Field compaction of bentonite-based backfilling

This report describes the application and field compaction of a tunnel backfill, which consists of a mixture of commercial Na bentonite (MX 80) powder and suitably graded ballast material. The ballast material consists of quartz-rich sand and feldspar rich filler. Important characteristics for the tunnel backfill are low permeability, low compressibility and a certain swelling potential.     

Volatiles associated with the alkaline – carbonatite magmatism at Alnö, Sweden: a study of fluid and solid inclusions in minerals from the Laångarsholmen ring complex

The Alnö alkaline-carbonatite complex consists in its northernmost part at Laångarsholmen of a ring-type intrusion composed of pyroxenite, sövite and ijolite, emplaced in that order. The intrusion is surrounded by a breccia zone. The petrography, mineral chemistry and fluid/solid inclusion studies suggest that the ring complex and the main intrusion at Alnö have had a somewhat different magmatic evolution, implying different evolution of fluid phases also. At Laångarsholmen, a mafic silicate magma started to crystallize Al-diopside of 0.11 CaTs (Tschermak’s) content during a mid-crustal stage of evolution (ca. 5–6?kbar and 1175°?C). At that stage, the mafic magma was coexisting with a Mg-bearing calcitic melt, recorded in the abundant inclusions, trapped by the crystallizing Al-diopside. The two immiscible melts appear to have separated at ca. 5?kbar and 1150°?C, in good agreement with recent experimental studies. The silicate magma crystallized di+ap+magnetite during its ascent, and was in contact with a saline hydro-carbonic fluid trapped as inclusions in diopside (di) and apatite (ap) (type B2 inclusions reluctant to dissolution up to 550°?C). As P_H2O started to increase, Fe-pargasite began to replace the pyroxene. It appears that the fluid present at that stage was aqueous and contained ca. 40%?NaCl. With decreasing PT, the fluid separated into two immiscible phases of high- and low-salinity (type B1 of 65%?NaCl and Cl of 7%?NaCl), respectively. At the shallow depths of the final emplacement, the composition of the fluid phase was most probably controlled by supply of meteoric water as indicated by the dilution trend of some B1 type inclusions. After separation, the carbonatite magma fractionated calcite+ap+dol (as shown by dolomite inclusions in early crystallizing apatite). Around 4?kbar, a CO₂-bearing aqueous fluid of low salinity (d=0.85) was coexisting with the melt, and became trapped in the apatite formed during the mid-crustal stage (type A1 fluid inclusions). The residual melt was emplaced into the shallow crust and gave rise to phlogopite-bearing sövite. Fluid inclusions (type A2) trapped in calcite and in recrystallized apatite indicate that the fluid phase evolved towards a late (Na+K) hydro-carbonic fluid during cooling at the shallow depths of the final emplacement. The ijolite does not show signs of liquid immiscibility with the sövite at Laångarsholmen, and exhibits mostly post-magmatic activity of fluid phases.     

Potentiometrically measured Eh in groundwaters from the Scandinavian Shield

Measurement and interpretation of electrochemical Eh values in natural reducing groundwaters is a complex task. SKB, the company in charge of disposal of nuclear fuel wastes in Sweden, has developed a refined methodology for the determination of this parameter in packered sections in boreholes. The methodology consists of the simultaneous use of three different electrodes (Pt, Au and C) both at depth and at the surface, and maintaining continuous logging over a long period of time. Apart from Eh, the logging also includes other parameters such as pH, dissolved O₂, conductivity and temperature. This methodology has been used since the 80s in the framework of the hydrogeochemical characterisation programs supported by SKB at different sites in the Scandinavian Shield. All the existing databases have been revisited in this work using a uniform set of criteria to select Eh values of the Swedish groundwaters as a function of depth.     

The Svalbard Eocene‐Oligocene (?) Central Basin succession: Sedimentation patterns and controls

