Versão online: http://www.lneg.pt/iedt/unidades/16/paginas/26/30/125 Comunicações Geológicas (2012) 99, 2, 19-26 ISSN: 0873-948X; e-ISSN: 1647-581X

New elements on the Lower Cretaceous series of the Jerid area (Southern ): hydrogeological implications

Novos elementos das séries do Cretácico Inferior na área de Jerid (Sul da Tunísia): implicações hidrogeológicas

R. Guellala1*, M. H. Inoubli2, L. Moumni3, M. Ben Youssef1

Recebido em 28/09/2011 / Aceite em 05/03/2012 Artigo original Disponível online em Março de 2012 / Publicado em Dezembro de 2012 Original article © 2012 LNEG – Laboratório Nacional de Geologia e Energia IP

Abstract: In the Jerid (South-West Tunisia), the Lower Cretaceous 1. Introduction series have an important hydrogeological interest. Strata contain the so called “Continental Intercalaire” aquifer, a potential target for water The North African is characterized by the immense supply. aquifer system of the “Continental Intercalaire” (CI) covering The seismic sections and the deep wells data in this sector have 840.000 km2 of the Algerian- Tunisian-Libyan domain highlighted a brittle syn-sedimentary deformation, which induced two (UNESCO, 1972; OSS, 2003). different depositional areas. Normal faults have controlled the facies The “Continental Intercalaire” was defined as a sequence and thickness distribution of the Jerid lower cretaceous formations. The highlighted sedimentary and tectonic phenomena have influenced of continental or dominantly continental deposits between the the “Continental Intercalaire” aquifer characteristics. The permeability, Paleozoic and the Upper Cretaceous marine sediments (Kilan, the porosity and the artesian flow increase towards the South where the 1931). This definition applies well to many basins around the coarse sedimentation is abundant. Hoggar. Elsewhere, the “Continental Intercalaire” began or Interaction between the sedimentary layout and tectonic deformation continued beyond the stratigraphic limits fixed by Kilan has induced the basin geometry, filling and reservoirs evolution. (Lefranc & Guiraud, 1990). This paper aims to rationalize the future hydrogeological research in The “Continental Intercalaire” aquifer has been the Jerid area. recognized since the XIXth century (Ville, 1872; Flamand, Keywords: Jerid, Southern Tunisia, Lower Cretaceous series, Syn- 1908). Its exploitation was started in 1891 in Algeria by an sedimentary deformation, “Continental Intercalaire”, aquifer artesian well deep of forty meters. The oil discoveries which characteristics. th marked the XX century (Savornin, 1947; SCG, 1963; SCET, Resumo: Em Jerid (Sudoeste da Tunísia), as séries do Cretácico 1963; Cornet, 1964; GEOPETROLE, 1964) provided many Inferior tem um importante interesse hidrogeológico. Os estratos informations about the aquifer. They encouraged the contêm o aquífero denominado de “Continental intercalar”, um alvo launching of various hydrogeological studies (Rouatbi, 1970; potencial para o fornecimento de água. UNESCO, 1972; Ricolvi, 1974; Mekrazi, 1975; Ben Baccar, Os dados de cortes sísmicos e de poços profundos neste sector têm 1982; PNUD, 1983; Pizzi & Sartori, 1984; Farhat et al., 1985; destacado uma deformação frágil sin-sedimentar que induziu duas áreas Mamou, 1990; Zammouri, 1990; Chalbaoui, 2000; OSS, distintas de deposição. Falhas normais têm controlado a fácies e a 2003; Ould Baba Sy, 2005; Guellala et al., 2008; 2009a; espessura das formações cretácicas inferiores de Jerid. Os fenómenos sedimentares e tectónicos destacados têm influenciado Guellala, 2010). as características do aquífero “Continental Intercalar”. A The Jerid area, located in the Southwestern Tunisia permeabilidade, a porosidade e o fluxo artesiano aumenta para o sul (Fig.1) is an arid region (pluviometry between100 and 200 onde a sedimentação grosseira é abundante. mm/year) where the underground water exploitation is a Interacção entre a sedimentação e a deformação tectónica induziu a necessity. The “Continental Intercalaire” aquifer (CI), formed geometria da bacia, o preenchimento e a evolução de reservatórios. by the Lower Cretaceous permeable formations, (Mamou, Este artigo procura racionalizar a futura investigação hidrogeológica na 1986; Moumni, 2001) appears as potential resource able to região de Jerid. provide interesting flows. However, previous geological and Palavras-chave: Jerid, Sul da Tunísia, séries do Cretácico Inferior, hydrogeological studies were not sufficient to propose zones deformação sin-sedimentar, “Continental Intercalar”, características do and strategies for the exploitation of this resource. aquífero. Usually, the aquifers prospection is the privileged

