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See detailEarly Carboniferous events along the north-eastern Gondwanan margin: an example from the Mobarak Formation of the Central Alborz Mountains, Northern Iran.
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Poty, Edouard ULg et al

Poster (2015, July 14)

The transition from the Late Devonian to the Early Carboniferous was marked by tectonic events, environmental change and global oceanic biological turnover that influenced sedimentary regimes. The end ... [more ▼]

The transition from the Late Devonian to the Early Carboniferous was marked by tectonic events, environmental change and global oceanic biological turnover that influenced sedimentary regimes. The end-Devonian faunal extinction event, for example, eliminated most of the reef building taxa, which, coupled with an increasing rate of subsidence in response to the opening of the Paleo–Tethys and a sea-ward shift of carbonate factories during the Lower Carboniferous, led to the formation of extensive carbonate ramp platforms along the Laurasian and Gondwanan margins. This development has already been reported from the western Gondwanan and southern Laurasian margins but not from northern to north-eastern Gondwanan margin yet. We aim to improve the knowledge on the main factors controlling the development and growth of carbonate ramps during the Lower Carboniferous by examining the Alborz basin along the northern margin of Gondwana. The Lower Carboniferous Mobarak Formation records the development of a storm-sensitive pervasive carbonate factory on the southern Paleo-Tethys passive margin following the opening of the Paleo-Tethys Ocean into the Alborz basin along the northern margin of Gondwana. Four outcrops in the central Alborz Mountains were studied: the Jaban, Aroo, Shahmirzad and Labnesar sections. Four events have been described as the principal factors controlling carbonate platform evolution in the Lower Carboniferous: (1) A transgression linked to global temperature rise in the Early Tournaisian (Middle Hastarain) resulted in the formation of thick-bedded argillaceous limestones. This interval is represented by massive beds of dark mudstones–wackestones to packstones that laterally interfinger with finely laminated limestones, and with bed thickness ranging on the centimeter to meter scale. This interval correlates with Lower Tournaisian nodular to argillaceous limestones of the Moravia Basin (Czech Republic), the Rhenish Slate Mountains (Poland) and the Dinant Basin (Belgium). (2) Late Hastarian–Early Ivorian glaciations were identified in Southern Gondwana but had not been evidenced in Northern Gondwana yet. This glaciation regime is recorded through the appearance of inner-ramp channel-form facies in mid– and outer-ramp settings. (3) During Late Ivorian–Early Visean?, a differentiation block faulting regime along the basin’s margin caused uplift of the westernmost parts of the Alborz basin and resulted in a sub-marine collapse in the eastern part of the central basin. This caused vast sub-aerial exposure and brecciation the top of the Mobarak Formation at the Jaban and Aroo sections. The sub-marine collapse was recorded through the occurrence of Zoophycos bearing fine-grained limestones in the top of the Labnesar and Shahmirzad sections. (4) Tectonic activity that coincided with considerable and abrupt sea level falls as an indirect consequence of the Viséan and Serpukhovian glaciations phases. This progressive sea level drop led to the stagnation of the carbonate factory, which is expressed as an erosional surface at the top of the Mobarak Formation. [less ▲]

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See detailMechanical approach for the characterization of loess deposits from the CBR’s Romont quarry (Eben-Emael, Belgium) and correlations with loess stratigraphy
Delvoie, Simon ULg; Boulvain, Frédéric ULg; Cerfontaine, Benjamin ULg et al

Conference (2015, June 01)

Aeolian silts (loess) are near surface deposits covering about 10% of the continent surfaces . Therefore a good knowledge of their mechanical behavior is an issue for designing subsurface engineering ... [more ▼]

