Distribution of rare earth elements in marine sediments from the Strait of Sicily (western Mediterranean Sea): evidence of phosphogypsum waste contamination

Concentrations of rare earth elements (REE), Y, Th and Sc were recently determined in marine sediments collected using a box corer along two onshore-offshore transects located in the Strait of Sicily (Mediterranean Sea). The REE + Y were enriched in offshore fine-grained sediments where clay minerals are abundant, whereas the REE + Y contents were lower in onshore coarse-grained sediments with high carbonate fractions. Considering this distribution trend, the onshore sediments in front of the southwestern Sicilian coast represent an anomaly with high REE + Y concentrations (mean value 163.4 μg g⁻¹) associated to high Th concentrations (mean value 7.9 μg g⁻¹). Plot of shale-normalized REE + Y data of these coastal sediments showed Middle REE enrichments relative to Light REE and Heavy REE, manifested by a convexity around Sm-Gd-Eu elements. These anomalies in the fractionation patterns of the coastal sediments were attributed to phosphogypsum-contaminated effluents from an industrial plant, located in the southern Sicilian coast.     

Ground penetrating radar survey finalized to the recovery of the “S. Agata alla Badia” church in Catania (eastern Sicily,Italy)

Numerous archaeological sites dating to the greek-roman period have been found in the underground of the city of Catania (eastern Sicily, Italy). Their presence is a testimony of the several settlements that have followed in this area over time. In this work we have conducted electromagnetic surveys, consisting of ten georadar profiles, inside the church of “S. Agata alla Badia”, damaged during the earthquake occurred in eastern Sicily on 13 December 1990. The aim was to investigate the area where the church is located to obtain information useful for its structural recovery. Mechanical drillings were also carried out to reconstruct the local stratigraphy, which could be complicated by the presence of underground cavities and artefacts, as evidenced by recent excavations beneath the Catania Cathedral, in the nearby Piazza Duomo. From the interpretation of the GPR data, the presence of ancient masonry structures underlying the recent foundations was highlighted. In addition, the GPR survey allowed us to identify and locate reflective horizons in the subsurface, probably due to the presence of materials with different state of aggregation and/or to buried structures.     

A new facies model for the Upper Gypsum of Sicily (Italy): chronological and palaeoenvironmental constraints for the Messinian salinity crisis in the Mediterranean

The Upper Gypsum unit of the Caltanissetta Basin (Sicily) records the last phase of the Messinian salinity crisis comprising the so‐called ‘Lago Mare’ event. A new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies, and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization. A basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies. A marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost (seventh) gypsum body. The terrigenous Arenazzolo Formation, in turn followed by the lower Pliocene Trubi Formation, is considered here to form the uppermost part of the Upper Gypsum unit. The rhythmic alternation in the sandy marls and gypsum/sandstone bodies records the response of sediments from shelfal to deltaic systems to precession‐driven arid‐wet climate fluctuations causing cyclical changes of both base‐level and water concentration. During wet climate phases (at insolation maxima) marl and sandstone were deposited in a hypohaline environment as suggested by: (i) the typical Lago Mare faunal assemblage and (ii) the negative δ¹⁸O values. During arid phases (at insolation minima) the reduced meteoric supply, recorded by higher δ¹⁸O values in the carbonate, caused the development of a negative hydrological budget leading to evaporite precipitation. At a basinal scale the Upper Gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia (the so‐called ‘Calcare di Base’) and/or clastic gypsum. Towards the basin centres, where the basal contact becomes conformable, a primary gypsum cumulate horizon is present. This layer is interpreted as a possible lateral equivalent of the Halite unit present only in the deepest depocentres. Based on astronomical calibration of the depositional cycles, the Upper Gypsum unit, including the Arenazzolo Formation, spans the interval between 5·33 and 5·53 Ma. This new age calibration allows the deposition of the Halite unit to be dated between 5·6 Ma (top of the Lower Evaporites) and 5·55 Ma (base of the Upper Evaporites) corresponding to isotopic stages TG12 and/or TG14.     

