Structural development along the Billefjorden Fault Zone in the area between Kjellströmdalen and Adventdalen/Sassendalen, central Spitsbergen

The Billefjorden Fault Zone represents a major lineament on Spitsbergen with a history of tectonic activity going back into the Devonian and possibly earlier. Recent structural, sedimcntological and stratigraphical investigations indicate that most of the stratigraphic thickness variations within the Mesozoic strata along the Billefjorden Fault Zone south of Isfjordcn are due to Tertiary compressional tectonics related to the transpressive Eocene West-Spitsbergen Orogeny. No convincing evidence of distinct Mesozoic extensional events, as suggested by previous workers, has been recognized. Tertiary compressional tectonics are characterized by a combined thin-skinned/thick-skinned structural style. Decollement zones arc recognized in the Triassic Sassendalen Group (tower Décollement Zone) and in the Jurassic/Cretaceous Janusfjellet Subgroup (Upper Décollement Zone). East-vergent folding and reverse faulting associated with these decollement' zones have resulted in the development of compressional structures, of which the major arc the Skolten and Tronfjellct Anticlines and the Advcntelva Duplex. Movements on one or more high angle east-dipping reverse faults in the pre-Mesozoic basement have resulted in the development of the Juvdalskampcn Monocline, and are responsible for out-of-sequence thrusting and thinning of the Mesozoic sequence across the Billefjorden Fault Zone. Preliminary shortening calculations indicate an eastward displacement of minimum 3-4 km, possibly as much as 10 km for the Lower Cretaceous and younger rocks across the Billefjorden Fault Zone.     

Methane‐related microbial gypsum calcitization in stromatolites of a marine evaporative setting (Münder Formation,Upper Jurassic,Hils Syncline,north Germany)

Fossil stromatolites may reveal information about their hydrochemical palaeoenvironment, provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made. Tithonian stromatolites of the Münder Formation at Thüste, north Germany, have traditionally been considered as formed by intertidal cyanobacterial communities. However, thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement, but no algal or cyanobacterial filament traces. Moreover, high Fe²⁺ and Mn²⁺ contents, oxygen‐isotope and sulphur‐isotope ratios of carbonate‐bound sulphates, and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that CaCO₃ precipitation occurred near the oxic–anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity. Furthermore, anaerobic oxidation of methane by Archaea may have driven CaCO₃ precipitation in deeper parts of the biofilm community, as reflected by high concentrations of squalane with a strongly negative δ¹³C in conjunction with evaporite pseudomorphs showing extremely low δ¹³C_Carb ratios. Consequently, the Thüste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms. Subsequently, early Mg‐calcitic calcitization within the biofilms occurred because of combined bacterial iron, manganese and sulphate reduction, with an increasing contribution of anaerobic oxidation of methane with depth. This model plausibly explains the prominent preservation of signals derived from oxygen‐independent metabolic pathways, whereas virtually no geochemical record exists for an aerobic community that may, nevertheless, have prevailed at the stromatolite surface. Photic‐zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in, and indicative of, oxygen‐depleted sulphate‐bearing environments with high rates of methane production, conditions that possibly were fulfilled at the Archaean to Proterozoic transition.     

A Strontium and Neodymium Isotopic Investigation of the Fongen--Hyllingen Layered Intrusion, Norway

