Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Ahnet and Mouydir basins, Central Sahara)

Abstract. The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The structural framework of the platform results from the accretion of Archean and Proterozoic terranes during the Pan-African orogeny (750–580 Ma). The Ahnet and Mouydir basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches, bounded by inherited Precambrian sub-vertical fault systems which were repeatedly reactivated or inverted during the Paleozoic. Major unconformities are related to several tectonic events …

Deep-rooted “thick skinned” model for the High Atlas Mountains (Morocco). Implications for the structural inheritance of the southern Tethys passive margin

A re-interpretation of the deep structure of the High Atlas is presented through integration of geophysical and geological data, highlighting the architectural significance of the southern Tethys palaeomargin. Previous crustal models suggest the occurrence of a flat intra-crustal detachment at a depth of � 20 km, a zone where surface thrusts merge and below which the lower High Atlas crust appears continuous. However, within this study seismic refraction data, electrical resistivity surveys and gravity modelling all appear to detect a jump in crustal thickness between the High Atlas and the northern plains. We interpret these data as penetration by thrusts within the ‘‘South-Atlasic fault’’…

Micro- to macro-scale internal structures, diagenesis and petrophysical evolution of injectite networks in the Vocontian Basin (France): implications for fluid flow.

27 pages; International audience; This study discusses the characteristics of two Lower Cretaceous injectite networks in the Vocontian Basin (SE France) using combined structural, sedimentary, diagenetic, and petrophysical analyses. Internal structures, at both the macro- and micro-scale, and diagenetic phases characterising these injectite networks have been described. Simultaneously, precementation porosity values were estimated and parameters controlling the geographical distributions of these values were analysed and statistically tested. All of the data were integrated so as to reconstruct the spatial evolution of the porosity from the time of injection to modern times through five maj…

Sedimentary dynamics and extensional structuring related to early Cretaceous rifting of Neocomian and Barremian deposits of the interior basin of Gabon.

18 pages; International audience; Recent field and subsurface data about the early Neocomian N'dombo series and the Neocomian to mid-Barremian Schistes series of the interior basin of Gabon further our understanding of the initial stages of early Cretaceous N40–60E extensional rifting. The syn-rift series comprise fluvial–lacustrine claystones–sandstones, rare conglomerates, and carbonates. The syn-rift fill begins with braided-stream feldspathic sandstones. These are overlain first by fluvial–lacustrine deposits and then by predominantly lacustrine–palustrine claystones, which are potential petroleum source rocks. The claystones are eroded in part and are capped by the pre-Aptian angular u…

Geometric and morphologic evolution of normal fault planes and traces from 2D to 4D data

Abstract The detailed 3D geometry of normal fault planes is described and analysed using datasets from outcrop studies (2D), seismic surveys (3D) and analogue models (4D). Different geometric configurations of simple isolated normal faults are studied by reference to processes of normal fault propagation. When a normal fault propagates without interacting with other fault zones, the entire border of the principal plane displays characteristic connected secondary structures. These secondary structures cause bifurcations of the principal fault terminations. The along-strike terminations of the principal plane display typical bifurcation configurations (‘ear geometry‘). The orientation of the …

Le bassin stéphanien des Cévennes (Massif Central) : un exemple de relation entre sédimentation et tectonique extensive tardi-orogénique dans la chaîne varisque

ResumeLa nature syn-sedimentaire des failles bordieres du bassin houiller stephanien des Cevennes est mise en evidence par la distribution des depots conglomeratiques et greseux de cone alluvial au pied des paleoreliefs de socle. Elle est egalement attestee par les fortes variations d’epaisseur caracterisant les niveaux greseux, silteux et de charbon se distribuant au centre des sous-bassins ainsi que par les directions centripetes d’apport sedimentaire.A l’echelle du bassin, la nature extensive de la structuration syn-sedimentaire est mise en evidence par des failles normales d’orientation NW-SE, NE-SW et NNW-SSE, a fort pendage, structurant les sous-bassins en demi-graben a geometrie sync…

