Bar for scale = 10 mm Chikhi-Aouimeur, F., Abdallah, H., Pons, J.M., and Vicens, E. African margin. It occurs together with porifers, ostreids, gastropods, benthic foraminifers and ostracods, indicating a platform margin setting preceding the wide Late Cenomanian transgression. Durania arnaudi and D. blayaci are well represented in the Bahloul fine-stratified limestones, below the Lower Turonian levels with ammonites, as Thomasites rollandi or Pseudaspidoceras flexuosum. These radiolitids correspond then to the Upper Cenomanian/basal Turonian transition. Vaccinites cf. rousseli has been found in the upper part of the Bahloul limestones at Jebel Chemsi. Hippuritids may be locally abundant in the Gattar dolomites, as in Jebel Zitouna where Hippurites resectus occur in disseminated monospecific assemblages or together with radiolitids. The uppermost part of Gattar is referred to the lower part of the Mammites nodosoides Zone (uppermost Lower Turonian). At Jebel Ben Younès its upper part becomes rich in anhydrite (Beïda Anhydrite Member) and rudists are found in the uppermost beds (Eoradiolites liratus and Durania arnaudi). Mammites nodosoides and Choffaticeras luciae indicating the uppermost Lower Turonian have been found in the lateral equivalent of these anhydrites. Overlying the Gattar, the Annaba Clays correspond to a transgression phase characterised by the sedimentation of clays with benthic and planktonic foraminifers. These last are composed of whiteinellids, heterohelicids and hedbergellids. Some scarce small Bournonia africana have been recovered from Jebel Ben Younès. Rudists are best represented in the limestones or the clayey limestones and evaporites of the Bireno Member. Radiolitid fauna is highly diversified: Radiolites praesauvagesi, R. trigeri, Praeradiolites ponsianus, and also Eoradiolites liratus generally quoted in the Cenomanian, are abundant. Biradiolites angulosus is scarce and Bournonia africana (synonym of B. lecoqui and B. fourtaui) occurs in dense assemblages at some beds. Some specimens of Distefanella bassani, Apricardia sp. and Hippurites libanus were also found. These assemblages are particularly well represented at Jebel Ben Younès, Jebel Chemsi and Jebel Zitouna. At Jebel Sidi Bouhlel, the tidal-flat facies of the upper part of Bireno change laterally to small bio-constructions of peculiar species. A level with a dense assemblage of small monopleurids, another with bouquets or lenticular assemblages of Radiolites lefebvrei, or a last one with large up-standing Vaccinites praegiganteus have been recorded. Unfortunately, the two last members (Annaba and Bireno) do not yield ammonite fauna. Biostratigraphy is based on benthic foraminifers (Nezzazatinella picardi, Cuneolina pavonia,...), planktonics (Heterohelix reussi, Whiteinella paradubia, Hedbergella delrioensis,…) and ostracods (Brachycythere dumoni, Cythereis mdaouerensis, Cytherella gambiensis). According to their regional distribution these rudists can be attributed to the Mid Turonian. The species found have been mentioned from the Turonian-Coniacian platforms of the western Tethys. Nevertheless, their assemblages seem to have been affected by environmental conditions probably more difficult due to a warm climate on assemblages living in very shallow water. Emersion structures (bird eyes, mud-cracks) and salt accumulations are the omnipresent expression of this aridity that should explain the poor diversity within a single level in spite of their abundance as well as the smaller size of individuals when compared with European faunas. Jebel Zitouna This locality corresponds to an intermediate area where rudists developed during the HST. They show very high diversity and abundance. The assemblages are dominated by Bournonia or by Radiolites. CONCLUSIONS The region of Gafsa results to be of great interest for the study of the Cenomanian-Turonian rudists. The Upper Cenomanian yields Praeradiolites biskraensis. As this species is widespread and always found below Neolobites vibrayeanus along the southern margin of the Tethys, it is a good marker from Morocco to the Middle East. Durania is frequent in the deeper facies of the Upper Cenomanian- basal Turonian; such as in the basin deposits of the Bahloul and of the Gattar Equivalent occurring together with ammonites and planktonic foraminifers. At Mid Turonian, deposits are less differentiated and composed of shallow platform facies. Rudists are very abundant, particularly the radiolitids (Eoradiolites, Radiolites, Biradiolites, Bournonia, Distefanella,…). They are found in the highstand deposits and they disappear after the generalised emersion of the considered region. A better calibration of the Cenomanian-Turonian rudist fauna richness and distribution in south-central Tunisia would be possible by comparing this rudist fauna with that of the Kasserine region. References 1- Abdallah H., Ben Youssef M. and Saïd-Benzarti R., 2003- Biostratigraphy of the Annaba Clays and the Lower Bireno succession, Middle Turonian, Gafsa area, northern southern Tunisia. Revue de Paléobiologie, Genève (juin 2003), 22, pp. 439-456. 