Climate control on stacked paleosols in the Pleistocene of the Po Basin (northern Italy)

Paleosols are recurrent features in alluvial successions and provide information about past sedimentary dynamics and climate change. Through sedimentological analysis on six sediment cores, the mud-dominated succession beneath the medieval ‘Two Towers’ of Bologna was investigated down to 100 m depth. A succession of weakly developed paleosols (Inceptisols) was identified. Four paleosols (P1, P2, P3 and PH) were radiocarbon-dated to 40–10 cal ka bp . Organic matter and CaCO₃ determinations indicate low groundwater levels during soil development, which spanned periods < 5 ka. The development and burial of soils, which occurred synchronously in the Bologna region and in other sectors of the Po Plain, are interpreted to reflect climatic and eustatic variations. Climatic oscillations, at the scale of the Bond cycles, controlled soil development and burial during Marine Isotope Stage (MIS) 3 (P1 and P2). Rapid sea-level oscillations probably induced soil development at the MIS 3/2 transition (P3) and favored burial of PH after 10 ka bp . Weakly developed paleosols in alluvial successions can provide clues to millennial-scale climatic and environmental variations. In particular, the paleosol-bearing succession of the Po Plain represents an unprecedent record of environmental changes across the Late Pleistocene (MIS 3 and 2) in the Mediterranean region.     

Paleomagnetic dating of the most recent silicic eruptive activity at Pantelleria (Strait of Sicily)

We report on the paleomagnetism of ten sites in the products of the most recent silicic eruptive cycle of Pantelleria, Strait of Sicily. Previously radiometrically dated at 5–10 ka, our comparison with proxies for geomagnetic field directions allows us to narrow considerably the time window during which these eruptions occurred. The strongly peralkaline composition causes the magmas to have low viscosities, locally resulting in strong agglutination of proximal fall deposits. This allows successful extraction of paleomagnetic directions from the explosive phases of eruptions. One of our sites was located in the Serra della Fastuca fall deposit, produced by the first explosive event of the eruptive cycle. The other nine sites were located in the most recent explosive (pumice fall and agglutinate from Cuddia del Gallo and Cuddia Randazzo) and effusive (Khaggiar lava) products. The (very similar) paleomagnetic directions gathered from eight internally consistent sites were compared to reference geomagnetic field directions of the last 5–10 ka. Directions from Cuddia del Gallo agglutinate and Khaggiar flows translate into 5.9- to 6.2-ka ages, whereas the Fastuca pumices yield a slightly older age of 6.2–6.8 ka. Hence, the most recent silicic eruptive cycle lasted at most a millennium and as little as a few centuries around 6.0 ka. Paleomagnetically inferred ages are in good agreement with published (and calibrated by us) ¹⁴C dates from paleosols/charcoals sampled below the studied volcanic units, whereas K/Ar data are more scattered and yield ∼30% older ages. Our data show that the time elapsed since the most recent silicic eruptions at Pantelleria is comparable to the quiescence period separating the two latest volcanic cycles.     

Glaucony from the Cretaceous of the Sierra de Guadarrama (Central Spain) and its application in a sequence-stratigraphic context

Detailed sedimentological and geochemical analyses of Upper Cretaceous glaucony-bearing deposits from the middle portion of the Castro de Fuentidueña Formation, in Central Spain, enable identification of a multiphase history of glaucony accumulation. Despite its relatively high maturity (K₂O > 7%), glaucony from the transgressive subtidal sandstones has anomalously low concentration in the host rock (generally <10%), suggesting remobilization from a different source. The remarkable thickness of the glaucony-bearing horizons, concurrently with concentration of glaucony in laminae, small size, and high degree of roundness and sorting provide further evidence for an allochthonous origin of the green grains. In contrast, authigenic glaucony from the overlying offshore clays exhibits higher abundance (up to 45%) and lower maturity (K₂O < 7%) and is interpreted to have formed in situ. Allochthonous glaucony originally developed in more distal areas during a prolonged period of sediment starvation. The green grains were then swept away from their place of origin and concentrated into tidal bars and channels within the upper transgressive systems tract of the third-order depositional sequence. Maximum concentration of autochthonous glaucony is recorded at the transition from tidal-influenced to offshore deposits: this glaucony, which is relatively less evolved due to lower time available for maturation, is interpreted to reflect the turnaround from transgressive to highstand conditions, marking the condensed section of the depositional sequence. As postulated by previous sequence-stratigraphic models, this study documents that allochthonous glaucony can be widespread throughout the transgressive systems tract (TST), while the condensed section (CS) typically hosts autochthonous glaucony. Contrary to the existing literature, however, this study shows that glaucony from the TST may be even more mature than glaucony from the CS, if enough time for maturation during transgression is allowed before the ultimate concentration of the green grains. Identification of spatial and temporal characteristics of glaucony, thus, is critical to a reliable sequence-stratigraphic interpretation of the glaucony-bearing deposits.     

