Synclinal Basin Research Articles

Delineation of Groundwater Storage and Recharge Potential Zones Using Multi-Influencing Factors (MIF) Method: Application in Synclinal Coastal Basin of Essaouira (Western High Atlas of Morocco)

Unpredictable rainfall caused by climate change and pollution directly impacts groundwater demand, making the exploitation of groundwater reserves necessary. To achieve this, a study in the synclinal basin of Essaouira (Western High Atlas) used GIS, remote sensing, and the Multi-Influencing Factors (MIF) method, to identify areas ideal for the installation of productive wells. An overlay analysis created a groundwater potential zone (GWPZ) map, showing 30% of the basin with high potential, 51% with moderate potential, and 19% with low to very low potential. The groundwater potential zone map was validated using geophysical surveys, piezometric data, and well water levels, showing a 69.3% prediction accuracy with the ROC curve.

South Anze Structure and Its Control on Coalbed Methane Aggregation in the Qinshui Basin and the Mechanism of Syncline Gas Enrichment in the Qinshui Basin

The phenomenon of coalbed-methane synclinal accumulation in the Qinshui Basin has been widely reported, but it has mainly been observed in the core block of the Qinshui Syncline. The questions arise: does this phenomenon exist in the wing of the Qinshui Syncline and, if so, what is the mechanism behind it? Further study is required to answer these questions. This paper focuses on the South Anze No. 3 coal seam in the Qinshui Basin as an example. It conducts a systematic sorting of coalbed-methane geological characteristics and an analysis of the effects of structural assemblage characteristics, genetic mechanisms, and structural control on coalbed-methane accumulation. Additionally, it examines the basin structure and evolution during the critical period of the Qinshui Basin, as well as the gas geological characteristics of adjacent areas, in order to discuss the gas-rich mechanism of the syncline in the Qinshui Basin. Key insights obtained from the study include the following: (i) The whole South Anze is a nosing structure that plunges from west to east and superposes secondary folds and faults in different directions. Four deformation zones can be identified based on the characteristics of structural assemblage, including NEN-oriented compressive structures, ENE-trend shear fractures, EW-trend compressive fractures, and EW-trend compressive folds. The formation of structural assemblage in the study area is attributed to the compression in the Indosinian and Yanshanian, and the fault inversion in the Himalayan period. (ii) The ENE-trend shear fracture deformation area located in the nosing uplift is a low CBM (coalbed methane) content area due to gas diffusion during the Himalayan extension. The syncline in the combination of NEN-trend and EW-trend “ejective folds” in the west and south of the study area is a high-value area of coalbed-methane content. It is further verified that the law of syncline gas accumulation in the Qinshui Basin is also applicable to the wing of the Qinshui Syncline. (iii) Since the formation of the Qinshui Syncline, the main coal seam has been in an extensional environment below the neutral plane, resulting in the main dissipation of coalbed methane. During its geological history, surface water penetrated the aquifer above the main coal seam through two channels: the extensional area above the neutral plane of the adjacent anticline and the shear fracture. A hydrostatic pressure seal is formed in the Qinshui Syncline and the secondary syncline is superimposed upon it, which is the cause of gas enrichment in the syncline of the Qinshui Basin. (iv) Weak deformation in the syncline basin is the focus of global coalbed-methane exploration and development. The mechanism proposed in this paper can provide ideas and references for further understanding of coalbed-methane enrichment in this type of basin.

Structural control of inherited salt structures during inversion of a domino basement-fault system from an analogue modelling approach

Abstract. The geometries of inverted rift systems are different depending on a large variety of factors that include, among others, the presence of decoupling layers, the thickness of the pre- and syn-extension successions, or structural inheritances. Our study focuses on the inversion of an extensional domino-style basement-fault system with a pre-extension salt layer using analogue models to understand the role of pre-existing structural features during inversion. Models investigate how different overburden and salt thicknesses, inherited extensional structures, and salt distributions condition the evolution during inversion. The experimental results show that models with thick salt can partially or totally preserve the extensional ramp–syncline basin geometry independently of the overburden thickness. In contrast, models with a thin salt layer result in a total inversion of the ramp–syncline basins with the development of crestal collapse grabens and extensional faults affecting the overburden. Inversion also triggered the growth or reactivation of salt-related structures such as primary weld reopening and/or obliteration, diapir rejuvenation, salt thickening, or thrust emplacement. The use of analogue modelling allowed us to address the processes that controlled the growth and evolution of these structural elements during the inversion. Experimental results also provide a template of different structural styles resulting from the positive inversion of basins with a pre-extensional salt layer that can help subsurface interpretation in areas with poor seismic imaging.

