Surface changes on crystalline stones due to salt crystallisation

This study assesses the changes on the surface of crystalline stones due to salt crystallisation. Efflorescence was forced to grow on the surface of granite and marbles through 60 cycles of salt crystallisation with sodium sulphate. Changes on surface roughness, gloss and colour were measured every 15 cycles and the specimens were examined with naked eye and SEM. Sodium sulphate produces damage which depends on mineral composition. Results show that granites experience a mechanical decay with an increase in roughness. Peaks of mica can be observed on the surface and cracks widen and grow deeper. Colour and gloss do not show any significant change, although gloss decreases with an increase in surface roughness. In marbles, the decay is mainly chemical. Surface roughness increases due to dissolution of the calcite. White marbles exhibit yellowing. Gloss decreases during the first cycles—as grain boundaries become more visible—but tends to regain almost its initial value as the number of cycles increases. In this case, gloss does not show any relation with surface roughness.     

New ichnospecies of scratching traces from phosphatic nodules (Cenomanian, England)

Surfaces of phosphorite nodules and pebbles from the “Cambridge Green Sand” (Cenomanian, South England) yielded several discernible types of scratches. These originated before the burial of nodules/pebbles as evidenced by fossil epibiotic oysters cemented to cover the scratches. The individual forms of scratches differ in size and shape; therefore, the set of “scratching instruments” also had to be different. The scratches described differ from scratches generated by glacial processes, namely by the regularity of length and intervals, parallel orientation, existence of recurrent forms and placement along the nodule edges. We interpret the scratches as trace fossils of the ichnogenus Machichnus. Three new species, namely M. normani, M. harlandi and M. jeansi, are erected for them herein. The series of scratches originated probably by teeth on a couple of jaws; the makers possibly scraped bacterial or algal film off the surface of nodules that were covered with the phosphate gel. Both homodont and heterodont animals (probably fish) were involved.     

Determination of ecological significance based on geostatistical assessment: a case study from the Slovak Natura 2000 protected area

The Sitno Natura 2000 Site covers an area of 935,56 hectares. The Sitno region is significant due to the number of rare and endangered species of plants, and as a result is considered a location of great importance to the maintenance of floral gene pools. The study area suffers human impacts in the form of tourism. The main purpose of this study is to the measure landscape elements, determine the ecological significance of habitats within the Sitno area, and from this data, organize the study area into conservation zones. The results of this landscape quantification are numerical values that can be used to interpret the quality of ongoing ecological processes within individual landscape types. Interpretation of this quantified data can be used to determine the ecological significance of landscapes in other study areas. This research examines the habitats of Natura 2000 Sites by a set of landscape metrics for habitat area, size, density, and shape, such as Number of patches (NP), Patch density (PD), Mean patch size (MPS), Patch size standard deviation (PSSD) and Mean shape index (MSI). The classification of land cover patches is based on the Annex Code system.     

Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes (Harrat Kishb, Saudi Arabia)

Al Wahbah Crater is one of the largest and deepest Quaternary maar craters in the Arabian Peninsula. It is NW-SE-elongated, ～2.3 km wide, ～250 m deep and surrounded by an irregular near-perpendicular crater wall cut deeply into the Proterozoic diorite basement. Very few scientific studies have been conducted on this unique site, especially in respect to understanding the associated volcanic eruption processes. Al Wahbah and adjacent large explosion craters are currently a research subject in an international project, Volcanic Risk in Saudi Arabia (VORiSA). The focus of VORiSA is to characterise the volcanic hazards and eruption mechanisms of the vast volcanic fields in Western Saudi Arabia, while also defining the unique volcanic features of this region for use in future geoconservation, geoeducation and geotourism projects. Al Wahbah is inferred to be a maar crater that formed due to an explosive interaction of magma and water. The crater is surrounded by a tephra ring that consists predominantly of base surge deposits accumulated over a pre-maar scoria cone and underlying multiple lava flow units. The tephra ring acted as an obstacle against younger lava flows that were diverted along the margin of the tephra ring creating unique lava flow surface textures that recorded inflation and deflation processes along the margin of the post-maar lava flow. Al Wahbah is a unique geological feature that is not only a dramatic landform but also a site that can promote our understanding of complex phreatomagmatic monogenetic volcanism. The complex geological features perfectly preserved at Al Wahbah makes this site as an excellent geotope and a potential centre of geoeducation programs that could lead to the establishment of a geopark in the broader area at the Kishb Volcanic Field.     