Spécimens à la loupe. Les collections naturalistes du Muséum national d'histoire naturelle

À proposLe Muséum national d'histoire naturelle de Paris, partenaire privilégié pour l'enseignement des sciences de la nature et de l'homme, compte près de 66,8 millions de spécimens d'une valeur inestimable. Cet ouvrage permet aux enseignants de mieux appréhender la richesse des collections des muséums de Paris et de province, trouver des points d'appui pour travailler avec leurs élèves, d'envisager des animations sur place, avec les muséums, ou en ligne, grâce aux collections numérisées, s'approprier ces objets d'étude au service de la connaissance et aux fondements de la culture scientifique.Rédigé de manière accessible par des scientifiques, chaque article montre différentes facettes de…

Characterisation of Mesozoic–Cenozoic deformations and palaeostress fields in the Central Constantinois, northeast Algeria

Abstract Tectonic analysis in conjunction with the microtectonic study of Mesozoic–Cenozoic series of the Central Constantinois of Algeria are used to reconstruct the sequence of tectonic phases since Cretaceous times. The retrotectonic method used to marshal the microtectonic data makes it possible to distinguish deformations related to Mesozoic tectonic phases from those associated with Cenozoic pre- and post-thrust sheet phases. A N120°E extensional and a N180°E compressional phase are highlighted in Albian–Cenomanian and latest Maastrichtian times, respectively. The Cenozoic era is marked by a series of three compressional phases oriented N90°–120°E in the Late Eocene, and N20°–30°E and…

Progress on bringing together raptor collections in Europe for contaminant research and monitoring in relation to chemicals regulation.

Paola Movalli et al.

Early Jurassic normal faulting in a carbonate extensional basin: characterization of tectonically driven platform drowning (High Atlas rift, Morocco).

18 pages; International audience; This paper describes a tectonostratigraphic model of the synrift evolution of the Early Jurassic High Atlas rift of Morocco. The model is constrained by mapping of a set of inverted extensional blocks, by facies analysis of carbonate platform and turbiditic to hemipelagic synrift deposits, and by high-resolution (n 3 100 ka) biostratigraphy of the Early Jurassic succession. The chronostratigraphic packages of the High Atlas of Rich vary significantly in thickness, facies and architecture from one tectonic block to another. Our study shows how synrift strain varied in space and time over a long time interval (14 Ma) around the High Atlas rift. Initially, in …

The origin and glaciodynamic significance of sandstone ridge networks from the Hirnantian glaciation of the Djado Basin (Niger)

The Djado Basin (Niger) was located beneath the inner part of the Late Ordovician ice sheet. The Felar-Felar Formation consists mainly of glaciomarine deposits, associated with the major ice sheet recession within the glaciation, and is bounded by two glacial unconformities. Structures corresponding to sandstone ridges are found within the Felar-Felar Formation. Sandstone ridges are several metres high, about 10 m wide and hundreds of metres long. These structures are organized in extensive anastomosed to subpolygonal networks. The association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub-glacial conditions for their origin. San…

Erratum to “Sedimentary dynamics and extensional structuring related to Early Cretaceous rifting of Neocomian and Barremian deposits of the interior basin of Gabon” [J. African Earth Sci. 51 (5) (2008) 239–256]

Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)

The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposi…

Correlations et interpretations genetiques dans les formations recifales oxfordiennes de la haute vallee de l'Yonne (sud-est du bassin de Paris, France)

Abstract Novel palaeoenvironmental interpretations and high-resolution correlations in Oxfordian reefal formations (fig. 1, 2) are provided by genetic stratigraphy. The main objectives of this study are: (1) to determine environmental conditions and the zonation of depositional environments; (2) to propose a genetic sequence framework and correlations of the outcrop sections; (3) to evaluate a possible tectonic control on coral buildup settlement and growth both at local scale.

