South Tethyan Margin Research Articles

Mixed marine, brackish water, non-marine, and subaerial microfaunal association in the Red Marls Formation of the Western Aurès Basin (Upper Paleocene)

In the western part of the Aurès Basin (northeastern Algeria), the Red Marls of El Kantara Formation records a mixed microfaunal association of non-marine-brackish ostracoda, marine foraminifera, lacustrine charophytes, and subaerial Microcodiums. Based on the recovered biotic component, it is considered that the Red Marls of El-Kantara Formation date from the upper Paleocene (Thanetian). Seven species of brackish water (Neocyprideis raoi) and non-marine ostracoda (Frambocythere tumiensis anjarensis, Paracypretta jonesi, Paracypretta verruculosa, Limnocythere deccanensis, Darwinula torpedo and Zonocypris spirula), have been discovered for the first time in Algeria and on the south Tethyan margin. Paleoenvironmentally, the overall biotic assemblage recovered indicates the presence of a freshwater palustrine/lacustrine depositional system connected to a low energy stream/river. This indicates that marginal marine conditions were prevalent in northeastern Algeria’s far inland regions. Paleobiogeographically, the seven known ostracod species have limited distributions that are until now common only with India. However, this disproved the theory that these species are endemic to the Indian Subcontinent, which is confirmed by their association with cosmopolitan charophytes. Keywords: limnic ostracoda, charophytes, paleobiogeography, Thanetian, western Aurès, Algeria.

Biostratigraphy, carbon isotope and sequence stratigraphy of South Tethyan Valanginian successions in the Essaouira-Agadir Basin (Morocco)

A detailed stratigraphic analysis was carried out on Valanginian deposits of six Moroccan sections of the Essaouira-Agadir Basin (EAB, South Tethyan margin) in order to characterize the Weissert Event and propose correlations with the North Tethyan margin (south–east France Basin). The studied successions consist of alternating marlstone and limestone beds with sandy intercalations, and are well exposed and relatively rich in ammonites. Ammonite biostratigraphy and sequence stratigraphy were established for all successions, whereas calcareous nannofossil and carbon stable isotope analyses were performed for two and five sections, respectively. For each succession, an accurate ammonite zonal scheme allows to recognize the standard zonation established for the Mediterranean Province. A calcareous nannofossil zonation is provided for Zalidou and Aït Hamouch, considered as reference sections. The detailed biozonations allowed to ascribe an accurate age for most of the sedimentary discontinuities and depositional sequences identified in the EAB. East–west and north–south transects are established for the Valanginian depositional system. Despite some stratigraphic gaps, the Valanginian carbon isotope excursion (CIE) was recognized in most of the studied sections. The Moroccan successions are correlated with those of reference sections of south–east France i.e., the Vocontian Basin (Vergol-La Charce) and Provence Platform (Carajuan), using bio-sequence-chemo-stratigraphy. These inter-basin correlations allowed to evidence major “mid-Valanginian” and upper Valanginian eustatic regressions; the possible role of tectonics and glacio-eustacy is also discussed.

The Valanginian Weissert Event on the south Tethyan margin: A dynamic paleoceanographic evolution based on the study of calcareous nannofossils

Paleoceanographic conditions across the Valanginian Weissert oceanic anoxic event were reconstructed for the first time on the central Moroccan margin from a quantitative-based calcareous nannofossil study. Two onshore successions in the Essaouira-Agadir Basin and one offshore from DSDP Hole 416A were studied, providing a proximal-distal transect on the central Moroccan margin. The paleoceanographic conditions were reconstructed in an accurate chronostratigraphic framework. The sedimentary evolution of the Essaouira-Agadir Basin shows that sea-level variations controlled the paleogeographic context, clastic input, and nutrient availability. A thick photic zone and mesotrophic conditions favored the development of a diverse nannofossil community before the Weissert Event in the early Valanginian. In all studied successions, a collapse of the nannofossil community was recorded during the onset of the Weissert Event at the early-late Valanginian transition, and was caused by a major sea-level fall. The nannofossil community gradually recovered and reached its highest nannofossil production associated with high surface-water fertility during the Weissert Event in the late Valanginian. This eutrophication is coeval with the high and stable δ13Ccarb values of the carbon-isotope positive shift. After the Weissert Event, surface-water fertility and nannofossil production decreased but remained higher than during the early Valanginian. Additionally, the nannoconid decline started in the early Valanginian and was linked to a low sea-level. Their recovery in the early late Valanginian occurred during conditions of high sea-level and of high surface-water fertility. The central Moroccan margin is integrated into a global paleoceanographic reconstruction.