Assessment of Groundwater Quality and the Main Controls on Its Hydrochemistry in a Changing Climate in Morocco (Essaouira Basin)

Groundwater is essential for both water supply and environmental conservation, especially in semi-arid and desert areas. Managing groundwater resources requires a thorough understanding of groundwater characteristics and dynamics. The hydrogeochemical properties and evolution of groundwater in the Essaouira synclinal basin in northwest Morocco were studied in this research, with 105 water samples collected in 2009, 2017, 2018, and 2019. The Water Quality Index (WQI) and Irrigation Water Quality Index (IWQI) were developed to determine groundwater quality for consumption and irrigation purposes. The chemical evolution of groundwater is mainly dominated by evaporite, mineral carbonate dissolutions, and cation exchange. Contamination by nitrates is particularly severe in agricultural and tourist areas. The WQI of the 2019 campaign showed that 6.7% of groundwater samples are unsuitable for drinking; 76.7% are poor quality water; and 13.3% are very poor-quality water; while only 3.3% are drinkable. According to IWQI, the total study area has been split into 50% (good), 43.3% (bad), and 6.6% (unfit), respectively, and no excellent groundwater areas have been identified. Therefore, the water is suitable for agriculture but must be treated for drinking. The presence of evaporation and maritime intrusion and the contribution of recent precipitations to aquifer recharging were demonstrated by stable isotope content.

Geological heritage of the Taguelft syncline (M'Goun Geopark): Inventory, assessment, and promotion for geotourism development (Central High Atlas, Morocco)

The Taguelft syncline, located south of the Béni Mellal city, is one of the synclinal basins of the central High Atlas. It contains significant geological heritage that should be inventoried, valorized, and protected. The present study aimed to inventory and evaluate the syncline's geological heritage and then propose geotourism and geodidactic promotion allowing their sustainable geoconservation. This is done by applying the University of Lausanne methodology, based on the quantitative and qualitative assessment of the scientific (considered central) and additional values. Results highlight geodiversity elements with high scientific (≃0.84) and aesthetic (≃0.85) values related to the strong representativeness of the regional geological phenomena (genesis modes of magmatic bodied, tabular structure of Jbel Sgat, gabbroic intrusion of the Ait Boulmane wrinkle). The assessment also shows that the study area hosts a valuable palaeontological heritage enclosing fossil wood, ammonites, and dinosaur remains (bones and footprints). Moreover, it has underlined an important cultural and architectural interest of the tribe of Ait Sokhmane. Taken together, the diverse geological and cultural heritage identified can constitute a valuable tool for geoconservation and geotourism purposes. Due to their high touristic and educational potential, the geosites of the syncline are a preferred tourist destination for many visitors and can serve as valuable educational excursion sites for the dissemination of geosciences through different tools such as interpretation panels, digital media, leaflets, and guided tours. This exceptional geodiversity, and the rich cultural heritage, constitute a support for the development of geotourism and a tool for reinforcing local socio-cultural development. The knowledge and understanding of the different facets of the geological and cultural heritage as well as the management and planning of these resources all contribute to sustainable and developed tourism.

