Eustatic and climatic controls on the development of the Wahiba Sand Sea, Sultanate of Oman

Aeolian sand sea accumulations can serve as valuable archives of climate change in continental environments. The Wahiba Sand Sea is situated at the northern margin of the area presently affected by Indian Summer Monsoon Circulation and it records environmental changes associated with this major climatic boundary over the last 160 000 years. The internal stratigraphy and evolution of the sand sea is investigated using a combination of outcrop, borehole, seismic and luminescence data. Proximity to the Indian Ocean means that the sand sea succession shows the influence of sea level changes on the sedimentary architecture and composition of the dune deposits. During the last two glacial periods, low global sea level was associated with a high input of bioclastic grains, reflecting the significance of subaerially exposed shelf areas as one of the main sources of aeolian sediment. The onset of aeolian sediment transport and deposition was related to the breakdown of stabilizing vegetation during arid periods that equate with sea level lowstands. The preservation of aeolian sediments by the formation of supersurfaces and associated palaeosoils took place during times of increased wetness and elevated groundwater tables. This interplay of constructive and destructive periods greatly influenced the sedimentary architecture. Oscillations of wet and dry periods between 160 000 and 130 000 years and 120 000–105 000 years ago are attributed to the evolution of a wet aeolian system. Younger periods of aeolian deposition around and after the last glacial maximum were characterized by dry aeolian conditions. No soil horizons developed during these times.     

Chemical Characterisation of Geological Raw Materials Used in Traditional Ceramics

A wide range of natural raw materials is used in the manufacture of traditional ceramic products such as ceramic tiles, frits, glazes and pigments. The chemical composition of these raw materials needs to be strictly controlled to assure end-product quality and enable the identification of the origin of defects caused by impurities or contamination. Six types of ceramic raw materials (silica sand, clays and kaolin, feldspars and related minerals, calcium and magnesium carbonates, sodium and calcium borates, and zirconium silicates) have been analysed in this study. X-ray fluorescence (XRF), potentiometry, coulometry and atomic absorption spectrometry (AAS) were used in this chemical characterisation. A methodology has been established for characterising each studied raw material, by identifying the chemical elements to be determined, selecting the most appropriate technique and validating each measurement. The reference materials used for validation were BCS CRM 267, 313/1, 393 and 388 (BAS), GBW 03103, GBW 07404, NIST SRM 181, 201a and 1835, Euronorm CRM 782-1 and Syenite SY-2. The results showed that most of the elements present in the geological samples used as traditional ceramic raw materials could be determined by XRF. The determination of light elements, such as lithium, fluorine and boron, is more suitably conducted by ICP-AES/AAS, potentiometry or potentiometry/ICP-AES respectively. Organic and inorganic carbon could be determined by coulometry. Inorganic carbon (CO₂) could also be determined by coulometry or by thermogravimetry, if samples did not contain clay minerals. Loss on ignition was always determined by gravimetry.     

Determination of Platinum-Group Elements in Geological Reference Materials by High Resolution-ICP-MS after Nickel Sulfide Fire-Assay Collection and Te Co-Precipitation

Inductively coupled plasma-mass spectrometry (ICP-MS) after NiS fire assay-Te co-precipitation was employed in the determination of Ru, Rh, Pd, Os, Ir and Pt at ng g^-1 levels in six platinum-group element (PGE) geological reference materials. In general, the average of several results was in good agreement with the certified values taking into account respective uncertainties. High relative standard deviations were observed for the reference materials GPt-3 and GPt-4. Problems associated with the NiS fire assay procedure and PGE determination at the sub-10 ng g^-1 level are reviewed and discussed.     

Rapid tectonic exhumation, detachment faulting and orogenic collapse in the Caledonides of western Ireland

Collision of the oceanic Lough Nafooey Island Arc with the passive margin of Laurentia after 480 Ma in western Ireland resulted in the deformation, magmatism and metamorphism of the Grampian Orogeny, analogous to the modern Taiwan and Miocene New Guinea Orogens. After 470 Ma, the metamorphosed Laurentian margin sediments (Dalradian Supergroup) now exposed in Connemara and North Mayo were cooled rapidly (>35 °C/m.y.) and exhumed to the surface. We propose that this exhumation occurred mainly as a result of an oceanward collapse of the colliding arc southwards, probably aided by subduction rollback, into the new trench formed after subduction polarity reversal following collision. The Achill Beg Fault, in particular, along the southern edge of the North Mayo Dalradian Terrane, separates very low-grade sedimentary rocks of the South Mayo Trough (Lough Nafooey forearc) and accreted sedimentary rocks of the Clew Bay Complex from high-grade Dalradian meta-sedimentary rocks, suggesting that this was a major detachment structure. In northern Connemara, the unconformity between the Dalradian and the Silurian cover probably represents an eroded major detachment surface, with the Renvyle–Bofin Slide as a related but subordinate structure. Blocks of sheared mafic and ultramafic rocks in the Dalradian immediately below this unconformity surface probably represent arc lower crustal and mantle rocks or fragments of a high level ophiolite sheet entrained along the detachment during exhumation.Orogenic collapse was accompanied in the South Mayo Trough by coarse clastic sedimentation derived mostly from the exhuming Dalradian to the north and, to a lesser extent, from the Lough Nafooey Arc to the south. Sediment flow in the South Mayo Trough was dominantly axial, deepening toward the west. Volcanism associated with orogenic collapse (Rosroe and Mweelrea Formations) is variably enriched in high field strength elements, suggesting a heterogeneous enriched mantle wedge under the new post-collisional continental arc.     