Sequences, discontinuities and water stratification in a low-energy ramp: the Early Albian sedimentation in central Tunisia

Based on a precise biostratigraphic framework stated previously, the detailed sedimentological study of eight sections of the early Albian succession of Central Tunisia made possible to refine the modalities of the Albian transgression and the related behavior of sedimentary system on the Tunisian margin. Major early Albian transgressive pulses occurred (i) at the base of the L. tardefurcata standard ammonite zone, (ii) around the top of the same zone, (iii) during the D. mammillatum standard zone, and (iv) near the top of the latter ammonite zone. They resulted in the progressive flooding of the Tunisian margin emergent since the Aptian boundary, in the disappearance of emergence evidences through time, in the southward backstepping of the carbonate shelf facies, and eventually in the homogeneization of the outer shelf marly sedimentation in the study area. The low energy of deposition of the early Albian sediments in this part of the South-Tethyan margin may be due to the deflection of winds and storms by the Coriolis forces toward the North-Tethyan margin, creating a clockwise gyre in this part of the ocean. This circulation may have enhanced upwelling currents likely responsible for phosphate mineralization, and for the oxygen depletion of deep waters, which progressively invaded the Tunisian margin, giving way to organic-rich deposits of late early Albian age. The early Albian sedimentation is then interrupted by a major hiatus of middle Albian to early late Albian age.

Early Jurassic climatic trends in the south-Tethyan margin

The Early Jurassic period was characterized by extreme environmental changes, as reflected by major global carbon isotope anomalies and abrupt changes in oxygen isotope and elemental records of marine organisms. Available data suggest an overall warm Early Jurassic climate interrupted by periods of severe cooling, with a climatic optimum during the early Toarcian. Available geochemical studies, however, have mainly focused on the northern margin of the Tethys Ocean, so that the palaeogeographic extent of these environmental perturbations, latitudinal palaeotemperature gradients and climate belt boundaries remain poorly constrained. Here we report the first stable isotope records of brachiopod shells (δ13C and δ18O values) from the Upper Sinemurian-Middle Toarcian interval in the southern margin of the Tethys Ocean (northwest Algeria). These data were used to better constrain the palaeoenvironmental evolution of the North Gondwana margin during the Early Jurassic, which likely played an important role on supra-regional climate. The diagenetic history of the analysed brachiopod shells was monitored using scanning electron microscopy, and elemental (manganese and strontium) compositions. The brachiopod δ13C and δ18O data show very similar trends as those reported for various Tethyan regions, and record negative carbon and oxygen isotope excursions near the Sinemurian–Pliensbachian and Pliensbachian–Toarcian transitions and during the Toarcian oceanic anoxic event (T-OAE). Despite these similarities, the carbon and oxygen isotope records are systematically offset towards more positive δ13C values (average +0.5‰) and more negative δ18O values (−1.0‰) compared to those obtained from sites of higher palaeolatitudes in the northern Tethyan margin. These offsets suggest a spatial heterogeneity in the stable isotope composition of dissolved inorganic carbon in the Early Jurassic Ocean and a marked latitudinal temperature gradient between the southern and northern margins of the Tethys.

