Figure 1. The Gergovie plateau from the ancient Sarliève Marsh, nowadays drained. Image by Alfredo Mayoral.
A new study in the Sarliève marsh, recently published in Quaternary Science Reviews, redraws the interaction between volcanos, climate, paleoenvironments and prehistoric societies during the Holocene in the Limagne plain (central France).
The Sarliève marsh is an ancient lake, nowadays drained, in the Limagne, the largest intra-mountanous plain in the Massif Central, near Clermont-Ferrand. Although there are many lakes and peat bogs in the Massif Central highlands, the Sarliève marsh is the only lacustrine sedimentary archive which can be used to reconstruct past environments in the lowlands of the Limagne plain (and is therefore crucial for any research about past socio-environmental interactions).
The area is very well known for its very abundant and multi-period archaeological occupations from the Neolithic to the Roman Period, including the mighty and renowned gallic oppidum of Gergovie. Many studies have tried to retrieve, date and analyze sediments from the marsh since 1960’s, however all failed in the crucial point: dating accurately the sedimentary sequence. This problem has been hampering the research for decades, and in practical terms limiting the use of all the available palaeoenvironmental data in the area. In order to bypass this challenge, we re-dated the sedimentary sequence and reviewed and reinterpreted the palaeoenvironmental history of the Sarliève marsh, as well as some crucial aspects of socio-environmental interaction in the catchment.
First, we drilled several sedimentary cores in the hearth of the marsh, carefully dating them by radiocarbon and constructing an age-depth model for the sedimentary sequence. This model is much more accurate and reliable that all the previous ones, which were significantly deviant and aged (and therefore unusable). We avoided the ‘reservoir effect’ that hindered accuracy by using reliable materials like wood or charcoal, and increased precision using a Bayesian model. Then, we performed high-resolution, multi-proxy sedimentological analysis (including grain-size analysis, magnetic susceptibility measurements, Loss on Ignition), geochemical and micromorphological analysis on the samples.
The results redefined the interaction between volcanos, climate, paleoenvironments and prehistoric societies during the Holocene:
- Five new tephras (volcanic fallouts) were discovered in the sedimentary sequence which match with regional volcanic events. A hitherto unsuspected phase of intense volcanic activity was detected in the middle Holocene (including degassing episodes, earthquakes and ash leaching). It impacted strongly the catchment, causing massive ash and sediment accumulation in the basin, and certainly also impacting contemporary Neolithic societies.
- A growing anthropogenic erosion is detected since 5500 cal BP approx, certainly due to impacts of Late Neolithic societies on soils. A strong break in erosion is detected in the middle Bronze Age, consistent with regional settlement dynamics which suggest habitat abandonments.
- In the Late Holocene we detected several dryer phases consistent with climatic-driven hydrological fluctuations detected in the western Alps, although these oscillations do not seem to have impacted Bronze age societies and soil erosion in the catchment.
- Our data suggest that the basin was drained in the Early Iron age c. 600 cal BC, i.e. several centuries before previously estimated. This allows to hypothesize that the Early Iron Age societies already had already a substantial capacity to modify the hydraulic environment in wetlands, well before the gallic and roman periods.
The results of this study, especially its chronological model, will be the cornerstone for all the forthcoming research about socio-environmental interaction in the area.
This research was performed by Dr. Alfredo Mayoral (GIAP-ICAC, GEOLAB), within a project funded by the Conseil Départemental du Puy-de-Dôme, in collaboration with GEOLAB, UMR 6042 Université Clermont Auvergne-CNRS; LMV, UMR 6524 Université Clermont Auvergne-CNRS; INRAP (Institut National de Recherches Archéologiques Préventives); EVS, UMR 5600 Université Lyon 2-CNRS and HNHP, UMR 7194, Muséum National d’Histoire Naturelle, Institut de Paléontologie Humaine, CNRS
Access the full text:
Alfredo Mayoral, Gérard Vernet, Olivier Voldoire, Jean-François Berger, Yannick Miras, Emmanuelle Defive, Times are changing: A new chronology for Holocene volcanic events and hydro-sedimentary history recorded in the Sarliève marsh (central France). Quaternary Science Reviews. Volume 272, 2021,107237. ISSN 0277-3791. DOI 10.1016/j.quascirev.2021.107237
