Numidian Flysch Research Articles

An AHP GIS-based Methodology for the Stability Assessment of the Djebel El Ouahch Collapsees on the Numidian Flysh Formation in Northeast Algeria's Constantine Region

This study presents a comprehensive investigation into the factors underlying the collapse incident that occurred in the Jebel El Ouahch Tunnel in the Numidian flysch, Constantine region, Northeast Algeria. This methodology focuses on evaluating landslide susceptibility through the application of the Analytic Hierarchy Process (AHP) along the reconfigured path of the collapsed A1 highway tunnel section in the Constantine region of northeastern Algeria. Various influential factors contributing to landslides were analyzed, including lithofacies, slope gradient, slope aspect, elevations, fault density, plan curvature, distance from streams, and distance from roads. Utilizing a Geographic Information System (GIS), these eight causative factors were prepared for assessment. The findings indicate that slope gradient and lithology play pivotal roles as primary controlling factors in landslide susceptibility. The model exhibited a commendable success rate of 93% in predicting landslide susceptibility, as demonstrated by the area under the curve (AUC) plot generated from the landslides susceptibility map. Most of the new road falls within the highly susceptible area to landslides. This validated model can serve as an effective tool for mapping landslide susceptibility zones along the newly established road path following the collapsed tunnel. Moreover, its applicability extends to similar environments, showcasing its potential as a valuable resource for hazard assessment and planning in comparable terrains. The deviation road, as well as tunnel T01 of the A1 highway, is in a state of proven instability. It is certain that they will experience continuous, recurrent, and intense landslides. A radical solution to all the geotechnical issues plaguing this section of the highway is to reroute it far away from the Subnumidian formations. A deeper comprehension of the geological and geotechnical intricacies in challenging terrains can significantly enhance the safety and reliability of transportation networks in these demanding contexts.

Use of Electrical Resistivity Tomography for Joint Geophysical and Geotechnical Landslide Characterization: A Case Study

Abstract Slope movement processes include complex soil and rock failure mechanisms. Their study benefits from a multidisciplinary approach based on a wide range of information including geological and geomorphological mapping, and geotechnical and geophysical investigations. This research paper focuses on the characterization of the Tamentout landslide that occurs in the southeast of Jijel province. The study area belongs to the Tellian domain in which the geological outcrops are dominated by Senonian formations, composed of marl deposits overlain by Numidian flysch of Aquitano-Burdigalian age, with a sloping topography ranging from 20° to 30°. The geophysical approach consists of processing the available geophysical data of resistivity, obtained by the Electrical Resistivity Tomography (ERT). This study aims to characterize the internal structure, and the changes in water saturation within the unstable mass and locate the depth of slip surface associated with this landslide. Through this work, we combined geological and geotechnical investigations with electrical resistivity tomography (ERT). This combination gave a more detailed image of the substrate geology and structure of the landslide zone. The 2D resistivity results show that the basement consists of two main formations. The first one is a highly conductive formation with a resistivity range between 2 and 25 Ωm, a depth of 0-8 m, and is interpreted as a saturated marl-clay overlaying. The second, a hard and compact formation with a resistivity range between 50 and 200 Ωm and a depth range of 8 to 40 m, was interpreted as a substrate of tellian marls. The presence of boulders of Numidian sandstone within the two formations is materialized by a very high resistivity value ranging from 500 to 1000 Ωm. The slip surface was located on the layer with low resistivity (2-25 Ωm). The precise determination of the depth of the shear zone is of vital use in implementing mitigation measures and carrying out the stabilization work of this unstable zone. Through this work, we will highlight the advantage of the combination of available results of the geological, geotechnical investigations and electrical resistivity tomography (ERT) carried out in the study area.

Detrital zircon ages of Oligocene to Miocene sandstone suites of the Southern Apennines foreland basin system, Italy

