Jurassic radiolarian-bearing series of Tunisia: biostratigraphy and significance to western Tethys correlations

摘要

Since the 1970s, radiolarians have been used extensively to study and characterize basin successions from the peri-Mediterranean regions. However, no data was ever produced in Tunisia in spite of the occurrence of Jurassic siliceous series previously described by many authors. Our study presents the biostratigraphical results obtained on sections from the Jédidi Formation, which characterizes the basinal series of the Tunisian Trough. We provide new direct age determinations from the base, the middle part and the top of the formation, which ranges from the latest Bajocian–middle Bathonian to the Oxfordian (Tethyan biozones UAZ 5-6 to 8-9). The onset of these radiolarian-bearing series of the Tunisian Trough, adjacent to partly coeval Ammonitico Rosso successions, is interpreted as resulting from regional palaeotopographical gradient and palaeoceanographical conditions. Inaccurately interpreted as “true” radiolarites, theses series are different from coeval radiolarites of the Maghrebian “Dorsale calcaire” and from more recent homologous deposits of the Flysch domain. They are instead correlative with series exposed in the Babors and the west-Numidian ranges of northern Algeria that belonged to the same Jurassic North African margin of western Tethys. During Alpine convergence s.l., this external domain was overthrust by nappe complexes of the Maghrebide inner zones and the Flysch domain units.