Subglacial to proglacial depositional environments in an Ordovician glacial tunnel valley, Alnif, Morocco

Abstract This paper presents the sedimentary analysis of an exceptional Ordovician glacial tunnel valley in the eastern part of the Anti-Atlas. The valley infill comprises two major glacial erosion surfaces (striated pavements) each overlain by a fining-upward glacial unit. These units are composed of five distinct facies associations, recording the evolution from subglacial to proglacial environments, and an additional sixth facies association, overtopping the tunnel valley infill, and associated with post-glacial environments. The tunnel valley infill also records a transitional environment between the subglacial and proglacial settings, which is compared with the Antarctic ice-sheet marg…

Marqueurs d'une structuration extensive jurassique en arrière de la marge nord-téthysienne (monts du Mâconnais, Bourgogne, France)

Structural analysis of extensional faults in the Mâconnais Hills shows that low-intensity extensional phenomena occurred back from the passive margin of the Ligurian Tethys, the axis of which lay some 400 km southeast of the study area in Mid-Jurassic times. Storm-induced rip current directions and coral lens positions suggest that the palaeotopography was maintained by early faulting.

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

Pluridisciplinary fieldwork highlights features generated by an extended ice-sheet in the Djado Basin during the Hirnantian. Two glacial palaeovalley systems associated with glacial pavements and separated by thin glaciomarine interstadial series are revealed. Rigid glacial pavements characterised by abrasion erosion are differentiated from soft glacial pavements characterised by soft-bed deformation. Glacial pavements are associated with subglacial bedforms such as megaflutes, flutes and meltwater channels. They are also associated with clastic dykes and glaciotectonic structures such as deformed flutes, subglacial folds and duplex structures. This record demonstrates that ice was warm-bas…

Modelo de cabalgamiento profundo para el Alto Atlas (Marruecos). Implicaciones sísmicas en la zona de colisión entre Eurasia y Africa

Previous crustal models of the High Atlas suppose the existence of a mid-crustal detachment where all the surface thrusts merged and below which the lower crust was continuous. However, both seismic refraction data and gravity modeling detected a jump in crustal thickness between the High Atlas and the northern plains. Here we show that this rapid and vertical jump in the depth of Moho discontinuity suggests that a thrust fault may penetrate the lower crust and offset the Moho (deep-rooted “thick skinned” model). The distribution of Neogene and Quaternary volcanisms along and at the northern part of the High Atlas lineament can be related to the beginning of a partial continental subduction…

Sedimentary dynamics and structural geology of pre-rift deposits of the interior basin of Gabon

Abstract Recent studies combining field data (facies and paleocurrent analyses, structural surveys), sub-surface data (core analyses, well logs, seismic sections) and palynological data provide insight into the sedimentary dynamics of pre-rift deposits of the interior basin of Gabon and their structural and paleoclimatic setting. These sedimentary deposits belong to the Noya, Agoula and M’vone series of Late Precambrian to Jurassic age. Although these deposits are potential sources of petroleum, they are partly known because of poor outcrop in a wet equatorial climate, low density and uneven distribution of exploration wells and poor seismic survey coverage. The pre-rift deposits reflect fl…

Lithospheric strenght control over depositional environments and foreland accommodation in the Western USA Basin during the Early Triassic

International audience

Mise en évidence d’une dynamique de fleuves de glace durant la glaciation ordovicienne par l’enregistrement géomorphologique

On Contemporary Ice streams the most important factor controlling polar ice-sheet sheet stability and ice flowing occurs in ice streams. On Pleistocene Ice Sheet, Ice stream can be located using several geomorphologic criteria predict from known characteristic of contemporary ice streams, these criteria defining the conceptual Ice Stream land system model. But nowadays, during fossil glaciations, ice streams characterization is still poorly documented and only few studies illustrate fast ice velocity. In this work, we characterize geomorphological markers of ice stream activity in order to define the Ordovician ice stream glacial landsystem. The study area is located in Sahara from Niger to…

