Stratigraphy and inversion tectonics in the St. Georges Channel area off SW Wales,U.K.

Transgressive Upper Cretaceous Chalk terminates (between SW Wales and SE Ireland) at approximately latitude 52°N as thinly bedded marginal facies; while the Tertiary sequences, previously considered to extend uninterrupted into both the South Celtic Sea area and the Nymphe Bank basin are preserved as isolated subcrops separated by Jurassic. The distinct subsidence history of St. Georges Channel basin, as compared to the Nymphe Bank basin which both belong to the North Celtic Sea graben, is attributed to inversion activity with the final phase occurring during the Paleogene.     

Stable isotope compositions and water contents of boninite series volcanic rocks from Chichi-jima, Bonin Islands, Japan

Measurements of stable isotope compositions and water contents of boninite series volcanic rocks from the island of Chichi-jima, Bonin Islands, Japan, confirm that a large amount (1.6–2.4 wt.%) of primary water was present in these unusual magmas. An enrichment of 0.6‰ in¹⁸O during differentiation is explained by crystallization of¹⁸O-depleted mafic phases. Silicic glasses have elevated δ¹⁸O values and relatively low δD values indicating that they were modified by low-temperature alteration and hydration processes. Mafic glasses, on the other hand, have for the most part retained their primary isotopic signatures since Eocene time. Primary δD values of −53 for boninite glasses are higher than those of MORB and suggest that the water was derived from subducted oceanic lithosphere.     

The damping of a group of sea waves

The signals from a wave probe, a buoy-mounted sensor at the water surface, and a three-component sonic anemometer were recorded during the passage of a discrete group of waves which were travelling against a light wind. Cross spectra between the wave signals and the pressure and sonic anemometer signals were obtained and are interpreted.Bedford Institute contribution No. 226.This work forms part of a Ph.D. dissertation at the Institute of Oceanography, University of British Columbia.     

Quantifying strain birefringence halos around inclusions in diamond

The pressure and temperature conditions of formation of natural diamond can be estimated by measuring the residual stress that an inclusion remains under within a diamond. Raman spectroscopy has been the most commonly used technique for determining this stress by utilising pressure-sensitive peak shifts in the Raman spectrum of both the inclusion and the diamond host. Here, we present a new approach to measure the residual stress using quantitative analysis of the birefringence induced in the diamond. As the analysis of stress-induced birefringence is very different from that of normal birefringence, an analytical model is developed that relates the spherical inclusion size, R _i, host diamond thickness, L, and measured value of birefringence at the edge of the inclusion, \Updelta n(R_\texti )_\textav \Updelta n(R_{\text{i}} )_{\text{av}} , to the peak value of birefringence that has been encountered; to first order \Updelta n_\textpk = (3/4)(L/R_\texti )  \Updelta n(R_\texti )_\textav \Updelta n_{\text{pk}} = (3/4)(L/R_{\text{i}} ) \, \Updelta n(R_{\text{i}} )_{\text{av}} . From this birefringence, the remnant pressure (P _i) can be calculated using the photoelastic relationship \Updelta n_\textpk = - (3/4)n³ q_\textiso P_\texti \Updelta n_{\text{pk}} = - (3/4)n^{3} q_{\text{iso}} P_{\text{i}} , where q _iso is a piezo-optical coefficient, which can be assumed to be independent of crystallographic orientation, and n is the refractive index of the diamond. This model has been used in combination with quantitative birefringence analysis with a MetriPol system and compared to the results from both Raman point and 2D mapping analysis for a garnet inclusion in a diamond from the Udachnaya mine (Russia) and coesite inclusions in a diamond from the Finsch mine (South Africa). The birefringence model and analysis gave a remnant pressure of 0.53 ± 0.01 GPa for the garnet inclusion, from which a source pressure was calculated as 5.7 GPa at 1,175°C (temperature obtained from IR analysis of the diamond host). The Raman techniques could not be applied quantitatively to this sample to support the birefringence model; they were, however, applied to the largest coesite inclusion in the Finsch sample. The remnant pressure values obtained were 2.5 ± 0.1 GPa (birefringence), 2.5 ± 0.3 GPa (2D Raman map), and 2.5–2.6 GPa (Raman point analysis from all four inclusions). However, although the remnant pressures from the three methods were self-consistent, they led to anomalously low source pressure of 2.9 GPa at 1,150°C (temperature obtained from IR analysis) raising serious concerns about the use of the coesite-in-diamond geobarometer.     

The Northwest Africa (NWA) 5790 meteorite: A mesostasis‐rich nakhlite with little or no Martian aqueous alteration

Northwest Africa (NWA) 5790 is the most recently discovered member of the nakhlite group. Its mineralogy differs from the other nakhlites with a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of olivine (4.0 ± 2.2 vol%). Furthermore, zoning of augite phenocrysts, and other petrographic and chemical characteristics suggest that NWA 5790 samples the chilled margin of its parent lava flow/sill. NWA 5790 contains calcite and rare clay minerals that are evidence for its exposure to liquid water. The calcite forms a cement to coatings of dust on the outer surface of the find and extends into the interior of the meteorite within veins. The presence of microbial remains within the coating confirms that the dust and its carbonate cement are terrestrial in origin, consistent with the carbon and oxygen isotope composition of the calcite. The clay minerals are finely crystalline and comprise ~0.003 vol% of the meteorite. δD values of the clay minerals range from ?212 ± 109‰ to ?96 ± 132‰, and cannot be used to distinguish between a terrestrial or Martian origin. As petrographic results are also not definitive, we conclude that secondary minerals produced by Martian groundwaters are at best very rare within NWA 5790. The meteorite has therefore sampled a region of the lava flow/sill with little or no exposure to the aqueous solutions that altered other nakhlites. This isolation could relate to the scarcity of olivine in NWA 5790 because dissolution of olivine in other nakhlites by Martian groundwaters enhanced their porosity and permeability, and provided solutes for secondary minerals.     

