Comparison of in-situ Field Measurements of Soil Magnetic Susceptibility with Laboratory Data

Results of magnetic susceptibility mapping around a coal-burning power plant were used to verify the field in situ measurements with data acquired in laboratory on soil samples collected at approximately the same measurement grid sites at different distance from the source. This comparison enables quantifying the field data obtained using the Bartington MS2 meter and to relate them, at least approximately, to mass specific values. Moreover, it is shown that certain diversity in the grid points of field measurements and soil sampling can slightly bias the field measurements. However, this shift is of minor significance and Bartington field readings can be considered as reliable.     

The way forward for coronal heating

Ineke De Moortel, Philippa K Browning, Stephen J Bradshaw, Balázs Pintér and Eduard P Kontar consider approaches to the longstanding and enigmatic problem of coronal heating, as presented at the RAS discussion meeting on 11 January 2008.     

Effect of the initial density and angular-velocity profiles of pre-stellar cores on the properties of young stellar objects

The physical properties of young stellar objects are studied as functions of the initial spatial distributions of the gas surface density Σ and angular velocity Ω in pre-stellar cores using numerical hydrodynamic simulations. Two limiting cases are considered: spatially homogeneous cores with Σ = const and Ω = const and centrally concentrated cores with radius-dependent densities Σ ∝ r ⁻¹ and Ω ∝ r ⁻¹. The degree of gravitational instability and protostellar disk fragmentation is mostly determined by the initial core mass and the ratio of the rotational to the gravitational energy, and depends only weakly on the initial spatial configuration of pre-stellar cores, except for the earliest stages of evolution, when models with spatially homogeneous cores can be more gravitationally unstable. The accretion of disk matter onto a protostar also depends weakly on the initial distributions of Σ and Ω, with matter from the collapsing core falling onto the disk at a rate that is slightly higher in models with spatially homogeneous cores. An appreciable dependence of the disk mass, disk radius, and the disk-to-protostar mass ratio on the initial density and angular velocity profiles of the parent core is found only for class 0 young objects; this relationship is not systematic in the later I and II stages of stellar evolution. The mass of the central protostar depends weakly on the initial core configuration in all three evolutionary stages.     

Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands

Waters from the Atlantic Ocean washed southward across parts of Anegada, east-northeast of Puerto Rico, during a singular event a few centuries ago. The overwash, after crossing a fringing coral reef and 1.5?km of shallow subtidal flats, cut dozens of breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime mud, and created inland fields of cobbles and boulders. Most of the breaches extend tens to hundreds of meters perpendicular to a 2-km stretch of Anegada??s windward shore. Remnants of the breached ridges stand 3?m above modern sea level, and ridges seaward of the breaches rise 2.2?C3.0?m high. The overwash probably exceeded those heights when cutting the breaches by overtopping and incision of the beach ridges. Much of the sand-and-shell sheet contains pink bioclastic sand that resembles, in grain size and composition, the sand of the breached ridges. This sand extends as much as 1.5?km to the south of the breached ridges. It tapers southward from a maximum thickness of 40?cm, decreases in estimated mean grain size from medium sand to very fine sand, and contains mud laminae in the south. The sand-and-shell sheet also contains mollusks??cerithid gastropods and the bivalve Anomalocardia??and angular limestone granules and pebbles. The mollusk shells and the lime-mud cap were probably derived from a marine pond that occupied much of Anegada??s interior at the time of overwash. The boulders and cobbles, nearly all composed of limestone, form fields that extend many tens of meters generally southward from limestone outcrops as much as 0.8?km from the nearest shore. Soon after the inferred overwash, the marine pond was replaced by hypersaline ponds that produce microbial mats and evaporite crusts. This environmental change, which has yet to be reversed, required restriction of a former inlet or inlets, the location of which was probably on the island??s south (lee) side. The inferred overwash may have caused restriction directly by washing sand into former inlets, or indirectly by reducing the tidal prism or supplying sand to post-overwash currents and waves. The overwash happened after A.D. 1650 if coeval with radiocarbon-dated leaves in the mud cap, and it probably happened before human settlement in the last decades of the 1700s. A prior overwash event is implied by an inland set of breaches. Hypothetically, the overwash in 1650?C1800 resulted from the Antilles tsunami of 1690, the transatlantic Lisbon tsunami of 1755, a local tsunami not previously documented, or a storm whose effects exceeded those of Hurricane Donna, which was probably at category 3 as its eye passed 15?km to Anegada??s south in 1960.     

