Bajo de la Carpa Formation

The Bajo de la Carpa Formation is a geologic formation that outcrops in Patagonia, in the provinces of Río Negro and Neuquén, Argentina. It is the first of two formations belonging to the Río Colorado Subgroup within the Neuquén Group. Formerly that subgroup was treated as a formation, and the Bajo de la Carpa Formation was known as the Bajo de la Carpa Member.

At its base, this formation conformably overlies the Plottier Formation of the older Rio Neuquén Subgroup, and it is in turn overlain by the Anacleto Formation, the youngest and uppermost formation of the Neuquén Group.

The Bajo de la Carpa Formation can reach 150 meters thick in some locations, and consists mainly of sandstones of various colors, all of fluvial origin, with thin layers of mudstone and siltstone in between. Geological features such as geodes, chemical nodules, impressions of raindrops, and paleosols (fossil soils) are commonly found in this formation as well.

Age
Era: Mesozoic Period: Late Cretaceous Faunal stage: Santonian Absolute Age: ~86 to ~83 mya

Paleontology


Animal fossils are abundant within the Bajo de la Carpa Formation:


 * a snake-necked turtle, Lomalatachelys
 * the snake Dinilysia
 * diverse crocodylomorphs occupying a range of ecological niches: Comahuesuchus, Cynodontosuchus, Lomasuchus, Neuquensuchus, Notosuchus, Peirosaurus
 * titanosaurian sauropods including Bonitasaura
 * the ceratosaurian theropods Velocisaurus
 * the bird-like theropod Achillesaurus and Alvarezsaurus
 * the enantiornithine bird Neuquenornis
 * the oldest known true flightless bird Patagopteryx

Small nests with eggs inside, found in this formation, probably belonged to Neuquenornis or a related taxon. Fossil wasp nests have also been found in these rocks.