Quick-clay landslides pose a major geohazard in formerly glaciated regions, not least in Norway, where marine clays have been exposed to freshwater leaching. Understanding the distribution and properties of these clays, as well as the post-glacial development, may contribute to identifying areas for further hazard assessment. The Tiller area in central Norway serves as an ideal study site due to its complex depositional history, postglacial landscape development, and the availability of extensive borehole data. Despite progress in quick-clay mapping and characterisation, uncertainties remain regarding the spatial variability of clay properties. The combination of depositional processes, postglacial erosion and hydrogeological conditions influences the occurrence and geotechnical properties of sensitive clays. However, the extent to which these factors contribute to observed clay property variations remains poorly understood. This study integrates laboratory data from boreholes, and spatial statistics to investigate marine clay properties and quick-clay distribution along three cross-sectional profiles in the Tiller area. The results demonstrate the spatial variability in water content, shear strength and layering, with pronounced differences between proximal and distal areas relative to the Tiller ice-contact ridge of Younger Dryas age. This emphasizes the influence of depositional and erosional history, overburden pressure, and drainage pathways in todays' clay properties. The insights gained contribute to the understanding of quick-clay development in postglacial terrains, thereby supporting planning and risk mitigation in areas with marine clay deposits.
The Forlandsundet Graben, located between the island of Prins Karls Forland and the west coast of Spitsbergen is a narrow, fault-bounded basin of proposed transtensional origin. It has been formed due to Paleogene dextral strike-slip movements between Svalbard and Greenland, which ultimately resulted in the establishment of the western Svalbard transform margin. Despite its geological significance, the evolution of this basin and its several-kilometre-thick fill, reportedly containing sediments of continental to deep-water origin, remains poorly understood. This study investigates the exhumed western basin margin, which exposes >3.5 km of sedimentary strata, to clarify the processes responsible for sediment deposition, focusing on the upper, marine portion of the basin fill. Our investigations identify a variety of conglomerate-to sandstone-dominated beds, representing deposits from diverse sediment gravity flows. These include cohesive to non-cohesive debris flows, gravel-and sand-rich high-density turbidity currents, low-density turbidity currents, and hybrid flows. The beds are organised into rhythmically alternating couplets: thin-bedded, sandstone-rich heterolithic units, and thick-bedded, conglomeratic sandstone units, representing submarine lobe fringe and lobe axis to off-axis deposits, respectively. Coarsening-and thickening-upward cycles, ranging from a few metres to several hundred metres, indicate a hierarchy of progradationally stacked lobe elements, lobes, and lobe complexes. This stacking pattern, and the degree of rounding observed in the conglomerates, suggest that the submarine lobes were fed by high-gradient streams. Overall, the succession indicates a deep-water basin that experienced substantial sediment influx through sediment gravity flows. A basin-wide deepening event marks the onset of rapid fault-induced subsidence likely driven by the regional transtensional regime, which established marine conditions from the middle/late Eocene. The basin served as a deep-water depocentre into the early Oligocene and persisted until exhumation later in the Cenozoic.
The western Trondheim Nappe Complex contains one of the most complete and best-exposed successions of Ordovician to Silurian sedimentary and volcanic rocks in the entire Scandinavian Caledonides. We present a new stratigraphic framework for the succession overlying the Ilfjellet and Holonda Groups, comprising four distinct stratigraphic groups separated by distinct unconformities. (1) The Holsjoen Group (c. 461-453 Ma), unconformably overlying the Ilfjellet Group, represents turbiditic deposition along a continental slope, with sediment contributions from both continental and ophiolitic/backarc sources. (2) The Trivja Group (c. 453-450 Ma) unconformably overlies the Holsjoen Group, representing a submarine slope with transitions into shallower settings, characterised by sediments derived mainly from continental sources, with minor input from a distal contemporaneous arc. (3) The Hogknippen Group (c. 450-444 Ma) marks a transition to shallow-marine and subaerial settings dominated by rhyolitic to dacitic tuffs and volcaniclastic deposits with a clear continental-arc geochemical signature. Hafnium isotope compositions of detrital Cambro-Ordovician zircons are consistent with a continental-arc provenance. (4) The Foss Group (<432 Ma) formed in shallow-marine to fluvial settings with epiclastic sediments sourced from the underlying units as well as more distal continental rocks, including exhumed c. 432 Ma felsic plutonic sources. Together, these groups provide a detailed record of Late Ordovician to Silurian basin evolution adjacent to a continental arc which developed along the Laurentian margin during the closure of the Iapetus Ocean.