Aeolian silts (loess) are near surface deposits covering about 10% of the continent surfaces . Therefore a good knowledge of their mechanical behavior is an issue for designing subsurface engineering structures. Usually this material is considered as homogeneous for an engineering point of view. Aeolian silt deposits are continuously well developed in Hesbaye Region (Belgium) reaching locally 20m thick (see document in attachment). They are mainly related to the last interglacial (Eemian) and glacial (Weichselian) periods . Nevertheless the pedostratigraphical, chronostratigraphical and paleoclimatic approaches have shown these silt deposits are usually composed of a series of paleosoils (i.e. Rocourt soil, Humiferous Complex of Remicourt, Harmignies Soil, Nagelbeek Tongued Horizon) interbedded with stratified or homogeneous aeolian silt layers. This study aims to characterize the variability of the in situ mechanical characteristics of the loess deposits from Hesbaye Region at the site scale and at the laboratory scale. Cone penetration tests (CPT), electrical resistivity tomographies (ERT) and drillings have been performed through a 10m thick loess layer in an investigation site located close to the CBR’s Romont quarry (Eben-Emael, Belgium) . Continuous undisturbed silt samples from drillings have been physically (granulometry, Atterberg limits, water content, organic matter content, carbonate content) and mechanically (oedometer test, triaxial test) characterized at the laboratory. Mechanical behavior and physical characteristics have underlined a series of layers with variable mechanical properties through depth. Some of these layers correlated with a detailed stratigraphy cross-section close to the investigation site could correspond to well-known paleosoils. [less ▲]

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See detailGenèse du sous-sol de la Wallonie
Boulvain, Frédéric ULg; Pingot, Jean-Louis

Book published by Académie royale de Belgique - 2e édition revue et augmentée (2015)

Cet ouvrage passe en revue les différentes formations géologiques de la Wallonie depuis un demi-milliard d’années. Elles sont décrites et interprétées en termes de paléoenvironnements et leur utilisation ... [more ▼]

Cet ouvrage passe en revue les différentes formations géologiques de la Wallonie depuis un demi-milliard d’années. Elles sont décrites et interprétées en termes de paléoenvironnements et leur utilisation ancienne et actuelle est précisée. Les deux orogenèses qui ont façonné nos paysages sont également abordées. La Wallonie est en effet un pays de pierres. Son histoire est tissée des nombreuses relations entre son sous-sol et ses habitants. L’exploitation immémoriale de ses ressources souterraines, depuis le silex jusqu’au calcaire, en passant évidemment par le charbon et le minerai de fer a façonné ses gens, ses paysages, ses monuments et son économie. Chaque terroir a ses racines plongées dans son sous-sol. Cette étonnante richesse géologique est aussi un atout qui doit continuer à être valorisé et protégé. Notre sous-sol est notre mémoire et ses roches doivent encore et toujours servir à embellir notre environnement. Un marbre rouge ou un grès du Condroz sont la signature d’une région, d’un village, d’une histoire. C’est une des raisons de ce livre : permettre à chacun de prendre conscience de cette richesse. [less ▲]

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See detailMagnetic susceptibility application – a window onto ancient environments and climatic variations
Da Silva, Anne-Christine ULg; Whalen; Hladil et al

Book published by geological Society of London (2015)

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See detailLes Grottes d'Azé: contexte géologique et encaissant calcaire jurassique
Dechamps, Sylvain ULg; Boulvain, Frédéric ULg; Barriquand, Lionel et al

Book published by Département de Saône-et-Loire (2015)

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See detailLower Carboniferous ramp sedimentation of the Central Alborz Basin, North Iran: integrated sedimentological and rock–magnetic studies.
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Mosaddegh, hossein et al

in Special Publication - Geological Society of London (2015), 414

The Lower Carboniferous Mobarak Formation in the Alborz Basin (northern Iran) was deposited along the northeastern margin of Gondwana in a carbonate ramp setting. This paper focuses on the Tournaisian ... [more ▼]