Homotrema rubrum (Lamarck) taphonomy as an overwash indicator in Marine Ponds on Anegada, British Virgin Islands

Marine hypersaline ponds on Anegada, British Virgin Islands contain stratigraphic evidence (Shell and Sand Sheet) of a A.D. 1650?C1800 overwash event that could have formed through a hurricane or tsunami. Candidates for the deposit include far-field (e.g. 1755 Lisbon tsunami) and local Puerto Rico Trench events (e.g. 1690), but hurricanes cannot be ignored. The goal of this study is to provide additional information to assess the origin of the deposit by examining the taphonomic characters of Homotrema rubrum, a common encrusting foraminifer in Caribbean reef settings. Surface samples (n?=?12) from major sub-environments (reef-flat, beach, storm wrack, and dune) and pond sections (n?=?6; 20?C80?cm thick) are analyzed for their Homotrema concentration (specimens/cm³) and taphonomic character. Particle-size analysis was conducted on the same sections and samples. Highly Preserved (red colored, angular, intact chambers) Homotrema dominate the beach, storm wrack, and reef-flat deposits relative to the dune sand, but the beach and storm wrack contain the largest specimens. The Shell and Sand Sheet in the pond has Highly Preserved and abundant Homotrema (specimens/cm³) versus other sedimentary units in the ponds (e.g. Mud Cap and Shelly Mud). Its taphonomic character is most similar (test size and condition) to the storm wrack deposit on the beach indicating an outside provenance for the sand. Concentration of Homotrema in the Shell and Sand Sheet declined southward indicating a northerly reef-flat provenance for the overwash, although it does not preclude a southern inundation as well. It is unclear whether Homotrema individuals originated from the reef itself or were eroded from older beach ridge deposits during the overwash event. Conclusions from Homotrema taphonomic analysis were limited by the lack of comparative data from known hurricane and tsunami deposits in other Caribbean regions.     

Iron titanium oxides in equilibrium with metallic iron

The iron titanium oxide phases ulvite, ilmenite and ferropseudobrookite were synthesized in equilibrium with metallic iron at 1000 ° C, 1130 ° C and 1300 ° C in CO₂/H₂ gas mixtures.The composition of the phases were determined by wet chemical and electron microprobe analyses and by direct oxygen determination.The chemical composition of the Fe-Ti oxide phases in equilibrium with metallic iron is sensitively influenced by temperature and by bulk composition.Ulvite in equilibrium with wüstite does not contrivalent titanium in the whole temperature range up to the eutectic temperature at 1312 °C.Ulvite+ilmenite phase assemblages contain trivalent titanium only at temperatures above 1200 ° C.A ferropseudobrookite phase is stable under the given conditions at temperatures above 1068 °C (Ender and Woermann, 1977).Ferropseudobrookite in equilibrium with metallic iron always contains trivalent titanium.Deviations from stoichiometric compositions of the solid solution phases are generally small. Thus recalculation of microprobe data to stoichiometric solid solutions does not involve a major error.From: Bruno Simons, Diplomarbeit Aachen, October 1974     

Volatiles in pillows of the Mid-Ocean-Ridge-Basalt (MORB) and vitreous basaltic rims

Temperature-resolved analyses of volatiles from Mid-Ocean-Ridge-Basalt (MORB) and vitreous basaltic rims were carried out to investigate the total volatile contents of basaltic melts and the influence of magma contamination on the degassing behaviour of volcanic rocks.With respect to the sources of methane evolution from the MORB the investigations are taken into consideration, the hydrocarbon (HC) release especially from the melt.The current paper presents data for H₂O, CO₂, SO₂, He, H₂, HF, HCl, CO, N₂, O₂, and HC degassing profiles of samples from the MORB sampling cruise 02.10.1983-11.11.1983 with FS Sonne 28 during the GEMINO-1 project near the Carlsberg Ridge (CR) and the Mid-Indian-Ocean-Ridge (MIOR).It aims to estimate the magnitude and nature of source magma volatiles and contamination (crustal material, seawater, atmospheric gases).The degassing of H₂O, CO₂, HCs as well as sulphur and chlorine species, or O₂ from vitreous specimens shows characteristic differences associated with sample position with respect to the lava surface.From the water release by bubbling and diffusion above 700 °C it must be concluded that any assimilation of sea water in vitreous rim is very low. The water content in the vitreous rim is about 0.1-0.2 wt%. The low interaction of melt with sea water is supported by the missing of a significant release of chlorine species during the heat treatment of the sample up to 1450 °C.Mixed H₂O/CO₂ bubbles escape between 700 and 800 °C from the vitreous rim. The CO₂ release in the temperature range of 1060-1170 °C from the basalt and the vitreous rim is interpreted as an indication for the primary carbon-dioxide content in the melt.Above 1100 °C CO₂ and SO₂ are evolved by both diffusion and small bubbles. The quantities of CO₂ in the vitreous rim and the basalt are similar (between 0.05 and 0.15 wt%), whereas the quantities of SO₂ escaping both from the vitreous rim and the crystalline basalt are between 0.013 and 0.024 wt%.Simultaneous with the CO₂ release by bubbling, HC species, especially CH fragments, were observed. The fact that the temperature of release maxima are above 1050 °C in both the vitreous rim and in the basalt is an indication for a geogenetic origin of HCs, e.g. methane.A low temperature of release for methane, which is consistent with biogenetic HC, was observed from the gas-release profiles of the basalts only. The maxima of the low-temperature gas releases are between 80 and 200 °C with a high correlation between the fragments m/z 13 and m/z 15. This correlation is a significant indication for a methane release.The oxygen release profiles of vitreous and crystalline basalts give significant indications for oxygen fugacity below the (QMF) of basaltic magma.Secondary minerals, generated by alteration of basaltic rocks, can be characterized by gas release profiles (GRPs) due to their decomposition in the temperature range below 800 °C. Only in the basalt were there observed indications of alteration processes. Small traces of carbonates (<0.0001 wt%) were detected by the gas release during the decomposition.Processes of degassing at temperatures higher than 800 °C are correlated to volatiles in the melt and to fluid inclusions of the minerals. There are no obvious correlations in the degassing characteristics between H₂O, CO₂ and SO₂. The different maxima of the degassing velocity, especially of CO₂, and SO₂, are indications of the different bonding forces of the site occupancy of the volatiles in the melt and in the glass. A micelle model for bonding sites in the basaltic glass for dissolved volatiles is discussed.     

