The Arén Formation or Arén Sandstone (Catalan: Calcàries i gresos d’Areny) is a geological formation in the around Arén, Catalonia, Spain whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation. The formation dates to the Campanian to Maastrichtian and underlies the Tremp Group.