The Lower Carboniferous Mobarak Formation in the Alborz Basin (northern Iran) was deposited along the northeastern margin of Gondwana in a carbonate ramp setting. This paper focuses on the Tournaisian stratigraphic interval of this formation that crops out at the Jaban section in the southwestern Central Alborz Basin. The following facies associations, representing different ramp palaeoenvironments, have been identified: (1) mudstone–wackestone outer-ramp facies; (2) crinoidal to skeletal grainstone–packstone mid-ramp facies; (3) peloidal to crinoidal grainstone–packstone inner-ramp facies; and (4) coastal facies, which include a variety of microbial laminated to oncoidal grainstones and mudstones with evaporitic pseudomorphs. This ramp profile was affected by frequent storms that were responsible for the formation of several skeletal to non-skeletal shoals in the distal mid-ramp to the most proximal inner-ramp areas. The development of the skeletal to non-skeletal shoals along the sea side of the ramp formed a semi-enclosed lagoon sensitive to the influence of both high tides and storm surges.The magnetic susceptibility (xin) of all the samples was measured and compared with that of the facies from which the sample was taken. There is a clear link between xin and the facies; the average xin values were higher for the distal facies than for the proximal facies. The xin profile of this Lower Carboniferous carbonate sequence reflects stratigraphic variations in response to relative changes in sea level and the input of detrital materials. In the context of the sequence stratigraphic framework, the average xin values for lowstand and transgressive systems tract deposits are higher than for the highstand systems tract deposits. The clear link between xin and facies indicates at least a partly preserved primary xin signal related to the detrital inputs. However, to obtain a better understanding of the nature and origin of the minerals carrying the xin, we performed hysteresis measurements on selected samples. It appears that the xin signal is mainly carried by lowcoercivity ferromagnetic minerals such as magnetite, with a mixture of relatively coarse grains (detrital fraction) and ultra-fine grains (probably formed during diagenesis). [less ▲]

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See detailMagnetic susceptibility application – a window onto ancient environments and climatic variations: Foreword
Da Silva, Anne-Christine ULg; Whalen; Hladil et al

in Special Publication - Geological Society of London (2015), 414

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See detailSedimentary development and magnetic susceptibility evolution of the Frasnian in Western Belgium (Dinant Synclinorium, La Thure section)
Pas, Damien ULg; Da Silva, Anne-Christine ULg; Develeeschouwer, Xavier et al

in Special Publication - Geological Society of London (2015), 414

Recent opening of the La Thure quarry in Western Belgium allowed the collection of new data from a poorly outcropping area of the Belgian Frasnian platform. The studied section covers an interval ... [more ▼]

Recent opening of the La Thure quarry in Western Belgium allowed the collection of new data from a poorly outcropping area of the Belgian Frasnian platform. The studied section covers an interval extending from thefalsiovalis to hassi s.l. Zones. Sedimentological analyses allowed the reconstruction of depositional settings in the northwestern part of the Dinant Synclinorium after the demise of the extended Givetian carbonate platform. Two depositional models are distinguished: (a) siliciclastic drowned platform during the Early Frasnian; and (b) a forereef depositional setting belonging to a rimmed shelf during the Middle Frasnian. Moreover, interpreted depositional settings in the northwestern part of the Dinant Synclinorium allowed to constraint the direction of the main facies belts for the Belgian Frasnian platform. Combination of MS and geochemistry demonstrates the inherent-parallel link existing between variation in MS values and proxy for terrestrial input (such as Si and Al). This observation means that, despite the remagnetization occurring within the Belgian Frasnian lithologies, the main trends in the MS signal from the La Thure section still reflect some syn-sedimentary conditions. The increase in MS and clastic input proxies recorded in distal fore-reef deposit within the punctata Zone are likely to be considered as enhanced by rapid and strong shallowing events recognized in the ‘puncataEvent’ interval. [less ▲]

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See detailThe astronomical calibration of the Givetian (Middle Devonian) timescale (Dinant Synclinorium, Belgium)
De Vleeschouwer, David; Boulvain, Frédéric ULg; Da Silva, Anne-Christine ULg et al

in Special Publication - Geological Society of London (2015), 414

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth’s ... [more ▼]

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth’s system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage’s duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35+0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10 5year-scale cyclicity is the result of climatic and environmental change [less ▲]

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See detailSedimentology and magnetic susceptibility of recent sediments from New Caledonia
Jadot, Hélène ULg; Boulvain, Frédéric ULg

in Special Publication - Geological Society of London (2015), 414

The interpretation of the primary origin of the minerals carrying the magnetic susceptibility (MS) signal from ancient rocks suffers notably from the scarcity of studies on Recent sediments. To bring new ... [more ▼]