application of the electrical method (De Stadelhofen, 1991; Zouhri et al., 2004; Guellala et al., 2005; 2009b). In this 1Laboratoire de Géoressources, CERTE, Pôle Technologique de Borj Cédria, 8020 study, the important depth of the Continental Intercalaire Soliman, Tunisia. aquifer (>1300 m) incites the use of the seismic method and 2 Département des Sciences de la Terre, FST, Université El Manar, 1060 deep boreholes data (lithological columns and well logs) to Tunis, Tunisia. 3Arrondissement des Ressources en Eaux de , Tunisia. specify tectonic and sedimentary phenomena that affect the *Corresponding author /Autor correspondente: [email protected] Jerid lower Cretaceous Formations and their impact on the aquifer characteristics. 20 R. Guellala et al. / Comunicações Geológicas (2012) 99, 2, 19-26

lithostratigraphic formations which are from the base to the top: the Sidi Khalif formation (UpperTithonian – Valanginian), the Meloussi formation (Hauterivian – Barremian), the Boudinar formation (Barremian) and the formation (Aptian – Albian) which includes the Bouhedma member (Aptian), the Sidi Aich member (Aptian) and the Orbata member (Aptian – Albian). Revising this subdivision, M’ Rabet (1981) highlighted the diachronism of Sidi Khalif, Meloussi and Bou Dinar formations deposited in a deltaic system. Equally, he substituted the Gafsa formation by the Gafsa group, composed of Bou Hedma, Sidi Aich and Orbata formations and he subdivided the Orbata formation in three members; lower member (Lower Gargasian), middle member (Upper Gargasien) and upper member (Clansayesian – Lower Albian). Since, many geologists studied the lower cretaceous series in the central and southern Atlas (Abdeljaoued, 1983; Ben Youssef et al., 1985; Ben Youssef & Peybernes, 1986; Ben Youssef, 1998; Zargouni, 1985; Fakraoui, 1990; Chaabani et al., 1992; Zouari, 1995). The new data concern essentially the Orbata formation; the lower and middle members were dated Bedoulian – Gargasian while the upper member is allotted to the Upper Albian (Ben Youssef et al., 1985; 1986). A sedimentary hiatus is highlighted between the Aptian and the Upper Albian. In the Saharian platform, the continental series intercalated between the Callovian – Oxfordian and the Upper Cretaceous marine sediments were qualified "Continental Intercalaire" by Lapparant (1960) and Purbeckian – wealdian by Busson (1967). Posterior studies (Ben Ismail, 1991 & Bouaziz, 1995) distinguished Merbah el Asfer formation (Lower Jurassic – Upper Aptian) surmounted by the Chenini sandstones (Upper Aptian – Lower Albian) and Oum ed Diab sands (Albian – Fig.1. (A) Structural location of the Jerid area. (B) Geological map of the Jerid area Cenomanian). and data location.

