Dynamic interaction between impact melt and fragmented basement at Manicouagan: The suevite connection

The interface between impact melt rocks and underlying footwall lithologies within the Manicouagan impact structure is defined by a zone of dynamic mixing (<20 m thick). This zone transitions as a continuum from clast‐free to clast‐bearing impact melt rocks, through melt‐bearing breccias to melt‐free breccias. Field observations; microscopy; and major, trace, and rare earth element analysis indicate that the breccias are derived by blending two endmembers during the impact process: impact melt and brecciated footwall. The product is a basal breccia sequence, which locally includes the rock type referred to as suevite. In this occurrence, the suevite is a submelt sheet variety, in contrast to similar lithologies that are developed atop impact melt sheets, or beyond crater rims. Dynamic mixing between impact melt and basal clastic material at Manicouagan is attributed to the initial high‐speed centrifugal outflow of superheated, low viscosity impact melt over underlying fractured and fragmented footwall, and its centripetal return during the earlier stages of the crater modification process. The interaction of two fluids (melt with a mobilized granular medium) possessing contrasting densities, and moving at different velocities, can facilitate shear instabilities and turbulent mixing that may be characteristic of Kelvin–Helmholtz behavior.     

Impact of rainfall on the hygienic quality of blue mussels and water in urban areas in the Inner Oslofjord,Norway

The effects of precipitation on the hygienic quality of water and blue mussels collected from five different localities in the urban areas in the Inner Oslofjord were investigated, with samples analysed for Escherichia coli, Salmonella spp., pathogenic Vibrio spp., Norovirus, Sapovirus, Cryptosporidium spp. and Giardia duodenalis. The sampling sites were located at varying distances from the outlet of combined sewer overflows (CSO)-impacted rivers/streams. In general, 1–3 log₁₀ increases in fecal indicator bacteria and human pathogens were observed after heavy rainfalls. Blue mussels appeared to be a useful indicator of the impact of sewage at these sites, and generally a good correlation was identified between concentrations of E. coli and other human pathogens in the mussels. Provision of general advice to the public of avoiding areas near the outlets of CSO-impacted rivers after heavy rainfall may reduce the risk of gastroenteritis by bathers and others that may swallow water during recreational activities.     

Trophic relationships in tidepool fish assemblages of the tropical Southwestern Atlantic

Trophic studies are fundamental to understanding the dynamics of assemblages and functional roles of species within ecosystems, contributing to the identification of factors responsible for the organization and structure of communities. This study aimed to analyse the trophic organization of tidepool fish assemblages in the tropical Southwestern Atlantic, based on the underlying idea that food resources are not limiting and that trophic guild formation is not driven by food competition. Diets were based on feeding index values of food categories for 12 representative species collected in six tidepools (20º49′ S, 40º36′ W) at quarterly intervals (2005 to 2007). The main food categories were small crustaceans, polychaetes and macroalgae. Multivariate techniques evidenced two multispecific trophic guilds: small‐prey carnivores, including Bathygobius soporator, Bathygobius geminatus, Malacoctenus delalandii and Halichoeres poeyi, and herbivores, including Sparisoma axillare and Acanthurus bahianus. Other species presented significantly different diets and were classified into the following guilds: omnivores feeding on filamentous algae and copepods (Abudefduf saxatilis); large‐prey carnivores (Labrisomus nuchipinnis); omnivores feeding on polychaetes and filamentous algae (Stegastes fuscus); and polychaete feeders (Ahlia egmontis). Gymnothorax funebris and Gymnothorax moringa were classified as carcinophagores and piscivores, respectively. Trophic organization appears related to species convergence toward the use of abundant food resources, driven by a combination of factors allowing some resource partitioning through inter‐specific differences in consumer size, microhabitat, behavior, and trophic specialization.     

