EVIDENCE FOR A GEOMAGNETIC EXCURSION RECORDED IN THE SEDIMENTS OF LACST FRONT, FRANCE - A LINK WITH THE LASCHAMP EXCURSION

Anomalous paleomagnetic directions, accompanied by low intensities of natural remanent magnetization are recorded at 17 m depth in the sedim ents cored from Lac St. Front (Massif Central, France). The rock magne tic properties and the parameters characterizing anisotropy of suscept ibility of samples taken from the sediment horizons carrying these ano malous directions, spanning some 30-40 cm, are identical to those of s amples taken from the other stratigraphic intervals, carrying a record of normal geomagnetic secular variation. Therefore the sequence of an omalous directions is interpreted as a geomagnetic excursion. Furtherm ore, it is concluded that this excursion occurred at a time when the p aleointensity field was low. The excursion is dated at about 33 C-14 ( similar to 37 ka B.P.) by correlating the susceptibility and paleomagn etic logs from Lac St. Front with the corresponding logs from the near by Lac du Bouchet sedimentary sequence. The excursional directions in Lac St. Front can be averaged out with a triangular window of 20 cm. T hese smoothed excursional directions resemble the directional variatio ns observed in the corresponding Lac du Bouchet interval. This finding indicates that the absence of this excursion in Lac du Bouchet may be due to a larger smoothing of the geomagnetic signal.