Continental margin magmatism and migmatisation in the west-central Fennoscandian Shield

The Ljusdal Batholith (LjB) is a major component of the central Svecofennian Domain in Sweden. It is separated from the Bothnian Basin to the north by the 1.82–1.80 Ga crustal-scale Hassela Shear Zone (HSZ). The LjB has emplacement ages of 1.86–1.84 Ga, is mainly alkali-calcic, metaluminous, has _Nd values between − 0.3 and + 1.2 and was formed in a magmatic arc setting.

During the Svecokarelian orogeny the LjB was affected by at least three fold episodes. Large-scale folded screens of migmatised metasedimentary rocks occur in the eastern part of the batholith, and to the north of the HSZ, there is a 50 km wide diatexite belt. The Transition Belt (TrB), consisting of 1.88–1.85 Ga granitoids, is located at the northwestern extension of this belt. A calc-alkaline and peraluminous composition combined with negative _Nd values (− 1.7 to − 0.8) indicates a large proportion of metasediments in the source for these granitoids.

U–Pb SIMS data on zircon rims from migmatites and leucogranites to the north and east of LjB yield ages of 1.87–1.86 Ga, i.e. coeval with the granitoids of the LjB and the TrB. There is thus a close relationship between the LjB, the TrB and the migmatites in both space and time. Syn-migmatitic shearing along the HSZ indicates that a proto-HSZ was initiated already at c. 1.86 Ga, and the location of the proto-HSZ is inferred to be controlled by two older nuclei present in the lower parts of the crust. As crustal-scale shear zone systems are known to act as ascent pathways for sheet-like flow in active orogenies the TrB may represents accumulations of melts that were attracted and extracted by the proto-HSZ and intruded in a block that was not pervasively affected by subsequent shear along the HSZ.

An active continental margin setting for the LjB implies subduction at c. 1.86 Ga, and provides a heat source for both the migmatites and the TrB.

A later migmatisation at 1.82 Ga has been recorded to the south of the HSZ. Within the LjB the 1.82 Ga stromatic migmatites are folded by F₂ folds, and the fabric is truncated by 1.80 Ga pegmatites.     

Changing late Holocene flooding frequencies on the Columbia River, Washington

Data from prehistoric fluvial deposits can be used to extend the flood history of a river valley beyond historical records, thus increasing our understanding of variability in large, low-frequency flood events and providing a valuable means for paleoenvironmental reconstruction. We have applied this form of analysis to fluvial deposits from an archaeological site on the upper Columbia River in the state of Washington dating from 120 A.D.^* to 1948 A.D. It was our expectation that, had flood frequencies remained constant, sedimentation event frequency would conform to an exponential function derived from the Wolman and Leopold model of vertical floodplain accretion. Our findings deviate from this model, showing that flood frequencies comparable to those of the twentieth century existed prior to 1020 A.D.^* and after 1390 A.D.^* Large floods were three to four times more common during the intervening centuries. On the basis of field evidence, we can rule out changing channel geometry, leaving climatic conditions as the most probable factors controlling this variation in flood frequency.     

Environmental effects of the use of oil-based drilling muds in the North Sea

The environmental effects of oil-based drilling mud cuttings have been evaluated using all the data available from monitoring around North Sea platforms. Beneath the platforms making extensive use of oil-based drilling muds the natural sediment is buried by cuttings and the hydrocarbon concentration 250 m from the platforms may be 1000 times background, but the concentration gradient is very steep and background levels are usually reached 2000–3000 m from the platform.The extent of the biological effects appear to be greater from the use of oil-based muds than from water-based muds. Beyond the area of physical smothering the effects of oil-based mud cuttings may be due to organic enrichment or to the toxicity of the aromatic fraction of the oil. Despite the large scale of inputs, in all the fields studied the major deleterious biological effects occurred within 500 m of the platform. Surrounding the area of major impact was a transition zone in which subtle biological effects could be detected as community parameters returned to normal, generally within 400–1000 m.The shape and extent of this zone varied and was largely determined by the current regime and scale of the drilling operation. Elevated hydrocarbon concentrations were detected beyond the areas of biological effects.     

Some questions arising from the application of hydraulic theory to the Faroe Bank Channel deep-water flow

The results from a recent oceanographic field experiment in the Faroe Bank Channel are discussed from the standpoint of determining how well the classical hydraulic assumptions of stationarity and a quiescent upper layers were fulfilled. Evidence from these as well as previous measurements indicated that both prerequisites for the application of simplified hydraulic theory are not always fulfilled in the Channel. The implications of these results for the theoretical treatment of the hydraulic problem are discussed.     

