Journal of African Earth Sciences 124 (2016) 289e310 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci 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