Fig.1. (A) Localização estrutural da região de Jerid. (B) Mapa geológico da região de Jerid e localização dos dados. 3. Stratigraphy The Jerid Lower Cretaceous series are identified using the 2. Geological context lithological columns of deep boreholes (Fig.1). The well logs allowed a precise restitution of these columns and consequently Part of the Arabian Maghreb, Tunisia is characterized by two a better characterization of the Lower cretaceous formations. different geological domains: the folded and faulted Atlas in the North and the stable saharian platform in the South (Caire, 3.1. Berriasian - Hauterivian 1971; Missenard, 2006). The Jerid area occupies an intermediate position between these domains. The GNT-1 (Gantass-1) petroleum well located at the North The anticline structures of Draa Jerid and Sidi Bouhlel, of Chott El Gharsa, shows the Berriasian – Hauterivian situated between El Gharsa Chott and Jerid Chott, constitute the series, represented from the base to the top by the Sidi western extent of the Chotts fold belt (Fakraoui, 1990) which Khalif, Melloussi and Boudinar Formations (Fig.2). corresponds to the most Southern structures of the Atlasic The Sidi Khalif Formation 120 m thick is constituted of domain (Zargouni, 1985; Ben Ayed, 1986; Fakraoui, 1990; clays with limestones intercalations. The Melloussi Boukadi, 1994; Zouari, 1995; Bouaziz, 1995; Bédir, 1995; Formation deep of 3880 m reveals a thickness of 360 m. It is Hlaiem, 1999; Zouaghi et al., 2005). formed by clays, limestones and sands. The Boudinar In the Jerid area, the outcrops age range from the Upper Formation is composed of sands, sandstones and thin clayey Cretaceous to the Quaternary (Fakraoui & Mahjoub, 1995; beds. It is found at a depth of 3643 m and reaches a thickness Mahjoub, 1995). The Lower Cretaceous outcrops characterize of 248 m. the bordering domains of the Jerid: in the Southern Atlas, at The NF (Nefta) water well drilled to a depth of 2645 m Jebel Orbata, Jebel Ben Younes, Jebel Bou Ramli, Jebel did not reach the base of the Boudinar Formation. It shows Bouhedma and the Chotts belts and in the Saharan platform. In 200 m of this Formation. The Gamma Ray log in the NF well these domains, the Lower Cretaceous was the subject of many (Fig.3) shows bell-shaped electrosequences indicating that stratigraphic studies (Burollet, 1956; Busson, 1967; Tlig, 1978; the Boudinar Formation is composed of upward–fining M’Rabet, 1981; Burollet et al., 1983; Kammoun, 1988; sequences (Serra, 1985). This sequence type characterizes the Chaabani et al., 1992; Ben Youssef, 1998; Ouaja, 2003; Lazzez fluvial channels which are abundant in the deltaic plain et al., 2008; Gallala et al., 2009). (Galloway, 1975). A delta invaded Tunisia in the Berriasian– In the central and southern Atlas, Burollet (1956) Hauterivian period was described by M’ Rabet (1981). subdivided the lower cretaceous deposits in four The Lower Cretaceous series of Jerid, Tunisia 21

3.2. Barremian Most of the deep wells in the Jerid recognized the Barremian deposits composed of Bouhedma and Sidi Aich Formations. In the GNT-1 well, the Bouhedma Formation deep of 3229 m and thick of 406 m consists of clays with limestones and sandy intercalations. In the DG () water well, the Gamma Ray log corresponding to the Bouhedma Formation (thick of 220 m) describes mostly high values indicating the dominance of clays. In the NF water well, the low radioactivity intervals are more developed. They often characterize sandstones. In some cases they correspond to gypsum and dolomites. The radioactivity responses evolution from DG well to NF well (Fig.4) translates the Bouhedma Formation enrichment in sandstones and gypsum towards the South-West.

Fig.2. Lithostratigraphic correlation.

Fig.2. Correlação litostratigráfica.

Fig.4. Characterization of Bouhedma Formation from Gamma Ray logs in DG and NF water wells.

