Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organi... more In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organisation; frequently arranged on rzj$t reray and in elementaly scale, they show torsion and simple or multiple uirgations. This geometrical evolution indicates a cutting up on tectonic strips on dextral shears: limited by two great corridors of dextral strike-slip faults: N!90 of Kasserine and N12& 130 of Gafsa. 0 Acadhie des sciences / Elsevier, Paris.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organi... more In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organisation; frequently arranged on rzj$t reray and in elementaly scale, they show torsion and simple or multiple uirgations. This geometrical evolution indicates a cutting up on tectonic strips on dextral shears: limited by two great corridors of dextral strike-slip faults: N!90 of Kasserine and N12& 130 of Gafsa. 0 Acadhie des sciences / Elsevier, Paris.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
ABSTRACT In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bund... more ABSTRACT In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organisation; frequently arranged on right relay and in elementary scale, they show torsion and simple or multiple virgations. This geometrical evolution indicates a cutting up on tectonic strips on dextral shears; limited by two great corridors of dextral strike-slip faults: N90 of Kasserine and N120–130 of Gafsa.
In the south-western Anti-Atlas of Morocco (Dra Plain), a continuous exposure of Lower Devonian s... more In the south-western Anti-Atlas of Morocco (Dra Plain), a continuous exposure of Lower Devonian sedimentary successions more than 400 km long provides an example of mixed siliciclastic-carbonate shelf sequences. The carbonates were deposited adjacent and down-dip to large lobes of storm-dominated deltaic complexes during sea-level lowstands, and subsequently transgressed over the 200 m thick prograding siliciclastic wedges during sea-level rise, depositing limestone units between 5 and 20 m thick. The deltaic lobes switched through time and caused alternating siliciclastic supply along the shoreline oblique-parallel transect. Condensed limestone successions formed in clastic sediment starved areas due to delta-complex abandonment. Down-gradient, in outer ramp environments, the direct juxtaposition of carbonate and siliciclastic lithofacies associations comprising rhythmic lime mudstones/marls and massive shelf sandstones, provides the opportunity for mutual interpretation of their mode of deposition and bathymetry. This lateral relationship suggests that significant amalgamation took place in falling stage systems tracts to produce laterally extensive shelf sandstone-sheets on the outer ramp. Two types of stacking patterns are observed in prograding siliciclastic wedges. A normal progradational shoreline pattern with well developed parasequence sets in the proximal ramp, and an abrupt-regressive succession in which the amalgamated shelf sandstones rest more or less directly on offshore siltstones in the distal ramp. In the latter case, the falling stage systems tract sandstones are overlain by a relatively thick cyclic alternation with brachiopod-rich storm-beds below a marked transgressive surface at the base of the capping transgressive limestones. The cyclic alternation is interpreted as lowstand systems tract deposits. Marked flooding surfaces on parasequence sets are Fe-enriched and contain abundant articulated brachiopods, indicating breaks in sedimentation and an overall deepening-upward facies from the underlying maximum regression and sequence boundary. These aggradational to retrogradational stacked lowstand systems tracts are thus rather 'transgressive', not regressive in character, as is commonly described in sequence stratigraphic ramp models.
This work characterizes the source rock potential of the Tarfaya Basin and enabled us to reconstr... more This work characterizes the source rock potential of the Tarfaya Basin and enabled us to reconstruct its geochemical history. Outcrop samples covering different stratigraphic intervals, plus the northwestern part of the Zag/Tindouf Basin (Bas Draa area), were analyzed for total organic carbon (C org ) and total inorganic carbon contents and total sulfur content. Rock-Eval analysis and vitrinite reflectance measurements were performed on 56 samples chosen on the basis C org content. A set of 45 samples were extracted and non-aromatic hydrocarbons were analyzed by way of gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (GC-MS). Non-isothermal open system pyrolysis at different heating rates was applied to obtain kinetic parameters for modelling petroleum generation from four different source rocks.
... Seismic and well data for this study have been made available by ONHYM. This study, as PhD pr... more ... Seismic and well data for this study have been made available by ONHYM. This study, as PhD project of Axel Wenke, has been funded by RWE Dea. ... In: Macgregor et al.: Petroleum Geology of North Africa – Geol. Soc. Spec. ...
The early Toarcian is characterized by the occurrence widespread black shale deposits, recorded e... more The early Toarcian is characterized by the occurrence widespread black shale deposits, recorded extensively across Europe and interpreted to be related to an Oceanic Anoxic Event. In order to investigate the source-rock potential of lower Toarcian deposits in Morocco, detailed sedimentary logging accompanied by outcrop spectral gamma-ray measurements were carried out on four sections representative of different palaeo-depositional settings in the Central High Atlas. Authigenic uranium enrichment is used as a proxy for oxygen-depleted depositional conditions, and may thus indicate potential organic-rich lithologies. Of the four measured sections, only one (the Amellago section, which represents the deepest marine setting) shows relative authigenic uranium-enrichment. Complimentary TOC analyses (with maximum value of 3.24%) over this interval confirm an associated enrichment trend in organic matter. The organic matter recovered from the outcrop samples is however highly oxidised, and thus the absolute value is not regarded as being a true record of the rocks' organic content. It is concluded from this study that early Toarcian potential source rocks were deposited within restricted sub-basins in the Central High Atlas. It is therefore possible that organicrich deposits of Toarcian age are present in similar palaeogeographic settings in other areas of Morocco. This increases the exploration potential of Moroccan basins in which Jurassic deposits are potential source rocks.
