Journal of African Earth Sciences 124 (2016) 289e310

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Journal of African Earth Sciences

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Stratigraphical and sedimentary characters of Late Cretaceous formations outcropping in central and southern Tunisia, Tethyan southern margin

* J. Jaballah , M.H. Negra

Tunis El Manar University, Faculty of Sciences of Tunis, UR (Petrologie sedimentaire et cristalline), Campus Universitaire, 2092, Manar II, Tunis, Tunisia article info abstract

Article history: The main goals of our approach are to identify some local to global events in relation with tectonic in- Received 2 May 2016 stabilities and/or sea-level changes, occurring during the deposition of Cenomanian-Coniacian carbonate Received in revised form series in Tunisia. Several sections surveyed in Central-Southern Tunisia, along a North-South transect 4 August 2016 extending from Sidi Bouzid to Gafsa area, show that the Cenomanian-Coniacian series include rudist-rich Accepted 20 September 2016 facies associated to other shallow marine to deeper deposits. Available online 21 September 2016 Detailed sedimentological studies supported by new biostratigraphical data (provided by H. Bismuth, oral comm.), have allowed to add more precisions on the lithostratigraphical stacking and thus on the Keywords: Rudist-bearing limestones Central Tunisia Stratigraphic Chart. Some carbonate members such as the Middle Turonian Bireno and fi fi Cenomanian-Turonian the Late Turonian-Coniacian Douleb have been identi ed in certain localities for the rst time. Indeed, Central-southern Tunisia these members were never described before at Jebel el Kebar and Jebel Meloussi. Turonian tectonics In the Sidi Bouzid area, especially at Jebel el Kebar, the Cenomanian-Coniacian carbonate members are Platform drowning characterized by frequent and rapid changes, related to the existence of highs (horsts, probably) and depressed depositional domains (grabens, probably), which formed during the deposition of the two lower Units of the Middle Turonian Bireno Member. Above, the Late Turonian to Coniacian deposits, have tended to seal the irregular paleotopography affected, at least locally, by Middle Turonian extensional tectonic movements. They could be related, in contrast, to a drowning linked to a sea level rise. Similar events were described abroad during Late Turonian times; a partial drowning of carbonate platforms was already identified in other localities of the African Tethyan margin. However, the global drowning corresponding to the C/T event was not identified in the present study, although previous works have described this event North of the studied sector. As demonstrated in other localities, a global eustatic event could be locally interrupted by tectonic events, which could mask the eustatic message and leave their record in the deposit cycle. © 2016 Elsevier Ltd. All rights reserved.

1. Introduction In Tunisia, previous works (Masse and Philip, 1981; Philip, 1985; Razgallah et al., 1994; Abdallah et al., 2000; Philip and Floquet, Cenomanian-Turonian rudist-rich facies are well represented in 2000) described rudist-rich facies in Cenomanian-Turonian car- the Southern Tethyan margin, especially in Central and Southern bonate members, particularly within the Uppermost Cenomanian- Tunisia (Masse and Philip, 1981; Philip,1985; Skelton and Gili,1991; Lowermost Turonian carbonates (called Gattar Member; Fig. 2). In Abdallah et al., 2000; Dercourt et al., 2000; Philip and Floquet, addition, in terms of sequence stratigraphy, the rudist-rich Gattar 2000; Philip, 2003; Scott, 2003; Skelton, 2003, Fig. 1). The distri- carbonates constitute the upper part of a transgressive-regressive bution of the rudist-rich carbonates exhibits abrupt vertical and cycle starting with pelagic carbonates rich in ammonites and lateral changes, which coincide with the succession of major events planktonic foraminifera (Razgallah et al., 1994). occurring from Cenomanian to Turonian times. These pelagic carbonates within the Gattar Member constitute a lateral equivalent of the Late Cenomanian-Early Turonian black- shales (called Bahloul Formation). These latter, which were stud- * Corresponding author. ied North of our studied area, in a deeper environment E-mail address: [email protected] (J. Jaballah). http://dx.doi.org/10.1016/j.jafrearsci.2016.09.020 1464-343X/© 2016 Elsevier Ltd. All rights reserved. 290 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 corresponding to an outer-ramp setting, constitute an expression of tectonic movements. the global Cenomanian-Turonian transgressive event (Caron et al., On the whole, the main objectives of this paper are therefore: 1) 2006; Zagrarni et al., 2008; Negra et al., 2011). to provide sedimentological data about the main facies deposited The Middle Turonian carbonates (called Bireno Member; Fig. 2) during the Cenomanian-Coniacian interval; 2) to better understand were interpreted as shoal rimmed platform carbonates (Marie et al., the lateral changes of facies at a local to a regional scale; 3) to focus 1984; Negra et al., 1994; Negra et al., 2002; Troudi et al., 2002; on the main factors controlling these facies changes. Zagrarni et al., 2003, 2008). Our recent studies using a detailed sedimentological and bio- 2. Geographic and geological setting stratigraphical approach based on a logging of the Cenomanian- Coniacian series, starting from the Sidi Bouzid area, have focused The Cenomanian-Coniacian carbonates widely crop out in the on the subdivision of this series into members, units and eventually Sidi Bouzid-Gafsa area, which is located in Central and Southern cycles. These latter have to be compared to those identified in the Tunisia (Southern Tethyan margin). Southern Tethyan margin and abroad. Central Tunisia is included in the “Tunisian Central Atlas” According to regional correlations, the Cenomanian-Turonian characterized by the deposition, during the Cretaceous, of shallow platform carbonates show lateral variations in thickness, facies marine platform facies, generally affected by extensional tectonic compositions and geometry. All these changes could be governed movements responsible for the occurrence of horsts, grabens and/ by varied processes, which could be local such as the paleogeo- or half grabens and locally tilted blocks (Chihi et al.,1984; Ben Ayed, graphical setting and contemporaneous tectonic activities, or 1986; El Euchi, 1993; Bouaziz et al., 2002). To the South, the global, implying climatic variations, sea level changes and/or “Tunisian Southern Atlas” includes the “Gafsa trough” grading

Fig. 1. Structural setting of Central and Southern Tunisia on the simplified structural map of Tunisia (Bouaziz et al., 2002; modified). J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 291