Characterization of Cu-complexes in smectite with different layer charge location: chemical, thermal and EXAFS studies

The retention of Cu and Cu-amino acid complexes by montmorillonite and beidellite, before and after repeated acidified aqueous solution treatments, was studied using X-ray diffraction, chemical and thermal analyses, mass spectrometry and synchrotron-based X-ray absorption spectroscopy (XAS).The results indicate that the extraction of metal complexes from smectites depends on the nature of the layer charge and on the kind of organic species. Cu-cysteine complexes are strongly retained in the interlayer position, whereas Cu-glycine complexes are mostly adsorbed in cationic form which can be easily removed from the silicate layer. The layer periodicity for Cu-smectites treated with glycine shows little or no layer expansion, whereas significant swelling of the layer periodicity is observed in smectites treated with cysteine.Thermal decomposition of both smectites with sorbed Cu-amino acid species shows the evolution of H₂O, NO, CH₃CH₃, and CO₂. In Cu-cysteine treated smectites, the release of H₂S, NO₂, SO₂, and N₂O₃ also occurs.X-ray absorption spectroscopy (XAS) was used to assess the relationships between the structure of the Cu complexes and their desorption from smectites. In Cu-exchanged smectites, the first coordination shell agrees with the hypothesis that the Cu coordinates to oxygen atoms to form monomer and/or dimer complexes. The first coordination shell of Cu in smectites treated with glycine shows four atoms at distances of ∼2 Å. Two of these bonds are with nitrogen and two with oxygen atoms. For copper-cysteine complexes XAS data are compatible with the existence of Cu-N clusters, thus suggesting that Cu links to the amino acid by the aminic group.     

Late Eocene brachiopods from the Euganean Hills (NE Italy)

Five species belonging to five genera and an unidentified rhynchonellid have been recognised in a Late Eocene (Priabonian) brachiopod assemblage from Castelnuovo in the Euganean Hills, north-eastern Italy. One genus and two species are new, i. e. Venetocrania euganea gen. et sp. nov. and “Terebratula” italica sp. nov. Orthothyris pectinoides (von Koenen 1894) is recorded for the first time from Italy. The other species are Terebratulina sp. cf. T. tenuistriata (Leymerie 1846) and Lacazella mediterranea (Risso 1826), both already known from the Italian Eocene.     

Crystal morphology and surface structures of orthorhombic MgSiO3 in the presence of divalent impurity ions

Many rheological and transport properties of rocks are determined by the grain boundary structures of their constituent minerals. These grain boundaries often also hold a high concentration of dopant ions. Here, as a first step towards modelling the transport and rheological behaviour of the lower mantle, we report the results of lattice static simulations on the surface structures of Fe²⁺ and Ca²⁺-doped orthorhombic MgSiO₃-perovskite. For all the surfaces we studied, the energies of the doped structures are lowered, sometimes by more than 1 J/m², with respect to the pure surfaces. From our calculated crystal morphologies, we predict that the grains become more tabular as the concentration of Fe²⁺ ions increases, while under equilibrium conditions the grains are cubic. By calculating the replacement energies of Mg²⁺ by Fe²⁺ and Ca²⁺ ions in the six outermost surface layers, we conclude that these divalent ions would tend to segregate onto the crystal surfaces. We suggest, therefore, that the grain boundary structure and rheology of MgSiO₃-perovskite dominated rocks will be strongly affected by the presence of minor elements in the lower mantle.     

Are Seafarers Migrants? ‐ Situating Seafarers in the Framework of Mobility and Transnationalism

Seafarers are a unique occupational group who are recruited, by international agencies and work under contract on board ships of different kinds: merchant cargo and container ships; deep sea fishing vessels; and cruise ships. Seafarers “travel” either globally or regionally over varying distances. This paper seeks to find a place for the movement of seafarers in the existing theoretical context of labour migration. They undertake a particular type of circulatory or ‘transversal’ labour migration, and have established a special form of social identity. Locating them within theoretical migration and transnational concepts will contribute a new perspective.