Marine and Petroleum Geology 79 (2017) 222e256
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Marine and Petroleum Geology
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Review article Middle Triassic (Anisian-Ladinian) Tejra red beds and Late Triassic (Carnian) carbonate sedimentary records of southern Tunisia, Saharan Platform: Biostratigraphy, sedimentology and implication on regional stratigraphic correlations
* Mohamed Soussi a, , Grzegorz Nied zwiedzki b, Mateusz Tałanda c, Dawid Dro zd_ z_ c, d, Tomasz Sulej d, Kamel Boukhalfa a, e, Janusz Mermer c,Błazej_ Błazejowski_ d a University of Tunis El Manar, Faculty of Sciences, Department of Geology, 2092 Tunis, Tunisia b Uppsala University, Department of Organismal Biology, Evolutionary Biology Center, Norbyvagen€ 18A, 752 36 Uppsala, Sweden c _ University of Warsaw, Faculty of Biology, Department of Paleobiology and Evolution, Biological and Chemical Research Centre, Zwirki i Wigury 101, 02-089 Warszawa, Poland d Polish Academy of Sciences, Institute of Paleobiology, Twarda 51/55, 00-818 Warsaw, Poland e University of Gabes, Faculty of Sciences of Gabes, City Riadh, Zerig 6029, Gabes, Tunisia article info abstract
Article history: The “red beds” of the Triassic succession outcropping at Tejra-Medenine (southern Tunisia, Saharan Received 10 July 2016 Platform) have yielded rich fossil assemblages of both freshwater and brackish-marine invertebrates and Received in revised form vertebrates. The new discovered fauna indicates an Anisian-Lower Ladinian age for the Tejra section. Its 11 October 2016 lowermost part is considered as equivalent of Ouled Chebbi Formation, while the medium and upper Accepted 20 October 2016 parts are considered as equivalent of the Kirchaou Formation. Both sedimentological characteristics and Available online 22 October 2016 fossil assemblages indicate the increasing marine influences within the middle part of the section and the migration of brackish and freshwater fauna into the lacustrine/playa environment at the top. The Keywords: Biostratigraphy marine fauna-rich interval of the Tejra section correlates well with the well-known Myophoria-rich fi Sedimentology carbonate stratigraphic marker con rming the Middle Triassic (Ladinian) major transgression well Triassic recorded eastward in the Tunisian Jeffara basin and in Libya. The use of this Ladinian stratigraphic event TAGI in addition to the Carnian carbonate transgressive events of the Jeffara escarpment outcrops was of great Saharan Platform help for regional lithostratigraphic correlations between the Triassic outcropping series and those Tunisia currently buried in Ghadames and Berkine basins. The age of the sandstones of “Trias Argilo-Greseux Inferieur ” (TAGI) which forms the main oil and gas reservoir in the Saharan domain is attributed to the Anisian-Carnian and considered as coeval of Ouled Chebbi and Kirchaou Formations of the Dahar escarpment. An updated synthetic stratigraphic chart is proposed for the Triassic of Saharan Platform domain on the basis of the compilation of the new obtained results and the subsurface data taken from published literature. © 2016 Elsevier Ltd. All rights reserved.
Contents
1. Introduction and scope ...... 223 2. Regional geology ...... 225 2.1. Southern Tunisia Triassic stratigraphy ...... 225 2.2. Central Tunisia Triassic stratigraphy ...... 226 2.3. Triassic paleogeography ...... 226 3. Material and methods ...... 227
* Corresponding author. E-mail address: [email protected] (M. Soussi). http://dx.doi.org/10.1016/j.marpetgeo.2016.10.019 0264-8172/© 2016 Elsevier Ltd. All rights reserved. M. Soussi et al. / Marine and Petroleum Geology 79 (2017) 222e256 223
3.1. Field investigations ...... 227 3.2. Subsurface investigations ...... 228 4. New data on Tejra triassic stratigraphy and sedimentology (Northern Province) ...... 228 4.1. Stratigraphy...... 228 4.1.1. Lithological subdivision ...... 228 4.1.2. Fossil contents ...... 228 4.1.3. New biostratigraphic interpretation for Tejra section ...... 237 4.1.4. Palaeoecology ...... 238 4.2. Sedimentolgy: facies associations and depositional environments ...... 238 4.2.1. Facies associations ...... 238 4.2.2. Depositional environments of Tejra succession ...... 239 4.3. Stratigraphy and sedimentology of Hmaïma el Kbira section (Northern Province) ...... 239 5. Additional data on the stratigraphy and sedimentology of jebel Rehach and Kef Touareg sections (Central Province) ...... 241 6. Outcrops to subsurface correlation ...... 243 6.1. Subsurface stratigraphy of the Triassic Ghadames basin ...... 243 6.1.1. EB135well ...... 243 6.1.2. EB63well ...... 244 6.1.3. SN-1Well...... 245 6.2. Correlation of the Jeffara outcrops to El Borma field wells ...... 245 7. Correlation of El Borma and Berkine petroleum wells ...... 247 7.1. Correlation of the Triassic series of southern Tunisia with those of Zarzaitine outcrops ...... 248 7.1.1. Why this correlation? ...... 248 8. Middle-Upper Triassic stratigraphic framework of the Saharan platform and the TAGI reservoir age attribution ...... 248 9. Tectonic control on the triassic sedimentation of the Saharan platform ...... 251 10. Conclusions ...... 253 Acknowledgements ...... 253 References...... 253
