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Malehmir A.,Uppsala University | Saleem M.U.,Uppsala University | Bastani M.,Geological Survey of Sweden
Journal of Applied Geophysics

We present high-resolution reflection seismic data from four lines (total 1.9. km) that cross a quick-clay landslide scar located close to the shore of the Göta River in southwest Sweden, and compare the results with geotechnical data from boreholes. The seismic data allow the imaging of bedrock topography and normally to weakly consolidated sediments to a subsurface depth of about 100. m. Different types of seismic sources, including sledgehammer, accelerated weight-drop and dynamite were utilized and compared with each other. Analysis of their power spectra suggests that weight-drop and dynamite have higher frequency content and energy than the sledgehammer, which makes these two sources suitable also for waveform tomography and surface-wave data analysis. The shallowest non-bedrock reflector is observed at about 10-20. m below the surface, it overlays the bedrock, and is interpreted to originate from the contact between clay formations above and a coarse-grained layer below. The coarse-grained layer appears to be spatially linked to the presence of quick-clays. It is a regional scale formation, laterally heterogeneous, which deepens to the west of the study area and correlates well with the available geotechnical data. Continuity of the coarse-grained layer becomes obscured by the landslide scar. There may be a link between the coarse-grained layer and landslides in the study area, although this possibility requires further hydrogeological and geotechnical investigations. Reflectors from the top of the bedrock suggest a depression zone with its deepest point below the landslide scar and a bowl-shaped structure in the northern portion of one of the seismic lines. © 2013 Elsevier B.V. Source

Reinholdsson M.,Lund University | Snowball I.,Lund University | Snowball I.,Uppsala University | Zillen L.,Geological Survey of Sweden | And 2 more authors.
Earth and Planetary Science Letters

Magnetotactic bacteria (MTB) are known to biosynthesise single-domain magnetite (Fe3O4) for geomagnetic navigation and their relict magnetosomes (called magnetofossils) can control the magnetic properties of lake and marine sediments. Magnetotactic bacteria also produce greigite (Fe3S4) magnetosomes but, compared to those made of magnetite, relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles. We studied the magnetic properties of sediment cores from two basins (the North Central Baltic Proper and eastern Gotland Basin) that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels, which are a signal of past occurrences of anoxia and hypoxia in the Baltic Sea. Magnetic concentrates extracted from the laminated sapropels were characterised by transmission electron microscopy and energy dispersive X-ray spectrometry and we identified only single-domain greigite (Fe3S4) particles with a mean size of 55×75nm, which we interpret as magnetofossils due to diagnostic chains of individual particles separated by an intact dividing membrane. The degree of magnetic enhancement in the laminated sapropels has a positive relationship with loss-on-ignition data, which indicates a link between the production of greigite magnetosomes, organic matter supply and preservation and redox conditions. The coercive force of collections of non-interacting greigite magnetofossils is ~13mT, which is considerably lower than the magnetite counterparts (~30mT) and strictly non-bacterial and larger greigite single-domain grains (~60mT). The values of the interparametric ratios of SIRM/χ, χARM/SIRM and χARM/χ that we obtain for our greigite magnetofossils overlap with those previously considered to be diagnostic of magnetosomal magnetite. The presence of bacterial greigite, which is easily detected by magnetic measurements, forms a proxy for hypoxia and anoxia, thus aiding the palaeoenvironmental interpretation of how oxygen conditions in the Baltic Sea have changed over time. © 2013 Elsevier B.V. Source

Ulmius J.,Lund University | Andersson J.,Geological Survey of Sweden | Moller C.,Lund University
Precambrian Research

