Optical, infrared and radio observations of the Seyfert galaxy Markarian 315

We report on new optical, infrared and radio observations of the Seyfert galaxy Markarian 315. We confirm the detection at all wavelengths of a secondary peak of emission, which lies ≈ 2 arcsec east of the Seyfert nucleus. Moreover, we detect a chain-like structure which surrounds the active nucleus, with peculiar behaviour westward of the nucleus. We consider different interpretations for the origin of the secondary peak emission.     

Climate response to astronomical forcing

Power spectrum analysis of the oxygen isotopic records of deep-sea cores cannot be directly used for correlation studies with the astronomical forcing functions because of the rapidity of the major deglaciations. The ensuing step change in the isotopic curves, repeated at somewhat irregular intervals, produces, in fact, substantial spectral energy in a wide frequency band that includes the frequencies of the precessional parameters.The isotopic fluctuations within the ramp sections of a composite core curve have been found to be highly correlated with the precessional parameters, indicating a linear response of climate to these parameters and verifying, at the same time, the essential correctness of the time scale adopted.A direct correlation of eccentricity with the major glacial/interglacial cycle is doubtful because some of the eccentricity minima have absolute values of the same order as some of the maxima, while the isotopic amplitude remains essentially constant. In order to test if the major cycle could be related to a terrestrial parameter exhibiting an asymmetric relaxation fluctuation, we have added an asymmetric saw-tooth function to an artificial curve constructed from the precessional parameters on the basis of optimal response amplitude. The curve thus generated reproduces the original isotopic curve with a similarity sufficient to warrant a close search and analysis of the relaxation process.     

Lunar glass compositions: Apollo 16 core sections 60002 and 60004

Approximately 500 glasses between 1 mm and 125 μm in size have been analyzed from fourteen samples from the Apollo 16 core sections 60002 and 60004. The majority of glasses have compositions comparable to those found in previous studies of lunar surface soils; however, two new and distinct glass compositions that are probably derived in part from mare material occur in the core samples. The major glass composition in all samples is that of Highland Basalt glass, but it also appears that high-K Fra Mauro Basalt (KREEP) glass is more common at the Apollo 16 site than was previously thought. The relative abundance of glasses within the core samples is random in distribution: each sample is characterized by a particular assemblage and distribution of the constituent glass compositions.     

40Ar-39Ar dating of high pressure metamorphic micas from the Gran Paradiso area (Western Alps): Evidence against the blocking temperature concept

The⁴⁰Ar-³⁹Ar method has been applied to high pressure (HP) white micas from the Gran Paradiso crystalline massif and from the overthrust Schistes Lustrés of its western slope. Preliminary petrographic and microanalytical investigation of the phengite micas showed that their celadonite-content decreases with time (from Si_3.65 to Si_3.05), and that less foliated samples are the most suitable for the metastable persistence of the high celadonite-content of the early HP stage during subsequent metamorphic evolution.Such samples were investigated together with one where mica is a pure retrogressive product. Two groups of plateau-ages have been found: (a) 60 to 75 Ma on HP phengites and early paragonites of unretrograded HP parageneses, thus dating the early HP metamorphic stage; (b) 38–40 Ma on HP phengites (most often in slightly retrograded HP parageneses) and on the purely retrogressive mica. For the HP phengites in (b), this age is considered to reflect the end of Ar readjustement during the later lowerP and/or higherT metamorphic stage, and not their crystallization.This disparity in plateau-ages for micas sampled within the same area shows that under the sameP-T conditions some systems were open while others remained closed. This can be closely related to the mineralogical behaviour: chemically active systems are isotopically active, whereby the reverse is not necessarily true. Thus, although temperature exceeded by far the usually assumed sealing-temperature of white micas, many systems have remained unaffected during the late Eocene event. Therefore, temperature cannot be the determining parameter for the opening of a system. Chemical reactivity, starting mineralogy and, primarily, pervasive deformation and the related fluid behaviour appear to be the effective controls.This implies that thermally activated diffusion processes (volume diffusion...) cannot be geologically significant. Consequently, the blocking temperature concept which rests on the opposite assumption now appears questionable. The fact that a mica does not necessarily behave as open above its blocking temperature necessitates at least a clear distinction between opening- and sealing-temperatures.     

Stable isotope studies of fluid inclusions in speleothems and their paleoclimatic significance

Fluid inclusions found trapped in speleothems (cave deposited travertine) are interpreted as samples of seepage water from which enclosing calcium carbonate was deposited. The inclusions are assumed to have preserved their D/H ratios since the time of deposition. Initial ¹⁸O/¹⁶O ratios can be inferred from δD because rain- and snow-derived seepage waters fall on the meteoric water line (δD = 8δ¹⁸O + 10). Estimates of temperature of deposition of the carbonate can be calculated from inclusion D/H ratios and δ¹⁸O of enclosing calcite in Pleistocene speleothems. For most speleothems investigated (0–200,000 yr old) δ¹⁸O of calcite appears to have decreased with increasing temperature of deposition indicating that the dominant cause of climate-dependent change in δ¹⁸O of calcite was the change in K_cw, the isotope fractionation equilibrium constant, with temperature; δ¹⁸O of meteoric precipitation generally increased with increasing temperature, but not sufficiently to compensate for the decrease in K_cw.     

Relations entre contraintes tectoniques et propriétés magnétiques des roches volcaniques permiennes de la vallée du Guil (briançonnais,Alpes Françaises)

Résumé Les roches volcaniques permiennes de la vallée du Guil présentent une ARN de direction voisine du plan de la schistosité alpine qui les affecte. Leur aimantation permienne a probablement été modifiée, lors de l'orogénèse alpine, par les efforts tectoniques (modification d'origine purement mécanique, ou acquisition d'une nouvelle aimantation par effet de pression). L'ARN des roches du Guil ne peut donc pas être prise en référence pour une étude géotectonique de l'arc alpin.

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Summary The Guil valley permian volcanic rocks have NRM whose direction is very near to the plane of alpine schistosity affecting these rocks. During the alpine orogeny, their permian magnetization was probably modified by tectonic stresses (mechanical modification, or new magnetization by piezo-magnetic effect). The NRM of the Guil valley rocks cannot be used as a reference for geotectonic study of the Alps.

     

Glacial stratigraphy of East and Central Jutland

Glaciostratigraphic investigations at one key locality (Haldum), 9 major and about 160 minor localities in East and Central Jutland, Denmark, together with laboratory work, have led to the establishment of a stratigraphy consisting of 10 till units, usually separated by meltwater deposits. The stratigraphy is in some degree supported by thermoluminescence datings. The complete sequence includes one till unit with associated meltwater deposits of Menapian age, three till units with intercalated meltwater deposits of Elsterian age, marine sediments deposited during the Holsteininan, and three till units with intercalated of Elsterian age, marine sediments deposited during the Holsteinian, and three till units with intercalated glaciofluvial sedimants of Saalian age. Eemian deposits are present above this level, and the whole sequence is capped by till and meltwater deposits related to three glacial advances during the Weichselian.     

Influence of cluster environments on X-ray cluster morphology

We investigated the influence of environment on cluster morphology by examining the alignment of the cluster position angle with respect to the nearest neighbour cluster. The cluster position angle and ellipticity were measured using high spatial resolution X-ray data taken from the Chandra archive, while the nearest neighbour sample was extracted from the Abell cluster catalogue. We found high confidence for an alignment when neighbour distance (Dn) was less than  70  h ⁻¹  Mpc, while we found no significant variations of the confidence level at various values of Dn less than  70  h ⁻¹  Mpc.