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See detailInsights into a million-year-scale Rhenohercynian carbonate platform evolution through a multi-disciplinary approach: example of a GIvetian carbonate record from Belgium
Pas, Damien ULg; Da Silva, Anne-Christine ULg; Devleeschouwer, Xavier et al

in Geological Magazine (2016)

In this paper we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year past palaeoenvironmental changes. First, we provide ... [more ▼]

In this paper we formulate answers to three important questions related to Givetian carbonate records and their use for reconstructing million-year past palaeoenvironmental changes. First, we provide detailed illustrations of the fascinating diversity that shaped a significant shallow reefal platform during the early- to late-Givetian in the Rhenohercynian Ocean; secondly we improve the sedimentological model of the extensive Givetian carbonate platform in the Dinant Basin and thirdly we evaluate the application of magnetic susceptibility (MS) as a tool for long-term trend correlations and palaeoenvironmental reconstructions. These goals are reached by making sedimentological, geophysical and geochemical study of the La Thure section. Through the early-late Givetian interval we discerned eighteen microfacies ranging from a homoclinal ramp to a discontinuously rimmed shelf and then a drowning shelf. The comparison of these sedimentological results with those published in the south of the Dinant Syncline allowed us to provide an up to date model of the vertical and lateral environmental development for one of the largest Givetian carbonate platforms in Europe. This comparison also increased the knowledge on the facies belts distribution into the Dinant Basin and allowed us to highlight the Taghanic Event. Palaeo-redox proxies reveal a substantial change in the oxygenation level, from oxygen-depleted to more oxic condition, between middle and late Givetian. We demonstrated the relationship between variation in MS values and proxies for siliciclastic input (such as Si, Al). The La Thure is considered as a key section for the understanding of internal shelf settings bordering Laurussia’s south-eastern margin. [less ▲]

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See detailMiddle Devonian Jawed polychate fauna from the type Eifel area, western Germany, and its biogeographical and evolutionary affinities
Tonarova, Petra; Hints, Olle; Könighsof, Peter et al

in Palaeontology (2016)

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See detailSILURIAN – DEVONIAN BLACK SHALES IN THE ORIENTAL ALGERIAN SAHARA: implication of new field data from Tassili n'Ajjer outcrops and Berkine Basin (SE, Algeria).
Djouder, Hocine ULg; Boulvain, Frédéric ULg; Da Silva, Anne-Christine ULg et al

Scientific conference (2015, November)

The Silurian (Llandovery) and the Devonian (Frasnian) are a periods of interest because sediments and organic-rich shales were deposited in many places that form important hydrocarbon reservoirs and ... [more ▼]

The Silurian (Llandovery) and the Devonian (Frasnian) are a periods of interest because sediments and organic-rich shales were deposited in many places that form important hydrocarbon reservoirs and source rocks throughout North Africa basins and Middle East (Boot et al., 1998 ; Lüning et al., 2000). These organic-rich shales lead Algeria to hold the fourth position in terms of the estimates of technically recoverable shale oil and shale gas resources, based on major basin assessment in the world (EIA, 2013). In the prolific Illizi and Berkine basins (western Ghadames, Algeria) a basin-wide approach is needed, especially with the new “shale gas and shale oil” frontier in the upcoming years, in order to capture regional trends and re-assessment the Siluro-Devonian successions. Wireline-logs from more than 146 (Berkine – Illizi Basin) Algerian petroleum exploration wells have been studied (Djouder et al., 2012; Djouder et al., 2014). In addition, a complete logging of spectacular large-scale and well exposed outcrops of the Siluro-Devonian sediments was carried out at the south margin (SE, Tassili n’Ajjer) of the Illizi-Berkine basins. The following analysis incorporates biostratigraphic, ichnological, sedimentological, magnetic susceptibility and high resolution stratigraphic data. It would allow providing a framework of deposits, ranging from offshore to deltaic deposits for the Silurian and from fluvial to normal-marine depositional conditions for the Devonian. References cited: Boote, D.R.D., Clark-Lowes, D.D., Traut, M.W., 1998. Palaeozoic petroleum systems of North Africa. In: Macgregor, D.S., Moo- dy, R.T.J., Clark-Lowes, D.D. (Eds.), Petroleum Geology of North Africa. Geol. Soc. London Sp. Publ., vol. 132, pp. 7–68. Lüning, S., Craig, J., Loydell, D.K., Štorch, P., Fitches, B., 2000. Lower Silurian ‘hot shales’ in North Africa and Arabia: regional distribution and depositional model. Earth-Science Reviews, 121-200. EIA – U.S. Energy Information Administration, 2013. Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States. Rapport de 730 p. Djouder, H., Pagel, M., Murat, B., Orsingher, M., 2012. Le Silurien du Bassin de Berkine. Projet « Shale Gas » Profond. 10éme Colloque du Groupe Français des Argiles, Présentation Orale, Limoge, France 14-18 Mai 2012. http://hdl.handle.net/2268/171556 Djouder, H., Boulvain, F., Da Silva, A-C., Cornet, P., Lüning, S., 2014. Tassili n’Ajjer (Sahara Oriental Algérien) – Résultats préliminaires sur le Silurien – Dévonien : Journée Thématique de l’Association des Sédimentologistes Français (ASF) – Diagenèse : avancées récentes et perspectives, Présentation Poster, Orsay-Paris, France 04 Juillet 2014. http://hdl.handle.net/2268/171557 [less ▲]