Linear and angular momentum conservation in hydraulic jump in diverging channels

This paper addresses the integral conservation of linear and angular momentum in the steady hydraulic jump in a linearly diverging channel.The flow is considered to be divided into a mainstream that conveys the total liquid discharge, and a roller where no average mass transport occurs. It is assumed that no macroscopic rheological relationship holds, so mass, momentum and angular momentum integral balances are independent relationships. Normal stresses are assumed to be hydrostatic on vertical, cylindrical surfaces. Viscous stresses are assumed to be negligible with respect to turbulent stresses. Assuming that the horizontal velocity distribution in the mainstream is uniform and that the horizontal momentum and angular momentum in the roller are negligible with respect to their mainstream counterparts, an analytical solution is obtained for the free surface profile of the flow. This solution is fundamental for finding the sequent depths and their positions. Consequently, it permits solving for the length of the jump, which is assumed to be equal to the length of the roller. Mainstream and roller thicknesses can also be derived from the present solution. This model may also be theoretically used to derive the average shear stresses exerted by the roller on the mainstream and the power losses per unit weight. This second relationship, which returns the well-known classical expression for total power loss in the jump, demonstrates that the strongly idealized mechanical model proposed here is internally consistent.     

Geometric characteristics and evolution of a tidal channel network in experimental setting

This paper reports on a laboratory study that aims to reproduce a tidal channel network, in order to enhance the understanding of the morphodynamic evolution of the channel characteristics as the network expands and finally reaches equilibrium. A high‐resolution laser system scanned the bed topography at different time steps creating multiple digital elevation models of the channel network. Two hundred and seventy individual channel segments are analyzed and cross‐correlated in terms of their width, depth and length. The laboratory results show positive linear correlations between depth and width as well as between length and width of channel segments of the network configuration at final equilibrium. In a downstream direction, channels appear to widen more than they deepen, indirectly a sign that discharge has a stronger control on channel width than on depth. In contrast to fluvial drainage networks that commonly display fractal and scale‐invariant behavior, the geometric properties of the experimental tidal creek network shows scale dependence. Channel attributes exhibit consistent patterns of exponentially decreasing abundance, with increasing creek length, depth and width. The nature of the observed exponential distributions within creek attributes (width, depth, length) allows for statistical predictability of relative creek attribute dimensions downstream and through time. Copyright © 2010 John Wiley & Sons, Ltd.     

Magnetic properties and cation ordering of nanopowders of the synthetic analogue of kuramite, Cu3SnS4

An extensive characterisation of the magnetic properties of synthetic powders of kuramite, with formal composition Cu₃SnS₄, was performed. Powders were investigated through superconducting quantum interference device (SQUID) magnetometry, electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM) and microanalysis. SEM and TEM reveal the presence of nanodimensioned particles. XRPD clearly shows that Cu₃SnS₄ crystallised in a cubic sphalerite-type structural model, in spite of the stannite-type tetragonal structure described for the natural phase. This difference arises from a full random distribution of cations. Synthetic kuramite nanopowders exhibit a marked paramagnetism, originated by the presence of Cu(II), definitely assessed by EPR measurements. Moreover, the overall magnetic behaviour of the sample cannot be simply ascribed to diluted paramagnetism, and this suggests the presence of strong superexchange interactions among Cu(II) ions even at room temperature. The main consequences of these results are the definitive assessment of the chemical formula Cu(I)₂Cu(II)SnS₄ and of a random distribution of Cu(II), Cu(I) and Sn(IV) ions within the available tetrahedral sites.     

Spectroscopic Characterization of Compost at Different Maturity Stages

We studied the physicochemical and molecular changes of compost during its maturation within 60, 90, and 150 days after the composting process. Moreover, the changes were also studied in compost residues after sequential removal of lipidic compounds. Infrared DRIFT spectrometry and ¹³C‐CPMAS‐NMR spectroscopy indicate that the molecular composition of compost changes dramatically during the stabilization period. The most decomposable components, mainly represented by bioavailable lipidic and peptidic structures, were progressively mineralized passing from 60 days to longer periods of compost stabilization. At increasing maturity stages, the composition of organic matter underwent a progressive enrichment in stable hydrophobic and ligno‐cellulosic material. The sequential extraction of lipidic compounds allowed an improved characterization of substrates and confirmed the outlined progressive transformation of compost. Compost may well be chosen on the basis of selected characteristics for environmental applications.     

POLARIX: a pathfinder mission of X-ray polarimetry

Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 10⁵ s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled.     

Major changes in volcano behaviour after a sector collapse: insights from Stromboli, Italy

In recent years, increasing numbers of volcanoes are being recognized as having undergone large sector collapses. How far such events can change the succeeding behaviour of the volcano is poorly known, despite the importance for natural hazards and economic applications. By analysing the last 100‐kyr geological history of Stromboli (Italy), which has involved multiple collapses, this paper illuminates the feedback effect between sector collapse and magma upwelling and emplacement. The collapsed zone of Stromboli is episodically unbuttressed, draining magma preferentially with formation of eruptive centres in the collapse amphitheatre and dyking along the collapse shoulders. After a collapse, there were no further linear eruptions across the cone on opposing middle–lower slopes, but these occurred again after rebuilding of the cone. The time‐averaged eruption rate increased immediately before the first collapse and remained higher during the succeeding period of frequent collapses.