Fig. 2. Late Cretaceous stratigraphic chart of Central and Southern Tunisia. southward to the “Southern Saharian Platform”. deposited during a shallowing upward cycle. Toward the South, in Numerous studies have been carried out in our studied area. the Gafsa basin, this carbonate platform sequence laterally passes Most previous studies were carried out by Khessibi (1978), Philip to deeper water ammonite-bearing facies (Razgallah et al., 1994). (1985), Ouali et al. (1986), Chaabani et al. (1990), Razgallah et al. In terms of paleogeographic considerations during the (1994), Abdallah (2000), Abdallah et al. (2000), Philip (1985) has Cenomanian-Turonian period, the distribution of rudist-rich facies, studied the rudist Formations in Tunisia, especially the paleon- in Central and Southern Tunisia, appear partly controlled by local tology and paleobiogeography of Cretaceous rudists in Central and synsedimentary tectonic movements (Chihi et al., 1984; Ben Ayed, Southern Tunisia. Ouali et al. (1986) have highlighted the main 1986; Bouaziz et al., 2002) and sea level changes (Gargouri- Cretaceous extensional tectonic features in the Jebel el Kebar sector. Razgallah, 1983; Abdallah and Meister, 1996; Abdallah, 2002; Around the Cenomanian-Turonian boundary in Central and Caron et al., 2006; Zagrarni et al., 2008; Negra et al., 2011). Southern Tunisia, detailed biostratigraphical and paleoenvir- During the Cenomanian, Central and Southern Tunisia is char- onmental studies have been provided by Chaabani et al. (1990), acterized by the development of varied deposition environments, Razgallah et al. (1994), Abdallah et al. (2000). particularly carbonate platforms. These latter, which behaved as a A representative section of the studied sector, logged in Jebel el carbonate ramp (Zghal and Arnaud-Vanneau, 2005; Zagrarni et al., Kebar, shows, from base to top, the following succession (Fig. 2): 2008) include “the upper limestone Member” of the Zebbag For- mation (Burollet, 1956; M'Rabet et al., 1995), and “the pelagic - The Cenomanian-Early Turonian Zebbag Formation composed limestone Member” (Gargouri-Razgallah, 1983) which is contem- of five members (Zebbag A, Zebbag B, Zebbag C, Zebbag D and porary with the Cenomanian-Turonian transition marked by a Gattar Members; Khessibi,1978; M'Rabet,1981). The Uppermost global anoxic event well expressed in Tunisia (Abdallah and Cenomanian-Lowermost Turonian Gattar Member is mainly Meister, 1996; Abdallah, 2002; Caron et al., 2006; Zagrarni et al., constituted by well-bedded dolomitized limestone rich in 2008). rudistids and flint nodules (Razgallah et al., 1994). The Late Cenomanian transgressive event is expressed in Central - The Early Turonian Annaba Member formed of thick marl de- and Southern Tunisia by the deposition of carbonates including posits with rare intercalations of argillaceous limestone thin rudist-rich facies (the Zebbag carbonate platform known as the beds. Gattar Member; Philip and Floquet, 2000). However, during this - The Middle Turonian Bireno carbonates composed of three units event, the Gafsa basin of Southern Tunisia is characterized by the (Figs. 2 and 3). development of pelagic series. At Jebel Berda, according to Abdallah - The Late Turonian-Coniacian Douleb carbonate Member. and Meister (1996), the Uppermost Cenomanian-Lowermost - The Coniacian-Early Campanian Upper Aleg Member. Turonian Gattar Member is represented by well laminated, chalky limestones locally showing floating rudist fragments and is also Concerning sequence stratigraphy, for a better understanding of composed of alternating layers rich in organic matter. Toward the the third and fourth order sequences of the Cenomanian-Turonian NE, in the Jebel Chemsi section, located in the El Ayacha village Gattar and Bireno Members, Razgallah et al. (1994) have identified (Razgallah et al., 1994), the Gattar Member exhibits almost the transgressive-regressive cycles, especially within the Gattar Mem- same lithostratigraphic characters and thickness as in Jebel Berda ber. The latter corresponds to a carbonate platform sequence (Fig. 4). Farther North, in the platform domain, the Uppermost 292 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

3. Material and methods

The present study was based on a synthesis of previous works conducted in our studied area, followed by field observations, detailed geological mapping and sedimentological analyses. In this regard, several sections were studied along a North-South transect, including Jebels el Kebar (in the southwestern sector, at the Oued el Khecha section; Fig. 5), Meloussi (at the Khanguet Zebbag section; Fig. 6) and Berda (in the northeastern limit, at the Oued Berda section; Fig. 7). More than 350 thin sections have been prepared in order to determine the composition and microfacies characteristics. The microfacies analysis has been obtained by means of semi- quantitative component analysis; concerning limestone classifica- tion, we used the schemes of Dunham (1962). For additional biostratigraphical precisions, we have extracted microfauna (e.g., benthic and planktonic foraminifera) from soft marly or clay sediments. Paleontological determinations were provided by H. Bismuth (oral comm.). Moreover, detailed mapping in the Rous el Kebar area (Jebel el Kebar section) has allowed to identify a detailed subdivision of the Gattar Member, based on changes in geometry and composition of the rudist-rich bodies.

4. The Cenomanian-Turonian rudist-rich lithofacies and their lateral changes

4.1. The Uppermost Cenomanian-Lowermost Turonian Gattar Member

In Central and Southern Tunisia, the Cenomanian-Turonian boundary is contained within a carbonated stratigraphic unit named the “Gattar Member” (e.g., Burollet, 1956; Basse De Menorval and Choubert, 1959; Barnaba, 1965; Busson, 1967, 1972; Gargouri-Razgallah, 1983; Chaabani et al., 1990; Razgallah et al., 1994; Abdallah, 1995; Abdallah and Meister, 1996; Chaabani, 1996). The Gattar Member, as identified in Central and Southern Tunisia outcrops, shows significant lateral facies changes (Chaabani et al., 1990; Razgallah et al., 1994, Figs. 4 and 8).

Fig. 3. Palaeogeographic map of Tunisia during the Middle Turonian (the Bireno Member, Marie et al., 1984; Troudi et al., 2002; modified). 4.1.1. The Gattar Member in central Tunisia (Sidi Bouzid area) In the Sidi Bouzid area, in Jebel el Kebar, the Gattar Member is well represented, especially at the Oued el Khecha section (Fig. 9A). Cenomanian-Lowermost Turonian Gattar Member in Jebel Orbata, In this locality, the Gattar Member has been logged and studied by shows an obvious increase in thickness associated to an abrupt several authors (e.g., Khessibi, 1978; Razgallah et al., 1994). Ac- lateral facies variation expressed by the occurrence of bio- cording to Razgallah et al. (1994), the Early Turonian Gattar constructed limestones and well laminated dolomites (Razgallah Member is represented by a bioconstructed unit, mainly consti- et al., 1994; Fig. 4). Therefore, during the Late Cenomanian-Early tuted by Durania arnaudi var. intermedia (Choffat) and is topped by Turonian interval, these lateral variations, starting from Jebel a Hard Ground. Berda and reaching Jebel Orbata through Jebel Chemsi, could be in Our recent studies show that the Gattar Member is also well relation with the pre-existing paleomorphology (e.g., Gafsa represented at the Rous el Kebar area. At Oued el Khecha and Rous “graben” and Orbata platform “horst”; Touir et al., 1989). The el Kebar, it is composed of three units exhibiting varied geometries Middle Turonian Bireno Member (as part of the Aleg Formation, and compositions (Fig. 9B, C, D, E and F). The geometry, expressed which directly overlies the Zebbag Formation) is made of carbon- by a lensoid-shape of the rudist-rich carbonates, is also character- ates (Bireno 1 and Bireno 3 Units) separated by a marly intercala- ized by rapid variations in thickness and facies. tion (Bireno 2 Unit). During the Middle Turonian, Central Tunisia is To the South, in Jebel Meloussi (Khanguet Zebbag section), the mostly occupied by rimmed platform (Fig. 3; Marie et al., 1984; Gattar Member (37 m in thickness) has been strongly affected by Negra et al., 1994; Troudi et al., 2002; Zagrarni et al., 2003). dolomitization and fracturing. The top of this dolomitic unit shows During the Early Turonian, it appears that only salt tectonic bioclastic debris and abundant flint nodules (Fig. 6). movements (Boukadi and Bedir, 1996; Abdallah, 2000)have affected the distribution of rudist-rich series in Central and 4.1.2. The Gattar member in south Tunisia (Gafsa area) Southern Tunisia. These movements have raised particular com- In Jebel Berda, the lateral equivalent of the Gattar Member partments limited by major faults (Abdallah, 2000), inducing consists of about 35 m of fine-grained bedded limestones con- spectacular thickness and facies changes observed from one section taining scarce, well preserved rudists, other bivalves and ammon- to another. ites (flexuosum Zone) indicating an Early Turonian age (Razgallah J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 293

