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Soua M.,Entreprise Tunisienne dActivites Petrolieres ETAP | Zaghbib-Turki D.,Tunis el Manar University | Jemia H.B.,Entreprise Tunisienne dActivites Petrolieres ETAP | Smaoui J.,Entreprise Tunisienne dActivites Petrolieres ETAP | Boukadi A.,Petroleum Research and Development Center
Acta Geologica Sinica | Year: 2011

In Tunisia, five Bahoul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian-Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/al and K/ al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahoul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo- environmental relevant indicators. High Ba xs values and Uauth may indicate anoxic conditions at least at the water-sediment interface during the Bahoul Formation deposition and provide information about low to moderate sulfate-reduction reactions.

Aridhi S.,Entreprise Tunisienne DActivites Petrolieres ETAP | Aridhi K.,Tunis el Manar University | Ghanmi M.,Tunis el Manar University | Zargouni F.,Tunis el Manar University | Mercier E.,CNRS Nantes Laboratory of Planetology and Geodynamics
Arabian Journal of Geosciences | Year: 2014

Bir M'Cherga-Ain Asker area, situated in the hinterland of Zaghouan thrust (Tunisian dorsal), was the land example treated with metric and cartographic scale in order to identify duplex genesis criteria and to include thrusting tectonics associated with tear faults, which are in fact the directory response generating duplex structures identified in outcrop for the first time through Tunisia in this case. Given its geological location between the "dôme" and the "dorsal" zone of Tunisia, this area was the most exposed to a highly paleostress history expressed by a huge fault system remobilization and reactivation through several tectonic events from NE-SW middle Cretaceous distension to a NW-SE and NNW-SSE Paleogene compression. Regarding fault planes generated analysis, they show numerous streak generation of normal, strike-slip, and reverse faults that go with geodynamic and paleostress evolution of the studied area; we note that each streak generation is perfectly matching with one of the tectonic event (mentioned before) affecting the area. In this paper, we analyze duplex structure elaboration scenarios to assess the involved kinematics and their geometrical recognition criterious. We propose to discuss the causes of duplex structures installation in a thrust belt system and the predictable geometrical styles after its installation on foreland or backland. Using the geometrical criteria acquired through this analysis, we will show that such, however, exceptionable structures exist on the land, and that they record the mechanisms of their genesis linked to the tear faults acting in this case. We describe "tear faults" as the sliding breaks which disunite two compartments during deformation, allowing them to undergo different independent deformations in their drawing and their width (for example more or less stretched folds). These types of faults differ from that of the true stick-slip faults, which slice and shift preformed structures (it's even this shift which makes it possible to highlight them); here, there are no shift but dissimilarity of the structures on both sides of the fault; therefore, deformations are the direct results of displacements; they are expressed in thrust belts by ramp folds, intense internal deformations, and even by complex duplex structures. A duplex feature that is not mainly studied is made up by tilted imbricate sedimentary sequences (or horses), separated by link thrusts and underlined respectively at their tops and bottoms by roof and floor thrusts. Imbrications cause a shortening, a thickening, or a thinning of stratigraphic columns and even its crushing and inverting. In thrust belts, duplexes are usually set up following two or even more deformational events; those structures start typically with decollement and imbricate sedimentary unit ones which are made cover by a roof thrust sometimes visible at outcrop. Through this paper, we suggest to discuss geometrical duplex criteria, and we will try a zooming through different scales, from regional to local one in order to show how the shape (expression) of the deformation differs. © 2013 Saudi Society for Geosciences.

Aridhi K.,Tunis el Manar University | Aridhi S.,Entreprise Tunisienne DActivites Petrolieres ETAP | Bagga M.A.O.,Gabes University | Abdeljaouad S.,Tunis el Manar University | And 2 more authors.
Arabian Journal of Geosciences | Year: 2013