The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biolog... more The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes, which coincide with a general decrease of calcium carbonate production and an increase of organic carbon burial, culminating in the so-...
The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biolog... more The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes. These coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial, and culminate in the so-called Toarcian Oceanic Anoxic Event. It is believed that the environmental crisis was triggered by the activity of the Karoo-Ferrar large igneous province. In order to further document the Early Toarcian palaeoenvironmental perturbations, carbon isotope, total organic matter, calcareous nannofossils and phosphorus content of the Amellago section in the High Atlas rift basin of Morocco were investigated. This section is extremely expanded compared to the well-studied European sections. Its position along the northern margin of the Gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western Tethyan realm. The carbon isotope curve shows two negative excursions of equal thickness and amplitude, at the Pliensbachian-Toarcian boundary and at the transition from the Polymorphum to the Levisoni Zone. This confirms the supra-regional nature of these shifts and highlights the possible condensation of the first "boundary" shift in European sections. Phosphorus content is used to trace palaeo-nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels, confirming that these episodes are related to enhanced continental weathering, probably due to elevated greenhouse gases in the atmosphere. In the High Atlas Basin, the increase in nutrient levels at the Pliensbachian-Toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the Saharan carbonate platform. A middle Toarcian event, centered on the boundary between the Bifrons and Gradata Zones, characterized by a positive carbon isotope excursion and nutrient level rise, is documented in the Amellago section.
The Tafilalt is one of a number of generally unexplored sub-basins in the eastern Anti-Atlas of M... more The Tafilalt is one of a number of generally unexplored sub-basins in the eastern Anti-Atlas of Morocco, all of which probably underwent a similar tectono-stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000 km of 2-D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi-phase deformation history for the Palaeozoic-aged Tafilalt sub-basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic-aged strata, producing a structural style characteristic of thin-skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault-propagation folding related to the thrust imbricates that ramp up-section from the décollement.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organi... more In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organisation; frequently arranged on rzj$t reray and in elementaly scale, they show torsion and simple or multiple uirgations. This geometrical evolution indicates a cutting up on tectonic strips on dextral shears: limited by two great corridors of dextral strike-slip faults: N!90 of Kasserine and N12& 130 of Gafsa. 0 Acadhie des sciences / Elsevier, Paris.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organi... more In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organisation; frequently arranged on rzj$t reray and in elementaly scale, they show torsion and simple or multiple uirgations. This geometrical evolution indicates a cutting up on tectonic strips on dextral shears: limited by two great corridors of dextral strike-slip faults: N!90 of Kasserine and N12& 130 of Gafsa. 0 Acadhie des sciences / Elsevier, Paris.
Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science, 1998
ABSTRACT In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bund... more ABSTRACT In the southern-central Atlas of Tunisia, the anticlines megastructures show a fold bundle organisation; frequently arranged on right relay and in elementary scale, they show torsion and simple or multiple virgations. This geometrical evolution indicates a cutting up on tectonic strips on dextral shears; limited by two great corridors of dextral strike-slip faults: N90 of Kasserine and N120–130 of Gafsa.
In the south-western Anti-Atlas of Morocco (Dra Plain), a continuous exposure of Lower Devonian s... more In the south-western Anti-Atlas of Morocco (Dra Plain), a continuous exposure of Lower Devonian sedimentary successions more than 400 km long provides an example of mixed siliciclastic-carbonate shelf sequences. The carbonates were deposited adjacent and down-dip to large lobes of storm-dominated deltaic complexes during sea-level lowstands, and subsequently transgressed over the 200 m thick prograding siliciclastic wedges during sea-level rise, depositing limestone units between 5 and 20 m thick. The deltaic lobes switched through time and caused alternating siliciclastic supply along the shoreline oblique-parallel transect. Condensed limestone successions formed in clastic sediment starved areas due to delta-complex abandonment. Down-gradient, in outer ramp environments, the direct juxtaposition of carbonate and siliciclastic lithofacies associations comprising rhythmic lime mudstones/marls and massive shelf sandstones, provides the opportunity for mutual interpretation of their mode of deposition and bathymetry. This lateral relationship suggests that significant amalgamation took place in falling stage systems tracts to produce laterally extensive shelf sandstone-sheets on the outer ramp. Two types of stacking patterns are observed in prograding siliciclastic wedges. A normal progradational shoreline pattern with well developed parasequence sets in the proximal ramp, and an abrupt-regressive succession in which the amalgamated shelf sandstones rest more or less directly on offshore siltstones in the distal ramp. In the latter case, the falling stage systems tract sandstones are overlain by a relatively thick cyclic alternation with brachiopod-rich storm-beds below a marked transgressive surface at the base of the capping transgressive limestones. The cyclic alternation is interpreted as lowstand systems tract deposits. Marked flooding surfaces on parasequence sets are Fe-enriched and contain abundant articulated brachiopods, indicating breaks in sedimentation and an overall deepening-upward facies from the underlying maximum regression and sequence boundary. These aggradational to retrogradational stacked lowstand systems tracts are thus rather 'transgressive', not regressive in character, as is commonly described in sequence stratigraphic ramp models.
