Rhyolitic ignimbrites in the region of Afyon (Central Anatolia)

Occurrence and field relations of an extensive ignimbrite sheet near Afyon in Central Anatolia are described. These rhyolitic ignimbrites are part of the important Neogene volcanic activity in Turkey and belong to the alignment of volcanic complexes along the inner border of the Taurian ranges. In close stratigraphical connection and in the same tectonic position as the rhyolites there occurs an assemblage of high-potassic, intermediate to basic volcanic rocks (alkali trachytes, mela-trachytes, latites and leucite-bearing rocks). Petrological and magmatological considerations led to the conclusion that the rhyolites and the potassic series, in spite of the close geological connection, are not related by processes of magmatic differentiation. Arguments in favour of an anatectic origin of the rhyolitic melt are presented. The occurrence of garnet and allanite as accessory minerals and as inclusions in the salic minerals of the ignimbrite are interpreted as relictic witnesses of a sialic parent rock. However, the trace elements, especially high Rb connected with low Sr, Ba and Zr and K/Rb ratios below 100 give a pattern generally explained by strong fractionation processes.     

Origin of rhyolites by anatectic melting of granitic crustal rocks

Rhyolitic pumice deposits on some East Aegean Islands are the remnants of a tuff sheet which covered formerly more than 2500 km². The rhyolites originated by melting of granitic crustal rocks. The petrological properties leading to this conclusion are as follows:

-mineralogical composition of the pumice being 60 wt % of glass and 40 % of relictic granitic minerals (quartz, plagioclase, potash feldspar, biotite) in «phenocrysts» up to 1 cm Ø.

-phenomena of strong corrosion, resorption and melting of all light colored «phenocrysts» in the rhyolitic pumice.

-mineralogical and chemical identity between pumice and granitic xenolites found in great quantity in the pumice tuff.

-structurally transitional types between pumice and the granites in different state of melting.

-eutectic composition of the pumice glass for a pressure of 2 kb.

     

Über das Alter von Rundhöckern bei Lysekil (Bohuslän) an der schwedischen Skagerrak-Küste

Zusammenfassung In Bohuslän an der schwedischen Skagerrak-Küste befinden sich bei Lysekil Rundhöcker, die aus klüftigem Granit bestehen. Das Gefügeinventar ist sehr umfangreich, doch fällt eine Hauptrichtung auf, welche die Eisbewegung steuerte. Außer den tektonischen Klüften tritt die Entspannungsklüftung in ihrer typischen Art insofern auf, als sie morphoparallel ist und die Außenform der Rundhöcker nachbildet. Durch das Vorhandensein einer Diskordanz zwischen der Aufgleitfläche des Eises und den Entspannungsflächen im Granit ist über das Alter der Rundhöcker auszusagen, daß ihre Anlage älter als die Eisbedeckung ist. Das Eis benutzte die Entspannungsflächen teilweise als Bewegungsbahn oder kappte sie. Das Alter der Rundhöcker und ihre räumliche Anordnung wird daher präglazial sein und ist in das Tertiär zu stellen. Die vorgefundenen älteren Formen überprägte das Eis oft am stärksten auf der Leeseite und schuf dann steilwandige Nischen mit ortsfremden Findlingen als Inhalt.

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In the Bohuslän District, on the Swedish Skagerrak coast, humps may be found near Lysekil, which consist of jointed granite. The fabric is very comprehensive, but there is one main direction guiding the ice movement. Besides these joints, there are relaxation planes in their typical formations; they run parallel to the morphology and re-shape the exterior forms of the humps.The presence of a discordance between the gliding surface and the relaxation planes in the granite determines the age of the humps, i. e., their origin is older than the ice cover. The ice made use of these planes by moving on or by cutting them. The age of the humps and their arrangement in space should, therefore, be preglacial and be assigned to the tertiary. The older forms encountered re-formed the ice most strongly on the leeward side, and there are precipitous niches containing erratic blocks.