Fig. 4. N-S Uppermost Cenomanian-Lowermost Turonian Gattar Member correlation in the Gafsa area. 294 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 5. Sedimentological Log of the Oued el Khecha section, OKh (southern flank of Jebel el Kebar). et al., 1994, Fig. 7). According to Abdallah and Meister (1996, 1997), 4.2. The middle Turonian Bireno member Abdallah (2000) and Abdallah et al. (2000), this series is subdivided in ascending order into: Zebbag Formation dated by Praeradiolites Based on its sedimentary features, the Bireno Member (Burollet, biskraensis Coquand, considered as a Late Cenomanian biomarker 1956; Touir et al., 1989; Troudi, 1998; Zagrarni, 1999; Zagrarni et al., (Philip and Floquet, 2000; Abdallah et al., 2000), and the Bahloul 2008), Middle Turonian in age, can be subdivided into two main Formation, which yielded Vascoceras (Paravascoceras) aff. durandi lithological facies, which are identified in Central Tunisia and West (Thomas & Peron) indicating a Late Cenomanian-Early Turonian of Kasserine. age (Abdallah et al., 2000). In addition, the uppermost part of the Bahloul Formation shows thinly-bedded argillaceous-limestones 4.2.1. . The Bireno Member in the Jebel el Kebar; central Tunisia containing: Choffaticeras sp. associated to planktonic foraminifera In the Southwestern part of Jebel el Kebar, at the Oued el Khecha (Hedbergella, Heterohelix, Whiteinella) indicating an Early Turonian section, the Bireno Member (77 m in thickness), which is identified age (Abdallah et al., 2000). The Gattar Member, Lowermost Turo- and described here for the first time, comprises two limestone units nian in age, yielded Choffaticeras sp., Thomasites cf. rollandi (Peron), separated by marly-dolomitic intercalations. From base to top, Baculites aff. yokoyamai Tokunaga & Shimizu, Choffaticeras gr. these units are as follows (Fig. 5): pavillieri Pervinquiere, C. sp., Hoplitoides aff. ingens (Von Koenen), Neoptychites gr. cephalotus (Courtiller), Thomasites rollandi - The lower carbonate Unit: mainly composed of shallowing up- Pervinquiere, Choffaticeras luciae Pervinquiere, C. aff. luciae, Hop- ward cycles starting by bioturbated and bioclastic dolomite and litoides sp., Spathites (Jeanrogiceras) aff. reveliereanum (Courtiller) ending up with laminated dolomite containing stromatolites (Abdallah et al., 2000). and scarce bivalve debris. Fig. 6. Sedimentological Log representing the Jebel Meloussi section (KZ). 296 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 7. Sedimentological Log representing the Jebel Berda section (OB).

- The middle unit of the Bireno Member: contains marls inter- 4.2.2. The Bireno Member in Jebel Meloussi; central Tunisia bedded with dolomitized limestones showing flint nodules and In Khanguet Zebbag, due to the intense dolomitization, the birds-eyes structures. dolostone of the Bireno Member (74 m in thickness) consist of - The upper Unit of this Member: consists of well bedded bedded dolomite containing scarce floating rudists associated with wackestone to packstone rich in corals and/or sponges, scarce other bivalves, scarce sponges and/or corals, and showing cross rudists, and other bivalves associated with echinoderm debris. stratifications at the upper part of the Bireno Member (Fig. 6). J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 297

Fig. 8. N-S correlation of the Uppermost Cenomanian-Lowermost Turonian Gattar Member from Jebel el Kebar (the Rous el Kebar and Oued el Khecha sections) to Jebel Meloussi (the Khanguet Zebbag section).