Albian salt-tectonics in Central Tunisia: Evidences for an Atlantic-type passive margin

Tunisia is part of the south-Tethyan margin, which comprises Triassic evaporites and a thick series of Jurassic and Cretaceous, mainly marine deposits, related to the Tethyan rifting evolution. A survey of various Cretaceous outcrops of central Tunisia (Kasserine-El Kef area), combined with literature descriptions, shows that the style of Albian deformation changes from the proximal (South) to the distal part (North) of the margin. The southern part is dominated by tilted blocks and growth faults, which evolve to the north to turtle-back and roll-over structures. Farther North, deformation is dominated by the extrusion of diapirs and salt walls. Such a distribution of deformation strongly suggests that the whole sedimentary cover glided northward on the Triassic evaporites during Albian times, as described for the Atlantic passive margin or for the Gulf of Mexico. Subsequently, these halokinetic structures have been folded during Alpine compressional tectonics.

Gravity Data from the Teboursouk Area (“Diapirs Zone”, Northern Tunisia): Characterization of Deep Structures and Updated Tectonic Pattern

Located between eastern segments of the Atlas and Tell-Rif oro-genic belts, the “Dome zone” of northern Tunisia is characterized by the juxtaposition of various structures that mainly controlled the long geody-namic history of this part of the south-Tethyan Margin. To better understand the organization and deep extension of these structures, gravity data from the Teboursouk key area are proposed. These data include the plotting of Bouguer anomaly map and related parameters such as vertical and horizontal gradients, upward continuation and Euler solution. Compared to geological and structural maps available, they allow the identification of new deep structures and greater precision regarding the characteristics and organization of known ones; consequently, an updated structural pattern is proposed.

Link between cyclic eustatic sea-level change and continental weathering: Evidence for aquifer-eustasy in the Cretaceous

Cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic, because absence or subordinate presence of polar ice during these periods precludes an explanation by glacio-eustatic forcing. An alternative concept suggests that the water-bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge, as a function of the temperature-related intensity of the hydrological cycle, may have driven eustasy during warm climates. However, this idea has long been neglected for two reasons: 1) the large storage potential of subsurface aquifers was confused with the much smaller capacity of rivers and lakes and 2) empirical data were missing that document past variations in the hydrological cycle in relation to eustasy.In the present study we present the first empirical evidence for changes in precipitation, continental weathering intensity and evaporation that correlate with astronomically (long obliquity) forced sea-level cycles during the warmest period of the Cretaceous (Cenomanian–Turonian). We compare sequence-stratigraphic data with changes in the terrigenous mineral assemblage in a low-latitude marine sedimentary sequence from the equatorial humid belt at the South-Tethyan margin (Levant carbonate platform, Jordan), thereby avoiding uncertainties from land–ocean correlations. Our data indicate covariance between cycles in weathering and sea level: predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products (clays) in deposits that represent sea-level fall (aquifer charge>discharge). Conversely, preservation of weathering-sensitive minerals (feldspars, epidote and pyroxenes) in transgressive sediments reflects decreased continental weathering due to dryer climate (aquifer discharge>charge). Based on our results we suggest that aquifer-eustasy represents a viable alternative to glacio-eustasy as a driver of cyclic 3rd-order sea-level fluctuations during the middle Cretaceous greenhouse climate, and it may have been a pervasive process throughout Earth history.

Submarine allochthonous salt sheets: Gravity-driven deformation of North African Cretaceous passive margin in Tunisia – Bled Dogra case study and nearby salt structures

