Reconnaissance survey of the Duolun ring structure in Inner Mongolia: Not an impact structure

The Duolun basin, which is located in Inner Mongolia, China, has been proposed to be an impact structure with an apparent rim diameter of about 70, or even 170 km. The designation as an impact structure was based on its nearly circular topography, consisting of an annular moat that surrounds an inner hummocky region, and the widespread occurrences of various igneous rocks, polymict breccias, and deformed crustal rocks. Critical shock metamorphic evidence is not available to support the impact hypothesis. We conducted two independent reconnaissance field surveys to this area and studied the lithology both within and outside of the ring structure. We collected samples from all lithologies that might contain evidence of shock metamorphism as suggested by their locations, especially those sharing similar appearances with impact breccias, suevites, impact melt rocks, and shatter cones. Field investigation, together with thin‐section examination, discovered that the suspected impact melt rocks are actually Early Cretaceous and Late Jurassic lava flows and pyroclastic deposits of rhyolitic to trachytic compositions, and the interpreted impact glass is typical volcanic glass. Petrographic analyses of all the samples reveal no indications for shock metamorphic overprint. All these lines of evidence suggest that the Duolun basin was not formed through impact cratering. The structural deformation and spatial distribution pattern of the igneous rocks suggest that the Duolun basin is most likely a Jurassic–Cretaceous complex rhyolite caldera system that has been partly filled with sediments forming an annular basin, followed by resurgent doming of the central area.     

The German Bight (North Sea) is a nursery area for both locally and externally produced sprat juveniles

To better understand the role of the German Bight (GB) as a nursery area for juvenile North Sea sprat Sprattus sprattus we sought to determine whether the area may receive only locally or also externally produced offspring. We sampled juveniles during 3 trawl surveys in the GB in August, September, and October 2004 and applied otolith microstructure analysis in order to reconstruct their distributions of the day-of-first-increment-formation (dif). These were contrasted with spatial and seasonal patterns of sprat egg abundance in the GB and its adjacent areas, observed during 6 monthly plankton surveys. It was found that the majority of juveniles originated mainly from April/May 2004, coinciding with high spawning activity west of the GB, whereas spawning and larval production inside the GB peaked notably later, in May/June. This indicated that a large proportion of juveniles was produced outside the GB and transported subsequently into it through passive and/or active migration. Shifts to later mean difs from one survey to the next and length distributions indicative of the simultaneous presence of multiple cohorts, supported the notion that the GB is a complex retention and nursery area for sprat offspring from different North Sea spawning grounds and times. Later born juveniles had significantly faster initial growth rates than earlier born conspecifics, which was likely temperature-mediated, given the strong correlation between back-calculated growth histories and sea surface temperature as a proxy for thermal histories of juveniles (r² = 0.52).     

Dissolved organic matter dynamics during the spring snowmelt at a boreal river valley mire complex in Northwest Russia

Boreal mire landscapes are rich in soil carbon and significantly contribute to the carbon input of aquatic ecosystems. They are composed of different mesoscale ecohydrological subunits, whose individual contributions to the water and carbon export of mire catchments are not well understood. The spring snowmelt period is the major hydrological event in the annual water cycle of the boreal regions and strongly influences the carbon flux between the terrestrial and aquatic systems. The aim of this study was (1) to provide a conceptual understanding of the spatial and temporal dynamics of the surface water chemistry along a swamp forest‐fen‐bog gradient during the snowmelt period, (2) to quantify the exported dissolved organic carbon (DOC) content in the runoff and (3) to identify the ecohydrological landscape unit that contributes most to DOC export during the snowmelt period in a heterogeneous mire complex in Northwest Russia. The highest DOC concentrations were detected in the swamp forest, and the lowest concentrations were observed at the treeless bog by the end of the snowmelt period (swamp forest: 37–43 mg l^?1, bog: 13–17 mg l^?1). During the spring snowmelt period, a significant amount (~1.7 g C m^?2) of DOC was transferred by the ~74 mm of runoff from the catchment into the river. Variability in the thawing periods led to differences in the relative contributions of each ecohydrological zone to the carbon export measured at a stream channel draining the studied part of the mire complex. An increased understanding of the variation in DOC concentrations and contributions from the mesoscale ecohydrological subunits to carbon export can help to predict the potential regional loss of DOC based on land cover type under climate change. Copyright © 2015 John Wiley & Sons, Ltd.     

