Opaline chert nodules in maar lake sediments from Camp dels Ninots (La Selva Basin, NE Spain)

Chert nodule samples from three different well cores (CC, CP1 & CA) from the lacustrine infill of the Camp dels Ninot maar-diatreme (La Selva Basin) have been studied by means of X-ray diffraction, and optical and electron microscope technique. The chert nodules replace diatomites and carbonates layers, and varies in mineralogy between opal-A to opal-A/CT. The microtexture of the opal-A rich nodules is characterized by smooth microspheres of ~2μm in diameter that forms aggregates of amalgamated microspheres. Commonly, the nodules contain diatoms and their moulds when replacing diatomites, and dolomite or ankerite crystals and their moulds when replacing carbonates. The opal-A/CT rich nodules exhibit a microtexture consisting of microspheres of ~8μm in diameter that form aggregates with botryoidal and finger-like morphologies. Results indicate that the early diagenetic transformation of opal-A to opal-CT is not complete in the studied sediments.Peer Reviewe

Structural and high-pressure properties of rheniite (ReS2) and (Re,Mo)S2

Rhenium disulfide (ReS2), known in nature as the mineral rheniite, is a very interesting compound owing to its remarkable fundamental properties and great potential to develop novel device applications. Here we perform density functional theory (DFT) calculations to investigate the structural properties and compression behavior of this compound and also of the (Re,Mo)S2 solid solution as a function of Re/Mo content. Our theoretical analysis is complemented with high-pressure X-ray diffraction (XRD) measurements, which have allowed us to reevaluate the phase transition pressure and equation of state of 1T-ReS2. We have observed the 1T-to-1T' phase transition at pressures as low as ~2 GPa, and we have obtained an experimental bulk modulus, B0, equal to 46(2) GPa. This value is in good agreement with PBE+D3 calculations, thus confirming the ability of this functional to model the compression behavior of layered transition metal dichalcogenides, provided that van der Waals corrections are taken into account. Our experimental data and analysis confirm the important role played by van der Waals effects in the high-pressure properties of 1T-ReS2

High-pressure Raman scattering in bulk HfS2: comparison of density functional theory methods in layered MS2 compounds (M = Hf, Mo) under compression

We report high-pressure Raman-scattering measurements on the transition-metal dichalcogenide (TMDC) compound HfS2. The aim of this work is twofold: (i) to investigate the high-pressure behavior of the zone-center optical phonon modes of HfS2 and experimentally determine the linear pressure coefficients and mode Grüneisen parameters of this material; (ii) to test the validity of different density functional theory (DFT) approaches in order to predict the lattice-dynamical properties of HfS2 under pressure. For this purpose, the experimental results are compared with the results of DFT calculations performed with different functionals, with and without Van der Waals (vdW) interaction. We find that DFT calculations within the generalized gradient approximation (GGA) properly describe the high-pressure lattice dynamics of HfS2 when vdW interactions are taken into account. In contrast, we show that DFT within the local density approximation (LDA), which is widely used to predict structural and vibrational properties at ambient conditions in 2D compounds, fails to reproduce the behavior of HfS2 under compression. Similar conclusions are reached in the case of MoS2. This suggests that large errors may be introduced if the compressibility and Grüneisen parameters of bulk TMDCs are calculated with bare DFT-LDA. Therefore, the validity of different approaches to calculate the structural and vibrational properties of bulk and few-layered vdW materials under compression should be carefully assessed

Significance of Fracture-Filling Rose-Like Calcite Crystal Clusters in the SE Pyrenees