Structural imaging of Mesozoic sediments of Kachchh,India, and their hydrocarbon prospects

Travel-time modelling of first and second arrivals has been used to produce P-wave velocity models of the shallow sub-surface structure of Kachchh, India, using new wide-angle reflection/refraction profiles. Results obtained from the 2-D tomographic modelling have also been corroborated with magnetotelluric and borehole data within the proximity of these profiles. Based on multiple geophysical data, a composite sub-surface model is presented in this article. The prominent features of the model include the presence of more than 3 km thick Mesozoic sediments residing above the Precambrian basement. Its correlation with available lithological knowledge shows that the Mesozoic rocks have been deposited from early Triassic to late Cretaceous until the eruption of the Deccan Flood basalts at the Cretaceous-Tertiary boundary. The new results suggest that the Mesozoic rocks of Kachchh can be sub-divided in two major parts which correspond to late and early Mesozoic deposits respectively. The sub-surface models successfully demarcate the regional variations in the basaltic layer across the region and show maximum thickness of 1.2 km. The modelling results also exhibit that the Precambrian basement in this region varies between 4 and 6 km depth. The new data provide a much clearer picture than was hitherto available of the entire sedimentary succession in the basins that underlie the Kachchh region. They show a significant variability in thickness of the various sedimentary layers, and in particular illustrate a marked topographic irregularity at the base of the sedimentary succession.     

Visible–near infrared spectral indices for mapping mineralogy and chemistry with OSIRIS‐REx

The primary objective of the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS‐REx) mission is to return to Earth a pristine sample of carbonaceous material from the primitive asteroid (101955) Bennu. To support compositional mapping of Bennu as part of sample site selection and characterization, we tested 95 spectral indices on visible to near infrared laboratory reflectance data from minerals and carbonaceous meteorites. Our aim was to determine which indices reliably identify spectral features of interest. Most spectral indices had high positive detection rates when applied to spectra of pure, single‐component materials. The meteorite spectra have fewer and weaker absorption features and, as a result, fewer detections with the spectral indices. Indices targeting absorptions at 0.7 and 2.7–3 μm, which are attributable to hydrated minerals, were most successful for the meteorites. Based on these results, we identified a set of 17 indices that are most likely to be useful at Bennu. These indices detect olivines, pyroxenes, carbonates, water/OH‐bearing minerals, serpentines, ferric minerals, and organics. Particle size and albedo are known to affect band depth but had a negligible impact on interpretive success with spectral indices. Preliminary analysis of the disk‐integrated Bennu spectrum with these indices is consistent with expectations given the observed absorption near 3 μm. Our study prioritizes spectral indices to be used for OSIRIS‐REx spectral analysis and mapping and informs the reliability of all index‐derived data products, including a science value map for sample site selection.     

Gender and occupational perspectives on adaptation to climate extremes in the Afram Plains of Ghana

Although sub-Saharan Africa does not contribute significantly to greenhouse gas emissions, significant adverse impacts of climate change are anticipated in this region. Countries in West Africa, which are heavily dependent on rain-fed agriculture, are projected to experience more frequent and intense droughts, altered rainfall patterns and increases in temperature through the end of this century. Changes in hydrology and temperature are likely to affect crop yields, thereby placing pressure on scarce resources in a region that is characterised by limited social, political, technical and financial resources. The success with which communities cope with the impacts of climate change is influenced by existing conditions, forces and characteristics which are peculiar to each of these communities. This paper assesses the preferred adaptation strategies during floods and droughts of males and females in three different occupations (farming, fishing, and charcoal production). Findings are based upon an analysis of focus group discussions and a ranking of preferred adaptation options in three communities in the Afram Plains of Ghana. Assessments of this nature should aid in the selection and implementation of adaptation options for communities and households, which is the level at which climate change adaptation is likely to occur in West Africa.     