1. Introduction and scope southeast, in Sidi Toui area (Fig. 1C), numerous dispersed small outcrops of Ladinian-Carnian age are also present (Kamoun et al., The Triassic series of Tunisia, both in outcrops and subsurface, 2001). are known particularly in Saharan Platform of southern Tunisia and To the south and southeast in the Jeffara plain, covered of Mio- to a lesser extent in the Atlas along the so-called North-South Axis Plio-Quaternary deposits unconformably overlying older series, the (NOSA, Jebel Rheouis) (Fig. 1A). In northern Tunisia, they are mainly Triassic series have been crossed by several wells. They are very evaporitic and are involved within diapiric structures (Salt Dome thick (more than 2000 m) and are represented by fluvio-deltaic Zone: SDZ) and/or to thrust sheets structural units (Perthuisot and sandstones and red clays including numerous rich benthic fauna Rouvier, 1992). carbonate horizons (Trigui, 1989; Kamoun et al., 1998, 1999; Kilani- In southern Tunisia, the Triassic series outcrop along the Dahar Mazraoui et al., 1990; Dridi and Maazaoui, 2003). escarpment and are encountered in subsurface within the Jeffara In Ghadames and Berkin basins, as it is well documented both in and Ghadames basins and further to the north in the Chotts Basin Tunisia and Algeria, the Triassic series are unconformably lying on (Fig. 1A). Along the Dahar escarpment, the Triassic series outcrop in different terms of deformed Paleozoic rocks and are dominantly Tebaga-Medenine area (Northern Province) and in Jebels Kirchaou, represented by fluvio-deltaic to lacustrine siliciclastic deposits Rehach and Charchara which belong to the “Central Province” (Trias Argilo-Greseux Inferieur or TAGI). They grade upwards to a (Fig. 1C and D). sequence dominantly made up of carbonates, shales and evaporites Within the Northern Province, the Triassic series ranged in (Trias Argilo-CarbonateorTAC)( Busson, 1967; Boudjema, 1987; Ouled Chebbi Formation and assigned to the Anisian (Middle Ben Tahar, 1990; Turner et al., 2001; Bourquin et al., 2010. Triassic), are well exposed along the northern segment of the Dahar The siliciclastic Triassic strata of the Jeffara Plain and Dahar escarpment at several accessible localities (Ouled Chouamekh, J. escarpment, as part of the northern margin of the Saharan Platform, Mogor-Ksar Jdidi village and Jebel Semoumnia). In Jebel Tebaga encompasses several units composed of red beds which have not area which corresponds to an E-W monoclinal structure formed by been deeply investigated by paleontologists and their biostratig- Upper Permian barrier reefs complex constituting the unique raphy remained inaccurate and subject of conjectures. As a conse- Permian marine outcrops in Africa (Toomey, 1991; Angiolini et al., quence their stratigraphic relationships and correlation with their 2008; Verna et al., 2010), the Permian-Triassic transition can be equivalents, encountered through boreholes in the Jeffara, Gha- seen at Halk Jmel section. In this locality, the Upper Permian (Jul- dames and Berkine basins, are not yet well established and fian) Cheguimi shallow marine sandstones are overlain by a distinct continue to be the subject of debate. red shaly unit. Nevertheless, the stratigraphic relationships be- These red beds which are well exposed in numerous clay pits in tween the Permian (Julfian) Cheguimi of Halk Jmel section and the Medenine area (Burollet, 1963; Biely and Rakus, 1991) are generally Ouled Chebbi sandstones of Ouled Chouamekh locality are still not unconformably overlain by Middle Jurassic to Cretaceous sedi- well established. ments (Busson, 1967; Bouaziz, 1986; Raulin et al., 2011). Those of In the central Province, the Triassic series outcrop mainly in the Tejra quarries yielded abundant fossils of good preservation. Jebels Rehach and Charchara where they comprised the Ladinian Our field works carried out in 2013 and 2014 led to the finding Kirchaou and the Carnian Azizia formations (Busson, 1967; Kamoun within the red beds of Tejra section of numerous species of bivalves, et al., 1999; Ben Ismail, 1991 and Bouaziz et al., 2002). Towards the gastropods, brachiopods, conchostracans, horseshoe crabs, Download English Version: https://daneshyari.com/en/article/6434317
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