Fracture-filling rose-like clusters of bladed calcite crystals are found in the northern sector of the Cadí thrust sheet (SE Pyrenees). This unusual calcite crystal morphology has been characterized by using optical and electron microscope, X-ray diffraction, Raman spectroscopy, 18O, 13C, 87Sr/86Sr, clumped isotopes, and major and rare earth elements + yttrium (REEs + Y) analysis. Petrographic observations and powder X-ray diffraction measurements indicate that these bladed crystals are mainly made of massive rhombic crystals with the conventional (104) faces, as well as of possibly younger, less abundant, and smaller laminar crystals displaying (108) and/or (108) rhombic faces. Raman analysis of liquid fluid inclusions indicates the presence of aromatic hydrocarbons and occasionally alkanes. Clumped isotopes thermometry reflects that bladed calcite precipitated from meteoric fluids at ~60-65 C. The 87Sr/86Sr ratios and major elements and REEs content of calcite indicate that these fluids interacted with Eocene marine carbonates. The presence of younger 'nailhead' calcite indicates later migration of shallow fresh groundwater. The results reveal that rose-like calcite clusters precipitated, at least in the studied area, due to a CO2 release by boiling of meteoric waters that mixed with benzene and aromatic hydrocarbons. This mixing decreased the boiling temperature at ~60-65 C. The results also suggest that the high Sr content in calcite, and probably the presence of proteins within hydrocarbons trapped in fluid inclusions, controlled the precipitation of bladed crystals with (104) rhombohedral faces

Abellaite, NaPb2(CO3)2(OH), a new supergene mineral from the Eureka mine, Lleida province, Catalonia, Spain

The new mineral abellaite (IMA 2014-111), ideally NaPb2 (CO3)2 (OH), is a supergene mineral that was found in one of the galleries of the long-disused Eureka mine, in the southern Pyrenees (Lleida province), Catalonia, Spain. Abellaite is found as sparse coatings on the surface of the primary mineralization, it forms subhedral crystals not larger than 10μm as well as larger pseudohexagonal platelets up to ~ 30μm. Individual crystals commonly have a tabular to lamellar habit and form fairly disordered aggregates. The mineral is associated with a large number of primary minerals (roscoelite, pyrite, uraninite, coffinite, 'carbon', galena, sphalerite, nickeloan cobaltite, covellite, tennantite and chalcopyrite) and supergene minerals (hydrozincite, aragonite, gordaite, As-rich vanadinite andersonite, čejkaite, malachite and devilline). Abellaite is colourless to white, with a vitreous to nacreous lustre. The mineral is translucent, has a white streak and is non-fluorescent. The aggregates of microcrystals are highly friable. The calculated density using the ideal formula is 5.93 g/cm3. The chemical composition of the mineral (the mean of 10 electron microprobe analyses) is Na 3.88, Ca 0.29, Pb 72.03, C 4.17, O 19.47 and H 0.17, total 100.00 wt% (H, C and O by stoichiometry assuming the ideal formula). On the basis of 7 O atoms, the empirical formula of abellaite is Na0.96 Ca0.04 Pb1.98 (CO3)2 (OH). The simplified formula of the mineral is NaPb2 (CO3)2 (OH). The mineral is hexagonal, space group P 63 mc, a = 5.254(2), c = 13.450(5) Å, V = 321.5(2) Å3 and Z = 2. The strongest powder-diffraction lines [d in Å (I) (h k l)] are: 3.193 (100) (0 1 3), 2.627 (84) (1 1 0), 2.275 (29) (0 2 0), 2.242 (65) (0 2 1, 0 0 6), 2.029(95) (0 2 3). Abellaite has a known synthetic analogue, and the crystal structure of the mineral was refined by using crystallographic data of the synthetic phase. The mineral is named in honour of the mineralogist and gemmologist Joan Abella i Creus (b. 1968), who has long studied the deposits of the Eureka mine and who collected the mineral

Borehole image techniques applied to identification of chert and dolomite layers in lacustrine sediments

Geophysical logging tools, particularly ultrasonic acoustic borehole image techniques, are applied on two different wells (CP1 and CP2) to identify and characterize the lacustrine interval (40m) of the Camp dels Ninots maardiatreme infill (Pliocene, Catalan Coastal Ranges). The CP1 well was cored and also geophysical logs and oriented borehole images were acquired. CP2 hole was partially cored but logging (geophysics and borehole images) was fully undertaken. Continuous core recovery in CP1 is compared with oriented images and is further used to identify and characterize highly reflective signals in a section of CP2 borehole that was not cored. These signals are related to silicified zones and belong to discontinuous centimetric chert nodules, while indurated massive carbonates are characterized as intervals of continuous reflectance. Despite opal nodules (chert) can be relatively small, they have a distinctive response in the ultrasonic borehole images.Peer Reviewe

