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Abstract

(Begin page 885)

AAPG Bulletin, V. 85, No. 5 (May 2001), P. 0885-0908.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Subsurface Mesozoic basins in the central Atlas of Tunisia: Tectonics, sequence deposit distribution, and hydrocarbon potential

Mourad Bédir,1 Noureddine Boukadi,2 Saïd Tlig,3 Fatima Ben Timzal,4 Lahoucine Zitouni,5 Rabah Alouani,6 Fawzi Slimane,7 Claude Bobier,8 Fouad Zargouni9

1Laboratoire de Géoressources, I.N.R.S.T, BP 95, 2050 Hammam-Lif, Tunisia; email: [email protected]
2Département de Géologie, Faculté des Sciences, Campus Universitaire 1060 Tunis, Tunisia; email: [email protected]
3Département de Géologie, Faculté des Sciences, Campus Universitaire 1060 Tunis, Tunisia
4Laboratoire de Géoressources, I.N.R.S.T, BP 95, 2050 Hammam-Lif, Tunisia
5Laboratoire de Géoressources, I.N.R.S.T, BP 95, 2050 Hammam-Lif, Tunisia
6Faculté des Sciences de Bizerte, Zone Industrielle de Zarzouna, Tunisia
7Division Cartographie, Compagnie des Phosphates de Gafsa, Gafsa, Tunisia
8Département de Géologie, Université de Bordeaux I, Avenue des Facultés 33405 Talence Cedex, France
9Département de Géologie, Faculté des Sciences, Campus Universitaire 1060 Tunis, Tunisia

AUTHORS

Mourad Bédir is professor and researcher of geology at the National Institute of Scientific and Technical Research of Tunisia and director of the Georesources Laboratory. He earned a Ph.D. in geology in 1988 and a Doctorat d'Etat in 1995 from the University of Tunis. He is author of several national and international publications and director and member of several research programs. His research experience includes the basin structuring of the North African Atlassic margin and petroleum geology.

Noureddine Boukadi is professor of geology at the Faculty of Science of Tunis. He earned a Ph.D. in geology from the University of Strasbourg in France in 1984 and a Doctorat d'Etat in 1994 from the University of Tunis. He specializes in the structural geology of the Atlassic fold belt of Tunisia. He is author of several national and international publications and director and member of several research programs.

Saïd Tlig is professor of geology at the Faculty of Science of Tunis. He received his Doctorat d'Etat in 1982 from the University of Orsay, France. He is a geochemist and has broad experience in field geology and mineral deposits of the septentrional Atlassic fold belt of Tunisia. He also works on basin dynamics related to mineralization. He is the director of several research programs.

Fatima Ben Timzal received a Ph.D. from the University of Tunis in 2000. She specializes in subsurface seismic stratigraphy and tectonics of Mesozoic Atlassic basins of the North African Tunisian margin and is author of several publications.

Lahoucine Zitouni earned a Ph.D. from the University of Tunis in 1997. He specializes in subsurface basin analyses of the Mesozoic and has experience in the central and meridional Atlassic fold belt zones. He is author of several publications.

Rabah Alouani is assistant professor at the Faculty of Science of Bizerte, Tunisia. He earned a Ph.D. in 1991 at the Faculty of Science of Tunis. His specialties are sedimentary geology, mineralogy, and geodynamics of basins, and he has experience in the Atlassic fold belt regions of Tunisia. He is author of several publications.

Fawzi Slimane earned his M.S. degree in geology from the University of Tunis in 1983 and his Research Studies Diploma in sedimentology and structural geology from the University of Pau in France in 1984. He has been a principal geologist engineer in the Phosphate Mining Company of Gafsa (CPG) since 1984. He has experience in sedimentology, tectonics, and geologic mapping of the Mesozoic and Tertiary series of the meridional Atlas of Tunisia. He is author of several national publications.

Claude Bobier earned his Doctorat ès Sciences degree in geophysics from the University P. et M. Curie, Paris, VI, in 1971. He is professor in the Department of Geology and Oceanology and Laboratory of Didactic for Sciences and Techniques at the University of Bordeaux I, where he studies structural evolution in the wrench faults in the fronts of the African plate, South American plate, and North American plate. He is author of several international publications in geodynamics.

Fouad Zargouni is professor of geology at the Faculty of Science of Tunis. He earned a Ph.D. in 1973 at the University of Paris, France, and received his Doctorat d'Etat in 1985 from the University of Strasbourg, France. He specializes in structural geology and tectonics and has broad experience in the Atlassic fold belt of Tunisia. He is author of several national and international publications.

ACKNOWLEDGMENTS

We thank the Research Ministry of Tunisia, the Ministry of Education and High School of Tunisia, the University of Tunis II, the University of Bordeaux I (France), the Phosphate Exploration Company of Gafsa (CPG) (Tunisia), and the Petroleum Societies, who supported this work. We thank J. W. Tucker, T. L. Patton, and K. P. Corbett for their constructive criticism and suggestions that resulted in the final version of the article.

ABSTRACT

The Mesozoic and Cenozoic outcrops of the central and meridional Atlas of Tunisia have been studied by structural, biostratigraphic, and sedimentologic approaches. We extend these studies to the subsurface, employing seismic and well data addressing structures, sequence stratigraphy, and hydrocarbon potential. The basin structures are related to strike-slip fault systems associated with Triassic evaporites. Mesozoic sedimentary sections in the areas of the Gafsa, Sidi Ali Ben Oun, Sidi Aïch, and Majoura blocks were studied by an integrated seismic sequence stratigraphic and tectonic approach calibrated to wells and surface geologic controls. We identified tectonic corridors where Upper Triassic evaporites intruded younger Mesozoic rocks beginning in the Jurassic. The organization of the tectonic blocks is characterized by the distribution of subsiding basin zones of graben and rim synclines and resistant areas of platforms. Triassic intrusions induced by the strike-slip movements formed salt pillows and domes that accentuate the border elevations between the rim syncline depocenters and the platforms. Mesozoic sequence deposits are distributed along the flanks of the basin-platform borders according to lowstand prograding downlap systems tracts overlapped by aggrading and retrograding onlap and toplap deposits. The time-space distribution of the systems tract deposits indicates the possibility of formation of Triassic, Jurassic, and Cretaceous carbonate and sandstone prograding turbidites, reefs, structural and stratigraphic pinch-outs, and unconformities in the flanks of salt domes and basins. The geometry and distribution of reservoir and seal systems tracts permit the consideration of new Triassic, Jurassic, and Cretaceous combined stratigraphic and structural hydrocarbon traps around the basins and the platforms. This (Begin page 886) is a new tectonic model of the central Atlas of Tunisia that shows new potential objectives and traps.

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