Fouad Zargouni

Erratum to: Neogene sediment deformations and tectonic features of northeastern Tunisia: evidence for paleoseismicity

The Neogene stratigraphic series is characterized by predominant clayey facies alternated by other sand layers. The outcrop and subsurface studies show varied and complex styles of deformations and lead to relate the structures to paleoseismic events. The seismicity of eastern onshore and offshore Tunisian margin follows the master fault corridors oriented globally N–S, E–W, and NW–SE that correspond to the bordering faults of grabens and syncline corridors and associated faulted drag fold structures oriented NE–SW. Epicenters of magnitudes between 3 and 5 are located along these border fault corridors. The Neogene strata record brittle structures, including numerous and deep faults and fractures with straight and high-angle dipping planes. The structuring of NE–SW en echelon folds and synclines inside and outside NW–SE and E–W right lateral and N–S and NE–SW left lateral tectonic corridors indicates the strike-slip type of bordering faults and their seismogenic nature. Wrench fault movements that induce mud and salt diapirs, mud volcanoes, and intrusive ascensions are related to seismic shocks. Seismic waves caused by activity along one, or most likely, several tectonic structures would have propagated throughout the Quaternary cover producing seismites. The similarity of deposits, structuring, and seismites between the Tunis-Bizerte to the North and Hammamet-Mahdia to the South accredits the hypothesis that the seismic episodes might have affected sedimentation patterns along the Sahalian large geographic area. The paleoseismic events in northeastern Tunisia might be related to tectonic fault reactivations through time. This hypothesis is consistent with the geomorphologic context of the study area, characterized by several morphostructural lineaments with strong control on the sediment distribution, as well as uplifted and subsiding terrains. The estimated magnitude of the seismic events and the great regional tectonically affected areas demonstrate that the northeastern Tunisia experienced stress through the last geological episodes of its evolution. This Neogene kinematic reconstruction highlights the neotectonic system inducing the actual seismicity on this margin. Therefore, there is a straight relationship between deepseated faults and seismicity.

Neogene sediment deformations and tectonic features of northeastern Tunisia: evidence for paleoseismicity@@@تغيرات رواسب العهد النيوجيني وميزات التكتونية في شمال شرق البلاد التونسية: علاقتها بالأحداث الزلزالية القديمة