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See detailSILURIAN – DEVONIAN OF THE ORIENTAL ALGERIAN SAHARA: implication of new field data from Tassili n'Ajjer outcrops and Berkine Basin (SE, Algeria) for shale gas exploration.
Djouder, Hocine ULg; Boulvain, Frédéric ULg; Da Silva, Anne-Christine ULg et al

in EPC'2015 THE THIRTEENTH TUNISIAN PETROLEUM EXPLORATION & PRODUCTION CONFERENCE (2015, October)

The Silurian – Devonian succession have been deposited in wide sags and sub-basins in a cratonic setting, along the northwestern passive margin of the Gondwana during the opening of the proto-Tethyan ... [more ▼]

The Silurian – Devonian succession have been deposited in wide sags and sub-basins in a cratonic setting, along the northwestern passive margin of the Gondwana during the opening of the proto-Tethyan ocean. During this Siluro-Devonian Period, a high subsidence occurs stacked sediment bodies and organic-rich shales were deposited in many places that respectively form important hydrocarbon reservoirs and source rocks throughout North Africa basins and Arabia (Boot et al., 1998 ; Lüning et al., 2000), which lead Algeria to hold the fourth position in terms of the estimates of technically recoverable shale oil and shale gas resources, based on major basin assessment in the world (EIA, 2013). In the prolific Illizi and Berkine basins (western Ghadames, Algeria) a basin-wide approach is needed, especially with the new “shale gas and shale oil” frontier in the upcoming years, in order to capture regional trends and re-assessment on organic-rich (‘hot’) shale unites which in smaller-scale industrial studies are overlooked. Berkine Basin covers nearly 102.000 km2. This basin has been a thick sedimentary series of 7000 m corresponding to complex reservoirs but also black shales of the basal Silurian and Frasnian respectively major and secondary source rock systems. Wireline-logs from more than 146 (Berkine – Illizi Basins) Algerian petroleum exploration wells have been studies (Djouder et al., 2012; Djouder et al., 2014), and recently 03 months extensive field study of outcrops of the Siluro-Devonian sediments was carried out at the south margin (SE, Tassili n’Ajjer) of the basin. The following analysis incorporates biostratigraphic, ichnological, sedimentological and high resolution stratigraphic data, which provides a framework evolution from offshore to deltaic deposition for the Silurian then fluvial to normal-marine depositional conditions for the Devonian. A total of 06 short-term, third-order sequences can be identified for the Silurian deposits: (i) 'Hot Shale' Oued Imihrou Formation, organic-rich shales with carbonates nodules (Si-1); (ii) above is the Atafaïtafa Formation 500 to 650 m thick with HCS, gutter casts and Cruziana Ichnofacies (Si-2, Si-3); (iii) then overlaid by coarsening-shallowing-upward units. These sequences (Si-4, Si-5 & Si-6) with Storm-wave dominated and Skolithos Ichnofacies are interpreted to reflect deltaic origin. This delta is the result of a significant sea-level drop during the Upper Silurian (Beuf et al, 1971) but also from the high sedimentation rates prograding northwards (Eschard et al., 2005). Devonian deposit also can be divided into fourth third-order sequences (Dev-1 to 4), by the same previous analysis. The base of the cycle is the Caledonian unconformity linked to a tectonic event which affected most of the Gondwanan margin at the Silurian – Devonian boundary and a major relative sea-level fall (Eschard et al., 2005). Previous sequences defined from Tassili n’Ajjer outcrops are well recognized at the basin-scale (Berkine Basin) and can be correlated in the subsurface of the Illizi – Berkine basins (Djouder et al., 2012). Finally, the full depositional cycle for the Silurian – Devonian is reached and capped by the Frasnian maximum flooding surface, with black shales across North Africa (Algeria, western Libya and southern Tunisia) and which are also developed in many parts of the world (Lüning et al., 2003). [less ▲]

