Abstract The Taraises and lower Tamaulipas formations of the Early Cretaceous (Berriasian–Valanginian) are basinal sedimentary sequences in northeastern and eastern Mexico, respectively. The first unit was penetrated in the San Javier 1 and 2 wells at depths between 1800 and 3200 m (5905 and 10,499 ft), and the second was drilled in the Bejuco 6 and the La Laja 8 wells between 2000 and 2500 m (6562 and 8202 ft). In the Bejuco 6 well, the lower Tamaulipas Formation represents a condensed section. Geophysical logs and ammonites allow the characterization and age dating of these units. Two important ammonite groups (Ancyloceratoidea and Perisphinctoidea) are described from cores in the four wells and from surface occurrences. Four new genera are proposed, Misantlites, Wiedmannites, Parvaites , and Parrasites ; new species are M. reyesi, Aegocrioceras eguiluzi, Capeloites lajense, C. peyroullesense, Thurmanniceras kleini, Neohoploceras bartolinii, Parvaites aguirrei, P. leanzai ; and one new subfamily is proposed, Capeloitinae.

Abstract The Berriasian–Aptian succession in the Neuquén Basin is mainly marine in the lower part and non-marine in the upper portion. A detailed ammonite zonation is presented for the Berriasian–?Early Barremian interval. While some ammonite taxa are endemic, others are widely distributed and there are several levels where correlation can be suggested with the 'standard' stages and zones of the Tethyan Mediterranean area. Several nannofossil bioevents are recognized, and these provide evidence for correlation with Tethyan areas. Correlations suggested by both groups are reasonably consistent. Berriasian–Aptian palynomorphs include both terrestrial and marine forms. Several terrestrial assemblages can be recognized, but the marine forms are mainly long-ranging taxa, especially in the Agrio Formation.