Oxalate Patinas on Stone Monuments in the Venetian Lagoon: Characterization and Origin

Calcium oxalate patinas have been sampled on architectural elements of two ancient churches located on Torcello Island (Venetian Lagoon) and subsequently analyzed. The site had been selected presenting patinas of exceptional amount and thickness, elsewhere generally found as thin alteration layers covering stone surfaces or within black crusts on monuments in urban environments. Optical and mineralogical analyses suggest that these patinas are not the result of a simple deposition process, but originate as surface “transformations” of the substrate, and are mainly composed of dihydrate calcium oxalate (weddellite) and gypsum. Among the experimental techniques, isotope analyses (C and S) have been specifically carried out aiming at achieving a better understanding of their origin and possible causes of formation. The observed carbon isotopic fingerprint reveals in fact a strong biological fractionation recorded in the oxalate patina (δ¹³C ranging from ?22.3‰ to ?28.0‰), almost exclusively attributable to C3 pathway photosynthesis processes. Slightly negative sulfur isotope ratio values seem to be inversely correlated with patina exposure to atmospheric agents and pollutants. The results obtained prove that calcium oxalate originates from a biomineralization process induced by lichen colonization in specific environmental conditions.     

Identification of pigments used in rock art paintings in Gode Roriso-Ethiopia using Micro-Raman spectroscopy

In this paper we present results on the rock art painting materials from the Gode Roriso rock shelter, located in the eastern Hararghe region of Ethiopia. This analysis included X-microfluorescence, Micro-Raman spectroscopy and microstratigraphy. As far as the results of the analysis are concerned, a white natural wax (beeswax), carbon black and iron oxides (a mixture of haematite and magnetite) along with charcoal particles (forming as a red colourant) have been applied on a natural substrate constituted of granite containing feldspar crystalline forms. Although very much a science-based piece of research, the results have far-reaching outcomes for understanding the sequencing of pigment application.     

Roman Rhine settlement dynamics evidenced by coin distribution in a fluvial environment (Oedenburg,Upper Rhine,France)

On the basis of archaeological and alluvial records, this paper presents the first spatial analysis of artefacts in relation to the evolution of the Rhine River, at the Gallo-Roman site of Oedenburg, during the first four centuries AD. The dataset consisted of several thousand Roman artefacts found by pedestrian prospecting over the last twenty years, over half of which were coins. This dataset was used together with high-resolution topography and geomagnetic mapping, to reconstruct settlement evolution, both on the terrace and in the floodplain. A comprehensive monetary chart has been compiled for the Oedenburg site, which highlights four major phases of settlement. These results provide a possible causal link connecting historical factors and alluvial events with intra-site evolution. Therefore, while changes observed during Phases I (until AD 68), II (AD 69 to AD 180) and III (AD 180 to AD 295) seem largely related to historical and societal events, Phase IV (AD 295 to AD 402) shows patterns of abandonment of the lower part of the floodplain that may well be related to an unusually humid period in the fourth century. These results are set in a broader context, from the Rhine catchment area to the Alps, and are in agreement with the wet conditions also documented in alluvial, lacustrine, geomorphological and palynological records in Germany (Lahn River, Lake Constance, Lake Nussbaumen, Kaisersthul area and the Black Forest). Studying the intra-site spatial distribution of artefacts with high temporal constraints, at a long-lived site with contrasted topography, opens new avenues for the detection of discreet events such as a higher water table, affecting only the lower zone.