The southernmost Baltic Shield exposes polymetamorphic continental crust that was largely formed and accreted during a series of 1.92-1.66. Ga Paleoproterozoic orogenic events and later reworked during the 1.14-0.90. Ga Sveconorwegian orogeny. An intermediate period of metamorphism, deformation and magmatism at 1.47-1.38. Ga has been attributed to the Hallandian orogeny, but due to overprinting by Sveconorwegian high-grade metamorphism and deformation, the P-T-t evolution and deformation of the Hallandian event have remained obscure. This study presents the first quantitative P-T model of the Hallandian event using high-temperature aluminous gneisses in the south-easternmost marginal part of the Sveconorwegian orogen. The high-grade metamorphism and spatially associated granite magmatism are dated using U-Pb SIMS analysis of zircon. Petrography, bulk and mineral geochemistry, and pseudosection models demonstrate prograde staurolite-sillimanite-grade metamorphism reaching granulite-facies temperatures (700-750. °C) at low pressures (4-5. kbar), with the formation of Crd. +. Sil. +. Grt. +. K-fsp. +. Ilm. +. Melt. ±. Bt. The rocks followed a clockwise P-T path. Later stages involved the formation of sillimanite. +. biotite at the expense of garnet and cordierite. Local low-temperature and fluid-assisted retrogression also caused the formation of chlorite and muscovite at the expense of cordierite. Both granite and aluminous gneisses contain complex zircon with inherited 1.70. Ga igneous cores and high-U, secondary zircon, mainly formed by reworking of protolith cores. The latter date the Hallandian high-grade metamorphism at 1451. ±. 6. Ma and the granite magmatism at 1445. ±. 8. Ma. The presence of 1.70. Ga igneous zircon cores in both metamorphic and magmatic rocks suggests that they formed from similar protoliths. The protolith ages correlate with the youngest generation of magmatic rocks of the Transscandinavian Igneous Belt. The aluminous gneisses are of supracrustal origin, and may have formed by chemical alteration of magmatic rocks. Hallandian regional metamorphism took place under a strongly elevated geotherm and was associated with granitic magmatism, suggesting an accretionary orogenic setting. The Hallandian event may demonstrate an 1.47-1.38. Ga Andean-type continental margin at the SW margin of Baltica. © 2015 Elsevier B.V.. Source

Sanchez-Garcia L.,University of Stockholm | Cato I.,Geological Survey of Sweden | Gustafsson O.,University of Stockholm
Marine Chemistry

A growing literature proposes that combusted-derived black carbon (BC) dominates the sorption and, by inference, the environmental distribution and bioavailability of many hydrophobic pollutant classes. There is a paucity of studies simultaneously evaluating the distribution of both BC geosorbents and pollutant sorbates in the actual field. Here, 120 surface sediments collected by the Geological Survey of Sweden along the 2000 km continental shelf along the Swedish coast facilitated evaluation of the relative influences of BC and non-BC organic carbon (OC) on the spatial distribution of polycyclic aromatic hydrocarbons (PAHs). The sum of 15 out of the 16 EPA PAHs ranged from 0.12 to 9.6 μg/g dry weight (dw), with the highest levels being found in the southern half of the Swedish Shelf (SS) area and in the vicinity of larger cities (Stockholm, Göteborg, Malmö and Umeå). Source-diagnostic PAH ratios such as ANT/(PHE + ANT), FLT/(FLT + PYR), BaA/(BaA + BPE), IPY/(IPY + BPE), CombPAH/ΣPAH and LMW/HMW suggested that pyrogenic sources are dominating the load of PAHs in Swedish Baltic and North Sea sediments. The sediment TOC was 4.8-168 mg/gdw (median 43 mg/gdw), while a BC concentration of 0.6-18 mg/gdw (median 1.8 mg/gdw) yielded BC:TOC ratios spanning a wide range of 1.7-47% (median 4.6%). Empirical distribution function tests indicated that the use of linear regression statistics was inappropriate. Instead, evaluation with the non-parametric Spearman function yielded higher correlation coefficient (rS) for total PAHs versus BC (0.54, p < 0.01) than versus either TOC (0.28, p < 0.01) or OC (TOC-BC; 0.26, p < 0.01). The results from this field study, encompassing an order of magnitude more observations than any previous sediment study, constitute a broad field manifestation of the importance of BC in affecting the distribution of planar aromatic pollutants in aquatic environments. © 2009 Elsevier B.V. All rights reserved. Source

Zillen L.,Geological Survey of Sweden | Lenz C.,Lund University | Jilbert T.,University Utrecht
Quaternary Geochronology

The prehistory of the Baltic Sea has for a long time suffered from imprecise dating, due to the large uncertainties associated with bulk radiocarbon dating of Baltic Sea sediments. To constrain the timing of environmental changes in the Baltic Sea it is critical to apply new dating approaches. This study identifies lead pollution isochrones in Baltic Sea sediments, which have previously been recorded in lake sediment and peat deposits in northern Europe and ice cores from Greenland. These isochrones have formed through the deposition of atmospheric lead associated with historic lead production and silver mining in Europe, and more recently with the increased industrial emissions that peaked in the 1970's. Lead concentration and stable lead isotope analyses ( 206Pb/ 207Pb ratios) reveal three distinct lead pollution horizons in the Baltic Sea, i.e. a Roman peak at 1 AD, a Medieval peak at 1200 AD and a peak in the 1970s. The new data will improve the chronological accuracy and precision of paleoenvironmental studies in the Baltic Sea, and for the first time, allow synchronization of Baltic Sea geological records within the basin and across Europe and the North Atlantic region (including Greenland). © 2011 Elsevier B.V. Source

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