The Neogene stratigraphic series is characterized by predominant clayey facies alternated by other sand layers. The outcrop and subsurface studies show varied and complex styles of deformations and lead to relate the structures to paleoseismic events. The seismicity of eastern onshore and offshore Tunisian margin follows the master fault corridors oriented globally N–S, E–W, and NW–SE that correspond to the bordering faults of grabens and syncline corridors and associated faulted drag fold structures oriented NE–SW. Epicenters of magnitudes between 3 and 5 are located along these border fault corridors. The Neogene strata record brittle structures, including numerous and deep faults and fractures with straight and high-angle dipping planes. The structuring of NE–SW en echelon folds and synclines inside and outside NW–SE and E–W right lateral and N–S and NE–SW left lateral tectonic corridors indicates the strike-slip type of bordering faults and their seismogenic nature. Wrench fault movements that induce mud and salt diapirs, mud volcanoes, and intrusive ascensions are related to seismic shocks. Seismic waves caused by activity along one, or most likely, several tectonic structures would have propagated throughout the Quaternary cover producing seismites. The similarity of deposits, structuring, and seismites between the Tunis-Bizerte to the North and Hammamet-Mahdia to the South accredits the hypothesis that the seismic episodes might have affected sedimentation patterns along the Sahalian large geographic area. The paleoseismic events in northeastern Tunisia might be related to tectonic fault reactivations through time. This hypothesis is consistent with the geomorphologic context of the study area, characterized by several morphostructural lineaments with strong control on the sediment distribution, as well as uplifted and subsiding terrains. The estimated magnitude of the seismic events and the great regional tectonically affected areas demonstrate that the northeastern Tunisia experienced stress through the last geological episodes of its evolution. This Neogene kinematic reconstruction highlights the neotectonic system inducing the actual seismicity on this margin. Therefore, there is a straight relationship between deepseated faults and seismicity.الخلاصةتتميز ستراتيغرافيا العهد النيوجيني (Neogene) بطبقات طينية سميكة تتخللها طبقات أخرى من الرمل. وتظهر الدراسات الميدانية و تحت سطح الأرض (جيوفيزيائية) أنماط متنوعة ومعقدة من التشوهات، تؤدي إلى ربطها بأحداث زلزالية قديمة. تبدو الزلازل في شرق البلاد قد اتبعت ممرات الصدوع الرئيسية والمتجهة عموما شمال-جنوب، شرق-غرب و شمال غرب-جنوب شرق توافقا مع الصدوع المتاخمة للهياكل المنخفضة و المقعرة (grabens) وما يرتبط بها من طيات ذات اتجاه شمال شرق-جنوب غرب. ويتراوح مركز الزلزال بين 3 و 5 درجات على مقياس ريشترRichter))، على امتداد ممرات الصدوع. تظهر طبقات النيوجين هياكل هشة تحتوي على صدوع عديدة وعميقة ذات زاويا مرتفعة. كما أن هيكلة الطيات و المنخفضات المتجهة شمال شرق-جنوب غرب داخل وخارج الممرات التكتونية ذات التحرك الجانبي الأيمن والمتجهة شمال غرب-جنوب شرق و شرق-غرب والأخرى ذات التحرك الجانبي اليساري والمتجهة شمال-جنوب و شمال شرق-جنوب غرب، تشير إلى نوعية الصدوع و طبيعة السيسموجينية (seismogenic) المرافقة لها. إن التحركات الجانبية للصدوع والتي رافقتها هياكل نتيجة تحركات و صعود الطين (mud diapirs) والملح (salt diapirs) والبراكين، قد ارتبطت بالصدمات الزلزالية. و يبدو أن الموجات الناجمة عن نشاط واحد أو العديد من الهياكل التكتونية قد انتشرت عبر طبقات العصر الرباعي منتجة بذالك العديد من السايسميت (seismites). إن تشابه الترسبات والهياكل و السايسميت بين جهتي تونس-بنزرت من الشمال والحمامات-المهدية من الجنوب، يدعم فرضية أن الحلقات الزلزالية قد أثرت على أنماط الترسيب على مساحة جغرافية واسعة من الساحل التونسي. تبدو الأحداث الزلزالية القديمة (paleoseismic events) في شمال شرق البلاد التونسية ذات صلة بعودة النشاط التكتونى للصدوع (tectonic fault reactivations) عبر الزمن. و تتلاءم هذه الفرضية مع الإطار الجيومورفولوجي (geomorphologic) لمنطقة الدراسة و الذي يتميز بعدة عناصر مورفو بنيوية (morphostructural) تتحكم في توزيع الرواسب والتضاريس المرتفعة و المنخفضة. إن حجم الأحداث الزلزالية وأهمية التكتونية الإقليمية تثبت أن شمال شرق البلاد التونسية قد تعرض لضغوط خلال الحلقات الجيولوجية الأخيرة من تطوره. وتبين نماذج التغير الديناميكي للعهد النيوجيني أهمية التكتونية الحديثة (neotectonic) في تحفيز الأحداث الزلزالية في الوقت الحالي. لذالك توجد علاقة مباشرة بين توزيع الصد وع العميقة و نوعيتها وتحركاتها عبر الزمن، و الأحداث الزلزالية المسجلة.

The Chotts Fold Belt of Southern Tunisia, North African Margin: Structural Pattern, Evolution, and Regional Geodynamic Implications

At the North of the old African continent, craton and shields having more than two billion years, Tunisia, Algeria and northern Morocco underwent a complex geodynamic and structural evolution during the Mesozoic and Cenozoic times (Dercourt et al., 1985; Bouillin, 1986; Frizon de Lamotte et al., 2009). This evolution resulted in the development of varied paleogeographic fields, in relation with the Tethyan and Atlantic movements. Its end led to the genesis of the North-African alpine orogen (Dercourt et al., 1985; Martinez et al., 1990) formed by the Maghrebid and Atlassic domains (Fig. 1). Tunisia occupies the eastern part of this orogen, located at the north of a large Saharan platform, developed on the stable African craton, not deformed during the alpine cycle and bounded by a major structural lineament « South Atlassic fault » composed of complex overlapping folds trending NE-SW, E-W and NW-SE (Caire,1971; Zargouni, 1985; Turki, 1988; Zouari et al., 1990; Ben Ayed, 1993; Boukadi, 1994; Bedir, 1995; Bouaziz, 1995; Zouari, 1995; Bouaziz et al., 1999, 2002; Abbes, 2004; Zouaghi et al., 2005a, b, 2011; Ouali, 2007; Melki et al, 2010). Structures of the North African margin were usually subject of discussion. This domain could be considered as a passive margin, close to the oceanic opening, characterized by a strong subsidence marked by accumulations of prograding deposits (Dercourt et al., 1985; Biju-Duval et al., 1976). For others, it is a transform margin related to displacements of the African plate compared to the Eurasian plate. These movements generated opening of the Paleo-Tethys (Arthaud and Thomas, 1977). The Africa-Europe relative motions would be at the origin of the recent ocean floor spreading of the Mediterranean (Taponnier, 1977; Reading, 1980; Olivet et al., 1982; Alvarez et al., 1984; Ricou, 1994). The study area belongs to the North African margin and the northern edge of the Saharan platform. Studies undertaken on Paleo-Tethys show the development of deformed and subsiding zones between the cratonic blocks and the basins (Caire, 1974; Arthaud and Thomas, 1977; Aubouin and Debelmas, 1980; Bernoulli and Lemoine, 1980; Durand-Delga and Fonrbote, 1980; Bousquet and Philip, 1981; Dercourt et al., 1992). The geodynamic

