Native antimony emplaced by methane‐rich hydrothermal fluid in an orogenic fault‐zone

Antimony‐rich gold deposits represent a subclass of orogenic hydrothermal systems. The study of the Lapa gold deposit in the Abitibi greenstone belt shows that antimony occurs during two different stages: (1) as early prograde Sb–Ni disseminated sulphides in talc schists, associated with CO₂‐bearing fluids, and (2) as a late native antimony association, associated with methane‐bearing fluids indicating a reducing environment. Methane could be related to the serpentinization of the ultramafic rocks of the Piché Group hosting the Lapa deposit. Several deposits display the same methane antimony association along fault zones.     

Aquifer–peatland connectivity in southern Quebec (Canada)

In areas where peatlands are abundant, they are likely to play a significant role in the hydrological and hydrogeological dynamics of a watershed. Although individual case studies are reported in the literature, there is a large range of aquifer–peatland interactions and there is a need to understand the controls of these interactions. The objectives of this study were (1) to better understand aquifer–peatland connections and how these may be predicted by geology and geomorphic location and (2) to provide a variety of reference sites for glacial geological settings. Slope and depression peatlands were studied in the Abitibi‐Témiscamingue region and in the St. Lawrence Lowlands, two contrasting regions of southern Quebec. A total of 12 transects that span a shallow aquifer–peatland interface were instrumented with piezometers. Field investigations included peatland characterization, monthly water level monitoring, and continuous hydraulic head measurements with pressure transducers. The results indicate that 7 of the 12 transects receive groundwater from the surrounding shallow aquifer. At the peatland margin, four lateral flow patterns were identified and associated with slope peatlands (parallel inflow and divergent flow) and with depression peatlands (convergent flow and parallel outflow). Vertical hydraulic gradients suggest that water flows mainly downwards, i.e. from the peatland to the underlying mineral deposits. Vertical connectivity appears to decrease as the distance from the peatland margin increases. All of these exchanges are important components in the sustainability of peatland hydrogeological functions. The regional comparison of aquifer–peatland flow dynamics performed in this study provides a new set of referenced data for the assessment of aquifer–peatland connectivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Origin and history of ureilitic material in the solar system: The view from asteroid 2008 TC3 and the Almahata Sitta meteorite

Asteroid 2008 TC₃ (approximately 4 m diameter) was tracked and studied in space for approximately 19 h before it impacted Earth's atmosphere, shattering at 44–36 km altitude. The recovered samples (>680 individual rocks) comprise the meteorite Almahata Sitta (AhS). Approximately 50–70% of these are ureilites (ultramafic achondrites). The rest are chondrites, mainly enstatite, ordinary, and Rumuruti types. The goal of this work is to understand how fragments of so many different types of parent bodies became mixed in the same asteroid. Almahata Sitta has been classified as a polymict ureilite with an anomalously high component of foreign clasts. However, we calculate that the mass of fallen material was ≤0.1% of the pre‐atmospheric mass of the asteroid. Based on published data for the reflectance spectrum of the asteroid and laboratory spectra of the samples, we infer that the lost material was mostly ureilitic. Therefore, 2008 TC₃ probably contained only a few percent nonureilitic materials, similar to other polymict ureilites except less well consolidated. From available data for the AhS meteorite fragments, we conclude that 2008 TC₃ samples essentially the same range of types of ureilitic and nonureilitic materials as other polymict ureilites. We therefore suggest that the immediate parent of 2008 TC₃ was the immediate parent of all ureilitic material sampled on Earth. We trace critical stages in the evolution of that material through solar system history. Based on various types of new modeling and re‐evaluation of published data, we propose the following scenario. (1) The ureilite parent body (UPB) accreted 0.5–0.6 Ma after formation of calcium‐aluminum‐rich inclusions (CAI), beyond the ice line (outer asteroid belt). Differentiation began approximately 1 Ma after CAI. (2) The UPB was catastrophically disrupted by a major impact approximately 5 Ma after CAI, with selective subsets of the fragments reassembling into daughter bodies. (3) Either the UPB (before breakup), or one of its daughters (after breakup), migrated to the inner belt due to scattering by massive embryos. (4) One daughter (after forming in or migrating to the inner belt) became the parent of 2008 TC₃. It developed a regolith, mostly ≥3.8 Ga ago. Clasts of enstatite, ordinary, and Rumuruti‐type chondrites were implanted by low‐velocity collisions. (5) Recently, the daughter was disrupted. Fragments were injected or drifted into Earth‐crossing orbits. 2008 TC₃ comes from outer layers of regolith, other polymict ureilites from deeper regolith, and main group ureilites from the interior of this body. In contrast to other models that have been proposed, this model invokes a stochastic history to explain the unique diversity of foreign materials in 2008 TC₃ and other polymict ureilites.     

Spatial and temporal assessment of drought in the Northern highlands of Ethiopia

With the development of global changes, researchers from all over the world increasingly pay attention to drought detection, and severe droughts that may have resulted from climate change. In this paper, spatial and temporal variability of drought is evaluated based on precipitation data and remotely sensed images. The standard precipitation index (SPI) and vegetation condition index (VCI) are used to evaluate the spatial and temporal characteristics of meteorological and vegetative drought in Tigray, Northern Ethiopia. Based on the drought critical values of SPI and VCI defining drought, the spatial and temporal extent of droughts in the study area is established. We processed 396 decadal images in order to produce the multi-temporal VCI drought maps. The results of the SPI and VCI analysis reveal that the eastern and southern zones of the study region suffered a recurrent cycle of drought over the last decade. Results further show that there is a time lag between the period of the peak VCI and precipitation values obtained from the meteorological stations across the study area. A significant agreement was observed between VCI values with the current plus last two-months of precipitation. The study demonstrates the utility of the vegetation condition index in semi-arid and arid regions.     

