Vertebrates from the Late Triassic Thecodontosaurus-bearing rocks of Durdham Down,Clifton (Bristol,UK)

Since the discovery of the basal sauropodomorph dinosaur Thecodontosaurus in the 1830s, the associated fauna from the Triassic fissures at Durdham Down (Bristol, UK) has not been investigated, largely because the quarries are built over. Other fissure sites around the Bristol Channel show that dinosaurs represented a minor part of the fauna of the Late Triassic archipelago. Here we present data on microvertebrates from the original Durdham Down fissure rocks, which considerably expand the taxonomic diversity of the island fauna, revealing that it was dominated by the sphenodontian Diphydontosaurus, and that archosauromorphs, including sphenosuchian crocodylomorphs, coelophysoid theropods, and the basal sauropodomorph Thecodontosaurus, were diverse. Importantly, a few fish teeth provide new information about the debated age of the fissure deposit, which is identified as lower Rhaetian. Thecodontosaurus had been assigned an age range over 20–25 Myr of the Late Triassic, so this narrower age determination (209.5–204 Myr) is important for studies of early dinosaurian evolution.     

Explosion quakes at Stromboli (Italy)

This paper reports the results of two seismic experiments aimed at determining the wave field of explosion quakes at Stromboli Island (Mediterranean Sea, Southern Italy). The typical Strombolian activity mostly consists of explosive phenomena causing pyroclastic, materials to be emitted together with jets of volcanic gases from one or more craters. Stromboli is an active volcano characterized by persistent seismic activity consisting of explosion quakes that are seismic events associated with the explosive volcanic phenomena. Explosion quakes are short lived seismic events occurring intermittently whose amplitude tends to decrease with distance from the vent. A distinctive feature of explosion quakes is the presence on seismograms of two, often clearly distinct, seismic phases. The first, low-frequency seismic phase (<2 Hz) is in fact usually followed by a high-frequency seismic phase (>3–4 Hz) after one second or more. The first seismic phase of explosion quakes has been shown to be characterized by a nearly radial linear polarization and by an apparent propagation velocity estimated at 600–800 m/s. The second phase is characterized by a more chaotic motion and a lower apparent propagation velocity of 150–450 m/s. The wavefield associated with the first low-frequency seismic phase appears to be generated by a resonating P-wave seismic source accompanying gas explosion and emission of pyroclastic materials. The wavefield associated with the second high-frequency seismic phase of explosion quakes appears to be mainly composed of scattered and converted waves due to the critical topography of the volcano.     

MIDI observations of 1459 Magnya: First attempt of interferometric observations of asteroids with the VLTI

The Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) can be used to obtain direct determination of the sizes and the albedos of asteroids. We present results of the first attempt to carry out interferometric observations of asteroids with the Mid Infrared Interferometric Instrument (MIDI) at the VLTI. Our target was 1459 Magnya. This is the only V-type asteroid known to exist in the outer main-belt, and its IRAS-albedo turns out to be rather low for an object of this taxonomic class. Interferometric fringes were not detected, very likely due to the fact that the flux emitted by the asteroid was lower than expected and below the MIDI threshold for fringe detection. However, by fitting the Standard Thermal Model to the N-band infrared flux measured by MIDI in photometric mode and to the visible absolute magnitude, obtained from quasi-simultaneous B- and V-band photometric observations, we have derived a geometric visible albedo of 0.37±0.06 and an effective diameter of 17±1 km. This new estimate of the albedo differs from that previously obtained by IRAS and is more consistent with the V-type taxonomic classification of 1459 Magnya.     

Thorough wetting and drainage of a peat lysimeter in a climate change scenario

A peat deposit (Zennare basin, Venice coastland, Italy) was monitored in previous field studies to investigate the hydrological response of organic soil to meteorological dynamics. Field tests and modelling predictions highlighted the risk of the complete loss of this peat layer during the next 50 years, due to oxidation enhanced by the increased frequency of warmer periods. Unfortunately, despite the considerable impacts that are expected to affect peat bogs (in this area and worldwide), only a few experimental studies have been carried out to assess the hydrologic response of peat to severe water scarcity. Because of that, an undisturbed 0.7 m³ peat monolith was collected, transferred to the laboratory and instrumented. The total weight (representative of the water content dynamics of the peat monolith as a whole), and two vertical profiles of matric potentials and water content were monitored in controlled water-scarce conditions. After an extended air-drying period, the monolith was used as an undisturbed peat lysimeter and a complete cycle of wetting and drainage was performed. Supplementary measurements of matric potential ψ and water content θ were collected by testing peat subsamples on a suction table apparatus. A set of water retention curves was determined in a range of matric potentials broader (ψ down to −7 m) than the current natural conditions in the field (minimum ψ = −1 m). While water content at saturation showed values similar to those in the original natural conditions (θ ≅ 0.8), a remarkable loss of water holding capacity (even for low potentials) has been highlighted, especially in deep layers that are now permanently below the water table. The retention curves changed shape and values, with a more pronounced hysteresis visible in an increasing distance between wetting and drying data. Hydraulic non-equilibrium between the water content and water potential could be a possible cause and it is worth modelling in future studies. The parameters of the van Genuchten retention curves were obtained for the wetting and the drying phases.     