The Fongen—Hyllingen Intrusion, situated 60 km SE of Trondheim,Norway, is a synorogenic layered mafic intrusion of Caledonianage . The intrusion is divided into four evolutionary stages based on cryptic variations: StageI—a basal reversal; Stage II—unchanged mineral chemistryor slight normal evolution; Stage III—a gradual regression;Stage IV— a strong normal fractionation trend Magma replenishmentdominated during most of the crystallization, i.e. during StagesI, II and III Replenishing magma was more dense than resident,evolved magma, and continuing influx eventually caused a compositionallystratified magma column to form. Cryptic lateral variation isan important feature in the southern part of the complex andformed by in situ crystallization from a stratified magma alongan inclined floor, where modal layering formed parallel to thecrystallization front. Initial Sr- and Nd-isotopic ratios inthe cumulates vary as a result of assimilation of country rockand subsequent mixing between uncontaminated, replenishing magmaand contaminated, resident magma. The parental magma had a moderatelydepleted isotope composition, relative to Bulk Earth, with _Nd=584and Sr_i=070308, whereas the main contaminant was a partialmelt of metapelitic country rock with _Nd=-874 and Sr_i=07195(Sr_i is the initial ⁸⁷Sr/⁸⁶Sr). Sr_i in the analysed cumulatewhole-rock samples ranges from 070308 to 070535 and initial_Nd ranges from. 158 to 584. There is a strong correlationbetween mineralogical composition and isotopic trends in mostof the cumulates: the most primitive samples are the least contaminated,as reflected by relatively high ed and low Sr,, and more evolvedsamples have progressively lower eNi and higher Sry A gradualregression of several hundred metres thickness characterizesStage III; stratigraphically upwards mineral compositions becomemore primitive and isotope compositions more depleted (higher_Nd and lower Sr_i), implying a process of. progressive mixing-inof replenishing, primitive and uncontaminated magma. Magma influxin Stage III took place by fountaining, whereas magma additionwas more tranquil in the earlier stages. The fountaining influxentrained resident, relatively evolved and contaminated magma,resulting in a hybrid magma which ponded at the floor. Duringprolonged magma addition with concomitant crystallization, thelowermost magma layer was replaced by progressively more primitivehybrid magma, creating a gradual regression in the crystallizingcumulate sequence. A detailed two-dimensional study revealslateral variations in mineral compositions both at the baseand top of Stage III, whereas lateral variations in Sr- andNd-isotopic compositions are present at the top, but not atthe base. This implies that the lowest crystallizing part ofthe magma column was essentially isotopically homogeneous, butcompositionally stratified, before influx in Stage III. Isotopicgradients in the magma were strong close to the roof, wheremost of the assimilation occurred, and decreased downwards,merging into isotopically homogeneous magma. This stratifiedsystem was destroyed by turbulent mixing between replenishingand resident magma during fountaining influx in Stage III, anda new stratification was established with both an isotopic anda compositional gradient. After the final influx, crystallizationcontinued in an essentially closed system, in which the remainingmagma column eventually became homogenized, as magma layersmixed when their densities converged owing to release of buoyant,residual liquid during fractional crystallization. Corresponding author     

Oxidized Nitrogen in the Remote Pacific: The Role of Electrical Discharges over the Oceans

Simulations of oxidized nitrogen performed withglobal transport tracer models systematicallyunderestimate the concentrations of total nitrate atremote marine locations in the Mid-Pacific. Higheremission rates in the models of nitrogen oxides( ) from continental sources or alarger influx from the stratosphere do not seem tobe able to account for the shortfall. We are led toconclude that there has to be a substantial sourcelocated in oceanic areas. We speculate that -emission from electrical discharges overthe oceans could be the source we are looking for.Airborne observations of atmospheric concentrationsof oxidized nitrogen and ozone in the remoteatmosphere and observations of nitrate wetdeposition in remote sites are used as additionalconstraints to check the plausibility of thishypothesis. We find that a larger emission of due to lightning activity over the oceansindeed results in a much improved simulation oftotal nitrate in the remote Pacific, particularly inthe Equatorial and Tropical South Pacific and thatsuch a scenario is generally consistent withavailable observations of nitrate wet deposition andatmospheric concentrations of oxidized nitrogen andozone. An alternative hypothesis is that there is ahitherto unknown in situ source of over thePacific Ocean.     

The Wilhelmøya Formation (Upper Triassic-Lower Jurassic) at Bohemanflya, Spitsbergen

An 18.5 m thick shale sequence of Norian-Rhaetian age is described from the Bohemanfiya-Syltoppen area (north of Isfjorden, central Spitsbergen). Lithological, petrographical and palynological analyses show that the sequence represents a marginal development of the lower part of the Wilhelmeya Formation. The depositional history at the Triassic-Jurassic transition is discussed in the light of this new evidence. The Wilhelmøya Formation was probably deposited during a weak marine transgression over an area of low relief. Low sediment supply and current and wave reworking of the sediments characterized the depositional conditions.     

Depositional environment of the Laptev Sea (Arctic Siberia) during the Holocene

The Holocene depositional setting of the Laptev Sea was studied using three marine sediment cores from water depths between 77 and 46 m. Based on sedimentary parameters (TOC content, δ¹³C_org, sedimentation rates) controlled by radiocarbon age models the palaeoenvironment of a strongly coupled river-shelf system was reconstructed since ˜11 ka BP. Caused by a transgressing sea after the last glaciation, all cores reveal progressive decreases in sedimentation rates. Using the sedimentary records of a core from the Khatanga-Anabar river channel in the western Laptev Sea, several phases of change are recognized: (1) an early period lasted until ˜10 ka BP characterized by an increased deposition of plant debris due to shelf erosion and fluvial runoff; (2) a transitional phase with consistently increasing marine conditions until 6 ka BP, which was marked at its beginning near 10 ka BP by the first occurrence of marine bivalves, high TOC content and an increase in δ¹³C_org; (3) a time of extremely slow deposition of sediments, commencing at ˜6 ka BP and interpreted as Holocene sea-level highstand, which caused a southward retreat of the depositional centres within the now submerged river channels on the shelf; (4) a final phase with the establishment of modern conditions after ˜2 ka BP.     

