Tiziano Boschetti

Climatic factors influencing the isotope composition of Italian olive oils and geographic characterisation

The purpose of this study was to investigate the possibility of identifying oil source areas by means of simple measurements on the natural samples avoiding time-consuming sample treatments. The oxygen and carbon isotopic values of 150 samples of extra-virgin olive oil from eight different Italian regions and from three different years of production were measured according to well-established techniques. Statistical treatments of the results obtained show a very good correlation of the delta(18)O of oil with latitude, mean annual temperature, and mean relative humidity at the collection site. No correlation is found with elevation and mean annual precipitation. The shift of the oil delta(18)O per degree centigrade of the mean annual temperature is quantitatively close to that calculated for atmospheric precipitation in continental areas. Accordingly, in our measurements, the year of oil production can be identified on the basis of the delta(18)O value (mean 2004 temperatures were higher than 2005 temperatures). On the contrary, the oil delta(13)C values show no correlation with the above variables but only with latitude and, consequently, are less suitable for discriminating the geographic origin of oil. However, the delta(13)C values are suitable to indicate biological differentiation while the delta(18)O values are not.

Chemical and isotopic compositions of water and dissolved sulfate from shallow wells on Vulcano Island, Aeolian Archipelago, Italy

Abstract Twenty-two cold and thermal waters from shallow wells sampled in June 1995 in the Vulcano Porto area, Vulcano Island, were analyzed for major and minor chemical constituents, oxygen and hydrogen isotopes and tritium contents, and sulfur isotopes in the dissolved sulfate. The sulfur isotopic composition of the dissolved sulfate ranges between +0.6 and +6.5‰ (mean +3.7±1.7‰), and is interpreted as deriving mainly from fumarolic SO 2 undergoing oxidation in deep and shallow aquifers, with possible minor contributions from oxidation of H 2 S. Dissolution of secondary anhydrite may have been a minor source of the isotopically heavy aqueous sulfate in the cold groundwaters. The chemical and isotopic features of the waters support previous interpretative hydrologic models of Vulcano Porto, which comprise a number of aquifers fed basically by two major end-members, i.e. meteoric water and crater-type fumarolic inputs, the latter in the form of absorbed emissions or condensate. These data, along with the sulfur isotopes of aqueous sulfate, exclude involvement of seawater in the recharge of the groundwater system of the island.

Sulfur and oxygen isotope compositions of Upper Triassic sulfates from Northerm Apennines (Italy): palaeogeographic and hidrogeochemical implications

Upper Triassic bedded evaporite sulfate of the Burano Formation outcropping at Cerreto Pass between Tuscany and Emilia-Romagna in the Northern Apennines were analyzed for sulfur and oxygen isotope compositions, yielding d34S and d18O values of 15.5±0.4‰ and 10.8±1.2‰, respectively (mean ±99% confidence intervals). Combining these values with those of other Burano Formation sulfate deposits along the Apennine chain, mean for d34S and d18O values are obtained (15.2±0.2‰ and 10.9±0.5‰, respectively). These isotopic signatures are interpreted as preserved primary features, despite the fact that the Burano Formation underwent anchizone to epizone metamorphism during the Apennine orogenesis. An overall d18O value of 10.9±1.5‰ (mean ± pooled standard deviation), obtained by combining consistent sets of data from Italy and Spain, closely approaches that of gypsum deposited from the Tethys ocean during the Late Triassic. In addition, reviewing the isotope data published on Late Triassic evaporite sulfates from the Mediterranean area and abroad, several d34S values appear to be lower than the inferred primary isotopic signature, and seemly decrease from East to West in the Mediterranean region, suggesting a similar trend for the Tethys ocean sulfate. Possibly, 34S-depleted sulfate entered the ocean through oxidation of volcanic SO2 emitted in the atmosphere and degassed from the seafloor during the development of Late Triassic rifting. On the other hand, positive shifts of d34S and d18O values also occur, defining a common trend that may be related to synsedimentary biological effects or post-depositional metasomatic-metamorphic effects, the latter affecting particularly the d18O signature. Therefore, the d34S and d18O signatures of evaporite sulfate may provide a like “slide-rule” diagram to distinguish between isotopic effects related to biological or abiological processes, thus contributing to the reconstruction of paleoenvironments and paleogeographic settings. Based on the d34S-d18O “slide-rule”, the isotopic composition of sulfate dissolved in spring and stream waters of northern Tuscany was interpreted in terms of origin of the sulfate and modifying processes in solution. It was concluded that sulfate in springs derives from Upper Triassic evaporite existing locally at depth (Burano Formation), whereas sulfate in streams is manifestly a mixture of Burano Formation sulfate with supergene sulfate from oxidation of sulfide in the rocks. In sulfurous springs, both sulfur and oxygen isotope fractionations with respect to the source sulfate signatures may be ascribed to bacterial effects. However, the oxygen isotope exchange of sulfate with water should have been a very minor process as supported by the nearsurface temperature values estimated by sulfate-water oxygen isotope thermometry.

