The geometry and petrogenesis of hydrothermal dolomites at Navan, Ireland

The dolomites at Navan, Ireland, formed in Courceyan peritidal and shallow-shelf limestones. The dolomite body has a plume-like geometry, cross-cutting both lithological boundaries and diagenetic barriers generated by sea-floor cementation and emergence. The dolomitizing fluids rose parallel to major faults to diffuse laterally through the succession, controlled by variations in permeability that reflect both facies variation on deposition and pre-dolomitization diagenesis. Cathodoluminescent zones reveal three principal stages of dolomite emplacement, separated by dissolution surfaces, with each stage reflecting several changes in the character of dolomitizing solutions. The predominance of dull zones indicates burial rather than surface conditions. The dolomites formed some time after burial in response to an areally limited hydrothermally-driven flow. Isotope values (σ¹⁸O of — 6σ6 to — 10.4%_δ and σ¹³C of — 0σ2 to +2σ5%_δ PDB), and fluid inclusion data, suggest that these fluids had compositions similar to those of Carboniferous seawater. However, these became hotter with time, with temperature increasing from 60 to 160δC. The Navan dolomites are closely associated with Europe's largest zinc-lead deposit. The distribution of the ores follows the same trend as that of the dolomites and paragenetic relationships indicate that dolomitization and mineralization were temporally and genetically related.     

Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean

It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin…     

Speed bumps and barricades in the carbon cycle: substrate structural effects on carbon cycling

The observation that a fraction of organic matter produced in marine systems evades the concerted efforts of microbial communities and is buried in sediments suggests that there are ‘speed bumps’ in carbon degradation pathways that impede microbially driven remineralization processes. The initial step in degradation of macromolecules, extracellular enzymatic hydrolysis, is often stated to be ‘the’ rate-limiting step in carbon remineralization. Experimental investigations described here, however, demonstrate that at least in certain cases, microbes produce extracellular enzymes on time scales of hours to tens of hours in response to substrate addition, and hydrolysis is extremely rapid. If enzymatic hydrolysis can be rapid, what factors slow or stop organic matter degradation? A lack of the correct inducer to initiate enzyme production, and/or a lack of the correct organism to produce the required enzyme, may result in a complete lack of hydrolysis in certain environments—a barricade, rather than a speed bump. Preliminary evidence supporting this hypothesis includes a comparison of polysaccharide hydrolysis in seawater and sediments, which demonstrates that the spectrum of enzymes active in seawater and sediments are fundamentally different. Furthermore, a survey of enzyme activities in surface waters from a range of locations suggests that pelagic microbial communities also differ widely in their abilities to express specific extracellular enzymes. Trans-membrane transport through porins is yet another potential location of structure-related selectivity.Our efforts to identify speed bumps and barricades are hampered by our inability to structurally characterize in sufficient detail the macromolecular structures present in marine systems. Furthermore, assessments of organic matter ‘quality’ from a chemical perspective do not necessarily accurately reflect the availability of organic carbon to microbial communities. For these communities, in fact, ‘quality’ may be a variable, which depends on the enzymatic and uptake capabilities of community members. To begin to assess substrate structure and quality from a microbial perspective, we will have to combine specific knowledge of macromolecular structures with detailed investigations of the enzymatic and transport capabilities of heterotrophic marine microbes.     

Stellar contents of two young open clusters: NGC 663 and 654

UBVRI CCD photometry in a wide field around two young open clusters, NGC 663 and 654, has been carried out. Hα and polarimetric observations for the cluster NGC 654 have also been obtained. We use the photometric data to construct colour–colour and colour–magnitude diagrams, from which we can investigate the reddening, age, mass and evolutionary states of the stellar contents of the these clusters. The reddening across the cluster regions is found to be variable. There is evidence for anomalous reddening law in both clusters; however, more infrared and polarimetric data are needed to conclude about the reddening law. Both clusters are situated at about a distance of 2.4 kpc. Star formation in both clusters is found to be a continuous process. In the case of NGC 663, star formation seems to have taken place sequentially, in the sense that formation of low-mass stars precedes the formation of most massive stars. Whereas, in the case of NGC 654, formation of low-mass stars did not cease after the formation of most massive stars in the cluster.     