4.2.3. The Bireno Member in Jebel Berda; south Tunisia sedimentological and biostratigraphical data, allowed us to propose In Oued Berda, as shown in Central Tunisia, the Bireno Member a new subdivision of the massive rudist-rich carbonate and to focus (43 m thick) comprises two calcareous units separated by a marly on their vertical and lateral changes and thus, to reconstitute their unit (Fig. 7). depositional environments. In fact, from the Sidi Bouzid to the The lower Unit (Bireno 1), about 15 m thick, is mainly composed Gafsa areas, the Late Cenomanian-Turonian rudist-rich facies are of massive limestone beds corresponding to wackestone- regionally common in term of facies and thickness, in spite of local, packstones containing rudists (Radiolitidae), brachiopods and significant variations. scarce coral or/and sponge debris. The middle Unit (Bireno 2), about 12 m thick, is formed of green marls alternating with thin bedded 5.1. The most representative Late Cenomanian-Coniacian facies in nodular limestones rich in unbroken bivalves and echinoderms. the Jebel el Kebar section The upper Unit (Bireno 3), about 16.5 m thick, consists of limestone beds showing bioturbations and cross beddings. The upper lime- Numerous sections (Rous el Kebar, RKSA, Oued el Khecha, OKh, stone bed is capped by a hard-ground. Oued Dakhla, OD, Jebel el Frayou, JF and the North flank of Jebel el Kebar, FNK) were surveyed at the SE flank, the SW periclinal tip and 5. Stratigraphic setting and sedimentary features of the Late the NW flank of Jebel el Kebar, respectively (Fig. 10). The rudist-rich Cretaceous rudist-rich facies in central and southern Tunisia carbonates deposited during the Late Cretaceous suggest that they were deposited in a low energy, middle to outer platform envi- The Late Cretaceous carbonate series has been studied in three ronment, except in some areas expressing a local deepening, main sections (Jebels el Kebar, Meloussi and Berda) of Central and consistent with the deposition of pelagic sediments within the Southern Tunisia. Our recent observations, based on Bireno Member. These variations could be governed by local normal 298 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 9. Field photographs from the Jebel el Kebar section. A, South-Western part of Jebel el Kebar (Okh section) showing the massive carbonate unit of the Uppermost Cenomanian- Lowermost Turonian Gattar Member overlying the bedded carbonates of the Zebbag “D” Member. B, General view at Jebel el Kebar showing the three units of the Gattar Member (G1, G2 and G3 Units). The Gattar Member of the Rous el Kebar section. C, Graded bioclastic Packstone-Grainstone made almost exclusively by rudist debris. The Gattar 1 Unit of the Rous el Kebar section. D, Bedding plane view of joined transverse-oblique section of rudist. The Gattar 2 Unit of the Rous el Kebar section. E, Longitudinal-oblique section showing a rudist (Durania) within the Gattar Member. The Gattar 2 Unit of the Rous el Kebar section. F, Photograph showing a detailed structure of “Durania”. The Gattar Member of the Oued el Khacha section. faults, as expressed by local slump marks preferentially located suggests an evolution toward a shallower and more restricted near the fault planes, and tectonic breccias (Figs. 12 and 14A, B), paleoenvironment (Fig. 11E, F). The middle Unit (Bireno 2, 12.5 m), which affect the Cenomanian-Turonian series. Correlations be- consists of marl interbedded with well bedded dolomitized lime- tween the five sections surveyed in Jebel el Kebar show the stone. The latter consist of wackestone rich in benthic foraminifera, following local changes: mainly represented by miliolids, associated with rare debris of echinoderms and bivalves. This association suggests a shallow, - At the northwestern flank of Jebel el Kebar (FNK), the Late sheltered and rather more or less open environment. The upper Cretaceous rudist-rich carbonates are mainly represented by the carbonate Unit (Bireno 3, 12 m), which is composed of well bedded Middle Turonian Bireno Member, which is included within the dolomitic limestone, ends up with corals-rich packstones. The Aleg Formation. In fact, the Bireno Member, recently identified Bireno 3 Unit is overlain by stromatolite-rich carbonates. The car- and dated (29 m thick), is composed of two units of slightly bonates constituting the summital part of the Bireno 3 Unit, consist dolomitic limestone separated by a marly unit. of packstones rich in corals and/or sponges, scattered red algae, debris of echinoderms and common inoceramids. This composition The Bireno 1 Unit (4.5 m), comprises, at its lower part, well suggests a more open marine environment. The overlying bedded limestone with wackestone-packstone textures, rich in stromatolite-rich carbonates suggest a vertical change to a shal- inoceramids and bivalve debris associated with scattered red algae lower environment showing tidal flat conditions. and very rare benthic foraminifera, suggesting a middle to inner Farther South, at Jebel el Frayou (Fig. 10), only the Bireno 3 Unit platform environment (Fig. 11D). The uppermost part of this unit is cropping out. This 14.5 m thick unit consists of well bedded exhibits well bedded limestone with grainstone texture, very rich dolomitized limestone (wackestone to packstone), rich in corals in miliolids. This vertical change in microfaunal composition and/or sponges associated to red algae debris, inoceramids and J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 299 echinoderms debris. The composition and texture of these car- platform environment than that in the JF section (located about bonates are consistent with a shallow, open marine environment. 1.75 km more to the NE, Fig. 10). The Bireno 3 Unit is directly overlain by fossiliferous marls, alter- nating with thin beds of bioclastic limestone (29 m). The latter are - At Oued el Khecha (OKh section, Figs. 5 and 8), the Cenomanian- rich in bioclasts of echinoderms, oysters and bivalves. Above, we Turonian Zebbag carbonates and the Middle Turonian- recently identified the Late Turonian-Coniacian Douleb Member Coniacian Bireno and Douleb series are well represented. This (5 m), which consists of stratified dolomitic limestone containing succession, which is bounded to the West by a normal fault inoceramids debris associated with echinoderms and red algae, (N105), shows the following succession: suggesting a relatively open marine, middle shelf environment. The Uppermost Cenomanian-Lowermost Turonian Gattar - At Oued Dakhla (section OD, Fig. 13), in addition to the Bireno Member is composed of massively bedded dolomite rich in rudists. Member, a Late Turonian-Coniacian carbonate series was iden- According to Razgallah et al. (1994), rudists are Durania arnaudi tified (H. Bismuth, oral comm.). (Choffat), Durania arnaudi var. intermedia (Choffat) and Caprinids. In addition, the Gattar Member has been subdivided into three The Bireno 1 Unit (12 m) shows the same composition as pre- units, which are from base to top: viously described in the Northern el Kebar section (FNK; Fig. 13). It is mainly represented by bioturbated and bioclastic dolomitized - G1: Bedded carbonates rich in fragmented rudists, which limestone containing poorly preserved echinoderms, frequent red include wackestone-packstone cycles. algae and common to abundant inoceramids and bivalve debris - G2: Massively bedded and lensoid lithosomes (Skelton and Gili, (Fig. 11C). This assemblage suggests a shallow marine and high 1991; 2001; Skelton, 2003) rich in joint, complete rudists rep- energy platform environment. resented by Durania arnaudi (Razgallah et al., 1994). The overlying Bireno 2 Unit (12 m) consists of green marl - G3: Thin beds of carbonates, onlapping the convex top of the interbedded with thin beds of bioclastic, slightly dolomitized lensoid rudist rich carbonates, containing scattered rudist debris limestone. These beds present wackestone-packstone textures and flint nodules covering the upper part of the G2 Unit. including coral debris and echinoderms associated with peloids and miliolids, illustrating a more restricted depositional environ- Above, the Annaba marls, which are frequently covered by ment. The Bireno 3 Unit (23 m) is represented by a massive grey- quaternary alluvium are directly overlain by the Middle Turonian beige limestone. In thin sections, this limestone shows packstone Bireno Member (Figs. 5 and 13). The Bireno 1 Unit (32 m) starts textures constituted of well preserved benthic foraminifera (espe- with bioturbated and bioclastic limestone, consisting of packstone cially miliolids, which represent 30% of the observed allochems), containing frequent planktonic foraminifera (Praehelvetoglobo- rare bioclastic debris of bivalves, rare planktonic foraminifera (5%) truncana helvetica, Whiteinella paradubia; 50% of the observed and echinoderms. This composition suggests a relatively shallow allochems), including chambers filled with black coloured organic and restricted environment. In fact, due to the probable influence of matter, and associated with rare benthic foraminifera (2% of the a major NE-SW normal fault (Fig. 12), which separates the “FNK” observed allochems), glauconite and phosphate grains (Fig. 11A, B). and “OD” sections (Figs. 10 and 13), the Bireno Member is clearly The bioturbated bed showing glauconite and phosphate grains thicker (47 m) in the OD section, compared to the same unit in the could be interpreted as a Maximum Flooding Surface. The Bireno 1 FNK section (29 m). The Bireno 3 Unit is directly overlain by marls Unit ends up with wackestones containing benthic foraminifera admitting scarce thin bed of argillaceous limestone. and bioclasts suggesting a relatively shallowing episode. The Bireno Above, the Douleb Member (10 m thick) is mainly made of partly 2 Unit (33 m, Fig. 13) includes marls alternating with thin bioclastic dolomitized limestone containing large inoceramids debris, micri- limestone beds. The latter consist of wackestone rich in planktonic tized red algae and echinoderms, suggesting a relatively more open foraminifera, which support the deepening trend previously