U–Pb spot ages on detrital zircons from turbidite quartzarenites, quartz-feldspathic and volcaniclastic sandstones of the Tufiti di Tusa (TTF), Numidian Flysch (NF), Bifurto (BF), Gorgoglione (GF) and Serra Palazzo (SPF) formations, exposed in southern Italy, were detected to define their provenance signatures aiming to contribute to reconstructing the complex geodynamic evolution of the southern Apennine chain. The deposition ages of these sandstones range from Rupelian (TTF), Burdigalian p.p. -Early Langhian (NF and BF) and Langhian-Serravallian -Early Tortonian (GF and SPF). The detrital zircon ages in each deposit show different clusters. In TTF, the zircon age clusters are: 610 ± 6 Ma; 390 ± 4 Ma; 287 ± 3 Ma; 157 ± 2 Ma; 78 ± 1 Ma and 67 ± 1 Ma; 33 ± 1 Ma. In NF and BF formations, the prevalent zircon ages are clustered at 661 ± 10 Ma, 607 ± 8 Ma and 547 ± 8 Ma. In GF sandstones, the ages of detrital zircons are clustered around 672 ± 28 Ma, 458 ± 9 Ma, 297 ± 8 Ma and 24 ± 1 Ma. The sandstones of SPF contain zircons showing age clusters at 649 ± 10 Ma, 486 ± 7 Ma and 315 ± 5 Ma. Zircons and lithic fragments from TTF display a dominant provenance from Oligocene calc-alkaline effusive products located on western domains of the Mesomediterranean Microplate, and minor detritus from granitoids and metamorphic rocks of Variscan ages. Zircons of NF and BF indicate a provenance of detritus from the African Craton without evidence of Variscan or Alpine signatures. Zircons from GF and SPF show a provenance from both Variscan crystalline basement rocks forming the Alpine chain (Calabria-Peloritani Terranes) and Variscan magmatic and metamorphic rocks unaffected by Alpine tectonics, similar to Sardinia–Corsica (pro-parte) block. In addition, the Oligocene magmatic component dated at 24 Ma in GF sandstones is evidence for the maximum age of sedimentation for these deposits. In light of the recent and preliminary geochronological data acquired, a revised paleogeographic restoration could be inferred for the location of sedimentary basins during the Apennines tectonic evolution. The Rupelian sedimentation age of TTF suggests that the deposition domains of the Numidian sequences and the successive deposits of GF and SPF, were located in a more complex paleogeographic scenario along the orogenic system.

Structural styles of the Tellian fold-and-thrust belt of Tunisia based on structural transects: Insights on the subsurface oil and gas pre-salt plays

We present several structural transects throughout the internal part of the Tunisian Tell focusing on some representative structures and domains. We used also an interpreted seismic cross-section and a 3-D structural view to highlight the styles within the Tellian units in the Fernana-Adissa allochthon domain. The structural style is mainly represented by active roof-thrust and duplex structures affecting the Mesozoic-Cenozoic sequences belonging respectively to the infra-Kasseb and Kasseb units. The main decollement thrusting layer is located in the Triassic evaporites, while the roof thrust corresponds to the Upper Cretaceous or to the Paleocene shaly levels. The structural transects allow viewing that the Numidian Flysch unit presents different structural configurations and relationships with its subsurface supporting units; (1) it rests on an apparent stratigraphic contact above the underlying Kasseb nappe or even over pre-existing Triassic salt structures while elsewhere (2) it is detached above these infra-Numidian units reworking an originally downlap contact. The area is also characterized by important halokinetic movements controlling the overall architecture of the Tell fold-and-thrust belt that allows the thrusting of the whole Tellian wedge. In addition, originally apical parts of former diapiric structures were remobilized subsequently as sole thrust allowing the displacement of the Numidian Flysch. The Upper Miocene syn-folding sequences sourced by the erosion of the precedent uplifted reliefs are folded and tectonically transported along some active thrusts by the Tell tectonic units suggesting a recent reactivation and rejuvenation of thrust during the Upper Miocene to Quaternary Alpine events. Since the Late Miocene, shortening is still active today, allowing the refolding of older nappes contacts as well as rejuvenation of inherited faults.

Sedimentological and stratigraphic constraints on Oligo–Miocene deposition in the Mogod Mountains, northern Tunisia: new insights for paleogeographic evolution of North Africa passive margin

Understanding the sediment distribution and basin context of the different Oligo–Miocene successions in the eastern Maghrebides thrust belt of northern Tunisia is challenging and several contrasting models have been proposed. We present the results of detailed field mapping together with facies, microfacies and microfaunal analyses of the NE Mogod Mountains that allowed refining the Bizerte geologic map and reconstructing the Oligocene–early Miocene depositional environment of northern Tunisia. Facies characterization of the Jebel Sebaâ, Cap-Blanc and Bizerte Town sections demonstrate their deposition by submarine gravity flows typical of the Numidian Flysch Formation, rather than the Fortuna Formation as previously proposed. This is supported by the occurrence of deep marine microfossils. The association of deepwater massive sandstone facies and a high proportion of shale-clast conglomerates in the Jebel Zoukar, Ras El Korane and Jebel Sebaâ sections are interpreted as bypass channel facies, representing proximal deposition. The section at La Baie des Carrieres is distinguished by its high glauconite content, a rich microfauna of larger benthic foraminifera, Ditrupa and echinoids is typical of a shallow marine depositional environment and interpreted as part of the Gres de Bejaoua Formation. The Oligocene sections at Beni Aouf and Nefza also show Gres de Bejaoua affinities, but with some deepening of the marine environment represented by pelagic foraminifera-rich mudstones, and calcareous glauconitic sandstones. The facies distribution, depositional environments and the sediment routing of these time equivalent deposits appears to be dictated by topographic highs and inherited faults (e.g. salt dome paleohigh, El Hairech-Ichkeul ridge, Zaghouan Thrust fault and faults affecting the basin-floor). Within this framework, the northern part of the salt dome area acted as topographic high that guided the fluvial drainage pattern of the Fortuna Formation along a SW-NE trend. The absence of early Miocene deposits in the Tellian domain indicates that this area has been part of a forebulge setting since the late Oligocene. Corresponding foredeep subsidence led to submergence of the Bizerte-Nefza area and deposition of the deep marine Numidian Flysch Formation. The advance of the fold-and-thrust belt since the late Burdigalian–Langhian induced the vertical stacking of foredeep deposits over the forebulge succession.