Drilling and Grouting Works for Pressurised Groundwater Conditions of the Semmering Base Tunnel

Geotechnical and Geological Engineering - The Semmering Base Tunnel (SBT), with a total length of 27.3 km, is one of the leading construction projects of the Baltic-Adriatic Railway...     

A contribution to the crystal chemistry of the voltaite group: solid solutions, Mössbauer and infrared spectra, and anomalous anisotropy

Voltaite is a mineral of fumaroles, solfatares, coal-fire gas vents, and acid-mine drainage systems. The nominal composition is K₂Fe₅ ²⁺Fe₃ ³⁺Al(SO₄)₁₂·18H₂O and the nominal symmetry is cubic, $Fd\overline{3}c$ . The tetragonal (I4₁/acd) superstructure of voltaite is known as the mineral pertlikite. In this study, we investigated 22 synthetic voltaite samples in which Fe²⁺ was partially or completely replaced by Mg, Zn, Mn, or Cd, by single-crystal and powder X-ray diffraction (both in-house and synchrotron). Two samples contained NH₄ ⁺ instead of K⁺. The structure of voltaite is based on a framework defined by kröhnkite-like heteropolyhedral chains which host both M³⁺ and M²⁺ in octahedral coordination. Unit cell dimensions of the end-members scale almost linearly with the size of M²⁺. In the Fe²⁺-Mg-Zn solid solutions, the Fe²⁺-Mg and Fe²⁺-Zn solutions are linear (ideal) in terms of their lattice-parameter variations. The Mg-Zn solid solution, however, is strongly non-ideal. A detailed analysis of the topology of the chains showed that this behavior originates in expansion and contraction of individual M²⁺-O bonds within the chains. In the Mg-Zn solid solution, some of the M²⁺-O bonds expand while none contract. In the other solid solutions, expansion of some M²⁺-O bonds is always compensated by contraction of the other ones. Parts of the nominally cubic crystals are optically anisotropic and their symmetry is found to be tetragonal by single crystal X-ray diffraction measurements. The coexistence of cubic and tetragonal sectors within a single crystal without any detectable difference in their chemical composition is difficult to explain in terms of growth of such composite crystals. Mössbauer and infrared spectra collected on our synthetic crystals conform with previously published data.     

Does the complexity in temporal precipitation disaggregation matter for a lumped hydrological model?

ABSTRACT

Flood peaks and volumes are essential design variables and can be simulated by precipitation–runoff (P–R) modelling. The high-resolution precipitation time series that are often required for this purpose can be generated by various temporal disaggregation methods. Here, we compare a simple method (M1, one parameter), focusing on the effective precipitation duration for flood simulations, with a multiplicative cascade model (M2, 32/36 parameters). While M2 aims at generating realistic characteristics of precipitation time series, M1 aims only at accurately reproducing flood variables by P–R modelling. Both disaggregation methods were tested on precipitation time series of nine Swiss mesoscale catchments. The generated high-resolution time series served as input for P–R modelling using a lumped HBV model. The results indicate that differences identified in precipitation characteristics of disaggregated time series vanish when introduced into the lumped hydrological model. Moreover, flood peaks were more sensitive than flood volumes to the choice of disaggregation method.     

spatialCopula: A Matlab toolbox for copula-based spatial analysis

The spatialCopula toolbox contains a set of Matlab functions that provides utilities for copula-based analysis of spatially referenced data, a topic which has re cently attracted much attention in spatial statistics. These tools have been developed to support the work flow in parameter estimation, spatial interpolation and visualization. They offer flexible and user-friendly software for dealing with non-Gaussian and extreme value data that possibly contain a spatial trend or geometric anisotropy. The objective of this paper is to give an introduction to the concept behind the software and to outline the functionality of the toolbox. We illustrate its usefulness by analyzing a data set here referred to as the Gomel data set, which includes moderately skewed radioactivity measurements in the region of Gomel, Belarus. The source codes are freely available in Matlab language on the author’s website (fam.tuwien.ac.at/~hakazian/software.html).     

