Geochemistry of the Kola River, northwestern Russia

The Kola River in the northern part of the Kola Peninsula, northwestern Russia, flows into the Barents Sea via the Kola Bay. The river is a unique place for reproduction of salmon and an important source of drinking water for more than 500,000 people in Murmansk and the surrounding municipalities. To evaluate the environmental status of the Kola River water, sampling of the dissolved (<0.22 μm) and suspended (>0.22 μm) phases was performed at 12 sites along the Kola River and its tributaries during 2001 and 2002. Major (Ca, K, Mg, Na, S, Si, HCO₃ and Cl) and trace (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, Ti, and Zn) elements, total and particulate organic C (TOC and POC), N and P were analysed. Comparison with the boreal pristine Kalix River, Northern Sweden, shows that, except for Na, Cl, Al, Cu and Ni, which exceed the concentrations in the Kalix River by as much as 2–3 times, the levels of other major and trace elements are close to or even below the levels in the Kalix River. However, the results also demonstrate that pollutants from the three major sources: (1) the Cu–Ni smelter in Monchegorsk, (2) the open-pit Fe mine and ore concentration plant in Olenegorsk, and (3) the Varlamov, the Medveziy and the Zemlanoy creeks, draining the area of the large agricultural enterprises in the lower part of the watershed, have a major influence on the water quality of the Kola River.     

A new approach to interpreting Rock-Eval S2 and TOC data for kerogen quality assessment

A simple method for application in source potential mapping is used to assess the original oil and gas potentials in source rock horizons based upon Rock-Eval potential (S₂) and total organic carbon (TOC) values. The method assumes that kerogens consist of mixtures of end-members with assigned hydrogen index values. Based on suggested algorithms, the average amounts of oil-prone, gas-prone and inert organic material over source rock intervals are determined in TOC units. The method uses regression lines from plots of remaining hydrocarbon potentials (S₂) versus total organic carbon (TOC), and “quick-look” transparent overlays are used to read the appropriate kerogen mixture.Mineral matrix effects during pyrolysis, when strong, can cause erroneous results. This effect which occurs for oil-prone kerogens and adsorptive minerals can cause problems particularly for lean samples (S₂ = 0–3 mg HC/g rock) whilst the errors for richer samples are less.The method is applied on three sections of Upper Jurassic organic-rich rocks from the Danish North Sea sector, which are at different maturity stages. One of these sections is dominated by gas-prone material, one is dominated by oil-prone material and the third section contains a mixture of oil- and gas-prone material.The method has been compared with other methods that split kerogens in oil and gas generating potential and has given reasonable results.Experience using the method and a presented example suggest that sedimentological, system tract information may be derived from S₂ to TOC cross-plots. A constructed modelling example suggests that the end-member concept used in this approach may be used in forward type source rock prediction models when combined with sedimentological models. The resulting S₂–TOC plots can be used in order to check the forward modelling results against observed values.     

Isotopic anomalies of noble gases in meteorites and their origins—III. LL-chondrites

