Lower Paleozoic extensional tectonics in the limit between the West Asturian-Leonese and Central Iberian Zones of the Variscan Fold-Belt in NW Spain

The limit between the West Asturian-Leonese and Central-Iberian Zones in the NW of the Iberian Peninsula is described in the area of Caurel-Truchas (Provinces of Orense and León). From the distribution of the sedimentary formations and the Variscan structures it is inferred that the transition between the two zones was a fault system, which was active during, at least, the Ordovician and Lower Silurian. The faults were supposedly normal, though they had probably some strike-slip component, and gave rise to a half-graben in which a syn-rift sequence was deposited. The latter underwent inversion at the onset of the Variscan tectonism, producing a ramp anticline-syncline pair that forms the more important folds in the area. The varying geometry of these folds is interpreted partly as being due to the existence of previous en échelon folds related to the strike-slip component of the faults and, partly, as a result of the variable intensity of the shear strain undergone during the first variscan phase.

---

Zusammenfassung Die Grenze zwischen der West-Asturischen-Leonesischen und Zentral-Iberischen Zone im NW der Iberischen Halbinsel wird aus dem Gebiet von Caurel-Truchas (Provinz Orense und León) beschrieben. Aufgrund der Verteilung der sedimentären Formationen, sowie der variszischen Strukturen wird abgeleitet, daß der Übergang zwischen den beiden Zonen durch ein Störungssystem bedingt wurde, das zumindest zwischen Ordovizium und Untersilur aktiv war. Dabei handelte es sich vermutlich um Abschiebungen mit einer Horizontalverschiebungskomponente. Diese Ausbildung führte zu einem Halbgraben mit darin abgelagerter sedimentärer Syn-Riftsequenz. Letztere wurde während der Anfangsphase der variszischen Tektonik invertiert, so daß es zu einem Rampen-Antiklinal-Synklinal Paar kam, welches die wichtigsten Falten der Gegend bildet. Die variable Geometrie der Falten wird zum einen der Existenz von frühen En-échelon Falten zugeschrieben, die durch die Horizontalverschiebungskomponente der Störungen hervorgerufen wurden; zum anderen sind sie das Resultat der veränderlichen Intensität der Scherspannung während der ersten variszischen Phase.

---

Resumen Se describe el límite entre las Zonas Asturoccidental-Leonesa y Centroibérica en el NO de la Península Ibérica en el área del Caurel-Truchas (Provincias de Orense y León). Partiendo de la distribución de las formaciones sedimentarias y de la geometría de las estructuras varíscicas, se deduce que la transición entre las dos zonas fue un sistema de fallas, que fue activo al menos durante el Ordovício y el Silúrico Inferior. Se supone que la principal componente de las fallas fue normal, aunque debió de existir también una componente de desgarre, y su juego originó un semi-graben en el que se acumuló una secuencia sin-rift. Esta última experimentó una inversión al principio de la tectogénesis Varíscica, formándose un par de pliegues de rampa que son los pliegues más importantes del área. La geometría variable de esos pliegues se interpreta como debida, en parte, a la existencia previa de pliegues en escalón relacionados con la componente de desgarre de las fallas y, en parte, como consecuencia de la variable intensidad de la deformación por cizallamiento sufrida durante la primera fase de deformación varíscica.

---

- - - Caurel-Truchas, Orense León. , , . , , . . , - . , - , , , , -, .

     

The oldest galactic open clusters: New CCD photometry and colour-magnitude diagrams

We present CCD photometry for stars in three fields centered on the old open cluster NGC 188 and in four fields on the intermediate-age cluster NGC 7789, which has been performed with the aim of investigating the HR diagram distribution of the cluster's Main-Sequence (MS) stars. A sufficiently well-defined sequence of subgiant, turn-off (TO), and MS stars have been detected, extending the observed lower MS down to aboutV=20 mag.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Direct barite determination using SEM/EDS-ACC system: implication for constraining barium carriers and barite preservation in marine sediments

Barite (BaSO₄) in marine sediments is considered as a proxy of surface ocean productivity and is widely used for paleo-productivity reconstructions. However, direct barite determination is not achieved by currently used methods, which rely on the measurement of total barium by inductively coupled plasma–mass spectrometry (ICP-MS) and instrumental neutron activation analysis (INAA) and correction from the allogenic Ba contribution. We report here on a technique that directly counts individual barite crystals using a scanning electron microscope (SEM) coupled to an energy dispersive spectrometer (EDS) equipped with an automated particle counting and classification (ACC) system. We show that barite–Ba concentrations can be deduced from the abundance, shape and size distributions of barite crystals with current precision and sensitivity as high as ±5 wt.% (2σ confidence limit) and 10 ppm, respectively. This technique, coupled with ICP-MS and INAA techniques for total Ba measurements, was applied to sediment samples from the tropical North Atlantic and the Central North Pacific oceans. Results show that: (1) barite and detrital aluminosilicates are the two main carriers of Ba in the investigated sediments; (2) calculated Ba/Al ratios range from 0.005 to 0.008 with an average value around 0.0066, in close agreement with previously reported values; (3) barite might not be the major source for released barium out of sediments and we suggest instead adsorbed barium as a potential source.     

Marine systems: moving into the genomics era

The study of biological systems has been revolutionized by the use of genomic technologies. Most of the knowledge gathered over the last few years refers to terrestrial models. The study of marine systems using genomic technologies has, apart from a focus on microbial systems, been generally neglected although there are signs that this situation may be changing. This review analyses recent progress made in the field of marine genomics and identifies the broad areas in which this new technology is having the greatest impacts. These studies include comparative, functional and environmental genomics of metazoan animals. In many cases, as well as benefiting marine science, studies on marine taxa are having wide‐ranging impacts on our global understanding of genomes and genomics.     