2- Abdallah H., Sassi S.,Meister C and Souissi R., 2000- Stratigraphie séquentielle et paléogéographie à la limite Cénomanien-Turonien dans la région de Gafsa- Chotts (Tunisie centrale).Cretaceous Research, 21, pp. 35-106. 3- Abdallah H., Sassi S., Souissi F., Meister C., Néraudeau D., Saadi A. and Saïd-Benzarti R., 2003- Sequence Stratigraphy at the Cenomanian-Turonian Boundary in the Northern Chotts Range, Southern Tunisia. In The Geology of Northwest Libya, Sedimentary Basins of Libya- Second Symposium, eds M.J. Salem and K.M. Oun, volume 1, pp. 99-138. 4- Meister C. and Abdallah H., 2005- Précision sur les successions d’ammonites du Cénomanien- Turonien dans la région de Gafsa, Tunisie du centre-sud. Revue de Paléobiologie, Genève (juin 2005), 24 (1), pp. 111-199. Jebel Sidi Bouhlel As the western part of the Northern Chotts Range (NCR) is tilted westwards, the lower part of the series is buried in this locality. The upper Cenomanian and the lowermost Turonian correspond to deep anoxic facies. During mid Turonian, sedimentation became uniformly shallow through the NCR and allowed rudists installation. Three monospecific assemblages are found and are restricted to this locality. Jebel Chemsi Is a part of a high block tilted westwards and separating two basins (Zammour and Sidi Mansour). Isolated Durania are present in deep environment but rudists become abundant in the shallow water of the mid Turonian. Assemblages are diversified but Radiolites is generally the dominant genus. Jebel Ben Younès This structure is limited in its southern part by the Gafsa Fault, it belonged to the Mejel Belabes Basin where evaporites deposited during the early-mid Turonian are very thick (Anhydrites Beida Member). The evaporites concentration is very high inside the basin while on the margin rudists can grow in small thickets. (1) Université H. Boumediènne, Bab Ezzouar - BP 32 El Alia, Algiers 16000, Algeria; [email protected] (2) Laboratoire de Géoressources, CERTE, Technopôle de Borj Cédria, BP 95, 2050 Hammam-Lif, Tunisia; [email protected] (3, 4) Universitat Autònoma de Barcelona, Departament de Geologia, Facultat de Ciències, Edifici Cs. 08193 Bellaterra, Spain. During Late Cenomanian and Turonian the Gafsa region presented a framework of basins and highs where rudists became well represented when local conditions were favourable. Recent studies in the area on ammonites and microfossils (1, 4) have refined the biostratigraphy, and others on sedimentology the depositional history (2, 3), allowing a fairly precise biostratigraphical and environmental setting of the rudist formations. Nevertheless, this fauna although frequent and well preserved has not been adequately described. Sampling carried on the northern, southern, and eastern margins of the Gafsa- Metlaoui Basin allowed us to describe its composition and distribution. Praeradiolites biskarensis is frequent in a bed 30 cm-thick in the alternating clays and carbonates of the uppermost Zebbag Formation s.s. (Jebel Zitouna, Jebel Ben Younès). This bed is located few meters below the chalky limestones with Neolobites vibrayeanus, as in many other localities of the Tethyan The Cenomanian – Turonian rudists of the Gafsa region, Tunisia 1, 2, 3 Radiolites trigeri (Coquand, 1859) 4, 5 Bournonia africana Douvillé, 1910 6 Eoradiolites liratus (Conrad, 1852) 7 Hippurites resectus Defrance, 1821 8 Praeradiolites biskarensis (Coquand, 1862) 1 2 3 5 6 7 8 4 Gattar Anhydrites Beida 1 Biradiolites angulosus (d’Orbigny, 1850) 2 Hippurites libanus Douvillé, 1913 3, 4 Praeradiolites ponsianus (d’Archiac, 1835) 5 Durania arnaudi Choffat, 1891 6, 7 Durania blayaci (Toucas, 1903) 1 2 3 6 5 4 7 1 Vaccinites praegiganteus Toucas, 1904 2, 3, 4 Radiolites lefebvrei Bayle in Rolland, 1881 5 Monopleura sp. 1 2 3 5 4 1, 6, 7, 8 Bournonia africana Douvillé, 1910 2, 3 Distefanella bassanii Parona, 1901 4, 5 Radiolites praesauvagesi Douvillé, 1908 9 Hippurites resectus Defrance, 1821 1 2 3 5 4 6 7 8 9 Praeradiolites biskraensis Durania arnaudi Durania blayaci Apricardia sp. Monopleura sp. Eoradiolites liratus Radiolites praesauvagesi Radiolites lefebvrei Praeradiolites ponsianus Bournonia africana Biradiolites angulosus Radiolites trigeri Distefanella bassanii Hippurites libanus Vaccinites rousseli Hippurites resectus Vaccinites praegiganteus Pseudaspidoceras flexuosum S. (Jeanrogericeras) reveliereanus Mammites nodosoides Neolobites vibrayeanus Thomasites rollandi rollandi Neoptychites cephalotus Choffaticeras luciae Heterohelix reussi Whiteinella paradubia Thomasinella punica Heterohelix globulosa Nezzezatinella picardi Cuneolina pavonia Paracypris mdaouerensis Brachycythere dumoni Spinoleberis yotvataensis Cytherella gambiensis Pterygocythere pennata Annaba Clays Lower Bireno Gattar / Eq. Gattar Beida Anhydrites Bahloul / Eq. Bahloul Upper Zebbag s.s. RUDISTS AMMONITES FORAMINIFERS OSTRACODS Upper Cenomanian Uppermost Cenomanian - Lower Turonian Lower Turonian Lower - Middle Turonian Middle Turonian Lithostratigraphy