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During the Early Jurassic, a group of large, aberrant bivalves called lithiotids proliferated in proximal, shallow marine environments. These lithiotids formed bioherms and extensive biostromes in the western and southern margins of the Tethys Ocean as well as eastern Panthalassa. In the Central High Atlas of Morocco, Pliensbachian and Toarcian (Lower Jurassic) lithiotid and lithiotid-coral reefal deposits occur within carbonate and mixed carbonate/siliciclastic neritic depositional settings. This study describes the stratigraphic distribution, taxonomy, and architecture of these lithiotid-rich deposits. The studied lithiotid and lithiotid-coral deposits from Morocco occur in sheltered, near-shore lagoons along tropical carbonate ramps and platforms. These facies are abundant in upper Pliensbachian strata as well as in the early Toarcian. The persistence and similarity of lithiotid-coral buildups across the stage boundary indicate that these ecosystems were not significantly affected by the Pliensbachian/Toarcian extinction in Morocco (at least, not until the Toarcian Oceanic Anoxic Event). In both the upper Pliensbachian and lower Toarcian, lithiotids (Lithioperna and Cochlearites) are frequently associated with phaceloid corals (Retiophyllia in the Pliensbachian and Phacellophyllia and Archaeosmiliopsis in the Toarcian) and solitary corals (Haimeicyclus and Archaeosmilia) as well as other corals and bivalves (Gervilleioperna, Mytiloperna, Opisoma, and rare megalodontids); however, the spatial distribution of taxa is patchy. The close association of lithiotid bivalves and corals is rarely documented in the literature, and lithiotid-coral reefal deposits are rare. Thus, these Moroccan biostromes and bioherms that record the interaction of corals and lithiotids are of particular scientific importance. Furthermore, multiple generations and successions of lithiotid-coral framestones can be observed in both Pliensbachian and Toarcian strata, which provide insight into the evolution of these communities and their resilience to ecosystem perturbations. Despite the success of lithiotid-coral communities in the Pliensbachian and Toarcian, these ecosystems were decimated by the Toarcian Oceanic Anoxic Event and never recovered.

Sea-level fluctuation is an important parameter controlling the sedimentation in deep-marine environments and influenced also the expansion of oxygen-depleted conditions in neritic settings during oceanic anoxic events (OAEs). Despite this fundamental role, sea-level fluctuation remains on a short timescale (

Mesozoic sea-level fluctuations have been a matter of debate for several decades, especially the extend and origin of sea-level cycles that have a periodicity of about 1 Myr or less. The debate lies in the main driving mechanism for sequence development (global sea-level or sediment flux variations) as well as the reason behind water exchanges between the continents and the oceans (glacio- or aquifer-eustatism). In this study, we focus on the carbonate-dominated sedimentary record of the Bajocian (Middle Jurassic) in the Central High Atlas Basin of Morocco. Several aspects make this basin an appropriate location for discussing Middle Jurassic sea-level changes. Firstly, the outstanding exposures of the High Atlas Mountains, with continuous exposures for 10s of kilometres, allow to describe and track sedimentary packages and their bounding surfaces from proximal to distal settings. Moreover, a combination of ammonite and brachiopod biostratigraphy with carbon-isotopes chemostratigraphy allows to temporarily constrain their development, which permits to correlate and compare the Central High Atlas sedimentary record to other basins. Finally, due to high-subsidence rates, thick Bajocian sedimentary sequences have accumulated, minimizing condensation and hiatus that might prevail in other basins due to a lack of accommodation space creation. Two Bajocian long-term transgressive-regressive (T-R) packages are observed throughout the basin. They are modulated by several medium-term T-R packages, that have each an approximate duration of 1 Myr. These sequences can also be correlated on a basinwide scale. Combined with sedimentological and facies analyses, architectural evidence along proximal-to-distal transect illustrates that several of the medium-term sequences are characterized by the presence of a falling stage and lowstand systems tracts, demonstrating that medium-term T-R stacking patterns are not solely linked to fluctuation in sediment supply, but also to episodes of relative sea-level fall of at least 30m of amplitude. This is confirmed by backstripping analysis performed in a composite section from the center of the Basin. Comparison with Bajocian deposits from France and Scotland, where good biostratigraphic dating is also available, shows that similar contemporaneous sea-level fall can be observed, highlighting their potential global character. The two long-term Bajocian sequences are more difficult to correlate on a global scale, suggesting that they are rather primarily linked to fluctuation in regional sediment supply or dynamic topography processes. The exact cause of the Bajocian medium-term sea-level falls is currently unknown, but it is here interesting to note that a relatively cool globate climate has been postulated for the Middle Jurassic, suggesting that glacio-eustasy was their most likely driver.