Deep groundwater circulation in a syncline in Rucheng County, China

Deep groundwater circulation is closely related to the earth surface processes of water, energy and matter, and imposes great influences on the earth critical zone. It is still unknown whether a deep groundwater circulation occurs in a syncline structure. Hydrogeochemical investigations of hot spring, cold spring and shallow groundwater were carried out in a syncline basin in Rucheng County, China. The water source, circulation depth, reaction temperatures, and mixing processes were evaluated by water chemistry and thermodynamic methods to reveal the pattern and controlling factors of the deep groundwater circulation. Results showed that two deep circulation groundwater systems with meteoric origin were developed in the syncline. The Tangkou system is related with the northwest wing of the syncline, the main fault F2, and the RS01 thermal spring. The Luoquan system is related with the southeast wing, the main fault F1, and the RS02 thermal spring. The main faults are water-blocking faults, separating the two systems. The mean elevations of recharge areas of the two systems were 1200m and 850m, respectively. The deep groundwater circulation depths of two systems reached 5.5 ± 0.5 and 3.6 ± 0.3 km, respectively. Within the geothermal reservoirs, deep circulating groundwater was heated up to 156°C for RS01 and 108°C for RS02. Before arriving at the ground, cold shallow groundwater mixed into the deep circulation systems. The mixing ratios of deep circulating groundwater were 14.8% at RS01 and 35.6% at RS02. The HCO3-Ca type deep circulating groundwater was slightly mineralized karst or karst-related water. Carbonate dissolution was the dominant water-rock interaction. The mixing obviously diluted the deep circulating groundwater, but didn’t alter its water type. In our case, the large-scale synclinal structure is favorable to deep groundwater circulation, which is closely related with the carbonate stratum and faults. The depth of the deep groundwater circulation can be determined by recharge area elevation and geothermal reservoir depth, which is a simple and effective method.

Hyperextension and polyphase rifting: Impact on inversion tectonics and stratigraphic architecture of the North West Shelf, Australia

Restoration of interpreted 2D deep seismic lines across Australia's North West Shelf indicates that rifting style changed significantly during multiple phases of extension and continental breakup. Early phase rifting during the Neo-Proterozoic and Early Paleozoic, characterised by low-angle detachment faults, crustal-scale necking and hyperextension of the crust (Metamorphic Core Complex Mode), was localised over pre-existing Proterozoic orogenic belts formed adjacent to major cratonic blocks. Subsequent extensional events in the Late Paleozoic and Mesozoic reactivated these low-angle rift fault systems. However, a series of narrow rift basins (Narrow Rift Mode), bound by high-angle normal faults that cut into the upper mantle, also began forming due to changes in the rheological architecture of the lithosphere following previous extension, crustal thinning and post-rift cooling. Wide rift mode extension, wherein extensional deformation was distributed over broad areas, may have occurred prior to, or in conjunction with, the development of more localised narrow rifts (dual mode rifting) in areas such as the Northern Carnarvon and Browse basins. Extensional deformation progressively localised into the narrow rift basins, which in some cases, matured into seafloor spreading centres during breakup, typically outboard of the major low-angle detachment fault systems. The resulting general structural architecture evolution is consistent with several other hyperextended margins from around the world.The rift events were punctuated by periods of thermal sag, often in conjunction with pulses of compressional deformation associated with plate-scale tectonic events. Structural restoration of 2D regional seismic lines shows a marked difference in the way the different polyphase rift basin elements responded to shortening. Low-angle detachment faults were relatively well oriented for reactivation under compression, leading to the development of inversion anticlines and associated convergent unconformities towards the inboard basin margin. In contrast, high-angle normal fault systems associated with the pre-existing narrow rift basins were poorly oriented for reactivation during compression and tend to be characterised by minor wrench/flower structures, generally with relatively limited uplift and erosion on the basin margins. Regional in-plane compressional stresses also worked in combination with vertical loading due to thermal decay to downwarp the lithosphere, forming broad rapidly subsiding synclinal basins above axes of the pre-existing rift basins. The evolving structural architecture developed during the compressional events had significant impacts on the associated sequence stratigraphic architecture.

Groundwater fluoride concentrations in the watershed sedimentary basin of Quetta Valley, Pakistan.

