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.     

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.     

Recharge estimation from discrete water-table datasets in a coastal shallow aquifer in a humid subtropical climate

A time-series approach to the estimation of recharge rate in unconfined aquifers of highly variable water level is proposed. The approach, which is based on the water-table fluctuation method (WTF), utilizes discrete water-level measurements. Other similar techniques require continuous measurements, which makes them impossible to apply in cases where no data from automatic loggers are available. The procedure is deployed at the Ressacada Farm site, southern Brazil, on a coastal shallow aquifer located in a humid subtropical climate where diurnal water-level variations of up to 1 m can follow a precipitation event. The effect of tidal fluctuations on the groundwater levels is analyzed using a harmonic component builder, while a time-variable drainage term is evaluated through an independent analysis and included in the assessment. The estimated recharge values are compared with those obtained from the continuous measurements showing a good agreement with the approaches for discrete dataset intervals of up to 15 days. Subsequently, the estimated recharge rates are incorporated into a transient groundwater-flow model and the water levels are compared showing a good match. Henceforth, the approach extends the applicability of WTF to noncontinuous water-level datasets in groundwater recharge studies.     

Generalised ultimate loads for pile groups

Acta Geotechnica - Foundation piles can be used as a means for increasing the capacity of the foundations under static loads or, at the same time, can be regarded as an additional source of energy...     

Effect of two different habitats on spine and gonad colour in the purple sea urchin Paracentrotus lividus

This study investigates the effect of different Mediterranean habitats on spine and gonad colouring and gonadal index in the purple sea urchin Paracentrotus lividus (Echinodermata: Echinoidea). Specimens were collected in winter 2012 in Posidonia oceanica meadows and rocky bottom areas at two sites in Southern Sardinia (Italy, Tyrrhenian Sea). Colorimetric analyses of spines and gonads were conducted with a digital colorimeter using CIELAB colour spaces, which defines the colour in terms of three coordinate values: lightness (L*), redness (a*) and yellowness (b*). Lightness and redness of the spines differed significantly between habitats, whereas colour spaces of the gonads did not. A careful analysis of the gonad index showed it to be significantly affected by habitat, registering higher values in rocky bottom locations. In conclusion, it seems that habitat does affect spine colour but not gonad colour. Spine colour seems to be site‐dependent, whereas the gonad index depends solely on the habitat.     

Transformations of Benzene Photoinduced by Nitrate Salts and Iron Oxide

This paper reports the results of a study on the transformation of benzene in the presence of solid nitrate salts (NaNO₃, NH₄NO₃) under irradiation in a gas-solid photoreactor. Sodium and ammonium nitrate have been chosen as representative of the composition of atmospheric particulate, benzene as a model aromatic molecule. The purpose is to simulate the transformations that aromatic compounds undergo on the surface of dispersed particles in the atmosphere. Irradiation of sodium nitrate causes hydroxylation and nitration of benzene, yielding phenol and nitrobenzene. This is most likely due to the generation of ^•OH and ^•NO₂ radicals upon nitrate photolysis, with ^•OH + O₂ leading to the formation of phenol and ^•OH + ^•NO₂ yielding nitrobenzene. The percentage of oxygen in the reaction environment influences the transformation pathways, with phenol formation being favoured and nitrobenzene formation depressed by high O₂ concentration. In the presence of hematite (α-Fe₂O₃, another component of atmospheric particulate) very relevant formation of nitrobenzene takes place even with 21% oxygen (simulated air), indicating that the interaction between hematite and nitrate can lead to the formation of aromatic nitroderivatives on the surface of atmospheric particulate. The effect of hematite is possibly due to protonation of peroxynitrite, formed upon nitrate photoisomerisation, to peroxynitrous acid, a powerful nitrating agent. A similar effect leads to relevant formation of nitrobenzene under atmospheric conditions upon irradiation of the acid salt ammonium nitrate.     

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.