Standard sequence stratigraphy interpretations are commonly built upon the premise of fairly constant sediment supply, leaving vast uncertainties about sequence architecture and sea-level change recorded during major paleoenvironmental disturbances, usually associated with carbonate productivity collapse and increased siliciclastic sediments supply. During relative sea-level rise, this process is referred to as drowning event. However, drastic collapse of carbonate productivity during relative sea-level drop remains poorly documented. The Pliensbachian/Toarcian boundary in Morocco provides an outstanding example of such a case, referred here to as poisoning event. Using bio-, chemo- and high-resolution sequence stratigraphic approaches on horizontal seismic-scale outcrop data, we characterize the architecture of vertically and laterally mixed siliciclastic/carbonate systems. During poisoning event, the standard sequence Lowstand-Transgressive-Highstand system tracts is altered into Highstand-Transgressive-Falling Stage system tracts with little or no evidence for Highstand deposits. Noteworthy, it is important to note that poisoning and drowning events can be confused together in sedimentary records where the shoreline trajectory cannot be clearly tracked, as it has often been the case in previous Pliensbachian/Toarcian studies. The outcome of this study calls thus for a closer re-examination of other carbonate factory collapse event attributed to drowning events without an unambiguous knowledge of their coeval shoreline trajectory.

The red detrital formations of the Central and Eastern High Atlas of Morocco continue to spark a large scientific debate around their age varying from the middle Jurassic to the upper Cretaceous period . Through this paper, we present the results of lithological correlations of five detailed geological sections, covering the Jurassic–Cretaceous “red beds'' series, measured in the Central High Atlas along the Errachidia–Msemrir transect. These detrital strata are outcropped in syncline basin centres, delimited by raised ridges that are formed by lower and middle Jurassic formations. Important lateral variations of facies and thicknesses occur between the eastern and western parts of the studied transect. In the eastern part of the study area, the “red beds'' can be attributed to three lithostratigraphic formations, two formations that are generally sandstone-rich (Guettioua and Jbel Sidal Formations), separated by a third one which is clay-rich (Iouaridene Formation). In contrast, in the western part, the “red beds'' series is best allocated to the sandstone-rich of the Guettioua Formation. During the deposition of the Jurassic–Cretaceous “red beds”, the Central High Atlas Basin was subjected to important tectonics and salt diapirism events. Hence, the important variation of facies and thickness in the “red beds'' series may be best explained by the geodynamic evolution of the Central High Atlas and its control of the building of differential depositional areas. Together with global sea-level and climatic fluctuation, changes in differentiated local subsidence rate are hence pictured as a major driving parameter for facies and age differentiations between the eastern and western parts of the Central High Atlas Basin.

