Primary vs. secondary curved fold axes: Deciphering the origin of the Aït Attab syncline (Moroccan High Atlas) using paleomagnetic data

The Aït Attab syncline, located in the Central High Atlas, displays a curved geometry in plan view, and is considered as one of the most spectacular fold shapes in the Central High Atlasic belt. We conducted a paleomagnetic study in Jurassic-Cretaceous red beds to investigate the origin of this geometry. The Natural Remanent Magnetization (NRM) is dominated by a secondary magnetization carried by haematite with unvarying normal polarity that has been dated at about 100 Ma. The regional fold test performed in both limbs of the syncline is positive and the paleomagnetic vectors (after tectonic correction) are parallel throughout the curvature, indicating a negative oroclinal bending test. These results are inconsistent with previous works that consider the bent geometry of this syncline to result from subsequent distortion of originally NE–SW trending structures by rotation about a vertical axis. We interpret the NRM data to demonstrate that the changing trend of the Aït Attab syncline is a primary feature, resulting from the influence of pre-existing, NE–SW and E-W-striking extensional faults that developed during a strike-slip regime. Paleomagnetic results also reveal that the tilting observed in the sampled red beds is post Albian, probably linked to the Cenozoic inversion of the High Atlasic belt

Tectonic fabrics vs. mineralogical artifacts in AMS analysis: A case study of the Western Morocco extensional Triassic basins

New magnetic fabric data from 48 sites in Upper Triassic red beds from the Argana, Asni and Tizi n''Tichka areas in the western High Atlas, in combination with rock magnetic analyses, SEM observations and qualitative chemical analyses, reveal that mineralization processes can affect the primary (extensional) or secondary (post-depositional) magnetic fabrics. Twenty out of the 48 analyzed sites show tectonic-related fabrics consistent with the rifting stage (primary). Their orientation suggests that the extensional Atlasic (for the Asni area) and Atlantic (for Argana area) distinct directions prevailing during Liassic times are already present in the Upper Triassic sediments. The other 28 sites show axes switching (including different possibilities, kmax-kmin or kint-kmin), indicating their secondary development related to mineralogical changes after deposition. However, orientation of magnetic susceptibility axes (without considering their relative value) is consistent with the main directions obtained for the rifting stage. This magnetic fabric study also suggests that (i) extension had a small transtensional component and (ii) there is a limited influence of compressional inversion tectonics

Evolution of the ridges of Midelt-Errachidia section in the High Atlas revealed by paleomagnetic data

New paleomagnetic data (43 sites) from Mesozoic sediments are contributed in this work, verifying the presence of a pervasive syntectonic Early Cretaceous remagnetization in the easternmost area of the Moroccan High Atlas. Using the small circle intersection method, we have calculated the characteristic remagnetization direction (Dec: 337.3, Inc: 38.4) that fits with a 100-Ma age, according to the Apparent Polar Wander Path of Africa. The paleomagnetic vectors of remagnetization are used to obtain the geometry during the remagnetization stage (100Ma) of one of the most renowned geological cross sections of the High Atlas, the Midelt-Errachidia profile. The partial restoration of the cross section at 100Ma allows us to determine the dips of the beds at the remagnetization stage in five structures (ridges or anticlines). Our results indicate that the five ridges that configure the Midelt-Errachidia profile were initiated to different degrees prior to wholesale compressive deformation during the Cenozoic. This configuration can be explained according to two different scenarios that we discuss in this paper: transpression and diapirism. The geological model obtained, both at present and at 100Ma, indicates the existence of a Mesozoic cover substantially decolled from the Paleozoic basement, what strongly contrasts with previously published transects of the same area

Electromagnetic Field Effect or Simply Stress? Effects of UMTS Exposure on Hippocampal Longterm Plasticity in the Context of Procedure Related Hormone Release