Calculating the long-term displacement rates of a normal fault from the high-resolution stratigraphic record (early Tethyan rifting, French Alps)

Displacement rates of normal faults deduced from stratigraphic data are often unreliable. Here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a highresolution time-frame established by biostratigraphy and physical stratigraphy. Our example is the Ornon normal fault bounding the Early Jurassic Bourg-d’Oisans Basin formed during Tethyan rifting. We show that motion on the fault was discontinuous when examined at high resolution and over a long time interval. During a first interval (Hettangian to Sinemurian Arietites bucklandi zone) a low rate of displacement (= 202–423 m Myr -1 ) coeval with diffused exte…

Porewater pressure control on subglacial soft sediment remobilization and tunnel valley formation: A case study from the Alnif tunnel valley (Morocco)

25 pages; International audience; In the eastern part of the Moroccan Anti-Atlas Mountains, the Alnif area exposes a buried Ordovician glacial tunnel valley (5 km wide, 180 m deep) cut into preglacial marine sediments. The preglacial sedimentary sequence, deposited in a marine environment, is characterized by a typical "layer-cake" configuration of permeable (sand) and impermeable (clays and early-cemented sandstones) layers. At the base of the tunnel valley, a discontinuous and fan-shaped glacial conglomeratic unit 10 to 15 m thick occurs, erosively deposited over preglacial marine sediments. The conglomeratic unit is composed of preglacial intraclasts embedded within a sandy matrix. Both …

Dynamique sédimentaire des dépôts post-rift du bassin intérieur du Gabon.

14 pages; International audience

Sedimentation in the Kandi extensional basin (Benin and Niger): fluvial and marine deposits related to the Late Ordovician deglaciation in West Africa

Abstract The Lower Paleozoic detrital succession of the half-graben Kandi Basin in West Africa (Niger-Benin) is about 600 m thick and rests unconformably on the Pan-African basement. Along the western edge of the basin, the base of the succession locally features large glacial fault-bounded paleovalleys. These valleys are filled by the lowermost continental deposits of the Were Formation characterized by massive diamictites with dropstones, and coarse to conglomeratic sandstones associated with large-scale channel structures and internal erosional truncations. The uppermost braided-river deposits of the Were Formation deposited across the entire basin are overlain by the Late Ordovician–Ear…

Fluid-pressure controlled soft-bed deformation sequence beneath the surging Breiðamerkurjökull (Iceland, Little Ice Age).

16 pages; International audience; The general subject of this paper is subglacial deformation beneath Breiðamerkurjökull, a surging Icelandic glacier. More specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation. During Little Ice Age maximum, the two outcrops studied, North Jökulsarlon (N-Jk) and Brennhola-Alda (BA), were located at 2550 m and 550 m respectively from the front of the Breiðamerkurjökull. Sedimentological analysis at the forefield of the glacier shows thick, coarse glaciofluvial deposits interbedded with thin, fine-grained shallow lacustrine/swamp deposits, overlain by a deformed till unit at N-Jk. BA…

Segmentation and differential post-rift uplift at the Angola margin as recorded by the transform-rifted Benguela and oblique-to-orthogonal-rifted Kwanza basins.

29 pages; International audience; We analyse tectonic and sedimentary field and subsurface data for the Angola onshore margin together with free-air gravity anomaly data for the offshore margin. This enables us to characterize the mode of synrift tectonism inherited from the Precambrian and its impact on the segmentation of the Angola margin. We illustrate that segmentation by the progressive transition from the Benguela transform-rifted margin segment to the oblique-rifted South Kwanza and orthogonal-rifted North Kwanza margin segments. The spatial variation in the intensity of post-rift uplift is demonstrated by the study of a set of geomorphic markers detected in the post-rift succession…

Neocomian to early Aptian syn-rift evolution of the normal to oblique-rifted North Gabon Margin (Interior and N'Komi Basins).