The imbrication's area in northern Tunisia is the most external segment of Alpine range, where several associated folds types with thrust ramps are recognized within imbricate units beneath Numidian front slope. Their presence help to understand thrusting mechanisms installation through studied area. In fact, this zone was considered as a result of Paleogene gravitary slop (Kujawski (Ann Miner Géol Tunis (24):281, 1969); Caire (Ann Min Géol Tunis 26:87-110, 1973); Rouvier 1977), which is proved to be affected by major deep decollement, given rise to various structures, some are propagation folds, specific of foreland front, limited to this area, and those in more external position: Tunisian Atlas (Creusot et al. (C R Acad Sci Paris 314(Sér II):961-965, 1992); Ouali and Mercier (PII: S0191-8141(97):00048-5, 1997); Ouali 1984; Ahmadi et al. (J Struct Geol 28:721-728, 2006)). Various categories of fold ramps could be identified: frontal folds ramp NE-SW and others as lateral or oblique ramp with NW-SE trend (Aridhi et al. (C R Geosci 343:360-369, 2011)). The relation between various structures has been used as recognition tools of thrusting sequences and to propose a new deformation chronology. Delimited outcropping of these structures between two both parallel faults strikes with regional displacement, leads to interpret these faults as cogenetic tear faults of propagation thrusts; this fault separates two domains with different deformation styles from each other side. © 2011 Saudi Society for Geosciences.

Dkhaili N.,University of Carthage | Bey S.,University of Tunis | El Abed M.,Entreprise Tunisienne dActivites Petrolieres ETAP | Gasmi M.,University of Carthage | Inoubli M.H.,University of Tunis
Tectonophysics | Year: 2015

An integrated study of available seismic and calibrated wells has been conducted in order to ascertain the structural development and petroleum potential of the Cretaceous Formations of the Western Gulf of Gabes. This study has resulted in an understanding of the controls of deep seated Tethyan tectonic lineaments by analysis of the Cretaceous deposits distribution. Three main unconformities have been identified in this area, unconformity U1 between the Jurassic and Cretaceous series, unconformity U2 separating Early from Late Cretaceous and known as the Austrian unconformity and the major unconformity U3 separating Cretaceous from Tertiary series. The seismic analysis and interpretation have confirmed the existence of several features dominated by an NE-SW extensive tectonic regime evidenced by deep listric faults, asymmetric horst and graben and tilted blocks structures. Indeed, the structural mapping of these unconformities, displays the presence of dominant NW-SE fault system (N140 to N160) bounding a large number of moderate sized basins. A strong inversion event related to the unconformity U3 can be demonstrated by the mapping of the unconformities consequence of the succession of several tectonic manifestations during the Cretaceous and post-Cretaceous periods. These tectonic events have resulted in the development of structural and stratigraphic traps further to the porosity and permeability enhancement of Cretaceous reservoirs. © 2015 Elsevier B.V.

Hezzi I.,French National Center for Scientific Research | Hezzi I.,Tunis el Manar University | Aifa T.,French National Center for Scientific Research | Khemiri F.,Entreprise Tunisienne d'Activites Petrolieres ETAP | Ghanmi M.,Tunis el Manar University
Arabian Journal of Geosciences | Year: 2015

The eastern part of Tunisia is made up of the Atlasic chain foreland, a domain connected to a continental crust which thins northeastward. It is limited to the west and northwest by the corridor of the NS axis faults and by the Zaghouan fault which separates it from the Atlasic domain and trends toward the Pelagian Sea eastwards. It is regarded as a stable zone. The signs of the main events which generated the Atlasic structures are hidden under a thick Plio-Quaternary cover. From surface observations, microtectonic measurements, and lithostratigraphic sections and logs, including those of oil well log data and seismic profiles onshore and offshore, one notes (i) an in-depth and lateral variation of the lithostratigraphic series and (ii) a considerably faulted area at subsurface characterized by a complex structural evolution and shears associated with basins. Such variations are controlled by tectonics and eustatism. The eastern platform is affected only by N45° oriented folds, often accompanied by reverse faults and associated with N90–110° dextral and N160–180° sinistral shears. It corresponds to a tectonic foreland domain representing a folded and sheared deformation zone. The tectonic deformations recognized by seismic data only affect narrow corridors, lengthened and oriented according to three major directions: N45°, N100–120°, and N160–180°. These zones, mobile at several geological periods and tectonically complex, delimit large sectors which have undergone minimal deformation or none at all. Well developed in the Sahel, the reservoirs are carbonated and fractured types such as the limestones of Abiod, Metlaoui, Souar and Chérahil, Aïn Grab, and the Oum Dhouil group. Structural traps for the accumulation of hydrocarbons were formed following these Atlasic compression and folding phases. The deposit of thick argillaceous series during the Eocene (Souar and Chérahil) and during the Miocene (Oum Dhouil) constitutes good continuous covers which sealed the folded and faulted reservoir structures. The seismic profiles show traps which are associated with folded and closure structures by faults and stratigraphic traps through facies changes. The structural inversions and the thrust tectonics in eastern Tunisia play a significant role in the structuring of the cover and also in the evolution of the oil system emplacement. The reservoirs are supplied by bed rocks of the Cretaceous (Bahloul Formation) and the Eocene (Metlaoui Formation). © 2015 Saudi Society for Geosciences

