In the present work, we comment on Amri et al. Arab J Geosci 11(253) (
2018
) publication. This latter contains many taxonomic misinterpretations and confusions. That is why, in the present work, we ...propose accuracy on the chronostratigraphy of the Abiod Formation. So, we demonstrate that this Formation remains in the Late Cretaceous in age as originally defined by its author, Burollet Ann Mines Géol 18:388 (
1956
), and widely accepted by other geologists working on Cretaceous and Paleogene series in the Grombalia area as well as elsewhere in northern and central Tunisia. It cannot be Paleocene in age indeed. We discuss also much incoherence both in the text and illustrations (figures and plates) provided by Amri et al. Arab J Geosci 11(253) (
2018
). In order to correct their taxonomic misinterpretation, we use the main characters allowing the distinction of globotruncanids from morozovellids and globigerinids. We also describe Rh section in Jebel Rhorfa from the Grombalia area and we plot the genuine respective range of foraminiferal species. Consequently, we demonstrate that the Abiod Formation is rich in globotruncanids including Upper Cretaceous species belonging to genera
Globotruncana
,
Globotruncanita
,
Globotruncanella
,
Radotruncana
, and
Rugoglobigerina
. This formation is well and truly devoid of morozovellids and globigerinids indicative of Paleocene. Hence, no possible reworked Paleocene fauna exists and their proposed scenario with an assumed reworking can be no longer defensible.
Detailed gravity data integrated with geological data and mining well data are analysed to constrain the shape of the Triassic evaporitic body at Jebel El Mourra (northern Tunisian Atlas) and the ...mechanism of its emplacement at the surface. The gravity data analysis included the construction of a gravity anomaly maps, and synthetic and forward 2.5D gravity models. The complete Bouguer and residual gravity anomaly maps indicate a positive amplitude gravity anomaly over the Triassic evaporitic outcrops and prominent NE–SW‐trending features associated with the boundary of the Triassic rocks and surrounded layers. A NW–SE‐trending gravity model that crosses the Triassic evaporitic outcrop at Jebel El Mourra shows that the positive gravity anomaly can be explained by a deep‐rooted salt diapir. Conventional models of salt dome formation suggest that they produce negative gravity anomalies; however, this study shows that this model is not universal. The studied area is an example of a diapir expressed by positive gravity anomaly and this result is supported by synthetic gravity models at different stages of salt piercing.
Gravity data, integrated with seismic refraction/reflection data, well data and geological investigations, were used to determine the location of the paleogeographic boundary between the Precambrian ...Saharan domain and the younger Tunisian Atlas domain. This boundary (North Saharan Flexure or NSF) has not been as clearly defined as it has been to the west in Algeria and Morocco. The gravity data analysis, which included the construction of complete Bouguer and residual gravity anomaly maps, revealed that the Atlasic domain is characterized by relative negative gravity anomalies and numerous linear gravity trends implying a thick and deformed sediment cover. The Saharan domain is characterized by relatively positive gravity anomalies with few gravity trends implying a thin and relatively undeformed sediment cover. An edge-enhancement analysis of the residual gravity anomalies revealed that the NSF is characterized by a series of discontinuous east- and northwest-trending linear anomalies south of 34°N that are not related to the well-known faults within the Gafsa and Accident de Medenine regions. Based on the continuity of the amplitudes of seismic reflection data and the trends of the residual gravity anomalies, the NSF is not an abrupt discontinuity but a series of step faults dipping toward the Atlasic domain. To obtain a more quantitative representation of the southern edge of Tunisian Atlas, a regional gravity model constrained by two wells and seismic reflection/refraction data was constructed along a north-south trending profile which confirms the presence of thicker sediments north of the NSF. Our analysis shows that the NSF has controlled the depositional environment of the sedimentary rocks within the region since at least Triassic time and has acted as a barrier to Atlasic deformation south of the NSF. The NSF is considered an important tectonic feature that has controlled the paleogeographic evolution of the southern margin of the Tethys Ocean, and it continues to be active today based on seismicity hazard studies.PUBLICATION ABSTRACT
This article focuses on the neotectonics of the southern Atlas of Tunisia based on morphometric analyses. Five major relevant morphometric parameters were processed and analyzed: residual topography, ...hypsometric index, drainage anomalies, maximum vertical curvature, and terrain roughness, and compared to the structural and tectonics of the study area. These are relevant to describe the topographic changes, and therefore suggest possible neotectonic activity.
The analysis of these morphometric indices reveals that two structures in the study area (Jebels Ben Younes and Bou Ramli) are distinguished by a specific morphometric footprint: high residual topography, high hypsometric integral value of some watersheds (HI > 0.6), high frequency of drainage anomalies, high maximum vertical curvature, and high roughness index. The correlation of these geomorphic indices with the structural pattern of the study area confirms the neotectonic reactivation (dating from the Quaternary) and the dextral strike-slip component of the Gafsa fault (the major tectonic feature in the southern Atlas of Tunisia). Thus, the morphometric analysis of the Digital Elevation Model and the drainage network provide a more accurate insight into the morphodynamics of the study area.
