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Boulvain Frédéric - One of the best experts on this subject based on the ideXlab platform.

  • Silurian Succession from North Africa (Algeria) – A Review for a New Era of Hydrocarbon Exploration
    2018
    Co-Authors: Djouder Hocine, Uysal Tonguç, Boulvain Frédéric, Bourdet Julien, Da Silva Anne-christine, Todd Andrew, Ramanaïdou Erick
    Abstract:

    audience: researcher, professionalThe diagenetic grade and thermal history of the widespread graptolitic Silurian Oued Imihrou black shales (Llandoverian in age) and the overlying sandstone levels of the Atafaïtafa Formation (late Llandoverian to Wenlockian) from the Tassili n'Ajjer plateau have been investigated by integrating a variety datasets, such as illite crystallinity, graptolite-derived organic matter reflectance, source-rock maturity and illite K–Ar ages. Combination of X-ray diffraction and petrographic examinations allowed to confirm the occurrence of three distinct minerals of authigenic origin, i.e. kaolinite, illite, and iron-rich chlorite, within the Silurian succession. These clay minerals, as well as pyrite and quartz overgrowths, were neoformed at different times during diagenetic-to-hydrothermal conditions and conversion-precipitation reactions. Furthermore, formation processes of these minerals are found to be broadly controlled by the stratigraphical level, lithology of the host rocks and the paleogeographical location of the studied outcrop sections from the eastern- and western-Tassili n'Ajjer plateau (Djouder et al., 2018). The illite crystallinity (i.e. Crystallinity index standards or CIS-calibrated IC values range between 1.58 to 0.38 Δ°2θ), paleotemperature estimates (~113–190°C) and graptolite reflectance (vitrinite reflectance equivalent, 0.65–1.5% VReqv) correspond to low grade diagenesis/anchi-metamorphic illite crystallization conditions and the oil-to-wet gas hydrocarbon generation zone. A paleothermal gradient towards the West is clearly present. This higher thermal maturity of the most western part of the Tassili (Tmax=466–483°C) is intimately linked to the migration of hot fluids, notably along N-S lineaments mega-shear zones in the Hoggar Shield. The latter were repeatedly reactivated during the Phanerozoic orogenies and rifting phases. K−Ar dating results indicate at least two generations of authigenic micrometric illite crystals, which are interpreted to reflect the timing of fluid flow events in association with fault reactivations within the Tassili n'Ajjer plateau at the northern Hoggar Shield. The older illite of 335 ± 8 Ma is consistent with the timing of the early Hercynian tectono-thermal activity in the region, accompanied probably by the first hydrocarbon generation, i.e. Carboniferous age ‘Visean’. While, the younger illite precipitations at 238 ± 11 Ma (Mid–Upper Triassic) and at 204 ± 6 to 179 ± 4 Ma (Triassic–Jurassic transition) can be attributed to high temperature fluid flow and kerogen maturation of the Early Silurian black shales, following Tethys rifting and the later development of the Central Atlantic Magmatic Province, respectively

  • Silurian Succession from North Africa (Algeria) – A Review for a New Era of Hydrocarbon Exploration
    2018
    Co-Authors: Djouder Hocine, Uysal Tonguç, Boulvain Frédéric, Bourdet Julien, Da Silva Anne-christine, Todd Andrew, Ramanaïdou Erick
    Abstract:

    The diagenetic grade and thermal history of the widespread graptolitic Silurian Oued Imihrou black shales (Llandoverian in age) and the overlying sandstone levels of the Atafaïtafa Formation (late Llandoverian to Wenlockian) from the Tassili n'Ajjer plateau have been investigated by integrating a variety datasets, such as illite crystallinity, graptolite-derived organic matter reflectance, source-rock maturity and illite K–Ar ages. Combination of X-ray diffraction and petrographic examinations allowed to confirm the occurrence of three distinct minerals of authigenic origin, i.e. kaolinite, illite, and iron-rich chlorite, within the Silurian succession. These clay minerals, as well as pyrite and quartz overgrowths, were neoformed at different times during diagenetic-to-hydrothermal conditions and conversion-precipitation reactions. Furthermore, formation processes of these minerals are found to be broadly controlled by the stratigraphical level, lithology of the host rocks and the paleogeographical location of the studied outcrop sections from the eastern- and western-Tassili n'Ajjer plateau (Djouder et al., 2018). The illite crystallinity (i.e. Crystallinity index standards or CIS-calibrated IC values range between 1.58 to 0.38 Δ°2θ), paleotemperature estimates (~113–190°C) and graptolite reflectance (vitrinite reflectance equivalent, 0.65–1.5% VReqv) correspond to low grade diagenesis/anchi-metamorphic illite crystallization conditions and the oil-to-wet gas hydrocarbon generation zone. A paleothermal gradient towards the West is clearly present. This higher thermal maturity of the most western part of the Tassili (Tmax=466–483°C) is intimately linked to the migration of hot fluids, notably along N-S lineaments mega-shear zones in the Hoggar Shield. The latter were repeatedly reactivated during the Phanerozoic orogenies and rifting phases. K−Ar dating results indicate at least two generations of authigenic micrometric illite crystals, which are interpreted to reflect the timing of fluid flow events in association with fault reactivations within the Tassili n'Ajjer plateau at the northern Hoggar Shield. The older illite of 335 ± 8 Ma is consistent with the timing of the early Hercynian tectono-thermal activity in the region, accompanied probably by the first hydrocarbon generation, i.e. Carboniferous age ‘Visean’. While, the younger illite precipitations at 238 ± 11 Ma (Mid–Upper Triassic) and at 204 ± 6 to 179 ± 4 Ma (Triassic–Jurassic transition) can be attributed to high temperature fluid flow and kerogen maturation of the Early Silurian black shales, following Tethys rifting and the later development of the Central Atlantic Magmatic Province, respectively

  • Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy
    2018
    Co-Authors: Djouder Hocine, Da Silva Anne-christine, Lüning Sebastian, Abdallah Hussein, Boulvain Frédéric
    Abstract:

    The economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern- to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow- to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.Peer reviewe

  • Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy
    'Elsevier BV', 2018
    Co-Authors: Djouder Hocine, Da Silva Anne-christine, Lüning Sebastian, Abdallah Hussein, Boulvain Frédéric
    Abstract:

    peer reviewedaudience: researcher, professional, student, popularization, otherThe economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern- to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow- to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.Silurian deltaic progradation rock record, under storm- and fluvial-influenced setting (Gondwana): Sedimentology, ichnology, sequence stratigraphy, clay mineralogy, and implications for thermal maturity evolution

Pierreandre Bourque - One of the best experts on this subject based on the ideXlab platform.

  • sea level synsedimentary tectonics and reefs implications for hydrocarbon exploration in the silurian lowermost devonian gaspe belt quebec appalachians
    Bulletin of Canadian Petroleum Geology, 2001
    Co-Authors: Pierreandre Bourque
    Abstract:

    ABSTRACT Sea-level changes and synsedimentary tectonics affected the development of three potential hydrocarbon reservoir intervals in the Silurian-lowermost Devonian part of the Gaspe Belt on the margin of Laurentia. A relative sea-level curve is based on sequence analysis of facies and distribution of benthic faunas. The succession recorded two major, low-order sedimentary cycles, each composed of a regressive-transgressive couplet and represented by shallowing- and deepening-upward sequences. The first shallowing episode (S1) covered the Rhuddanian-Sheinwoodian (Llandovery-early Wenlock) interval, whereas a rapid deepening episode (D1) followed during the Homerian (late Wenlock). A second shallowing episode (S2) started during the late Homerian, and ended in the late Ludfordian (late Ludlow) or earliest Pridolian, and was then followed by a latest Silurian-Early Devonian deepening episode (D2). Potential reservoir rock units developed mostly during sea-level lowstands or early transgressions in the Gaspe Belt. Comparison of the Gaspe relative sea-level curve with eustatic curves, proposed for the same time interval, indicates that the Gaspe curve was significantly influenced by local synsedimentary tectonics. Salinic extensional tectonics, a predominantly Late Silurian-Early Devonian (Ludlovian-Pragian) event, resulted in block faulting and tilting along normal listric faults. Interaction between block faulting and eustatic sea-level fall at the end of the Ludlovian-early Pridolian exposed the highest parts of the blocks to subaerial erosion and diagenesis, and allowed reefs and reef complexes to settle at the margins of the blocks, or on erosional remnants. Salinic extensional tectonics may also have provided suitable pathways for hydrocarbon migration and charge at various times during the mid-Silurian to Early Devonian, particularly for hydrocarbons that may have been generated in the underlying Cambro-Ordovician shales. In the northeastern part of the Gaspe Belt, which is the most promising area for hydrocarbon reservoirs in the Gaspe Peninsula, block faulting and tilting have changed the fluid migration pattern from an updip-northeastward flow from the basin centre to basin margin during the Late Ordovician to early Late Silurian, to a potential updip-southwestward flow in each faulted block during the early Late Silurian. Basin tectonics may have played a significant role in driving hydrocarbon-rich fluids toward potential reservoirs, such as the Llandoverian Val-Brillant sandstone bodies, the Sayabec carbonate sands and knob reefs, or the West Point reefs. RESUME Les fluctuations du niveau marin et la tectonique synsedimentaire ont influence le developpement de trois horizons susceptibles de constituer des reservoirs petroliferes dans le Silurien - tout debut Devonien de la Ceinture de Gaspesie a la marge de Laurentia. Une courbe relative des niveaux marins a ete construite a partir de l' analyse sequentielle des facies et de la distribution des faunes benthiques. La succession a archive deux grands cycles principaux, chacun forme d' un couple regression-transgression et exprime par une sequence a bathymetrie decroissante, puis croissante. Le premier episode a bathymetrie decroissante (S1) couvre l' intervalle de temps Rhuddanien-Sheinwoodian (Llandovery-Wenlock precoce); il fut suivi par un rapide episode a bathymetrie croissante (D1) durant l' Homerien (Wenlock tardif). Un second episode a bathymetrie decroissante (S2) a debute a l' Homerien tardif pour culminer au Ludfordien (Ludlow tardif) ou au tout debut du Pridolien; il fut suivi par un episode a bathymetrie croissante (D2) a la toute fin du Silurien ou au debut du Devonien. Les unites de la Ceinture de Gaspe presentant un potentiel en reservoirs petroliferes se sont deposees durant End_Page 217------------------------ un bas niveau marin ou le tout debut d'une transgression. La comparaison de la courbe relative des niveaux marins de Gaspesie avec des courbes eustatiques etablies pour le meme intervalle de temps montre que la courbe gaspesienne a ete influencee de facon importante par la tectonique synsedimentaire locale. La tectonique d' extension salinique a predomine au Silurien tardif-Devonien precoce (Ludlovien-Praguien) et a produit des blocs failles bascules le long de failles normales listriques. L'interaction entre le basculement des blocs et la chute eustatique du niveau marin a la fin du Ludlovien-debut Pridolien a expose les parties hautes des blocs a une erosion et une diagenese aeriennes et permis l'implanatation de recifs ou de complexes recifaux en peripherie des blocs ou sur des hauts-fonds herites de l'erosion. La tectonique d'extension salinique peut aussi avoir produit une tuyauterie adequate pour la migration et l'emmagasinage d'hydrocarbures qui auraient pu etre generes dans les shales cambro-ordoviciens sous-jacents. Dans le nord-est de la Ceinture de Gaspesie, qui est le secteur le plus prometteur pour les reservoirs petroliferes, le basculement de blocs failles a modifie le patron de migration des fluides, d'un ecoulement amont-pendage vers le nord-est, i.e. du centre vers les marges du bassin, de l'Ordovicien tardif au debut du Silurien tardif, a un ecoulement amont-pendage vers le sud-ouest dans chacun des blocs. Cette inversion peut avoir joue un role important en dirigeant des fluides riches en hydrocarbures vers des reservoirs potentiels, tels les gres llandoveriens de Val-Brillant, les sables calcaires et les buttes recifales de Sayabec ou les recifs West Point. Traduit par l'auteur.

  • paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec
    Geological Society of America Bulletin, 2000
    Co-Authors: Pierreandre Bourque, Michel Malo, Donna Kirkwood
    Abstract:

    The Silurian–Lower Devonian sequence of the Gaspe Belt at the Laurentia margin south of the Quebec reentrant and St. Lawrence promontory was deposited during the period between the two main orogenies that created the northern Appalachians: the Late Ordovician Taconian and the Middle Devonian Acadian orogenies. Although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies, significant tectonic activity attributed to the Salinic disturbance began during late Llandoverian (Telychian) time and persisted until the Acadian orogeny. This tectonic activity has profoundly influenced the composition and distribution of the Silurian–earliest Devonian sedimentary facies. The shelf and shelf edge history at the Laurentia margin along the Quebec reentrant–St. Lawrence promontory is summarized according to four broad phases. Phase 1 is a Llandoverian–Wenlockian regressive phase (R1) related to post-Taconian successor basin filling, that culminated with extensive carbonate platform development. Phase 2 is a late Wenlockian–Ludlovian transgressive phase (T1). Phase 3 corresponds to a later Ludlovian–Pridolian second regressive phase (R2). Phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting, on top of which block reefs and reef complexes settled and built a reef tract all the way along the Gaspe-Temiscouata shelf. Phase 4 is an Early Devonian phase of accelerated subsidence (transgression T2) affecting the northwestern part of the segment (Quebec reentrant area), while the southeastern part (St. Lawrence promontory area) was already uplifted due to the ongoing collision between Laurentia and the western margin of Gondwana-related terranes to the south. Composition and distribution of sedimentary facies were controlled by the interaction of tectonics, sediment influx, and sea-level fluctuations. Construction of a post-Taconian–pre-Acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the Gaspe-Temiscouata segment at the margin of the Laurentia craton during the Silurian–earliest Devonian time interval.

Djouder Hocine - One of the best experts on this subject based on the ideXlab platform.

  • Silurian Succession from North Africa (Algeria) – A Review for a New Era of Hydrocarbon Exploration
    2018
    Co-Authors: Djouder Hocine, Uysal Tonguç, Boulvain Frédéric, Bourdet Julien, Da Silva Anne-christine, Todd Andrew, Ramanaïdou Erick
    Abstract:

    audience: researcher, professionalThe diagenetic grade and thermal history of the widespread graptolitic Silurian Oued Imihrou black shales (Llandoverian in age) and the overlying sandstone levels of the Atafaïtafa Formation (late Llandoverian to Wenlockian) from the Tassili n'Ajjer plateau have been investigated by integrating a variety datasets, such as illite crystallinity, graptolite-derived organic matter reflectance, source-rock maturity and illite K–Ar ages. Combination of X-ray diffraction and petrographic examinations allowed to confirm the occurrence of three distinct minerals of authigenic origin, i.e. kaolinite, illite, and iron-rich chlorite, within the Silurian succession. These clay minerals, as well as pyrite and quartz overgrowths, were neoformed at different times during diagenetic-to-hydrothermal conditions and conversion-precipitation reactions. Furthermore, formation processes of these minerals are found to be broadly controlled by the stratigraphical level, lithology of the host rocks and the paleogeographical location of the studied outcrop sections from the eastern- and western-Tassili n'Ajjer plateau (Djouder et al., 2018). The illite crystallinity (i.e. Crystallinity index standards or CIS-calibrated IC values range between 1.58 to 0.38 Δ°2θ), paleotemperature estimates (~113–190°C) and graptolite reflectance (vitrinite reflectance equivalent, 0.65–1.5% VReqv) correspond to low grade diagenesis/anchi-metamorphic illite crystallization conditions and the oil-to-wet gas hydrocarbon generation zone. A paleothermal gradient towards the West is clearly present. This higher thermal maturity of the most western part of the Tassili (Tmax=466–483°C) is intimately linked to the migration of hot fluids, notably along N-S lineaments mega-shear zones in the Hoggar Shield. The latter were repeatedly reactivated during the Phanerozoic orogenies and rifting phases. K−Ar dating results indicate at least two generations of authigenic micrometric illite crystals, which are interpreted to reflect the timing of fluid flow events in association with fault reactivations within the Tassili n'Ajjer plateau at the northern Hoggar Shield. The older illite of 335 ± 8 Ma is consistent with the timing of the early Hercynian tectono-thermal activity in the region, accompanied probably by the first hydrocarbon generation, i.e. Carboniferous age ‘Visean’. While, the younger illite precipitations at 238 ± 11 Ma (Mid–Upper Triassic) and at 204 ± 6 to 179 ± 4 Ma (Triassic–Jurassic transition) can be attributed to high temperature fluid flow and kerogen maturation of the Early Silurian black shales, following Tethys rifting and the later development of the Central Atlantic Magmatic Province, respectively