We used structural, stratigraphic and sedimentologic data, together with a comparison of nearby structures and a Bouguer gravity map, to evaluate the evolution of the Bled Dogra salt structure (northern Tunisia) during the Cretaceous. Triassic salt sheets are recognized in the northwestern region of the Tunisian Atlas. These salt sheets are the result of Cretaceous thick and/or thin-skinned extension along the south Tethyan margin. The Bled Dogra salt structure is one of these submarine allochthonous salt sheets, which was emplaced during the Early Cretaceous. The geologic framework, during this period, produces conditions for a predominantly gravity-driven deformation: extension has produced space for the salt to rise; vigorous differential sedimentation created differential loading that resulted in the emplacement and extrusion of a large volume of Triassic salt and formation of large submarine salt sheets. Geologic field data suggest an interlayered Triassic salt sheet within Albian sequences. Salt was extruded at the sea floor during the Early–Middle Albian and was initially buried by Middle–Late Albian strata. The Coniacian corresponds to a second transgressive cover onto the salt sheet after the gliding of the first salt cover (Late Albian–Turonian). In addition, this northwest Tunisian area exposes evidences for salt flow and abundant slump features at the base of a northward facing submarine slope, which was probably dominant from the Early Cretaceous to Santonian. Two gravity deformation processes are recognized: gravity gliding and gravity spreading. Acting concurrently, these two processes appear indistinguishable in this geologic context. Like the present-day salt-involved passive margins – such as the northern Gulf of Mexico, the Atlantic margin of Morocco, the Brazilian Santos basin, the Angola margin, Cadiz in western Iberia, and the Red Sea – the North African Cretaceous passive margin in Tunisia provides evidences that deformation in a passive-margin salt basin is predominantly gravity-driven deformation.

New tectono-sedimentary evidences for Aptian to Santonian extension of the Cretaceous rifting in the northern Chotts range (southern Tunisia)

Based on new structural, sedimentary, stratigraphic and seismic reflection data from Cretaceous sequences of the Zemlet el Beidha anticline of the northern Chotts range (South Tunisia), this study yields fresh insights into the geodynamic evolution of the South Tethyan margin. The rifting of the margin started in the Triassic–Jurassic and continued during the Aptian–Albian. In this last period N to NE trending extension was associated with WNW and NW trending normal faults, bounding the developing horsts and grabens structures. This tectonic framework is highlighted by strong thickness and facies changes in the Aptian–Albian series associated with slumps and syntectonic conglomerates. During the Coniacian to Santonian times, the study area was characterized by continued subsidence. Consequently, the Coniacian–Santonian series are represented by sedimentary infilling consisting of post-rift marl-rich sequences followed by limestone and marl sequences.Folds geometry and associated faults system and tectonics analysis, confirm the role of the Aptian–Albian rifting inheritance faulting in the structuring and the development of the folds and thrusts belts of the southern Tunisian Atlas during the Cenozoic inversion, in particular in the development of the ENE striking structures such as the Zemlet el Beidha anticline.

Palynofacies analysis of the Permian–Triassic transition in the Amb section (Salt Range, Pakistan): Implications for the anoxia on the South Tethyan Margin

The uppermost Chhidru Formation and the lower part of the Mianwali Formation were sampled in the Amb Valley, Salt Range, Pakistan for the study of the particulate organic matter (POM) content in order to evaluate the depositional environment during the Permian–Triassic transition. The POM content was assigned to four distinct palynofacies (palynofacies A–D). Palynofacies A recovered from siltstone within the white sandstone unit of the Upper Permian Chhidru Formation indicates a shallow marine oxic shelf setting. Recorded from the siltstone intercalations in the Kathwai Member of the basal Mianwali Formation, the Griesbachian palynofacies B is characterised by abundant acritarchs indicating a transgressive event. Palynofacies C recovered from the siltstone of the lowest Ceratite Marls (middle Dienerian) is dominated by terrestrial organic particles and indicates shallowing of the depositional environment, whereas 40cm above, palynofacies D represents transgressive oxygen depleted conditions. The comparison with sections from the Australian Tethyan margin shows that oxygen depleted conditions occurred during the Griesbachian in the Perth Basin, while in the Bonaparte Basin oxygenated conditions prevailed. Hence, oxygen depleted facies do not correspond to a single, synchronous Permian–Triassic oceanic anoxic event but depend on local geography and bathymetry.