The interpretation of the primary origin of the minerals carrying the magnetic susceptibility (MS) signal from ancient rocks suffers notably from the scarcity of studies on Recent sediments. To bring new data, a study of tropical coastal sediments of New Caledonia was undertaken. This island is surrounded by a nearly uninterrupted reef barrier, isolating a wide lagoon from the open ocean. The erosion of extremely varied rocks (from mantle rocks to laterites) produces different types of detrital sediments, which are mixed with the indigenous precipitated carbonates. This generates different types of coastal sediments, detrital- or carbonate-dominated or mixed. More than 300 samples were analysed for grain size, nature of sediment, MS and geochemistry (major elements). The first results show that: (a) carbonate sands and carbonate silts are characterized by lower MS than detrital sediments; (b) the MS signal of mixed sediments is mostly influenced by the proportion of detrital sediments; (c) MS is directly correlated with Mn and Fe content; (d) beachrocks are characterized by lower MS than equivalent loose sediment; (e) the MS signal of carbonate sediments is locally positively correlated with granulometry; (f) there is no MS change between surface and 20 cm deep samples; and (g) when the subsurface sediment is reducing, the MS is higher than that from surface sediment. [less ▲]

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See detailUnderstanding of the diversity of earthquake turbiditic flows in a single lake: the case of the Lake Hazar on the East Anatolian Fault
Lamair, Laura ULg; Hage, Sophie ULg; Hubert, Aurelia ULg et al

Poster (2014, August)

The East Anatolian Fault (EAF) is a major left-lateral strike-slip fault accommodating with the conjugate North Anatolian Fault the westward extrusion of the Anatolian Plate away from the Arabia-Eurasia ... [more ▼]

The East Anatolian Fault (EAF) is a major left-lateral strike-slip fault accommodating with the conjugate North Anatolian Fault the westward extrusion of the Anatolian Plate away from the Arabia-Eurasia collision zone. The East Anatolian Fault ruptured over most of its length during the 19th century in a series of magnitude ~7 earthquakes. During the 20th century this fault was less active with only two events of magnitude greater than 6. This absence of large earthquakes has resulted in relatively little attention being paid to the East Anatolian Fault compared to the North Anatolian Fault, which has ruptured during the last century in several earthquakes of Ms~7. To constrain the seismic history of the East Anatolian Fault in its central part, we focus on the Hazar Lake, occupying a 20 km long pull-apart basin. Short cores and long sedimentary cores were collected at three different sites to retrieve a paleoseismic record. Small correlative coarse-grained sedimentary events are identified in all cores. The age of the events is inferred combining radiocarbon and radionuclide (137 Cs and 210Pb) dating. We present here detailed analyses of three sedimentary events assigned respectively to the historical earthquakes occurring in 1789, 1513-1514, 1285. The source of the sedimentary events is different at the three sites. We combine X-ray imagery, magnetic susceptibility, grain-size and XRF measurements with thin section analysis to investigate the nature of sedimentary events. The analyses show first that the three sedimentary events are different. The magnitude of the terrigenous signal varies significantly. Second the correlative events have a different expression at the three sites. So each site has a different and specific sensitivity. In particular, an individual event can be composed of several coarse-grained sub-events of different magnitude with a time lapse in between greater than a week. The latter is reveals by the presence of bioturbation in particular by chironomids in individual thin sand layers. Thin section also shows that subevents are gradded. Each coarse-grained layer is thus a separated turbiditic flow. The site with the highest sensitivity is the one located near the near-shore steep submarine southern slopes overhanged by the steep subaerial slopes of the Hazar Mountains. The rivers draining the Hazar Mountains are ephemeral and provide a restricted sedimentary supply. In addition, seismic reflection data show that the submarine slopes do not to accumulate a significant sedimentary load. However on these steep slopes, an earthquake intensity of 6 or less is enough to trigger a slope failure and the associated turbiditic flow. We conclude that the different sub-events at this site may record a complete earthquake sequence, i.e the main-shock and its foreshocks and aftershocks. [less ▲]

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See detailDiversity and correlation of Givetian records in southern Belgium
Pas, Damien ULg; Poulain, Geoffrey; Labaye, Corentin et al

in Berichte des Institutes für Erdwissenschaften der Karl-Franzens-Universität Graz (2014, August), 19

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See detailTassili n’Ajjer (Sahara Oriental Algérien) – Résultats préliminaires sur le Silurien-Dévonien
Djouder, Hocine ULg; Boulvain, Frédéric ULg; Da Silva, Anne-Christine ULg et al

in Journée Thématique de l’Association des Sédimentologistes Français (ASF) « Diagenèse : avancées récentes et perspectives » (2014, July)

