Paja Formation
The Paja Formation (Spanish: Formación Paja, K1p, Kip, Kimp, b3b6p) is an Early Cretaceous geologic formation of central Colombia. The formation extends across the northern part of the Altiplano Cundiboyacense, the Western Colombian emerald belt and surrounding areas of the Eastern Ranges of the Colombian Andes. In the subsurface, the formation is found in the Middle Magdalena Valley to the west. The Paja Formation stretches across four departments, from north to south the southernmost Bolívar Department, in Santander, Boyacá and the northern part of Cundinamarca. Well known fossiliferous outcrops of the formation occur near Villa de Leyva, also written as Villa de Leiva, and neighboring Sáchica.
| Paja Formation | |
|---|---|
| Stratigraphic range: Late Hauterivian-Late Aptian ~ | |
Desmatochelys padillai from the Paja Formation | |
| Type | Geological formation |
| Sub-units | Lutitas Negras Inferiores, Arcillolitas Abigarradas & Arcillolitas con Nódulos Huecos Members |
| Underlies | San Gil Group, Simití & Tablazo Formations |
| Overlies | Ritoque & Rosablanca Formations |
| Area | 450 km (280 mi) |
| Thickness | up to 940 m (3,080 ft) |
| Lithology | |
| Primary | Black shale, claystone, sandstone and limestone concretions |
| Other | Gypsum, chalcopyrite, galena, malachite, pyrite, sphalerite |
| Location | |
| Coordinates | 5.5°N 73.5°W |
| Approximate paleocoordinates | 3.7°N 42.2°W |
| Region | Bolívar, Boyacá, Cundinamarca & Santander |
| Country | Colombia |
| Extent | Altiplano Cundiboyacense Eastern Ranges, Andes Middle Magdalena Valley |
| Type section | |
| Named for | Quebrada La Paja |
| Named by | Wheeler |
| Year defined | 1929? |
| Coordinates | 7°01′33.4″N 73°19′27.8″W |
| Region | Betulia, Santander |
| Thickness at type section | 625 m (2,051 ft) |
Outcrops of the Paja Formation near Villa de Leyva | |
The formation was named after Quebrada La Paja in Betulia, Santander, and stretches across 450 kilometres (280 mi) from northeast to southwest. The Paja Formation overlies the Ritoque and Rosablanca Formations and is overlain by the San Gil Group and the Simití and Tablazo Formations and dates from the late Hauterivian to late Aptian. The Paja Formation comprises mudstones, shales and nodules of sandstones and limestones, deposited in an anoxic environment, in the warm and shallow sea that covered large parts of the present Colombian territory during the Cretaceous.
Initially considered to host Colombian emeralds, the emerald-bearing part was redefined as a separate formation; the Muzo Formation. The Paja Formation Lagerstätte is famous for its vertebrate fossils and is the richest Mesozoic fossiliferous formation of Colombia. Several marine reptile fossils of plesiosaurs, pliosaurs, ichthyosauras and turtles have been described from the formation and it hosts the only dinosaur fossils described in the country to date; Padillasaurus. The formation also has provided many ammonites, fossil flora, decapods and the fossil shark Protolamna ricaurtei.