Discrimination between wave‐ravinement surfaces and bedset boundaries in Pliocene shallow‐marine deposits,Crotone Basin,southern Italy: An integrated sedimentological,micropalaeontological and mineralogical approach

The lower Pliocene Belvedere Formation, cropping out in the Crotone Basin, southern Italy, exhibits a metre‐scale to decametre‐scale shallow‐marine cyclicity that shares features of both high‐frequency sequences linked to shoreline shifts and controlled by minor relative sea‐level and/or sediment supply changes, and sedimentological cycles unrelated to shoreline shifts. In order to better understand the high‐frequency sequence stratigraphic framework of this succession, an integration of sedimentological, micropalaeontological (micro‐foraminifera assemblages) and mineralogical (heavy mineral abundance) data is used. From a sedimentological/stratigraphic point of view, wave‐ravinement surfaces bounding high‐frequency sequences, and associated substrate‐controlled ichnofacies, are prominent in outcrop and document environmental and water‐depth changes, whereas bedset boundaries separating sedimentological cycles have a more subtle field appearance and are only associated with changes of environmental energy. Moreover, condensed deposits are present only above wave‐ravinement surfaces, and the high‐frequency sequences bounded by these surfaces have a thickness that is an order of magnitude greater than that of the bedsets. Micro‐foraminifera assemblages may change, and the content of heavy minerals usually increases, across wave‐ravinement surfaces, whereas both parameters do not change significantly across bedset boundaries. The abundance of heavy minerals is systematically higher, with respect to the underlying and overlying deposits, in the condensed shell beds that overlie wave‐ravinement surfaces. An integrated sedimentological, micropalaeontological and mineralogical approach represents a powerful tool to discriminate between wave‐ravinement surfaces bounding high‐frequency sequences and bedset boundaries, and in general to investigate at the intra high‐frequency sequence scale. This integrated approach is expected to be very useful in the study of potentially all shallow‐marine successions composed of small‐scale cycles, in order to delineate a detailed sequence stratigraphic framework and understand the factors that controlled the cyclicity.     

Precursor activity in bright, long BATSE gamma-ray bursts

We study a sample of bright, long Burst and Transient Source Experiment (BATSE) gamma-ray burst (GRB) light curves in the 200 s before the detection of the GRB prompt emission. We find that in a sizable fraction of cases (∼20 per cent) there is evidence of emission above the background coming from the same direction as the GRB. This emission is characterized by a softer spectrum with respect to the main spectrum and contains a small fraction (0.1–1 per cent) of the total event counts. The precursors have typical delays of several tens of seconds extending (in few cases) up to 200 s (the limit of the investigated period). Their spectra are typically non-thermal power-law spectra, aside from a few cases. Such long delays and the non-thermal origin of their spectra are hard to reconcile with any model for the progenitor.     

MgAl2O4 spinels from Allende and NWA 763 carbonaceous chondrites: Structural refinement,cooling history,and trace element contents

MgAl₂O₄ spinels from Allende and NWA 763 carbonaceous chondrites were studied by X‐ray single crystal diffraction, SEM, electron microprobe, LA‐ICP‐MS, and Raman spectroscopy. Those from Allende are almost pure, but, in one case, we found a strong FeO_tot zonation. Spinels from NWA 763 show Mg‐Fe²⁺ substitutions. Almost pure MgAl₂O₄ spinels from both meteorites underwent slow cooling and reached their intracrystalline closure temperature (T_c) in the range 460–520 °C. The NWA 763 spinel with higher FeO content shows a T_c of about 720 °C. X‐ray single crystal diffraction and Raman spectroscopy suggest a slow cooling and an ordered structure with trivalent cations in M site and divalent in T site. Among the trace elements, Ti and Co are enriched with respect to the terrestrial analogs, while Mn, Ni, and Sn show intermediate values between different terrestrial occurrences. Vanadium cannot be used as a tracer of extraterrestrial origin as for Cr‐spinels, because its content is similar in extraterrestrial and terrestrial spinels. In the zoned crystal from Allende, Co show a strong zonation similar to that of FeO.     

Constraints on the bulk Lorentz factor in the internal shock scenario for gamma-ray bursts

We investigate, independently of specific emission models, the constraints on the value of the bulk Lorentz factor Γ of a fireball. We assume that the burst emission comes from internal shocks in a region transparent to Thomson scattering, and before deceleration caused by the swept-up external matter is effective. We consider the role of Compton drag in decelerating fast-moving shells before they interact with slower ones, thus limiting the possible differences in the bulk Lorentz factor of shells. Tighter constraints on the possible range of Γ are derived by requiring that the internal shocks transform more than a few per cent of the bulk energy into radiation. Efficient bursts may require a hierarchical scenario, where a shell undergoes multiple interactions with other shells. We conclude that fireballs with average Lorentz factors larger than 1000 are unlikely to give rise to the observed bursts.