Les anomalies de drainage révèlent cartographiquement les alternances lithologiques et/ou les discontinuités structurales (failles actives ou non par exemple). C’est pourquoi elles sont considérées ...comme l’un des paramètres géo-morphométriques significatifs pour les études de géomorphologie structurale et néotectonique. Dans cet article, et afin de minimiser l’erreur effectuée par tout opérateur qui effectue une analyse manuelle de l’information, nous proposons une nouvelle méthode semi-automatique facilitant l’extraction des anomalies de drainage. Les données d’entrée de cette méthode sont la topographie du terrain et le réseau hydrographique. Ces données sont intégrées dans une série de géo-traitements informatiques à l’aide d’un système d’information géographique (SIG). Ainsi, plusieurs notions de la morphométrie sont exploitées pour accomplir cette tâche : interpolation des données topographiques, calcul de surface enveloppe sommitale, calcul de l’orientation de la pente, etc. Par la suite, et pour expérimenter l’efficacité de cette méthode, nous l’avons appliquée à la zone centrale de l’Atlas Méridional de la Tunisie connue par sa sismicité relativement importante. L’application de cette méthode nous a permis de localiser une forte concentration d’anomalies de drainage sur les flancs nord-est du Jebel Ben Younes, du Jebel Bou Ramli et du Jebel Orbata. La comparaison avec les modèles tectoniques déjà existants montre que les portions des drains sélectionnés sont situées à l’aplomb et à proximité de l’accident tectonique le plus important de la région : la faille de Gafsa. Ainsi, ces anomalies de drainage révèlent l’empreinte sur le relief d’un mouvement tectonique récent de cette faille déjà souligné par certains auteurs. De ce fait, on peut en déduire que la méthode exposée dans cet article est très efficace pour l’extraction des anomalies de drainage, ce qui peut être de grande utilité dans les études morphométriques.
Bouguer gravity and aeromagnetic data are analyzed to determine the extent of Miocene magmatism in the Nefza and Tabarka regions of northwestern Tunisia. Construction of magnetic intensity and ...enhanced analytic signal (EAS) maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the Nefza and Tabarka regions. Because of the lack of lateral resolution of the EAS techniques, 3-D magnetic and 2.5-D gravity models were constructed over the anomalies at Nefza and Tabarka. The final models indicate that the maximum depths of the igneous bodies are between 2.5 and 2.7 km with maximum widths between 15 and 22 km. The final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust (at least 3 km). These widths greatly expand the region of known Miocene magmatism in northwestern Tunisia. Combined with geochemical and petrological data of the surface volcanic rocks, the gravity and magnetic models imply a wider range of Miocene volcanic activity in northern Tunisia, probably related to a subduction zone.
Gravity data were analyzed to determine the structural development of the northern boundary of the Ghadames Basin in southern Tunisia. The Ghadames Basin which also occurs in eastern Algeria and ...northwestern Libya is one of the most prolific hydrocarbon producers in North Africa with several of the largest oil fields occurring along its northern boundary. The Ghadames Basin was formed during a series of tectonic events ranging from the Early Paleozoic to the Early Cenozoic. These tectonic events produced a basin in southern Tunisia that has a complex basement configuration which is not completely known. A residual gravity anomaly map constructed using polynomial trend surfaces, and vertical and horizontal gravity derivative maps indicate that the northern boundary contains a series of maxima and minima anomalies that trend in two prominent directions: northeast–southwest and east–west. The horizontal and vertical derivative gravity anomaly maps indicate that the width of the basement structures range between 10 and 20km in width. Three-dimensional (3D) Euler deconvolution and 3D forward modeling constrained by well data, one seismic reflection profile and remote sensing data confirm the width of the basement structures and indicates that the depth of basin varies between 1.5 and 5km, with deeper sections in general more numerous in the southern sections of the boundary. The gravity analysis constrained by the seismic reflection profile and well data implies that the basement topography may have been formed during the Pan African and/or late Mesozoic rifting. However, additional seismic reflection and well data are needed to confirm this conclusion. The discovery of the numerous basement structures suggests that there may exist additional hydrocarbon traps within the northern boundary of the Ghadames Basin.
•The Ghadames Basin is more structurally complex than previously known.•Basement structures trend northeast and east.•Basement structures may be structural petroleum traps.
The geodynamic evolution of the Southern Tethyan Margin of Tunisia is investigated using geophysical studies. Analysis of gravity and seismic reflection data in the Maghrebian domain and Southern ...Tunisia reveals the geodynamic role played by the North Saharan Flexure (NSF) in the evolution of the Southern Tethyan Margin. The Saharan Atlas Mountains (Atlasic Basin) and the African Craton (Telemzan High) are separated by the NSF which is a regional-scale feature that may represent a significant basement discontinuity that has controlled the Paleozoic, Mesozoic, and Cenozoic evolution of the Tunisian and Maghrebian Tethyan Basin.
Detailed observation of the Upper Pleistocene deposits of Rafraf (Bizerte, Northeastern Tunisia) provides new data about the significant variations in facies, thickness, and faunal assemblages. This ...work reports, for the first time, the occurrence of a
Persististrombus latus
level in the Rafraf sea coast. Facies analyses added to the recorded sedimentary features were carried in order to recognize stratigraphy, paleontology, and sea level highstands. They revealed complex succession of various Upper Pleistocene environments ranging from coastal dunes to inner platforms with scatter builds by
Vermetus triquetrus
and
P. latus
. The marine Upper Pleistocene deposits rich in the Senegalese fauna
P. latus
draw scale steps outcropping at diverse altitudes varying between 1 and 14 m. Serial sections along the border of the Rafraf beach show the action of many faults trending EW and NW-SE. Even though these faults got low values of vertical throw, their cumulative throw values led to these different altitudes of strata containing
P. latus.
These altitude variations are mainly the result of the inherited geomorphology, the environmental distribution, the sea level fluctuations and the tectonic activities.
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