Fig. 10. Geological map of Jebel el Kebar showing the studied cross sections (RKSA, OKh, OD, JF and FNK cross sections; Ouali et al., 1986). 300 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 11. Microfacies of the Bireno 1 Unit of the Jebel el Kebar section. A, Packstone containing frequent well-sorted planktonic foraminifera associated to scarce glauconitic and phosphatic grains. The lower part of the Bireno Member (the Bireno 1 Unit) at the Oued el Khecha section (PL, G*2.5*4). B, Detailed view showing partly dolomitized planktonic foraminifera (red arrows) associated to floating bioclastic debris. The Bireno 1 Unit of the Oued el Khecha section (PL, G*10*4). C, Photomicrograph exhibiting bioclastic debris mainly represented by inoceramids debris (red arrow). The upper part of the Bireno 1 Unit of the Oued el Dakhla section (NL, G*2.5*4). D, Bioclastic facies of the lower part of the Bireno 1 Unit. The “FNK” cross section (NL, G*10*4). E, Grainstone rich in miliolids (yellow arrow) associated to well-sorted peloids (red arrow). The upper part of the Bireno 1 Unit of the “FNK” cross section (PL, G*2.5*4). F, Close view showing intraparticular porosity (red arrow) and totally micritized peloid (yellow arrow). The upper part of the Bireno 1 Unit of the “FNK” cross section (PL, G*5.1*4). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) detected. In contrast, the upper part of the Bireno Member (Bireno (12 m thick; Figs. 5 and 14C) recently identified and described, is 3, 12 m), is formed of massively bedded limestones rich in corals formed of dolomitic limestone beds containing large inoceramids and/or calcareous sponges (Chaetetidae, probably). In detail, the debris, echinoderms, glauconite and phosphate grains. These beds Bireno 3 Unit shows an obvious cyclicity; each cycle starts with a consist of wackestone topped by a surface showing organic borings limestone rich in benthic foraminifera (and sometimes scarce and oxides, which could be interpreted as a hard ground (Fig. 14D). planktonic foraminifera) suggesting its deposition in a relatively This Member appears homogenous in terms of thickness and facies deep marine episode. The same cycle ends with a packstone rich in along the South Western periclinal end of Jebel el Kebar. miliolids and corals and/or sponges, suggesting a vertical transition to a shallower environment. The frequency of miliolids suggests a - At Rous el Kebar (RKSA section, Fig. 8), the Uppermost sheltered environment. Cenomanian-Lowermost Turonian rudist-rich Gattar Member Laterally, toward the South, at Oued Dakhla (OD, Fig. 13) and to (52 m) consists of highly dolomitized limestones subdivided the North, at Jebel el Frayou (JF) sections, the relatively deep marine into 3 main units (G1, G2, G3), which show the same features as planktonic foraminifera-rich limestone of the Bireno 1 Unit changes in Oued el Khecha (OKh section, Fig. 8). In the RKSA section, the to shallower carbonates deposited in a relatively high energy, Gattar Member is locally directly overlain by a 16.5 m thick se- middle platform environment. However, in all sections (OD, JF and ries of evaporites, which constitutes the Early Turonian Beïda OKh), the Bireno 3 Unit is sealed by fossiliferous green marls Member (Khessibi, 1978). The latter consists of massively admitting the intercalation of thin bioclastic limestone beds (Figs. 5 bedded gypsum alternating with thin argillaceous layers. The and 13). overlying Annaba Member of Early Turonian age (56 m) is Above, during the Late Turonian-Coniacian, the Douleb Member mainly formed by fossiliferous marl rich in planktonic J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 301

Data, provided by the measurement of the slumps axis trend (N130 to N140), suggest the existence of a NE-ward dipping slope (nearly N40; Fig. 14A, B). Similar sliding features were identified within the 29 m thick carbonate beds of the Bireno 3 Unit at the Rous el Kebar section (RKSA).

5.2. The Late Cretaceous facies in the Jebel Meloussi section

At Jebel Meloussi, abrupt changes in facies and thickness are identified. These changes were mainly observed within the Zebbag “C”, rudist-rich Member (Figs. 6 and 15), which was identified for the first time, in Khanguet Zebbag, located on the northern flank of Jebel Meloussi. It consists of a 5.5 m thick, massively bedded member, showing joint entire rudists (cf. Eoradiolites sp.). Rudists are mainly abundant within the lower part of the “C” Member of the Zebbag Formation (Khessibi, 1978; M'Rabet, 1981, Fig. 2). In Jebel el Kebar, the equivalent of the Zebbag “C” Member (26.5 m in thickness) is mainly formed of well bedded, bioclastic and bio- turbated limestones. The latter consist of packstones containing peloids associated with echinoderms and bivalve debris. The Gattar Member becomes thicker (37 m) than its lateral equivalent at the Oued el Khecha section (30 m) and consists of highly dolomitized limestones showing scarce floating rudist debris and flint nodules (Fig. 8). The overlying Bireno and Douleb carbonate units are thicker comparatively to their equivalents at Jebel el Kebar (Fig. 16). They constitute two massive members totally dolomitized, showing scarce-floating rudists, corals and/or sponges and cross stratifica- tions, which suggest a shallow platform environment. On the whole, the thickening of the Jebel Meloussi carbonate units could be related to a subsidence activity preferentially characterizing the Jebel Meloussi area (Negra et al., 2002; Kadri et al., 2015).