During the past 25 years, the University of Bergen (Norway), in collaboration with national international partners, has collected extensive research data along the Arctic Mid-Ocean Ridges - that is, along the spreading-ridge system north of Iceland encompassing the Kolbeinsey, Mohns and Knipovich Ridges, the Lena Trough, and the Gakkel Ridge. The meta-database is a result of a massive research effort and data collection that includes water column (CTD) profiles, sediment cores, rock and biological samples (dredges, ROV sampling), and high-resolution video, imagery and bathymetric maps. Each individual data point provides detailed geographic information, sampling type, and additional information. We present open access, interactive, map-based meta-database that integrates these datasets, displaying the spatial distribution of samples and surveys, and highlighting advancements in sampling methods. The platform holds to the FAIR principles by making metadata findable, accessible, interoperable, and reusable through a standardised and openly available framework. It is accessible through an online ArcGIS interface, allowing both national and international users to explore sample metadata, multimedia, and links to associated publications. Our meta-database provides a critical tool for exploring the geological processes, resource potential, and biodiversity of the segment of Arctic Mid-Ocean Ridge system located within Norwegian waters.
Many unstable rock slopes in Norway were activated during the Late Glacial or early Holocene and have experienced rock-slope failure activity ever since. This exposes nearby infrastructure and communities to potential consequences such as direct landslide impact or displacement waves generated by an impact into a water body. At Rombakst & oslash;tta in Nordland county, northern Norway, four unstable rock sections, representing a total of eight potential failure scenarios, have been identified at the head scarp of a 28-34 x 10(6) m(3 )failure niche. They are characterised by highly fractured mica gneiss and valley-parallel open tension cracks, with clear signs of post-glacial deformation. Based on geological mapping and exposure dating, at least two rock-avalanche events originated from that niche during the Late Glacial and after the Younger Dryas deglaciation (10 ka ago). In addition, extensive and active colluvium indicates continuous rockfall activity throughout the Holocene, with a historical record documenting the ongoing rockfall activity. The largest rockfalls have affected the Ofotbanen railway track with an average return period of 3-4 years since 1992. Runout simulations suggest that potential future failures ranging from only a few cubic metres to several tens of thousands of cubic metres could significantly impact the railway. Given projected increases in rainfall frequency and intensity and continued permafrost degradation, rock-slope failure activity at Rombakst & oslash;tta is likely to continue and increase, including the potential for larger failures from the identified unstable rock sections.
The bedrock of Jutulsessen in Gjelsvikfjella, Dronning Maud Land (Antarctica), experienced highgrade metamorphism during the Ediacaran-Cambrian orogeny associated with the assembly of Gondwana. This event caused partial melting of granodioritic gneiss and the formation of metatexite migmatites. This study investigates in situ melting, melt mobilisation, and extraction, with emphasis on how deformation structures influence melt generation and transport. Petrographic evidence for incipient melting includes quartz films along plagioclase grain boundaries, cuspate outlines of quartz and K-feldspar, and "string of beads" textures. Neosomes contain poikilitic hornblende formed by fluid-present, incongruent melting of biotite. Field observations document progressive melt evolution, as evidenced by several sets of neosomes and leucocratic veins. In situ N1 neosomes form first, followed by axial-plane-parallel N2 neosomes, which later coalesce into a network of cross-cutting leucocratic veins (V3). Melt migration is closely linked to deformation-related dilation sites, which localise melt segregation and facilitate transport, indicating that folding, partial melting, and melt movement occurred simultaneously at the outcrop scale. Aplite and pegmatite dykes, observed elsewhere in the Jutulsessen area, cut the regional foliation and record post-kinematic emplacement. Their field relations and geochronological constraints suggest mid-crustal crystallisation. These observations fit within the established tectonic framework for Dronning Maud Land, which involves continental collision followed by post-collisional extension and orogenic collapse. Within this context, the Jutulsessen metatexites provide a well-constrained example of crustal anatexis in an orogenic environment and provide insight into the generation and transport of granitic magmas in the continental crust.
