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《Journal of African Earth Sciences》2000,30(2):295-311
Le groupe du Neoproterozoique inférieur de Kelaat Mgouna est constituéde cinq formations silico-clastiques. II aétéconsidérécomme le dépoˆt dans un bassin d'arrière-arc en relation avec une zone de subduction située plus au SW au niveau de I'accident majeur de l'Anti-Atlas. Un tel arc aurait constituéla principals source d'alimentation en matériel détritique.En fait, l'analyse de la composition modale des grauwackes de ce groupe, l'étude de la charpente lithique de ses conglomérats et l'étude des zircons détritiques montrent que la source est continentals et appartientáune marge passive formée d'un socle métamorphique et d'une ceinture orogénique anté-néoprotérozoïques. Le groupe de Kelaat Mgouna se serait déposéalors en contexte passif dans un bassin en ouverture contemporain de l'extension pré-panafricaine. 相似文献
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Z. Mounzi M. Ferricha-Alami A. Safsafi M. Bennai 《Journal of Astrophysics and Astronomy》2016,37(2):13
We propose a new solution to the η-problem in supergravity using a shift symmetric Kähler potential in the context of the Randall–Sundrum type II model. We focus on a F-term supergravity inflation with a minimal Kähler potential taking into account the radiative corrections. The slow-roll conditions are ensured by the shift symmetry where a very small value of η(η?1) is obtained. In this context, we derive all known spectrum inflationary parameters which are widely consistent with Planck 2015 data for a particular choice of brane tension and coupling constant values. A suitable observational central value of n s=0.96 is also obtained in the case of minimal Kähler potential. 相似文献
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《New Astronomy》2014
We present the photoionisation modelling of the intrinsic absorber in the bright quasar HS 1603 + 3820. We constructed the broad-band spectral energy distribution using the optical/UV/X-ray observations from different instruments as inputs for the photoionisation calculations. The spectra from the Keck telescope show extremely high Civ to Hi ratios, for the first absorber in system A, named A1. This value, together with high column density of Civ ion, place strong constraints on the photoionisation model. We used two photoionisation codes to derive the hydrogen number density at the cloud illuminated surface. By estimating bolometric luminosity of HS 1603 + 3820 using the typical formula for quasars, we calculated the distance to A1. We could find one photoionization solution, by assuming either a constant density cloud (which was modelled using cloudy), or a stratified cloud (which was modelled using titan), as well as the solar abundances. This model explained both the ionic column density of Civ and the high Civ to Hi ratio. The location of A1 is 0.1 pc, and it is situated even closer to the nucleus than the possible location of the Broad Line Region in this object. The upper limit of the distance is sensitive to the adopted covering factor and the carbon abundance. Photoionisation modelling always prefers dense clouds with the number density n0 = 1010 − 1012 cm−3, which explains intrinsic absorption in HS 1603 + 3820. This number density is of the same order as that in the disk atmosphere at the implied distance of A1. Therefore, our results show that the disk wind that escapes from the outermost accretion disk atmosphere can build up dense absorber in quasars. 相似文献
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The present work is an analytical study of the influence of geometrical parameters, such as length, thickness and immersion of the plate, on the reflection coefficient of a regular wave for an immersed horizontal plate in the presence of a uniform current with the same direction as the propagation of the incident regular wave. This study was performed using the linearized potential theory with the evanescent modes while searching for complex roots to the dispersion equation that are neither pure real nor pure imaginary. The results show that the effects of the immersion and the relative length on the reflection coefficient of the plate are accentuated by the presence of the current, whereas the plate thickness practically does not have an effect if it is relatively small. 相似文献
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Determining the relationships of mid-Late Cretaceous African taxa is central to understanding the timing and resultant palaeobiogeographical patterns of Gondwanan fragmentation. The early Late Cretaceous (Cenomanian) Kem Kem beds of southeastern Morocco preserve a diverse vertebrate fauna, including sauropod dinosaurs. Sauropod material includes the holotype of the rebbachisaurid diplodocoid Rebbachisaurus garasbae and fragmentary remains representing indeterminate titanosauriforms and rebbachisaurids. Here, we describe two new specimens from the Kem Kem beds. A dorsal neural arch with complex internal pneumaticity is tentatively attributed to a somphospondylan titanosauriform. A caudal vertebra possessing several rebbachisaurid synapomorphies is excavated by a large and pervasive lateral pneumatic foramen, a feature undocumented in other rebbachisaurids. However, caudal vertebrae are currently unknown for the sympatric R. garasbae, so this element could be referable to that taxon or a second, previously unknown, rebbachisaurid species. Interestingly, this new caudal vertebra displays a mosaic of features otherwise restricted to limaysaurine or nigersaurine rebbachisaurids, suggesting a placement basal to these clades, which is the position usually recovered for R. garasbae in phylogenetic analyses. A review of the mid-Cretaceous African sauropod fossil record removes the Cretaceous record of dicraeosaurids from Africa, restricting this clade to a single post-Jurassic occurrence in Argentina. All diagnostic sauropod remains can be attributed to titanosauriforms or rebbachisaurids. Whereas rebbachisaurids were seemingly restricted to northwestern Africa and disappeared post-Cenomanian, titanosauriforms were widespread across the African continent and survived until the latest Cretaceous. The development of the mid-Cretaceous Trans-Saharan Seaway might have acted as a dispersal barrier for rebbachisaurids and other vertebrate groups. In contrast, titanosauriforms might have been able to cross this barrier, but it is possible that they were also unable to disperse, and that northwestern African titanosauriforms were not closely related to taxa from the rest of the African continent. New materials and a better understanding of titanosaur interrelationships will be crucial in teasing these scenarios apart. 相似文献
