Irish Carboniferous conodonts record maturation levels and the influence of tectonism, igneous activity and mineralization

Organic maturation patterns in the Lower Carboniferous of Ireland have been determined from conodont colour alteration indices (CAI) for some 750 localities. Onshore Ireland conodonts record increasing maturation in the Carboniferous rocks from the oil-window rocks of the north-east, southwards to the greenschist meta-argillite regime of the Munster Basin. In detail the Caledonoid trend has a marked influence in the Midlands, whilst in the south sharp variations in CAI are interpreted as being caused by thrusting of the Variscan Orogeny. In the south-east low maturities in the Wexford Half-graben indicate that the region was shielded from orogenic stresses, probably by the Leinster Massif. Igneous centres such as the Carlingford Complex and Croghan Hill produce local sites of increased palaeotemperature. Significant CAI variations have also been noted in proximity to major base-metal orebodies. The CAI results highlight north-east Ireland and the Wexford Half-Graben as areas with hydrocarbon potential.     

The eso nearby abell cluster survey (ENACS)

A statistically reliable distribution of velocity dispersions free from biases and systematic errors for a sample of ACO clusters is obtained. This distribution is compared with other data and model predictions.Published in Astrofizika, Vol. 38, No. 4, pp. 654–658, October–December, 1995.     

A comparison of FeO-rich,porphyritic olivine chondrules in unequilibrated chondrites and experimental analogues

Abstract Experimentally produced analogues of porphyritic olivine (PO) chondrules in ordinary chondrites provide an important insight into chondrule formation processes. We have studied experimental samples with PO textures grown at three different cooling rates (2, 5 and 100 *C/h), and samples that have been annealed at high temperatures (1000–1200 °C) subsequent to cooling. These are compared with natural chondrules of similar composition and texture from the ordinary chondrites Semarkona (LL3.0) and ALH 81251 (LL3.3). Zoning properties of olivine grains indicate that the Semarkona chondrules cooled at comparable rates to the experiments. Zoning in olivine from chondrules in ALH 81251 is not consistent with cooling alone but indicates that the chondrules underwent an annealing process. Chromium loss from olivine is very rapid during annealing and calculated diffusion coefficients for Cr in olivine are very similar to those of Fe-Mg interdiffusion coefficients under the same conditions. Annealed experimental samples contain an aluminous, low-Ca pyroxene which forms by reaction of olivine and liquid. No similar reaction texture is observed in ALH 81251 chondrules, and this may be evidence that annealing of the natural samples took place at considerably lower temperatures than the experimental analogues. The study supports the model of chondrule formation in a cool nebula and metamorphism of partly equilibrated chondrites during reheating episodes on the chondrite parent bodies.     

The Dynamics of Objects in the Inner Edgeworth–Kuiper Belt

Objects in 3:2 mean motion resonance with Neptune are protected from close encounters with Neptune by the resonance. Bodies in orbits with semi-major axis between 39.5 and about 42 AU are not protected by the resonance; indeed due to overlapping secular resonances, the eccentricities of orbits in this region are driven up so that a close encounter with Neptune becomes inevitable. It is thus expected that such orbits are unstable. The list of known Trans-Neptunian objects shows a deficiency in the number of objects in this gap compared to the 43–50 AU region, but the gap is not empty. We numerically integrate models for the initial population in the gap, and also all known objects over the age of the Solar System to determine what fraction can survive. We find that this fraction is significantly less than the ratio of the population in the gap to that in the main belt, suggesting that some mechanism must exist to introduce new members into the gap. By looking at the evolution of the test body orbits, we also determine the manner in which they are lost. Though all have close encounters with Neptune, in most cases this does not lead to ejection from the Solar System, but rather to a reduced perihelion distance causing close encounters with some or all of the other giant planets before being eventually lost from the system, with Saturn appearing to be the cause of the ejection of most of the objects.     

COUNTER-URBANIZATION IN SOCIETAL CONTEXT: LONG-DISTANCE MIGRATION TO THE HIGHLANDS AND ISLANDS OF SCOTLAND*

Recent growth in long-distance migration by non-Scots to remote parts of the Scottish Highlands is evaluated in relation to key explanatory themes in counter-urbanization literature: rural-urban convergence, expansion of the affluent middle class, and changing residential preferences. A survey of in-migrants' motivations and livelihood adjustments reveals the primacy of quality of life considerations and a ‘satisficing’ approach to work, lifestyle and residential location. It is concluded that peripheral area counter-urbanization could be maintained without the context of societal affluence that spawned the movement in the 1960s.     

Cyclic development of large,complex, calcite dendrite crystals in the Clinton travertine,Interior British Columbia,Canada

Bands of large (up to 4 cm long) three-dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near Clinton, British Columbia. The dendrites, with their long axes perpendicular to the terrace front, are characterized by numerous levels of branching. Each branch is formed of multitudes of skeletal rhombs, four- and six(?)-sided bipyramidal crystals, or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts. Although individual branches are formed of one type of subcrystal, neighbouring branches may be formed of different subcrystal types.Highly supersaturated waters that were generated by rapid CO₂ degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation. The presence of growth lines indicates that growth was episodic. Type I growth lines probably formed annually in response to seasonal climate changes whereas Type II growth lines, which formed less frequently, may reflect changes in the flow velocity and/or flow patterns of the spring waters.Early diagenetic modification of the dendrites involved crystal face enlargement, cements formed of trigonal prisms or needle-fiber crystals, microbial infestation that mediated substrate dissolution, and/or deposition of detrital calcite crystals that formed in the water column. Much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing.The dendrites in the Clinton travertine are an excellent example of complex, episodic calcite crystal growth that was extensively modified by early diagenetic processes in a surface environment. The same spring waters from which the dendrites were precipitated mediated much of the early diagenesis.