Les gisements atypiques non-conventionnels, à roches sédimentaires faiblement perméables, ainsi que les « sources rocks » constituent une source pétrolière majeure, attirant de plus en plus l’industrie ... [more ▼]

Les gisements atypiques non-conventionnels, à roches sédimentaires faiblement perméables, ainsi que les « sources rocks » constituent une source pétrolière majeure, attirant de plus en plus l’industrie pétrolière, d’où un regain d’intérêt potentiel au sein du Bassin de Berkine. En effet, rien que les argiles radioactives (‘hot’) shales du Silurien sont à l’origine de 80 à 90% des hydrocarbures de la plaque Nord-africaine, et les argiles radioactives du Frasnien (source secondaire) avec des valeurs de TOC allant jusqu’à 14% (Lüning et al., 2000). L'objectif de la thèse s’agira dans un premier temps de l’analyse des diagraphies de forages (Berkine ‘subsurface’) conditionnée aux données de terrain (Tassili n’Ajjer sur affleurements) et de sismique réflexion. Ceci afin de réaliser la modélisation 2D et 3-D des corps réservoirs et de la roche mère, à l’aide du logiciel Petrel©. Et au final, la cartographie des unités de la série Silurien-Dévonien dans le but de définir les « Plays » potentielles aux futures plans d’exploration. Au second volet, la mise au point d’une méthodologie rigoureuse, permettant l’étude minéralogique et l’évolution diagénétique des faciès, sous différents aspect ; la quantification de la porosité, la définition des relations entre porosité et minéralogie. Ensuite caractériser les argiles radioactives du Llandoverien-Frasnien respectivement Silurien, Dévonien et minéraux associés (Lüning et al., 2004). Plus précisément les processus et mécanismes qui contrôlent les transformations des minéraux argileux (minéralogies et cristallochimies) en composante latérale mais aussi en fonction de la profondeur. Dans ce contexte, des missions de terrains seront entreprises dans les massifs du Fadnoun (Tassili Central), Oued Taïni, Oued Khabkhab ainsi que dans l’Oued Amassine (Tassili Occidental) qui nous permettront de décrire en surface les formations du Siluro-Dévonien (profondément étudiées par : Asses, A., 1987 - Massa, D., 1988 - Bekkouche, D., 1992 – IFP, Sonatrach, Beicip., 1999) qui renferment les argiles radioactives (‘hot’) shales et les niveaux réservoirs, situées à quelques centaines de kilomètres au Nord (Bassin de Berkine), sous 2500 à 3000 m de sédiments. Une première mission de terrain est déjà réalisée, ayant reçu un support financier de la R&D (Séjour de Recherche à l’étranger), ainsi que des facilitées administratives et logistiques respectivement du Ministère de la Culture et de l’office national du parc culturel du Tassili n’Ajjer (patrimoine mondial de l’UNESCO depuis 1982). D’autres missions ultérieures seront à organiser en fonction du planning du déroulement de la thèse. La première mission géologique de terrain a duré un mois sur le Plateau de Fadnoun (Tassili n’Ajjer central). Ceci dans différentes coupes géologique-type des affleurements du Silurien-Dévonien : l’Oued Imihrou, l’Oued Farzal, Gara Tihouririne (sur la route Illizi-Fort Tarat) et Isoutar (Djouder et al., 2014). Durant cette mission terrain nous avons pu assurer la concordance entre les thématiques et objectifs de départ et les réalisés sur terrain, entre autre : 1) la meilleure compréhension de la géométrie des corps sédimentaires, au sein du Plateau de Fadnoun et donc par extension dans le bassin ; 2) la description et l’analyse des faciès, grâce aux affleurements peu connus dans les oueds. Ils permettront une analyse, notamment en termes d’environnements sédimentaires, des formations du Silurien-Dévonien ; 3) application première dans son genre de la susceptibilité magnétique comme nouvel proxy, pour les corrélations lithostratigraphiques des unités du Silurien-Dévonien aux Tassilis. 4) réalisation d’un échantillonnage serré à différents niveaux pour couvrir tout l’intervalle de la dépression intra-Tassilienne et des Grès du Tassili Externe, et puis l’expédition du matériel, nécessaire aux analyses de laboratoires notamment à Liège, et collaborateurs. La confection de lames-minces (en cours) permettra l’étude de la minéralogie et de la pétrographie, et donc une meilleure compréhension des faciès et microfaciès, c’est à dire de leurs propriétés intrinsèques (systèmes hétérogènes et complexes). Les lames palynologiques permettront des datations précises de chaque niveau. Enfin, différentes analyses sur roche (minéraux argileux dans un Laboratoire partenaire de l’Université de Poitiers en France, susceptibilité magnétique, cathodoluminescence, analyses géochimiques des majeurs et des traces à l’ULg) permettront d’affiner les paramètres du paléoenvironnement (Da Silva et al., 2013). [less ▲]