Fig.4. Caracterização da Formação Bouhedma a partir de logs de raios-Gamma nos poços de água DG e NF. The Sidi Aich Formation is constituted by sands and sandstones with clayey intercalations. The comparison of the Gamma Ray logs corresponding to this Formation (Fig.5) reveals that the high radioactivity intervals are thick and very frequent in the MR (Mergueb) well. They are less developed in NF (Nefta) well. There are some intervals in HZ (Hezoua) well. This comparison reflects a lithological change of the Sidi Aich Formation; the clayey elements abundant in the North-East are reduced in favor of coarse elements towards the South-West. Exceptionally, in the BR (Bir Roumi) water well (Fig.2)

implanted in the Southern extremity of the Jerid area, the Sidi Fig.3. Characterization of Boudinar Formation from Gamma Ray log in NF water Aich Formation overlain a unit formed by sands, sandstones, well. green clays and some gypsum beds usually located at the base. Fig.3. Caracterização da Formação Boudinar a partir de log de raios-Gamma no This unit 265 m thick is similar to Purbeckian–Wealden facies poço de água NF. described in the Saharan platform (Busson 1967). 22 R. Guellala et al. / Comunicações Geológicas (2012) 99, 2, 19-26

In certain areas of the Saharan platform, the Purbeckian– The Northern part shows the six Formations defined in the Wealden deposits recently named Merbah El Asfer Formation Southern Atlas (Burollet, 1956) with similar facies that are from (Ben Ismail, 1991; Bouaziz, 1995; Ben Youssef, 1998) are the base to the top: the Sidi Khalif Formation, Melloussi surmounted by a lithological unit composed of sands, Formation, Boudinar Formation, Bouhedma Formation, Sidi Aich sandstones, conglomerates and clays. This unit dated Formation and Orbata Formation (Fig.2). Barremian–Lower Aptian can be the lateral equivalent of the In the Jerid Southern extremity, in the Bir Roumi area, the Sidi Aich Formation defined in the Atlas domain (Burrollet, Sidi Aich Formation and Orbata Formation cover a dominantly 1956; M’ Rabet, 1981). continental series similar to the Purbeckian–Wealden facies (Fig.2) described in the Saharan platform (Busson, 1967). In the North, the Lower Cretaceous Formations are thick and rich of fine sediments. Towards the South, they reveal enrichment in coarse elements and thickness decrease. This evolution translates the position of the Jerid area between two different paleogeographical domains: the subsident basin Gafsa– Chotts in the North and the Saharan platform, near the emergence stage, in the South.

Fig.5. Comparison of Gamma Ray logs corresponding to Sidi Aich Formation.

Fig.5. Comparação dos logs de raios-Gamma da Formação Sidi Aichr.

3.3. Aptian –Albian In the Jerid area, the Aptian-Albian episode is represented by the Orbata Formation which reveals heterogeneous composition. The lower part of this Formation is marked by dolomites, clays, marls and clayey sandstones. The upper part is constituted by dolomitic limestones, marls and laminated gypsum. Fig.6. Characterization of Orbata Formation.

In each deep well in the Jerid area, the Orbata Formation Fig.6. Caracterização da Formação Orbata. base corresponds to a dolomitic bar (Fig.6). This bar is dated Aptian and its thickness ranges between 25 and 75 m. It is the lateral equivalent of Sidi Bou Laaba dolomites 4. Tectonic control in the area (Bismuth et al., 1982), of the lower dolomitic cornice of Jebel Orbata (M’Rabet, 1981), of the The G1 seismic section (Tab.1) crosses the Jerid Chott (Fig.1). It expresses its structure and develops its deformation during the Berrani member in the Chotts belt (Ben Youssef & Peybernes, 1986) and of the Aptian dolomite in the Saharan platform Jurassic - Lower Cretaceous period. (Busson, 1967). Table 1. G1 seismic section: acquisition and processing. The Jerid Aptian dolomite is surmounted by a sandstone layer thicker towards the South; its thickness is 5m in Mahassen Tabela 1. Secção sísmica G1: aquisição e processamento. region whereas it exceeds 40 m in Bir Roumi region (Fig.6). The sandstone layer can be the lateral equivalent of "Foum El Argoub sandstones and sands" in the Southern chain of Chotts (M’Rabet, 1981; Ben Youssef et al., 1985; Chaabani et al., 1992). According to the previous descriptions, different lithostratigraphical Formations characterize the Lower Cretaceous in the Jerid area. The Lower Cretaceous series of Jerid, Tunisia 23