5.3. The Late Cretaceous facies in the Jebel Berda section

In the southernmost area, at Jebel Berda (Figs. 7 and 16), the well-exposed and continuous section of Oued Berda is crossing all the Cenomanian-Coniacian units (Chaabani et al., 1990; Razgallah et al., 1994; Chaabani, 1996; Abdallah et al., 2000). Our recent observations and biostratigraphical interpretations allowed us to distinguish several rudist-rich facies stacked at different stratigraphic positions (Figs. 7 and 17A). From base to top, rudists are mainly included in the following carbonate Members:

- The Zebbag 'D0 Member (middle part of the Cenomanian Zebbag Formation), about 0.5 m thick, is constituted of rudist bearing bedded limestones (Praeradiolites biskraensis) associated with corals or/and sponges (Fig. 17B, C; Abdallah, 2000). Fig. 12. A, General view showing folded features related to the effect of the NE-SW major normal fault (Khessibi, 1978). B, Detailed view showing the fault plane of the These well-bedded wackestone-packstones include coarse sec- NE-SW major normal fault (Khessibi, 1978) and associated features (streaks and tec- ondary gypsum crystals, diverse bivalve debris, shark teeth and tonic breccias). C, Detailed view showing tectonic breccias. small smooth ostracods (Cytherella, Loxoconcha, Xestoleberis) indi- cating a Cenomanian age (H. Bismuth, oral comm.) and a very foraminifera (60% of the observed allochems) and intercalated shallow platform environment. with well-bedded dolomitic limestone rich in bivalve debris, suggesting an open marine environment. The Middle Turonian - The Gattar Member (upper part of the Cenomanian Zebbag Bireno Member includes three distinctive units (Bireno 1, Bireno Formation), 35 m thick, is formed of bedded limestones 2 and Bireno 3 Units, Fig. 18). Only the third Unit (Bireno 3) is (Fig. 17D) containing scarce rudist debris and various ammonite comparable, in terms of composition, to those of the already associations (Choffaticeras luciae Pervinquiere, C. aff. Luciae, described sections (OKh, OD, FNK, Figs. 13 and 18). However, the Haplitoides sp., Spathites (Jeanrogiceras) sp., Abdallah, 2000) Bireno 1 Unit (10.5 m), which is formed of well-bedded, highly indicative of an Early Turonian age. This Member includes some dolomitized limestone, exhibits, only at Rous el Kebar (RKSA rudist-rich carbonate bodies (Fig. 7) suggesting an inner plat- section), sliding features mainly represented by slump marks. form environment with no evidences of reefs or build up (Abdallah, 2002). 302 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 13. A, NNE-SSW correlation of the Middle Turonian Bireno Member from “FNK” section to the Oued Dakhla, OD, section at Jebel el Kebar. B, NNW-SSE correlation of the Middle Turonian Bireno Member from the “FNK” to Oued el Khecha, OKh, sections (Jebel el Kebar).

- The upper part of the Annaba Member consists of bioclastic marl consists of marl very rich in planktonic foraminifera suggesting rich in Calcisphaerulids (Pithonella sphaerica) and benthic fora- a deeper marine environment, as compared to the same unit at minifera (Gavelinella?), which are associated to planktonic Jebel Berda (Fig. 16). foraminifera (Hedbergellidae), indicative of a Turonian age (H. Bismuth, oral comm.). However, farther North, at Oued el Khe- Moreover, the Bireno 1 Unit (43.5 m) is constituted of massively cha (Jebel el Kebar), the upper part of the Annaba Member bedded, lime rudist bafflestone and complete rudists (Radiolitidae; J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 303

Fig. 14. Outcrop photographs from the Jebel el Kebar section. A, Panoramic view showing sliding features mainly represented by slump marks (red arrows); The Bireno 1 Unit of the Middle Turonian Bireno Member of the Rous el Kebar, RKSA, section. B, Detailed view of the photo (A) showing slump marks (red arrows). C, General view at the Oued el Khecha section showing the Late Turonian-Coniacian Douleb Member. D, Organic boring features on top of the Late Turonian- Coniacian Douleb Member; The Oued el Khecha section (OKh). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 15. Outcrop photographs from the Khanguet Zebbag section. A, Panoramic view at Jebel Meloussi showing the Orbata and Zebbag Formations. B, Panoramic view at the Jebel Meloussi section showing the lower and the middle part of Zebbag Formation (Zebbag A, B and C Members). C, The Zebbag ‘C’ Member of the Zebbag Formation showing frequent entire rudists (red arrows); the Jebel Meloussi section. D, Detailed view showing longitudinal (yellow arrow) and transverse oblique sections of rudists (red arrow); the Jebel Meloussi section. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

P.W. Skelton, oral comm., 2014; Fig. 17E, F) indicating a shallow and - The Douleb Member (15 m) is formed of fossiliferous limestone open marine carbonate platform environment. containing entire inoceramids, gastropods, echinoderms and 304 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 16. N-S Cenomanian-Turonian facies correlation in Oued el Khecha (OKh), Khanguet Zebbag (KZ) and Oued Berda (OB) sections.

rare bivalves suggesting a relatively low energy middle platform 6. Lateral evolution of facies: correlation of the Cenomanian- environment Turonian series in central and southern Tunisia

On the whole, lateral variations in thickness, geometry and North-South correlations of the Cenomanian-Turonian rudist- facies composition affected all the identified Cenomanian- rich carbonate series show lateral variations in thickness and facies Coniacian rudist-rich facies (Figs. 8, 13 and 16). The distribution (Fig. 16). From North to South, these variations are: of these shallow marine carbonate facies, along Central and In Jebel el Kebar, the Zebbag “D” Member (middle part of the Southern Tunisia, have been closely influenced by several processes Zebbag Formation, M'Rabet, 1981) is characterized by the alterna- (e.g., paleoecological conditions, particularly bathymetry, sub- tion of clays, marls and bioclastic carbonates including stromato- strates, water energy, etc., sea-level changes and locally extensional lites, bivalves and echinoderms, suggesting intertidal to tidal flat Turonian tectonic movements). depositional environments. These well bedded carbonate layers are J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 305

Fig. 17. Field photographs from the Oued Berda section. A, Panoramic view at Jebel Berda showing the Cenomanian-Turonian Formations (Zebbag and Aleg Formations). B, A general view showing the upper-most part of Zebbag “D” Member. C, Detailed view showing coral and/or sponge debris (arrows) (the carbonate layers of the upper part of the Zebbag ‘D’ Member). D, General view showing the bedded limestone Unit of the Gattar Member. E, Panoramic view showing the three units of Bireno Member (A. Bireno 1, B. Bireno 2 and C. Bireno 3). F, Detailed view showing transverse oblique sections of rudists (arrow) of the Bireno 1 Unit. locally overlain by mud cracks indicating periodic emersion phases. or half grabens are mainly identified in Oued el Khecha (OKh sec- Immediately above, the Gattar Member shows rudist-rich dolo- tion, Jebel el Kebar, Figs. 5 and 18). The deepening occurred during mitic limestones. The Bireno Member mainly consists of well- the deposition of the Turonian Bireno 1 and Bireno 2 Units, as bedded dolomitized limestone rich in corals and/or sponges, con- indicated by the high planktonic/benthonic ratio (around 25) taining scarce rudists and other bivalves associated with bioclastic recorded within the carbonate deposits. The deepening seems debris. more pronounced to the North (Rous el Kebar area), where sliding On the whole, during the Turonian period, the deposition features (essentially slump marks) are frequent in the Bireno 1 Unit. environment, at Jebel el Kebar, was a platform domain affected by Measurements of the slump marks axis trend, suggest the existence an extensional tectonic activity, which induced a local subsidence of a sloping profile dipping northward, which could be generated and probably a deepening, which is illustrated by the development during the Turonian extensional faulting. This deepening, which is of relatively deep marine depressions (grabens or half grabens; e.g., also confirmed by the high content in pelagic microfauna of the in the Oued el Khecha section). This extensional tectonic activity is Early Turonian Annaba marls and the Bireno 1 Unit carbonates, expressed by numerous features such as tectonic breccias and could also be associated to a sea level rise occurring immediately slump marks (Figs. 12 and 14A, B). after the deposition of the Gattar carbonates. According to rapid lateral facies changes, 3 paleogeographic blocks could be identified: (1) relatively deep marine blocks; (2) 2- The relatively shallower marine blocks shallower blocks; and (3) subsident blocks. Immediately to the SW of Oued el Khecha, in Oued Dakhla (Jebel 1- The relatively deep marine blocks el Kebar), the relatively deep marine facies of Bireno 1 and Bireno 2 Units abruptly change to shallower carbonate facies, in which the The relatively deep marine blocks which consist of grabens and/ planktonic/benthonic ratio (near 0.2) is clearly low. Peloids, red 306 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