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Résumé A Bohuslän sur la côte suédoise de Skagerrak se trouvent à côté de Lysekil des roches moutonnées, formées de granit diaclase. La structure en question est très riche, mais une direction principale se distingue, celle qui réglait le mouvement glaciaire. Apart les diaclases intervient une diaclase de relaxation dans sa forme typique aussi loin qu'elle est morphoparallèle et qu'elle imite la forme extérieure des roches moutonnées. A travers l'existence d'une discordance mécanique entre la surface de glissement du glacier et les surfaces de relaxation dans le granit peut on déterminer l'âge des roches moutonnées, que leur formation est plus vieille que celle de la couverture glaciaire. Le glacier utilisait les surfaces de relaxation comme voie de déplacement, ou bien il les coupait. C'est pour cela que l'âge des roches moutonnées et leur disposition dans l'éspace est préglacial, et est à ranger dans l'ère tertiaire. Le glacier influença les anciennes formes trouvées, souvent le plus fort sur le côté sous le vent, et fit des nids à falaises abruptes contenant des blocs erratiques venant d'autre part.

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IUE observations of faint comets

Ultraviolet spectra of seven comets taken with the same instrument are presented. Comets P/Encke (1980), P/Tuttle (1980 h), P/Stephan-Oterma (1980 g), and Meier (1980 q) were observed during November-December 1980 with the International Ultraviolet Explorer (IUE) satellite observatory, while comets P/Borrelly (1980 i) and Panther (1980 u) were observed with IUE on 6 March 1981. The spectra of these comets are compared with those of comet Bradfield (1979 X), studied extensively earlier in 1980 with IUE, as well as with each other. In order to simplify the interpretation of the data and to minimize the dependence upon a specific model, the spectra are compared at approximately the same value of heliocentric distance whenever possible. Effects due to heliocentric velocity, geocentric distance, and optical depth are also discussed. All of the cometary spectra are remarkably similar, which suggests that these comets may have a common composition and origin.     

The Rio Sassito sedimentary succession (Ordovician): a pinpoint in the geodynamic evolution of the Argentine Precordillera

In the Precordillera of western Argentina, an isolated outcrop of Llandeilian siliciclastics and Caradocian limestones (Rio Sassito succession) reveals a complex interplay between the tectonic and the sedimentary history of the Precordillera during Middle and Late Ordovician times. The succession is composed of a lower siliciclastic interval and an upper carbonate interval and is bounded below and above by erosional unconformities. Dating of these unconformities, which in many places merged to form one single surface, demonstrates that the most important erosional event took place prior to the deposition of the Rio Sassito succession. This erosional event is correlated to extensional tectonics during continental breakup and the separation of the Precordillera from Laurentia. Block faulting with the formation of horst and graben structures provided the topography for the establishment of a pelagic carbonate platform during the Caradoc. In our view, there are no indications that these phenomena are related to the accretion of the Precordillera to Gondwana or to the formation of an Ordovician supercontinent. The carbonate sediments are typical of temperate-water settings, characterized by the absence of ooids, oncoids, and algae, and by the presence of abundant abraded bioclasts, intraclasts, and peloids. The inference of a temperate-water environment does not, as previously supposed, indicate the accretion of the Precordillera to Gondwana, but is more likely related to global cooling prior to the Ashgillian glaciation.     

Alkalibasalts from the Tyrrhenian sea Basin: Magmatic and geodynamic significance

Petrological characteristics of basaltic rocks from the Tyrrhenian deep-sea are discussed and related to the geotectonic situation. For the first time, distinctly alkaline basalts (hawaiites) have been found in the Tyrrhenian deep-sea. These are typical within-plate basalts related to the tensional fracturing of the Tyrrhenian area. A suggested age of 100,000 years is among the youngest indications for the Tyrrhenian Sea volcanism. Since the Miocene, magmatic activity in the inner Tyrrhenian sea basin evolved from ocean-floor basalts to ocean island tholeiites and transitional basalts, with alkaline basalts as the most recent products. Seamounts in the southern part of the Tyrrhenian deep-sea (Palinuro, Marsili) add shoshonitic and calcalkaline lavas (some with high Mgvalue) to the complexity of the Tyrrhenian magmatic evolution.     

