The Argiles d'lignite du Soissonnais is a geologic formation in the Oise department of northern France.

The Argiles d'lignite du Soissonnais dates back to the Ypresian stage of the Eocene period.

[1] 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.