Litho-geochemical characteristics of low and high fluoride (F-) groundwater along with hydrological processes were investigated to delineate its genesis and enrichment mechanism in a watershed sedimentary basin. In this study, groundwater F- concentration ranged from 0 to 20mg/L with a mean and standard deviation of 2.8 and ± 3.7mg/L, respectively. Out of N = 87, 63% of samples exceeded the World Health Organization (WHO) limit of 1.5mg/L. The order of cationic and anionic dominance in groundwater samples with mean was found in decreasing order as Na+ > Mg2+ > Ca2+ > K+ and HCO3- > SO42- > Cl- > PO43- > NO3- measured in milligrams per liter. Groundwater chemistry changed from Ca-HCO3 to Na-HCO3 type and low to high fluoride as we moved from mountain foot towards the synclinal basin. Low fluoride groundwater reflected weathering, recharge, and reverse ion exchange processes with Ca-HCO3- and Ca-Mg-Cl-type water while high fluoride groundwater revealed base ion exchange, mixing, and desorption as dominant hydrological processes with Na-HCO3 and Na-Cl types of water. Gibb's diagram showed rock weathering and mineral dissolution as the major geochemical processes controlling water chemistry with an insignificant role of evaporation in the semi-arid area. Fluoride was undersaturated with mineral fluorite, indicating fluoride in groundwater is released by secondary minerals. However, due to complex geological features, groundwater fluoride enrichment was affected by a broad-scale process across a wide area such as depth, residence time, and most important geomorphological units hosting the aquifer.

Stratigraphic and geodynamic characterization of Jurassic–Cretaceous “red beds” on the Msemrir–Errachidia E–W transect (central High Atlas, Morocco)

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.

Taking the Pulse of Salt‐Detached Gravity Gliding in the Eastern Mediterranean

AbstractDespite having a profound impact on the structural evolution of salt‐influenced basins, spatial and temporal variations in rates of salt flow, and their key controls, remain largely unconstrained. We investigate early stage salt‐detached gliding using a 3D seismic data set from the Levant Margin in the Eastern Mediterranean, where gravitational instability due to margin uplift has caused north‐westward translation of the Messinian salt sheet and its overburden. Large base‐salt anticlines mean that basinward translation is recorded by the development of supra‐salt ramp syncline basins (RSBs) and fluid escape pipes, the latter forming due to the leakage of fluid from the anticline crests. The trails of pipes provide kinematic vectors of transport direction, while the stratigraphic record of the RSBs not only constrains the relative ages of the pipes, but allows us to quantify the magnitude and approximate rate of translation. We correlate intra‐RSB horizons across the margin to analyze lateral variations in translation rate, and how these vary through time. We show that translation rates are broadly uniform on the length‐scale of individual anticlines (c. 10 km), but that there is significant margin‐scale (c. 100 km) lateral variability in both the direction and magnitude of translation. We attribute temporal variations in local rates of translation to cyclical “pulses” of salt flow due to volumetric flux imbalances across the anticlines, while the distribution of elastic strain in the overburden modulates the overall basin‐scale trend. These results demonstrate the importance of local stresses in controlling the local direction and rate of salt flow, and further our understanding of salt and overburden rheology.

Paleohydrogeology of the Karstic System of Fuentetoba Spring (Soria, Spain): An Interdisciplinary Approach

As a preliminary phase in the conservation and sustainable management of a karst system in Fuentetoba, Soria, Spain, an interdisciplinary study was carried out to determine its hydrogeological evolution. The hydrogeological history of this aquifer system began during the late Miocene, where discharges were driven by paleo-emergences in the moor, and associated conduits were developed under phreatic (or vadose) conditions—for example, the upper syngenetic galleries in the main known karst cave (Majada del Cura cave). Later on, the nearby karstic massifs, a general flattening of the relief, occurred during the Quaternary Period, during which the karstic base level had been in decline. The aquifer flow was then derived and modified towards the Fuentetoba spring from the earliest stages through the galleries of the aforementioned cave. The observations made in this cave indicate the existence of a unique type of hydrogeological organization. The hypogean network is the result of the excavation of the same water flow that has been entrenching and abandoning the vadose regimen toward the free regimen. The dating of the tuffaceous buildings, associated with the emergences, indicates that since almost the Middle Pleistocene, flow lines have converged in the Fuentetoba spring, inducing a high grade of karstification in the saturated zone of the syncline basin. Moreover, a major drainage conduit was developed by dissolution. During the late Upper Pleistocene, an essential component of the groundwater flow had been derived towards the source of the Mazos River spring. Tufa and paleogour datings in caves indicate that the aquifer has undergone different climatic stages during the latest Quaternary and, therefore, different feeding and recharge processes. These tufas and paleogours are interrelated as well, as they are associated with the warm stages during the most recent Quaternary, according to the regional context, when there was less natural recharge. The simulation of the springs’ flow enabled an approximate quantification of the variation in the aquifer’s hydraulic balance during the different climatic stages. For example, during the last glaciation, the natural recharge was impacted by snowmelt and increased by 160%.

