Cerrejón Formation

Cerrejón Formation Stratigraphic range: Mid-Late Paleocene ~60–58 Ma PreЄ Є O S D C P T J K Pg N ↓
Section of the Cerrejón coal mine
Type	Geological formation
Sub-units	Lower, middle, upper
Underlies	Tabaco Formation
Lithology
Primary	Coal, mudstone, siltstone
Other	Sandstone
Location
Region	La Guajira, Cesar
Country	Colombia
Type section
Named for	Cerrejón

The Cerrejón Formation is a geologic formation in Colombia dating back to the Middle-Late Paleocene. It is found in the El Cerrejón subbasin of the Ranchería basin of La Guajira. The formation consists of bituminous coal fields that are an important economic resource. Coal from the Cerrejón Formation is mined extensively from the Cerrejón open-pit coal mine, one of the largest in the world. The formation also bears fossils that are the earliest record of Neotropical rainforests.

The Cerrejón Formation is subdivided into lower, middle, and upper groups based on the thickness and distribution of coal beds. On average the coal beds are 3 metres (9.8 ft) thick, and range from 0.7 metres (2.3 ft) to 10 metres (33 ft) in thickness. The thickest beds are in the upper part of the formation. The Cerrejón Formation is laterally equivalent with the Los Cuervos and Bogotá Formations to the south; Llanos Orientales and Altiplano Cundiboyacense respectively.

Based on lithofacies associations and paleofloral composition, the depositional environment fluctuated from an estuarine-influenced coastal plain at the base of the formation to a fluvial-influenced coastal plain at the top.

In the geologically recent past, some coal in the formation has spontaneously and naturally combusted to form clinker, red and brick-looking burnt coal. These rocks outcrop irregularly and are up to 100 metres (330 ft) thick. Clinker is found near deformed zones such as faults or tight folds, and is older than the deformities themselves. They are thought to have combusted after the development of the Cerrejón thrust fault and alluvial fan.