Allen Formation

The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian. Dinosaur remains are among the fossils that have been recovered from the formation. Indeterminate chelid remains and other vertebrates have also been discovered in this formation.

Description
The stratotype of the formation was defined by Uliana and Dellapé in 1981 in the eastern area of the Bajo de Añelo, where the relation between base and top is clearly exposed. The deposits are mostly clastic, interbedded with banks of limestone and layers of anhydrite, which were defined continental and shallow marine facies associated with semiarid conditions.

The interpreted sedimentary paleoenvironments range from purely continental such as ephemeral lacustrine, aeolian and fluvial systems to coastal marine paleoenvironments with development of estuaries and tidal flats, followed by a lagoon sedimentary stage from marsh to sea with carbonate precipitation in an area protected from waves, ending with a retraction leading to the accumulation of evaporites.

A detailed facies analysis of the formation was performed by Armas and Sánchez in 2015, where the authors concluded the formation represents a hybrid coastal system of tidal flats, dominated by Atlantic ingressions, with a large storm influence in some areas linked to aeolian systems.

Dinosaurs
Dinosaur eggs are known from the formation.

Ornithischians

 * Ankylosaurs
 * Hadrosaurs

Saurischians

 * Sauropods

Pterosaurs
Fragmentary fossils are known from the formation.

Frogs
Unnamed frogs belonging to the family Calyptocephalellidae and Leptodactylidae, and those with no family designation were also found.

Mammals
The mammal fauna of the Allen Formation is known from seven teeth, which document the presence of several species.