Mechanism for large-scale canyon deformations due to filling of large reservoir of hydropower project

Large storage dam projects may modify geo-environmental conditions in many ways. The reservoir impoundment of the 285.5 m high Xiluodu arch dam located on the Jinsha River (China) caused large-scale canyon deformations, including significant canyon contraction and uplift movements from reservoir to downstream valley. The dam experienced subsequent tilting towards upstream and raised a safety concern of the project. A Thermo-Hydro-Mechanical (THM) mechanism is proposed for this extraordinary behavior. Due to reservoir impounding and seepage, significant temperature drops and fluid pressure increase within the underlying geothermal limestone aquifer in a synclinal basin are primary root causes. Finite element THM simulations successfully reproduce these unique deformations. Recent observations of large quantities of thermalized discharge water downstream and high pore pressure in the limestone layer provide further support for the proposed mechanism. Furthermore, refined numerical modeling is adopted to evaluate the safety of Xiluodu dam subjected to potential larger canyon contractions. We conclude that these unprecedented phenomena are dominantly the consequence of THM response to regional hydrogeological evolution following the build-up of a large reservoir. The accumulated canyon contractions at the current stage would not pose a direct threat to the dam safety, but a tripled situation may cause severe safety issues.

The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension

The Albian Gap is a uniquely large (up to 65 km wide and >450 km long), enigmatic salt-related structure in the Santos Basin, offshore Brazil. It is located near the basin margin and trends NE (i.e. subparallel to the Brazilian coastline). The gap is characterized by a near-complete absence of Albian strata above depleted Aptian salt. Its most remarkable feature is an equivalently large, equally enigmatic, basinward-dipping, supra-salt rollover that contains a post-Albian sedimentary succession that is up to 9 km thick. Owing to its unique geometry, size and counter-regional aspect, the origin and evolution of the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models; that is, did it form as a result of thin-skinned (i.e. supra-salt) extension, or progradational loading and salt expulsion? The extension-driven model states that the Albian Gap (and overlying rollover) formed as a result of post-Albian gravity-driven extension accommodated by slip on a large, counter-regional, listric normal fault (the Cabo Frio Fault). Conversely, the expulsion-driven hypothesis states that the Albian Gap was established earlier, during the Albian, and that post-Albian deformation was controlled by differential loading, vertical subsidence and basinward salt expulsion in the absence of significant lateral extension. This study utilizes a large ( c . 76 000 km 2 ), dense (4–8 km line spacing), depth-migrated, 2D seismic dataset that fully covers and thus permits, for the first time, a detailed, quasi-3D structural analysis of the entire Albian Gap. In this study we focus on (1) the evolution of base-salt relief and the original salt thickness variations and (2) the geometry of the post-Albian rollover, and its related faults and salt structures. To constrain the kinematics of the Albian Gap, and how this relates to the evolution of the base-salt relief, we also apply novel structural restoration workflows that incorporate flexural isostasy, in addition to a detailed, sequential reconstruction of the intra-gap rollover sequences. Our results show that the geometry and kinematics of the Albian Gap vary along-strike, and that both post-Albian extension and expulsion play a significant role in its evolution. Basinward-dipping growth wedges, salt rollers and listric normal faults record extension, whereas sigmoidal wedges, halokinetic sequences and upturned near-diapir flaps, the latter two associated with large diapirs bounding the downdip edge of the gap, record basinward salt expulsion and inflation. Where the Albian Gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results are consistent with the amount of basinward translation inferred from the analysis of ramp–syncline basins located downdip on the São Paulo Plateau. Our results seemingly reconcile one of the longest-running debates in salt tectonics, as well as having more general implications for understanding the regional kinematics and dynamics of salt-related structures in other salt basins, in particular the controls on the development of large, counter-regional faults. Supplementary material: Uninterpreted versions of the seismic sections are available at https://doi.org/10.6084/m9.figshare.c.5023088

