The Jurassic/Cretaceous boundary in the Apulco area by means of calpionellids and calcareous dinoflagellates: An alternative to the classical Mazatepec section in eastern Mexico

- We detected the Jurassic/Cretaceous boundary in Eastern Mexico by means of calpionellids.
- The calpionellid biostratigraphy was possible due to a detailed sampling.
- The calpionellid distribution in Mexico is similar to that of the rest of the Tethys.

A detailed bed-by-bed sampling within the Pimienta and the Lower Tamaulipas Formations from a section in the Apulco area (Puebla State, Eastern Mexico), allows the delimitation of the Jurassic/Cretaceous boundary. The Late Tithonian was identified by the presence of calpionellids of the Crassicollaria Zone (Colomi Subzone) and calcareous dinocysts of the Proxima Zone. The Tithonian/Berriasian boundary was placed at the acme of Calpionella alpina (small forms) between samples MZT 45-46. The Berriasian was divided into two main units, namely the Calpionella Zone, further subdivided into the Alpina, Ferasini and Elliptica subzones, and the Calpionellopsis Zone, within which only the Oblonga subzone was identified. The vertical distribution of calpionellids and their assemblages in the biozones of this Mexican section fit those from other Tethyan areas.