Sulphide-bearing waters in Northern Apennines, Italy : general features and water rock interaction

Sulphide-bearing Ca-carbonate, Na-carbonate, Na-hydroxide, Na-chloride and Ca-sulphate waters from Northern Apennines were investigated in order to determine their main chemical and isotopic composition and draw inferences on water-rock interaction. δ2H and δ18O values suggest an origin mostly meteoric for the analysed waters but a well drilled in Miocenic sediments. The Na-carbonate and the Ca-sulphate waters are the most interesting geochemically. Na-carbonate type, which sometimes reaches extreme composition (Na/Ca up to 228, equivalent ratio), may have been derived through prolonged interaction of Ca-carbonate waters with rocks containing feldspar, montmorillonite and illite under calcite saturation/oversaturation; the high F and pH and the very low PCO2 agree with prograde dissolution of silicates and lasting water-rock interaction. However, Ca–Na ion exchange, involving clays of marine origin, cannot be excluded in addition. The Ca-sulphate waters, occurring in Messinian gypsum-bearing sediments, are saturated in gypsum and calcite and exhibit very high total H2S (up to 219 mg dm-3) and PCO2 (up to 0.32 bar). Mass balance of sulphate sulphur, sulphide sulphur and delta34S suggests sulphate – derived from gypsum – as source for H2S; CH4 and organic matter generate the reducing conditions and sulphate reduction is mediated by bacteria. One Na-chloride water from a well in Miocenic sediments has unusual composition, containing about 700 mgdm-3 of potential CaCl2 and having δ2H and δ18O (-47.5 and -4.9‰ respectively) which plot far from the meteoric water lines; probably it is derived by mixing of meteoric and formation waters. The Na-hydroxide water, with very high pH (11.2), is generated through protracted interaction of meteoric waters with ultramafites.

Seawater intrusion in the Guanahacabibes Peninsula (Pinar del Rio Province, western Cuba): effects on karst development and water isotope composition

The water resources in the Guanahacabibes Peninsula are distributed in two areas. The northeastern area is characterized by swamps, wetlands and lagoons, with a low contribution of seawater, whereas the area in the southwestern plain shows a considerable development of the karst structures that limits the existence of superficial waters but permits the ingression of the surrounding seawater. In this latter area, the groundwater showed a marked increase in salinity with the depth. In particular, groundwater with a seawater fraction of 0.1 had the lowest Ca-(Mg)-carbonates saturation indexes calculated by modeling the mixing between freshwater and seawater using different software, thermodynamic databases and equations for activity coefficients. Generally, seawater and groundwaters with an added seawater fraction above 0.60–0.65 showed similar oversaturated indexes in high-Mg calcites and pure Ca-carbonates (calcite and aragonite). Differently, in the groundwater that showed carbonates undersaturation (generally with a seawater fraction between 0.02 and 0.60), the saturation indexes in high-Mg calcites were 0.2 lower than pure Ca-carbonates. Locally, the bacterial reduction of the dissolved sulfate enhanced the dissolution of the limestone, contributing to the increased development of the karst structures and the seawater intrusion. Finally, the presence near the coastline of fresh Ca- and Na-bicarbonate waters was in accordance with the upward flow of the shallow freshwater during the formation of the saline wedge. However, the oxygen and hydrogen stable isotope composition of the waters showed a probable contribution to the area from a deep aquifer that is recharged in the highest reliefs of the province (Cordillera de Guaniguanico).