Influence of minibasin obstruction on canopy dynamics in the northern Gulf of Mexico

AbstractIn salt‐detached gravity‐gliding/spreading systems the detachment geometry is a key control on the downslope mobility of the supra‐salt sequence. Here, we used regional 3D seismic data to examine a salt‐stock canopy in the northern Gulf of Mexico slope, in an area where supra‐canopy minibasins subsided vertically and translated downslope above a complex base‐of‐salt. If thick enough, minibasins can interact with, and weld to, the base‐of‐salt and be obstructed from translating downslope. Based on the regional maps of the base of allochthonous salt and the base of the supra‐canopy sequence, the key controls on minibasin obstruction, we distinguished two structural domains in the study area: a highly obstructed domain and a highly mobile domain. Large‐scale translation of the supra‐canopy sequence is recorded in the mobile domain by a far‐travelled minibasin and a ramp syncline basin. These two structures suggest downslope translation on the order of 40 km from Plio‐Pleistocene to Present. In contrast, translation was impeded in the obstructed domain due to supra‐canopy bucket minibasins subsiding into feeders during the Pleistocene. As a result, we infer that differential translation occurred between the two domains and argue that a deformation area between two differentially translating supra‐canopy minibasin domains is difficult to recognize. However, characterizing domains according to base‐of‐salt geometry and supra‐canopy minibasin configuration can be helpful in identifying domains that may share similar subsidence and downslope translation histories.

Sedimentación fluvial y lacustre sintectónica ligada a un sinclinal de “buttressing” paralelo a una falla en el sector de Nigüella (NW Cordillera Ibérica)

En este artículo se discute la evolución sedimentaria del relleno neógeno de un área situada en la parte Noroeste de la Cordillera Ibérica que presenta depósitos fluviales y lacustres, y su relación con la tectónica alpina compresiva que afectó a una falla anteriormente extensional. Los análisis estratigráficos permiten caracterizar tres unidades tectosedimentarias, con un espesor total de 120m. Las Unidades 1 y 2 están formadas dominantemente por litofacies clásticas, y están separadas por una discordancia y su correlativa conformidad. La Unidad 3 está formada por calizas tobáceas y micríticas, y representa un salto litológico brusco con la Unidad 2 en toda su extensión. Estas unidades están involucradas en dos estructuras de escala kilométrica con dirección alpina NNW-SSE: 1) la Falla de Nigüella, que pone en contacto materiales triásicos con cenozoicos en los bloques levantado y hundido, respectivamente, y 2) el Sinclinal de Nigüella, subparalelo a la falla anterior, con buzamiento de estratos entre 19º y 70º. En las unidades 1 y 2, cuatro asociaciones de facies sedimentarias representan el depósito en áreas proximales y medias de abanicos aluviales, procedentes de relieves locales, y un sistema fluvial braided con reducida llanura de inundación, procedente del Norte. Ambos ambientes registran sedimentación carbonática fluvial y lacustre. Otras tres asociaciones de facies representan el depósito dominante de carbonatos, tanto en entornos palustre-fluvial-lacustres como en lacustres. En las tres unidades, los rudstones de oncoides y fitoclastos se formaron en canales de aguas someras, con baja sinuosidad y en zonas encharcadas, con extensas zonas palustres tobáceas, con desarrollo de plantas hidrófilas. Por el contrario, las calizas micríticas con ostrácodos y las margas corresponden al depósito de calcita en zonas lacustres de aguas tranquilas y permanentes. Por tanto, el sistema sedimentario evolucionó desde un ambiente aluvial-fluvial dominante hasta un ambiente lacustre. Este hecho, junto con el desarrollo de calcretas en las unidades 1 y 2, indica condiciones más húmedas y posiblemente el paso a un lago cerrado hidrológicamente. La falla de Nigüella funcionó a principios del Jurásico como una falla normal, y durante la compresión del Cenozoico provocó la formación de una cuenca sinclinal mediante buttressing del bloque NE contra la falla. Este contexto condicionó la distribución y extensión de litofacies miocenas a lo largo del espacio y del tiempo y la localización de depocentros. La disminución de la actividad tectónica a lo largo del intervalo estudiado favoreció la incisión fluvial, la captura del acuífero mesozoico y la salida del agua subterránea rica en Ca2+ y HCO-3, dando lugar al depósito generalizado de carbonato cálcico y, finalmente, a la expansión del lago.

