Spectroscopic and Chemometric Comparison of Local River Sands with the Aggregate Component in Mortars from Ancient Roman Buildings Located in the X Regio Between the Livenza and Tagliamento Rivers, Northeast Italy

A combined spectroscopic–chemometric approach is used to investigate the possible sources of material exploited by the Romans to build four domus and a public thermae complex (I century BC–II century AD) located in the X Regio portion between the rivers Livenza and Tagliamento in northeast Italy. The rounded grain shapes observed in the aggregates recovered from the mortar fragments suggest that the rivers flowing close to the archaeological sites are the most likely sources of material. Coarse-grained sediment samples from nine rivers and streams in this area are examined and their similarities to the aggregate samples evaluated. The diffuse reflection Fourier transform infrared (FT-IR) spectra of the sand samples in the 63–420 µm fraction, consisting mainly of carbonates and silicates, are studied and compared in suitable spectral ranges through principal components analysis. As an additional step, the relationship between the most significant scores plots and the composition of the samples is investigated using appropriate descriptive indexes obtained from the spectra. The analysis performed on the river sand spectra alone shows that the samples from the easternmost Lemene and Tagliamento rivers present a behavior distinct from that of the western rivers (Cosa, Livenza, Meduna, Meschio, and Noncello), in agreement with their present location and past history. All the aggregate spectra investigated are compatible with the spectral characteristics of the samples from the Tagliamento and Lemene rivers, except for those from the Torre di Pordenone site, which are more similar to the sand spectra of the western rivers.