Modelling the relationship between sexual reproduction and rhizome growth in Posidonia oceanica (L.) Delile

The relationship between flowering and growth performance of Posidonia oceanica (L.) Delile in meadows distributed along the south‐eastern coast of Sicily (Italy) was investigated by means of a statistical model (generalized linear mixed model) combined with the lepidochronological analysis. Over a 28‐year period, 67 floral stalk remains were observed. The highest flowering index was recorded in lepidochronological year 1998 (10.1%) and the Inflorescence Frequency per age showed a clear decrease corresponding to 15‐year‐old shoots. The sexual reproductive event had positive effects on rhizome elongation (cm year^?1) and leaf production (no. leaves year^?1) in the same flowering year, whilst no effect on the rhizome production (mg year^?1) was observed. Rhizome growth variables showed significant negative lagged responses in the two years following flowering. On the whole, we calculated that the effect exerted by flowering, in terms of loss on rhizome elongation and production, was about 27% and 38%, respectively. Although it has been demonstrated that recovery from the stress induced by sexual reproduction is limited to the two years after flowering, the magnitude of the reproductive cost may become quite considerable especially in comparison with the whole lifespan of individual shoots.     

Direct evidence of Middle Oligocene extension in the Calabria–Peloritani terrane from co-seismic faulting: the pseudotachylyte-bearing shear zones of Palmi (southern Calabria, Italy)

The Variscan crystalline basement of the Calabria–Peloritani terrane (CPT) in southern Italy was partly reworked by ductile and brittle shear zones throughout the Alpine tectonic evolution (from thickening to exhumation). Although evidence of extensional tectonics in the CPT has already been found and roughly constrained to the Oligocene onward, no attempt has ever been made to directly date brittle fault movements. Structural (meso- and micro-scale), kinematic and petrographic analyses and ⁴⁰Ar–³⁹Ar laser experiments reveal that the pseudotachylyte-bearing shear zones of the Palmi area in southern Calabria formed in response to extensional shearing ∼33.5 Ma ago and overprinted compressional tectonic structures. Results provide the first direct evidence of Middle Oligocene co-seismic faulting in the area and confirm the role of extensional tectonics in promoting the Oligocene exhumation of the Calabria basement.     

A structural and geophysical approach to the study of fractured aquifers in the Scansano-Magliano in Toscana Ridge, southern Tuscany, Italy

Fresh water availability has recently become a serious concern in the Italian Apennines, as various activities rely on a predictable supply. Along the ridge between Scansano and Magliano in Toscana, in southern Tuscany, the situation is further complicated by contamination of the nearby alluvial aquifers. Aquifers locally consist of thin fractured reservoirs, generally within low-permeability formations, and it can be difficult to plan the exploitation of resources based on conventional techniques. An integrated study based on geological data investigated the link between tectonics and groundwater circulation, to better define the hydrological model. After the regional identification of fault and fracture patterns, a major structure was investigated in detail to accurately map its spatial position and to understand the geometry and properties of the associated aquifer and assess its exploitation potential. The subsurface around the fault zone was clearly imaged using ground probing radar, two-dimensional and three-dimensional resistivity tomography, and three-dimensional shallow seismic surveys. The vertical and horizontal contacts between the different geological units of the Ligurian and Tuscan series were resolved with a high degree of spatial accuracy. Three-dimensional high-resolution geophysical imaging proved to be a very effective means of characterising small-scale fractured reservoirs.     

The thin layer of Warm Ionized Gas: towards a 3-D reconstruction of the spatial distribution of HII regions

HII regions are known to contribute to the so-called thin layer of the diffuse Warm Ionized Gas. In order to constrain thiscontribution, we reconstruct the 3-D distribution of the sources.A detailed spatial analysis of the largest up-to-date sample of HIIregions is presented.     

A seismic source zone model for the seismic hazard assessment of the Italian territory

We designed a new seismic source model for Italy to be used as an input for country-wide probabilistic seismic hazard assessment (PSHA) in the frame of the compilation of a new national reference map.

We started off by reviewing existing models available for Italy and for other European countries, then discussed the main open issues in the current practice of seismogenic zoning.

The new model, termed ZS9, is largely based on data collected in the past 10 years, including historical earthquakes and instrumental seismicity, active faults and their seismogenic potential, and seismotectonic evidence from recent earthquakes. This information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model ZS4.

