Ben Nevis—remnant of a lost volcanic landscape

The summit region of Ben Nevis, Britain's highest mountain, consists of late Silurian to Early Devonian age volcanic rocks originally interpreted as a thick sequence (> 600 m) of andesite lavas and agglomerates that were down‐faulted during caldera subsidence. New digital field mapping of the Ben Nevis area, including both the steep north and south faces of the mountain, has revealed that the volcanic rocks consist largely of volcaniclastic debris flows, and extensive block and ash flow deposits with minor air‐fall tuff units. There is no evidence of any andesite lava flows or a volcanic vent. The volcanic detritus was derived from a volcanic centre situated to the NW of Ben Nevis, perhaps several tens of kilometres away. The rocks forming the summit region of the mountain have been re‐interpreted as a large roof pendant or keel of the former late Silurian to Early Devonian volcanic land surface that once covered much of the SW Highlands of Scotland.     

Digital field mapping—making the change from paper to touchscreen technology

Current desktop technology is largely mouse‐driven, but many analysts predict that in less than five years we will have a professional workforce that have only experienced learning in a touchscreen environment. Midland Valley have developed a digital mapping tool for smartphones called FieldMove Clino, which has been downloaded more than 20 000 times over the past year. The free version offers an effective way of introducing students to digital field mapping. However, many geoscience departments and teachers of field mapping have yet to make the switch from traditional paper‐based methods to digital technology. This article aims to answer some of the frequently asked questions about digital field mapping and outlines some of the advantages for improving field skills and geological thinking in students.     

Indications of P450 monooxygenase activities in beluga (Delphinapterus leucas) and narwhal (Monodon monoceros) from patterns of PCB, PCDD and PCDF accumulation

Selective accumulation of PCDDs, PCDFs and PCB congeners was investigated in beluga (Delphinapterus leucas), narwhal (Monodon monoceros) and several species at the same trophic level in two areas of Canada. There was a much higher relative abundance of meta-para-unsubstituted PCBs in the cetaceans compared with other species. This suggests that activity of cytochrome P450 monooxygenase enzymes causing CYP2B-type metabolism was relatively low in beluga and narwhal. Lower relative levels of 2,3,7,8-TCDD occurred in beluga from both areas, and selective reduction of toxic non-ortho PCBs occurred in the highly PCB-contaminated St Lawrence beluga. These compounds are potent inducers of cytochrome P450 CYP 1A-type enzymes, suggesting that such an enzyme with the capability of metabolizing TCDD-like substrates is present in beluga and narwhal. SIMCA principal components analysis of PCB congener patterns showed that the two cetaceans were in a statistically significant different class than the other species. Variables (congeners) with the greatest separation power between classes were mainly those defined by the selective metabolism rules.     

U–salinity relationships in the Mediterranean: Implications for Th:U particle flux studies

Knowledge of the ²³⁸U concentration in seawater is important for ²³⁴Th:²³⁸U disequilibrium studies of particle fluxes. However, these concentration data are normally obtained through a standard relationship between ²³⁸U and salinity, which has been determined for the open ocean. This study examines ²³⁸U data from both the open Mediterranean and the coastal Thermaikos Gulf, Greece, and compares it to the open ocean. No deviation from the open ocean ²³⁸U–salinity relationship was found for the Thermaikos Gulf, but some enhancement was noted close to Thessaloniki in the vicinity of a phosphate fertiliser plant. The open Mediterranean data showed a small enhancement relative to the open ocean. Although an analytical bias could not be ruled out, a review of ²³⁸U and salinity data in the literature shows that the standard relationship may not be as robust as is often assumed and the 1% uncertainty typically used is not justified at the present time. Nevertheless, salinity-based derivations continue to be the most appropriate means of determining ²³⁸U concentrations for routine applications. We propose a new relationship that accounts for the uncertainties observed, i.e. ²³⁸U (dpm l^− 1) = (0.0713 ± 0.0012) × salinity.     