Tithonian Chitinoidellids of the South-Tethyan Margin of the Maghreb: New data from northern Tunisia

Recent investigations based on bed-by-bed sampling of the Béni Kleb Formation (Fm) of Northern Tunisia (Kimmeridgian-Middle Berriasian) provide new data on Tithonian chitinoidellid associations. Fourteen species from seven genera ( Daciella Pop, Borziella Pop, Longicollaria Pop, Dobeniella Pop, Cubanella Pop, Popiella Reháková and Chitinoidella Doben) are first documented in Tunisia. Their stratigraphic range fits the standards proposed for other Tethyan regions. In addition, three new species are described: Chitinoidella carthagensis sp. nov., Ch. hegarati sp. nov. and Ch. popi sp. nov. They are compared to the recently revised taxa from the southern Carpathian ranges where the chitinoidellid populations were observed at various levels and revealed to be well diversified. The established biozonation is discussed and a phyletic pattern is proposed.

Albian Rudist Fauna from the Karaburun Peninsula, İzmir Region, Western Turkey

Platform carbonates bearing shallow water foraminifera and dasycladale assemblages with an Albian stratigraphic significance, crop out at two localities on the Karaburun Peninsula: Barbaros and Zeytineli. Rudist faunas collected from these localities include Toucasia seunesi Douvillé, Pseudotoucasia catalaunica Astre , Mathesia darderi (Astre), Petalodontia ? sp., and Eoradiolites sp. aff. murgensis. The overall stratigraphic significance of this fauna is consistent with the Albian age derived from micropalaeontological data. Some taxonomic elements, e.g. Toucasia seunesi, Pseudotoucasia catalaunica and Mathesia darderi possess a broad Mediterranean palaeobiogeographic distribution. By contrast, Eoradiolites sp. aff. murgensis, an advanced form resembling Eoradiolites murgensis, restricted to the Mediterranean South Tethyan margin, has a potential to be a marker for the corresponding biome. These findings fill a gap in our knowledge on Mediterranean Albian faunas considered hitherto virtually absent from Anatolia.

The “Aptian Crisis” of the South-Tethyan margin: New tectonic data in Tunisia

The distribution of Cretaceous sedimentary basins in the central Tunisian Atlas is controlled by major faults. The reactivation of these faults and the diapiric activity of the Triassic evaporites has resulted in a complex tectonic history. Most studies show that the Saharan platform in Tunisia, located on the South-Tethyan margin, was compartmentalized by an extensive tectonic phase towards the end of the Aptian, during an episode known as the “Aptian Crisis”. In the study area located in Central-Western Tunisia, the Aptian series of Jebel El Hamra and Jebel El Ajered form the core of an anticlinal fold. The Aptian russet-coloured dolomites (Serj formation) are rimmed by alternating marls and limestones of end-Aptian age and the Fahdene formation composed of Albo-Cenomanian marls. The structural and tectono-sedimentary study of Jebels El Hamra and El Ajered highlights the prominent influence of paleostructures acquired during the evolution of the South-Tethyan basin and their control on the existing geometry of the fold belt. Indeed, the present geometry of folds and faults results directly from the block tectonics developed during the Aptian. This Aptian tectonic style is characterized by extensive and/or transtensive deformation leading to multiscal fracturing in structural blocks. This deformation is characterized by a normal or strike-slip normal fault and drape fold system. The age and the extension direction (SW–NE) are fully consistent with the regional extensional phase probably disturbed by diapirism. This “Aptian Crisis” can be related to the opening of the equatorial Atlantic and Tethys oceans.

Modèle de sédimentation au passage Cénomanien/Turonien pour la formation Bahloul en Tunisie

Several multidisciplinary studies were undertaken on the Cenomanian/Turonian organic-rich Bahloul Formation. These studies, as well as our new data, led to some new palaeogeographic and palaeoceanographic interpretations. Based on these data, a depositional model was elaborated, pointing out that at the C/T transition an oxygen minimum zone (OMZ) impinged onto the South Tethyan margin through the Tunisian intrashelf basins formed during Early Cretaceous. This model allows correlating the Bahloul Fm. to other OAE-2 formations throughout the world. It also indicates that the δ 13C organic carbon seems to be a better correlation tool than δ 13C carbonate.