Surface and subsurface architecture of the Kasseb structures: implications for petroleum exploration beneath the Tellian allochthon, the easternmost portion of the Maghrebides

In this study, we present field investigations based on structural analyses and interpretations in the onshore part of the Tunisian Tell, at the front of the Numidian Flysch units. Field observations allow the deciphering of the main structural styles and tectonic events in the Tell domain of Northern Tunisia, especially at the type locality of the Kasseb units. New field data collected in the Kasseb area, a key area to understand the structures of the Tunisian Tell, outline a major north-dipping normal fault located between the Numidian Flysch and the underlying imbricated fan of the Kasseb basinal units. Detailed observations allow the viewing of the Numidian allochthon as a passively transported domain at the top of the underlying duplexes, which implies an overall duplex configuration within the Tellian thrust wedge in the Kasseb area. The Kasseb basinal units represent the southernmost extent of pelagic carbonate series issued from a paleo-basinal domain situated farther north. These pelagic carbonate units have been progressively tectonically accreted within a dominantly submarine environment since the Oligocene, before reaching their current position just after the Langhian. Currently, shallow marine Oligocene-Langhian siliciclastic series rest unconformably on top of these Late Cretaceous-Eocene pelagic carbonate units. The post-Langhian compression events induced a progressive inversion of the underthrust foreland platform domain, as well as the re-folding of the overlying thin-skinned structures of the Tell domain as observed today. The Kasseb units show duplications with duplex configurations with a sole thrust located in the Paleocene shales and synsedimentary thrust tectonics active presumably during the Eocene, as the Oligocene to Early Miocene Numidian Flysch rests unconformably on top of the underlying thrust structures. The tectonic style is therefore a combination of thin-skinned and thick-skinned deformations: the thin-skinned structures correspond to the nappe structures and Tellian units thrust contacts. By contrast, the thick-skinned deformational structures correspond to the rejuvenation of deeper structures accounting for the inversion of underlying foreland structures with deep-seated thrust faults, pop-up and pop-down folded structures. For the oil/gas exploration, we propose a tectono-stratigraphic and oil occurrence conceptual model for the Tell, outlining the structural control on the hydrocarbon occurrences in different potential structural traps associated with (1) ramps and duplexes anticlines within the thin-skinned allochthonous structures as well as (2) inversional thick-skinned structures such as pop-up anticlines in the subsurface of the Tellian allochthon. We discuss potential traps associated with the nappes anticlines which should be viewed as important petroleum structural prospects emphasizing their future exploration and drilling.

Inventory and assessment of significant scientific Algerian geoheritage: Case of remarkable geosites from Orania (Western Algeria)

Orania, located in northwestern Algeria, is characterized by a diversified and fascinate geology. Ten geosites, namely Nedroma granite, Souk el Khemis Messinian Reef, Tadmaya Plateau Basalt Columns, Sassel Beach Messinian Stromatolites, Tafraoui Canyon, Ouillis Quarry, Cedar Forest Numidian Flysch, Ain Ouarka Diapir, Ain Ouarka mid-Jurassic Reefs and Tiout Sandstones Rock Art, have been selected based to their scientific and additional values. These geosites have a relatively high scientific, geoeducational and pedagogical values, due to their uniqueness, rarity, representativeness of geological elements, exceptionality, scientific knowledge and geodiversity. Regarding geotouristic values, they have high aesthetic and moderate cultural values. This inventory shows the scientific importance of the area, which may be frequented by both native and foreign visitors, including undergraduate and graduate geology students. Some geosites are affected by a degradation risk and they are damaged by human activities. The main threat of this anthropogenic pressure is from vandalism, lack of care by local community and visitors, mineral extraction, urbanization and conflagrations. Finally, Management procedures, establishment of geoparks and organization of conferences and meetings must be planned and implemented in order to increase the sustainable use and geoconservation of the analyzed sites, which have all the potential to be recognized as a geoheritage sites and deserve to be declared as a National Geological Monuments.