  • Silurian Succession from North Africa (Algeria) – A Review for a New Era of Hydrocarbon Exploration
    2018
    Co-Authors: Djouder Hocine, Uysal Tonguç, Boulvain Frédéric, Bourdet Julien, Da Silva Anne-christine, Todd Andrew, Ramanaïdou Erick
    Abstract:

    The diagenetic grade and thermal history of the widespread graptolitic Silurian Oued Imihrou black shales (Llandoverian in age) and the overlying sandstone levels of the Atafaïtafa Formation (late Llandoverian to Wenlockian) from the Tassili n'Ajjer plateau have been investigated by integrating a variety datasets, such as illite crystallinity, graptolite-derived organic matter reflectance, source-rock maturity and illite K–Ar ages. Combination of X-ray diffraction and petrographic examinations allowed to confirm the occurrence of three distinct minerals of authigenic origin, i.e. kaolinite, illite, and iron-rich chlorite, within the Silurian succession. These clay minerals, as well as pyrite and quartz overgrowths, were neoformed at different times during diagenetic-to-hydrothermal conditions and conversion-precipitation reactions. Furthermore, formation processes of these minerals are found to be broadly controlled by the stratigraphical level, lithology of the host rocks and the paleogeographical location of the studied outcrop sections from the eastern- and western-Tassili n'Ajjer plateau (Djouder et al., 2018). The illite crystallinity (i.e. Crystallinity index standards or CIS-calibrated IC values range between 1.58 to 0.38 Δ°2θ), paleotemperature estimates (~113–190°C) and graptolite reflectance (vitrinite reflectance equivalent, 0.65–1.5% VReqv) correspond to low grade diagenesis/anchi-metamorphic illite crystallization conditions and the oil-to-wet gas hydrocarbon generation zone. A paleothermal gradient towards the West is clearly present. This higher thermal maturity of the most western part of the Tassili (Tmax=466–483°C) is intimately linked to the migration of hot fluids, notably along N-S lineaments mega-shear zones in the Hoggar Shield. The latter were repeatedly reactivated during the Phanerozoic orogenies and rifting phases. K−Ar dating results indicate at least two generations of authigenic micrometric illite crystals, which are interpreted to reflect the timing of fluid flow events in association with fault reactivations within the Tassili n'Ajjer plateau at the northern Hoggar Shield. The older illite of 335 ± 8 Ma is consistent with the timing of the early Hercynian tectono-thermal activity in the region, accompanied probably by the first hydrocarbon generation, i.e. Carboniferous age ‘Visean’. While, the younger illite precipitations at 238 ± 11 Ma (Mid–Upper Triassic) and at 204 ± 6 to 179 ± 4 Ma (Triassic–Jurassic transition) can be attributed to high temperature fluid flow and kerogen maturation of the Early Silurian black shales, following Tethys rifting and the later development of the Central Atlantic Magmatic Province, respectively

  • Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy
    2018
    Co-Authors: Djouder Hocine, Da Silva Anne-christine, Lüning Sebastian, Abdallah Hussein, Boulvain Frédéric
    Abstract:

    The economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern- to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow- to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.Peer reviewe

  • Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy
    'Elsevier BV', 2018
    Co-Authors: Djouder Hocine, Da Silva Anne-christine, Lüning Sebastian, Abdallah Hussein, Boulvain Frédéric
    Abstract:

    peer reviewedaudience: researcher, professional, student, popularization, otherThe economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern- to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow- to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.Silurian deltaic progradation rock record, under storm- and fluvial-influenced setting (Gondwana): Sedimentology, ichnology, sequence stratigraphy, clay mineralogy, and implications for thermal maturity evolution