GEOLOGICAL STRUCTURES MAPPING USING AEROMAGNETIC PROSPECTING AND REMOTE SENSING DATA IN THE KARSTIC MASSIF OF BENI MELLAL ATLAS, MOROCCO.

The current study exposes the results of aeromagnetic data interpretation and a combined analysis of 1-A sentinel radar image that cover the study area of Beni Mellal Atlas in order to describe the structural geometry and to understand its tectonic evolution.The map of the reduced to pole of residual magnetic field highlights various magnetic anomalies with high amplitudes that correspond to Jurassic-Cretaceous basaltic formations outcropping synclinal basins of Beni Mellal Atlas. The interpretation of magnetic data using tilt derivative (TDR), horizontal gradient technique coupled to upward continuation and Euler Deconvolution allows us to distinguish the fractures network that is affecting the study area. In order to complete this analysis, the Sentinel-A radar image is processed and filtered using SNAP ESA Sentinel-1 toolbox software to extract lineaments. The final structural map reveals four faults groups oriented respectively NE-SW, ENE-WSW to E-W, N-S and NW-SE Their depths estimated by the application of Euler deconvolution exceed 1500 m.Thoses faults have played a major role in structural evolution of Beni Mellal Atlas.

Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)

Abstract. The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposits with condensed and erosional surfaces, whereas the syncline basins exhibit thicker and well-preserved successions. In addition, the vertical facies succession evolves from thin Silurian to Givetian deposits into thick Upper Devonian sediments. Synsedimentary structures and major unconformities are related to several tectonic events such as the Cambrian–Ordovician extension, the Ordovician–Silurian glacial rebound, the Silurian–Devonian Caledonian extension/compression, the late Devonian extension/compression, and the Hercynian compression. Locally, deformation is characterized by near-vertical planar normal faults responsible for horst and graben structuring associated with folding during the Cambrian–Ordovician–Silurian period. These structures may have been inverted or reactivated during the Devonian (i.e., Caledonian, Mid–Late Devonian) compression and the Carboniferous (i.e., pre-Hercynian to Hercynian). Additionally, basement characterization from geological and geophysics data (aeromagnetic and gravity maps), shows an interesting age-dependent zonation of the terranes which are bounded by mega-shear zones within the arches–basins framework. The old terranes are situated under arches while the young terranes are located under the basins depocenter. This structural framework results from the accretion of Archean and Proterozoic terranes inherited from former orogeny (e.g., Pan-African orogeny 900–520 Ma). Therefore, the sedimentary infilling pattern and the nature of deformation result from the repeated slow Paleozoic reactivation of Precambrian terranes bounded by subvertical lithospheric fault systems. Alternating periods of tectonic quiescence and low-rate subsidence acceleration associated with extension and local inversion tectonics correspond to a succession of Paleozoic geodynamic events (i.e., far-field orogenic belt, glaciation).