Numidian clay deposits as raw material for ceramics tile manufacturing

We investigate the potential use in traditional ceramics of several clays collected in the Numidian Flysch Formation (Upper Oligocene) at Tabarka, and Sejnane; Northern part of Tunisia). The valorisation of these adopts the technique of dry process, which requires a mixture of powdered clay with 7% water. This allows rapid drying of uncooked tiles. The tiles are fired at four different temperatures (1000 °C, 1050 °C, 1100 °C and 1150 °C) in order to optimize technological parameters such as shrinkage, water absorption and flexural strength. The obtained tiles show acceptable drying and firing shrinkage (not exceeding 3%), and bending strength (between 13 and 16 N/mm2) which are close to the required standards (EN ISO 10545–4, 15N/mm2 for wall tiles). The absorption ranges from 10 to 20%, which classifies these products in group BIII according to the international standards (ISO 13006 and EN ISO 10545–3). Variation of shrinkage and water absorption with the firing temperature reveals that optimal range is 1125–1150 °C for the Tabarka samples, whereas the Sejnane products might be fired at lower values (~1025 °C). The Tabarka fired pieces exhibit strong brightness. These results suggest that these latter clays could be used for white products such as sanitary ware formulations while those from Sejnane ones are more appropriated for colored (red) applications. The X-ray diffraction on the fired tiles powders shows the formation of quartz which is initially present in the crude clays, and mullite that is present at all firing temperatures. Moreover, the presence of mullite due to the richness of Al2O3 in Tabarka clays could support their refractory properties.

U-Pb detrital zircon ages and compositional features of Bifurto quartz-rich sandstones from Southern Apennines (Southern Italy): comparison with Numidian Flysch sandstones to infer source area

Two samples of quartz-rich sandstones belonging to Bifurto Formation in Southern Apennines, were studied for their petrographical, geochemical and geochronological (U-Pb detrital zircon ages) features and compared with those of sandstones from five stratigraphic sections of the Numidian Flysch in SouthernItaly. The purpose of this comparison is to assess the homogeneity and provenance of detritus because quartz-rich sandstones of both formations are coeval having Burdigalian p.p. - Early Langhian age.The depositional domain of the Bifurto formation was located on the sinking Campania-Lucania carbonate platform whereas that of Numidian Flysch was within the Lagonegro-Molise Basin east of the Campania-Lucania Platform. The Bifurto sandstones have sub-arkose - quartzarenitic composition with high Fe2O3 contents (Fe2O3 in the range 2.85 wt% - 4.83 wt%), however, the whole composition varies in the same compositional range of the Numidian Flysch sandstones.The U-Pb detrital zircon ages in Bifurto sandstones range from 2551±40 Ma to 425±9 Ma and 93% of these age data is comprised in the same time lapse of detrital zircon ages of Numidian Flysch sandstones (3047±13 to 516±19 Ma). These ages suggest a provenance area consisting of ancient orogens in which Precambrian and Silurian rocks are present. The absence of Paleozoic - Mesozoic ages excludes provenance from Variscan or Alpine rocks. On this basis, the African Craton represents the exclusive source area of Bifurto sandstones as well as of Numidian Flysch sandstones outcropping in Southern Apennines. Similar deductions have been proposed for Numidian sandstones outcropping along the Betic and Maghrebian chains from Spain to Morocco, Algeria and Sicily.

Effects of clay properties in the landslides genesis in flysch massif: Case study of Aïn Draham, North Western Tunisia

Heavy rainfall in Aïn Draham province in the North-Western of Tunisia lead to the formation of some landslides which could poses danger to lives and properties. The geological outcrops of the region mainly consist of Numidian flysch rocks. In this study, field based 15 undisturbed samples were taken, from 11 boreholes drilled in 4 landslide points, to understand the real behaviour of soils when landslides occur. For this purpose, the geotechnical characterization of all samples was carried out. The grain size distribution shows that the clay and silt fractions prevail. The clay fraction ranges between 4% and 64% with an average of 40.4%, the silt fraction ranging from 19% to 71% averaging 39.8% and the sand fraction was between 6% and 44% with an average of 19.8%. The Casagrande plasticity chart indicates that 33.3% of samples were in the high plasticity group (CH group) and 66.6% having a medium to low plasticity. The water content varies between 12% and 31%. The direct shear strength test shows that the cohesions values range from 41 KPa to 77 KPa and the internal friction angle values range widely from 12° to 27°. A statistical approach was taken to determine the most important factors responsible for the decrease of the cohesion and friction angle which are in charge of slope failure. For this, a correlation matrix of all soil properties was done. The coefficients of correlation show that the clay fraction is the most correlated parameter to the cohesion with an index of −0.872. Unfortunately, the internal friction angle is very low correlated to all geotechnical parameters. The clay fraction, as the most correlated to the cohesion, and the water content, which depends on rainfall (landslide triggering factor), were considered as two independent parameters for the establishment of a multiple linear and non-linear regression models of the cohesion. The multiple linear model showed that the cohesion decrease with the increase of water content and especially the increase of clay fraction with coefficients of −0.083 and −0.441, respectively. The non linear model showed that the cohesion decrease exponentially and linearly with the increase of the clay fraction and water content, respectively. The statistical study of the effect of geotechnical parameters on the landslide triggering, shows that the clay formations and also the increases of soils clay fraction by alteration phenomena is the crucial factor in landslides genesis. During rainfall the increase of the water content of clayey soils decreases the shear strength of soils more and more.

