Paja Formation, Geological formation in central Colombia

The Paja Formation spans hundreds of kilometers across several departments in central Colombia and consists of alternating layers of black shale, claystone, sandstone, and limestone concretions. These rock layers are extremely thick and reveal the complex geological history of the region.

This formation developed during the Early Cretaceous period, approximately 130 to 113 million years ago, when central Colombia was covered by a warm, shallow sea. The sediments that accumulated during this time recorded an important phase in the marine history of South America.

The formation's name comes from Quebrada La Paja, a tributary of the Sogamoso River in Betulia, Santander, where the type section is exposed on the quebrada's northern banks. Its three members are the Lutitas Negras Inferiores, Arcillolitas Abigarradas and Arcillolitas con Nódulos Huecos. Near Villa de Leyva and Sáchica, its outcrops lie in the La Candelaria Desert, a microclimatic spot spanning Villa de Leyva, Santa Sofía and Sáchica.

The type section lies on the northern banks of Quebrada La Paja at its confluence with the Sogamoso River in Betulia, Santander, where the exposed sequence reaches 625 m. Fossil-rich outcrops near Villa de Leyva and Sáchica are the usual starting points, and the La Candelaria Desert area around Villa de Leyva, Santa Sofía and Sáchica is where the formation appears in the hills. Access is on foot over open country, so plan for rain and mud.

The formation's only named dinosaur, Padillasaurus leivaensis, was described in 2015 from remains found near Villa de Leyva, making it Colombia's first named dinosaur. The same beds also yielded the fossil shark Protolamna ricaurtei, described in 2019.