Ammonite age-calibration of the EL Chango Fossil-Lagerstätte, Chiapas state (SE Mexico)

- We study the ammonoid record of the El Chango.
- We identify the genera Graysonites and Metengonoceras.
- Graysonites allows us to assign this locality to the lowermost early Cenomanian age.
- We propose the use of the Cintalapa Formation for the studied stratigraphic interval.

This paper dates the El Chango Lagerstätte (Chiapas, SE Mexico), known for its exceptionally well-preserved marine fishes, plant remains, crustaceans, insects and mollusks, based on ammonite biostratigraphy. The age of the El Chango fauna is imprecisely assigned to either the late Albian or Cenomanian. We document here an ammonite assemblage comprising Graysonites and ?Metengonoceras. Graysonites, which gives a lowermost early Cenomanian age, Cintalapa Formation pro parte. We noticed that the terminology of lithostratigraphic units in the studied area is confusing and varies considerably depending on the author, therefore proposing the use of Cintalapa Formation for the El Chango section and the Sierra Madre as a group that includes it.