The Biéroc archaeological site in La Mondrée cove is currently the only submerged habitat of the Middle Paleolithic known in Europe. It lies by approximately 20 m water depth and shows a remarkable state of preservation, making this site scientifically valuable.

Fig. 1 : Location of study area

The settlement level is associated with an organic-rich strata containing pollens suggesting an open landscape in a mild climatic context (Clet-Pellerin, 1988 ; Coutard, 2003 ; Coutard et Cliquet, 2005 ; Cliquet et al., 2009). OSL dating yielded an age around -70 ky (boundary between marine isotopic stage 5a and 4) in agreement with the palynological interpretations (Mercier et al., à paraître).

The main objectives of this survey was to caracterise the territory traveled by the Neanderthal hunter-gatherers (incised valley morphology, thickness of deposit, position of the site in relation to the watercourse,,...) and to collect informations to prepare a coring campaign that would aim at identifying the succession of occupation levels.

Fig. 2 : Bathymetric DTM (A), Backscatter mosaïc (B), Substrate map (C), Zoom on backscatter mosaïc to show screes at the foot of Bieroc rock bar as previously described by divers (D).

Sediment thickness at archaeological site is thin, corresponding to sediment "pockets" located at the foot of Bieroc rock bar and well preserved from erosion during glacial periods (MIS 4 and 2) and Holocene transgression. Two incised valleys systems were identified with seismic data. The first one flowed along Biéroc rock bar and the second one in the middle of the bay. They have been infilled with Holocene deposits.

Fig. 3 : Seismic profil (sediment profiler) on archaeological deposit suggesting preservation of pre-LGM deposit (A) and location of the profil on bedrock depth DTM (B).

An pre-LGM (Late Glacial Maximum) sediment cover could have been preserved in the surveyed area especially in the axis of the paleovalleys.

At the archeological site, the thin pre-LGM sediment cover thickness combined to difficult accessibility to the Biéroc rock bar would probably compromise the feasibility of a coring campaign.

Fig. 4 : Isopach map of pre-LGM sediment cover (A) and total sediment thickness on Biéroc archaeological deposit (B).

According to our data, the site was located nearby the river (less than 300m-distance) and its elevation was only 10 m above river bed level. Pollens analyses suggest that archaeological artefacts dated to MIS 5a. At this time, sea level was 20 m below the present sea level (Edwards et al., 1997 in Shackleton et al., 2003) and coastline would have been located at 500-m distance from the site (Fig. 5).

Fig. 5 : Paleoenvironmental context of La Mondrée cove at MIS 5a and artistic evocation of paleolandscape.

But considering OSL dating obtained in 2010 yielding an age of 70 ky to sediment on which artefacts sit on, sea level was 80 m lower than the present (Siddall et al., 2003). Assuming that the location of the site in relation to the streams did not change, then coastline would have been located 30 km away from the Bieroc archaelogical deposit. The site was thus overhanging an extensive floodplain. Chalk outcrops from upper cretaceous (nowadays submerged) were accessible and could be considered as potential sources for flint discovered at Biéroc site. A dedicated study, which results are expected for april 2020, is being conducted to determine flint deposit source. (Fig. 6).

Fig. 6 : Paleoenvironmental context of La Mondrée cove 70 ky ago.