Apatite fission-track analyses on basement granites from south-western Meseta, Morocco: Paleogeographic implications and interpretation of AFT age discrepancies

This work is based on apatite fission-track analysis of samples (mostly granites) from the basement of the Cretaceous-Tertiary Phosphate and Ganntour Plateaus, exposed in the Jebilet and Rehamna massifs (Western Meseta, Morocco). This basement belongs to the Carboniferous-Early Permian Variscan Belt, and the earlier marine onlap is Late Triassic in age. However, the AFT ages are post-Triassic and different in the Jebilet (186-203 Ma) and Rehamna (148-153 Ma). Track length modelling support the occurrence of moderate heating events during the Jurassic and the Eocene, respectively, with cooling during the Permian and Cretaceous intervals. These results are partly accounted for by considering a moderate subsidence during the Late Triassic-Liassic, which is a noticeable change in the regional paleogeographic concept of “West Moroccan Arch”. However, the discrepancies between the AFT results from the studied massifs make necessary to explore further explanation. We interpret the observed discrepancies by the difference in age and depth of crystallization of the sampled granites in the Variscan Orogen, i.e. 330 Ma, 5-6 km in the Jebilet versus ~ 300 Ma, 8-10 km in the Rehamna. The importance of the Late Jurassic-Early Cretaceous uplift and erosion of the entire Meseta and that of its Late Eocene burial are emphasized.     

GIS-based evaluation of groundwater quality and estimation of soil salinization and land degradation risks in an arid Mediterranean site (SW Tunisia)

Arabian Journal of Geosciences - The present work is concerned with the valorization of clay minerals of the Aleg formation (Coniacian-middle Campanian) in the clinker manufacturing. The studied...     

Saghro Group in the Ougnat Massif (Morocco), an evidence for a continuous Cadomian basin along the northern West African Craton

The Saghro Group (SG) is a folded, low-grade volcano-sedimentary series up to 8 km thick that crops out within and to the north of the Pan-African suture zone in the central and eastern Anti-Atlas. Here we describe the SG of the Ougnat inliers that are exposed in the easternmost Anti-Atlas beneath the unconformable, Late Ediacaran Ouarzazate Group (OZG) volcanic rocks. The Ougnat SG mostly consists of volcaniclastic greywackes accumulated in a peritidal-to-shallow basin. The basin infilling was deformed by NNE-trending, mostly upright folds with axial-planar slaty cleavage and low-grade metamorphism. The deformed SG rocks were intruded by the ～550 Ma Mellab hypovolcanic granodiorite. The latter also crosscuts the lowest OZG rocks that are dated to 574–571 Ma in the western Saghro region. The SG rocks that form the Siroua and Saghro inliers have an oldest age of 620–610 Ma and were folded at ～610–580 Ma at the onset of the Cadomian orogenic events. We show that the SG rocks are similar to the “Série verte” (SV) rocks that are exposed in the Ougarta and western Hoggar east of the Pan-African suture. We infer that the SG and SV rocks accumulated in a same, continuous basin that was bounding the West African Craton to the north and the east. This strongly subsiding basin formed close to a volcanic arc and was folded during the last Pan-African synmetamorphic events. Fold orientation and age of folding differ however along the edge of the West African Craton. The orogenic greywackes that form the remnants of the SG-SV basin thus constitute a precious record of the diachronic Cadomian event s.l. along the West African Craton northern margin.     

Temporal shoreline change and infrastructure influences along the southern Red Sea coast of Saudi Arabia

Jizan is one of the Saudi Arabian coastal cities endowed with diverse natural settings, which includes Ash Shuqayq in the north, Turfah in the centre and Jizan in the South. This work analysed specific environmental characteristics, such as spits, sabkhas and wadis. Assessments used Landsat imagery to examine coastal change between 1973 and 2011. The cumulative temporal change identified regression trends given by coefficients of determination that explained a significant percentage of data variation for Jizan (R ² = 69%) and Turfah (R ² = 72%), while Ash Shuqayq was insignificant (R ² = 14%). Inter-survey results predicted future change, although trends were not significant, i.e. Jizan (R ² = 22%), Turfah (R ² = 14%) and Ash Shuqayq (R ² = 3 and 61% with outlying value removed). Aerial photos showed regional coastal changes, which included a maximum accretion of 36.4 m and maximum erosion of 12.9 m. These are scientifically effective techniques to monitor regional coastal change, i.e. erosion and accretion and identified rates of 0.59, 1.80 and 3.53 myr^?1 for Ash Shuqayq, Turfah and Jizan. Changes were linked to infrastructure developments, e.g. tourism, port development and natural causes, e.g. spit formations and wadi outfalls.     