Data provided by the oil well (Nefta-1) NF-1: the depths of 5. Hydrogeological implications the lithostratigraphic formations and the relation time-depth allowed the identification of various reflectors on the seismic The lithological columns description and the well logs interpretation section: The Lower Cretaceous roof founded at a depth of 1687 revealed that the Sidi Aich Formation, the Boudinar Formation and m corresponds to 1184 ms on the G1 section. the Purbeckian–Wealden facies are rich in coarse sediments. They The seismic interpretation (Fig. 7) highlights normal faults constitute the best reservoirs of the “Continental Intercalaire” that indicate an extensive tectonic regime in Chott Jerid during aquifer in the Jerid area. The Sidi Aich Formation catchment is the Lower Cretaceous period. These faults, inducing a half- made in the majority of deep water well. The Boudinar Formation graben structure opened towards the North, controlled the and the Purbeckian–Wealden facies are respectively exploited by sediments distribution. In fact, the Lower Cretaceous deposits NF well and BR well. which are reduced in the raised block show remarkable Data provided by the Jerid deep water wells allowed the thickening in the subsided block. determination of the Sidi Aich and the Purbeckian–Wealden reservoirs characteristics such as the permeability, the porosity and the clay content.

5.1. Reservoirs characteristics evaluation Aquifer transmissivity values, deduced from pumping tests (Mamou 1986; Moumni 2001; Moumni 2005) were useful for the permeability evaluation. The following relation is applied:

T (m2/s) = K (m/s) x e (m) (Castany, 1982) Fig.7. Interpretation of the G1 seismic section. Where T is the transmissivity, K is the permeability Fig.7. Interpretação do corte sísmico G1. coefficient and e is the reservoir thickness. Therefore, the thickness and facies variations of the Jerid The reservoirs porosity is estimated using the resistivity Lower Cretaceous deposits are closely related to a brittle logs. The Archie formula (1942) is applied: synsedimentary deformation (Fig.8) during the Jurassic-Lower R =R aϕ-m Cretaceous extension described in Tunisia (Turki, 1985; Ben Ayed, T w

1986 ; Ben Ismail, 1990 ; Soussi, 1990; Alouani, 1991 ; Bouaziz, Where R is the rock resistivity (Ohm.m), R is the water 1995; Chikhaoui et al., 1998; Zghal et al., 1998; Melki et al., 2010) T w resistivity (Ohm.m) and ϕ is the Porosity (%). For and corresponding in the more general context to the Tethyan unconsolidated formations, case of the Jerid Continental rifting (Dercourt et al., 1985; Guiraud & Maurin,1991; Ricou, Intercalaire reservoirs, a = 0, 62 and m = 2.15 (Humble Formula, 1994). in Chapellier 1987). The Negrine–Tozeur fault is defined as the most western The radioactivity logs were exploited to determine the clay’s section of the south atlasic accident in Tunisa (Zargouni, 1985; content in the Continental Intercalaire reservoirs. The Chapellier Ben Ayed, 1986). This fault which extends from Negrine until formula (1987) is applied: Kébili through Tozeur has guided cretaceous and tertiary sedimentation in the northern chains of Chotts (Fakraoui, 1990). I =GR -GRproper/GRclay-GRproper At Jerid Chott, the Negrine-Tozeur accident was detected sh X by satellite images and radioactive anomalies (Rabia, 1984). Where I is the Clay index or the clay percentage (%), GR However, the seismic section G1 crossing the totality of Jerid sh X is the radioactivity in X point (API), GRproper is the Chott (Fig.7) does not show this major fault. radioactivity of sandy or limestone bed (API), GR clay is the radioactivity of clayey bed (API). The value of 15 API, corresponding to the Aptian dolomite is considerate for the GR proper. The value of 120 API characterizing the clayey bank which marks the uppermost part of the Sidi Aich Formation is adopted for GR clay.