Fig. 18. NE-SW correlation of Turonian facies from the Rous el Kebar, RKSA and Oued el Khecha, OKh to the Oued Dakhla, OD sections (Jebel el Kebar). algae, coral debris and other bioclastic debris are the dominant level rise that is common in that time. components. In addition, the Bireno 2 Unit, which includes To the South, in the Khanguet Zebbag section, at Jebel Meloussi, frequent marly intercalations in the Oued el Khecha section, the evidence of an active subsidence linked to distensive tectonic changes to a dolomitized carbonate member, without marly in- movements is well marked within the Upper Cretaceous series. In tercalations. These facies are also characterized by the occurrence fact, the Zebbag “D” Member becomes thicker than its lateral of miliolids, which suggests a protected depositional environment. equivalent at the Jebel el Kebar and shows frequent decametric In fact, these data lead to expect more elevated blocks to the SW evaporite intercalations expressing intertidal to sabkha deposi- (Figs. 18 and 19). tional environments. The Gattar Member, which constitutes a topographic land-mark 3- The subsident blocks at Kanguet Zebbag, is thicker, slightly bioclastic and highly dolo- mitized, compared to its equivalent at Jebel el Kebar. The overlying Comparatively to the deep marine domain, the subsident Bireno Member contains scarce entire rudists, preferentially in domain is characterized by a thickening of the deposits, which is Jebel Meloussi. In this sector, the Cenomanian to Turonian Gattar not accompanied by facies changes; this thickening which is well and Bireno Members were deposited in a middle to outer platform illustrated in Jebel el Kebar, mainly interests the Gattar carbonates. environment. In fact, the whole thickness of the Gattar Member abruptly changes On the whole, all these lateral variations in composition and from 30 m in the Oued el Khecha section, to 52 m in the Rous el thickness of the Zebbag “D”, Gattar and Bireno Members (from Jebel Kebar section. This relatively abrupt thickening, which concerns the el Kebar to Jebel Meloussi) appear to be due to the activity of NE- 3 constitutive units of the Gattar Member, appears in relation with SW trending, synsedimentary normal faults (Zouaghi et al., 2007; the Oued el Khecha normal fault oriented N105 and dipping Kadri et al., 2015, Figs. 1, 8 and 16). northeast-wards (Fig. 8). This NE-SW regional fault limits Jebel el Kebar to the South and As first conclusions, the “subsident blocks” and the “relatively subdivides the Sidi Bouzid section into elevated blocks, which are deep marine blocks” are the same and occupy the same deposition favorable to the development of rudist-rich facies (Jebel el Kebar) sites (to the North of Jebel el Kebar). However tilting movements, and half grabens toward the South, which present more depressed which started during the deposition of the Late Cenomanian Gattar area (Jebel Meloussi, probably constituting an outer ramp setting) Member, became significant enough to control the sedimentation showing thicker carbonate series, with less rudist. of the lower part of the Bireno member, during the Early Turonian. However, in Jebel Berda in the Gafsa trough, which is an inner The deepening, which preferentially occured in the northern part of basin of intertidal to subtidal environment (Chaabani et al., 1990), Jebel el Kebar during the Early Turonian, was also due to the sea the facies change is sometimes abrupt. The Zebbag “D” Member is J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310 307

Fig. 19. Sketches illustrating the vertical and lateral distribution of the Middle Turonian Bireno Member and the Late Turonian-Coniacian Douleb Member in Jebel el Kebar (The Oued el Khecha and Oued Dakhla sections). thinner than at Jebel Meloussi, and it is composed of marl and and Gafsa areas evidences particular facies distributions, which are limestone interbedded with evaporites indicating intertidal to mainly expressed by vertical and lateral facies changes. sabkha depositional environments. The upper part of this Member is made of well bedded bioclastic limestone rich in corals and/or sponges associated with scarce rudists, expressing the evolution to 7.1. Cenomanian-Coniacian lithostratigraphic stacking a more open environment. Moreover, from Jebel Meloussi to Jebel Berda, the Gattar Member is generally comparable in terms of Starting from Jebel el Kebar (Sidi Bouzid area), the Cenomanian- thickness and composition. In details, in Jebel Berda it appears Coniacian series exhibits the stacking of three main carbonate relatively thinner and more calcareous (with floating rudist debris) members corresponding to: (a) The uppermost Cenomanian- than its equivalent at Jebel Meloussi. In contrast, changes in lowermost Turonian Gattar Member; (b) the Middle Turonian thickness and facies are obvious within the Bireno Member. In Jebel Bireno Member; (c) the Late Turonian-Coniacian Douleb Member. Berda, the Bireno Member, which becomes thinner and is topped by These members are mainly characterized by shallow marine plat- a hard ground (highly bioturbated and bored surface), is more form deposits. Rudist-rich carbonates are common within the calcareous and characterized by massively bedded limestones Gattar Member; however, they appear only in Jebel Berda, within richer in joined Radiolitids in life position, than in Jebel Meloussi. the lower part of the Bireno Member. As demonstrated in previous studies (Khessibi, 1978; Razgallah et al., 1994; Abdallah et al., 2000; Zouaghi et al., 2007; Kadri 7.2. Lateral changes et al., 2015), the combination of outcrop observations and subsur- face seismic data show major normal fault networks, which have The three carbonated members were identified within the been reactivated during the Cenomanian-Turonian period. These whole studied area. However, minor to major variations in thick- faults have subdivided Central and Southern Tunisia platforms into fi a succession of horsts (elevated blocks) and grabens (restricted ness and facies were locally or regionally identi ed: depressed blocks). These particular structures have directly influ- enced the deposition of the Cenomanian-Turonian carbonates. - Concerning the Gattar Member, only minor changes were observed from Sidi Bouzid to the Gafsa area. The thickness of the Gattar Member (about 40 m) appears comparable in the whole 7. Discussion and conclusions studied sector. However, below the Gattar Member, the pelagic micritic limestones, rich in ammonites and planktonic forami- The detailed logging of several sections of Cenomanian- nifera, illustrating the C/T drowning event (Razgallah et al., Turonian rudist-rich carbonate series surveyed in the Sidi Bouzid 1994), were not identified in the Sidi Bouzid area. 308 J. Jaballah, M.H. Negra / Journal of African Earth Sciences 124 (2016) 289e310