Hydrographic data modeling methods for determining precise seafloor topography

Acoustic and light detection and ranging are the recent methods used in hydrographical surveying. Depth values depending on X and Y horizontal coordinates are measured in both methods. While processing the hydrographical data, all data with different density are interpolated and modeled for determining the seafloor model using different interpolation techniques. In this study, effects of different surface modeling methods are investigated. Data obtained from single-beam echo sounder (SBES) are modeled using inverse distance, kriging, local polynomial, minimum curvature, moving average, nearest-neighbor, and Delaunay interpolation methods. Interpolation results are compared with the multibeam echo sounder data which were collected on the same area for determining the accuracy of modeling methods. Depending on the maximum total vertical uncertainty values in hydrographic survey standards, the best results were determined by using the kriging method. The Delaunay, minimum curvature, and inverse distance methods can be used for modeling the SBES data in shallow waters.     

A powder diffraction quantification method (ALJOR) for atmospheric particulate matter

The percentage calculation of crystalline phases in atmospheric particulate matter samples by means of an adiabatic approach of the matrix-flushing method with preferred preparations that avoids preferential orientations, should never be interpreted as absolute values. On the contrary, it should be seen as an indicator of the significant differences between each and every analyzed sample. Factors such as the application of constants, which are only useful for preparations of polycrystalline samples free of preferential orientation, and/or like the deficient resolution shown by the diffraction diagrams for certain phyllosilicate phases, bring a high degree of uncertainty to these percentage calculations. An alternative method of crystalline and amorphous phase quantification is presented below. Once the majority phases in the samples were identified, appropriate pure phases corresponding to each of them were selected. Then, the corresponding calibration curves were built using corundum (number 676 NIST) as a reference pattern phase. After validating the obtained calibration curves, the constants corresponding to each phase and selected spacing were calculated. The ALJOR method has been used for the quantification of five samples.     

Modelling shallow landslide susceptibility: a new approach in logistic regression by using favourability assessment

A new method for estimating shallow landslide susceptibility by combining Geographical Information System (GIS), nonparametric kernel density estimation and logistic regression is described. Specifically, a logistic regression is applied to predict the spatial distribution by estimating the probability of occurrence of a landslide in a 16 km² area. For this purpose, a GIS is employed to gather the relevant sample information connected with the landslides. The advantages of pre-processing the explanatory variables by nonparametric density estimation (for continuous variables) and a reclassification (for categorical/discrete ones) are discussed. The pre-processing leads to new explanatory variables, namely, some functions which measure the favourability of occurrence of a landslide. The resulting model correctly classifies 98.55% of the inventaried landslides and 89.80% of the landscape surface without instabilities. New data about recent shallow landslides were collected in order to validate the model, and 92.20% of them are also correctly classified. The results support the methodology and the extrapolation of the model to the whole study area (278 km²) in order to obtain susceptibility maps.     

Thermal expansion and high-temperature P21/c–C2/c phase transition in clinopyroxene-type LiFeGe2O6 and comparison to NaFe(Si,Ge)2O6

