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

Uliana and Dellapé defined the formation's stratotype in 1981 in the eastern area of the Bajo de Añelo, where the relation between the base and top is clearly exposed. The deposits are mostly clastic, interbedded with banks of limestone and layers of anhydrite, which were defined as 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.
Armas and Sánchez performed a detailed facies analysis of the formation 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.
A study of pollen found in outcrops of the middle member of the Allen Formation supported a late Maastrichtian age for these layers.

Fossil content

Dinosaurs

Dinosaur eggs are known from the formation.

Ornithischians

; Ankylosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Ankylosauria	Indeterminate	Arriagada Farm		Two teeth, five osteoderms, and a partial sacrum	Fossil remains possibly belonging to a parankylosaur distinct from Patagopelta
Patagopelta	P. cristata	Salitral Moreno locality	Lower	Tooth, three posterior dorsal vertebrae, caudal vertebrae, two caudal centra, right femur, partial cervical half ring, and osteoderms	A possible parankylosaur

; Hadrosaurs

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Bonapartesaurus	B. rionegrensis	Salitral Moreno and Islas Malvinas.	Lower	A partial skeleton.	A hadrosaur
Kelumapusaura	K. machi	Cerro Matadero, Arriagada Farm	Upper	Partial skull, a cervical vertebrae, several sacrals, sternal rib and sternal plate, and multiple referred specimens found in a bonebed	A saurolophine hadrosaur
Lapampasaurus	L. cholinoi	Islas Malvinas	Lower	Elements of the axial and appendicular skeleton of a subadult individual	A hadrosaur
Willinakaqe	W. salitralensis	Salitral Moreno site.	Lower	A right premaxilla.	A saurolophine hadrosaur

Saurischians

;Sauropods

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Aeolosaurus	Indeterminate		Lower		A titanosaur
Bonatitan	B.reigi		Lower	Braincases, caudal vertebrae, and several limb elements	A titanosaur
Menucocelsior	M. arriagadai		Lower	Seventeen caudal vertebrae and several appendicular bones: a right humerus, a left fibula and some metapodial.	A titanosaur
Panamericansaurus	P. schroederi			"Five tail vertebrata, sacral vertebrae, left humerus and rib fragments"	A titanosaur
Pellegrinisaurus?	P. powelli		Lower	"Dorsal and caudal vertebrae, partial femur"	A titanosaur
Rocasaurus	R. muniozi		Middle	"Partial postcranial skeleton"	A titanosaur
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