The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.[1] Dinosaur remains are among the fossils that have been recovered from the formation.[2] Indeterminate chelid remains and other vertebrates have also been discovered in this formation.[3]
Allen Formation | |
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Stratigraphic range: Mid Campanian-Maastrichtian ~ | |
Type | Geological formation |
Unit of | Malargüe Group |
Underlies | Jagüel Formation |
Overlies | Anacleto Formation |
Thickness | up to 70 m (230 ft) |
Lithology | |
Primary | Mudstone, sandstone |
Other | Limestone |
Location | |
Coordinates | 40°00′S 66°36′W / 40.0°S 66.6°W |
Approximate paleocoordinates | 42°48′S 52°12′W / 42.8°S 52.2°W |
Region | Neuquén, Río Negro & La Pampa Provinces |
Country | Argentina |
Extent | Neuquén Basin |
Type section | |
Named by | Uliana & Dellapé |
Year defined | 1981 |
Allen Formation (Argentina) |
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.[4]
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.[4]
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.[5]
Dinosaur eggs are known from the formation.[6]
Ankylosaurs reported from the Allen Formation | ||||||
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Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Patagopelta | P. cristata | Lower | Tooth, three posterior dorsal vertebrae, caudal vertebrae, two caudal centra, right femur, partial cervical half ring, and osteoderms. |
Hadrosaurs reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Bonapartesaurus | B. rionegrensis | Lower | ||||
Kelumapusaura | K. machi | Upper | Partial skull, a cervical vertebrae, several sacrals, sternal rib and sternal plate and multiple referred specimens found in a bonebed | |||
Lapampasaurus | L. cholinoi | Lower | Elements of the axial and appendicular skeleton of a subadult individual | |||
Willinakaqe | W. salitralensis | Lower |
Sauropods reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Aeolosaurus | Indeterminate | Lower | ||||
B.reigi[12] |
Río Negro Province[12] | Lower | Braincases, caudal vertebrae, and several limb elements | |||
Menucocelsior | M. arriagadai | Lower | Seventeen caudal vertebrae and several appendicular bones: a right humerus, a left fibula and some metapodial. | |||
Panamericansaurus | P. schroederi | "Five tail vertebrata, sacral vertebrae, left humerus and rib fragments" | ||||
Pellegrinisaurus? | P. powelli | Lower (if it is from the formation) | "Dorsal and caudal vertebrae, partial femur" | |||
Rocasaurus | R. muniozi | Lower | "Partial postcranial skeleton" |
Theropods reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Austroraptor | A. cabazai | Lower | A fragmentary skeleton including parts of the skull, lower jaw, a few neck and torso vertebrae, some ribs, a humerus, and assorted bones from both legs | A dromaeosaurid. | ||
Bonapartenykus | B. ultimus | Upper | ||||
Lamarqueavis | L. australis | Lower | "Right coracoid with damaged sternal and omal extremities, and lacking acrocoracoidal process" | A prehistoric bird. | ||
Limenavis | L. patagonica | Lower | "Partial forelimb" | A prehistoric bird. | ||
Niebla | N. antiqua | Upper | Braincase, fragmentary jaw and teeth, relatively complete scapulocoracoid, dorsal ribs, and incomplete vertebrae. | An abelisaurid[18] | ||
Quilmesaurus | Q. curriei | Upper | Femur and distal tibia | An abelisaurid. |
Fragmentary fossils are known from the formation.[6]
Pterosaurs reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Aerotitan | A. sudamericanus | Bajo de Arriagada | Uppermost Allen Fm. | Partial rostrum | The first unambiguous azhdarchid from South-America[20] |
Fish reported from the Allen Formation[3] | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Diplomystidae | indeterminate | 4 incomplete pectoral spines | ||||
Siluriformes | indeterminate | 5 incomplete pectoral spines | ||||
Lepisosteidae | indeterminate | 6 vertebral centra | ||||
Teleostei | indeterminate | 10 isolated teeth | ||||
cf. Percichthyidae | indeterminate | 19 fragmentary vertebrae | ||||
Ceratodontiformes | indeterminate | 3 tooth plates | ||||
Chondrichthyes | indeterminate | 11 vertebral centra |
Squamates reported from the Allen Formation[3] | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Patagoniophis | P. parvus | incomplete trunk vertebra | ||||
Alamitophis | A. argentinus | incomplete trunk vertebra | ||||
Madtsoiidae | indeterminate | incomplete trunk vertebra |
Rhynchocephalia reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Lamarquesaurus | L. cabazai | Cerro Tortuga | [21] |
Plesiosaurs reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Kawanectes | K. lafquenianum |
Unnamed frogs belonging to the family Calyptocephalellidae and Leptodactylidae, and those with no family designation were also found.[22][3]
Frogs reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Kuruleufenia | K. xenopoides | Pipid frog.[23] |
The mammal fauna of the Allen Formation is known from seven teeth, which document the presence of several species.[24]
Mammals reported from the Allen Formation | |||||
---|---|---|---|---|---|
Genus | Species | Location | Material | Notes | Images |
Mesungulatum | M. lamarquensis | Cerro Tortuga | Two upper molars and a fragmentary lower molar | A dryolestoid | |
Groebertherium | G. stipanicici | Cerro Tortuga | One upper molar | A dryolestoid | |
cf. Brandonia | sp. | Cerro Tortuga | One lower molar | A dryolestoid | |
Barberenia | B. allenensis | Cerro Tortuga | One upper molariform | A dryolestoid | |
Trapalcotherium | T. matuastensis | Cerro Tortuga | One first lower molar | A gondwanathere |
Plants reported from the Allen Formation | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Podocarpoxylon | P. mazzonii | Valcheta Petrified Forest, Río Negro Province.[25] | Fossil wood.[25] |