Geochemical fixation of rare earth elements into secondary minerals in sandstones beneath a natural fission reactor at Bangombé, Gabon

To study geochemical processes for migration and fixation of fissiogenic rare earth elements (REE) in association with uranium dissolution, in situ isotopic analyses using an ion microprobe were performed on U- and REE-bearing secondary minerals, such as coffinite, françoisite, uraniferous goethite, and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at Bangombé, Gabon. Phosphate minerals such as phosphatian coffinite and françoisite with depleted ²³⁵U (²³⁵U/²³⁸U = 0.00609 to 0.00638) contained large amount of fissiogenic light REE, while micro-sized uraninite grains in a solid bitumen aggregate have normal U isotopic values (²³⁵U/²³⁸U = 0.00725) and small amount of fissiogenic REE components. The proportions of fissiogenic and non-fissiogenic REE components in four samples from the core of BAX03 vary in depth ranging from 30 cm to 130 cm beneath the reactor, which suggests mixing between fissiogenic isotopes from the reactor and non-fissiogenic isotopes from original minerals in the sandstone. Significant chemical fractionation was observed between Ce and the other REE in the secondary minerals, which shows evidence of an oxidizing atmosphere during their formation. Pb-isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of U-Pb decay system due to recent geologic alteration. However, systematic Pb-isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes, Pb and U from the reactor in association with dolerite dyke intrusion ∼0.798 Ga ago and the formation of the secondary minerals by mixing event between 2.05 Ga-old original minerals and reactor materials due to recent alteration.     

Engagement in the Third U.S. National Climate Assessment: commitment,capacity, and communication for impact

This paper examines the dynamics of energy investments and clean energy Research and Development (R&D) using a scenario-based modeling approach. Starting from the global scenarios proposed in the RoSE model ensemble experiment, we analyze the dynamics of investments under different assumptions regarding economic and population growth as well as availability of fossil fuel resources, in the absence of a climate policy. Our analysis indicates that economic growth and the speed of income convergence across countries matters for improvements in energy efficiency, both via dedicated R&D investments but mostly through capital-energy substitution. In contrast, fossil fuel prices, by changing the relative competitiveness of energy sources, create an economic opportunity for radical innovation in the energy sector. Indeed, our results suggest that fossil fuel availability is the key driver of investments in low carbon energy innovation. However, this innovation, by itself, is not sufficient to induce emission reductions compatible with climate stabilization objectives.     

Use of remote sensing in lineament analysis for tectonic evolution and resource study of a part of Vindhyan Basin,Jhalawar area,India

Synoptivity and the exemplified fracture systems exhibited by the space borne imagery data has helped in solving many of the geological enigma in various parts of the world. The study conducted, using such remotly sensed data, in Jhalawar anticline, part of Proterozoic Cratonic Vindhyan Basin, Rajasthan, India, led to infer the history of tectonic evolution of peribasinal deformation which has been a matter of controversy for a century and more. In Landsat MSS data the Jhalawar region displays a panorama of lineaments and their analysis through azimuthal frequency diagrams, isofracture, lineament incidence and lineament intersection incidence density maps shows that the mean orientation of the lineaments fall in NW-SE and NE-SW and the shape of the various lineament density contours also show NE-SW and NW-SE orientations. In aerial photographs the area exhibits four sets of lineaments in NE-SW, NW-SE, N-S and E-W directions. Amongst these the former two sets are expressed as wide open master fracture systems with prolific vegetation fills along them and the latter two sets are characteristically observed as thin vegetation linears with frequent strike slip faulting along them. The further analysis of these fracture/lineament systems derived from multi-level remote sensing data shows that the Jhalawar anticline, which followed the pattern of flexural slip fold mechanism, was evolved by horizontally disposed σ1 (greatest principal stress) and 3σ (least principal stress) with the former oriented in NE-SW and the latter aligned in NW-SE directions with vertically disposed 2σ. The inference of such palaeostress environment of the Jhalawar region lead in the identification of a buried rigid basement high southwest of Jhalawar anticline, beneath the Deccan pile and loci of ground water, silica sand and probable igneous plug.