Itaboraí Formation
The Itaboraí Formation (Portuguese: Formação Itaboraí) is a highly fossiliferous geologic formation and Lagerstätte of the Itaboraí Basin in Rio de Janeiro, southeastern Brazil. The formation reaching a thickness of 100 metres (330 ft) is the defining unit for the Itaboraian South American land mammal age (SALMA), dating to the Early Eocene, approximately 53 to 50 Ma.
| Itaboraí Formation | |
|---|---|
| Stratigraphic range: Early Eocene (Itaboraian) ~ | |
| Type | Geological formation |
| Sub-units | See text |
| Underlies | Early Eocene basalt & Late Eocene to Early Oligocene conglomerates (Rio Frio Formation) |
| Overlies | Precambrian basement |
| Area | 1 km2 (0.39 sq mi) |
| Thickness | up to 100 m (330 ft) |
| Lithology | |
| Primary | Limestone, marl |
| Other | Travertine, lignite |
| Location | |
| Coordinates | 22.1°S 41.6°W |
| Approximate paleocoordinates | 25.0°S 30.0°W |
| Region | Rio de Janeiro |
| Country | Brazil |
| Extent | Itaboraí Basin |
| Type section | |
| Named for | Itaboraí |
| Named by | Leinz |
| Year defined | 1938 |
Itaboraí Formation (Brazil) | |
The formation is restricted to the Itaboraí Basin, a minibasin of 1 square kilometre (0.39 sq mi) around the city of Itaboraí, 34 kilometres (21 mi) northeast of Rio de Janeiro, and comprises limestones, marls and lignites, deposited in an alluvial to lacustrine environment, dominated by heavy rainfall. The formation overlies Precambrian basement and is overlain by Early Eocene basalts and Late Eocene to Early Oligocene conglomerates.
The up to 100 metres (330 ft) thick formation has provided many fossil mammals of various groups among which the marsupials and related metatherians dominate, birds, snakes, crocodiles, amphibians, and several species of gastropods. Several genera and species were named after the formation; the marsupials Itaboraidelphys camposi and Carolopaulacoutoia itaboraiensis, the birds Itaboravis elaphrocnemoides, Eutreptodactylus itaboraiensis and Eutreptodactylus itaboraiensis, the snake Itaboraiophis depressus and the caiman Eocaiman itaboraiensis and the gastropods Itaborahia lamegoi, Biomphalaria itaboraiensis and Gastrocopta itaboraiensis.
The formation is the richest Cenozoic fossiliferous formation of Brazil, leading to the establishment of the Parque Paleontológico de São José de Itaboraí ("São José de Itaboraí Paleontological Park") in 1995. The site is a candidate for becoming a UNESCO World Heritage Site.