Pegadas De Vertebrados Nos Eolianitos Do Plistocénico Superior
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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 Tunisia): 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 Sahara 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 Tunis El Manar, 1060 deep boreholes data (lithological columns and well logs) to Tunis, Tunisia. 3Arrondissement des Ressources en Eaux de Tozeur, 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 Gafsa 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.