Identification of parietal carbonates' annual precipitation rate for a microchronological setting of pyrogenic archaeological occupations: the Grotte Mandrin (Malataverne, Drome, France) case

In rock shelters and caves, the geo-archaeological reading of sediments can allow, in favourable cases, a micro-chronological study of traces of anthropogenic activities and in particular in the use of fire. If the recurrence in the use of fireplaces can sometimes be identified by a micromorphological study of these ground structures, it is very uncertain that all the different combustion episodes can be identified. It turns out that paleo-fire events can be recorded elsewhere than in the hearths. For instance, they can be recorded as soot marks trapped in speleothems, which are witnesses of fires made inside the caves. Thus they can be the object of a fuliginochronological study (lat. fuligo, fuliginosus: soot), which consists in studying the succession of soot deposits trapped in a matrix. Some limestone speleothems have another advantage, which is to be annually laminated. When it can be demonstrated, the joint study of soot films and calcite doublets allows the construction of precise paleo-fire chronicles. In this study, we demonstrate, with the help of both crystalline fabric analysis and seasonal variations of strontium (Sr) content, that the calcite doublets observed in the fine parietal carbonated crusts of the Grotte Mandrin archaeological site are indeed annual. We used LIBS technics (Laser Induced Breakdown Spectroscopy), which reveals relative variations of minor and traces elements, within speleothems carbonates, on an annual or sub-annual level. Soot film sequences can then be indexed to the annual carbonates precipitation calendar, giving precise paleo-fire chronicles. The study of the rhythmicities of human occupations at the Grotte Mandrin then becomes accessible with an unequalled precision.

Automated summary

Geo-archaeological reading of sediments in rock shelters and caves can provide a micro-chronological study of anthropogenic activities and fire use. The joint study of soot films and calcite doublets allows for the construction of precise paleo-fire chronicles. The use of LIBS techniques reveals relative variations of elements within speleothems carbonates, leading to accurate paleo-fire chronicles.