Petrological characterization of flint from Montmaneu's Limestones Formation (Eastern sector of the Ebro Basin)

[EN] Flint from Montmaneu's Limestones Formation of Rupelian age (Oligocene) is being here characterized. The analysis of the compositional texture, mineralogy and geochemical features has revealed this flint is highly pure and of microcrystalline texture, with a significant content of moganite. This flint is product of an early diagenetic replacement of limestone from littoral lacustrine facies. This flint was exploited by human populations in a regional range, especially in the early stages of the Neolithic.[ES] Se caracteriza el sílex de la Formación calizas de Montmaneu, de edad Rupeliense (Oligoceno). El análisis textural, mineralógico y de sus rasgos geoquímicos indica que se trata de un sílex microcristalino, bastante puro, con una proporción significativa de moganita. Es producto del reemplazamiento diagenético temprano de calizas de facies lacustres litorales. Este sílex fue objeto de una explotación regional, especialmente en los primeros momentos del Neolítico.Este trabajo forma parte del proyecto de constitución de una litoteca de rocas silíceas del NE peninsular (LITOcat). Los estudios sobre la explotación prehistórica del sílex de Montmaneu se llevan a cabo en el marco del proyecto "Aprofitament prehistòric i històric del sílex a Catalunya: contextos extractius i de primera transformació". Ambos proyectos son financiados por el CSIC-IMF y el Departamento de Cultura de la Generalitat de Catalunya.Peer reviewe

What burned the forest? Wildfires, climate change and human activity in the Mesolithic – Neolithic transition in SE Iberian Peninsula

Climate variability such as higher or lower temperatures, changing precipitation patterns, shifts in plant communities and other climate-related changes have particularly affected areas with Mediterranean-type climates. A multi-proxy analysis including pollen, sedimentary charcoal, mineralogy and Summed Probability Distributions (SPD) of archaeological 14C dates, allowed the reconstruction of landscape change, geomorphological evolution and fire history at the Laguna de Villena, in the southeastern Iberian Peninsula, during the Mesolithic-Neolithic transition. The Villena paleolake was sensitive to Early Holocene and Middle Holocene regional climatic variability that included several arid phases (around 8.2 ka cal BP, 6.8 ka cal BP and 5.9 ka cal BP) according to geochemical and pollen data. During this period, landscape dynamics show the degradation of oak forests and expansion of pyrophytic pine forests and shrublands, as well as open spaces predominated by grasses. The charcoal record shows a decreasing trend of biomass burned from 8.5 ka cal BP onwards, although fire peaks occurred recurrently during the Early and Middle Holocene. The most intense phase of fire activity was experienced in the last millennia of the Early Holocene, with five fire episodes from 9.1 to 8.4 ka cal BP, coinciding with a phase of higher archaeological evidence in the area. A decrease in archaeological evidence coincides with a gap in fire episodes during the Early Holocene-Middle Holocene transition, suggesting an effect of the abrupt 8.2 ka cal BP event on human activity and on landscape dynamics. After 8.0 ka cal BP, lowerer biomass burned is explained by the configuration of a more open landscape due to the combination of climate (increasing aridity) and increasing human activities in the region. The mineralogical and palynological data highlighted the interaction between human activities, climate and fire dynamics. The sedimentary charcoal record evidenced how most of the fire peaks did not occur in the context of dry episodes, as often assumed, deriving on an anthropogenic explanation related to Early and Late Mesolithic burning practices during a phase of higher archaeological evidence in the Villena paleolake surroundings. Afterwards, combined agropastoral activities from the Early Neolithic onwards and increasing aridity during the Middle Holocene maintained the forest clearances, in the context of fire episodes characterised by decreased biomass burned. This study shows how Middle Holocene palaeoecological records reflect complex histories blending climate and anthropogenic processes that derived in major landscape changes explaining the origin of current landscapes.This research has received funding from the European Research Council (ERC) under the Horizon 2020 research and innovation programme (Grant agreement No. 683018) to JFLdP. Additional analyses on the pollen data sets have been produced in the context of the research project PID2020-113664RB-100 supported by the Spanish Ministry of Science and Innovation. JFLdP is additionally supported by the Plan Gen-T program (Ref. CIDEGENT-18/040) of the Generalitat Valenciana. CSG is currently supported by a Margarita Salas fellowship (ref. MARSALAS21-22) funded by the European Union-Next Generation EU, the Spanish Ministry of Universities and the University of Alicante. JR, IE and FB are members of the research group GAPS (2017 SGR 836). JR acknowledges postdoctoral fellowship support from the Spanish “Juan de la Cierva Incorporación (IJC2020)” program (MICINN, Spain). The Institut Català de Paleoecologia Humana I Evolució Social (IPHES-CERCA) has received financial support from the Spanish Ministry of Science and Innovation through the “María de Maeztu'' program for Units of Excellence (CEX2019-000945-M). LS is granted by the ICREA Academia Program