This work characterizes the source rock potential of the Tarfaya Basin and enabled us to reconstr... more This work characterizes the source rock potential of the Tarfaya Basin and enabled us to reconstruct its geochemical history. Outcrop samples covering different stratigraphic intervals, plus the northwestern part of the Zag/Tindouf Basin (Bas Draa area), were analyzed for total organic carbon (C org ) and total inorganic carbon contents and total sulfur content. Rock-Eval analysis and vitrinite reflectance measurements were performed on 56 samples chosen on the basis C org content. A set of 45 samples were extracted and non-aromatic hydrocarbons were analyzed by way of gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (GC-MS). Non-isothermal open system pyrolysis at different heating rates was applied to obtain kinetic parameters for modelling petroleum generation from four different source rocks.
... Seismic and well data for this study have been made available by ONHYM. This study, as PhD pr... more ... Seismic and well data for this study have been made available by ONHYM. This study, as PhD project of Axel Wenke, has been funded by RWE Dea. ... In: Macgregor et al.: Petroleum Geology of North Africa – Geol. Soc. Spec. ...
The early Toarcian is characterized by the occurrence widespread black shale deposits, recorded e... more The early Toarcian is characterized by the occurrence widespread black shale deposits, recorded extensively across Europe and interpreted to be related to an Oceanic Anoxic Event. In order to investigate the source-rock potential of lower Toarcian deposits in Morocco, detailed sedimentary logging accompanied by outcrop spectral gamma-ray measurements were carried out on four sections representative of different palaeo-depositional settings in the Central High Atlas. Authigenic uranium enrichment is used as a proxy for oxygen-depleted depositional conditions, and may thus indicate potential organic-rich lithologies. Of the four measured sections, only one (the Amellago section, which represents the deepest marine setting) shows relative authigenic uranium-enrichment. Complimentary TOC analyses (with maximum value of 3.24%) over this interval confirm an associated enrichment trend in organic matter. The organic matter recovered from the outcrop samples is however highly oxidised, and thus the absolute value is not regarded as being a true record of the rocks' organic content. It is concluded from this study that early Toarcian potential source rocks were deposited within restricted sub-basins in the Central High Atlas. It is therefore possible that organicrich deposits of Toarcian age are present in similar palaeogeographic settings in other areas of Morocco. This increases the exploration potential of Moroccan basins in which Jurassic deposits are potential source rocks.
The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biolog... more The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes, which coincide with a general decrease of calcium carbonate production and an increase of organic carbon burial, culminating in the so-...
The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biolog... more The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes. These coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial, and culminate in the so-called Toarcian Oceanic Anoxic Event. It is believed that the environmental crisis was triggered by the activity of the Karoo-Ferrar large igneous province. In order to further document the Early Toarcian palaeoenvironmental perturbations, carbon isotope, total organic matter, calcareous nannofossils and phosphorus content of the Amellago section in the High Atlas rift basin of Morocco were investigated. This section is extremely expanded compared to the well-studied European sections. Its position along the northern margin of the Gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western Tethyan realm. The carbon isotope curve shows two negative excursions of equal thickness and amplitude, at the Pliensbachian-Toarcian boundary and at the transition from the Polymorphum to the Levisoni Zone. This confirms the supra-regional nature of these shifts and highlights the possible condensation of the first "boundary" shift in European sections. Phosphorus content is used to trace palaeo-nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels, confirming that these episodes are related to enhanced continental weathering, probably due to elevated greenhouse gases in the atmosphere. In the High Atlas Basin, the increase in nutrient levels at the Pliensbachian-Toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the Saharan carbonate platform. A middle Toarcian event, centered on the boundary between the Bifrons and Gradata Zones, characterized by a positive carbon isotope excursion and nutrient level rise, is documented in the Amellago section.
The Tafilalt is one of a number of generally unexplored sub-basins in the eastern Anti-Atlas of M... more The Tafilalt is one of a number of generally unexplored sub-basins in the eastern Anti-Atlas of Morocco, all of which probably underwent a similar tectono-stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000 km of 2-D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi-phase deformation history for the Palaeozoic-aged Tafilalt sub-basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic-aged strata, producing a structural style characteristic of thin-skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault-propagation folding related to the thrust imbricates that ramp up-section from the décollement.
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