Berriasian–Valanginian calpionellid biostratigraphy and associated microfossils from the upper Pimienta and lower Tamaulipas formations (Hidalgo state, Mexico): paleoenvironmental and paleobiogeographic signifi cance.

A section measured from the upper part of the Pimienta Formation and the lowest part of the Tamaulipas Formation located in the central-eastern part of the state of Hidalgo, NE Mexico was studied. The lower part of the succession consists of an argillaceous and laminated dark gray limestone, black shale, black calcareous shale, siltstone and bentonite; the Pimienta–Lower Tamaulipas transition is marked by the sporadic appearance of light-colored limestone in the upper part of the Pimienta and the shift to a succession dominated by thicker beds of yellowish and bioturbated limestone. The microfossil assemblage consists of calpionellids, radiolarians, and planktonic and benthic foraminifers. The biostratigraphic study of the calpionellids enabled three zones to be identifi ed: Calpionella, Calpionellopsis and Calpionellites as well as fi ve subzones, Elliptica, Oblonga, Murgeanui, Darderi and Major, ranging from early late Berriasian to early Valanginian. This allows a chronostratigraphic correlation to be drawn between the Tethys and the Southeastern Pacifi c provinces. In addition, we report the occurrence of abundant radiolarians and planktonic and benthic foraminifers. The paleoenvironmental inferences in the studied section are documented from the predominant wackestone texture and microfossil association, indicating a pelagic basin environment. The abundant occurrence of radiolarians mostly in the Elliptica and Oblonga subzones could suggest an increase in the input of nutrients. [ABSTRACT FROM AUTHOR]