Climate change and infectious diseases: Can we meet the needs for better prediction?

The next generation of climate-driven, disease prediction models will most likely require a mechanistically based, dynamical framework that parameterizes key processes at a variety of locations. Over the next two decades, consensus climate predictions make it possible to produce forecasts for a number of important infectious diseases that are largely independent of the uncertainty of longer-term emissions scenarios. In particular, the role of climate in the modulation of seasonal disease transmission needs to be unravelled from the complex dynamics resulting from the interaction of transmission with herd immunity and intervention measures that depend upon previous burdens of infection. Progress is also needed to solve the mismatch between climate projections and disease projections at the scale of public health interventions. In the time horizon of seasons to years, early warning systems should benefit from current developments on multi-model ensemble climate prediction systems, particularly in areas where high skill levels of climate models coincide with regions where large epidemics take place. A better understanding of the role of climate extremes on infectious diseases is urgently needed.     

An alkaline spring system within the Del Puerto Ophiolite (California,USA): A Mars analog site

Mars appears to have experienced little compositional differentiation of primitive lithosphere, and thus much of the surface of Mars is covered by mafic lavas. On Earth, mafic and ultramafic rocks present in ophiolites, oceanic crust and upper mantle that have been obducted onto land, are therefore good analogs for Mars. The characteristic mineralogy, aqueous geochemistry, and microbial communities of cold-water alkaline springs associated with these mafic and ultramafic rocks represent a particularly compelling analog for potential life-bearing systems. Serpentinization, the reaction of water with mafic minerals such as olivine and pyroxene, yields fluids with unusual chemistry (Mg–OH and Ca–OH waters with pH values up to ～12), as well as heat and hydrogen gas that can sustain subsurface, chemosynthetic ecosystems. The recent observation of seeps from pole-facing crater and canyon walls in the higher Martian latitudes supports the hypothesis that even present conditions might allow for a rock-hosted chemosynthetic biosphere in near-surface regions of the Martian crust. The generation of methane within a zone of active serpentinization, through either abiogenic or biogenic processes, could account for the presence of methane detected in the Martian atmosphere. For all of these reasons, studies of terrestrial alkaline springs associated with mafic and ultramafic rocks are particularly timely. This study focuses on the alkaline Adobe Springs, emanating from mafic and ultramafic rocks of the California Coast Range, where a community of novel bacteria is associated with the precipitation of Mg–Ca carbonate cements. The carbonates may serve as a biosignature that could be used in the search for evidence of life on Mars.     

Magnetic properties of metal-substituted haematite

Mineral and isothermal magnetic properties of Al-, Mn- and Ni-substituted haematites were characterized and their relationships evaluated in order to interpret better the results of magnetic analyses of soils and recent sediments. Aluminium, manganese and nickel haematites generally behaved as single-domain (SD) particles. The influence of incorporated Al on the magnetic behaviour of haematite was consistent with Al acting as a paramagnetic dilutent. Mass magnetic susceptibility ( χ ) and SIRM₈₀₀ decreased as the level of Al substitution increased. Incorporation of Mn and Ni increased χ , which could be associated with enhancement of the spin canting effect of haematite. The stability of SIRM₈₀₀ to demagnetization for Al-haematite appears to be related to a defect mechanism associated with the development of smaller crystallites arising from Al substitution. Magnetic domain rotation or flipping was probably inhibited, being blocked by structural defects during magnetization and demagnetization, and resulted in a low but stable partial SIRM (SIRM₈₀₀ ). %IRM/SIRM₈₀₀ demagnetization curves and estimated ( B _o )_CR values of ≤100  mT for Mn-haematite indicate pseudo-single-domain/multidomain-like behaviour despite Mn-haematite having particle and crystallite dimensions similar to Ni-haematite, which did not show this behaviour. Data indicate that parameters involving unsaturated, partial SIRM should be used with caution in magnetic studies of soils and sediments.     

On the deep‐water fetch laws for wind‐generated surface gravity waves

Abstract

With the object of providing an accurate set of open‐sea wave spectra in a variety of conditions, we deployed, in conjunction with CASP, an array of 9 wave buoys (3 directional, 6 non‐directional) along a 30‐km line offshore from Martinique Beach, N.S. A large set of high‐quality wave spectra was collected in conjunction with extensive meteorological information. The data set is unique in the sense that a large onshore swell component was normally present.

Offshore‐wind cases for three windows: ±5°, ±15° and ±30° with respect to the shore normal, have been considered. Wind speed was found to be a strong function of fetch, and attempts were made to allow for this in the analysis. Power‐law regressions have been produced of dimensionless sea energy, peak frequency and high‐frequency spectral level (the Kitaigorodskii “alpha” parameter) vs dimensionless fetch and wind speed (inverse wave age). The regressions are compared with earlier work: the Joint North Sea Waves Project (Jonswap) and the Canada Centre for Inland Waters (CCIW) Lake Ontario study.

The comparisons indicate that dimensionless wave energies, peak frequencies and alpha values in this experiment are comparable with those from earlier experiments; in spite of different wind analysis methods, the CASP and CCIW fetch‐limited growth laws are consistent within the contexts of the two experiments. Differences among the estimated parameters are as large within the analyses of the three windows as they are among the three experiments we compare.