The growth and survival of the Arctic and boreal bivalve Mya truncata during the Early to Mid-Holocene in Billefjorden, central Svalbard, was predominantly influenced by basin-specific environmental factors. This study revealed that lack of nutrient availability caused by influx of large amounts of glacial meltwater and seabed conditions were critical in shaping population dynamics, shell morphology and growth rates. In stable environments M. truncata developed larger shell sizes and exhibited longer lifespans, averaging c. 20 years, approaching the species' maximum age for High Arctic conditions. Conversely, basins with higher sediment dynamics and nutrient scarcity resulted in smaller, thinner-shelled individuals. Morphological variations across basins reveal two distinct M. truncata morphotypes: thick-shelled specimens in stable, nutrient-rich basins and thinner-shelled forms in nutrient-poor, dynamic environments. Despite warmer conditions during the Holocene Thermal Maximum (HTM; similar to 9-6 cal. ka BP), shell growth rates were limited due to a decline in nutrient input from large influxes of glacial meltwater. Age-dependent growth patterns further highlight the influence of basin factors, with older populations in stable basins displaying enhanced growth compared with younger populations in dynamic parts of the fjord-system. The size and longevity of M. truncata could be used as a proxy for past winter sea-ice extent. This study underscores the critical interplay of local hydrological, oceanological and sedimentological conditions in shaping M. truncata populations. These findings emphasize that lack of nutrient availability caused by influx of glacial meltwater and seabed dynamics, rather than temperature alone, was a decisive factor during the Holocene. M. truncata serves as a valuable palaeoenvironmental indicator, reflecting basin-specific ecological dynamics in Arctic marine systems during a period characterised by climatic and environmental change.
Provenance studies based on U-Pb dating of detrital zircons are routinely applied in basin analysis and source-to-sink studies to decipher ancient sediment pathways and the tectonic events that shaped them. The Norwegian Svalbard Archipelago, situated in the high Arctic, hosts a well-preserved upper Paleozoic sedimentary succession, deposited in the aftermath of the Caledonian Orogeny and influenced by shifting regional tectonics, which led to the formation of diverse sedimentary basins. The lower, clastic-dominated portion of the succession records a transition from extensive, pre-rift basins hosting UpperDevonian-Mississippian strata (Billefjorden Group) to narrow, fault-bounded, north-south trending rift basins hosting late MIssissippian-lowermost Permian strata (lower Gipsdalen Group). Despite its significance, the detrital zircon age signatures and sediment provenance of this succession have received limited attention. In this study, we present new detrital zircon age data from 41 samples spanning Upper Devonian to lower Permian strata across all major late Paleozoic basins in Svalbard. We analyse the zircon age signatures of individual basin-fill successions and explore the role of regional and local tectonics in driving spatial and temporal changes in sediment provenance and routing during the late Paleozoic. Particular attention is given to the connectivity of pre-rift sedimentary basins, and shifts in provenance linked to the onset of localized rifting during the late MIssissippian. Our data reveal significant provenance variability across the basins. Key findings include evidence of predominant sediment sourcing from northeastern Greenland during deposition of the Billefjorden Group (latest Devonian to Mississippian pre-rift phase). Similar zircon age signatures across the investigated basins suggest connectivity between pre-rift depocentres. The Billefjorden Trough shows signs of increasing isolation with continued rifting and subsidence. This study provides new insights into the post-Caledonian tectonosedimentary evolution of the region.
