Tenejapa-Lacandón Formation

The Tenejapa-Lacandón Formation is a geological formation and lagerstätte in southern Mexico and western Guatemala. It preserves fossils dating to the Early Paleocene.

It is located primarily in the Mexican state of Chiapas, but outcrops lie as far west as Petén, Guatemala. Some consider it as two distinct formations, the Tenejapa Formation to the west and the Lacandón Formation to the east, which are contiguous and contemporary with each other. The Lacandón Formation was deposited in a shallow inshore marine habitat, whereas the Tenejapa Formation was deposited in a deep offshore habitat. They appear to preserve a marine ecosystem deposited on the western margin of the Caribbean Sea.

The most prominent exposures are at the División del Norte and Belisario Domínguez quarries near Palenque, Chiapas, which contain articulated fish skeletons belonging to a variety of taxa of both Cenozoic and Mesozoic affinities. This formation was also the source of the limestone used to build the ancient Mayan city of Palenque, with one other fossil-bearing locality being an unnamed quarry used by the Mayans. The inhabitants of ancient Palenque were aware of the fossils present in the formation, and used them in ways such as painting articulated fossils for the purpose of decoration.

The Tenejapa-Lacandón Formation is, temporally and geographically, the "closest" geological formation to the Chicxulub impact crater; it is located only 500 km from the Chixculub crater and was deposited approximately 3 million years after the impact. For this reason, it is important evidence for understanding the recovery of ocean ecosystems in the wake of the Cretaceous-Paleogene extinction event, especially near the Chixculub crater. The high number of well-preserved fossil fish specimens, likely relating to mass mortality events, makes it a lagerstätte. It represents one of the richest known faunas of articulated Paleocene acanthomorphs.