Oxidation states and speciation of secondary products on pyrite and arsenopyrite reacted with mine waste waters and air

Summary Three morphologically distinct generations of Fe-oxyhydroxides were identified on pyrite surfaces reacted with unsaturated zone waters of a waste rock pile from the CON Mine (Northwest Territories, Canada). The paragenetic sequence includes an early mottled coating and a late massive (featureless) coating, separated by a generation of Fe(III)-oxyhydroxide of crystalline habit. Gypsum and halite precipitation were the last paragenetic events, and indicate intense wetting and drying in the unsaturated zone of the waste rock pile prior to collection.Fe 2p X-ray photoelectron spectra (XPS) of tarnished pyrite surfaces indicate at least two distinct secondary Fe(III)-oxyhydroxide phases, and combined with O 1s spectra, indicate ferrihydrite, goethite, hematite or maghemite. Minor As(IV) and As(III) are incorporated into these coatings.Fresh arsenopyrite surfaces reacted with air for 14 days, 16 months and 25 years develop exceptionally thin oxidized secondary coatings no more than about 50 A thick. XPS Fe 2p, O 1s and As 3d spectra indicate that the overlayer is composed of Fe(III)-hydroxides, arsenate (AsO[OH]3 or FeAsO₄), and reduced arsenic species, including arsenite (As[OH]3 or FeAsO₃). The abundance of reduced arsenic species is explained by diffusion of reduced As (e.g. As) from the unoxidized interior of the mineral to the near-surface where it reacts with oxidants. Continuous supply of reduced As from the bulk, and progressive oxidation of arsenic in the near-surface, result in an effective passivating layer. Whereas these oxidized coatings passivate the surface against airoxidation, aqueous solutions cause extensive leaching of arsenopyrite surfaces beneath the oxidized coatings. Apparently, the coatings offer little protection against leaching by oxidizing aqueous solutions, perhaps because the oxidized overlayer is compromised by dissolution of acidic and ferric arsenite and arsenate salts.

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Oxidationszustand und Spezifikation sekundärer Produkte auf Pyrit und Arsenkies nach Reaktion mit Grubenwässern und Luft

Zusammenfassung Drei morphologisch definierte Generationen von Eisen-Oxyhydroxyden wurden auf den Oberflächen von Pyrit nachgewiesen, der mit Wässern der ungesättigten Zone einer Abraumhalde der CON Mine (Nordwest-Territorium, Kanada) reagiert hat. Die paragenetische Abfolge umfaßt einen frühen fleckigen und einen späten massiven Überzug der durch eine Generation von Fe(III)-Oxyhydroxyden von kristallinem Habitus getrennt werden. Gips und Steinsalz Ausfällung waren die letzten paragenetischen Stadien und weisen auf intensive Befeuchtung und Trocknung in der ungesättigen Zone der Abraumhalden vor der Probennahme hin. Fe2p Röntgenfotoelektronspektren (XPS) von angelaufenen Pyritoberflächen weisen auf zumindest zwei unterscheidbare sekundäre Fe(III)-Oxyhydroxydphasen hin; in Kombination mit O is Spektren zeigen sie auch, daß Ferrihydrit, Goethit, Hämatit oder Maghemit vorliegen. Geringere Mengen von As(IV) und As(111) liegen in diesen Überzügen vor.Frische Arsenkiesoberflächen, die mit Luft für 14 Tage, 16 Monate und 25 Jahre reagiert haben, entwickeln außerordentlich dünne sekundäre Oxydationsfilme, die nicht mehr als 50 A dick sind. XPS, Fe 2p, O l s und As 3d Spektren zeigen, daß diese aus Fe(III)-Hydroxyden, Arsenat (AsO[OH]₃ oder FeAsO₄), und reduzierten Arsenphasen, die Arsenit (As[OH[]₃ oder FeAsO₃) umfassen, bestehen. Die weite Verbreitung von reduzierten Arsenphasen wird durch die Diffusion von reduziertem As (e.g. As°) aus dem nichtoxidierten Teil des Minerals in den Oberflächenbereichen erklärt, dort reagiert es mit Oxidanzien. Kontinuierliche Zufuhr von reduziertem As aus dem Haldenmaterial und progressive Oxidation des Arsens nahe der Oberläche führt zur Bildung einer effektiv passivierenden Schicht. Während diese oxidierten Schichten die Oberfläche gegen Luftoxidation passivieren, verursachen wäßrige Lösungen umfangreiches Leaching von Arsenkiesoberflächen unter den oxidierten Schichten. Offensichtlich bieten diese Schichten geringen Schutz gegen Leaching durch oxidierende wäßrige Lösungen, wahrscheinlich weil die oxidierte Überschicht durch Auflösung von sauren sowie Ferritischen Arsenit- und Arsenatsalzen beschädigt ist.