18 pages; International audience; The North Gabon coastal rift basins consist of a set of 130–150 long-segment asymmetrically tilted half grabens (Interior Basin) and 000–020 short-segment en échelon half grabens (N'Komi Basin) separated by 040–060 major transverse faults. Tectono-sedimentary analysis of field and subsurface data reveals the control exerted by extensional tectonism over continental sedimentation. During Berriasian to early Barremian times, uniform uniaxial 040–060 extension was responsible for the stretching of the brittle upper crust over a 100-km wide domain. During late Barremian–early Aptian times, the main locus of extension stepped westward resulting in severe end-rif…

Tectonics of the Northern Bresse region (France) during the Alpine cycle

International audience; Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE-SW, E-W and NW-SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N-S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE-SW in the graben. After a tran…

Depositional model in subglacial cavities, Killiney Bay, Ireland. Interactions between sedimentation, deformation and glacial dynamics

Subglacial meltwater drainage and sedimentary processes play a major role in ice-sheet dynamic but there is a lack of study of subglacial environment because modern ice-sheet beds remain inaccessible. Previous authors already intended to provide diagnostic criterion and recent investigations suggest that fluid pressure variations are a key factor in subglacial environment. This paper investigated the late Devensian sedimentary record in order to describe subglacial sedimentological facies associations and deformation features related to fluid overpressures. We used an integrated approach, based on stratigraphy, sedimentology and deformations styles to demonstrate a subglacial depositional m…

Hafnium-neodymium isotope evidence for enhanced weathering and tectonic-climate interactions during the Late Cretaceous

<p>Over million-year timescale the carbon cycle evolution is driven by mantle CO<sub>2</sub> degassing (source) and by continental weathering that drawdowns atmospheric CO<sub>2</sub> through silicate weathering reactions (sink). Based on a novel geochemical proxy of chemical weathering intensity (i.e. using measurements of Hf and Nd isotope ratios in clay-size fractions of sediments) and clay mineralogy, we discuss the links between tectonic, continental weathering and climate evolution during the late Cretaceous. That period records the very first step of the last greenhouse to icehouse transition and is concomitant to …

Does porewater or meltwater control tunnel valley genesis? Case studies from the Hirnantian of Morocco.

18 pages; International audience; Several Ordovician tunnel valleys are exposed in the Moroccan Anti-Atlas Mountains, including the Alnif and the Foum Larjamme tunnel valleys, located 150 km away from each other. Sedimentological and deformational analyses of these two glacial troughs reveal that differing processes lead to their formations.The Alnif tunnel valley contains numerous deformation structures within sediments both below and above the main glacial erosion contact surface. Ball-structures and clastic dykes occur within preglacial sediments down to 35 m below glacial incisions while overlying glacial sediments contain fluted surfaces, clastic dykes, dewatering structures, folds and…

A geological field trip to the Côte d'Ivoire-Ghana transform margin

Abstract During the Equanaute survey (June 1992), fourteen submersible dives were performed between 4950 and 2250 m water depths across the southern slope of the Cote d'Ivoire-Ghana Marginal Ridge (CIGMR), in the eastern Equatorial Atlantic. The CIGMR, a high-standing topographic marginal ridge along the Cote d'Ivoire-Ghana transform margin, is believed to result from a complex structural evolution due to the specific wrench-related rifting between Western Equatorial Africa and Northeastern Brazil, in Early Cretaceous times. In this paper we report and discuss geological observations made during dives, and sample analyses to resolve the lithology, paleoenvironmental conditions, age and orig…

Sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice-contact fan deposits: A Pleistocene example (Ireland)

A pit located near Ballyhorsey, 28 km south of Dublin (eastern Ireland), displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice-contact fan deposits. The coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies. The lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space, mainly controlled by the position of an overlying ice roof during ice-bed decoupling. These sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments. The…

Variation of relief, siliciclastic flux and stratigraphic architecture of sedimentary basins: a database for the African passive margins

Distribution of Albian clastic deposits in the Benguela basin (Angola): evidence of a Benguela palaeocurrent?