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Sintubin Manuel Nefly Mohammed Rijpens Jan Van Zegbroek Bart 《Geologie en Mijnbouw》1997,76(3):187-195
At its eastern termination, the High Atlas Fault in the Western High Atlas in Morocco, consists of a splay of three faults. In the interjacent fault blocks, Neo- and Paleoproterozoic basement, forming the northernmost extremity of the NW-African Craton, is cropping out. The Precambrian basement witnesses a long history of brittle deformation starting at the end of the Pan-African Orogeny. A subsequent episode of normal faulting can be related to the development of a Hercynian basin along the northern passive margin of the cratonic promontory. With regard to the main tectonic activity in the Western High Atlas, basically two models exist: one emphasising block tectonics reflecting Mesozoic rifting followed by Alpine uplift and inversion, the other emphasising Late Paleozoic dextral wrench tectonics. The analysis of the fault activity along the splay faults reveals a predominantly Alpine history, consisting of the Triassic development of the Atlas Rift along the axial zone of the orogen, followed by uplift and inversion. The Late Jurassic to Cenozoic fault activity took place in a sinistral transpressive regime and was partitioned over the three splay faults. Dextral strike-slip fault activity could not be demonstrated in the fault blocks nor along the splay faults. Therefore the faults were probably not involved in Late Paleozoic dextral wrench tectonics. 相似文献
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We report the structural geometry and facies architecture of a small diapir-related carbonate-dominated basin from the Jurassic rift of the Moroccan High Atlas. The Azag minibasin is a lozenge-shaped depocenter completely enclosed by tectonic boundaries that we interpret as welds after former salt anticlines or salt walls. The exposed ca. 3000 m-thick infill of the Azag minibasin is asymmetric; layers are tilted to the W defining a rollover geometry. Areally-restricted sedimentary discontinuities and wedges of growth strata near the basin margins indicate sedimentation contemporaneous with diapiric rise of a Triassic ductile layer. Facies evolution through the basin reflects local accommodation by salt withdrawal and regional events in the High Atlas rift. The early basin infill in the Sinemurian and Pliensbachian shows thickness variations indicative of low-amplitude halokinetic movements, with reduced exposed thicknesses compared to surrounding areas. The exposed Toarcian and Aalenian deposits are also reduced in thickness compared to areas outside the basin. Subsidence increased dramatically in the Bajocian-early Bathonian (?), the main phase of downbuilding, when over 2600 m of carbonates and shales accumulated at a rate > 0.5 mm/a in the depocentral area of the minibasin governed by W-directed salt expulsion. The stratigraphic units distinguished often show maximum thicknesses and deeper facies in the depocentral area, and rapidly change to shallower facies at the basin margins. The Bajocian carbonate facies assemblage of the minibasin include: reservoir facies as microbialite-coral reefs in the basin margins (formed during periods of strong diapir inflation and bathymetric relief), basin-expansive oolite bars (formed during episodes of subdued relief), and organic-rich, dark lime mudstones and shales that show source-rock characteristics. The Azag basin is a good analog for the exploration of salt-related carbonate plays in rifts and continental margins where source-rock and reservoir can form in a same minibasin. 相似文献
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We report a new regional correlation for the Ediacaran succession in the Anti-Atlas belt on the northwestern margin of Gondwana, based on U-Pb LA-ICP-MS zircon geochronology of volcanic rocks in the NE edge of the Saghro inlier. The thick volcano-sedimentary succession comprises a diverse suite of rhyolitic-ignimbrite, basaltic to andesitic lava fields, rhyolitic lava, mafic hydroclastic complex, fallout and surge deposits, pyroclastic dyke, interbedded clastic sediment and subvolcanic bodies.Ten volcanic rocks yield crystallization ages ranging from 573 to 547 Ma, consistent with a lower and upper Ouarzazate Supergroup affinity respectively. Inherited zircon ages range from 623 Ma to 600 Ma, analogous to zircon peaks in the older volcano-sedimentary rocks of the Bou Salda, and Saghro groups in the Anti-Atlas, suggesting the continuity of the Saghro Group beneath the Ouarzazate Supergroup at the NE edge of the Saghro inlier.Rocks with a lower Ouarzazate Supergroup affinity include lithic-poor ignimbrites which yield ages of 573.6 ± 1.9 Ma, 571.8 ± 4.2 Ma, 571.3 ± 2.6 Ma, and 567.4 ± 2.9 Ma, two fallout deposits which yield ages of 563.5 ± 2.1 Ma and 569.2 ± 1.9 Ma, a surge deposit dated at 571.6 ± 2.8 Ma and a rhyolite lava dated at 562.5 ± 3.1 Ma. Two lithic-poor ignimbrites from the upper Ouarzazate Supergroup are dated at 557.3 ± 2.6 Ma and 547.9 ± 3.1 Ma.Volcanic activity at the NE edge of the Saghro inlier is related to West African Cadomian orogenic (WACadomian) activity between 620 and 560 Ma. During this period the Saghro and Bou Salda groups were deposited, followed by the lower Ouarzazate Supergroup. Later extension along the Gondwanan margin took place close to Ediacaran – Cambrian boundary, contemporaneous with upper Ouarzazate Supergroup deposition. 相似文献
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