The groundwaters of Fontevivo (Parma Province, Italy): Redox processes and mixing with brine waters

This paper describes the chemical and isotopic characterization of H2S-bearing groundwaters of the Fontevivo area, northern Italy. Groundwaters from Fontevivo (Parma Province) contain dissolved H2S and minor hydrocarbons, which are released from the truncated front of a buried geological structure (Calabrian– Miocene terrains) and through abandoned unsealed oil wells. H2S concentration is up to 5.54 mg/l in groundwaters from the topographical high of the village and its distribution in the investigated area is inversely related with those of NH4+ and SO42−. Groundwaters are dominantly Ca-HCO3 type with lesser Ca-SO4 and Na-Cl types and display two compositional trends: group A, waters from Ca-HCO3 to Ca-SO4; group B, waters from Ca-HCO3 to Na-Cl. Group A water compositions are influenced by redox processes including the oxidation of H2S to SO42−. Primary sulphate from dissolution of Messinian evaporite is rare. Group B waters represent mixing of meteoric water with small amounts of brine. The most Cl (Br, I)-rich groundwaters are located in the NE of the investigated area, where a Cl–Br–I-rich brine was encountered by an exploration well in the Calabrian stratum. Berner has provided a classification of redox environments starting from the observation of the sequence of reduction/oxidation processes as shown by groundwater composition. At Fontevivo the Berner redox zones show an areal distribution where the anoxic zones occur in the topographical high. The δ2H and δ18O values of groundwaters plot close to the Global Meteoric Water Line. They indicate that local precipitation recharges the shallow aquifer (<30 m deep), whereas rainwater from the higher elevated Apennine ridge recharges the deeper aquifer (≧30 m deep) via the Taro river and its alluvial fan. Dissolved H2S is depleted in 34S consistent with biogenic sulphate reduction. Secondary origin from oxidation of H2S in shallow groundwater is invoked for depleted δ34S (SO42−). The studied saline sample (27.8 g/l TDS) show a δ34S (H2S) value of +24.9‰, suggesting a nearly complete reduction of Messinian sulphate within a system closed to H2S. A hydrogeological model is presented based on a chemical-thermodynamic, trace element statistical, and multi-isotope approach.

Messinian Ca–Cl Brines from Mediterranean Basins: Tracing Diagenetic Effects by Ca/Mg Versus Ca/Sr Diagram

In natural resource exploration, Ca–Cl basinal brines are important for understanding the origin and spatial and temporal distribution of hydrocarbons and sedimentary ore deposits. Little attention has been paid to the possible connection between fossil basinal brines and paleo-seawaters and to the implications for reconstructing paleo-seawater compositions. Secular variations of Ca/Mg and Ca/Sr ratios in seawater have been documented mainly using fluid inclusions in halite, calcareous fossils and mineral analyses. However, brines and other sedimentary records connected to paleo-seawater or its evaporated residues may be chemically affected by burial diagenesis or the effects of continental waters of meteoric origin, thus complicating interpretations of the analytical results. To investigate these effects on fluids and minerals related to the Messinian salinity crisis of the Mediterranean basin, we re-evaluate published data from: (1) brackish-to-brine waters from onshore (Northern Apennine foredeep; Levantine basin) and offshore (porewaters from the Deep Sea Drilling Project); (2) Messinian parental seawater deduced from calcareous fossils, fluid inclusions and sulfate minerals; (3) meteoric waters dissolving evaporites. The compositional trends related to seawater evaporation, diagenesis and mixing that affect the Ca/Mg and Ca/Sr molar ratios of the basinal brines are effectively discriminated on a binary plot depicting the proper fields for seawater and meteoric-derived fluids. Brines showing stronger dolomitization start from Ca/Mg and Ca/Sr molar ratios of Messinian seawater deduced from the published analysis of fluid inclusions and open ocean fossils, that are therefore here validated ex post.

