Ammonoid and foraminiferal biostratigraphy from uppermost Valanginian to lowermost Barremian of the Jebel Boulahouajeb section (northern Tunisia)

摘要

A stratigraphic study was carried out on the Jebel Boulahouajeb section (Lansarine Chain; Tebourba area, northern Tunisia) in order to establish a relatively detailed biostratigraphic framework of the Hauterivian pelagic deposits of the Tunisian trough. The limestone-marl alternations are represented by five limestone-dominated intervals, named calcareous bundles H1 to H5, separated by thick marly-dominated intervals. The well exposed Jebel Boulahouajeb section (873 m in thickness) is relatively continuous, rich in ammonoid macrofauna, and provides an ideal succession for this approach. Concerning the Hauterivian ammonoid zonal scheme, the following (sub.)zones have been identified: Acanthodiscus radiatus, Crioceratites loryi, Lyticoceras nodosoplicatum, Balearites balearis (with B. balearis, Balearites binelli, Balearites krenkeli and Balearites angulicostatus Subzones) and Pseudothurmannia ohmi (with P. ohmi, Pseudothurmannia mortilleti and Pseudothurmannia picteti Subzones) Zones. Thus, except the Subsaynella sayni and Plesiospitidiscus ligatus Zones, the standard zonation of the Mediterranean Province has been recognized in this area of the Tunisian trough. The boundaries of the Hauterivian stage have been characterized by identifying the last zone of Valanginian (Criosarasinella furcillata Zone) and the first zone of Barremian (Taveraidiscus hugii Zone). The benthic and planktic foraminiferal assemblages have been used to characterize some stratigraphic levels of the studied section; however the lack of certain data did not allow to well recognize and establish a complete zonal scheme. Mainly on the base of ammonoid biostratigraphy, the Jebel Boulahouajeb section is correlated with the Jebel Oust section (north-west of Zaghouan) that is the Lower Cretaceous reference section of the Tunisia trough.