REY and Sr–Nd isotopes of soils from Ravenna (northern Italy) and their significance for environmental studies

The δ87Sr and εNd of 9 samples froma soil of the San Vitale Pinewood (P) and a nearby farm(F) soil fromRavenna in northern Italy have been determined after sequential chemical analysis. The REY (REE+Y) concentrations in the HCl extracts from the two soils have also been determined. The NH4-acetate extracts display the highest Sr and Ca concentrations (38–292 mg/kg, and 2.31–49.12 g/kg respectively), while the water extracts provide the lowest ones (0.5–6.1 mg/kg and 0.08–0.33 g/kg, respectively). The REY concentrations range narrowly in the P soil (24.3–31.4 mg/kg),while they distinguish along with Sr and Ca between the upper and lower horizons in the F soil (51.5–63.3 and 19.8–27.1 mg/kg respectively). In particular, as the lower horizons display concentrations similar to those of the P soil, this suggests a common origin of those sediments. The PAAS-normalized patterns in the HCl extracts of both the soils show either a middle REE enrichment, suggestive of phosphate dissolution and/or REY complexation with organicmatter, and a small positive Gd anomaly, referred to as the contribution from marine carbonates and phosphates. The range of δ87Sr (12.4–13) of the insoluble residue of the P soil indicates that Sr is is derived fromcrust silicates, that also provided the Sr of the insoluble residue of the F soil (δ87Sr= 9.3–17.1), but the larger range and the vertical decrease of values through the latter profile support the distinction in the upper and lower horizons. As these latter horizons display close δ87Sr to the values of the P soil, the common origin of these sediments is confirmed. The overlapping ranges of εNd of the insoluble residue from both the soils (from −8.4 to −6.85 and from −7.8 to −7, respectively) suggest that Nd is also derived from crust silicates. The range of δ87Sr of the NH4-acetate extracts of the P soil (from−0.8 to−0.41) is close to the corresponding range of the lower horizons (from−0.31 to−0.27) of the F soil suggest Sr origin fromLate Cenozoic carbonates. In contrast, the higher δ87Sr (from 0.09 to 0.25) of the upper horizons of the F soil, suggest some input of radiogenic Sr from crust silicates. The ranges of δ87Sr of the HCl extracts of the two soils largely overlap (the P soil from −0.9 to 0.3, the F soil from−0.72 to−0.34), suggesting a broadly common source, likely dolomite and phosphates of the Late Cenozoic. The narrow and overlapping ranges of εNd of the HCl extracts from the two soils (the P soil from−8.9 to −7.1, the F soil from −8.1 to −7.8) indicate that labile Nd is also provided by the same source, likely marine phosphates. Lastly, as the Sr–Nd isotopic ranges of geogenic and anthropogenic sources overlap in the study area, it is not possible to evaluate the potential impact of pollution on the two soils.