Integrated Biostratigraphy of Calcareous Nannofossils and Ammonoids. Implications for the Definition of the Stratotype of the Berriasian–Valanginian Boundary (139.4 Ma)
This work aims to identify the Berriasian–Valanginian boundary (139.4 Ma) in three sections in southeastern France (Vergol, Courchons, and Berrias) by using an integrated biostratigraphy approach, and supports the proposition of the Vergol section as a candidate for the global stratotype section and point (GSSP). An analysis of the distribution of calcareous nannofossils and ammonoids is used to construct a new biochronstratigraphic framework. We use interval zones for establishing ammonoids and nannofossil biozones. The identification of the Berriasian–Valanginian boundary is based on the first occurrence of Tirnovella pertransiens. Coccolith bioevents around the boundary are also helpful, such as the first occurrences of Percivalia fenestrata, Calcicalathina oblongata, and Zeugrhabdotus trivectis. Changes in the assemblages of nannofossils and ammonoids are also used to reconstruct palaeoenvironmental variations. A Nannoconus decline is identified as having occurred during the early Valanginian, which corresponds to a perturbation of the carbon cycle that took place between the early and middle Valanginian.
KeywordsCalcareous nannofossils Ammonoids Integrated biostratigraphy Berriasian–Valanginian boundary
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