Abstract The Albian clastic Tuenza Formation of the Benguela basin (south Angola) is described and its geographic distribution analysed in detail. From these observations, the existence of an Albian “PalaeoBenguela current” is proposed. This would imply that a marine longshore current reworked the sand transported by palaeorivers and settled it northward along the coast of the young Atlantic Ocean (during the Albian). A parallel between Albian clastic deposits and the modern sediments deposited by the Benguela current is drawn, focusing on the striking resemblance between the two currents, i.e. the actual Benguela current and the Albian marine current, and the associated sedimentary bodies.

Synthèse préliminaire des travaux menés sur le bassin de Benguela (Sud Angola) : implications sédimentologiques, paléontologiques et structurales.

12 pages; International audience; Les travaux menés dans le bassin de Benguela ont apporté une moisson de nouvelles données de terrain quant à la période apto-albienne de ce secteur ouest africain. Outre les résultats majeurs obtenus en ce qui concerne les faunes d'ammonites jusqu'alors peu étudiées dans ce bassin, et qui ont permis des corrélations indispensables pour la compréhension du fonctionnement de la sédimentation, cette étude a permis de mettre en évidence une compartimentation remarquable de la sédimentation et des structures de tectonique salifère. Des tels résultats ont une portée à la fois fondamentale et appliquée. En effet, il paraît que le bassin de Benguela soit un des rar…

Nodulisation et compaction différentielle dans une série crétacée du bassin intérieur gabonais.

6 pages; International audience

Community replacement of neritic carbonate organisms during the late Valanginian platform demise: a new record from the Provence Platform.

24 pages; International audience; The Valanginian is marked by amajor platform demise inducing a hiatus in the northern Tethyan neritic carbonate record from the top of the lower Valanginian to the lower Hauterivian. New biostratigraphic and chemostratigraphic data from the Ollioules section (Provence Platform, southern France) are presented here, demonstrating that a large part of the upper Valanginian is preserved in an inner platform environment. The thick, upper Valanginian, aggrading carbonate succession is observed in an aborted rift domain, implying relatively low subsidence. In this context, a relatively long-term sea-level rise was required to sustain a keep-up style of carbonate p…

Clastic injection dynamics during ice front oscillations: A case example from Sólheimajökull (Iceland).

18 pages; International audience; Soft-sediment deformation structures are being increasingly used as a tool for reconstructing palaeoenvironments and porewater pressure conditions in glacial settings. However, the potential of hydrofractures and clastic injections in the reconstruction of ice dynamics remains poorly constrained. This paper presents the results of a detailed study of a clastic injection network outcropping in the Sólheimajökull forefield (South Iceland). Sedimentological descriptions are combined with microscopic to macroscopic analyses of clastic injection geometries, sediment-fills, and cross-cutting relationships. The 250 m long and 20 m high exposure observed along the …

Typology of Hirnantian glacial pavements in SW Djado Basin (NE Niger).

11 pages; International audience

Evolution of neodymium isotopic signature of seawater during the Late Cretaceous: implications for intermediate and deep circulation.

20 pages; International audience; Neodymium isotopic compositions (εNd) have been largely used for the last fifty years as a tracer of past ocean circulation, and more intensively during the last decade to investigate ocean circulation during the Cretaceous period. Despite a growing set of data, circulation patterns still remain unclear during this period. In particular, the identification of the deep-water masses and their spatial extension within the different oceanic basins are poorly constrained. In this study we present new deep-water εNd data inferred from the Nd isotope composition of fish remains and Fe–Mn oxyhydroxide coatings on foraminifera tests, along with new εNd data of resid…