Origin of quartz cements in some sandstones from the Jurassic of the Inner Moray Firth (UK)

The extent of quartz cementation in shallow marine sandstones of the Brora Arenaceous Formation (Oxfordian) is closely related to the occurrence and abundance of Rhaxella perforata sponge spicules. Three cement morphologies are identified, chalcedonic quartz, microquartz and mesoquartz. Chalcedonic quartz forms matrix-supported cements which preserve moulds of Rhaxella spicules. Chalcedonic quartz crystals have inequant development of crystal faces, on average 0·1 μm in diameter, and are the first formed cement and reveal homogeneous dark grey tones on the SEM-CL/BEI. Microquartz forms 5–10 μm diameter crystals, which commonly grow on chalcedonic quartz substrates and show various grey tones under SEM-CL/BEI. Mesoquartz crystals grow in optical continuity with their host grains, have >20 μm a-axial diameter crystals, and exhibit distinctly zoned luminescence. Although no opaline silica is preserved, the quartz cement is interpreted to have formed from an opaline precursor. Detrital quartz has an average δ¹⁸O composition of + 12·2‰ and mesoquartz (syntaxial overgrowth) has an average δ¹⁸O composition of +20·0‰. Estimates of the δ¹⁸O compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types; mixtures of the two give consistently higher δ¹⁸O compositions than mesoquartz, the higher estimate being +39·2‰. From oxygen isotope data the formation of quartz, microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71°C in marine derived pore waters. Organic and inorganic maturation data constrain the upper temperature limit to less than 60°C.     

Measurements of Air Concentrations of SO2, NO2 and NH3 at Rural and Remote Sites in Asia

Sensitive diffusive samplers for concentration measurements in ambient airhave been used successfully in Sweden for several years. The samplers have theadvantage of being stable at room temperature before, as well as after,sampling, easy to handle, and cost-efficient. Furthermore, they do not requireelectricity or field calibration. In order to test their use in tropical andsubtropical environments and to obtain a preliminary set of data to validateatmospheric chemistry transport models in this part of the world, duplicatesamples were collected at 11 sites every second month during one year. Eightof the sites were background sites in Asia. It was not possible within theproject to compare the measured concentrations with other measurementtechniques. However, the reproducibility of the duplicates was satisfactoryover the whole measuring range (almost three orders of magnitude of theconcentration for SO₂) and reasonable agreement with modelcalculations was obtained at least for SO₂ andNH₃. Further testing of the measuring technique in tropicalareas is, however, warranted.     

Seasonal and interannual variability of Siberian river discharge in the Laptev Sea inferred from stable isotopes in modern bivalves

Stable oxygen and carbon isotope profiles from modern bivalve shells were investigated in order to reconstruct short-term hydrographical changes in the river-shelf system of the Laptev Sea. Oxygen isotopic profiles obtained from the aragonitic species Astarte borealis exhibit amplitude cycles interpreted as annual hydrographical cycles. These records reflect the strong contrast between summer and winter bottom water conditions in the Laptev Sea. The seasonal variations in δ¹⁸O are mainly controlled by the riverine freshwater discharge during summer with 0.5‰ per salinity unit. Corrected for a defined species-dependent fractionation offset of -0.37‰, time-dependent salinity records were reconstructed from these δ¹⁸O profiles. They indicate a good correspondence to seasonal hydrographic changes and synoptical data. Persistent trends with shell growth towards more negative δ¹³C values are observed in all specimens and appear to be related to metabolic changes of the bivalves during ontogeny. In contrast, short-term fluctuations are likely linked to seasonal variabilities of the river water outflow patterns and enhanced phytoplankton productivity during summer. This is corroborated by a clear watermass-related distinction of the various δ¹³C records made on the basis of water depth and distance from the riverine source.     

Glaciofluvial channels formed prior to the last deglaciation: examples from Swedish Lapland

At four localities in area east of the Sarek and Kebnekajse massifs in Swedish Lapland, glaciofluvial channels seem to have been overhidden by glaciers without having extensively modified. It is suggested that the channels were formed during an Early Weichselian stade. The last glaical advance had little effect on the pre-exiting landforms at these localities and probably also at many other places in the area. Earlier theories about glacial development and deglaciation patterns in this area are based on morphology and the assumption that the landforms were formed during the last deglaciation. These theories need to be revised.