This study presents a detailed analysis of the Middle Triassic Botneheia Formation in Svalbard, integrating sedimentology, geochemistry and palaeontology to understand the depositional environment. Fieldwork was conducted at five localities in central Spitsbergen and Edge & oslash;ya, with two additional localities in western Spitsbergen and Bj & oslash;rn & oslash;ya for comparison. Three carbon-isotope excursions are identified for the first time in the Botneheia Formation in central Spitsbergen and on Edge & oslash;ya- Carbon Excursion (ALICE), and positive Ladinian-Carnian Carbon Isotope Excursion (LICE). It is possible that OACIE is also present in western Spitsbergen and Bj & oslash;rn & oslash;ya and that LICE extends to Bj & oslash;rn & oslash;ya. We discuss their potential use as regional chronostratigraphic markers, drawing global comparisons. Systematic documentation of body and trace fossils from bulk sediment samples reveals benthic fossils in 153 out of 339 samples, and a higher diversity especially of bivalves than previously assumed for the Botneheia Formation. There are notable differences in benthic diversity and oxygenation between central Spitsbergen and Edge & oslash;ya, with lower diversities in the east, associated with more dysoxic conditions. These differences may be linked to the Ural Delta approaching from the east causing algal blooms and haloclines already in the Middle Triassic. The combination of geochemical proxies with fossil assemblages provides a detailed reconstruction of a Boreal Sea seabed during the Middle Triassic and highlights the influence of fluctuating oxygen levels in shaping benthic ecosystems and depositional environments.
Dike-fed fissure vent complexes are commonly linked to basaltic eruptions but are also proposed for some intermediate to silicic eruptions in Large Igneous Provinces (LIPs) and continental rifts. Direct evidence of these complexes is scarce however, and our understanding of the associated eruptive processes remains limited. Basaltic and trachy-andesite (i.e., rhomb-or rectangle-porphyry: RP) eruptions across the Oslo Rift (part of the Skagerrak-Centered LIP) are assumed to have erupted from similar dike-fed fissures, although no direct evidence of eruptive vents has been identified. We present observations illustrating the presence of a shallow (<80 m paleo-depth) RP fissure conduit in the central Oslo Rift recording explosive eruptive activity. Previous workers interpreted these outcrops as a partially preserved lava, suggesting the basaltic unit was cross-cutting due to deposition in an erosional depression. Our studies of outcrops, hand-samples, and thin-sections illustrate three primary textural zones: 1) a core zone with ductile deformation and moderate fragmentation; 2) a heavily-fragmented ash-rich margin zone with inclusions of both rhomb-porphyry and host rock (basalt); and 3) an edge zone variably characterised by un-brecciated rock or brecciated rockwith ash-filled fractures. Lateral textural gradations (over 1-3 m width) from core to brecciated host-rock and substantial overall width (similar to 40 to << 100 m), are consistent with a near-surface (<80 m) paleo-depth, whilst heavily fragmented margins suggest mild to moderate explosive activity towards the end of the associated eruptive episode. An exposure of a slabby-to rubbly-pahoehoe RP8 flow top with mingled and overlying pyroclastic (i.e., ash and lapilli) components additionally highlights explosive processes operating in the late stages of older RP eruptions. Our observations provide the first direct evidence of elongate eruptive-conduits (i.e., fissure-conduits) in the Oslo Rift, but textural characteristics illustrate that at least some rhomb-porphyry eruptions were punctuated by episodes of moderately explosive activity during waning eruptive activity.