Combining chemical and X-Ray microtomography investigations on crustal xenoliths at Mount Etna: evidence of volcanic gas fluxing

Crustal xenoliths embedded in lavas offer chances to provide information on the lithology of the volcano basement and the process occurring during magma ascent. In this work we studied seven xenoliths found among the scoriae ejected during several paroxysms occurred between 2011 and 2016 at the South East Crater (SEC) of Mount Etna volcano. These samples are characterized by massive presence of glass and vesicles resulting in a foam-like appearance of their texture. A detailed study of their textural and chemical features was carried out combining XRF, SEM-EDS, two-dimensional observation and Synchrotron X-ray microtomography (3D imaging). This multidisciplinary approach allowed us to identify and quantify the components of the samples, individuate the likely provenance rock, ascribable to the Numidian Flysch outcropping west of the Etnean edifice. 2D and 3D imaging were successfully applied to estimate the amount of the phases constituting the samples (grains + glass + vesicles) and the degree of partial melting that occurred during the interaction with the basaltic melt and gaseous phase. The sedimentary rocks underwent profound changes led by partial melting, gas fluxing, vesiculation and selective alkali enrichment. These processes could not be driven exclusively by the prolonged contact with the molten phase but must be considered as result of a significant contribution from the volatiles rising through the plumbing system and the sedimentary basement.

Biostratigraphy, Chronostratigraphy and Paleonvironmental Reconstruction of the Palermo Historical Centre Quaternary succession

Marine deposits from the Palermo Plain were historically relevant for the Quaternary Period definition. Here we show lithostratigraphic, biostratigraphic and chronostratigraphic data collected on three boreholes in the Palermo historical centre that recovered 36.8, 42.0 and 52.0 metres of sediments overlaying the Numidian Flysch. Marine sedimentary sequences span from the Calabrian Stage (calcareous nannofossil Zone MNN 19d) to the Middle Pleistocene (dominance of medium-sized gephyrocapsids within the MNN 19f Zone) and also include a short Holocene depositional event. Calcareous nannofossil, benthic and planktonic foraminifera assemblages point to a shallow coastal environment, possibly < 50 m deep. This study highlights the need of a modern and reliable stratigraphic interpretation of lithotypes, to identify stratigraphic gaps and to draw deep geological structures in an area extremely vulnerable to seismic and hydrogeological hazard.

Sicily in its Mediterranean geological frame

The Island of Sicily is generally considered to be the geological link between the North African Fold Belt and the Appennines, in Italy. This comes from a cylindristic meaning and is only partly exact. As a matter of fact, Sicily is essentially Greek; Ionian. Up to Middle Cretaceous time, the Sicilian area was a submerged shoal in the sea or the Panormide area, bordering the Ionian Ocean. This shoal lay between the future North African Fold Belt and the Appennines, forming an intermediate link between the Appenninic, Apulian, Panormian and Tunisian platforms. It was only during the Middle to Upper Cretaceous that the Atlantic and Ligure Oceans merged, making a continuous relationship between the Appenninic, Sicilian and North African sedimentary series. The key time periods are the Permian, Cretaceous and Oligo-Miocene periods leading to the formation of the actual Calabro-Sicilian arc. From the Permian to the present, the Sicilian geological history pertains to three oceanic domains: Ionian, Ligurian and Atlantic, of which the Ionian and Ligurian were under the influence of Tethys (Neo and Paleo-Tethys). The Tethysian identity of Sicily constitutes the major aspect of its geological history. However, the European and African plate tectonic movements complicated its structure. During the Middle Miocene subduction, southern Sicily became African, meanwhile its north-eastern part became, in Pliocene time, Maghrebian by accretion. Sicily is thus a truly geological patchwork, but its main section remains Ionian and now constitutes a link between North Africa and the Appennines. With older data, but also by means of recent results, we will replace Sicily in its Mediterranean frame, giving the mean stages of its paleogeographical and then its tectonic evolution. We will review the calabro-sicilian arc evolution from the Oligocene, developing the actual context and recalling the main fundamental play of the Numidian flysch.