Vlora-Elbasani-Dibra (Albania) transversal fault zone and its seismic activity

The transversal fault zone Vlora-Elbasan-Dibra (VED)with Northeastern strike dislocated the structure ofAlbanides along all their width. This transversalfault is distinguished by the flexure of Lushnja, thediapire dome of Dumrea, the transversal Quaternarydepression of Elbasani, the belt of transversalstructure of Labinoti, and then it continues towardsNortheast with transversal horst of Golloborda andgoes toward FYROM in NE direction. In the Southwesternpart of this transversal fault, near Fieri town, themolasse subsided toward North. The structures ofIonian and Kruja zone, near this transversal fault,also subsided and uplifted more toward North. Throughmarine investigation a transversal fault with ENEstrike direction was discovered near the Northern partof Sazani Island (Aliaj et al., 1996). We think itmay belong to the big transversal fault zone VED.The transversal fault zone VED is clearlyoutlined by the location of strong and weakearthquakes, migration of foci along this fault, themacroseismic field and focal mechanisms. Generally,along this transversal fault it is the transtensionalstrike-slip dextral motion that dominates.In our studies the transversal fault zoneVlora-Elbasani-Dibra was considered to be the mostpotential transversal seismogenetic belt in Albaniaand nearby. It has played, and is still playing,an important role in seismotectonics in Albania andits surrounding regions.     

Fluctuations of electrical conductivity as a natural tracer for bank filtration in a losing stream

A key parameter used in the assessment of bank filtration is the travel time of the infiltrated river water during the passage through groundwater. We analyze time series of electrical conductivity (EC) in the river and adjacent groundwater observation wells to investigate travel times of young hyporheic groundwater in adjoining channelized and restored sections of River Thur in North-East Switzerland. To quantify mixing ratios and mean residence times we perform cross-correlation analysis and non-parametric deconvolution of the EC time series. Measurements of radon-222 in the groundwater samples validate the calculated residence times. A simple relationship between travel time and distance to the river has not been observed. Therefore, we speculate that the lateral position and depth of the thalweg as well as the type of bank stabilization might control the infiltration processes in losing rivers. Diurnal oscillations of EC observed in the river and in nearby observation wells facilitate analyzing the temporal variation of infiltration. The diurnal oscillations are particularly pronounced in low flow situations, while the overall EC signal is dominated by individual high-flow events. Differences in travel times derived from diurnal and overall EC signals thus reflect different infiltration regimes.     

Distribution of Al between coexisting micas in metamorphic rocks from the Central Alps

In 61 pairs of coexisting biotites and muscovites from the Central Alps total Al scatters considerably, but in both series a gradual increase is noticed with increasing metamorphic grade. The ratio Al _Mu ^tot /Al _Bi ^tot remains virtually constant (1.61 average for greenschist facies, 1.57 for amphibolite facies). Tetrahedral Al varies little in biotites and increases in muscovites-phengites with rising metamorphic grade; accordingly the ratio Al _Mu ^IV /Al _Bi ^IV increases slightly with grade. Far the best control of metamorphism is evidenced by octahedral Al. In the muscovite series, and still more pronounced in the biotite series, Al^VI increases with increasing metamorphic grade. Consequently 1 $$K_D = \frac{{Al_{Mu}^{VI} }}{{Al_{Bl}^{VI} }}$$ decreases from 14 to 3. A map (Fig. 6) representing the regional distribution of the K_D values locates a 100 km long and 23 km broad central zone with low K_D. The outline of this central core almost coincides with the isograds anorthite-diopside-calcite and labradorite-pyroxene-hornblende of the Tertiary regional metamorphism; with some deviations this core also agrees with the zone in which phenomena of partial anatexis are observed. The K_D values of micas from anateotic pegmatites agree with those of associated gneisses and schists. The study demonstrates that in the course of progressive regional metamorphism equilibrium has been approached to an unexpected extent and that the two micas coexisted in a strict sense.