A synthesis has been undertaken based on regionally compiled data from the post early Eocene foreland basin succession of Svalbard. The aim has been to generate an updated depositional model and link this to controlling factors. The more than kilometer thick progradational succession includes the offshore shales of the Gilsonryggen Member of the Frysjaodden Formation, the shallow marine sandstones of the Battfjellet Formation and the predominantly heterolithic Aspelintoppen Formation, together recording the progressive eastwards infill of the foredeep flanking the West Spitsbergen fold‐and‐thrust belt. Here we present a summary of the paleo‐environmental depositional systems across the basin, their facies and regional distribution and link these together in an updated depositional model. The basin‐margin system prograded with an ascending shelf‐edge trajectory in the order of 1°. The basin fill was bipartite, with offset stacked shelf and shelf‐edge deltas, slope clinothems and basin floor fans in the western and deepest part and a simpler architecture of stacked shelf‐deltas in the shallower eastern part. We suggest a foredeep setting governed by flexural loading, likely influenced by buckling, and potentially developing into a wedge top basin in the mature stage of basin filling. High‐subsidence rates probably counteracted eustatic falls with the result that relative sea‐level falls were uncommon. Distance to the source terrain was small and sedimentation rates was temporarily high. Time‐equivalent deposits can be found outbound of Stappen High in the Vestbakken Volcanic Province and the Sørvestsnaget Basin 300 km further south on the Barents Shelf margin. We cannot see any direct evidence of coupling between these more southerly systems and the studied one; southerly diversion of the sediment‐routing, if any, may have taken place beyond the limit of the preserved deposits.     

The relation between degree-2160 spectral models of Earth’s gravitational and topographic potential: a guide on global correlation measures and their dependency on approximation effects

Comparisons between high-degree models of the Earth’s topographic and gravitational potential may give insight into the quality and resolution of the source data sets, provide feedback on the modelling techniques and help to better understand the gravity field composition. Degree correlations (cross-correlation coefficients) or reduction rates (quantifying the amount of topographic signal contained in the gravitational potential) are indicators used in a number of contemporary studies. However, depending on the modelling techniques and underlying levels of approximation, the correlation at high degrees may vary significantly, as do the conclusions drawn. The present paper addresses this problem by attempting to provide a guide on global correlation measures with particular emphasis on approximation effects and variants of topographic potential modelling. We investigate and discuss the impact of different effects (e.g., truncation of series expansions of the topographic potential, mass compression, ellipsoidal versus spherical approximation, ellipsoidal harmonic coefficient versus spherical harmonic coefficient (SHC) representation) on correlation measures. Our study demonstrates that the correlation coefficients are realistic only when the model’s harmonic coefficients of a given degree are largely independent of the coefficients of other degrees, permitting degree-wise evaluations. This is the case, e.g., when both models are represented in terms of SHCs and spherical approximation (i.e. spherical arrangement of field-generating masses). Alternatively, a representation in ellipsoidal harmonics can be combined with ellipsoidal approximation. The usual ellipsoidal approximation level (i.e. ellipsoidal mass arrangement) is shown to bias correlation coefficients when SHCs are used. Importantly, gravity models from the International Centre for Global Earth Models (ICGEM) are inherently based on this approximation level. A transformation is presented that enables a transformation of ICGEM geopotential models from ellipsoidal to spherical approximation. The transformation is applied to generate a spherical transform of EGM2008 (sphEGM2008) that can meaningfully be correlated degree-wise with the topographic potential. We exploit this new technique and compare a number of models of topographic potential constituents (e.g., potential implied by land topography, ocean water masses) based on the Earth2014 global relief model and a mass-layer forward modelling technique with sphEGM2008. Different to previous findings, our results show very significant short-scale correlation between Earth’s gravitational potential and the potential generated by Earth’s land topography (correlation +0.92, and 60% of EGM2008 signals are delivered through the forward modelling). Our tests reveal that the potential generated by Earth’s oceans water masses is largely unrelated to the geopotential at short scales, suggesting that altimetry-derived gravity and/or bathymetric data sets are significantly underpowered at 5 arc-min scales. We further decompose the topographic potential into the Bouguer shell and terrain correction and show that they are responsible for about 20 and 25% of EGM2008 short-scale signals, respectively. As a general conclusion, the paper shows the importance of using compatible models in topographic/gravitational potential comparisons and recommends the use of SHCs together with spherical approximation or EHCs with ellipsoidal approximation in order to avoid biases in the correlation measures.     

On the long-term stability of terrestrial reference frame solutions based on Kalman filtering

