Distribution and chronology of P leistocene permafrost features in F rance: Database and first results

Numerous periglacial features (polygons, nets, soil stripes, ice‐wedge pseudomorphs and sand‐wedge casts, involutions) have been recorded in F rance by examining bibliographical sources and aerial photographs. These data show that a large part of F rance was affected by permafrost during the P leistocene and only the southern A quitaine B asin and L anguedoc seem to have been beyond its maximum extent. The first OSL ages obtained from the aeolian infill of wedge structures indicate that at least two phases of thermal contraction cracking occurred in southwestern F rance between ∼25 and 36 ka. Chronostratigraphical data from loess in northern F rance indicate that these episodes correspond to the formation of ice‐wedge networks associated with tundra gleys. In the latter region, two additional permafrost episodes probably occurred during the L ast G lacial, the older one corresponding to the end of M arine I sotope S tage ( MIS ) 4 around 60 ka and the more recent one to MIS 2 around 19–16 ka. Although stratigraphical data indicate that these episodes were relatively short (about one millennium), relict permafrost may have existed for longer periods in northern F rance.