Rb-Sr provenance ages from weathered and stream transported quartz grains from the Harney Peak Granite,Black Hills,South Dakota

Weathered quartz grus and stream transported quartz of the Harney Peak Granite, Black Hills, South Dakota, contain low concentrations of Rb (generally 0.3–6.8 ppm) and Sr (0.2–2.0 ppm) and variable Sr isotopic ratios (0.759–1.070).Six of seven single grains of large composite quartz grus which recently entered the weathering environment define an apparent isochron age (about 1800 Myr) and initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio (0.7066) that approximate the whole-rock isochron age (1707 Myr) and initial ratio (0.7143) of the Harney Peak Granite. Apparently the Rb-Sr systematics of these grains were not significantly altered during initial weathering. Leached fluid inclusion material from a ca. 2 g aggregate of composite quartz grains contains very little Rb or Sr (0.019 and 0.17 μg, respectively) and has a very low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio (0.739). The Rb and Sr content of the quartz grains appears to be concentrated in minute, heterogeneously-distributed mineral inclusions.Five aggregates of more completely weathered, small non-composite quartz grains produce a widely scattered pattern on an isochron diagram with all samples plotting below the 1707 Myr isochron. Examination by SEM of these grains shows solution and precipitation features on their relatively large effective surface areas. The differential precipitation of Rb is believed to have been the major perturbating chemical process during weathering.Three aggregates of stream quartz grains define an apparent isochron age of 1777 Myr and an initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.720 that suggest the initial ‘igneous’ Rb-Sr characteristics of the stream quartz were re-attained during their transportation, probably as a result of removal of the outer weathered surface by abrasion. The apparent resistance to chemical weathering of stream quartz and quartz which has just entered the weathering environment suggests that this mineral may be extremely useful in studies of provenance and the geochronology of strongly weathered terranes.     

Contact and fracture ultramafic assemblages from Norway: Rb-Sr evidence for crustal contamination

Strontium isotopes are used as tracers of crustal contamination of alpine-type ultramafic rocks from the Basal Gneiss Complex of the Caledonides of southern Norway. Minerals from anhydrous assemblages that occur in the cores of these ultramafic lenses give Sr⁸⁷/Sr⁸⁶ ratios (0.7011 to 0.7047) that reflect the expected ambient Sr⁸⁷/Sr⁸⁶ conditions of the ancient upper mantle. Rb-Sr evidence for crustal contamination is found in hydrous assemblages that occur within fractures and around the margins of the ultramafio bodies. Olivine, enstatite, amphibole, and magnesite from these assemblages have present-day Sr⁸⁷/Sr⁸⁶ ratios (0.7049 to 0.7085) that are significantly higher than those of compositionally equivalent minerals from the interiors of the ultramafic bodies. The high Sr⁸⁷/Sr⁸⁶ values were acquired as a result of the reaction between the ultramafic rock and ion-charged hydrous solutions carrying strontium with the ambient Sr⁸⁷/Sr⁸⁶ ratio (around 0.713) of the enclosing country rook during the waning phases of the Caledonian Orogeny. Mineral separates from the interiors of these ultramafic bodies can yield useful information on the ancient upper mantle. Wholerock samples, however, will show some evidence of contamination from the crust as a result of the formation of at least trace amounts of secondary hydrous minerals. Most whole-rook Sr⁸⁷/Sr⁸⁶ ratios from alpine-type ultramafic rocks from other orogenic belts show evidence of this contamination.