Electron effective mass and mobility in heavily doped n-GaAsN probed by Raman scattering

We investigate inelastic light scattering by longitudinal optic phonon-plasmon coupled modes LOPCMs in a series of heavily Se-doped, n-type GaAs1−xNx epilayers with x 0.4%. We perform a line shape analysis of the LOPCM spectra to estimate the optical effective mass, mopt , and the scattering time of the conduction electrons in GaAsN. We use these results to evaluate an effective carrier mobility for our samples. The values thus obtained, which we compare with measured electron Hall mobilities, indicate that the x-dependence of the mobility in GaAs1−xNx is dominated by the scattering time, rather than by the variation of the electron effective mass. The Raman analysis yields mopt values that are lower than those obtained from the band anticrossing model. © 2008 American Institute of Physics.This work is supported by the Spanish Government Projects MAT 2004-0664 and MAT2007-63617, and Ramon y Cajal Program and the EPSRC, United Kingdom. 1M. Henini, Dilute Nitride Semiconductors Elsevier Science, AmsterdamPeer reviewe

Optical emission from Si O2 -embedded silicon nanocrystals: A high-pressure Raman and photoluminescence study

© 2015 American Physical Society. We investigate the optical properties of high-quality Si nanocrystals (NCs)/SiO2 multilayers under high hydrostatic pressure with Raman scattering and photoluminescence (PL) measurements. The aim of our study is to shed light on the origin of the optical emission of the Si NCs/SiO2. The Si NCs were produced by chemical-vapor deposition of Si-rich oxynitride (SRON)/SiO2 multilayers with 5- and 4-nm SRON layer thicknesses on fused silica substrates and subsequent annealing at 1150°C, which resulted in the precipitation of Si NCs with an average size of 4.1 and 3.3 nm, respectively. From the pressure dependence of the Raman spectra we extract a phonon pressure coefficient of 8.5±0.3cm-1/GPa in both samples, notably higher than that of bulk Si(5.1cm-1/GPa). This result is ascribed to a strong pressure amplification effect due to the larger compressibility of the SiO2 matrix. In turn, the PL spectra exhibit two markedly different contributions: a higher-energy band that redshifts with pressure, and a lower-energy band which barely depends on pressure and which can be attributed to defect-related emission. The pressure coefficients of the higher-energy contribution are (-27±6) and (-35±8)meV/GPa for the Si NCs with a size of 4.1 and 3.3 nm, respectively. These values are sizably higher than those of bulk Si(-14meV/GPa). When the pressure amplification effect observed by Raman scattering is incorporated into the analysis of the PL spectra, it can be concluded that the pressure behavior of the high-energy PL band is consistent with that of the indirect transition of Si and, therefore, with the quantum-confined model for the emission of the Si NCs.Work supported by the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 245977 (project NASCEnT). Financial support by the Spanish Government through projects LEOMIS (TEC2012-38540-C02-01) and MAT2012-38664-C02-02 is also acknowledgedPeer Reviewe