Effects of large organic material on channel form and fluvial processes

Stream channel development in forested areas is profoundly influenced by large organic debris (logs, limbs and rootwads greater than 10 cm in diameter) in the channels. In low gradient meandering streams large organic debris enters the channel through bank erosion, mass wasting, blowdown, and collapse of trees due to ice loading. In small streams large organic debris may locally influence channel morphology and sediment transport processes because the stream may not have the competency to redistribute the debris. In larger streams flowing water may move large organic debris, concentrating it into distinct accumulations (debris jams). Organic debris may greatly affect channel form and process by: increasing or decreasing stability of stream banks; influencing development of midchannel bars and short braided reaches; and facilitating, with other favourable circumstances, development of meander cutoffs. In steep gradient mountain streams organic debris may enter the channel by all the processes mentioned for low gradient streams. In addition, considerable debris may also enter the channel by way of debris avalanches or debris torrents. In small to intermediate size mountain streams with steep valley walls and little or no floodplain or flat valley floor, the effects of large organic debris on the fluvial processes and channel form may be very significant. Debris jams may locally accelerate or retard channel bed and bank erosion and/or deposition; create sites for significant sediment storage; and produce a stepped channel profile, herein referred to as ‘organic stepping’, which provides for variable channel morphology and flow conditions. The effect of live or dead trees anchored by rootwads into the stream bank may not only greatly retard bank erosion but also influence channel width and the development of small scour holes along the channel beneath tree roots. Once trees fall into the stream, their influence on the channel form and process may be quite different than when they were defending the banks, and, depending on the size of the debris, size of the stream, and many other factors, their effects range from insignificant to very important.     

Diet and gill morphology of the East Coast redeye round herring Etrumeus wongratanai off KwaZulu-Natal,South Africa

Stomach content analyses and measurements of gillraker morphology were used to assess the diet and feeding ecology of the East Coast redeye round herring Etrumeus wongratanai and provide data for comparisons with other small pelagic fishes off South Africa. Samples were collected by jigging from a kayak off Scottburgh, KwaZulu-Natal (KZN), over the period July 2013–May 2014. In total, 66 stomachs (containing 4 407 prey items) and 66 gill arches were examined. Stomach content analyses indicated that East Coast redeye round herring, at the time of sampling, fed on large (1 500–2 500?µm) particles, with ～2 500?µm particles making the greatest contribution to dietary carbon. The species feeds on larger particles than do anchovy Engraulis encrasicolus and sardine Sardinops sagax, but on particles of a similar size to those consumed by West Coast redeye round herring Etrumeus whiteheadi. There were significant differences in mean gillraker gaps between East Coast redeye round herring and both sardine and anchovy, but not between East Coast and West Coast redeye round herring. The differences in gillraker gaps between East Coast redeye round herring, sardine and anchovy are indicative of resource partitioning through differential feeding, based on zooplankton size. The data suggest that there is no resource partitioning between East and West coast redeye round herring, indicating that competition is likely to occur between them. However, such competition is minimised by limited spatial overlap between these two species.     

Evidence for surface variegation in Rosetta OSIRIS images of asteroid 2867 Šteins

The OSIRIS camera onboard Rosetta successfully acquired images of asteroid 2867 Steins through a variety of color filters during the flyby on 5 September 2008. The best images of this 5 km diameter asteroid have a resolution of 78 m per pixel. We process the images by deconvolving with the point spread function and enlarging through the Mitchell-Netravali filter. The enhanced set is analyzed by means of various techniques (PCA, band ratios, stereo anaglyphs) to study surface morphology and search for variegation. We identify a landslide, which supports a YORP origin for Steins’ unusual diamond shape. In addition, we find that the interior of one of two large craters on the south pole is bluer than the rest of the body.