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  • paleogeography and evolution of the ordovician silurian whiterockian Llandoverian continental margin in central nevada
    AAPG Bulletin, 1991
    Co-Authors: W Britt, California State
    Abstract:

    In central Nevada, stratigraphic successions of Whiterockian-Llandoverian lithofacies, transitional with autochthonous platform/shelf carbonates to the east, occur in isolated windows in outer slope to basinal lithotopes of the Roberts Mountains allochthon. Petrologic, chronostratigraphic and lithostratigraphic, and paleontologic comparison of those successions with platform/shelf facies to the east is integral for reconstruction of Ordovician-Silurian platform margin paleogeography and pre-Antler genesis of the western North American continental margin. Numerous facies changes and/or stratigraphic omissions in central Nevada can be related to sea level fluctuation and aggradation/progradation of the carbonate platform to the east, and not to a postulated, offshore geanticline (i.e., the Toiyabe Ridge). Stratigraphic omission of the Eureka Quartzite above Pogonip equivalents in transitional successions of the Toquima Range and the presence of correlative quartzite in outer slope/basinal parautochthonous facies of the Toiyabe Range suggest development of a possible bypass-margin during the Middle Ordovician. Deposition of Late Ordovician platform margin dolostones (Ely Springs Dolostone) and upper ramp limestones (Hanson Creek Formation and Martin Ridge strata) followed Late Ordovician transgression that drowned the margin and reestablished the carbonate factory. Glacioeustatic drawdown of Late Ordovician-earliest Silurian seas due to the Gondwanan glacial fluctuation can be recognized in strata along the platform margin andmore » upper ramp. Rapid, Early Silurian transgression produced dark-gray carbonates and may have induced marginal flexure and regional, massive slope failure in central Nevada, generating stratigraphic hiatuses west of the platform margin.« less

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  • Silurian Succession from North Africa (Algeria) – A Review for a New Era of Hydrocarbon Exploration
    2018
    Co-Authors: Djouder Hocine, Uysal Tonguç, Boulvain Frédéric, Bourdet Julien, Da Silva Anne-christine, Todd Andrew, Ramanaïdou Erick
    Abstract:

    audience: researcher, professionalThe diagenetic grade and thermal history of the widespread graptolitic Silurian Oued Imihrou black shales (Llandoverian in age) and the overlying sandstone levels of the Atafaïtafa Formation (late Llandoverian to Wenlockian) from the Tassili n'Ajjer plateau have been investigated by integrating a variety datasets, such as illite crystallinity, graptolite-derived organic matter reflectance, source-rock maturity and illite K–Ar ages. Combination of X-ray diffraction and petrographic examinations allowed to confirm the occurrence of three distinct minerals of authigenic origin, i.e. kaolinite, illite, and iron-rich chlorite, within the Silurian succession. These clay minerals, as well as pyrite and quartz overgrowths, were neoformed at different times during diagenetic-to-hydrothermal conditions and conversion-precipitation reactions. Furthermore, formation processes of these minerals are found to be broadly controlled by the stratigraphical level, lithology of the host rocks and the paleogeographical location of the studied outcrop sections from the eastern- and western-Tassili n'Ajjer plateau (Djouder et al., 2018). The illite crystallinity (i.e. Crystallinity index standards or CIS-calibrated IC values range between 1.58 to 0.38 Δ°2θ), paleotemperature estimates (~113–190°C) and graptolite reflectance (vitrinite reflectance equivalent, 0.65–1.5% VReqv) correspond to low grade diagenesis/anchi-metamorphic illite crystallization conditions and the oil-to-wet gas hydrocarbon generation zone. A paleothermal gradient towards the West is clearly present. This higher thermal maturity of the most western part of the Tassili (Tmax=466–483°C) is intimately linked to the migration of hot fluids, notably along N-S lineaments mega-shear zones in the Hoggar Shield. The latter were repeatedly reactivated during the Phanerozoic orogenies and rifting phases. K−Ar dating results indicate at least two generations of authigenic micrometric illite crystals, which are interpreted to reflect the timing of fluid flow events in association with fault reactivations within the Tassili n'Ajjer plateau at the northern Hoggar Shield. The older illite of 335 ± 8 Ma is consistent with the timing of the early Hercynian tectono-thermal activity in the region, accompanied probably by the first hydrocarbon generation, i.e. Carboniferous age ‘Visean’. While, the younger illite precipitations at 238 ± 11 Ma (Mid–Upper Triassic) and at 204 ± 6 to 179 ± 4 Ma (Triassic–Jurassic transition) can be attributed to high temperature fluid flow and kerogen maturation of the Early Silurian black shales, following Tethys rifting and the later development of the Central Atlantic Magmatic Province, respectively