The Early Bajocian witnessed a global environmental perturbation, characterized by faunal and floral turnovers and a positive carbon isotope excursion. In Italy, this environmental perturbation coincided with an eutrophication event and a carbonate crisis, but this has so far not been adequately reported from other settings, leaving doubt about the extent and nature of these phenomena. In this paper, we are reporting on an extensive neritic carbonate factory demise that occurs in the upper Lower Bajocian of Morocco, more precisely in the upper Propinquans – lower Humphriesianum Zones. This demise coincided with the acme of the global carbon isotope perturbation, recorded by a 3‰ positive carbon isotope excursion in the bulk organic matter of Morocco, but not in the micritic phase, due to the fact that the Moroccan carbonate δ13C record is more sensitive to local rather than global influences. Furthermore, we observe that the Lower Bajocian of Morocco is relatively enriched in arenitic siliciclastic deposits, suggesting increased weathering and nutrient levels along the northwestern margin of Africa during the Early Bajocian. However, comparison with neighboring European basins highlights the non-uniqueness and different timing of the response of shallow-water carbonates to the Early Bajocian environmental perturbations, as some regions present no sign of carbonate factory crisis. Hence, we postulate that local factors were important in mediating the response of neritic carbonate factories to this global environmental perturbation. We notably highlight the role of large Early Bajocian sea-level fluctuation as a trigger for carbonate factory change and demise in Morocco.

Preceding the early Toarcian Oceanic Anoxic Event by similar to 1 Myr, the Pliensbachian-Toarcian boundary event is in many aspects as severe and disturbing for the environment as its better-studied successor. Both events are associated with rapid and pronounced global warming, major faunal and floral turnover, increased hydrological cycling and dramatic collapses of carbonate production. To better characterize the Pliensbachian-Toarcian boundary event, a high-resolution, paired carbonate and organic matter carbon isotope survey of three sections from the Central High Atlas Basin of Morocco has been undertaken. A pronounced negative shift in the carbonate carbon-isotope record, not paralleled by a similar excursion in the organic carbon, can be linked to the collapse of the neritic carbonate factory in the earliest Toarcian. These results show that, contrary to the Toarcian Oceanic Anoxic Event, a rapid and massive injection of C-13-depleted carbon into the atmosphere is not responsible for the environmental perturbations observed during the Pliensbachian-Toarcian boundary event. However, input of isotopically non depleted carbon such as mantle source CO2 into the atmosphere as a potential cause for the Pliensbachian-Toarcian boundary event cannot be excluded. This would most probably be sourced from an early pulse of the Karoo-Ferrar Large Igneous Province. (C) 2015 Elsevier Ltd. All rights reserved.

Carbonate reservoirs pose significant challenges for reservoir modelling and flow prediction due to heterogeneities in rock properties, limits to seismic resolution and limited constraints on subsurface data. Hence, a systematic and streamlined approach is needed to construct geological models and to quickly evaluate key sensitivities in the flow models. This paper discusses results from a reservoir analogue study of a Middle Jurassic carbonate ramp in the High Atlas Mountains of Morocco that has stratigraphic and structural similarities to selected Middle East reservoirs. For this purpose, high-resolution geological models were constructed from the integration of sedimentological, diagenetic and structural studies in the area. The models are approximately 1200 x 1250 m in size, and only faults (no fractures) with offsets greater than 1 m are included. Novel methods have been applied to test the response of flow simulations to the presence or absence of specific geological features, including proxies for hardgrounds, stylolites, patch reefs, and mollusc banks, as a way to guide the level of detail that is suitable for modelling objectives. Our general conclusion from the study is that the continuity of any geological feature with extreme permeability (high or low) has the most significant impact on flow.