Tectonosedimentary evidence in the Tunisian Atlas, Bou Arada Trough: insights for the geodynamic evolution and Africa–Eurasia plate convergence

The Bou Arada Trough is an east–west-oriented structure located 80 km SW of Tunis, characterizing the central Tunisian Atlas. This trough is filled by a thick Quaternary sand and clay series and is bordered by complex systems of folds generally trending NE–SW. Contacts between the Bou Arada Trough and the neighbouring folds are accommodated by NE–SW- and NW–SE-oriented faults. In contrast to the other troughs of the Tunisian Atlas, which are related to the Pliocene–Quaternary orogenic period, the geodynamic evolution of the Bou Arada Trough began in the Maastrichtian and has continued until the present day. Structural, tectonosedimentary and seismic data analyses are undertaken in the study area to better understand the evolutionary scenario of this trough. The results obtained show that the Bou Arada Trough is fragmented into three NW–SE-oriented sub-basins and records a continuous history of downthrow. Indeed, during extensional to transtensional regimes, this trough has evolved in response to the two networks of perpendicular fractures whereas during compressive to transpressive periods, the collapse of the Bou Arada Trough has been induced by a pull-apart mechanism using the same network of faults but with a strike-slip movement. The Bou Arada Trough thus preserves a record of the convergence between the European and African plates since the Maastrichtian.

Grain size characteristics of superficial sediments of the Gulf of Tunis (NE Tunisia)

This work presents a recent grain size study characterizing superficial sediments of the whole sectors of the Gulf of Tunis which extends from Sidi Ali El Mekki to Sidi Daoued. In this study, a total of 112 samples were collected from different depths following 26 profiles perpendicular to the shore and from rivers. The determination of the proportions of coarse and fine fractions and the interpretation of the grain size results lead to dividing the Gulf of Tunis into two principal coasts: (1) the western coast situated between Sidi Ali El Mekki and Borj Cédria, which is characterized by three sedimentary facies: (a) a sandy facies along the coastline, (b) a mixed facies between Ghar El Melh and Raoued, near the Medjerda River, and between La Goulette and Ezzahra, near the Miliane River, and (c) a muddy facies between Ghar El Melh and Kalâat El Andalous and covered by fine to very fine sands, and (2) the eastern coast, which is characterized by a sandy facies and covered by medium to coarse sands. The dominant N–E and N–W waves generate longshore currents that provide sediment transport following the directions N–S, from Sidi Ali El Mekki to Kalâat El Andalous; SE–NW, from Gammarth to Raoued; NE–SW, from Sidi Bou Saïd to La Goulette and from Sidi Daoued to Bir El Jadi; SE–NW, from Hammam-Plage to Ezzahra; and SW–NE, from Port aux Princes to Rtiba.

Tectonique synsedimentaire d'age cretace superieur en Tunisie nord orientale; blocs bascules et reorganisation des aires de subsidence

Structural analysis of late Cretaceous sequences from the northeastern Tunisian Atlas, led to conclude on an active basin floor instability. Regional tectonics resulted in tilted blocks with a subsidence reorganization, since the Campanian time. These structural movements are controlled both by N140 and N100-120 trending faults. The Turonian-Coniacian and Santonian sequences display lateral thickness and facies variation, due to tectonic activity at that time. During Campanian-Maastrichtian, a reorganization of the main subsidence areas occurred, the early Senonian basins, have been sealed and closed and new half graben basins developed on area which constituted previously palaeohigh structures. These syndepositional deformations are characterized by frequent slumps, synsedimentary tilting materials, sealed normal faults and progressive low angle unconformities. These tilted blocks combined to a subsidence axis migration were induced by a NE-SW trending extensional regime. This extension which affects the Tunisian margin during the Upper Cretaceous, is related to the Tethyan and Mesogean rifting phase which resulted from the combined movements of the African and European plates.