The Pozzo del Sale Groundwaters (Irpinia, Southern Apennines, Italy): Origin and Mechanisms of Salinization

Chemical and water isotope ratios data for groundwaters from the Pozzo del Sale area in the Irpinia sector of the Southern Apennines are presented. The water chemistry of the aquifer system may initially be regarded as the result of easy and common, low temperature interaction between meteoric water and Late Messinian evaporites, which produce Ca-bicarbonate and Na-chloride passing through Ca-sulfate waters. However, a closer inspection reveals a more complicated geochemical setting consisting of: (1) two further Na-sulfate and Ca(Mg)-sulfate waters; (2) the existence of different meteoric recharge areas; (3) the mixing between the different groundwaters and allochthonous fluids from terrestrial mud volcanoes. The salinization mechanism and the local mineralogy were inferred by classical and novel ternary and binary diagrams. The presence of MgSO4- and Na2SO4-bearing minerals of non-marine or mixed origin other than gypsum and halite within the local evaporites suggests a mineralogical heterogeneity within the local Messinian evaporites. The paleoenvironment of this sector of the Gessoso–Solfifera Formation might have been composed of relatively small playa-lakes fed by seawater but also large amounts of continental waters of meteoric origin.

A conceptual hydrogeological model of ophiolitic aquifers (serpentinised peridotite): The test example of Mt. Prinzera (Northern Italy)

&NA; The main aim of this study is the experimental analysis of the hydrogeological behaviour of the Mt. Prinzera ultramafic massif in the northern Apennines, Italy. The analysed multidisciplinary database has been acquired through (a) geologic and structural survey; (b) geomorphologic survey; (c) hydrogeological monitoring; (d) physico‐chemical analyses; and (e) isotopic analyses. The ultramafic medium is made of several lithological units, tectonically overlapped. Between them, a low‐permeability, discontinuous unit has been identified. This unit behaves as an aquitard and causes a perched groundwater to temporary flow within the upper medium, close to the surface. This perched groundwater flows out along several structurally controlled depressions, and then several high‐altitude temporary springs can be observed during recharge, together with several perennial basal (i.e., low altitude) springs, caused by the compartmentalisation of the system because of high‐angle tectonic discontinuities.

Influence of soil on groundwater geochemistry in a carbonate aquifer, southern Italy

The role of soil compositions in influencing groundwater geochemistry in carbonate aquifers is still little known. Nothing is known regarding the influence of pyroclastic soils (andisol) within the carbonate Apennines in central-southern Italy, despite their wide distribution. In this study we analyze some physical and chemical properties of pyroclastic soil at the Acqua dei Faggi experimental site (southern Italy), to assess its influence on groundwater geochemistry. Chemical analyses were carried out on saturated paste extracts and a physical analogue model was developed through two column experiments. Physico-chemical properties of rainwater and spring water, and some microbiological features of the soil medium were also taken into consideration. The studied soil has a great influence in modifying rainwater chemistry during percolation. About the 50% of HCO 3 and Ca 2+ in spring water is due to interaction between percolation water and soil medium, and equilibrium with calcite is reached at this stage. The Na + /K + ratio is buffered by clay minerals in the soil by primary silicates in the pyroclastic cover. Cl and SO 4 2concentrations in spring water are very close to that of soil infiltration water during short-term interaction with soil, but a decline is showed during long-term cause to the anions adsorption effect in the andisol. Chemical and microbiological investigations show the existence of a soil microbial community that allows denitrification and nitrate reduction. Infiltration processes cause anoxic conditions within the soil medium, therefore the absence of NH 4 + in spring water throughout the observation period should be due to anammox processes. These findings suggest that hydrochemistry and spring chemographs may be significantly influenced by several factors, such as relationships between soil and rainwater, vegetation, and microbial communities, which are not necessarily correlated with lithological and structural features of carbonate aquifers.