Permian-Cenozoic deep-water carbonate rocks of the Southern Tethyan Domain. The case of Central Sicily

We present an integrated stratigraphy of the outcropping and buried Permian-Cenozoic deep-water carbonate successions, forming some of the tectonic units mostly buried beneath the Late Neogene sedimentary cover in the fold and thrust belt of Central Sicily. Three main successions, pertaining to the well known Lercara, Imerese and Sicanian domains, have been reconstructed on the basis of a detailed facies analysis, seismostratigraphic interpretation, bio -stratigraphy (mostly based on palynological data) and comparison between outcropping and subsurface deep-water sediments. The main results reveal a continuous sedimentation of the deep-water Southern Tethyan Sicilian succession since the Permian to Cenozoic. In detail: a ) the Permian-Middle Triassic terrigenous and carbonate deep-water successions, outcropping or buried in the Cerda, Lercara-Roccapalumba and Sosio Valley regions, are well comparable to each other and represent the common substrate of the Mesozoic-Paleogene Imerese and Sicanian carbonate successions; b ) the Mesozoic-Paleogene deep-water carbonates, when compared among them, reveal the occurrence of different sedimentary successions (Imerese and Sicanian); c ) the Oligo-Miocene foreland basin terrigenous sediments (Numidian flysch) clearly differ from the coeval foreland pelagic to open-shelf carbonates. The paleogeographic reconstruction envisages: a ) during the Permian-Triassic, a wide subsident continental rifting area, bordered by a shallow-water domain periodically supplying the basin with calciturbiditic to gravity flows sedimentation (rift stage of the Southern Tethyan margin); b ) during the Jurassic-Paleogene, two different deep-water basins developed in a context of a post-rift stage. The different sedimentation reflects the location of the Imerese and Sicanian basins, respectively, along adjacent rimmed shelf and stepped carbonate platform margins.

Gravity constraints on the underground structural framework and associated volcanism of the Maghrebian allochthonous domain: The Sejnene Numidian flysch, Tunisian Tell

Tectonic framework of the Neogene Numidian flysch is one of the primary subjects in the Tell of northern Tunisia for understanding the late Miocene kinematics around the Mediterranean Basin. Belonging to the extreme North of Tunisia, this domain is marked by a confuse structuring. Much of the Sejnene area is represented by thick Neogene Numidian flysch, which is widely exhibited around the Mediterranean and directly deposited on Mesozoic and Cenozoic strata.Gravity measurements covering the Sejnene area coupled with geological outcropping data were used to constrain the deep structural setting of the Neogene Numidian flysch and its associated volcanic outcrops. Integration of different gravity processed maps, leads us to highlight relationship between outcropping and sealed deformed structures and proposed a tectonic framework model for raised volcanic rock within the thrust sheet system. Maps resulted from gravity processing reveal structural variations marked by several geometries and oriented lineaments. This structuring suggests that the Sejnene study area is marked by two tectonic framework domains: to the North, the areas is mainly characterized by NE- and E- oriented subparallel lineaments corresponding to thrusts, reverse faults and strike slip reverse fault system. Conversely to the South, the same master trends are crossed by others NW- and N- trending transversal and deep-seated lineaments corresponding to strike slip reverse faults.Neogene NW- then N- striking compressional phases have induced inversion of inherited structures that are fossilized by rejuvenation of ancient faults affecting the basement. The final obtained structural setting suggests South-verging evolution of the Numidian domain under low-angle decollement layer to the North and under deep-seated thrusting and strike slip movements to the South. Master strike slip movements induced rising of lithospheric volcanic rocks.Geophysical and geological study of the Sejnene area provides a new insight into tectonic framework of the Numidian flysch and the associated Mogods volcanic rocks. Structuring of this Tellian domain well correlated with orogenic episodes of the western Mediterranean and seems to be related to the Alpine orogeny.

Deep controls on foreland basin system evolution along the Sicilian fold and thrust belt