In existing models of fjord-valley filling, terraces are primarily presented as the result of delta progradation and fluvial activity during higher sea levels following the last deglaciation. These models generally refer to large valleys with a relatively high sediment supply from upstream. However, these models are less applicable in distal segments of fjord valleys, in valleys with a lower sediment supply, in areas with thick valley-side deposits and/or significant tributary catchments. This is illustrated in the present study of northern Orkdal fjord-valley, Mid-Norway. The study is based on high-resolution digital elevation models, ground-penetrating radar, drillhole data and a few sedimentary exposures. Following deglaciation, the area was flooded by the sea with a local marine limit of 160 m a.s.l. Deposits in the fjord subsequently emerged during glacio-isostatic rebound. Terraces were constructed at successively lower relative sea-levels during Holocene emergence, and shoreline displacement data provide a chronological framework. As the studied fjord-valley segment was filled in relatively late, Holocene terraces only occur below 35 m a.s.l. The terraces are grouped according to elevation and position in the landscape. Some higher, solitary terraces formed after 5000 cal. yrs BP. Their formation reflects a combination of glacial activity, mass wasting, tributary river and/or marine processes. The mid-level terraces at 18-11 m a.s.l. formed when accommodation space was reduced, as aided by major mass-wasting events, and allowed for delta progradation in northern Orkdal 4000-2500 yrs ago. The youngest terraces and plains below 14 m a.s.l. formed during degradation of higher terraces in the late Holocene. The development of the landscape is synthesised into models that highlight the complexity of fjord-valley fills and add to the more generalised fjord-valley models. The study helps to explain the varied ground conditions in northern Orkdal, and the stratigraphy of comparable settings elsewhere.
We have studied several intrusions from the southern portion of the Oslo continental Rift, South Norway, including the Larvik Plutonic Complex (LPC) and surroundings. Samples from the Kodal lobe, the Kodal Fe-Ti-P deposit and smaller Fe-Ti-P mineralisation found within the area were also investigated to constrain their formation during the evolution of the Oslo Rift. The intrusions can be broadly divided into two groups comprising the older (295 to 288 Ma) LPC, and the younger (284 to 278 Ma), Kiste, L & oslash;kka, Rimstad, Siljan-Hvarnes and Skrim intrusions. Although most rocks from the Kodal lobe yield a similar crystallisation age to the LPC, those from the Kodal Fe-Ti-P deposit and its hosts yield crystallisation ages that belong to the younger group. Therefore, a cogenetic relationship between the Kodal deposit and the LPC, as previously proposed, is not supported. Older intrusions have higher epsilon Hft values (from +8 to +5.5) relative to younger intrusions (from +6 to +3.5). Such difference could be attributed to slight variations in mantle source, differing amounts of crustal assimilation, or variable contaminants. The composition of the different intrusions partly overlap and can be modelled from a parental magma similar to that for the LPC (alkali basalt); however, at least part of the younger intrusions equilibrated at slightly lower pressure relative to the LPC. The frequent association of Fe-Ti-P mineralisation with magma mingling zones, flow textures and sharp contact with host rocks, combined with our geochemical and geochronological data, indicates that silicate liquid immiscibility may have played a role in ore formation. The equilibration of the younger intrusions at lower pressure may favour the formation of an immiscible Fe-rich liquid because of a wider immiscibility field. Our results support that geological settings with intrusive intermediate alkaline rocks, such as the Oslo Rift, should be considered fertile forthe exploration of magmatic Fe-Ti-P deposits.
