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Mabrouk Boughdiri, Faculty of Sciences of Bizerte (Tunisia)
Mohamed Hédi Ben Ismail, Faculty of Sciences of Tunis (Tunisia)
Mohamed Soussi, Faculty of Sciences of Tunis (Tunisia)
Houaïda Sallouhi, Faculty of Sciences of Bizerte (Tunisia)
Sofiène Haddad, Faculty of Sciences of Tunis (Tunisia)
Kamel Maalaoui, Faculty of Sciences of Bizerte (Tunisia)
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The stratigraphic and geodynamic interpretation of Upper Jurassic-Lowermost Cretaceous units in Central and Northern tunisia is revised through updated radiolarian, ammonite and calpionellid biochronostratigraphy. More than ten sections from different palaeogeographical settings were bed-by bed sampled. A revised biostratigraphy of the 'Ammonitico Rosso' series of the Tunisian Dorsale (NE Tunisia) led to the identification of Middle Callovian-Oxfordian ammonite zones and subzones. A first direct datation of the partly coeval biosiliceous radiolarian-bearing series of the Tunisian Trough (NW Tunisia) was established. Upward within the Jurassic column, an integrated biochrostratigraphy (ammonites, calpionellids and associated biomicrofacies) allowed, for the first time, precise biozonations and scale correlations within the Kimmeridgian-Middle Berriasian interval that fit recent standards proposed for European Basins.
The heterogeneity of the Middle-Late Jurassic facies in northern Tunisia is the result of two main geodynamical and palaeogeographical events. The first corresponds to the fragmentation of the initial Early Jurassic platform linked to Tethyan rifting that led to a mosaic of raised and drowned blocks. The second event, coeval to radiolarian-bearing series of the Tunisian Trough, is expressed by a clear deepening in northwest Tunisian palaeoenvironments and, as a result, the partition of two major palaeogeographic realms separated by NE-SW-trending major faults: 1) a relatively resistant composite domain including the Tunisian Dorsale and 2) a deeper subsiding domain that differentiated from the Dorsale since the late Bajocian where the biosiliceous successions and the overlying carbonate units of the Béni Kleb Fm were deposited.
Within the Maghrebian belt, Upper Jurassic-Lowermost Cretaceous units are easily correlated with minor differences in age (local tectonic control). Three major facies groups characterize the series of these Maghrebian segments. From east to west, the first includes those from the Tunisian Dorsale and nearby exposures, to the South-Tellian border (Algeria) and to the internal Prerif and Mesorif successions. Within the second group are included the successions of the Tello-Rifan external zones of Algeria and Morocco that can be connected to those of the 'Tunisian Trough'. All are different from the flyschs domain facies and opposed to coeval, more internal units of the Kabylo-Rifan Dorsale and ancient massifs (third group). These affinities and differences confirm, on the one hand, the common geological history of the external segments of the African margin and, on the other hand, the distinct palaeogeographical evolution of the inner domain including the ?dorsales calcaires' and ancient massifs, both being separated by intermediate flyschs zone segments.
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