     

Sulphide mineralisation of the continental Devonian sediments of Orkney (Scotland)

Sulphide mineralisation in the Middle Old Red Sandstone fluviatile and lacustrine sediments of Orkney is ascribed to depositional and early diagenetic events. The cations involved are considered to have been introduced in the suspended load of the rivers. Deposition of aragonite led to co-precipitation and concentration of lead. Degradation of algal material produced the organometallic complexes which enabled transport of lead, zinc, and copper. Expulsion of pore water during compaction of the sediments is regarded as the main cause of fluid migration. Deposition of sulphides occurred in the presence of sulphate-reducing bacteria when the organic complexes became unstable.Herrn Prof. Dr.-Ing. habil. Hermann Borchert zum 70. Geburtstag am 2. Februar 1975 gewidmet     

Analysis of coupled axial and lateral deformation of roots in soil

Plant roots can help to stabilise slopes. Existing analytical models to predict their mechanical contribution are however limited: they typically focus on the ultimate limit state, employ various empirical factors, and ignore much of the underlying root-soil interaction. A new model was developed based on large deflection Euler-Bernoulli elastic beam theory that can be used to study the mobilisation of root strength under various loading conditions (direct shear and pull-out). Both lateral and axial loading of the root by the soil were incorporated, based on existing methodologies for foundation piles (p-y and t-z curves). The model is able to take the key parameters into account (root biomechanical properties, root architectural properties, and soil properties) while remaining quick to solve using a numerical boundary value problem solver. The model was compared with experimental direct shear test data using various root analogues (rubber, plastic, and wood) in dry sand with various densities and effective stress levels and was able to accurately predict the measured shear force-displacement behaviour. Comparison with experimentally measured pull-out force-displacement curves using rubber and wooden root analogues with various architectures in dry and partially saturated sands was also satisfactory. In the future, this model can aid with addressing long-standing problems in the root-reinforcement community: quantifying the effect of (sequential) mobilisation of root strength in direct shear, the effect of the angle at which the root crosses a shear plane, the effect of root topology on root-reinforcement or the effect of root bending, and root shear shear forces on root-reinforcement.     

Multiphase petrography of volcanic rocks using element maps: a method applied to Mount St. Helens, 1980–2005

Quantitative textural analyses including crystal size distributions (CSDs) provide insights into crystallisation kinetics of magmatic systems. Investigations of volcanic crystal textures often rely on greyscale variations on backscattered electron images to identify crystal phases, which must then be thresholded and/or traced manually, a laborious task, and investigations are typically restricted to a single crystal phase. A method is presented that uses energy-dispersive X-ray element maps to generate textural data. Each pixel is identified as a crystal phase, glass or vesicle according to relative chemical composition enabling concurrent acquisition of multiphase CSD, crystallinity and mineral mode data. Data processing is less time intensive for the operator but considerable instrument time is required to generate element maps. The method is applied to 17 dacite samples from the 1980–1986 and 3 from the 2004–2005 eruptive periods of Mount St. Helens volcano (USA) to provide quantitative insights into multiphase textural evolution. All of the CSDs are curved and concave-up in the standard CSD plot with curvature increasing with plagioclase content. To facilitate comparisons with previous studies, CSDs for microlites (<50?μm length crystals) are approximated as straight lines. The line intercepts and slopes provide information on n ⁰ (nucleation density) and characteristic length or Gτ (the product of growth rate (G) and residence time (τ)), respectively. These parameters, as well as the total groundmass crystallinity, show distinct differences between explosive deposits from summer 1980 and post-summer 1980 domes. Post-summer 1980 microlite n ⁰ values are mostly at the lower end of the range of those measured for summer 1980 samples. Total groundmass crystallinities during summer 1980 are between 10 and 30?vol.%, whereas post-summer 1980 crystallinity increases to between 39 and 51?vol.%. The range of n ⁰ values is similar to those previously published for Mount St. Helens but Gτ is consistently higher. Gτ of a May 1985 sample analysed in this study is approximately 2?μm higher compared with previously published data for the same sample when processed using similar methodologies. Groundmass crystallinity data show similar trends to those previously published for the 1980 to 1986 eruption, increasing sharply after summer 1980 then increasing more gradually during the dome-building phase of the eruption. The effects of varying L, the apparent crystal size, and crystal aspect ratio on resultant CSDs are also investigated. Whilst relative temporal variations in CSDs for a given dataset can be investigated, absolute values from different studies cannot be compared unless methods of data acquisition and processing are exactly the same.