Nine LL-chondrites were studied by a selective etching technique, to characterize the noblegas components in three mineral fractions: HF-HCl-solubles (silicates, metal, troilite, etc.; comprising ～ 99% of the meteorite), chromite and carbon (～ 0.3–0.7%) and Q (a poorly characterized mineral defined by its solubility in HNO₃, comprising ～ 0.05% of the meteorite but containing most of the Ar, Kr, Xe and a neon component of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 10.9 ± 0.8}$). The ${}^{20}\text{Ne}{}^{36}\text{Ar}$ ratio in Q falls wi petrologic type and rising ³⁶Ar content, as expected for condensation from a cooling solar nebula, but contrary to the trend expected for metamorphic losses. Chondrites of different petrologic types therefore cannot all be derived from the same volatile-rich ancestor, but must have formed over a range of temperatures, with correspondingly different intrinsic volatile contents.The CCFXe (carbonaceous chondrite fission) component varies systematically with petrologic type. The most primitive LL3s (Krymka, Bishunpur, Chainpur) contain substantial amounts of CCFXe in chromite-carbon, enriched relative to primordial Xe as shown by high ${}^{136}\text{Xe}{}^{132}\text{Xe}$ (0.359–0.459, vs 0.310 for primordial Xe). These are accompanied by He and by Ne with ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{≈ 8.0}$ and by variable amounts of a xenon component enriched in the light isotopes. The chromite in these meteorites is compositionally peculiar, containing substantial amounts of Fe(III). These meteorites, as well as Parnallee (LL3) and Hamlet (LL4) also contain CCFXe in phase Q, heavily diluted by primordial $\text{Xe}\text{(}{}^{136}\text{Xe}{}^{132}\text{Xe}\text{= 0.317–0.329)}$. On the other hand, LL5s and 6s (Olivenza, St. Séverin, Manbhoom and Dhurmsala) contain no CCFXe in either mineral. This deficiency must be intrinsic rather than caused by metamorphic loss, because Q in these meteorites still contains substantial amounts of primordial Ne.If CCFXe comes from a supernova, then its distribution in LL-chondrites requires three presolar carrier minerals of the right solubility properties, containing three different xenon components in certain combinations. These minerals must be appropriately distributed over the petrologic types, together with locally produced Q containing primordial gases, and they must be isotopically normal, in contrast to the gases they contain. On the other hand, if CCFXe comes from fission of a volatile superheavy element, then its decrease from LL3 to LL6 can be attributed to progressively less complete condensation from the solar nebula. Ad hoc assumptions must of the host phase Q, its association with ferrichromite and the origin of the associated xenon component enriched in the light isotopes.Soluble minerals in LL3s and LL4s contain a previously unobserved, solar xenon component, which, however, is not derived from the solar wind. Three types of ‘primordial’ xenon thus occur side-by-side in different minerals of the same meteorite: strongly fractionated Xe in ferrichromite and carbon, lightly fractionated Xe in phase Q, and ‘solar’ Xe in solubles. Because the first two can apparently be derived from the third by mass fractionation, it seems likely that all were trapped from the same solar nebula reservoir, but with different degrees of mass fractionation.     

The Blomskog granite — a possible diapiric structure

A group of granitic intrusions occurs in western Sweden, showing a regular spacing between consecutive intrusions. Their spacing suggests solid-state doming of granitic material. However the textures of the rock are most easily interpreted in terms of crystallization from a magma. This interpretation is also consistent with contact observations and chemical characteristics of the rock. A hypothesis simultaneously explaining the textures and the spacing is presented, where doming of a light layer of potassium-rich migmatite is suggested to be followed by partial melting of the same rock. The magma collects at the top of the thus-formed sinusoidal waves and later intrudes into the country rock, where it crystallizes before reaching the surface.     

Seismic investigations in the Weddell Sea Embayment

Seismic multi-channel data collected during Norwegian Antarctic Research Expeditions in 1976–1977 and 1978–1979 outline aspects of the Cenozoic depositional environment in the Weddell Sea Embayment. Acoustic basement, probably representing the East Antarctic craton, is exposed in a 50–100 km wide swath along the ice barrier between 78°S–75.5°S on the eastern side of the Crary Trough. The shelf prograded westward and northward from the craton into a subsiding basin colinear with the Transantarctic Mountain Range. Measured sediment thicknesses exceed 5 km. During middle and late Tertiary times a submarine fan complex—the Crary Fan—developed on the southeastern margin of the Weddell Sea Embayment. The glacially eroded Crary Trough is located at the contact between the craton and a sedimentary basin to the west. The entire sedimentary section is undisturbed by faulting or folding, which indicates that any movements related to Cenozoic uplift of the Trans-Antarctic Mountains and/or relative motion of East Antarctica had little effect in the area north of the Filchner Ice Shelf east of 41°W.     

A hydrothermal investigation of the system FeOFe2O3TiO2: A discussion with new data

New experimental data on the system FeOFe₂O₂TiO₂ using a new oxygen buffer are presented. It is found that there is a narrow range of oxygen fugacity above 550°C within which hematite and ilmenite coexist stably.