Harmful effects of electromagnetic fields (EMF) on cognitive and behavioural features of humans and rodents have been controversially discussed and raised persistent concern about adverse effects of EMF on general brain functions. In the present study we applied radio-frequency (RF) signals of the Universal Mobile Telecommunications System (UMTS) to full brain exposed male Wistar rats in order to elaborate putative influences on stress hormone release (corticosteron; CORT and adrenocorticotropic hormone; ACTH) and on hippocampal derived synaptic long-term plasticity (LTP) and depression (LTD) as electrophysiological hallmarks for memory storage and memory consolidation. Exposure was computer controlled providing blind conditions. Nominal brain-averaged specific absorption rates (SAR) as a measure of applied mass-related dissipated RF power were 0, 2, and 10 W/kg over a period of 120 min. Comparison of cage exposed animals revealed, regardless of EMF exposure, significantly increased CORT and ACTH levels which corresponded with generally decreased field potential slopes and amplitudes in hippocampal LTP and LTD. Animals following SAR exposure of 2 W/kg (averaged over the whole brain of 2.3 g tissue mass) did not differ from the sham-exposed group in LTP and LTD experiments. In contrast, a significant reduction in LTP and LTD was observed at the high power rate of SAR (10 W/kg). The results demonstrate that a rate of 2 W/kg displays no adverse impact on LTP and LTD, while 10 W/kg leads to significant effects on the electrophysiological parameters, which can be clearly distinguished from the stress derived background. Our findings suggest that UMTS exposure with SAR in the range of 2 W/kg is not harmful to critical markers for memory storage and memory consolidation, however, an influence of UMTS at high energy absorption rates (10 W/kg) cannot be excluded

Discussion sur l'âge et le cadre structural de la sédimentation néogène dans la zone des dômes en Tunisie septentrionale

Discussion about the age and the structural framework of the Neogene sedimentation within the "zone des dômes" in northern Tunisia. The sedimentation of the Neogene post-Tortonian in the dome zone of Northern Tunisia was carried in two kinds of basins corresponding to subsident syncline gutters born of the Tortonian folding and pull-apart basins associated to the dextral subequatorial strike-slips. The Neogene sediments contain a rearranged fauna of Cretaceous, Paleogene and Lower Miocene stages. This phenomenon indicates its post-tectonic character. The Neogene series are framed by two major unconformities which indicate its sedimentation in a compressif structural setting, characterizing the Northern Tunisian Atlas.La sédimentation du Néogène post-Tortonien moyen dans la zone des dômes, en Tunisie septentrionale, s'est effectuée dans deux types de bassins, correspondant soit à des gouttières synclinales subsidentes, issues des plissements tortoniens, soit à des fossés de type pull-apart développés sur des décrochements dextres subéquatoriaux. Les sédiments néogènes renferment de la faune crétacée, paléogène et même du Miocène inférieur, remaniée. Ceci permet de souligner leur caractère post-tectonique miocène. Ils sont encadrés par deux discordances majeures qui reflètent leur sédimentation dans un cadre structural compressif, caractéristique de l'Atlas tunisien septentrional.El Ouardi H., Turki Mohamed Moncef. Discussion sur l'âge et le cadre structural de la sédimentation néogène dans la zone des dômes en Tunisie septentrionale. In: Géologie Méditerranéenne. Tome 27, numéro 1-2, 2000. pp. 47-55

Tectonique salifère polyphasée dans la région de Mejez El Bab-Testour ("Zone des Dômes", Tunisie septentrionale) : contrôle de la sédimentation méso-cenozoïque

In Mejez el Bab-Testour area, Triassic domes are the continuity of ech-Chehid dome, they result from polyphased halokinetic motion. The different setting stages can be deduced from the phenomena that occur within the Mesozoïc-Cenozoïc deposits ; reduction in thickness, progressive bevels, stratigraphie gaps, intraformational unconformities, hydroplastic deformations and reworking of Triassic mate¬ rial. During the Quaternary and Miocene shortening phases, these dome structures have acquired the current mushroom-shape and have thrusted Barremian to Plio-Quaternary series.Les dômes de sels triasiques de la région de Mejez el Bab-Testour dans le prolongement nord est du dôme d'ech-Chehid, résultent d'une histoire halocinétique polyphasée. Les différentes phases halocinétiques sont enregistrées dans la couverture méso-cénozoïque par des phénomènes de réduction et de biseautage progressifs de séries, des lacunes stratigraphiques, des biseaux sédimentaires et des discordances intraformationnelles, des déformations hydroplastiques et des remaniements du matériel triasique. Lors des phases de serrage miocène et quaternaire, ces dômes ont acquis leur forme actuelle en "champignon" et ont chevauché des terrains allant du Barrémien jusqu'au Plio-Quaternaire.El Ouardi H., Turki Mohamed Moncef. Tectonique salifère polyphasée dans la région de Mejez El Bab-Testour ("Zone des Dômes", Tunisie septentrionale) : contrôle de la sédimentation méso-cenozoïque. In: Géologie Méditerranéenne. Tome 22, numéro 2, 1995. pp. 73-84