Contribution of logging tools to understanding helium porewater data across the Mesozoic sequence of the East of the Paris Basin

Helium concentration measurements made on water and rock samples collected at various depths along a 2000 m depth borehole drilled in the eastern part of the Paris basin and reaching the Triassic conglomerates were used to establish a vertical profile of dissolved helium concentration throughout the entire Mesozoic sedimentary pile. Wireline logging tools were used to measure rock density, porosity and U and Th contents every 15 cm in the various formations. Samples from the deepest Muschelkalk and Buntsandstein show a very good agreement between measured and calculated ⁴He porewater contents. Shallower levels show lower and lower ⁴He concentrations compared to calculated values when going upwards. The data set obtained by wireline logging measurements was used as inputs for numerical simulations of 1D He production/diffusion throughout the 2000 m profile. Several assumptions regarding the transport properties in the various sedimentary layers were tested and all were found to yield fairly good agreement between modeled and measured He concentrations. There is no need to invoke either a transient regime or a deep crustal He flux in this “quiet” (seismically inactive) part of the Paris basin. Moreover, the modeling results suggest that the Keuper massive halite level associated with the upper Muschelkalk pre-evaporitic series efficiently isolates the overlying layers from any input from deeper formations in the Meuse/Haute Marne area.     

Influence of high-resolution wind forcing on hydrodynamic modeling of the Gulf of Lions

The impact of the choice of high-resolution atmospheric forcing on ocean summertime circulation in the Gulf of Lions (GoL; Mediterranean Sea) is evaluated using three different datasets: AROME (2.5 km, 1 h), ALADIN (9.5 km, 3 h), and MM5 (9 km, 3 h). A short-term ocean simulation covering a 3-month summer period was performed on a 400-m configuration of the GoL. The main regional features of both wind and oceanic dynamics were well-reproduced by all three atmospheric models. Yet, at smaller scales and for specific hydrodynamic processes, some differences became apparent. Inertial oscillations and mesoscale variability were accentuated when high-resolution forcing was used. Sensitivity tests suggest a predominant role for spatial rather than temporal resolution of wind. The determinant influence of wind stress curl was evidenced, both in the representation of a mesoscale eddy structure and in the generation of a specific upwelling cell in the north-western part of the gulf.     

Effect of ramp size and sample spinning speed on CPMAS C NMR spectra of soil organic matter

Cross polarization (CP) magic angle spinning (MAS) ¹³C NMR spectroscopy is a solid state NMR technique widely applied to study the chemical composition of natural organic matter. In high magnetic fields (>7 T), fast sample spinning is required in order to reduce the influence of spinning sidebands underlying other chemical shift regions. As the spinning speed increases, the Hartmann-Hahn matching profiles break down into a series of narrow matching bands. In order to account for this instability variable amplitude cross polarization techniques (e.g. VACP, ramp-CP) have been developed. In the present study, we experimentally verified the stability of the Hartmann-Hahn condition under two MAS speeds for different samples with known structure and two different humic acids. For a complete restoration of flat matching profiles, large ramp sizes were needed. The matching profiles of the humic acids showed that both samples needed different ramp sizes to restore flat profiles. A set up based on the matching profiles of the commonly used glycine would have led to an insufficient ramp size for one of the humic acids. For the characterization of natural organic matter, we hence recommend to roughly set the matching conditions with a standard and subsequently optimize the matching conditions on a more complex, preferably representative, sample such as a humic acid. We would suggest to either run an array of different ramp sizes until maximum signal intensity is reached for all chemical shift regions or, in the case of unavailable measurement time, to use a ramp size twice the spinning speed.     

Taphonomy and palaeoecology of the gastropod fauna from a Late Cretaceous rocky shore, Sweden

A gastropod fauna comprising 17 species, each represented by a limited number of specimens, is described from a Late Cretaceous, late early Campanian rocky shore at Ivö Klack, southern Sweden. The gastropod fauna is associated with the most diverse ancient rocky shore fauna ever found. However, the low gastropod species diversity compared to the faunas of modern rocky shores is ascribed to taphonomic factors, notably dissolution of the aragonitic shells, but the predominance of epifaunal herbivores is indicative of a guild structure similar to that found on modern rocky shores. The presence of drill holes assigned to the ichnospecies Oichnus simplex suggests the former presence of muricid gastropods which have not been found as body fossils. A single drill hole is referred to Oichnus paraboloides and was probably made by a naticid gastropod. The infaunal mode of life of naticids makes preservation of such drill holes difficult, since the majority of infaunal prey such as burrowing bivalves has aragonitic shells which are not preserved. The relatively high number of species in comparison to many other Late Cretaceous rocky shore faunas, offers an opportunity to compare gastropod guild structure at Ivö Klack with modern counterparts, even though taphonomic processes such as mechanical destruction and aragonite dissolution have played an important role in the fossil gastropod assemblage.