Geometry and kinematics of salt-detached ramp syncline basins

Ramp-syncline basins (RSBs) are characterized by asymmetric depocentres formed by translation above salt detachments with basal steps. Recognition of these minibasins allows quantification of the magnitude and rates of overburden translation above a deforming salt layer. 3D seismic data from the São Paulo Plateau, Santos Basin, Brazil image a series of RSBs formed above thick salt, and distributed above and/or basinward of pronounced base-salt steps. The RSBs are composed of landward-dipping and gently folded sigmoidal strata, recording 28–32 km of SE-directed translation during the Late Cretaceous and Paleocene, at an average rate of 0.8–0.9 mm/year. We present several examples of RSBs, in addition to results from numerical forward models, to analyse the 3D kinematics of RSBs and their interaction with base-salt structures. The RSBs form not only by translation above basinward-dipping ramps, but also over landward-dipping ramps. Translation over stepped ramps generates stacked RSBs. Thickness maps show translation is higher at the centre of RSBs and that depocentres become progressively more affected by diapirism as they evolve. This study presents the first analysis of the 3D kinematics of ramp-syncline basins, and the first documentation of their occurrence above thick salt in the Santos Basin, Brazil. It applies realistic numerical models that treat the detachment as a volume of viscous material, improving our understanding of these systems. RSBs are important to understand slope and deep-basin tectono-stratigraphic architecture of supra-salt units and can also guide the identification of pre-salt structures, thus contributing to the exploration of salt basins.

Late Miocene Extensional Collapse of Northern Tunisia

AbstractTwo orthogonal extensional systems produced the extensional collapse of the Tell and Atlas thrust belts in northern Tunisia during the Late Miocene to Pliocene in a context of NW‐SE plate convergence between Africa and Eurasia. The older extensional system shows several low‐angle normal faults (LANFs) and associated high‐angle faults with ENE‐directed transport that produced half‐grabens and hanging‐wall syncline basins during the late Tortonian to Messinian. The direction of extension swinged towards the SE during the Messinian, cutting into, and tilting the previous detachments. Extension was accompanied by the extrusion of 8‐Ma rhyodacites and Messinian basalts, together with the development of mineralized fault breccias. Plio‐Quaternary NW‐SE directed shortening formed inversion arrowhead structures, reverse faults, refolded extensional rollover anticlines and folded the LANFs. ENE‐directed extension is concomitant with the opening of the Tyrrhenian basin. We consequently think that both processes are related and that tearing of the Calabrian slab along the northern Tunisia coast drove the ENE‐directed extension. Meanwhile, the SE‐directed extension that followed was probably related to SE‐directed peeling back of the Tunisian continental lithospheric mantle during NW subduction of the Maghrebian margin. This extension propagated eastwards from the late Tortonian until the Pliocene following the SE migrating subduction front and favored by lateral slab tearing along the Tunisian Atlas dextral Subduction Transfer Edge Propagator boundary. This new hypothesis for the tectonic evolution of northern Tunisia shows for the first time the importance of crustal extension in the denudation of the Tunisian Atlas and Tell foreland thrust belts and its relation to deep mantle tectonic mechanisms.

Mechanism of water inrush driven by grouting and control measures—a case study of Chensilou mine, China

Water inrush into coal mines from aquifers underlying coal seams often causes serious casualties and economic losses. The key to preventing the disaster is to discover a water inrush mechanism suitable for specific geological and hydrogeological conditions and apply reasonable control measures. A case of the Chensilou mine is studied in this paper. Complex geological and hydrogeological conditions, such as 12 aquifers in the floor and small distance between coal seam and aquifer, make the mining face in the synclinal basin have a great risk of water inrush. In addition, as an important way to prevent the disaster, grouting will aggravate the risk of water inrush from the floor. The slurry will drive groundwater in the limestone aquifers L8, even L7 and L6 along the horizontal (fracture zone in L11~L8) and vertical (Fs1 ~Fd1) water flow channel into the mining face and synclinal basin. A new water inrush mechanism driven by grouting is formed. In order to prevent this disaster, based on statistical law of hole deviation, the relative error of vertical depth and the angle between the borehole and the rock formation are obtained. Finally, an improved grouting method is proposed, which is useful to ensure the safe production of coal mine and reduce the cost of grouting.