The Global Geodetic Observing System requirement for the long-term stability of the International Terrestrial Reference Frame is 0.1 mm/year, motivated by rigorous sea level studies. Furthermore, high-quality station velocities are of great importance for the prediction of future station coordinates, which are fundamental for several geodetic applications. In this study, we investigate the performance of predictions from very long baseline interferometry (VLBI) terrestrial reference frames (TRFs) based on Kalman filtering. The predictions are computed by extrapolating the deterministic part of the coordinate model. As observational data, we used over 4000 VLBI sessions between 1980 and the middle of 2016. In order to study the predictions, we computed VLBI TRF solutions only from the data until the end of 2013. The period of 2014 until 2016.5 was used to validate the predictions of the TRF solutions against the measured VLBI station coordinates. To assess the quality, we computed average WRMS values from the coordinate differences as well as from estimated Helmert transformation parameters, in particular, the scale. We found that the results significantly depend on the level of process noise used in the filter. While larger values of process noise allow the TRF station coordinates to more closely follow the input data (decrease in WRMS of about 45%), the TRF predictions exhibit larger deviations from the VLBI station coordinates after 2014 (WRMS increase of about 15%). On the other hand, lower levels of process noise improve the predictions, making them more similar to those of solutions without process noise. Furthermore, our investigations show that additionally estimating annual signals in the coordinates does not significantly impact the results. Finally, we computed TRF solutions mimicking a potential real-time TRF and found significant improvements over the other investigated solutions, all of which rely on extrapolating the coordinate model for their predictions, with WRMS reductions of almost 50%.     

Indirect evaluation of Mars Gravity Model 2011 using a replication experiment on Earth

Curtin University??s Mars Gravity Model 2011 (MGM2011) is a high-resolution composite set of gravity field functionals that uses topography-implied gravity effects at medium- and short-scales (??125 km to ??3 km) to augment the space-collected MRO110B2 gravity model. Ground-truth gravity observations that could be used for direct validation of MGM2011 are not available on Mars??s surface. To indirectly evaluate MGM2011 and its modelling principles, an as-close-as-possible replication of the MGM2011 modelling approach was performed on Earth as the planetary body with most detailed gravity field knowledge available. Comparisons among six ground-truth data sets (gravity disturbances, quasigeoid undulations and vertical deflections) and the MGM2011-replication over Europe and North America show unanimously that topography-implied gravity information improves upon space-collected gravity models over areas with rugged terrain. The improvements are ??55% and ??67% for gravity disturbances, ??12% and ??47% for quasigeoid undulations, and ??30% to ??50% for vertical deflections. Given that the correlation between space-collected gravity and topography is higher for Mars than Earth at spatial scales of a few 100 km, topography-implied gravity effects are more dominant on Mars. It is therefore reasonable to infer that the MGM2011 modelling approach is suitable, offering an improvement over space-collected Martian gravity field models.     

Development of a prograding carbonate wedge during sea level fall: Lower Pleistocene of Rhodes, Greece

A Lower Pleistocene carbonate platform is described from north-east Rhodes, Greece. It comprises a succession of warm temperate calcarenites (the Cape Arkhangelos calcarenite facies group) developed in a steep-sided coastal basin. The depositional setting for the sediments is a carbonate wedge developed within a larger-scale forced regression. Deposition began with aggradation of storm-dominated lower and upper shoreface deposits. Later, the development of a prograding platform produced giant clinoform foresets. A marked alternation of cross-bedded and bioturbated clinoforms indicates seasonal transport of carbonate material off the platform. Periodically, the platform edge has been deeply scoured by exceptional storms, after which further deposition repaired the platform margin, and progradation resumed. More than 20 such major storm cycles are preserved. Applying sequence stratigraphy to this succession leads to two different possible interpretations: one with a lowstand systems tract and one with a forced regressive systems tract, depending on the scale of view. The implications of this are discussed. The present example shows clearly that the application of sequence stratigraphic models to real carbonate sequences requires careful consideration of scale and context before interpretations are made.     

Spatial variability in surface sediment composition characterised by near-infrared (NIR) reflectance spectroscopy

Near-infrared (NIR) spectral data were obtained from 165 surface sediment samples from a northern Swedish humic, mesotrophic lake (0.5 km2). The NIR spectra, together with data on water depth and loss-on-ignition (LOI), allow an evaluation of the source of spatial variance in sediment characteristics. The results show that water depth and organic matter (LOI) account for 20 and 16%, respectively, of the variance in the NIR-absorbance data. More importantly, the spatial variance in the spectral data suggest that NIR analysis of lake sediments mainly reflect sediment properties that cannot simply be explained by depth or amount of organic matter. The influence of inlets and land-use (e.g. clear-cutting) on sediment characteristics was more pronounced in the spectral data than would be expected from the LOI data. This is explained by differences in the chemical composition of the organic matter, as revealed by NIR spectroscopy, rather than in the amount of organic matter or depth-related sedimentation properties (e.g. particle size or density). This initial attempt to characterise sediment properties using NIR suggests that NIR analysis might become a valuable complementary tool to traditional sediment characterisation.