SPECIFIC RENEWAL OF FORAMINIFERS AND DEPOSITIONAL SEQUENCES IN THE LOWER CRETACEOUS OF THE SE FRENCH BASIN

In the Lower Cretaceous of the Vocontian basin, a remarkable coincidence exists between the biological crises which affect the foraminifers and the depositional sequences sensu Vail. It corroborates the fact that eustatism is the main driving force of the specific renewal. The most important changes are coincident with some transgressive maxima (but not with all of them) and with major crises affecting ammonities in the same basin and benthic formaninifers on the surrounding platforms. At the 3rd order cycle level, a faunal stasis is observed at the bottom (lowstand sea level); the species renewal begins during the sea level rise and generally culminates at the maximum of the transgression; its slows down or ends at the top of the cycle (highstand sea level). Newly appeared species often proliferate at that time. Appearances and disappearances of species occur simultaneously. The balance between them is dependent on the evolutionary stage of the fauna which is correlated with its place in the long term eustatic history. This study also demonstrates the utility of foraminiferal assemblages in identifying systems tracts in basin setting (through specific renewals and the evolution of their quantitative composition).