Noteworthy brachiopods of the Cenomanian stratotype: A synthesis of the biochronological, palaeoenvironmental and palaeoecological implications

This study contributes to a general revision of the Cenomanian stratotype that is currently in progress. Many organisms, including brachiopods, have been used to characterise the Cenomanian stratotype. Brachiopod species in the stratotype area have been previously only evoked or partially described; they include rhynchonelliform brachiopods belonging to Rhynchonellida, Terebratulida (Terebratulidina and Terebratellidina), and craniiform taxa. Their morphological descriptions are re-examined using new techniques, including scanning electron microscope analysis (SEM) of the shell microstructure and 3D reconstruction of the brachidium using X-ray micro-tomography. These new methodologies allow a better definition of taxa and therefore improve their biostratigraphical usage. Some brachiopod species are significant as biochronostratigraphical markers, especially for the middle (Jalais Level) and the upper Cenomanian (“Sables du Perche”, “Marnes à Ostrea biauriculata”, “Sables à Catopygus obtusus”, and “Craie à Terebratella carantonensis”). Some features, both on and in the brachiopod shell, indicate the mode of life of these brachiopods (e.g., ichnofacies, parental attachment), and some shell modifications (e.g., microboring activities) inform on the palaeoecological conditions in the contrasted environments of the Cenomanian stratotype.