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See detailTHE SILURO – DEVONIAN SUCCESSIONS IN THE TASSILI N'AJJER OUTCROPS (SE, ALGERIA): SEDIMENTOLOGY AND STRATIGRAPHY
Djouder, Hocine ULg; Boulvain, Frédéric ULg; Da Silva, Anne-Christine ULg et al

in IGCP 596 - SDS SYMPOSIUM : Climate change and Biodiversity patterns in the Mid-Palaeozoic (2015, September)

The sedimentary basins of North Africa have been accumulated a thick sedimentary succession of Palaeozoic, especially Siluro – Devonian sediments. These successions have been deposited in wide sags and ... [more ▼]

The sedimentary basins of North Africa have been accumulated a thick sedimentary succession of Palaeozoic, especially Siluro – Devonian sediments. These successions have been deposited in wide sags and sub-basins in a cratonic setting, along the northwestern passive margin of the Gondwana. This sedimentation is mainly controlled by rapid eustatic sea-level variations and by the opening of the proto-Tethyan Ocean during the Early Palaeozoic (Beuf et al., 1971; Boot et al., 1998). During this Siluro-Devonian Period, a high subsidence occurred, allowing a high pile of sediments and organic-rich shales were deposited in many places that form important hydrocarbon reservoirs and source rocks throughout North Africa basins and Middle East (Lüning et al., 2000). In the prolific Illizi and Berkine basins (Western Ghadames, Algeria) a basin-wide approach is needed, especially with the new “shale gas and shale oil” frontier in the upcoming years, in order to capture regional trends and re-assessment the Siluro-Devonian successions. Our project focuses on the Berkine Basin and its margin, which covers nearly 102.000 km2. This basin includes a thick sedimentary series of 7000 m corresponding to complex reservoirs but also black shales of the basal Silurian and Frasnian, which are respectively major and secondary source rock systems. Complete logging of spectacular large-scale and well exposed outcrops of the Siluro-Devonian sediments was carried out at the south margin (SE, Tassili n’Ajjer) of the Illizi-Berkine basins (Djouder et al., 2012; Djouder et al., 2014). The following analysis incorporates biostratigraphic, ichnological, sedimentological, Magnetic susceptibility (MS) and high resolution stratigraphic data. It would allow providing a framework of deposits, ranging from offshore to deltaic deposits for the Silurian and from fluvial to normal-marine depositional conditions for the Devonian. References Cited: Beuf, S., Biju-Duval, B., De Charpal, O., Rognon, P., Gariel, O., Bennacef, A., 1971. Les Grès du Paléozoïque inférieur au Sahara : Sédimentation et Discontinuité, Évolution Structurale d’un Craton. Publication de l‘Institut Français du Pétrole. N° 18, Edition Technip, Paris. p. 464. Boote, D.R.D., Clark-Lowes, D.D., Traut, M.W., 1998. Palaeozoic petroleum systems of North Africa. In: Macgregor, D.S., Moo- dy, R.T.J., Clark-Lowes, D.D. (Eds.), Petroleum Geology of North Africa. Geol. Soc. London Sp. Publ., vol. 132, pp. 7–68. Lüning, S., Craig, J., Loydell, D.K., Štorch, P., Fitches, B., 2000. Lower Silurian ‘hot shales’ in North Africa and Arabia: regional distribution and depositional model. Earth-Science Reviews, vol. 49, pp. 121-200. Djouder, H., Pagel, M., Murat, B., Orsingher, M., 2012. Le Silurien du Bassin de Berkine. Projet « Shale Gas » Profond. 10éme Colloque du Groupe Français des Argiles, Présentation Orale, Limoge, France 14-18 Mai 2012. http://hdl.handle.net/2268/171556 Djouder, H., Boulvain, F., Da Silva, A-C., Cornet, P., Lüning, S., 2014. Tassili n’Ajjer (Sahara Oriental Algérien) – Résultats préliminaires sur le Silurien – Dévonien : Journée Thématique de l’Association des Sédimentologistes Français (ASF) – Diagenèse : avancées récentes et perspectives, Présentation Poster, Orsay-Paris, France 04 Juillet 2014. http://hdl.handle.net/2268/171557 [less ▲]

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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 detailBelgium (Ardennes)
Da Silva, Anne-Christine ULg; Boulvain, Frédéric ULg

in Suttner, T.J.; Kido, E.; Königshof, P. (Eds.) et al Planet Earth in Deep Time. Palaeozoic Series. Devonian & Carboniferous (2015)