The Manicouagan impact structure as a terrestrial analogue site for lunar and martian planetary science

The 90 km diameter, late Triassic Manicouagan impact structure of Québec, Canada, is a well-preserved, undeformed complex crater possessing an anorthositic central uplift and a 55 km diameter melt sheet. As such, it provides a valuable terrestrial analogue for impact structures developed on other planetary bodies, especially the Moon and Mars, which are currently the focus of exploration initiatives. The scientific value of Manicouagan has recently been enhanced due to the production, between 1994 and 2006, of ∼18 km of drill core from 38 holes by the mineral exploration industry. Three of these holes are in excess of 1.5 km deep, with the deepest reaching 1.8 km. Here we combine recent field work, sampling and the drill core data with previous knowledge to provide insight into processes occurring at Manicouagan and, by inference, within extraterrestrial impact structures. Four areas of comparative planetology are discussed: impact melt sheets, central uplifts, impact-generated hydrothermal regimes and footwall breccias. Human training and instrument testing opportunities are also considered. The drill core reveals that the impact melt and clast-bearing impact melts in the centre of the structure reach thicknesses of 1.4 km. The 1.1 km thick impact melt has undergone differentiation to yield a lower monzodiorite, a transitional quartz monzodiorite and an upper quartz monzonite sequence. This calls into question the previous citing of Manicouagan as an exemplar of a relatively large crater possessing an undifferentiated melt sheet, which was used as a rationale for assigning different composition lunar impact melts and clast-bearing impact melts to separate cratering events. The predominantly anorthositic central uplift at Manicouagan is comparable to certain lunar highlands material, with morphometric analogies to the King, Tycho, Pythagoras, Jackson, and Copernicus impact structures, which have similar diameters and uplift structure. Excellent exposure of the Manicouagan uplift facilitates mapping and an appraisal of its formation and collapse mechanisms, enhanced by drill core data from the centre of the structure. Recent field studies at the edge of the central island at Manicouagan, and multiple drill core sections through footwall lithologies, provide insight into allochthonous (clastic and suevitic) and autochthonous breccia formation, as well as shock effects. The hydrothermal regimes developed at Manicouagan are akin to systems proposed for Noachian (>3.5 Ga) Mars that involve alteration of impact melts via meteoritic and surface waters, with the generation of phyllosilicates, zeolites, hematite, sulfates and sulfides that can contribute to martian soil formation and sedimentation processes.     

Will climate change impact on wind power development in the UK?

Partly in response to concerns about anthropogenic climate change, renewable energy production is growing rapidly in the United Kingdom (UK). The wind power industry takes advantage of the country having some of the highest mean wind speeds in Europe. Future climate change, however, has the potential to alter the characteristics of the UK wind climate. Small changes in mean wind speed could produce much greater changes in wind energy output as the power generated is related to the cube of wind speed. This paper aims to use a simple method to provide insight into projected future UK wind climate and how this might differ from current patterns. A discussion of the scale of the projected impacts on the wind energy industry follows.     

Pressure effects on the joint elastic‐electrical properties of reservoir sandstones

We conducted a laboratory study of the joint elastic‐electrical properties of sixty‐three brine‐saturated sandstone samples to assess the likely impact of differential pressure (confining minus pore fluid pressures) in the range 8–60 MPa on the joint interpretation of marine seismic and controlled‐source electromagnetic survey data. The samples showed a wide range of petrophysical properties representative of most sandstone reservoirs. We found that a regression equation comprising both a constant and an exponential part gave a good fit to the pressure dependence of all five measured geophysical parameters (ultrasonic P‐ and S‐wave velocity, attenuation and electrical resistivity). Electrical resistivity was more pressure‐sensitive in clay‐rich sandstones with higher concentrations of low aspect ratio pores and micropores than in clean sandstones. Attenuation was more pressure‐sensitive in clean sandstones with large open pores (macropores) than in clay‐rich sandstones. Pore shape did not show any influence on the pressure sensitivity of elastic velocity. As differential pressure increases, the effect of the low aspect ratio pores and micropores on electrical resistivity becomes stronger than the effect of the macropores on attenuation. Further analysis of correlations among the five parameters as a function of pressure revealed potentially diagnostic relationships for geopressure prediction in reservoir sandstones.