A Quantitive Micromorphological Study of Cultivated Paleosols in Campi-Flegrei Volcanic Ashes Beneath the New Chiaia Metro Station, Naples, Italy

The degree of preferred orientation of mineral grains in powder X-ray diffraction (XRD) samples prepared by standard techniques has been evaluated by means of a correction model implemented in the Rietveld program, BGMN. It is demonstrated that neither front- nor side-loading of mineral powders obtained by wet grinding in a McCrone micronizing mill yield powder mounts with randomly oriented particles. Despite fine grinding, the primary sizes and shapes of mineral grains contained in multi-phase samples influence the degree of preferred orientation in XRD powder mounts. Two minerals, both of platy habit, were found to show different degrees of preferred orientation in front- and side-loaded samples. In contrast to these methods of sample preparation, the spray-drying technique yielded perfect randomness of the particles. The experiments on artificial mineral mixtures demonstrate that the model applied can effectively correct for preferred orientation allowing reliable Rietveld quantitative phase analysis of moderately textured samples prepared by standard techniques.

The heavy atom content and distribution in chlorite were estimated using the relative intensities of basal X-ray powder diffraction (XRD) peaks. For these peaks to be meaningful, however, corrections had to be made for the effects of sample thickness, sample length, and preferred orientation of the mineral grains, all of which are 2θ dependent. The effects of sample thickness were corrected for by a simple formula. The effects of sample length were accounted for by using rectangular samples and by ensuring that the sample intersected the X-ray beam through the range of diffraction angles of interest. Preferred orientation of mineral grains were either measured directly or estimated. Estimated values were quicker and easier to obtain and were within 5% of measured values. A comparison of the compositional parameters of chlorite estimated before correcting for these sample effects with those estimated after the corrections had been applied indicate that the uncorrected values differed from the corrected values by as much as 55% of the latter values. Mounts of a single sample prepared by different filter-membrane peel and porous-plate techniques yielded widely different compositions until the measurements were corrected for sample effects. Analyses in triplicate indicated that the XRD intensity ratio 003/001 is preferred for calculating heavy atom distributions and abundances in chlorite because of the relative strength of the 001 peak.

Study on the effect of micro-geometric heterogeneity on mechanical properties of brittle rock using a grain-based discrete element method coupling with the cohesive zone model

A kinetic model of oriented nucleation under nonhydrostatic stress: Implications for the preferred orientation of columnar and platy minerals in metamorphic rocks

Grain-scale processes in actively deforming magma mushes: New insights from electron backscatter diffraction (EBSD) analysis of biotite schlieren in the Jizera granite, Bohemian Massif

A new method for calculating seismic velocities in rocks containing strongly dimensionally anisotropic mineral grains and its application to antigorite-bearing serpentinite mylonites

This thesis presents new and novel research on the satellite remote sensing of volcanic clouds, which was motivated by the need to mitigate the associated impacts of volcanic eruptions on civil aviation and provide deeper understanding on the radiative effects of volcanic ash. Afternoon train (A-train) sensors were used to characterise the horizontal and vertical evolution of the 2008 Chaiten eruption from 2–10 May in southern Chile. The combination of the Atmospheric InfraRed Sounder (AIRS) measurements with the Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) is demonstrated to be an effective synergistic technique capable of detecting volcanic ash in lidar backscatter returns. Geometrically thin (< 400 m) and low-level (< 10 km) volcanic ash clouds were identified. Ensemble forward trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model were generated to demonstrate how the new data could be used to improve Volcanic Ash Advisory Centre (VAAC) operations. The CALIOP/AIRS technique has also permitted identification of stratospheric volcanic aerosols. The particulate lidar ratio (Sp) for two classes of volcanic aerosols; fine ash and sulphate has been determined using CALIOP observations. For the volcanic ash layers produced by the Puyehue-Cordon Caulle eruption (June 2011) mean and median particulate lidar ratios of 72 ± 15 sr and 69 sr, respectively, were obtained. For the Kasatochi and Sarychev sulphates, mean (and standard deviation) of the retrieved lidar ratios were 68 ± 21 sr (median 62 sr) and 68 ± 17 sr (median 62 sr), respectively. The volume depolarisation ratio for fine ash was generally much higher (δv up to 0.30) than that found for sulphates (δv from ∼0.05–0.10). However, the Sarychev observations revealed an exponential decay in δv from 0.25 to 0.05. This finding highlights the key importance of depolarisation measurements in understanding the compositional evolution of volcanic aerosols. It is suggested that a criterion of δv < 0.2 could be used to discriminate between stratospheric ash and sulphate layers in CALIOP observations. Finally, A-train satellite measurements have been used to characterise the immediate radiative effects of the Calbuco (April 2015) volcanic ash clouds. The Calbuco ash layers were estimated to have produced a strong SW cooling (−60 W/m-2) at the top of the atmosphere (TOA). However, this cooling was offset by an even stronger LW warming (78 W/m-2), which resulted in an net warming of ∼18 W/m-2 at TOA. In contrast, a net cooling (−58 W/m-2) was induced at the surface. The LW heating rates of the Calbuco ash clouds were estimated to up to 20 K/day, while maximum SW heating was an order of magnitude lower (∼3 K/day).

