In order to elucidate the mechanisms driving this rhythmic sedimentary pattern, calcareous nannoplankton, benthic and nektonic faunas were studied, and geochemical analyses applied. Different fine-fraction elements were quantified in the nannofacies, namely micarb, pyrite, clays, etc.
Ammonoids represent almost the totality of the nektonic macrofauna.
Statistical analyses show significant variations of the absolute abundance of the six ammonite families which dominate the assemblage with respect to the carbonate content. Calcareous nannofossils are more abundant in calcareous marls, marls and shales than in limestones all along the section. Quantification of calcareous nannofossils in marls and organic-rich shales has evidenced a net dominance in the assemblage of coccoliths over nannoconids. In limestones, both coccoliths and nannoconids become very rare. Neither nannoconids nor coccoliths seem to have produced the bulk of carbonate mud, even if their contribution to the overall carbonate content is not negligible in discrete layers.