Carbonate stromatolites from a Messinian hypersaline setting in the Caltanissetta Basin, Sicily: petrographic evidence of microbial activity and related stable isotope and rare earth element signatures

Lower Messinian stromatolites of the Calcare di Base Formation at Sutera in Sicily record periods of low sea‐level, strong evaporation and elevated salinity, thought to be associated with the onset of the Messinian Salinity Crisis. Overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions, occasionally influenced by an influx of meteoric water. Evidence of bacterial involvement in carbonate formation is recorded in three dolomite‐rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre‐scale lamination and small fenestrae. The dominant microfabrics are: (i) peloidal and clotted dolomicrite with calcite‐filled fenestrae; (ii) dolomicrite with bacterium‐like filaments and pores partially filled by calcite or black amorphous matter; and (iii) micrite in which fenestrae alternate with dark thin wispy micrite. The filaments resemble Beggiatoa‐like sulphur bacteria. Under scanning electron microscopy, the filaments consist of spherical aggregates of dolomite, interpreted to result from calcification of bacterial microcolonies. The dolomite crystals are commonly arranged as rounded grains that appear to be incorporated or absorbed into developing crystal faces. Biofilm‐like remains occur in voids between the filaments. The dolomite consistently shows negative δ¹³C values (down to ?11·3‰) and very positive δ¹⁸O (mean value 7·9‰) that suggest formation as primary precipitate with a substantial contribution of organic CO₂. Very negative δ¹³C values (down to ?31·6‰) of early diagenetic calcite associated with the dolomite suggest contribution of CO₂ originating by anaerobic methane oxidation. The shale‐normalized rare earth element patterns of Sutera stromatolites show features similar to those in present‐day microbial mats with enrichment in light rare earth elements, and M‐type tetrad effects (enrichment around Pr coupled to a decline around Nd and a peak around Sm and Eu). Taken together, the petrography and geochemistry of the Sutera stromatolites provide diverse and compelling evidence for microbial influence on carbonate precipitation.     

Inconsistent patterns of historical seismicity and earthquake-triggered landsliding in southeastern Sicily: an alarm bell?

In southeastern Sicily, the distribution pattern of earthquake-triggered landslides is inconsistent with historically known seismic activity. In particular, historical seismicity has been stronger in the eastern sector, while earthquake-triggered landsliding is much more developed in the western sector, and this contrasts with expectations. This paper describes the patterns of seismicity and landsliding, and tackles the problem of whether greater landsliding in the western sector may be due (a) to seismicity of the eastern sector or (b) to a high-magnitude, low-recurrence seismicity generated in the western sector itself. It is statistically shown that lithostructural characteristics of rock masses and geometry of hillslopes cannot justify, either singly or jointly, greater landsliding in the western sector if triggering earthquakes are generated in the eastern sector. As a consequence, it is possible that landsliding of the western sector is due to earthquakes generated locally, but having higher magnitude and longer recurrence intervals than historically observed.     

Attenuation in Southeastern Sicily (Italy) by applying different coda methods

The attenuation in Southeastern Sicily has been investigated using 40aftershocks of the December 13 1990, earthquake. The quality factor ofcoda waves (Q_c) was estimated in the frequency range 1.5–24 Hz,applying three different methods in time and frequency domains. On thewhole, a clear dependence of Q_c on frequency was observed,according to the general law Q = Q₀(f/f₀)ⁿ . Thefrequency dependence relationships obtained from the analysis of codawaves at three lapse time windows (10, 20 and 30 seconds) show that, forall methods, Q₀ (Q_c at 1 Hz) significantly increases with lapsetime. In particular, Q₀ is approximately 20 at short lapse time (10s) and increases to about 70 at longer lapse time (30 s). This is attributedto the fact that larger lapse times involve deeper parts of the crust andupper lithosphere which may be characterized by larger quality factors.Moreover, the value of the exponent n decreases with increasing codalengths from about 1.3 to 0.9, suggesting a decrease in heterogeneity ofthe medium with depth.Finally, Q_c-values here found are of the same order as thosereported from other tectonic regions like the Anatolian Highlands orSouthern Spain, while significantly higher than in the neighboring volcanicarea of Mt. Etna.     

