Intérêts environnemental et chronologique des bioaccumulations à brachiopodes. Exemple de l’Oxfordien supérieur (Jurassique supérieur) du Bassin parisien (France)

In the Upper Jurassic of the eastern Paris Basin, brachiopods can be preserved in abundance in particularly thin levels. The apparent biodiversity is poor in such lithological units, which appear with rhythmicity throughout the series. However, the observed morphological changes within the dominant taxa (terebratulids, analyzed through morphometrical methods) traduce the palaeoenvironmental changes (deepness). Moreover, each unit showing such a brachiopod concentration characterizes a very short time slice (shorter than any ammonite bio-horizon); so, it provides an alternative, more powerful than the ammonites, for correlations. Unfortunately, they cannot be useful for large-scale correlations, due to their kilometrical geographical range.