Zouaghi T.,University of Carthage | Bedir M.,University of Carthage | Ayed-Khaled A.,Tunis el Manar University | Lazzez M.,Entreprise Tunisienne dActivites Petrolieres ETAP | And 3 more authors.
Journal of Structural Geology | Year: 2013

Two-dimensional seismic data and well data from the Sbiba graben in central Tunisia (North Africa) reveal its asymmetrical structural geometry affected by EeW, NeS, NWeSE, and NEeSW master strikeslip faults. These faults have been intruded by Upper Triassic evaporites, which can be classified into the following three types: (1) sealed evaporite anticlines and domes along folded structures; (2) extrusional wrinkles of "salt walls" at the borders of the graben related to along-strike displacement of the master fault zone; and (3) evaporite outpouring at the center of the graben interpreted as the result of fault and diapir movement. Detailed seismic-stratigraphic analysis highlights a complex interplay between fault growth and evaporite movement, which strongly controlled the evolution of the graben. During the Mesozoic, tectonic stresses induced multidirectional faulting along inherited faults. The vertical rising of the Upper Triassic evaporites was initiated locally at the intersection of master faults during regional extensional and transtensional events in the sub-evaporite basement. The interaction of normal faulting and evaporite diapirism caused lateral outpouring of surface-piercing evaporites. This phenomenon is well expressed in Upper Cretaceous (upper Cenomanian to lower Turonian) strata. The master faults, which cut the diapir at the border and the crest, have caused the extrusion of evaporites. The downward, gravity-driven flow of these evaporites across the slope surface and subsequent accumulation and preservation in Mesozoic sediments is related to the fault escarpment and the adjacent fault-induced depression. There is an apparent relation between tectonic inheritance and inversions of the graben, where interconnected deep faults and diapirs have been reactivated during extensional and contractional tectonic episodes, causing evolution of the structures with the associated sedimentary lapouts. Several autochthonous Triassic evaporites and associated fault escarpments have induced salt canopy structures. © 2013 Published by Elsevier Ltd.

Gharsalli R.,Rigo Oil Company | Zouaghi T.,University of Carthage | Soussi M.,Tunis el Manar University | Chebbi R.,Entreprise tunisienne dactivites petrolieres ETAP | And 2 more authors.
Comptes Rendus - Geoscience | Year: 2013

The Cap Bon Peninsula, belonging to northeastern Tunisia, is located in the Maghrebian Alpine foreland and in the North of the Pelagian block. By its paleoposition, during the Cenozoic, in the edge of the southern Tethyan margin, this peninsula constitutes a geological entity that fossilized the eustatic, tectonic and climatic interactions. Surface and subsurface study carried out in the Cap Bon onshore area and surrounding offshore of Hammamet interests the Miocene deposits from the Langhian-to-Messinian interval time. Related to the basin and the platform positions, sequence and seismic stratigraphy studies have been conducted to identify seven third-order seismic sequences in subsurface (SM1-SM7), six depositional sequences on the Zinnia-1 petroleum well (SDM1-SDM6), and five depositional sequences on the El Oudiane section of the Jebel Abderrahmane (SDM1-SDM5). Each sequence shows a succession of high-frequency systems tract and parasequences. These sequences are separated by remarkable sequence boundaries and maximum flooding surfaces (SB and MFS) that have been correlated to the eustatic cycles and supercycles of the Global Sea Level Chart of Haq et al. (1987). The sequences have been also correlated with Sequence Chronostratigraphic Chart of Hardenbol et al. (1998), related to European basins, allows us to arise some major differences in number and in size. The major discontinuities, which limit the sequences resulted from the interplay between tectonic and climatic phenomena. It thus appears very judicious to bring back these chronological surfaces to eustatic and/or local tectonic activity and global eustatic and climatic controls. © 2013 Académie des sciences.

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