Enregistrement de l'eustatisme par les foraminifères dans les séquences de dépôt du Crétacé inférieur du bassin vocontien (SE de la France)

Abstract

Long and short term variations (at the supercycle level and at the 3rd and lower order sequence levels) are observed within benthic foraminiferal assemblages of lower Cretaceous age from the Vocontian Basin. They are interpreted as a response of these bathyal organisms to eustatic or relative sea-level variations: the absolute or relative high sea-level associations are richer and more diversified, especially calcareous forms. This is true for Valanginian to late Hauterivian times (continuous sea-level rise). However, in upper late Hauterivian and early Barremian time (major sea-level highstand), some anoxic phenomena disturb this process. Nevertheless, foraminifers can be used within some limits for the interpretation of systems tracts in the basin, as is the case on the shelf margin. They also confirm the fact that in basinal setting the base of the sequence, which is mainly calcareous, represents a lowstand systems tract and that the top of the sequence, which is more shaly, represents transgressive and highstand system tracts, according to the sequence stratigraphy concepts sensu Vail.