The 2dF-SDSS LRG and QSO Survey: the spectroscopic QSO catalogue

We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG (luminous red galaxy) and QSO (2SLAQ) survey. This is a deep,  18 < g < 21.85  (extinction corrected), sample aimed at probing in detail the faint end of the broad line active galactic nuclei luminosity distribution at   z ≲ 2.6  . The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg² and contains new spectra of 16 326 objects, of which 8764 are QSOs and 7623 are newly discovered [the remainder were previously identified by the 2dF QSO Redshift Survey (2QZ) and SDSS]. The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12 702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission-line galaxies with a median redshift of   z = 0.22  .
We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host-galaxy contributions. This calculation shows that at   g ≃ 21.85  QSO colours are significantly affected by the presence of a host galaxy up to redshift   z ∼ 1  in the SDSS ugriz bands. In particular, we see a significant reddening of the objects in   g − i   towards the fainter g -band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2–3 Gyr.
The full catalogue, including completeness estimates, is available on-line at http://www.2slaq.info/ .     

A radar survey of M- and X-class asteroids II. Summary and synthesis

Using the S-band radar at Arecibo Observatory, we observed six new M-class main-belt asteroids (MBAs), and re-observed one, bringing the total number of Tholen M-class asteroids observed with radar to 19. The mean radar albedo for all our targets is , significantly higher than the mean radar albedo of every other class (Magri, C., Nolan, M.C., Ostro, S.J., Giorgini, J.D. [2007]. Icarus 186, 126-151). Seven of these objects (Asteroids 16 Psyche, 129 Antigone, 216 Kleopatra, 347 Pariana, 758 Mancunia, 779 Nina, 785 Zwetana) have radar albedos indicative of a very high metal content , and consistent with a remnant iron/nickel core interpretation (irons) or exotic high metal meteorite types such as CB. We propose designating these high radar albedo objects as Mm. Two asteroids, 110 Lydia and 678 Fredegundis, have more moderate radar albedos , but exhibit high values at some rotation phases suggesting a significant metal content. The remaining 10 objects have moderate radar albedos at all rotation phases. Most of our targets have visible/near-infrared spectra (Hardersen, P.S., Gaffey, M.J., Abell, P.A. [2005]. Icarus 175, 141-158; Fornasier, S., Clark, B.E., Dotto, E., Migliorini, A., Ockert-Bell, M., Barucci, M.A. [2009]. Icarus, submitted for publication) that indicate the presence of at least some silicate phases. All of the non-Mm asteroids show a positive correlation between visual and radar albedo but the reasons for this are not clear. All of the higher radar albedo targets (the 7 Mm asteroids, Lydia, and Fredegundis) show moderate to large variations in radar albedo with rotation phase. We suggest that their high radar reflectivity exaggerates irregularities in the asteroid shape to cause this behavior. One-third of our targets show evidence for asteroid-scale concavities or bifurcation. Based on all the evidence available, we suggest that most Tholen M-class asteroids are not remnant iron cores or enstatite chondrites, but rather collisional composites of silicates and irons with compositions more analogous to stony-iron meteorites and high-iron carbonaceous chondrites.     

Age of the peel sandstone group,isle of man

An Early Devonian age for the continental, red‐bed succession of the Peel Sandstone Group can be defined on the basis of: (1) a derived marine fauna of late Wenlock (Homerian) age, (2) a Scoyenia ichnofacies assemblage (including Beaconites and Diplichnites) characteristic of latest Silurian to Early Devonian (Lower Old Red Sandstone magnafacies) sediments in the British Isles, (3) a microflora of late Lochkovian to Pragian age, (4) a detrital palaeomagnetic remanence that pre‐dates local, Acadian palaeomagnetic directions and coincides with a prominent, southerly, Late Silurian to Early Devonian excursion in the local apparent polar wander path, and (5) a mid‐Devonian palaeomagnetic remanence that overprints (?)Acadian, thrust‐related folding. Data presented in this study confirm previous suggestions (Allen and Crowley 1983) that the Peel Sandstone Group represents a rare example of Early Devonian sedimentation preserved on the northern margin of the former Eastern Avalonia microcontinent. Potential correlations and linkages with other Lower Old Red Sandstone successions exposed in the Anglo‐Welsh Basin are developed and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Positive Relationship between Freshwater Inflow and Oyster Abundance in Galveston Bay,Texas

Analysis of fisheries-independent data for Galveston Bay, Texas, USA, since 1985 shows eastern oysters (Crassostrea virginica) frequently demonstrate increased abundance of market-sized oysters 1 to 2 years after years with increased freshwater inflow and decreased salinity. These analyses are compared to Turner’s (Estuaries and Coasts 29:345–352, 2006) study using 3-year running averages of oyster commercial harvest since 1950 in Galveston Bay. Turner’s results indicated an inverse relationship between freshwater inflow and commercial harvest with low harvest during years of high inflow and increased harvest during low flow years. Oyster populations may experience mass mortalities during extended periods of high inflow when low salinities are sustained. Conversely, oyster populations may be decimated during prolonged episodes of low flow when conditions favor oyster predators, parasites, and diseases with higher salinity optima. Turner’s (Estuaries and Coasts 29:345–352, 2006) analysis was motivated by a proposed project in a basin with abundant freshwater where the goal of the project was to substantially increase freshwater flow to the estuary in order to increase oyster harvest. We have the opposite concern that oysters will be harmed by projects that reduce flow, increase salinity, and increase the duration of higher salinity periods in a basin with increasing demand for limited freshwater. Turner’s study and our analysis reflect different aspects of the complex, important relationships between freshwater inflow, salinity, and oysters.     