Effets des oscillations eustatiques couplées à une tectonique syn-sédimentaire sur la marge sud de la Téthys au Sénonien: exemple du Jebel M'rhila, Tunisie centrale

The Senonian deposits that crop out in the Jebel M'rhila area of central Tunisia record signs of six third-order eustatic oscillation cycles. These may be totally or partially correlated with the global cycles. According to the planktonic foraminifera and ostracod distributions, the deposits are Late Coniacian–Maastrichtian p.p. in age. Their setting and stacking were simultaneously controlled by relative sea-level changes and local tectonic tensional movements. This local syn-sedimentary tectonic activity affected the palaeogeography of the Jebel M'rhila area, creating a stepped submarine topography in which the medial part was uplifted and became emergent after the Late Turonian. During the Senonian, the Jebel M'rhila area became integrated with the circa-littoral Tethyan domain where deposits rich in planktonic foraminifera were episodically injected by carbonate and siliciclastic gravity-flow sediments. The latter were re-mobilized from shoals towards adjacent troughs. The Jebel M'rhila exposure is a local but a significant example of the Tunisian succession and that of the south Tethyan margin as a whole.

Upper Cretaceous (Campanian) phosphorites in Jordan: implications for the formation of a south Tethyan phosphorite giant

A record of sedimentary, authigenic, and biological processes are preserved within the Upper Cretaceous (Campanian) Alhisa Phosphorite Formation (AP) in central and northern Jordan. The AP formed near the eastern extremity of the south Tethyan Phosphorite Province (STPP), a carbonate-dominated Upper Cretaceous to Eocene “phosphorite giant” that extends from Colombia, North Africa to the Middle East. Multidisciplinary research of the AP and associated cherts, chalks, and oyster buildups indicate that phosphatic strata formed on a highly productive, storm-dominated, east–west trending epeiric platform along the south Tethyan margin. The onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the Ajlun Group. Pristine phosphates are associated with well-developed micrite concretionary horizons and contain abundant non-keeled spiral planktic foraminifera and a low diversity benthic assemblage of Buliminacean foraminifera, suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter. The bulk sediment composition and absence of Fe-bearing authigenic phases such as glauconite, pyrite (including pyrite molds), siderite, and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that “iron-pumping” played a minimal role in phosphogenesis. Authigenic precipitation of phosphate occurred in a broad array of sedimentary environments—herein termed a “phosphorite nursery”—that spanned the entire platform. This is a non-uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings, wherever the conditions were suitable for phosphogenesis. Sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing, and storm-generated, shelf-parallel geostrophic currents. Economic phosphorites formed through the amalgamation of storm-induced event beds. Stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite. Syndepositional phosphogenesis, reworking, and amalgamation to form phosphorites contrasts sharply with the principles of “Baturin Cycling”. A transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis; storm reworking of pristine phosphate facies produced granular phosphorite; and amalgamation of storm-generated granular event beds formed economic phosphorite in a single systems tract.

Reconstitution du substratum jurassique-crétacé basal du domaine des Sellaoua (marge sud-téthysienne, Algérie nord-orientale) à partir des galets du bassin mio-pliocène d’Hamman N’Baïls

The Mio-Pliocene series filling up the intermontane basin of Hammam N’Baïls (Guelma region, NE Algeria) corresponds to a fluviatile sequence beginning by polygenic conglomerates that contain several Mesozoic carbonate pebbles. The inventory and the micropalaeontological study of these pebbles attest the occurrence, at the base of the Sellaoua unit (southern Tellian foreland of Maghrebides), of a Jurassic–Berriasian carbonate-dominated series, unknown in outcrops, showing some affinities with the synchronous North-Atlasic Algerian and Tunisian ones respectively to the W-SW and to the E-NE. This series was deposited on the South-Tethyan margin, to the south of the ‘Tethyan trough’ joining the incipient Atlantic Ocean and the Ligurian Ocean. The Upper Miocene and Pliocene extensional tectonics and the halokinetic motions, induced by the presence of large Triassic evaporites masses, have probably uplifted towards the surface this Mesozoic Sellaoua-type material, which, after erosion, has supplied the herein studied fluviatile conglomerates.