In Jebel el Kebar, carbonates of the Gattar Member are particu- carbonate members identified in the studied area, are included in larly rich in joined entire rudists (Durania arnaudi). However, rud- transgressive-regressive cycles. As demonstrated in previous works ists were not observed in Jebel Meloussi, and are scarce in the Gafsa (Razgallah et al., 1994), the Uppermost Cenomanian-Lowermost area. These observations confirm those of previous studies Turonian Gattar rudist-rich Member constitutes a Highstand Sys- (Razgallah et al., 1994). tem Tract of a third order transgressive-regressive cycle. The global drowning corresponding to the C/T event, which is - Conversely, the Bireno Member exhibits rapid lateral changes at responsible for the black shale deposits (Caron et al., 2006; Zagrarni local and regional scale. Most changes are identified at the Jebel et al., 2008; Negra et al., 2011), was identified in relatively deeper el Kebar. According to the carbonate composition, especially paleogeographic domains, located to the North of our studied their planktonic/benthonic ratio, two main environments were sector. The maximum-flooding surface on top of the Bahloul black identified: a relatively deep marine environment in the Oued el shales, has an age near 93.3 Ma (Hardenbol et al., 1998; Gradstein Khecha area and a relatively shallower marine environment in et al., 2004; Haq and Al-Qahtani, 2005; Snedden and Liu, 2010; Oued Dakhla. Negra et al., 2011), to near 93.6 Ma (Gradstein et al., 2012). In other localities, in Egypt, for example (Kuss, 1991; Kuss and At a regional scale, the Bireno carbonates are characterized by Conrad, 1991; Kuss and Bachmann, 1996; El Hawat, 1997; shallow-marine facies in the whole studied area. However, rudist- Mansour, 2004), this global eustatic event could be interrupted rich carbonates were identified only in Jebel Berda (Gafsa area). by local and/or global tectonic events that left their record in the In addition, the Bireno carbonates show a clear thickening, partic- sequence. ularly, in the Jebel Meloussi area, in which the whole Bireno In terms of marine connections, according to Masse and Camoin Member is dolomitized. (in Nairm et al., ed., 1995), the marine connection between Tethys and the southern Atlantic (Reyment and Dingle, 1987) constitutes - The Late Turonian-Coniacian Douleb Member shows similar one of the most important Cretaceous paleogeographic events. As a facies and thickness in the whole studied area. It is always consequence of this Albian event, the sea invaded the northern overlain by pelagic marl. African platform through narrow seaways both from the North (i.e. from the Neotethys) and from the South (i.e. from the South Atlantic; Philip et al., 1993a, b; Guiraud et al., 2005). 7.3. Interpretations On the other hand, at a local scale, especially in Jebel el Kebar, the rapid lateral changes in thickness and facies of the Middle According to Razgallah et al. (1994), the rudist-rich carbonates Turonian Bireno carbonates could be related to tectonic move- of the Gattar Member constitute the upper term of a transgressive- ments, which are common in Central Tunisia (Chihi et al., 1984; Ben regressive cycle, starting with pelagic limestone rich in ammonites Ayed, 1986; Ouali et al., 1986; Kadri et al., 2015). Most of the and planktonic foraminifera. The rudist-rich facies were inter- extensional movements seem to affect preferentially the two lower preted as Highstand System Tract platform deposits, directly units of the Bireno Member. Correlations established along a NW- overlying pelagic deposits of the Transgressive System Tract. SE trend crossing the Jebel el Kebar, reveal the existence of horsts Above, similar cycles were identified, especially in Jebel Berda, (e.g., OD and FNK highs), which favored the deposition of shallow where the upper part of the Annaba marls, rich in planktonic platform carbonate series) and depressed depositional “domains” foraminifera (Hedbergellidae), is directly overlain by the Bireno 1 (OKh and RKSA grabens and/or half grabens), occupied by more Unit rich in joined entire rudists. To the North, in Jebel el Kebar, a open marine and relatively deeper deposits. comparable cycle is identified within the Bireno 1 Unit, which ap- On the whole, excepted the Jebel el Kebar area, the Cenomanian- pears deposited in a relatively deeper environment comparatively Coniacian carbonate members are correlatable at a regional scale, at to that in Jebel Berda. In fact, the lower part of the Bireno 1 Unit, least from Sidi Bouzid to the Gafsa area. Thickness and facies var- which consists of well-bedded dolomitized limestone rich in iations may reflect a diachronic progradation of platform facies, planktonic foraminifera, is overlain by shallower bioclastic from South to North. Locally, particularly in Jebel el Kebar, exten- carbonates. sional tectonic movements expressed by a preferential tilting to the The local rapid changes in thickness and facies in the Middle North, may have enhanced this progradation. Bireno series, identified particularly in Jebel el Kebar, could be A partial drowning of carbonate platforms during Late Turonian governed by Turonian tectonic movements, as illustrated by the times was already identified in other localities of the African frequency of tectonic breccias and folding and sliding features such Tethyan margin (Camoin, 1991; Haq and Al-Qahtani, 2005; Floquet as slump marks. et al., 2006; Snedden and Liu , 2010). The drowning event identified At a regional scale, the similar composition of the Late Turonian- on top of the shallow marine platform carbonates of the Late Coniacian Douleb Member could express the regularization of the Turonian-Coniacian Douleb Member was also described at least at inherited paleotopography strongly affected by the Middle Turo- the Mediterranean scale (Camoin, 1991). nian tectonic extensional movements. The vertical abrupt change to pelagic marl, common in the whole studied area, suggests a Acknowledgements deepening of the depositional environment, rather linked to sea level rise. We would like to address our thanks to H. Bismuth and P.W. Skelton for the recent fauna determination respectively of plank- 7.4. Conclusions tonic foraminifera and rudists. We address our thanks to the two anonymous reviewers who have revised our paper and contributed North-South correlations starting from Jebel el Kebar (Sidi to improve its content. Bouzid area) and reaching Jebel Berda (Gafsa area) through Jebel Meloussi, show facies similarities within the Cenomanian- References Coniacian members that are deposited in a shallow marine plat- form/ramp paleogeographic context. Abdallah, H., 1995. Decouverte du Membre Bahloul au-dessous du Membre Gattar The three Cenomanian-Coniacian (Gattar-Bireno-Douleb) dans la chaîne nord des Chotts (Centre-Sud de la Tunisie): consequences de la J. Jaballah, M.H. 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