Particulate matter geochemistry of a highly industrialized region in the Caribbean:Basis for future toxicological studies

Air pollution has become an important issue,especially in Caribbean urban areas,and,particulate matter(PM)emitted by different natural and anthropogenic sources causes environmental and health issues.In this work,we studied the concentrations of PM₁₀ and PM_2.5 sources in an industrial and port urban area in the Caribbean region of Colombia.PM samples were collected within 48-h periods between April and October 2018 by using a Partisol 2000 i-D sampler.Elemental geochemical characterization was performed by X-ray fluorescence(XRF)analysis.Further,ionic species and black carbon(BC)were quantified by ion chromatography and reflectance spectroscopy,respectively.Using the Positive Matrix Factorization(PMF)receptor model,the contributions of PM sources were quantified.The average concentration of PM₁₀ was 46.6±16.2μg/m³,with high concentrations of Cl and Ca.For PM_2.5,the average concentration was 12.0±3.2μg/m³,and the most abundant components were BC,S,and Cl.The receptor model identified five sources for PM₁₀ and PM_2.5.For both fractions,the contributions of marine sea spray,re-suspended soil,and vehicular traffic were observed.In addition,PM_2.5 included two mixed sources were found to be fuel oil combustion with fertilizer industry emissions,and secondary aerosol sources with building construction emissions.Further,PM₁₀ was found to also include building construction emissions with re-suspended soil,and metallurgical industry emissions.These obtained geochemical atmospheric results are important for the implementation of strategies for the continuous improvement of the air quality of the Caribbean region.     

The imprint of the equation of state on the axial w-modes of oscillating neutron stars

We discuss the dependence of the pulsation frequencies of the axial quasi-normal modes of a non-rotating neutron star upon the equation of state describing the star interior. The continued fraction method has been used to compute the complex frequencies for a set of equations of state based on different physical assumptions and spanning a wide range of stiffness. The numerical results show that axial gravitational waves carry relevant information on both the structure of neutron star matter and the nature of the hadronic interactions.     

The chemical composition of rainwater over Büyükçekmece Lake, Istanbul

In the present study, the precipitation near Büyükçekmece Lake, which is one of the important drinking water sources of Istanbul city, was studied during October 2001–July 2002. Seventy-nine bulk precipitation samples were collected at two sampling stations near the Lake (41°2′35″N, 28°35′25″E and 41°5′30″N, 28°37′7″E). The study comprised the determination of H⁺, Cl⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Na, K, Mg, Ca, Al, Ba, Fe, Cu and Mn concentrations in bulk deposition rain event samples. The average volume-weighted pH value was found to be 4.81, which points out that the rain is slightly acidic. High sulfate concentrations were observed together with high H⁺ ion values. Sulfur emissions were the major cause for the observed high hydrogen ion levels. On the basis of factor analysis and correlation matrix analysis, it has been found that in this region, acid neutralization is brought about by calcium rather than the ammonium ion. The varimax rotated factor analysis grouped the variables into four factors, which are crustal, marine and two anthropogenic sources.     

Source and origin of glacial paleovalley-fill sediments (Upper Ordovician) of Sarah Formation in central Saudi Arabia

A study was carried out on the combination of petrographies, geochemistry (major and trace), weathering and the digenesis of 31 sandstones samples to determine their provenance and depositional tectonic setting of sedimentary basins. Based on the composition of Detrital grains (point counting), most of the Sarah sandstones were classified as quartz arenites types (99% on an average). The petrographic data indicated that the resultant mature sandstones are derived from recycled and craton interior tectonic provenance. Tectonic setting discrimination diagrams based on major elements suggest that sandstones were deposited in a passive margin and polycyclic continental tectonic setting. The relationship between K₂O/Na₂O ratio and SiO₂ showed that the Sarah sandstone samples fall into the passive margin field. The chemical index of alteration (CIA?=?63.84%) of sandstones suggested moderate weathering or reworking in the area. The concentration of trace elements indicates that the sediments were probably derived from the mixed sedimentary-meta sedimentary provenance and changes in sedimentary process due to climatic variations. The main diagenetic events were in the form of cements, which occur as grain coats and as pore fillings. An integrated approach showed that the parent area of paleovalley-fill sediment is probably a complex of granite, metasedimentary and pre-existing sedimentary rocks.