The Pliensbachian and Toarcian (Early Jurassic) ages are characterised by several, relatively short-lived carbon cycle perturbations, climate change and faunal turnover. The cause(s) of biotic and abiotic disturbances remain unclear but most probably involved increased magmatic activity in the Karoo-Ferrar large igneous province. The Toarcian oceanic anoxic event (T-OAE) might represent the most extreme of these events, and as such, is becoming increasingly well documented worldwide. So far, other critical time intervals of the Pliensbachian-Toarcian have received considerably less attention. Here, the effects of the Middle Toarcian Variabilis event on the neritic-epeiric realm are explored making use of three well-exposed and extended stratigraphic sections in the Central High Atlas, Morocco. The carbon and oxygen isotopic compositions of 112 bulk micrite samples were analysed and placed against 39 data points from carefully screened brachiopod valves in order to differentiate between palaeo-environmental and diagenetic patterns. Additionally, the phosphorus concentrations of 109 micrite samples were determined to evaluate the P-cycling. In all studied sections, an upper middle Toarcian major change from carbonate- to clastics-dominated sedimentation is recorded, pointing to a first-order carbonate production crisis. Our results reveal that these major sedimentological patterns coincide with an increase of oxygen-isotope ratios as well as a decrease of phosphorous accumulation rates. This suggests that the late middle Toarcian carbonate ramp crisis was related to a transient cooling event, potentially triggered by pulsed massive SO4 exhalation events in the context of the Karoo-Ferrar large igneous province. Short-term cooling was likely amplified by the drawdown of atmospheric CO2 levels related to the coeval decline of neritic carbonate precipitation and the warm water mass circulation disruption between the Tethys and the continental shelf. The data shown here provide the first evidence for coupled changes in carbon cycling, continental weathering and neritic systems in the aftermath of the T-OAE. (C) 2014 Elsevier B.V. All rights reserved.

The occurrence of neritic microbial carbonates is often related to ecological refuges, where grazers and other competitors are reduced by environmental conditions, or to post-extinction events (e.g. in the Late Devonian, Early Triassic). Here, we present evidence for Middle Jurassic (Bajocian) microbial mounds formed in the normal marine, shallow neritic setting of an inner, ramp system from the High Atlas of Morocco. The microbial mounds are embedded in cross-bedded oolitic facies. Individual mounds show low relief domal geometries (up to 3 m high and 4.5 m across), but occasionally a second generation of mounds exhibits tabular geometries (

Considerable effort has been devoted to the development of simulation algorithms for facies modeling, whereas a discussion of how to combine those techniques has not existed. The integration of multiple geologic data into a three-dimensional model, which requires the combination of simulation techniques, is yet a current challenge for reservoir modeling. This article presents a thought process that guides the acquisition and modeling of geologic data at various scales. Our work is based on outcrop data collected from a Jurassic carbonate ramp located in the High Atlas mountain range of Morocco. The study window is 1 km (0.6 mi) wide and 100 m (328.1 ft) thick. We describe and model the spatial and hierarchical arrangement of carbonate bodies spanning from largest to smallest: (1) stacking pattern of high-frequency depositional sequences, (2) facies association, and (3) lithofacies. Five sequence boundaries were modeled using differential global position system mapping and light detection and ranging data. The surface-based model shows a low-angle profile with modest paleotopographic relief at the inner-to-middle ramp transition. Facies associations were populated using truncated Gaussian simulation to preserve ordered trends between the inner, middle, and outer ramps. At the lithofacies scale, field observations and statistical analysis show a mosaiclike distribution that was simulated using a fully stochastic approach with sequential indicator simulation. This study observes that the use of one single simulation technique is unlikely to correctly model the natural patterns and variability of carbonate rocks. The selection and implementation of different techniques customized for each level of the stratigraphic hierarchy will provide the essential computing flexibility to model carbonate settings. This study demonstrates that a scale-dependent modeling approach should be a common procedure when building subsurface and outcrop models.

Discontinuity surfaces are widely recognized but often poorly understood features of epeiric carbonate settings. In sedimentary systems, these features often represent hiatus surfaces below biostratigraphic resolution and may represent a considerable portion of the time contained in the sediment record. From an applied perspective, discontinuities may represent horizontal flow barriers and result in reservoir compartmentalization. Here, a total of 80 condensed surfaces (S1), firmgrounds (S2) and hardgrounds (S3) from a Jurassic (Middle and Upper Bajocian Assoul Formation) ramp setting of the High Atlas in Morocco are carefully documented with respect to their morphology, their secondary impregnation by Fe and Mn oxides and phosphates and their palaeoecological record. A statistical frequency distribution of two surfaces of the S1 type, 1.1 surfaces of the S2 type and 0.4 surfaces of the S3 type per 10 section metres is observed along a 220 m long carbonate succession. Based on two stratigraphically and spatially separated study windows and correlative sections, the stratigraphic frequency distribution, the lateral extent and the nature of facies change across discontinuities are documented in a quantitative manner. Specific features of the study site include the considerable stratigraphic thickness of the Assoul Formation and the conspicuous absence of subaerial-exposure-related features. Based on the data presented here, firmground and hardground surfaces are best interpreted as maximum-regression-related features. Relative sea-level lowstand results in a lowered wave base, and wave orbitals and currents result in sea floor omission and lithification. Care must be taken to avoid overly simplistic interpretations, as differences in bathymetry and carbonate facies result in marked changes in discontinuity characteristics in proximal-distal transects. The data shown here are of significance for those concerned with the interpretation of shoal water carbonate environments and are instrumental in the building of more realistic carbonate reservoir flow models.