Volcanic ash significantly contributes to marine sediments, especially in regions with active onshore volcanoes. Alteration of volcanic ash releases bicarbonate and cations, which drive precipitation of authigenic carbonate and clay minerals. Furthermore, volcanic ashes are commonly enriched in reactive iron (Fe[III]), suggesting that ash alteration as a source of reactants plays an important role in (bio-)geochemical processes in marine sediments. Volcanic ash layers are ubiquitous in sediments of Site C0023, which was established down to 1180 m below seafloor (mbsf) in the Nankai Trough off Japan during International Ocean Discovery Program Expedition 370. Shipboard measurements show a release of dissolved Fe between 200 and 600 mbsf, coinciding with a high abundance of ash layers [1]. The release of Fe can be related to microbial reduction of structural Fe(III) in smectite promoting the smectite-to-illite transition, as recently proposed [2]. By combining shipboard pore-water data with sequential extractions of reactive Fe pools on ash layers and surrounding mud rock and stable Fe isotope (δ56Fe) analyses, we elucidate the role of ash alteration on (bio-)geochemical cycling at Site C0023. Our results demonstrate that reactive Fe(III) is unexpectedly lower in ash layers compared to the surrounding mud rock (0.6 and 1.2 wt%, respectively). This indicates that (1) Fe(III) originally deposited with tephra has either been used or (2) Fe(III) in tephra is generally lower due to a different chemical composition in the volcanic source material. The δ56Fe signature of hydroxylamine-extracted Fe, which represents easily reducible Fe-oxides and Fe bound in phyllosilicates, is isotopically light (-0.08 to -0.42‰) compared to terrestrial background values (~0.09‰; [3]). This suggests that this pool is diagenetically overprinted by the precipitation of authigenic smectite formed as a result of ash alteration and/or secondary Fe-oxides. Pore-water Fe is extremely negative with δ56Fe <-1.5‰, which points to microbial reduction of Fe(III) in authigenic smectite. Our results suggest a coupling between ash alteration, authigenic mineral precipitation, and microbially mediated Fe reduction in sediments of Site C0023. [1] Heuer et al., (2017), In Proc. IODP Volume 370. [2] Kim et al., (2019), Geology 47, 535-539. [3] Beard et al., (2003), Chem. Geol. 195, 87-117.

On the visibility of airborne volcanic ash and mineral dust from the pilot’s perspective in flight

&amp;lt;p&amp;gt;The deep subseafloor biosphere represents one of the Earth&amp;amp;#8217;s largest, but also least understood ecosystems with diverse species and mostly uncharacterized microbial communities. International Ocean Discovery Program (IODP) Expedition 370 (Temperature Limit of the Deep Biosphere off Muroto) established Site C0023 down to 1180 mbsf in the Nankai Trough off Japan to explore the upper temperature limit of microbial life in the deep sedimentary biosphere [1]. Site C0023 is characterized by a complex lithostratigraphic and depositional history with strongly changing sedimentation rates. Volcanic ash layers are ubiquitous in all lithological units. However, the highest abundance of ash layers could be observed between 400 and 700 mbsf. Previous studies have shown that volcanic ashes represent hotspots for microbial life [2] and are commonly characterized by high Fe(III) and Mn(IV) contents [3]. Onboard measurements show a release of dissolved Fe in the depth interval associated with the highest abundance of ash layers [1]. Therefore, we hypothesized that the release is related to microbial Fe reduction fueled by the mineralogy of the volcanic ash. In order to identify the source and reaction pathway of the liberated Fe, we applied sequential extractions of differently reactive Fe oxide pools on mud rock and ash layer samples as well as stable iron isotope (&amp;amp;#948;&amp;lt;sup&amp;gt;56&amp;lt;/sup&amp;gt;Fe) analyses on pore-water and solid-phase samples. Microbial Fe reduction leads to Fe isotope fractionation with an enrichment of light isotopes in the released Fe and a respective enrichment of heavy isotopes in the residual ferric substrate. Therefore, the &amp;amp;#948;&amp;lt;sup&amp;gt;56&amp;lt;/sup&amp;gt;Fe signals of different reactive Fe pools and the pore water are used to identify the pools actually involved in microbial respiration processes. Our results show that the total Fe content in mud rock of Site C0023 is relatively constant at ~4.2 wt%. Reactive Fe oxides represent 25% of the total Fe. The bulk Fe content in the ash layers varies between 1.4 and 6.8 wt%. Surprisingly, most ash samples contain less total Fe (3.35 wt% on average) compared to the surrounding mud rock. Similarly, the contents of the reactive Fe oxides are significantly lower. This indicates that either (1) ash layers do not represent the energy substrate for microbial Fe reduction, or (2) reactive Fe in ash samples has already been used up by microbes. The bulk Fe content in recent volcanic material from an active volcano on the Japanese island arc is ~4.4 wt% [4]. The higher Fe content in fresh volcanic material compared to ash samples at Site C0023 might suggest that reactive Fe in ash layers is already reduced. Alternatively, the dissolved Fe release might be related to microbial reduction of structural Fe(III) in smectite promoting the smectite-to-illite transition, which has previously been proposed for Site C0023 [5].&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;