Devonian and Carboniferous deposits are found in many places around the world. The record of climate change preserved in them is the best (and only) resource of information on the Earth`s climate system ... [more ▼]

Devonian and Carboniferous deposits are found in many places around the world. The record of climate change preserved in them is the best (and only) resource of information on the Earth`s climate system then, at a time, when current and future climatic change is one of society`s greatest challenges. This book introduces some of the key areas of Mid-Palaeozoic sediment occurrence worldwide, authored by 114 specialists from more than 30 countries. The areas were studied as part of the UNESCO/IUGS project on climate change and biodiversity patterns in the mid-Palaeozoic (Devonian and Carboniferous). This large-scale taxonomic, stratigraphic and palaeoecological study of mid-Paleozoic floras and faunas has resulted in 86 contributions and more than 25 artistic reconstructions characterizing the biosphere of the Devonian and Carboniferous. Each contribution describes (in English and the respective national language) the scope of the IGCP project in the respective country, exemplified by representative Devonian/Carboniferous age geological sections and/or regions there. The authors intend to enhance the visibility and the perception of relevance of research on mid-Palaeozoic deposits beyond the Earth Science community. [less ▲]

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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 Geological Society Special Publication (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 detailMagnetic susceptibility application: A window onto ancient environments and climatic variations: Foreword
Da Silva, Anne-Christine ULg; Whalen; Hladil et al

in Geological Society Special Publication (2015), 414

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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 Geological Society Special Publication (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 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 detailLower Carboniferous ramp sedimentation of the Central Alborz Basin, northern Iran: Integrated sedimentological and rock-magnetic studies
Sardar Abadi, Mehrdad ULg; Da Silva, Anne-Christine ULg; Mosaddegh, hossein et al

in Geological Society Special Publication (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 detailFreikofel Formation
Pondrelli, Monica; Pas, Damien ULg; Spalletta, Claudia et al

in Abhandlungen der Geologischen Bundesanstalt (2015), 69

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See detailShallow water facies setting around the Kačák Event – a multidisciplinary approach
Konighsof; Da Silva, Anne-Christine ULg; Suttner et al

in Special Publication - Geological Society of London (2015)

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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 detailMIDDLE DEVONIAN SCOLECODONTS OF THE EIFEL AREA, GERMANY
Tonarova, Petra; Hints, Olle; Königshof, Peter et al

in Cerdeno, Esperanza (Ed.) The history of life: a view from the Southern Hemisphere (2014)

Scolecodonts (polychaete jaws) are common and diverse microfossils in many types of Palaeozoic marine sediments. They bring useful information on phylogeny of polychaete annelids and can be used as ... [more ▼]

Scolecodonts (polychaete jaws) are common and diverse microfossils in many types of Palaeozoic marine sediments. They bring useful information on phylogeny of polychaete annelids and can be used as palaeoenvironmental indicators, and to a lesser degree in biostratigraphy. The number of studies on Devonian scolecodonts is, however, rather limited and in most cases single-element-based classification (parataxonomy) has been used. Here we report a well preserved assemblage of scolecodonts from the type Eifel area, Germany. The studied section lies within the Blankenheim syncline, between the villages of Blankenheim and Blankenheimerdorf. It comprises shallow shelf mixed carbonate and siliciclastic deposits of Eifelian age (kockelianus and ensensis conodont Biozones, beginning of the Kačák Event Interval) that were accumulated in near shore settings on the southern margin of the former Avalonia microcontinent. The family-level composition of the recovered Eifelian polychaete fauna is generally similar to the Silurian associations known from Baltica, Laurentia and Perunica, predominated by polychaetaspids, particularly of the genus Oenonites, mochtyellids (Mochtyella) and paulinitids (Kettnerites). However, characteristic of the Eifelian fauna is the occurrence of kielanoprionids (Kielanoprion), a family that is unknown from the pre-Devonian. In the studied samples kielanoprionids reach up to 20% of the assemblage. Representatives of atraktoprionids, skalenoprionids and tetraprionids are much less common. Comparison with contemporaneous polychaete faunas from other regions is complicated due to limited number of studies. However, the Eifelian assemblage seems to be very similar to those described previously from the Middle Devonian of North America and Upper Devonian of Poland. This suggests that many Devonian polychaetes were both long-ranging and geographically widespread. Good preservation of specimens at hand brings also new information on poorly known jawed polychaete taxa and helps to elucidate some aspects of the phylogeny of the group. The research was supported by the Czech Science Foundation (project P210/12/2018), the European Union through the European Social Fund (Mobilitas grant MJD407) and FWF P 23775-B17 (Austrian Science Fund). [less ▲]

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