A procedure for the measurement of 87Sr/86Sr in carbonates without off-line strontium separation was developed, validated and applied to Normandy chalkstones. The method is based on the injection of the...

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 87 Sr/ 86 Sr 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.

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<p>Rock avalanches are voluminous debris instabilities originated from a fallen portion of bedrock that suffers pervasive disintegration [1]. Tough rock avalanches are foreseen as low-frequency events, their volume (>10<sup>6</sup> m<sup>3</sup>) and runout distance (kilometric scale) make them extremely hazardous processes in populated mountain settings and key contributors to landscape denudation [2]. Deciphering the timing of recurrent rock avalanches is crucial to understand the triggering factors involved in their origin (e.g., role of seismicity) and for risk assessment.</p><p>This study focuses on a rock avalanche cluster preserved in the southern flank of Sierra de la Sobia; a limestone massif located in the Cantabrian Mountains (North Spain). The rock avalanche cluster analyzed is spatially related to the Marabio Fault trace, which shows unequivocal evidence of Quaternary activity [3]. Rock avalanches in this area have been interpreted as coseismic based on the following evidence [4]: (i) boulder populations show fractal block-size distributions consistently with dynamic fragmentation; (ii) the kinematic analysis of local minor transverse and parallel faults points to a horizontal N-S compression consistent with the regional stress field; and (iii) slope stability analysis indicates that headscarps will turn unstable if ground acceleration peak rises to 0.10–0.15 g during an earthquake, which is within the values expected according to the 2013 European Seismic Hazard Map. A first attempt of numerical dating was performed through the U-Th technique on calcite cements found in the oldest rock avalanches. Results suggest multiple episodes of cementation during the last ~280 ka, but age dispersion hinders the age bracketing of instability events<sup>4</sup>. Here we present a collection of twenty cosmic ray exposure ages relying on the isotope Cl-36 obtained from limestone boulders sampled in the youngest accumulation bodies of the Entrago and Carrea rock avalanches. Results allow to constrain up to 5 instability events spanning the last ~22 ka and occurring at average recurrence intervals of ~3.6 ka. The youngest rock avalanche event took place 8.5 ka ago and left boulder accumulations close to the headscarp of both rock avalanches. Boulder age dispersion increases accordingly with the increase in runout distance from the headscarp, possibly due to the spatial overlapping of accumulation bodies resulting from different instability events of seismic origin. These preliminary results are promising, because if extended to other rock avalanche clusters of the Cantabrian Mountains, they could help to decipher the recurrence time of severe earthquakes in mountain settings where tectonic deformation occurs at low to moderate rates.</p><p>[1] Hermanns, R. L. Encyclopedia of Natural Hazards. vol. 2 (2013).</p><p>[2] Davies, T. Rock Avalanches. In Oxford Research Encyclopedia of Natural Hazard Science 58 (Oxford University Press, 2018). doi:10.1093/acrefore/9780199389407.013.326.</p><p>[3] Fernández, F. J., Alonso, J. L. & Pando, L. Evidence for quaternary tectonic activity in the western cantabrian Zone (Passes of Marabio, Sobia nappe). Geogaceta 64, 1–3 (2018).</p><p>[4] Fernández, F. J., Menéndez-Duarte, R., Pando, L., Rodríguez-Rodríguez, L. & Iglesias, M. Gravitational slope processes triggered by past earthquakes on the Western Cantabrian Mountains (Sierra de la Sobia, Northern Spain ). Geomorphology 390, 107867 (2021).</p>