Effects of red mud on marine animals

Red mud is a waste product in the reduction of bauxite in the production of aluminium. The exact composition of red mud depends on the source of the bauxite and its treatment during production. This variation has been responsible for conflicting reports about the damage caused by dumping red mud at sea.     

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.     

Reprocessed emission from warped accretion discs with application to X-ray iron line profiles

Fluorescent iron line profiles currently provide the best diagnostic for engine geometries of active galactic nuclei (AGN). Here we construct a method for calculating the relativistic iron line profile from an arbitrarily warped accretion disc, illuminated from above and below by hard X-ray sources. This substantially generalizes previous calculations of reprocessing by accretion discs by including non-axisymmetric effects. We include a relativistic treatment of shadowing by ray-tracing photon paths along Schwarzschild geodesics. We apply this method to two classes of warped discs, and generate a selection of resulting line profiles. New profile features include a time-varying line profile if the warp precesses about the disc, profile differences between 'twisted' and 'twist-free' warps and the possibility of steeper red and softer blue fall-offs than for flat discs. We discuss some qualitative implications of the line profiles in the context of Type I and II Seyfert AGN and other sources.     

Land-use dominates climate controls on nitrogen and phosphorus export from managed and natural Nordic headwater catchments

Agricultural, forestry-impacted and natural catchments are all vectors of nutrient loading in the Nordic countries. Here, we present concentrations and fluxes of total nitrogen (totN) and phosphorus (totP) from 69 Nordic headwater catchments (Denmark: 12, Finland:18, Norway:17, Sweden:22) between 2000 and 2018. Catchments span the range of Nordic climatic and environmental conditions and include natural sites and sites impacted by agricultural and forest management. Concentrations and fluxes of totN and totP were highest in agricultural catchments, intermediate in forestry-impacted and lowest in natural catchments, and were positively related %agricultural land cover and summer temperature. Summer temperature may be a proxy for terrestrial productivity, while %agricultural land cover might be a proxy for catchment nutrient inputs. A regional trend analysis showed significant declines in N concentrations and export across agricultural (−15 μg totN L⁻¹ year⁻¹) and natural (−0.4 μg NO₃-N L⁻¹ year⁻¹) catchments, but individual sites displayed few long-term trends in concentrations (totN: 22%, totP: 25%) or export (totN: 6%, totP: 9%). Forestry-impacted sites had a significant decline in totP (−0.1 μg P L⁻¹ year⁻¹). A small but significant increase in totP fluxes (+0.4 kg P km⁻² year⁻¹) from agricultural catchments was found, and countries showed contrasting patterns. Trends in annual concentrations and fluxes of totP and totN could not be explained in a straightforward way by changes in runoff or climate. Explanations for the totN decline include national mitigation measures in agriculture international policy to reduced air pollution and, possibly, large-scale increases in forest growth. Mitigation to reduce phosphorus appears to be more challenging than for nitrogen. If the green shift entails intensification of agricultural and forest production, new challenges for protection of water quality will emerge possible exacerbated by climate change. Further analysis of headwater totN and totP export should include seasonal trends, aquatic nutrient species and a focus on catchment nutrient inputs.     

A probabilistic seismic hazard assessment for the Turkish territory: part II—fault source and background seismicity model

Over the years, several local and regional seismic hazard studies have been conducted for the estimation of the seismic hazard in Turkey using different statistical processing tools for instrumental and historical earthquake data and modeling the geologic and tectonic characteristics of the region. Recently developed techniques, increased knowledge and improved databases brought the necessity to review the national active fault database and the compiled earthquake catalogue for the development of a national earthquake hazard map. A national earthquake strategy and action plan were conceived and accordingly with the collaboration of the several institutions and expert researchers, the Revision of Turkish Seismic Hazard Map Project (UDAP-Ç-13-06) was initiated, and finalized at the end of 2014. The scope of the project was confined to the revision of current national seismic hazard map, using the state of the art technologies and knowledge of the active fault, earthquake database, and ground motion prediction equations. The following two seismic source zonation models are developed for the probabilistic earthquake hazard analysis: (1) Area source model, (2) Fault and spatial smoothing seismic source model (FSBCK). In this study, we focus on the development and the characterization of the Fault Source model, the background spatially smoothed seismicity model and intrinsic uncertainty on the earthquake occurrence-rates-estimation. Finally, PSHA results obtained from the fault and spatial smoothed seismic source model are presented for 43, 72, 475 and 2475 years return periods (corresponding to 69, 50, 10, and 2% probability of exceedance in 50 years) for PGA and 5% damped spectral accelerations at 0.2 and 1.0 s.