The difficulties of dating mafic dykes: an Antarctic example

Archaen gneisses of the Vestfold Hills of East Antarctica are transected by several compositionally discrete suites of tholeiitic dykes. A representative of one of those suites, which has been dated in the present study, shows that not only Rb–Sr whole-rock isochrons, but also U–Pb zircon techniques (if not properly applied) can produce erroneous crystallisation ages. Two zircon populations were recovered from the mafic dyke itself, one of which is 2,483±9 Ma in age and clearly of xenocrystic origin. The other yields an age of 1,025±56 Ma, which is not ascribed to the magmatic crystallisation of the dyke, but rather to the time that it underwent metamorphic/metasomatic alteration as a response to high-grade tectonism in the adjacent mobile belt. It is presumed that the zircon in question formed by the breakdown of another mineral or minerals (possibly magmatic baddeleyite), due either to ingress of a siliceous fluid, or more probably by the release of silica from the breakdown of pyroxene to amphibole. A cogenetic 1–2 cm wide felsic vein, of late magmatic/early hydrothermal origin, also contains two zircon populations. Again, most of the grains therein, which are interpreted as of xenocrystic origin, grew at 2,483±9 Ma. However, a few euhedral zircons with very high U and Th contents grew at 1,248±4 Ma, which is taken to be the formation age of both the felsic vein and the enclosing mafic dyke.     

Lake circulation induced by density currents: an experimental approach*

This short note reports a series of density current experiments designed to model turbidity underflows caused by flood-stage discharge of lake-tributaries. In a 5.8 m long tank filled with freshwater, saltwater was fed in continuously, flowing down a 15°‘delta’ slope onto a horizontal floor. These density currents maintained steady state characteristics. The main objectives of this investigation were to determine (1) the flow regime of the density currents and (2) the underflow-induced movements in the freshwater. Reynolds numbers for thirty-five runs ranged from 70 to 4100. Experiments with laminar flow reproduced kinematic (Froudian) models of underflows measured in the Walensee (Switzerland). Flow was rapid on the slope (Froude number, Fr > 1) and tranquil (Fr<1) on the floor. Turbulent flow experiments yielded velocity profiles (with a maximum at the flow interface) which approximate natural conditions. Movements in formerly stagnant water body are induced by interfacial shear stress: a layer of freshwater is dragged along by the density current and replaced by the backward flow of an equal amount of overlying water (mass conservation). Extrapolated to a natural setting, circulation induced by underflows is probably an important mechanism for oxygenating deep lacustrine basins.     

Depositional environments and diagenesis in Lake Parakeelya: a Cambrian alkaline playa from the Officer Basin, South Australia

Laminated and desiccated siliceous dolostones, dolomitic mudstones and dolomitic sandstones in the Cambrian Parakeelya Alkali Member of the Observatory Hill Formation accumulated in an alkaline playa. Four facies are recognized (from lake centre to lake edge): lake, saline mudflat, dry mudflat and sandflat facies. The facies occur in cycles. Cycles of tens of metres thickness record the gradual expansion and contraction of the playa. Superimposed smaller cycles of tens of centimetres thickness record minor oscillations in the position of the strandline in a shallow lake. The dominance of saline mudflat, dry mudflat and sandflat facies indicates that the lake was rimmed by broad flat areas with negligible relief. The high δ¹⁸O values of primary and penecontemporaneous diagenetic carbonates of +24 to +28‰ (SMOW) indicate strong evaporation of ground and surface waters within the lake system. Calcite pseudomorphs of the sodium carbonate minerals trona and shortite have δ¹⁸O values between + 19 and + 22.5‰, and contain fluid inclusions with variable salinites and homogenization temperatures up to around 110°C. This suggests that the euhedral alkaline evaporites were dissolved by heated waters; calcite pseudomorphs then precipitated from a mixed solution formed by the interaction of these incoming fluids with the relatively saline interstitial brines. The sodium bicarbonate solutions formed by dissolution of the evaporites would have been dispersed by the basinal brines so that despite the closed drainage, further groundwater concentration did not take place.     

Pb isotopic composition,colour, and microstructure of monazites from a polymetamorphic rock in Antarctica

A moderate- to high-grade regionally metamorphosed paragneiss from Antarctica contains monazites of several different colours — brown, yellow and grey. Each colour type has a distinctive U-Pb isotopic composition which appears to result from different proportions of radiogenic Pb loss. Isotopic differences are neither related to La, Nd, Ce, P, Ca, Ti (and/or Ba), nor to U or Th content. All colour types have similar structures at the submicron scale, as determined by both conventional and high-resolution transmission electron microscopy (TEM). These show that the grains are essenttially non-metamict but are composed of 100 Å crystalline domains misoriented from each other by no more than 2× 10^–3 radians, and separated by narrow confused boundary regions where misorientation is probably accommodated by imperfect atomic arrangements. These regions of mismatch form potential zones of high permeability/diffusivity which are believed to be fundamental to the isotopic and colour differences between grains. Colour type is apparently related to the capacity of different minerals to shield included monazite grains from fluids circulating in the rock system.The well aligned monazite U — Pb analyses produce concordia intercepts of 2429 _–16 ⁺¹⁷ Ma and 1087±29 Ma. Both ages are comparable to those of major geological events in this part of Antarctica. They are interpreted in terms of isotopic resetting through Pb loss, and original monazite crystallisation is thought to have occurred somewhat earlier, possibly at the time this terrain first underwent granulite-facies metamorphism, about 3070 Ma ago.