Journal of Geodynamics 47 (2009) 142–152 Contents lists available at ScienceDirect Journal of Geodynamics journal homepage: http://www.elsevier.com/locate/jog Deep structure and crustal configuration of the Jeffara basin (Southern Tunisia) based on regional gravity, seismic reflection and borehole data: How to explain a gravity maximum within a large sedimentary basin? H. Gabtni a,∗ , C. Jallouli b , K.L. Mickus c , H. Zouari d , M.M. Turki b a Département de Géologie, Faculté des Sciences de Gafsa, Université de Gafsa, Campus Universitaire Sidi Ahmed Zarrouk, 2112 Gafsa, Tunisia b Département de Géologie, Faculté des Sciences de Tunis, University Tunis El Manar, 2092 Manar II, Tunisia c Department of Geosciences, Missouri State University, Springfield, MO 65897, USA d Laboratoire de Géoressources, Centre des Recherches et de Technologies des Eaux, Technopôle Borj-Cedria, B.P. 73, 8020 Soliman, Tunisia article info Article history: Received 18 January 2008 Received in revised form 26 July 2008 Accepted 28 July 2008 Keywords: Tunisia Jeffara Sedimentary basin Gravity anomalies Modelling abstract The Jeffara basin of southern Tunisia contains a thick sequence of mainly Triassic and Permian sediments that is characterized by a gravity maximum. To explain the positive gravity signature over the Jeffara sed- imentary basin and to obtain a more quantitative representation of the subsurface structure, a regional 2.5D gravity model constrained by seismic reflection and borehole data was constructed along a NE–SW trending profile. The depth to the crust/mantle implies that the Jeffara basin is associated with crustal thinning. The gravity model also implies that subsidence is controlled by a basement stepped down by rel- atively low-displacement faulting. This sedimentary subsidence, as described by a listric-faulting model, is probably caused by a thinned crust. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction The Jeffara region of southeast Tunisia, situated in north Africa (Fig. 1A), consists of two geographic and geological provinces with vastly different features (Fig. 1B and C). Topographically these are: (1) a western section containing the large-scale Dahar Plateau asso- ciated with the Telemzan and Bounemcha structural highs and (2) an eastern part containing the Jeffara coastal plain where the topog- raphy averages near mean sea level. This entire region contains a large area of playa lakes that stretch from the lowlands of eastern Tunisia to northwestern Libya. The simplified geological map of southern Tunisia and north- west Libya (Lefranc and Guiraud, 1990)(Fig. 1C) shows two principal geological provinces: (1) The Jeffara coastal plain which consists of a NW–SE-trending (Fig. 1B), in Tunisia, to E–W-trending, in Libya collapsed block formed during the Late Cretaceous and Cenozoic by extensional faulting, which is overlain by Tertiary and Quaternary sediments (Benton et al., 2000) and (2) the Dahar Plateau which consists of a N–S-trending, in Tunisia, to E–W- trending, in Libya monocline (Jebel Nafusah). In Tunisia, the Dahar ∗ Corresponding author. Tel.: +216 72396799. E-mail address: gabtni hakim@yahoo.ca (H. Gabtni). Plateau is mostly composed of shallow W to SW dipping (less than 5 ◦ ) Triassic and Jurassic sequences that are capped by Late Creta- ceous limestones (Gabtni et al., 2005). Within the Dahar Plateau there is almost a complete stratigraphic sequence from Late Per- mian to Late Cretaceous with the Permian sequence in the Tebaga de Medenine (Fig. 1C) being the oldest outcrop in Tunisia (Castany, 1954; Busson, 1967; Bouaziz, 1995; Zouari, 1995; Bouaziz et al., 1996, 2002). Locally, the Permian sequence is displayed in a 20–30 ◦ south-dipping monocline affected by E–W striking faults along the northern edge of the Dahar Plateau. This structure seems to have controlled the deposition of the Late Permian deposits and played a major role in the formation and filling of the Tataouine basin (Busson, 1967; Bouaziz et al., 1994). The Jeffara basin has undergone a complex and polyphase structural history since Carboniferous time (Burollet and Desfoges, 1982; Ben Ayed, 1986). It has been affected by multiple episodes of tectonism, including a late Paleozoic collision with Laura- sia and subsequent early Mesozoic rifting associated with the opening of the Tethyan Ocean (Memmi et al., 1986; Gabtni et al., 2006). The effect of the several tectonic phases (Taconic (Ordovician), Caledonian (Devonian), Hercynian (Carboniferous), Austrian (Early Cretaceous), and Alpine (Late Cretaceous–Early Eocene)) on the Jeffara area has been the production of a large sedimentary basin in the eastern part (Jeffara basin) and a fault- 0264-3707/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jog.2008.07.004