Wavimeter

A method of extracting wave parameters from surface displacement measured from a moving platform is presented. The article first presents a method for accurately measuring surface displacement using a single beam altimeter and heave sensor. A least squares approach is presented to estimate wave parameters using vessel velocity and perceived wave frequency that eliminates Doppler due to vessel motion. Two techniques for estimating wave frequency are presented: a block data method using MUSIC and a real-time method using demodulation. Sea trial results demonstrate that this method is as effective as a WaveRider buoy for estimating wave parameters.     

Benzo[a]pyrene-dione-stimulated oxyradical production by microsomes of digestive gland of the common mussel, Mytilus edulis L

The potential of benzo[ a]pyrene (BaP) quinones (diones) to stimulate NAD(P)H-dependent hydroxyl radical (·OH) production (2-keto-4-methiolbutyric acid (KMBA) oxidation) by digestive gland microsomes of M. edulis was studied using iron/EDTA as a promotor of the Haber-Weiss reaction (O₂⁻ + H₂O₂ = ·OH + OH⁻ + O₂). Stimulation of basal rates of KMBA oxidation was observed for all three diones. Stimulation was similar for the 1,6- and 3,6-diones, but much less for the 6,12-dione, and greater for the NADH than the NADPH-dependent reaction, viz. % increases of 78 to 333 (NADH) compared to 0 to 78 (NADPH). Maximal KMBA oxidation was obtained at dione concentrations of 12.5 to 50 μm. Inhibition of KMBA oxidation by Superoxide dismutase and catalase indicated the involvement of respectively Superoxide anion radical (O₂⁻) and hydrogen peroxide (H₂O₂) in 1,6-dione stimulated NADPH-dependent · OH formation. The apparent K_m values of xenobiotic-stimulated KMBA oxidation were lower for BaP-diones than for the model redox cycling quinone menadione (2-methyl-1,4-naphthoquinone), viz. in μm, 0.6 to 14.6 (NADH) and 4.4 to 28.5 (NADPH) compared to 315 to 457 (NADH) and 72 to 103 (NADPH). The results are consistent with metabolism of BaP to diones and resultant enhanced generation of oxyradicals being a potential mechanism of pollutant-mediated toxicity in molluscs.     

Cross-sectional areas of mid-ocean ridge axes bounding the Easter and Juan Fernandez microplates

We have calculated cross-sectional areas for the ridges bounding the Easter and Juan Fernandez microplates, 22°–28°S and 31°–35°S, obtaining accurate results where complete bathymetric data exist and estimates in other regions with partial bathymetric coverage and predicted bathymetry. We consider the reliability and usefulness of global predicted bathymetry in these calculations and the possible application of this dataset in other localities. The spreading rates on ridges bounding these microplates span the range from slow to superfast, allowing an investigation of ridge axis inflation over most of the rates active on Earth today. The across-axis areas of the Easter microplate ridge axes range from –29 km² to 7 km², while the Juan Fernandez ridge axis areas range from –27 km² to 8 km². Positive values correlate with regions usually interpreted as magmatically robust. Negative values arise from calculations in areas of propagating rift tips and deep grabens, such as Pito and Endeavor Deeps. Geochemical trends of Easter microplate axial basalts show decreasing MgO toward propagating rift tips and slight positive correlations between variables such as MgO vs. cross-sectional area, Na_8.0 vs. axial depth, and Na_8.0 vs. cross-sectional area. We document the decrease in the axial area approaching segment ends and propagating rift tips along both the West and East ridges of the microplates. On the Easter microplate both East and West ridge systems undergo large variations in spreading rate from >130 km Myr^–1 to <50 km Myr^–1. Inflation on these ridge segments is highly variable and only weakly correlated with spreading rate. On the Juan Fernandez microplate, West ridge spreading rates vary only between 115–140 km Myr^–1 and are systematically faster than on the East ridge, where rates vary between 10–35 km Myr^–1. Cross axis areas are systematically greater and significantly less variable on the faster spreading West ridge. Overall, compared to oceanic spreading centers bounding major plates with similar spreading rates, the axial areas are smaller on the microplate ridge systems, possibly because their rapidly changing configurations create a lag in the mantle response to the rigid plate boundary.     

North Atlantic winter eddy-driven jet and atmospheric blocking variability in the Community Earth System Model version 1 Large Ensemble simulations

Climate Dynamics - The atmospheric jet and blocking distributions, especially in the North Atlantic sector, have been challenging features for a climate model to realistically reproduce. This study...     

The invasive Asian green mussel Perna viridis in South Africa: all that is green is not viridis

The Asian green mussel Perna viridis is an invasive Indo-Pacific species recently reported from South African harbours. To verify the invasion, a phylogenetic (and morphological) analysis of green-shelled mussels (n = 39), found in six South African harbours, was conducted using the mitochondrial cytochrome c oxidase subunit I gene (COI). Estimates of genetic distances using the neighbour-joining analysis identified P. viridis only from Durban Harbour. All other green mussels were more than 3.2% divergent from P. viridis and were identified as green-shelled variants of indigenous P. perna. The only reliable morphological differences distinguishing the two species were the poorly developed mantle papillae and the wavy pallial line in P. viridis. The confirmed occurrence of P. viridis in a South African harbour suggests that there is a possible threat of the species becoming established and then spreading onto the open coast and competing with indigenous P. perna.