5.2. Obtained results The permeability coefficient (K), calculated for the Sidi Aich Formation reservoirs is variable; it is of 1.6 10-5 m /s in Mahassen area. It reaches 1.4 10-4 m /s in Hezoua (Fig.9).The Purbeckian – Wealden series offers the most permeable reservoirs (2 10-4 m /s). Additionally, the Sidi Aich Formation reservoirs show a porosity increasing towards the South. It is on average 18% in Mergueb area. It reaches 20% in Hezoua. The higher porosity (21%) characterizes the Purbeckian–Wealden reservoirs.

Compared with the porosity values, the clay percentages Fig.8. Geological section showing the sedimentary and tectonic phenomena which show antagonistic evolution. In fact, the clay content in the Sidi affect the Jerid Lower Cretaceous deposits. Aich Formation reservoirs is higher in Mergueb region (15%) Fig.8. Corte geológico evidenciando fenómenos sedimentares e tectónicos que than in Hezoua (10%). The Purbeckian–Wealden reservoirs afectam os depósitos do Cretácico inferior de Jerid. reveal the lowest content (8, 5%). 24 R. Guellala et al. / Comunicações Geológicas (2012) 99, 2, 19-26

Therefore, the Continental Intercalaire reservoirs in the Jerid the Southern extremity, in Bir Roumi region, the Purbecko– area exhibit variable characteristics. From the North to the South, Wealdien facies constitute the most important reservoir. the permeability and the porosity show gradual increase The Permeability, the porosity and the artesian flows of the associated to clay content reduction. This distribution reflecting Jerid Continental Intercalaire aquifer increase from the North to the lithological change of the reservoirs formations is controlled the South. by the paleogeographical zonation of the Jerid area in the Lower This study presents an illustration of complementarity Cretaceous period. between various disciplines: interaction between geology, The variations of the CI reservoirs characteristics present hydrogeology and geophysics for the deep aquifers important hydrogeological implications from the time when they comprehension. The obtained results should be useful for the influence the groundwater flow. The permeability and the exploitation of the Continental Intercalaire aquifer in the Jerid artesian flow show the same spatial distribution; in fact in the Bir area. Roumi–Hezoua sector where the permeability is higher (1.4 10-4 -4 à 2 10 m/s), the artesian flow exceeds 150 l/s. Towards the References North, in Mahassen area, the permeability which is of 1.6 10-5 m/s corresponds to an artesian flow of 20 l/s. Abdeljaoued, S., 1983. Etude sédimentologique et structurale de la partie orientale de la chaîne nord des chotts. Unpublished PhD Thesis, University Tunis II, 143. Alouani, R., 1991. Le Jurassique du Nord de la Tunisie. Marqueurs géodynamiques d’une marge transformante: Turbidites, Radiolarites, Plissements et Métamorphisme. Unpublished PhD Thesis, University Tunis II, 202. Archie, G.E., 1942. The electrical resistivity log as an aid in determining some reservoir characteristics. Petroleum Transactions of AIME, 146, 54–62. Bédir, M., 1995. Mécanismes géodynamiques des bassins associés aux couloirs de coulissements de la marge atlasique de la Tunisie. Seismo- Stratigraphique, Seismo-Tectonique et Implications pétroliers. Unpublished Es–Sciences Thesis, University Tunis II, 315. Ben Ayed, N., 1986. Evolution tectonique de l’avant pays de la chaîne alpine de la Tunisie du début du Mésozoïque à l’actuel. Unpublished Es–Sciences Thesis, University Paris Sud, 327. Ben Baccar, B., 1982. Contribution à l’étude hydrogéologique de l’aquifère multicouche de Gabès Sud. Unpublished PhD Thesis, University Paris Sud, 244. Ben Ismail, H., 1991. Les bassins mésozoïques du Sud de la Tunisie: Stratigraphie