Triassic palaeogeography of Tunisia

A stratigraphic, palaeogeographic and palinspastic synthesis of the Triassic successions in Tunisia is herein documented from a SSE–NNN oriented profile (Saharan Platform, Gulf of Gabes offshore, Tunisian Atlas, Tellian Units) across the northern boundary of the Gondwana Plate and the future South-Tethyan Margin. It is principally based on a reinvestigation of old data and on recent results, particularly related to new lithostratigraphic subdivisions and palaeontologic datings obtained from assemblages of benthic foraminifera, algae, palynomorphs, ammonites and brachiopods. The various Triassic successions of Tunisia are compared at the scale of the formations and sequences in the most possible precise biochronologic framework. The corresponding chart is used as reference to seven maps of the dominating depositional environments, during the following time intervals: Induan/Olenekian, Anisian, Lower Ladinian, Middle–Upper Carnian, ‘Norian’, ‘lowermost part of Rhaetian’ and ‘uppermost part of Rhaetian’. In a Peri-Tethyan domain controlled both by eustasy and extensional tectonics, the proposed maps show the alternation of regressions (marked by fluvio-deltaic siliciclastics and paralic sebkha-type evaporites) and transgressions (marked by foraminifera-bearing limestones/dolomites of internal/proximal platform, sometimes open to pelagic influences). The transgressions were particularly widespread during Carnian and ‘Rhaetian’ times and probably came from a deeper trough situated towards ENE. During a first rifting phase, the motion of normal crustal faults, strongly inclined towards the north, induced well-marked differential subsidences. In conclusion, a new palinspastic reconstruction along a south–north/SSE–NNW oriented profile is proposed. It shows a succession of shoals (flanked by lateral steps), such as the Tebaga of Medenine shoal, sub-basins (Atlas) and tilted blocks (Hairech–Ichkeul) heralding the structuring of the South-Tethyan Margin during Jurassic times.

Associations de foraminifères benthiques dans les séquences de dépôt du Trias moyen?-supérieur de l'Atlas Tunisien central et méridional

In the Central and Southern Tunisian Atlasic Range, outcrops of the evaporite-dominating Mid?- andUpper Triassic series are restricted to tectonic thickening zones (NS and EW deep fault network), such as the Rhéouis and Sbiba domes, or at the base of Alpine overthrusts (North-South Axis, “Dorsale Tunisienne”). Poor in fossils, the Triassic of Tunisia nevertheless contains successive microfaunistic assemblages; they are Ladinian?-Carnian and Rhaetian in age, and occur within the oolitic carbonate wedges (TST of the 3 d order sequences) linked to the main sea level rises on this part of the South-Tethyan margin. The Ladinian?-Carnian foraminiferal assemblage with Aulotortus praegaschei-Triadodiscus eomesozoicus characterizes two distinct levels (F3b and F4) cropping out in the Rhéouis dome (North-South Axis) and situated within the “Calcaires noirs” and the “Gypses moyens” respectively correlated to the “Dolomies de Mekraneb” and the “Dolomies de Rehach” well known on the Saharian Platform. The Rhaetian assemblage F6 corresponds to the association of Hoyenella inconstans-Agathammina austroalpina-Gandinella falsofriedli, already identified in the Fkirine Fm. (“Dorsale Tunisienne”). In the studied area, it is present within oolitic dolostones included in the thick evaporites of the Rhéouis Fm., underlining the North-South Axis overthrust, just below the Liassic Nara Fm. dolomites. The F6 dolostones can be regarded as equivalent to the dolomites of the Saharian Zerzour Fm.