Speleothems used by Neanderthals, in the Bruniquel Cave, Southern France.

The Bruniquel Cave contains circular structures made of broken stalagmites, dated to 176.5 ka and attributed to Neanderthals (Jaubert et al., 2016). A key question concerns the origin of the speleothem pieces used in these structures (i.e., speleofacts) and whether Neanderthals intentionally broke stalagmites, or instead collected fragments already lying on the cave floor—an important distinction in terms of intentionality. A related issue is the provenance of these speleothems within the cave, implying a particular selection process indicating potential symbolic value of speleothems for Neanderthals.

Two broken stalagmite bases and one broken stalagmite near the structures in the Salle de la Structure were investigated. U-series dating of the outer layers of the broken bases and stalagmite, as well as of the initial calcite layers that subsequently covered them, yielded ages from 432.8 ± 29.8 ka to 121.3 ± 1.2 ka. The broken base BR-201, produced similar ages for the older and younger calcite, allowing a precise age of 176.5 ± 2.1 ka for the breakage of this ~20 cm diameter stalagmite—consistent with the age of the structures. This result strongly supports breakage by the same Neanderthals who built the structures, and suggests an opportunistic selection of building material.

Laser-Induced Breakdown Spectroscopy (LIBS) with an in-house portable device was performed on speleothems from different sectors of the cave, and on speleothem pieces incorporated into the structures. Multivariate statistical analysis (e.g., principal component analysis), reveal compositional differences, mainly in Mg content, between speleothems from the entrance zone and those from the deeper parts of the cave. To date, the geochemical signature of the speleothem pieces used in the structures matches that of speleothems from the interior of the cave, failing to attribute the building material to a specific place in the cave, which would be an argument for a specific symbolic value.

Other calcite deposits in the Salle de la Structure were dated to constrain the cave floor conditions during Neanderthal occupations. These ages range from 163.0 ± 39.3 ka to 2.8 ± 4.1 ka. The results indicate that calcite deposition occurred in some areas during or shortly after the construction of the structures, implying that the floor surface in these zones likely remained relatively stable thereafter. In contrast, other areas were covered by calcite only during the Holocene. These findings help identify surfaces where human traces may be preserved and contribute to reconstructing the cave’s morphology during Neanderthal times by spotting the more recent calcite deposits that should be removed from the 3D model of the cave.

The study is financed partly by the French Ministry of Culture (DRAC), the Belgian Science Policy Office (BELSPO) and the Research Foundation Flanders (K208822N)

Jaubert J., Verheyden S., Genty D., et al., 2016. Early Neandertal constructions deep in Bruniquel Cave in southwestern France. 2016. Nature 534: 111 114.