I compare 315 quality-ranked maximum displacement/length (D-max/L) ratios of Earthquake Surface Ruptures (ESR) against 720 D-max/L Geological Fault Systems (GFS) observations. High-quality ESR ratios rarely exceed 0.0002 whereas very, very few, and quality-unknown, GFS ratios are less than 0.001. Mathematical exercises suggest the ESR-GFS gap should not exist in nature. Its empirical presence raises four questions: 1) Might extreme scarps of certain gap-filling Post Glacial Faults (PGFs) represent cumulative displacement from multiple ESRs? 2) If so, why only in Fennoscandia? Should we not find more PGFs elsewhere? And ought there not be D-max/L evidence for incipient fault scarps in tectonically active parts of the world? 3) Given the difficulty in establishing evidence for Quaternary offset throughout much of Fennoscandia, can D-max/L be a first-order tool to help assess claims of neotectonic faulting? And 4): How well do we understand fault growth processes anyway? I present empirical evidence for the ESR-GFS gap. I put the gap to work by proposing a Single Modern Earthquake Rupture Scarp Height/length (SMERSH) cutoff of 0.0002 (>95% confidence) with permissible extension to 0.0004 (>99% confidence) under specific circumstances as helpful pointers towards PGF status. From the perspective of SMERSH I examine and reject Norway's controversial Nordmannvikdalen Feature as a single-rupture PGF. I discuss some general problems of fault growth and multiple-rupture PGFs, including Finland's Venej & auml;rvie Jauhoj & auml;rvi PGF complex. Although I cannot answer any of my four questions to satisfaction I conclude SMERSH does provide a useful tool for assessing proposed PGFs. Individual apparent displacements that by themselves fail SMERSH and cannot be linked with neighbouring offsets to form a single coherent, SMERSH-compliant rupture system were most likely not formed by neotectonic ESRs. Many PGFs should be given serious re-assessment - and any investigation of a suspected PGF must adhere to the strictest standards of paleo-seismic inquiry.
The Early Triassic saw the recovery of ecosystems after the most severe mass extinction event in Earth's history. However, the ecosystems of the Early Triassic and their patterns of recovery after the Permian-Triassic mass extinction are poorly known due to a scarce fossil record. This study uses dental material to provide information on the taxonomic diversity and dietary strategies of marine micro-and macro-vertebrates from the late Early Triassic (Spathian) Grippia bonebed, Spitsbergen, Svalbard. We compiled a collection of over 5,000 teeth and additional tooth-bearing bone elements, which we studied under the microscope and used for systematic interpretations, classification into morphotypes and a qualitative assessment of dental disparity of this assemblage. Multivariate analysis was done on a representative sample of 198 teeth to subdivide the teeth into different morphotypes. The results were used to inform occupied feeding guilds. Nine tooth morphotypes were defined and found to represent a diverse fauna of actinopterygians, marine temnospondyls and marine reptiles. The marine vertebrates of the Grippia bonebed can be divided into at least five different feeding guilds based on their tooth shape and dental features. These include soft-prey piercers/graspers, durophagous hard-prey crushers/grinders, relatively large generalist-feeders, and heterodont omnivores. Additionally, marine reptiles appear to have had a well-established and ecologically diverse presence. This diverse assemblage of marine vertebrates and their dietary strategies show that the marine ecosystem of the Boreal Sea was rapidly diversifying and that complex dietary structures were already established just a few million years after the Permian-Triassic mass extinction. This fits with similar patterns observed in Early Triassic marine strata from China and North America.
Ceraurinella ornata (Dalman, 1828) and Laneites ingricus (Schmidt, 1881) are two early representatives of the subfamily Cheirurinae in Baltoscandia. Neither species has been revised since their original description but type and new material provide additional insights into their morphology and spatial and temporal distribution. They occur in the Middle Ordovician (Volkhovian-Kundan) succession across the Baltoscandian platform, from the St. Petersburg area in Russia, through northern Estonia and central Sweden, Bornholm (Denmark) and the Oslo Region of Norway. Laneites ingricus ranges from the Volkhovian (BII gamma) Megistaspis limbata Zone through the lower Kundan (BIII alpha) Asaphus expanusZone. Specimens of L. cf. ingricus are known from the older Volkhovian (BII beta) Megistaspis simon Zone andL. aff. L. ingricus (Schmidt) sensu M & auml;nnil (1958) has been recorded from the lowermost Volkhovian (BII alpha) Megistaspis polyphemus Zone in Estonia. Ceraurinella ornata occurs in the A. expansus Zone in Sweden and in the A. raniceps (BIII beta) to M. gigas (BIII gamma) zones in Estonia. A total of 30 cheirurine taxa are known from the Middle and Upper Ordovician of Baltoscandia. Species diversity (including both formally described species and forms treated under open nomenclature) is greatest in Sweden with 14 occurrences, followed by Estonia (11), Norway (7), the St. Petersburg area (5), Denmark (Bornholm) with two and Finland with a single occurrence. Six genera are recorded: Ceraurinella Cooper, 1953; CerauriniumP & rcaron;ibyl & Van & ecaron;k in P & rcaron;ibyl et al., 1985; Hadromeros Lane, 1971; Laneites P & rcaron;ibyl & Van & ecaron;k in P & rcaron;ibyl et al., 1985; Paraceraurus M & auml;nnil, 1958; and Xylabion Lane, 1971. In Sweden, nearly half of the recorded occurrences are due to Hadromeros spp. in the Upper Ordovician, whereas Paraceraurus accounts for nearly half of the occurrences in the Middle Ordovician of Estonia. A gap in the occurrence of cheirurinae is seen across Baltoscandia between the Kukruse/Dalbyan and the Oandu/Mold & aring;an stages.
