Ground penetrating radar in the medieval oyster shell middens of Saint-Michel-en-l'Herm (Vendée, France). (April 2018)

• Record Type: Journal Article
• Authors: Cariou, Elsa; Baltzer, Agnès; Leparoux, Donatienne; Ledoyen, Julie; Debaine, Françoise
• Is Part Of: Journal of archaeological science. Volume 18(2018)
• Page Start: 186
• Page End: 196
• Publication Date: 2018-04
• Subjects: Ground penetrating radar -- Shell middens -- Internal geometry -- Ostrea edulis -- Middle ages -- European coasts; Archaeology -- Periodicals; Archaeology -- Research -- Periodicals; 930.1
• DOI: 10.1016/j.jasrep.2017.12.048
• Languages: English
• ISSNs: 2352-409X

Abstract

Abstract: This study presents the integrated results of GPR (Ground Penetrating Radar) and sedimentological analysis, performed on the giant shell middens of the medieval site of Saint-Michel-en-l'Herm (Vendée, France). Avoiding the use of destructive methods like large-scale digging, the purpose of this study was to determine the internal structure of the northern midden and the links with its substrate, and to obtain insight on the manner of its construction. Four GPR profiles were obtained along the main axis of the midden, on the shell mound, and at its foot, in an area leveled by the former extraction of shells. Sedimentological analysis is also presented from study of the extant parts of the midden and with hand auger cores taken along one of the GPR profiles. The integrated results show that each sedimentological facies is related to a specific radar facies, allowing the mapping of lateral and vertical facies variations along the GPR sections. Within these deposits, the major tilted reflectors correspond to thin soils and trampled surfaces. Their geometry and the stacking pattern highlight multiphase deposition triggered by successive inputs of large volumes of shells (in the range of 100 m 3 ), from west to east. Below the exploited parts of the midden, the data are interpreted to show the presence of undisturbed shells, although, an ancient dug area was also identified by GPR. Finally, sedimentological and GPR data both show evidence of a midden established on the west bank of a channel, progressively infilling the channel eastward. These results illustrate the relevance of GPR in answering major questions common to all large shell middens. Highlights: Lateral facies variations can be observed along Ground Penetrating Radar sections. GPR allows characterizing the shell midden basement and extension. GPR sections show in situ shells and pits below industrially leveled areas. GPR sections reveal unsuspected internal structures, and a multiphase building. The multiphase building of the midden filled a channel from its western bank.