Geoarchaeology and chronostratigraphy of the Lac du Puy intraurban protohistoric wetland, Corent, France

Abstract

This paper presents the first results of the geoarchaeological study of an unusual hilltop wetland, located within the protohistoric proto‐urban site of Corent in the French Massif Central. This small depression offers an exceptionally local sedimentary record that provided valuable data on long‐term human–environment interactions, as well as proto‐urbanization of the first millennium B.C.E. Field survey revealed a major archaeological discovery: a large ensemble of 114 Iron Age storage pits excavated in clayey deposits. The geoarchaeological analysis of stratigraphic logs and cross‐sections completed by geophysical survey and radiocarbon dating allowed us to refine the chronology of these structures. Here, we suggest these structures are probably contemporary with the Hallstatt occupation of the site (600–425 B.C.E.), consistent with the emergence at Corent of a short‐lived proto‐urban environment during this period. These investigations also allowed us to characterize the main evolution phases of the basin and the diversity of human impacts from first disturbance in the Early Neolithic to its final destruction in the Roman period. These findings highlight the nonlinear nature of the socio‐environmental interactions and the definitive shift to an “anthroposystem” as a consequence of major disturbance in the first Iron Age, centuries before the development of urban settlements in the oppida period.

1D sequential inversion of portable multi‐configuration electromagnetic induction data

“…The clay layer originates from a former wetland, and today, a small pond remains at the centre of the depression. Several archaeological trenches have been dug by Alfredo Mayoral and his team as part of the AYPONA project under the scope of the Auvergne Region (Mayoral and Dupreux ). The general stratigraphy of the topographic depression has been derived from the analysis of the trenches and is composed, from top to bottom, of a dry topsoil, a silty/sandy archaeological layer with remains of dump, lake clay deposit, an altered clay‐rich basalt layer, and the basaltic rock (Figure ).…”

Five millennia of human-environment interactions reconstructed from pedosedimentary archives of the Lac du Puy wetland (Corent, Fr.)

“…The Lac du Puy is typical of these rare contexts. The small wetland is situated within the extension of the large protohistoric archaeological site of Corent, located on a volcanic plateau dating from the Pliocene (Greffier et al, 1980;Nehlig et al, 2003;Mayoral et al, 2018). The plateau is located in a commanding position, controlling the north-south axis of the valley of the River Allier, 20 km south of Clermont-Ferrand (French Massif Central, see Fig.…”

“…The southern part of the plateau is a scoria cone with moderate slopes, while the Lac du Puy basin is situated in the northern area of the plateau, a basaltic lava flow with gentle topography. It is a closed circular depression (c. 2 Ha) interpreted as a pseudo-sinkhole (Mayoral et al, 2018), nowadays occupied by a dry (but seasonally wet) agricultural field with a small drained pond (20x20m) fed by runoff and subsurface flow. Aerial photography and historical maps suggest that before drainage operations in the early XIX th century , the open water area in the depression was probably more extensive (c. 100x80m) and could perhaps have been a valuable water source.…”

“…In the framework of the AYPONA palaeoenvironmental program, begun in 2013, palynological research and geoarchaeological survey (Mayoral and Depreux, 2017;Mayoral et al, 2018) were undertaken within this wetland. The objectives were to investigate long-term humanenvironment interaction, impacts of human settlements since the Neolithic, and localized impacts during the proto-urbanization episodes of the I st millennium BCE.…”

“…These patterns, together with other key features such as occurrences of non-native plant taxa, were interpreted as those of emerging proto-urban areas in the Late Bronze Age and the Late Iron Age . Further geoarchaeological research involved trench-based survey, developed in 2015 (Mayoral et al, 2018). The infilling of the basin, divided in 12 Stratigraphic Units (SU), is in general clayey and ranges from 30 cm to 2m in deeper central sectors of the basin, with very variable depth and often sharp lateral changes of pedo-sedimentary facies (Fig.…”