A synthetic clinopyroxene with composition LiFe³⁺Ge₂O₆, monoclinic s.g. P2₁/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) Å, β = 108.844(6)°, V = 442.75(16) ų, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P2₁/c to C2/c at a transition temperature T _tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T _tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T _tr the thermal volume expansion is due to dilatation of the structure in the $(\bar{1}\,0\,1) A synthetic clinopyroxene with composition LiFe³⁺Ge₂O₆, monoclinic s.g. P2₁/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) ?, β = 108.844(6)°, V = 442.75(16) ?³, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P2₁/c to C2/c at a transition temperature T _tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T _tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T _tr the thermal volume expansion is due to dilatation of the structure in the ([`1] 0 1)(\bar{1}\,0\,1) plane, mostly along [0 1 0], and pure shear in the (0 1 0) plane due to the decrease of β. From comparison with silicate analogues, the germanate clinopyroxenes are more expansible, while the P2₁/c expands more than the C2/c phase. The evolution of Q ² (calculated as the normalized intensity of b-type reflections) with T in the framework of the Landau theory has been done using a standard expression for a first order phase transition. We observe a jump of Q ₀² = 0.538(2) at T _tr, with T _c of 481(7) K, b/a = −2,290 K, and c/a = 3,192 K, and thus far from being tri-critical point. A closely related composition (LiFe³⁺Si₂O₆) shows an equivalent phase transition at 228 K, which is very close to the tri-critical point and 561 K cooler. This result indicates that a change in the composition of tetrahedral sites can have dramatic effects on the P2₁/c ↔ C2/c displacive phase transition in clinopyroxenes. The major changes observed in the evolution of the crystal structure with T are observed in the M2 polyhedron, with a volume decrease by ca. 13.3%, compared to ca. 1.3% observed in the M1 polyhedron. The tetrahedra behave as rigid units with neither a significant change of volume at T > T _tr (<1‰), nor a change of tilting of the basal plane. No change in coordination is observed at T > T _tr in the M2 polyhedron, which remains sixfold coordinated although a strong deformation of this polyhedron is observed. This deformation is related to a strong change by 51.4° at T _tr of the kinking angle (O3–O3–O3 angle) of the B-chain of tetrahedra, which switches from O-rotated to S-rotated [from 143.3(5)° to 194.7(6)°]. The A-chain is S-rotated at T < T _tr [206.8(5)° at 703 K] and extends by 12° at the transition.     

Eustatic and tectonic controls on Quaternary Ras Leona marine terraces (Strait of Gibraltar, northern Morocco)

Well-preserved Quaternary staircased marine terraces appear on Ras Leona limestone relief. This is a peculiar sector of the Betic-Rif Cordillera, lying in the four-way junction between the Atlantic and the Mediterranean, and Europe and Africa. The age and altitude correlation of the Ras Leona terraces with travertine-covered lateral equivalent terraces fashioned in the neighbouring Beni Younech area, and comparison with those along the Moroccan Atlantic coasts, would suggest that the Ras Leona terraces were mainly formed by eustatic factors. The importance of the eustasy is supported by further comparisons with Spanish and Moroccan Mediterranean terraces and with different marine terraces developed on passive-margin coasts around the world. A tectonic event occurred mainly during the period between the formation of the Maarifian and the Ouljian terraces (i.e., between 370 and 150 ka). The moderate Quaternary tectonic uplift deduced from the marine terraces and its comparison with uplifted marine terraces developed in active subduction setting disagrees with the model of an active eastwards subduction below the Gibraltar tectonic arc.     

Neoproterozoic–Cambrian synsedimentary magmatism in the Central Iberian Zone (Spain): geology,petrology and geodynamic significance

Petrographic, geochemical and field studies in low grade metamorphic areas (Ciudad Rodrigo-Hurdes-Sierra de Gata domain, CRHSG, central-western Spain) show that Neoproterozoic-Lowermost Cambrian series in the Central Iberian Zone (CIZ) record two kinds of provenance sources including: (1) detrital material derived from recycled orogens and (2) a Cadomian coeval juvenile contribution that governs their isotopic signature. Evidence of magmatism contemporaneous with Neoproterozoic-Cambrian sedimentation is provided by the presence of coherent, massive volcanic rocks (metabasalts, metaandesites, and metarhyolites), volcaniclastic shales, sandstones, conglomerates and breccias. The appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession, reinforces this evidence. Although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity, some of them display calc-alkaline affinity. Different trace element ratios, such as Sm/Nd, Nb/Yb and Ta/Yb, suggest a magmatic evolution in the same tectonic setting. The geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the Neoproterozoic–Lowermost Cambrian successions in the CIZ. In particular, the relatively high Nd _(T) values and the high range of f ^Sm/Nd ratios are consistent with an active margin during the Neoproterozoic–Early Cambrian. The existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks. All of these traits favour a geodynamic model in which the Iberian Cadomian segment represented in the CIZ would have been part of an active northern margin of Gondwana, with an associated magmatic arc and related basins during Neoproterozoic–Lower Cambrian times. A proposed link between the Ossa Morena and the Central Iberian Zones might account for late Cadomian pull-apart basins developed on both sides of the magmatic arc, sharing the same scenario and involving similar magmatic activity during the Neoproterozoic–Cambrian transition.