
facies; clayey sands rich in frequently
pyritised lignite, together with
amber and grey clayey sands with less lignite (1 to 12% of the sediment), with continental vertebrate fauna. These facies, the rarity of
mollusk shells and
charophytes, probably due to decarbonatation and the presence of
pyrrhotite (FeS4), reflect a
hypoxic environment. The strata were deposited at the bottom of two channels cutting into underlying
Thanetian marine green sands. The channels prograde toward the northeast and were discovered under
Oise River Quaternary deposits. == Fossil content ==