The Berriasian–Valanginian (Early Cretaceous) boundary transition at Santa Catarina Ticuá, Oaxaca state, southern Mexico: Ammonites, bivalves, calpionellids and their paleobiogeographic significance

• Stratigraphy and paleogeography of ammonites, bivalves and calpionellids from the Berriasian–Valanginian boundary at Santa Catarina Ticuá, Oaxaca, southern Mexico.
• Our results suggest that biogeographic correlation is possible between southern Mexico and the western Tethys.
• Our data allow for a calibration and correlation of faunal and environmental changes in the Berriasian–Valanginian interval of the western hemisphere.

Ammonites, bivalves and calpionellids of the late Berriasian-early Valanginian from southern Mexico are poorly known; those here described are from the Sabinal Formation at Santa Catarina Ticuá, Oaxaca state. Samples were collected and analyzed bed-by-bed. Ammonite assemblages correlate to the West Mediterranean late Berriasian Subthurmannia boissieri and early Valanginian Thurmanniceras pertransiens and Neocomites neocomiensiformis zones and contain taxa, which are majorly endemic, although a few European species are also identified. The bivalve Arctotis cretacea (Felix, 1891) is common in several horizons throughout the section. Calpionellids are present in the upper part of the Santa Catarina Ticuá section and are indicative of the middle Berriasian Remaniella cadischiana Subzone, the late Berriasian Calpionellopsis Zone (including the Calpionellopsis simplex and Cs. oblonga subzones) and the early Valanginian Calpionellites darderi Subzone. Our data indicate that biogeographic correlation of faunal and environmental changes is possible across the Berriasian–Valanginian boundary between southern Mexico and faunal realms of the southwestern Gulf of Mexico and the western Tethys, and thus throughout the western hemisphere.