A critical revision of published data along with new field data allow to draw up the succession of the fish faunas from the Lower Cenomanian to the Lower Turonian in the Tafilalt basin and surrounding areas (southeast Morocco). The analysis of these faunas shows changes from freshwater to marine palaeoenvironments. The palaeogeographic distribution of some taxa is discussed. It shows that the crossing of strictly freshwater organisms between Africa and South America was likely impossible at the time of the formation of the deposits resting around the Tafilalt basin and named ‘Kem Kem beds’. The Cenomano-Turonian transgression reached the Erfoud–Errachidia carbonate platform from the Central Tethys, and then connected the central Atlantic.

Although a few natural oases exist – for example the tufts of Doum palm trees in the Egyptian desert – the majority of the oases are human creations where humankind adapted to climatic fluctuations and preserved balance between its activities and the environment, until the 1950’s. Then climatic fluctuations occurred, which were noted through systematic weather measurements and recurring droughts in the North and the South of the Sahara.

Carbonate reservoirs pose significant challenges for reservoir simulation and flow prediction due to lateral and vertical heterogeneities that are difficult to predict. Limits to seismic resolution, heterogeneities in rock properties and limited constraints on subsurface data require the consideration of multiple geologic scenarios for flow predictions. Hence, a systematic and streamlined approach is needed to construct geologic models and to quickly evaluate key sensitivities in the flow models. This paper discusses results from a reservoir analogue study in a Mesozoic carbonate ramp in the High Atlas of Morocco. Here, geologic models have been constructed from the integration of sedimentological, diagenetic and structural studies in the area. Novel methods have been applied to develop a consistent approach for rock property definitions in outcrops and incorporate multi-scale fractures to test the response in flow simulations. In these simulations we have tested the response of presence or absence of specific geologic features, including hardgrounds, stylolites and fracture populations as a way to guide the level of detail that is suitable for modeling objectives. Based on these studies, we have been able to evaluate the relative impacts of some of the geologic features on flow behavior and gain further insights to effective recovery strategies.

The quality and level of resolution of 3D facies models are crucial factors for reservoir characterization and fluid flow prediction. This study presents a newly developed workflow from field acquisition to modeling approach, which can be used to model heterogeneities at different scale ranging from lithofacies, to Environment Of Deposition (EOD), to system tract deposited on a carbonate dominated ramp setting. This multi-scale approach integrates different data sets (stratigraphic sections, d-GPS points, LiDAR data) and allows to build three coherent models from these three scales of observations.

Date de l'operation : 1992 - 1994 (FP) Inventeur(s) : Boutie Paul (SUP) ; Ajaja Omar ; Banes Laurence ; Moles Valerie ; Kabiri Lahcen ; Gregoire Sophie Localisation Le lieu-dit Rec Mendil se situe dans le departement de l'Aude, sur le territoire de la commune de Port-la-Nouvelle, a mi-chemin entre les etangs de Lapalme et de Sigean [ (Fig. n°1 : Localisation du gisement entre les etangs de Sigean et de Lapalme) et (Fig. n°2 : Vue du massif dans lequel est creusee la cavite prise depuis l’et...