Sourcing of chalkstone used in medieval buildings in the Eastern Duchy of Normandy (10th−14th centuries) through geological and geochemistry analyses

Abstract

The provenance of medieval building stones links historic constructions with their quarrying areas, thereby revealing medieval trade routes and the spatial organization of past societies. In northern France, the Duchy of Normandy played a significant role in the medieval history of Europe, situated at the centre of the disputes between the English and French kingdoms. However, the historical documentation from this period is scarce, particularly in terms of the quarrying industry. Our study aims to define the quarrying areas and their diffusion zones and map the territorial organization of Eastern Normandy during the 10th–14th centuries. A multidisciplinary procedure using archaeological, geological and geochemical techniques was designed to establish the provenance of Normandy Chalkstone. First, we obtained a representative assembly of building stones by the selection and strategic sampling of 22 buildings. Second, we determined areas of chalk bedrock from a geological map rendered through GIS and sampled chalkstones from natural outcrops and quarries. In total, 118 samples from buildings, quarries and natural outcrops were characterized via optical microscopy and geochemical analyses for major, minor and trace elements (XRF, ICP-MS and ICP-OES), as well as for ⁸⁷Sr/⁸⁶Sr isotope ratios (MC-ICP-MS). The application in situ of pXRF analysis allows for the identification of Normandy Chalkstone sources preserved in archaeological sites. The results indicate that all chalkstones came from five local varieties of Normandy Chalkstone and one of Shelly Limestone imported from nearby regions. The suitability of chalkstone as construction material was evaluated in situ using a sclerometer, which revealed that the singular and local geological features of the chalkstone make it suitable for walling. Our study demonstrates the development of a prominent and relatively continued quarrying industry over the 10th to 14th centuries in Eastern Normandy. The main quarrying areas were constituted of three chalkstone diffusion zones that run coevally with smaller and apparently sporadic quarries. The chalkstone diffusion was strongly related to the occurrence of singular and local geological resources and the stone transport system, which favoured the use of effective fluvial and maritime navigation for transport over 50 km from the quarrying areas.