Abstract Neogene-Quaternary wedge-top-basins arose during the Sicilian fold and thrust belt (FTB) build-up. The infilling sedimentary successions are: i) middle-upper Miocene silicoclastics succession, accommodated on top of the accreted Sicilide and Numidian flysch nappes; ii) upper Miocene-lower Pliocene deepening-upwards sediments unconformably overlying the inner Meso-Cenozoic deep-water, Imerese and Sicanian thrust units; iii) Upper Pliocene-Quaternary coastal-open shelf deposits unconformably covering (in the outer sector of the FTB) a tectonic stack (Gela thrust system). These successions are characterized by a basal unconformity on the deformed substrate believed to be the depositional interface common both to the coeval wedge-top and foredeep basins. The tectono-sedimentary evolution of the syn-tectonic basins was controlled by the progressive deepening of the structural levels, which were active during the growing of the FTB. The palinspastic restoration of a crustal geological transect in central Sicily points to: i) the occurrence of two subsequent, basal main thrusts (MT1 and MT2) active during the Neogene-middle Pleistocene tectonic evolution, as well as ii) a decrease in slip- and shortening-rate, estimated for the later MT2 as compared to earlier MT1 basal main thrust. The foreland-basin system evolution recorded during these two steps suggests: – the regional lithofacies distribution, during late Tortonian-early Pliocene, accounted for a wide depozone including the Iblean plateau and its offshore;– a crucial change was recorded by the late Pliocene-Pleistocene wedge-top depozone, when the deeper basal main thrust (MT2) involved and thickened (in the inner sector of the FTB) the crystalline basement (thin- to thick-skinned thrust tectonics); this change influenced the depozones, progressively narrowing up to the present-day setting. As regards this general evolutionary framework, thin-skinned and thick-skinned thrust tectonics can be recognized in the Sicilian FTB evolution. The late Tortonian-early Pliocene, thin-skinned thrust tectonics include two main tectonic events, a “shallow-seated” Event 1 and a “deep-seated” Event 2, with the Pliocene-Pleistocene thick-skinned thrust tectonics representing a third tectonic event (Event 3).

First U–Pb detrital zircon ages from Numidian sandstones in Southern Apennines (Italy): Evidences of African provenance

Two samples of quartz-rich sandstones collected in the Numidian Flysch of Southern Apennines (Italy) have been studied to highlight the provenance of detritus using radiometric dating by LA-ICP-MS of detrital zircons and to compare the obtained ages with those of the Betic and Maghrebian Chains. The provenance of quartzose detritus from European or African Plates is still debated in these Chains, accordingly the ages of the detrital zircons can contribute significantly to discriminate the origin of the quartzose supply.The U–Pb zircon ages (n=47) vary from 3047±13Ma (Mesoarchean) to 516±19Ma (Cambrian). The predominance of Paleo-Proteozoic ages (2500–1600Ma) and the lack of Hercynian and Alpine ones suggest a provenance of the Numidian supply from North-African cratonic areas during the early–middle Langhian, when the Numidian successions of Southern Apennines were deposited. In addition, a cluster of ages at 773±24Ma and 668±12Ma in one sample and at 664±17Ma in the other sample, calculated on zircon domains with magmatic zoning, testify to an important contribution from Neo-proterozoic “granitic” rocks widely outcropping in the North-African Craton.The age data on detrital zircons from Numidian sandstones in Southern Apennines overlap those found in the Numidian sandstones widespread in the Betic Cordillera and in the Maghrebian Chain from south Spain to Sicily. This suggests that the entire depositional zone in which Numidian Flysch deposited, was fed from a southerly source represented by the African Craton where Archean, Proterozoic and Cambrian rocks widely crop out from the Atlantic coast to the Hoggar and Tibesti Massifs. Finally, it must be outlined that a Meso-Archean zircon age (3047Ma) has been found in the Numidian Flysch of the Southern Apennines whereas in the Numidian Flysch of the Maghrebian Chain, zircons older than Paleo-proterozoic (1840Ma) have not yet been found.

Stratigraphic and provenance evolution of the Southern Apennines foreland basin system during the Middle Miocene to Pliocene (Irpinia-Sannio successions, Italy)

The paper deals with original stratigraphic, petrographic and structural data concerning the evolution of the southern Apennines chain (Italy). The main Langhian to Pliocene deposits cropping out in the northern sector of the southern Apennines foreland basin system (Sannio-Irpinia area) have been studied and correlated in order to document the effects of tectonic changes on the evolution of sandstone detrital modes and stratigraphic architecture. The studied sandstone units can be grouped in five key intervals: a) Numidian Flysch, mostly formed by Langhian mature quartzarenitic deposits and conformable Serravallian post-Numidian successions, formed by arkosic and calciclastic arenaceous-pelitic beds (foreland depozones); b) Langhian to Tortonian San Giorgio Fm., mostly composed of quartzofeldspatic sandstones (foredeep depozone); c) Tortonian to Early Messinian, quartz-feldspatic and partly sedimentary-carbonatoclastic petrofacies, thrust-top successions (Vallone Ponticello, Villanova del Battista and San Bartolomeo fms.); d) Late Messinian quartzolithic to quartzofeldspatic sandstones (Torrente Fiumarella, Anzano Molasse and Tufo-Altavilla unit), which can be referred to infilled thrust-top basins; e) unconformity-bounded Pliocene quartzofeldspatic sandstone strata (wedge-top depozones), characterized by synsedimentary tectonic activity.Detrital modes of the Serravallian through Middle Pliocene sandstones of the southern Apennines foreland basin system testify clear provenance relations from the accreted terranes forming the southern Apennine thrust-belt. The studied clastics show almost the same blended (quartz-feldspatic) composition; this condition could be related to the tectonic transport over thrust ramp of source rocks, as suggested by the tectonic evolutionary model. This study, dealing with sedimentary provenance analysis and tectonostratigraphic evolution, provides an example of the close relations between clastic compositions and foreland basin system development in southern Apennines.