ZS9 is made out of 36 zones where earthquakes with M_w > = 5 are expected. It also assumes that earthquakes with M_w up to 5 may occur anywhere outside the seismogenic zones, although the associated probability is rather low. Special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates.

Although it was drawn following criteria that are standard practice in PSHA, ZS9 is also innovative in that every zone is characterised also by its mean seismogenic depth (the depth of the crustal volume that will presumably release future earthquakes) and predominant focal mechanism (their most likely rupture mechanism). These properties were determined using instrumental data, and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications. These attributes allow ZS9 to be used with more accurate regionalized depth-dependent attenuation relations, and are ultimately expected to increase significantly the reliability of seismic hazard estimates.     

Nonlinear regional economic dynamics: continuous-time specification,estimation and stability analysis

This paper presents an innovative approach to the study of regional economic dynamics within a nonlinear continuous-time econometric framework—a generalized specification of the Lotka–Volterra system of equations. This specification, which accounts for interdependent behavior of three industrial sectors and spillover effects of activities in neighboring regions, is employed in an analysis of five Italian regions between 1980 and 2003. For these regions, we report estimation results, characterize the varying systems dynamics, analyze the models’ local and global stability properties, and determine via sensitivity analyses which structural features appear to exert the greatest influence on these properties.

Ar-Ar laser dating of tektites from the Cheb Basin (Czech Republic): Evidence for coevality with moldavites and influence of the dating standard on the age of the Ries impact

Moldavites (Central European tektites) are genetically related to the impact event that produced the ∼24-km diameter Ries crater in Germany, representing one of the youngest large impact structures on Earth. Although several geochronological studies have been completed, there is still no agreement among ⁴⁰Ar-³⁹Ar ages on both moldavites and glasses from Ries suevites. Even recently published data yielded within-sample mean ages with a nominal spread of more than 0.6 Ma (14.24-14.88 Ma). This age spread, which significantly exceeds current internal errors, must be in part ascribed to geological and/or analytical causes.This study reports the results of a detailed geochronological investigation of moldavites from the Cheb area (Czech Republic), which have never been dated before, and, for comparison, of two samples from type localities, one in southern Bohemia and the other in western Moravia. We used ⁴⁰Ar-³⁹Ar laser step-heating and total fusion techniques in conjunction with microscale petrographic and chemical characterization. In addition, with the purpose of ascertaining the influence of the dating standards on the age of the Ries impact and making data from this study and literature consistent with the now widely used Fish Canyon sanidine (FCs) standard, we performed a direct calibration of multi-grain splits of the Fish Canyon biotite (FCT-3) with FCs. The intercalibration factors (), determined for eight stack positions in one of the three performed irradiations, were indistinguishable within errors and gave an arithmetic mean and a standard deviation of 1.0086 ± 0.0031 (±2σ), in agreement with previous works suggesting that biotite from the Fish Canyon Tuff is somewhat older (∼0.8%) than the coexisting sanidine.Laser total fusion analysis of milligram to sub-milligram splits of five tektite samples from the Cheb area yielded mostly concordant intrasample ⁴⁰Ar-³⁹Ar ages, and within-sample weighted mean ages of 14.66 ± 0.08-14.75 ± 0.12 Ma (±2σ internal errors, ages relative to FCs) that overlap within errors. These ages match those obtained for samples from western Moravia (14.66 ± 0.08 Ma) and southern Bohemia (14.68 ± 0.11 Ma), supporting the genetic link between Cheb Basin tektites and moldavites, and, consequently, between Cheb Basin tektites and the Ries impact. In contrast to samples from the Cheb area and Moravia, ⁴⁰Ar-³⁹Ar ages from total fusion experiments on the Bohemian specimen ranged widely from ∼14.6 to ∼17.0 Ma. Older apparent ages, however, were systematically obtained from fragments characterized by visible surface alteration. Laser step-heating experiments, although displaying slightly disturbed age profiles, were in line with total fusion analyses and yielded well-defined plateau ages of 14.64 ± 0.11-14.71 ± 0.11 Ma (±2σ internal errors, ages relative to FCs).A thorough comparison of our and previous ⁴⁰Ar-³⁹Ar ages on both moldavites and Ries suevite glasses, recalculated relative to the ⁴⁰Ar^∗/⁴⁰K ratio recently determined for FCs using intercalibration factors available in or derivable from the literature, reveals some inconsistencies which may be ascribed to either geological or analytical causes. Based on our data, decay constants in current use in geochronology, and ages calculated relative to FCs, we infer that the age of moldavites is 14.68 ± 0.11 Ma (±2σ, neglecting uncertainties in the ⁴⁰K decay constants).     