Lineaments, linear structures on the surface of the Earth, often represent the surface expressions of brittle structures, e.g., fault zones and fracture zones or ductile shear zones. In addition, they may also represent other geological features such as lithological contacts, tectonic boundaries and Quaternary structures, or potentially a superposition of any of these. Lineament mapping is usually the first step in the structural assessment of a crystalline bedrock setting, and the lineaments can further be used as basis for scientific research to more accurately determine the location of the previously mentioned various geological features. In this study, a multi-source lineament mapping was performed within a Geographic Information System (GIS) for the whole of Finland, based on light detecting and ranging (LiDAR), aerogeophysical and bathymetric raster data. Our approach was to produce three separate lineament datasets (topographic, magnetic and electromagnetic) and then integrate them into a single integrated lineament dataset in which lineaments from the separate source datasets are combined. The present work provides a new lineament database for Finland, which is more flexible for statistical analysis than prior interpretations and contains unique identifiers, along with crucial metadata for each interpreted lineament, to enable consistent references to the data and to allow tracking of the source of each lineament. The lineament database enhances the capability to produce more accurate geological maps for various geological purposes in Finland.
At Litlab & oslash; in western Norway, sulphide-ore tailings from Stord & oslash; Kisgruber were deposited directly into the Litlab & oslash; Basin of lake Storavatnet between 1912 and 1968. In this study water column samples and sediment cores from Storavatnet were investigated to evaluate the environmental impact of this water- covered tailings deposit and unveil the controlling (bio)geochemical processes. The results show that the water column in the Litlab & oslash; Basin is stratified with slightly elevated iron (Fe), manganese (Mn) and sulphate (SO4) concentrations in the upper <^>30 m and very high Fe, Mn, SO4 and ammonium (NH4) concentrations together with nearly complete oxygen (O2) depletion below this depth to the bottom of the basin (<^>50 m depth). Similar high ion concentrations in the porewater suggest ongoing anaerobic oxidation of sulphide minerals in the sediment, and successive transport of SO4 and Fe into stagnant bottom water. The results also suggest microbial oxidation of organic material coupled with reduction of Mn and Fe in the sediment followed by transport towards the oxygenated part of the water column, where they re-oxidise and settle as manganese/iron oxide/(oxy)hydroxide particles at the water-sediment boundary. Aggregates of tiny iron-sulphide crystals atthis boundary indicate, in addition, microbial sulphate reduction. Furthermore, the data suggest that the oxygen depletion and (bio)geochemical cycling of Fe, Mn and S in the deepest part of the water column were established at an early stage of the tailings deposition period, and that these conditions and processes are likely to continue for a long time. This is reinforced by the constant supply of Fe, Mn and organic material by the mine-drainage and runoff. Mobilisation of toxic heavy metals from the sediment to the water column will likely remain low as long as the anoxic conditions and relative high pH combined with microbial sulphate reduction and precipitation of secondary sulphide minerals continues.