  • Silurian Succession from North Africa (Algeria) – A Review for a New Era of Hydrocarbon Exploration
    2018
    Co-Authors: Djouder Hocine, Uysal Tonguç, Boulvain Frédéric, Bourdet Julien, Da Silva Anne-christine, Todd Andrew, Ramanaïdou Erick
    Abstract:

    The diagenetic grade and thermal history of the widespread graptolitic Silurian Oued Imihrou black shales (Llandoverian in age) and the overlying sandstone levels of the Atafaïtafa Formation (late Llandoverian to Wenlockian) from the Tassili n'Ajjer plateau have been investigated by integrating a variety datasets, such as illite crystallinity, graptolite-derived organic matter reflectance, source-rock maturity and illite K–Ar ages. Combination of X-ray diffraction and petrographic examinations allowed to confirm the occurrence of three distinct minerals of authigenic origin, i.e. kaolinite, illite, and iron-rich chlorite, within the Silurian succession. These clay minerals, as well as pyrite and quartz overgrowths, were neoformed at different times during diagenetic-to-hydrothermal conditions and conversion-precipitation reactions. Furthermore, formation processes of these minerals are found to be broadly controlled by the stratigraphical level, lithology of the host rocks and the paleogeographical location of the studied outcrop sections from the eastern- and western-Tassili n'Ajjer plateau (Djouder et al., 2018). The illite crystallinity (i.e. Crystallinity index standards or CIS-calibrated IC values range between 1.58 to 0.38 Δ°2θ), paleotemperature estimates (~113–190°C) and graptolite reflectance (vitrinite reflectance equivalent, 0.65–1.5% VReqv) correspond to low grade diagenesis/anchi-metamorphic illite crystallization conditions and the oil-to-wet gas hydrocarbon generation zone. A paleothermal gradient towards the West is clearly present. This higher thermal maturity of the most western part of the Tassili (Tmax=466–483°C) is intimately linked to the migration of hot fluids, notably along N-S lineaments mega-shear zones in the Hoggar Shield. The latter were repeatedly reactivated during the Phanerozoic orogenies and rifting phases. K−Ar dating results indicate at least two generations of authigenic micrometric illite crystals, which are interpreted to reflect the timing of fluid flow events in association with fault reactivations within the Tassili n'Ajjer plateau at the northern Hoggar Shield. The older illite of 335 ± 8 Ma is consistent with the timing of the early Hercynian tectono-thermal activity in the region, accompanied probably by the first hydrocarbon generation, i.e. Carboniferous age ‘Visean’. While, the younger illite precipitations at 238 ± 11 Ma (Mid–Upper Triassic) and at 204 ± 6 to 179 ± 4 Ma (Triassic–Jurassic transition) can be attributed to high temperature fluid flow and kerogen maturation of the Early Silurian black shales, following Tethys rifting and the later development of the Central Atlantic Magmatic Province, respectively

  • Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy
    2018
    Co-Authors: Djouder Hocine, Da Silva Anne-christine, Lüning Sebastian, Abdallah Hussein, Boulvain Frédéric
    Abstract:

    The economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern- to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow- to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.Peer reviewe

  • Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy
    'Elsevier BV', 2018
    Co-Authors: Djouder Hocine, Da Silva Anne-christine, Lüning Sebastian, Abdallah Hussein, Boulvain Frédéric
    Abstract:

    peer reviewedaudience: researcher, professional, student, popularization, otherThe economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region. The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern- to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow- to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called "Tigillites" pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha. The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.Silurian deltaic progradation rock record, under storm- and fluvial-influenced setting (Gondwana): Sedimentology, ichnology, sequence stratigraphy, clay mineralogy, and implications for thermal maturity evolution