Hydrochemistry and isotope geochemistry as tools for groundwater hydrodynamic investigation in multilayer aquifers: a case study from Lomellina, Po plain, South-Western Lombardy, Italy

A multicriteria approach in studying hydrodynamics of a multilayer aquifer system has been used in the Lomellina region (Northern Italy). It involves the reconstruction of the hydrogeological framework coupled to the definition of the hydrochemical and isotopic features of the aquifers. A shallow phreatic aquifer, reaching depths of about 60–80 m from the surface, and deeper aquifers containing confined groundwater, were distinguished. Groundwater generally shows mineralisation decreasing with depth; dissolved ions depict calcium-bicarbonate hydrochemical facies and stable isotopes define the recharge mechanisms, the origin of groundwater, and the hydraulic confinement of deep aquifers. The phreatic aquifer is fed by local infiltration and by streams and irrigation channels. Tritium and Carbon-14 groundwater dating indicate long residence times (on the order of thousands of years) for confined aquifers. The confined aquifers show essentially passive hydrodynamic conditions and maintain a higher piezometric level than the phreatic aquifer. This inhibits the possibility of recent water penetrating far below the surface. The hydrogeological setting of the Lomellina region displays features which are common to other sectors of the Po plain. As a consequence, the results of this study, although conducted on a restricted area, are highly illustrative of groundwater hydrodynamics in large sedimentary aquifers.     

The effect of chlorite interlayering on <Superscript>40</Superscript>Ar–<Superscript>39</Superscript>Ar biotite dating: an <Superscript>40</Superscript>Ar–<Superscript>39</Superscript>Ar laser-probe and TEM investigations of variably chloritised biotites

Biotite is one of the most common minerals dated by the ⁴⁰Ar–³⁹Ar method. It frequently shows K contents below the expected stoichiometric value, suggesting the presence of low-K impurities. The most common low-K alteration product of biotite is chlorite. Therefore, it is important to understand the effects of chlorite interlayering on ⁴⁰Ar–³⁹Ar ages in order to correctly interpret ⁴⁰Ar–³⁹Ar data. This study examines the outcome of ⁴⁰Ar–³⁹Ar dating analyses on variably chloritised biotites from Ordovician intrusive rocks. The infrared (IR) laser-probe technique and different gas extraction methods were adopted. Incremental laser-heating data on bulk samples yielded hump-shaped age profiles with meaningless young and old age steps. Both the extent of anomalous old age steps and the degree of discordance of the age spectra were much more pronounced in the more chloritised biotite samples. In contrast, in situ data on rock chips and total-fusion ages on single biotite flakes yielded ages concordant with, or younger than, the inferred emplacement ages. Transmission electron microscopy (TEM) was used to texturally characterise biotite samples at the nanometre scale. It was also used to document the complex decomposition-transformation process affecting interlayered biotite–chlorite during in-vacuo IR-laser heating to temperatures ranging from ~600 to >1,000 °C. TEM results suggest that hump-shaped age profiles result from an interplay between ³⁹Ar_K redistribution by recoil during sample irradiation and differential release of argon isotopes hosted in three main reservoirs. These reservoirs are (from least to most retentive): extended defects, chlorite and biotite. The final descending age segment is attributed to the progressive release of argon with increasing temperature from large biotite domains for which ³⁹Ar_K recoil loss was less important. ⁴⁰Ar–³⁹Ar data support previous findings, which suggest that ⁴⁰Ar–³⁹Ar ages when recoil effects are minimised, provide minimum estimates that approach the true biotite age, when the pristine domains are analysed. The most effective approach for obtaining meaningful ⁴⁰Ar–³⁹Ar ages was using individual total-fusion analyses on carefully selected, single flakes previously split along the basal cleavage by wet-grinding and corresponding to a sample mass of a few micrograms.Editorial responsibility: I Parsons