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See detailLe Silurien-Dévonien du Sahara Oriental Algérien (Bassin de Berkine et affleurements du Tassili n’Ajjer) : depuis la caractérisation de faciès jusqu’à la modélisation 3-D d’un réservoir non-conventionnel
Djouder, Hocine ULg; Boulvain, Frédéric ULg; Aït-Ouali, Rachid

Conference (2014, January)

Cette étude s'inscrit dans la thématique des projets Silurien-Dévonien Profond, sur la caractérisation des formations argileuses (source rock), des réservoirs gréseux conventionnels et non-conventionnels ... [more ▼]

Cette étude s'inscrit dans la thématique des projets Silurien-Dévonien Profond, sur la caractérisation des formations argileuses (source rock), des réservoirs gréseux conventionnels et non-conventionnels ainsi que de la matrice carbonatée, en partenariat institutionnel et industriel. Situé dans le Sud-Est algérien, à la limite des frontières algéro-tunisienne et libyenne, le Bassin de Berkine est un bassin intracratonique qui s’étend sur près de 102 000 km2. Au Paléozoïque inférieur, cette étendue était le siège d’une sédimentation silicoclastique puissante. Cette étude est focalisée sur le Silurien et le Dévonien. En effet, le Bassin de Berkine renferme des réservoirs potentiels : alternances argilo-gréseuses (AAG) du Silurien sommital et grès massifs du Lochkovien-Praguien et Emsien. Il renferme également des roches-mères, telles que les argiles radioactives (‘hot’) shales du Silurien, qui sont à l’origine de 80 à 90% des hydrocarbures et les argiles radioactives du Frasnien (source secondaire) avec des valeurs de TOC allant jusqu’à 14%. Au total 146 puits et une dizaine de carottes ont fait l’objet d’une analyse de facies/électrofacies et de stratigraphie séquentielle « Stacking Patterns » de haute résolution. Ceci a pour but de caractériser les séquences de dépôts et leurs environnements respectifs, puis de prédire la géométrie-cartographie des corps sédimentaires. Au final, de caractériser les propriétés pétrophysiques des « Plays » jugées potentielles. Cinq séquences principales sont mises en évidence pour le Silurien, dans le secteur de Menzel Lejmat et le Sillon de Marfag du Bassin de Berkine, à travers les puits MLEP-1 & BRD-5. Les séquences Si-1 et Si-2 sont datées du Llandoverien. Au cours de cette période, le bassin était le siège d’une importante sédimentation argileuse de (‘hot’) shales et d’argiles à graptolites de 500 à 650 m d’épaisseur. Ces faciès argileux de plate-forme externe profonde passent au sommet à des faciès carbonatés très vite surmontés par des sédiments gréseux (séquences Si-3, Si-4 et Si-5) initiateurs d’un contexte deltaïque progradant du Sud vers le Nord. Au Dévonien six unités, majoritairement gréso-carbonatées ont été décelées. Les Grès massifs de Tadrart ‘Unité b’ d’un prisme de bas niveau (LST) d’âge Lochkovien, sont constitués de dépôts fluviatiles. Ils sont surmontés par des sédiments ferrugineux de l‘Unité c’ (TST). L‘Unité d’ correspond au Praguien, suivi de la formation emsienne ‘Unité e’ (HST) à grès massifs de type fluviatile-estuarien et qui sont notamment caractérisés par des minéraux authigènes, tels que la chamosite. Ces revêtements chloriteux des grains préserve la porosité mais réduisent la perméabilité et contribuent à la destruction des propriétés pétrophysiques de ces réservoirs. L‘Unité f’ (Eifélien-Givétien) atteint environ 110 m d’épaisseur, avec un Givétien qui est essentiellement carbonaté. Au final, on observe l’installation définitive, en discordance, des argiles radioactives (‘Unité g’) d’âge Frasnien-Fammenien. L'originalité de la poursuite de cette étude consistera à coupler plusieurs techniques de caractérisation, afin de répondre aux multiples problématiques à la fois scientifiques et industrielles. Parmi les méthodes prévues pour cette étude, on retrouvera la spectrométrie DRX, la microspectrométrie InfraRouge (FTIR) ainsi que la pyrolyse Rock-Eval pour la caractérisation fine des assemblages argileux. L’étude minéralogique des faciès/microfaciès gréseux et carbonatés en microscopie (optique, MEB) et cathodoluminescence sera aussi entreprise afin de contraindre au mieux l’évolution diagénétique des réservoirs, de même que la quantification de la porosité par la méthode (14C-PMMA). Les inclusions fluides seront d’un grand apport pour comprendre l’histoire thermique du Bassin de Berkine ainsi que la relation avec les migrations primaires des hydrocarbures. L’ensemble de ces données seront exploitées dans le modèle 3D réservoirs, qui sera construit à l’aide du logiciel de l’industrie pétrolière Petrel©. [less ▲]