Impact of shore-parallel breakwaters on the microtidal coast of Hammam-Lif (North-East of Tunisia)

The Hammam Lif coast (North-East of Tunisia) suffered from erosion mainly after the storm that damaged the zone in 1981. To protect it, eight shore-parallel breakwaters were built. The present study is interested in presenting the effect of the protection works on the coastline behavior by using aerial photographs geo-referenced by the digital photogrammetric method and empirical relationships. The successive breakwaters made a general accretion with formation of seven tombolos and salient. The response of the coast to these structures was related to the characteristics of these latter (length, distance to coast, and spacing). The effectiveness of such protection works is shown by the evaluation of the accretion areas formed behind them. The breakwaters which are the longest, less distant from the shoreline, and less spaced formed well-developed tombolos. Whereas, the structures which are short, very far from the coastline, and far from each other caused very small tombolos and even a salient.ملخص تعرض شاطئ منطقة حمام الأنف المتواجد بخليج تونس، شمال غرب البلاد التونسية٬ إلى التعرية البحرية خصوصا بعد العاصفة التي أحلت بالجهة سنة 1981. لذلك، تم بناء ثمانية كاسرات أمواج موازية للشاطئ قصد حمايته اهتمت هذه الدراسة ببيان تأثير هذه الكاسرات في تطور الشريط الساحلي بالمنطقة وذلك بالاستعانة بصور جوية معالجة رقميا وبتطبيق معادلات نظرية. تمكنت كاسرات الأمواج المتتالية من إحداث ترسبات هامة خاصة وراءها، وقد كان تجاوب الشاطئ مرتبطا بالخاصيات التي تميز هذه الكاسرات مثل طولها،المسافة التي تفصلها عن الشاطئ والمسافة التي تفصل كل كاسرة عن التي تليها. إذ استنتجنا أن الكاسرات الأكثر طولا والأكثر اقترابا من الشاطئ ومن بعضها البعض كونت خلفها مساحات هامة من الترسبات، في حين أن المساحات الصغيرة تكونت خلف كاسرات الأمواج التي تتميز بقصرها، شدة ابتعادها عن الشاطئ وطول المسافة الفاصلة بين كاسرتين متتاليتين

Condition of development of collapse structure in the southern–central Atlassic Tunisia case study to Gafsa Basin

The Bou Omrane is an example of southern–central Atlassic Tunisian folds, this massive is presented by an anticline delimited by a NE–SW thrust. The geometry study of this anticline (hinge and subvertical layers) associated to structural and stratigraphic correlation confirms the development of structures according to “fault propagation fold” model. Using numerical software Rampe 1.3.0, the balanced cross-sections demonstrate the complicated growth of Bou Omrane anticline. The resulted structure is obtained by thrusting on breakthrough coupled to blockage of ramp on the back limb. All these condition confirm the role of diversity of tectonics events and the inheritance tectonics notion associated with the reactivation of pre-existing faults on the genesis of folds and the development of collapse structures according to more than one decollement level.

Sedimentology and environmental interpretation of the Coniacian deposits in the Saharan platform (SE Tunisia)

In southern Tunisia, the carbonate series of the Upper Cretaceous (from Turonian to Campanian) are widely present in the Saharan platform and the Chotts ridge. The study of several sections in this area permits analyzing these carbonates which help to determine their depositional environment. This study was based not only on a detailed facies but also on a microfacies analysis. Fourteen facies were identified. They could be organized in six facies associations which characterize a ramp environment ranging from tidal flat to middle ramp settings. These carbonates show considerable variations of facies and thickness with many syn-tectonic figures (slumps). This result contrasts the monotony of these series and indicates a very important sedimentary dynamics. This dynamic is controlled primarily by the reactivation of preexistent faults.

Sedimentology and sequence stratigraphy of the Zebbag formation (Upper Albian-Lower Turonian) from Saharan platform (Southeastern Tunisia)

Sedimentological and sequential analyses of the Zebbag formation, Upper Albian-Lower Turonian age, from the Tataouine basin have been carried out. These analyses were based on detailed logging of five field sections across the Dahar cliff (Southern Tunisia). Indeed, the study was built upon a detailed facies and microfacies analysis where five facies associations were found. In fact, they represent a spectrum of environments ranging from tidal flat, coastal lagoon, peritidal, shallow subtidal inner ramp, to shallow subtidal middle ramp settings. Our analysis allowed the recognition of five transgressive/regressive sequences which tend to decrease towards the south showing a progressive onlapping of the Zebbag formation carbonate on Saharan craton. The sedimentary infill of the basin documents one of the various types of lateral and vertical variations in component lithofacies assemblages. Besides, it appears that the Upper Albian-Lower Turonian time interval has recorded the interplay between the mostly eustatic and tectonic phases recorded on the Saharan platform of southern Tunisia.