Archaeological sites in Northwest Africa are rich in human fossils and artefacts providing proxies for behavioural and evolutionary studies. However, these records are difficult to underpin on a precise chronology, which can prevent robust assessments of the drivers of cultural/behavioural transitions. Past investigations have revealed that numerous volcanic ash (tephra) layers are interbedded within the Palaeolithic sequences and likely originate from large volcanic eruptions in the North Atlantic (e.g. the Azores, Canary Islands, Cape Verde). Critically, these ash layers offer a unique opportunity to provide new relative and absolute dating constraints (via tephrochronology) to synchronise key archaeological and palaeoenvironmental records in this region. Here, we provide an overview of the known eruptive histories of the potential source volcanoes capable of widespread ashfall in the region during the last ~300,000 years, and discuss the diagnostic glass compositions essential for robust tephra correlations. To investigate the eruption source parameters and weather patterns required for ash dispersal towards NW Africa, we simulate plausible ashfall distributions using the Ash3D model. This work constitutes the first step in developing a more robust tephrostratigraphic framework for distal ash layers in NW Africa and highlights how tephrochronology may be used to reliably synchronise and date key climatic and cultural transitions during the Palaeolithic.

Rotation of uniaxial ellipsoidal particles during simple shear revisited: the influence of elongation ratio, initial distribution of a multiparticle system and amount of shear in the acquisition of a stable orientation

The combination of an improved bacterial desorption method, scanning electron microscopy (SEM), diffuse reflectance and transmission infrared Fourier transform spectroscopy, and a desorption-leaching device like high-pressure liquid chromatography (HPLC) was used to analyze bacterial populations (adhering and free bacteria) and surface-oxidized phases (ferric arsenates and elemental sulfur) during the arsenopyrite biooxidation by Thiobacillus ferrooxidans. The bacterial distribution, the physicochemical composition of the leachate, the evolution of corrosion patterns, and the nature and amount of the surface-oxidized chemical species characterized different behavior for each step of arsenopyrite bioleaching. The first step is characterized by a slow but strong adhesion of bacteria to mineral surfaces, the appearance of a surface phase of elemental sulfur, the weak solubilization of Fe(II), As(III), and As(V), and the presence of the first corrosion patterns, which follow the fragility zones and the crystallographic orientation of mineral grains. After this short step, growth of the unattached bacteria begins, while ferrous ions in solution are oxidized by them. Ferric ions produced by the bacteria can oxidize the sulfide directly and are regenerated by Fe(II) bacterial oxidation. At this time, a bioleaching cycle takes place and a coarse surface phase of ferric arsenate (FeAsO(4) . xH(2)O where x approximately 2) and deep ovoid pores appear. At the end of the bioleaching cycle, the high concentration of Fe(III) and As(V) in solution promotes the precipitation of a second phase of amorphous ferric arsenate (FeAsO(4) . xH(2)O where x approximately 4) in the leachate. Then the biooxidation process ceases: The bacteria adhering to the mineral sufaces are coated by the ferric arsenates and the concentration of Fe(III) on the leachate is found to have decreased greatly. Both oxidation mechanisms (direct and indirect oxidation) have been stopped. (c) 1995 John Wiley & Sons, Inc.

Rotation of uniaxial ellipsoidal particles during simple shear revisited: the influence of elongation ratio, initial distribution of a multiparticle system and amount of shear in the acquisition of a stable orientation

The emplacement history of the Zaer pluton was studied, using structural data and field relationships. The pluton is one of the Hercynian granitoid bodies that crops out in the Central Paleozoic Massif of Morocco. The principal granitoid rocks are relatively mafic at the margins of the pluton and change inward with or without discontinuities to a more felsic facies, thus defining a concentrically zoned structure. The emplacement of the pluton was by forceful intrusion of the magma. The elements of granite tectonics observed in the enclosing metasedimentary rocks include deflection of regional trend around the pluton and abundant faulting with a predominantly radial pattern with respect to the granite contact. The emplacement of the pluton is conceived as a polyphase diapiric process that, in part, obliterated the gradation from biotite granodiorite to two-mica monzogranite. The margins of the plutonic body solidified first and were subjected to deformation during diapiric rise and expansion, resulting in a preferred orientation of mineral grains in the granitic rocks.