THE USE OF GEOPHYSICAL METHODS (SEISMIC-R EFRACTION AND ELECTRICAL SURVEYING) IN IDENTIFYING BODIES OF THE BRENETS LACUSTRINE INFILLING (DOUBS, FRANCE) SINCE THE LAST GLACIATION

The sedimentary infilling of Brenets paleolake is studied to character ize and quantify changes in material flows since the last glaciation. The lithology and geometry of the various sedimentary units are mapped from 35 boreholes. These spot observations are supplemented by geophy sical exploration including seismic refraction and electrical sounding . From the combined results, substrate morphology (limestone, marl-lim estone or moraine) can be recognized and at least two major entities m ay be characterized in the infilling: one composed of sandy gravels an d sandy clays (Gs/As) deposited between 12,500 and 9,000 B.P. and a se cond one of clayey silts and lacustrine chalk (Sa/Cl) laid down betwee n 9,000 B.P. and the present day. The combination of these two geophys ical techniques provides a quick and reliable survey of substrate topo graphy and of the two entities forming the infilling, facilitating sub sequent quantitative analysis.