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See detailInsight into the development of a carbonate platform through a multi-disciplinary approach - A case study from the Upper Devonian slope deposits of Mount Freikofel (Carnic Alps, Austria/Italy)
Pas, Damien ULg; Da Silva, Anne-Christine ULg; Suttner, Thomas et al

in International Journal of Earth Sciences (2014), 103

The development and behavior of Million year-scaled depositional sequences recorded within Palaeozoic carbonate platform has remained poorly examined. Therefore, the understanding of palaeoenvironmental ... [more ▼]

The development and behavior of Million year-scaled depositional sequences recorded within Palaeozoic carbonate platform has remained poorly examined. Therefore, the understanding of palaeoenvironmental changes that occur in geological past is still limited. We herein undertake a multi-disciplinary approach (sedimentology, conodont biostratigraphy, magnetic susceptibility and geochemistry) of a long-term succession in the Carnic Alps which offers new insights into the peculiar evolution of one of the best example of Palaeozoic carbonate platform in Europe. The Freikofel section, located in the central part of the Carnic Alps represents an outstanding succession in a fore-reef setting, extending from the latest Givetian (indet. falsiovalis conodont Zones) to the early Famennian (Lower crepida conodont Zone). Sedimentological analysis allowed to propose a sedimentary model dominated by distal slope and fore-reef slope deposits. The most distal setting is characterized by an autochthonous pelagic sedimentation showing local occurrence of thin-bedded turbiditic deposits. In the fore-reef slope, in a more proximal setting, there is an accumulation of various autochthonous and allochthonous fine- to coarse-grained sediments originated from the interplay of gravity-flow currents derived from the shallow-water and deeper-water area. The temporal evolution of microfacies in the Freikofel section evolves in two main steps corresponding to the Freikofel (Unit 1) and the Pal (Unit 2) Limestones. Distal slope to fore-reef lithologies and associate changes are from base to top of the section: (U1) thick bedded litho- and bioclastic breccia beds with local fining upward sequence and fine-grained mudstone intercalations corresponding, in the fore-reef setting, to the dismantlement of the Eifelian – Frasnian carbonate platform during the early to late Frasnian time (falsiovalis to rhenana superzones) with one of the causes being the Late Givetian major rift pulse; (U2) occurrence of thin-bedded red nodular and cephalopod-bearing limestones with local lithoclastic grainstone intercalations corresponding to a significant deepening of the area and the progressive withdrawal of sedimentary influxes toward the basin, in relation with late Frasnian sea-level rise. Magnetic susceptibility and geochemical analyses were also performed along the Freikofel section and demonstrate the inherent-parallel link existing between variation in magnetic susceptibility values and proxy for terrestrial input. Interpretation of magnetic susceptibility in term of palaeoenvironmental processes reflect that even though distality remains the major parameter influencing magnetic susceptibility values, carbonate production and water agitation also play an important role. [less ▲]

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