intégrée, Caractéristiques géophysiques et Evolution géodynamique. Unpublished Es–Sciences Thesis, University Tunis II, 446. Fig.9. Characteristics of the Jerid Continental Intercalaire reservoirs. Ben Youssef, M., Biely, A., Memmi, L., 1985. La Formation Orbata (Aptien) en Tunisie méridionale. Précisions biostratigraphiques Fig.9. Características dos reservatórios do Continental Intercalar de Jerid. nouvelles. Notes Service Géologique de Tunisie, 51, 105-120. Ben Youssef, M., Peybernes, B., 1986. Données micropaléontologiques et biostratigraphiques nouvelles sur le Crétacé inférieur marin du Sud, 6. Concluding remarks Tunisien .Journal of African Earth Sciences, 3, 217 -231. The deep wells data consisting of lithological columns and Ben Youssef, M., 1998. Stratigraphie génétique du Crétacé de Tunisie. wells logs were useful for the Jerid Lower Cretaceous series Micropaléontologie, Stratigraphie Séquentielle et Géodynamique des bassins de la marge Sud et péritéthysienne. Unpublished Es–Sciences identification and the follow-up of their lateral evolution. Thesis, University Tunis II, 300. In the North, the Lower cretaceous deposits presenting Bismuth, H.; Boltenhagen, C.; Donze, P.; Le Fevre, J., Saint-Marc, P., important powers are rich in clays and carbonates. Towards the 1982. Etude sédimentologique et biostratigraphique du Crétacé moyen South, they are progressively enriched in coarse sediments and et supérieur du Jebel Semmama (Tunisie Centre Nord). Cretaceous their thickness decreases. Research, 3, 171-185. In the Southern extremity of the Jerid area, the Lower Bouaziz, S., 1995. Etude de la tectonique cassante dans la plate-forme et Cretaceous series are thinner and composed by Purbeckian - l’Atlas sahariens (Tunisie méridionale): Evolution des paleochamps de Wealden facies which are dominantly continental. contraintes et implications géodynamiques. Unpublished Es–Sciences Thesis, University Tunis II, 485. The lithology and the thickness change of the Jerid Lower Boukadi, N., 1994. Structuration de l’Atlas de Tunisie: signification des Cretaceous Formations translate the position of this area between nœuds et des zones d’interférences structurales au contact des grands two different domains: the subsident basin of Gafsa –Chotts in couloirs tectoniques. Unpublished Es–Sciences Thesis, University the North and the raised Saharan platform in the South. Tunis II, 249. Seismic interpretation showed that the Jurassic - lower Burollet, P.F., 1956. Contribution à l’étude stratigraphique de la Tunisie Cretaceous extension, contemporary with the Tethys rifting centrale. Annales des Mines et de Géologie, Tunisie, 350. which is responsible of this paleogeographical zonation. Normal Burollet, P.F., Memmi, L., M’ Rabet, A., 1983. Le Crétacé inférieur de synsedimentary faults controlled the facies and thicknesses Tunisie. Aperçu stratigraphique et sédimentologiste. Zitteliana, 20, 255-264. distribution of the Jerid Lower Cretaceous deposits. Busson, G.,1967. Le Mésozoïque saharien. 1ère partie: L’Extrême Sud- This tectonic-sedimentation relation has an important impact tunisien. Centre National de la Recherche Scientifique de France, 194. on the Jerid hydrogeology. It controls the distribution of the Caire, A., 1971. Chaînes alpines de la méditerranée centrale (Algérie et Continental Intercalaire reservoirs and their potentials. Tunisie septentrionales, Sicile, Calabre et Apennin méridional). In the Northern part of the Jerid area, the Continental Unesco, Sciences de la Terre, 6, 61-90. Intercalaire reservoirs are Sidi Aich and Boudinar Formations. In Castany, G., 1982. Principes et méthodes de l’hydrogéologie. Bordas, Paris, 236. The Lower Cretaceous series of Jerid, Tunisia 25

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