Serge Cassen

Climatically-driven impacts on sedimentation processes in the Bay of Quiberon (south Brittany, France) over the last 10,000 years

The Bay of Quiberon (NW France), which is protected by the Quiberon Peninsula, provides well-preserved sedimentary archives for high-resolution reconstruction of Holocene climate variability. Very-high-resolution seismic profiles were obtained from two Seistec boomer seismic campaigns conducted in the bay. The seismic surveys reveal the deposition of five distinct sedimentary units. This succession is correlated with radiocarbon-dated sediments sampled in a long CASQ core (MD08-3204CQ). The analysis of the sediments shows significant changes in grain size, indicating a complex series of palaeo-climate events dated at 8800, 8600, 4270, 3860, 2470 and 1060 cal. yr BP. These may be correlated with millennial timescale climate variability corresponding to the phases of Holocene rapid climate changes (RCCs), associated with negative North Atlantic Oscillation (NAO) index and usually characterized by weaker winter storms. On the contrary, periods between RCCs are characterized by the predominance of westerly winds and stormy conditions for Brittany (i.e. positive NAO). However, only storm events occurring during the RCCs have been preserved in the Bay of Quiberon. This paper aims to reconstruct the Holocene sedimentary infill of the bay, highlighting the role of episodic acceleration phases of the sea-level rise on the preservation of sedimentary archives. Thus, the Bay of Quiberon provides substantially a complete sedimentation record of the last 10,000 years characterized by a series of complex palaeo-environmental changes.

Aroche (Huelva, Andalucía): a new Neolithic axehead of Alpine jade in the southwest of the Iberian Peninsula

The discovery of a Neolithic Alpine jade axehead in Aroche, in the southwest of Spain, revives the question of long-distance exchange between the Iberian Peninsula and the rest of Europe. This polished blade belongs to a typological model quite characteristic of Alpine production during the second half of the 5th millennium B.C. Different mineralogical approaches (macroscopic features examination, specific gravity, direct XRD, non-destructive μXRF spectroscopy, optical stereomicroscopy, magnetic susceptibility determination and microprobe analysis) have identified the rock as an omphacitic jadeitite (mixed jade) with some tiny garnets and a weak retromorphosis. This analysis and the comparison of the rock structure with the referential JADE of Alpine natural jade samples, as well as the extraction modalities and shaping of the axe, provide strong arguments to assign the Aroche axe to a production of Mont Viso: the origin of thousands of axes that circulated in Europe between Ireland and Sicily. The Aroche axe, discovered not far from the variscite mines of Encinasola, could be considered as part of a possible exchange system between the Iberian Peninsula and the Gulf of Morbihan, in Brittany.

Gavrinis: The raising of digital stones

The Tumulus of Gavrinis, which is located in Brittany, is one of the best known monuments of Neolithic art because of its extraordinary engravings. A joint team of archaeologists and architects began recording the monument using digital multiscalar technology in 2011. The scanning was complicated by the narrowness of the inner spaces, uncomfortable conditions, granulometry of the stone, and extensive vegetation coverage. A huge database was created by using a combination of photogrammetric technology and low-tech scanning methods. A lot of post-production work was needed to turn the cloud of data into a clean 3D model, since the original tumulus is irregular and lacks any repetitive patterns or predictive geometry. The goal was to obtain a detailed geometric analysis of the tumulus in order to develop a better understanding of its architecture and engravings, which are sometimes less than a millimeter deep. This article covers the technological solutions that we applied while confronting situations ranging from the need to enhance a carved figure to our effort to reconstruct the entire monument by collating the results of several different recording techniques.