THE MIDDLE AND UPPER PLEISTOCENE LOESSIC FORMATION OF LA JOUANNIERE AT BONNEVAL, EURE-ET-LOIR (FRANCE) : SEDIMENTOLOGY, GEOCHRONOLOGY, PALAEOENVIRONMENT AND PREHISTORY

摘要

A six meters thick loess formation has been discovered during an archaeological survey at la Jouanniere, Commune of Bonneval (Eure-et-Loir, France) on the western edge of the high Loir Valley. Multidisciplinary studies (sedimentology, micromorphology, geochronology Re-OSL and palaeobotanics) contribute to the partition of the ten layers (or stratigraphical units, US) of silty loessic deposits into two sequences. In the lower sequence (US 10 to 5), loess was deposited during Marine Isotopic Stages (MIS) 12 to 6. In this lower sequence, handaxes and cores were discovered in situ in US 6a and 5. They suggest the presence of Middle Palaeolithic hominins since the beginning of the MIS 8. The upper loess sequence (US 4 to 1) was altered and disturbed many times (cryoturbation, bioturbation, illuviation). A grey forest soil was observed. This upper sequence, when compared with the main loessic records of northern France, was probably deposited and altered during the Eemian-Weischelian Complex. Two flaking heaps with cores and flakes were excavated on the soil at the contact of US 4 and 3. The "chaines operatoires" are typical of Middle Palaeolithic flaking. The same types of flaking were also observed in the uppers US 2 and 1 that contained numerous but scattered Levallois cores and Mousterian handaxes. At Bonneval, the stratigraphical units are thinner than in the Saint-Pierre-les-Elbeuf stratotype in Normandy. However the la Jouanniere Formation is the second site in northern France that recorded the loess deposits and paleosoils succession since 450 000 years.