First African diamonds discovered in Algeria by the ancient Arabo-Berbers: History and insight into the source rocks

It is generally believed that the first diamonds ever found in Africa were discovered in South Africa in 1867. Actually, three diamonds had already been found in 1833 near Constantine (Algeria). One of these, still preserved, shows radiohalos that suggest an old age. It could be a Sahara diamond reworked in more recent sediments, possibly the Oligo-Miocene Numidian Flysch; however, this occurrence remains uncertain. The ancient Arabs or Berbers also knew of diamonds in the Reggane region (Algerian Sahara), at Bilād al-mās (▪: “country of the diamond”). Since 1975, some 1500 diamonds have been collected from the alluvial deposits of this area. A manuscript written in Arabic in 1851 mentions diamonds in this region and describes their source rock, looked for in vain by modern geologists. The description is unclear, but might refer to Devonian oolitic ironstones. Modern investigations would rather suggest a kimberlitic primary source with intermediate Early Cretaceous palaeoplacers.

The Numidian Flysch: a guide formation for the reconstruction of the paleogeography and tectono-sedimentary evolution of southern Apennines

Abstract The Numidian Flysch shows constant lithological features from the strait of Gibraltar to central Italy. It is characterized by quartzarenites showing grains of monocrystalline, rounded and frosted quartz, and by kaolinitic mudstones. This research has pointed out that in the southern Apennines 1) the Numidian Flysch was deposited exclusively in the Campania-Lucania carbonate platform and in the Lagonegro-Molise basin, both located on the Apulian continental margin, and never is present in tectonic units originated from the oceanic area located west of that margin; 2) in the axial zone of the Lagonegro basin it stratigraphically follows a formation consisting of varicoloured clays (Argille Varicolori Auct.); 3) its age is limited to the early-middle Langhian, that is to say, it begins to sediment about 7 million years later than in the Maghrebian chain and deposited for a time span limited to 1–1.5 Ma. The thickness of the Numidian Flysch gradually decreases towards the north from about 600–1,000 meters to a few tens of meters and in some of the northeastern outcrops it is represented only by some layers of quartzarenites. This is accompanied by a decrease in size of the particles becoming more and more finer. In addition, northwards and frequently in the same section, a lower mineralogical and textural maturity (from quartzarenites to litharenites, and presence of abundant matrix, sub-angular, polycrystalline and deformed quartz grains) is well recognizable. In the Campania-Lucania carbonate platform the Numidian Flysch evolves to pelagic marly-clayey deposits, followed by mineralogically immature turbidite sandstones of Serravallian age. In the Lagonegro basin the Numidian Flysch replaces Cretaceous-lower Miocene turbidite deposits, consisting of limestones and red marls, on the western side of the basin, variegated clays in the axial zone and calcareous turbidites or variegated clays in the eastern side. Since the late Langhian, it evolves to pelagic sediments followed by lower Tortonian immature turbidite sandstones. In the successions of the Molise basin the Numidian Flysch is interbedded in a succession consisting of calcareous turbidites and pelagic limestones and marls, reaching the Messinian. The lithological features and the age of the Numidian Flysch in central-southern Apennines, therefore, point out an evolution different from that of the Numidian Flysch of the Maghrebian chain. During the early Miocene, a paleogeographic barrier or other unknown obstacles prevent Numidian sands from reaching the south-Apenninic domains. In the early Langhian, the disappearance of these obstacles allows sands to reach the deep basins located on the Apulian margin. In the late Langhian the Numidian sedimentation is canceled and replaced by mainly pelagic sediments, which will evolve to foredeep deposits in the Serravallian-Messinian time span. In addition, the significant presence of feldspathic and lithic grains testifies a double detrital supply: polycyclic quartzose sands and kaolinitic mudstones from the African craton and metamorphic and plutonic grains from the Hercynian or older rocks of the internal units of the southern Apennines. The Numidian Flysch of the southern Apennines allows to assign the tectonic units in which is present to the Campania-Lucania carbonate platform or to different zones of the Lagonegro-Molise basin and therefore is of great importance in the reconstruction of both the Mesozoic-Cenozoic paleogeography and a tectono-sedimentary evolution very difficult to decipher, given the convergence of sedimentary facies in the Apenninic deep basins since Cretaceous to Miocene, the presence of several tectonic phases and of out of sequence and back-thrusts.