Statement of editorial and publication policies

The new European Macroseismic Scale 1992 (EMS) is applied to intensity estimation of data collected in field investigations of the 26 June 1993 Pollina (northern Sicily) earthquake and the results are compared with those obtained using the MSK-81 scale. The highest intensity estimated (VI–VII) fits with the low magnitude value (M _L = 4.7) and the low resistance level of buildings is responsible for some unexpected severe damage, thus raising the seismic vulnerability of the area. The tectonic framework shows significant elements of recent activity accounting for the frequent seismicity. The study also evaluated the validity of using vulnerability classes of buildings as defined in the EMS scale in the intensity assessment of historical earthquakes of the area.     

Soil-erosion assessment at basin scale through 137Cs content analysis based on pedo-morphological units

Soil loss evaluation by means of radioisotopic content measurements represents a promising technique, half-way between field surveys and theoretical models, which still suffers from its practical limits when applied at basin scale. A main limit is represented by the costs of field investigations and laboratory investigations on the high number of soil samples required by a traditional sampling scheme, such as regular grid or transects. A non-conventional soil sampling scheme was tested with the aim to consider a relative scanty number of soil samples and to verify the feasibility of this technique on large areas. This scheme was based on the hypothesis that land analysis and classification could point out areas characterised by homogeneous behaviour with respect to the ¹³⁷Cs deposition and transmission model. A Geographic Information System (GIS)-aided procedure allowed to classify the selected basin area in pedo-morphological units, representative of the different pedologic, morphologic and land-use conditions, to locate few sampling points for each unit. Outcomes pointed out a low correlation between ¹³⁷Cs contents and soil physical and compositional characteristics. Nevertheless, the isotopic methodology allowed to estimate a total soil loss value at basin scale almost consistent with both observed data, given by reservoir sedimentation measurements and estimates from the application of the RUSLE model. Thus, the results can be considered encouraging and they allow to deem that the isotopic methodology can be refined in order to account for erosion and deposition processes even at river basin scale and with a limited number of soil samples.     

A geophysical and geochemical approach for seawater intrusion assessment in the Acquedolci coastal aquifer (Northern Sicily)

Vertical electrical sounding (VES’) surveys and chemical analyses of groundwater have been executed in the coastal plain of Acquedolci (Northern Sicily), with the aim to circumscribe seawater intrusion phenomena. This urbanized area is representative of a more general problem interesting most of Mediterranean littoral areas, where intensive overdraft favors a heavy seawater intrusion through the coastline. Aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content in the main aquifer of the region. Schlumberger VES’, together with piezometric and chemical–physical information of groundwater, allowed us to perform hydrogeological and geophysical elaborations, to propose the occurrence of a relatively narrow belt marked by fresh–salt water mixing. In the considered plain, pollution risk studies have been already realized by authors with the proposal to identify—by parametric and synthetic zoning of significant hydrogeological elements—the most vulnerable sectors. In detail, an intrinsic vulnerability mapping has been already performed, applying the well-known SINTACS system. This paper intends to give—in this sector of Sicily—an example of integration of different methodologies, showing the role of geophysics to describe the degradation of aquifers on the whole as well as to assess their pollution risk better.     

Minimum 1-D velocity model in Southeastern Sicily (Italy) from local earthquake data: an improvement in location accuracy

The monitoring of seismic activity inSoutheastern Sicily (Italy) has beenrecently improved by a digital seismicnetwork. This effort has produced ahomogeneous and complete dataset which weused to define a reference 1-D velocitymodel. We have inverted P- and S-wavearrival times from 51 selected localearthquakes by using several initialvelocity and layer thickness models. Then,the range of possible velocity modelsobtained was tested with earthquakelocations to select the best velocitymodel. Improvements in location accuracy byusing the Minimum 1-D velocity model, withrespect to the locations obtained by usingthe routine velocity model, were evidencedfrom the reduced residuals, the smallerestimated location errors, and theincreased tendency of foci to cluster. Thedistribution of relocated hypocentersconfirmed the lack of seismic activity inthe central part of the area.