Paleoclimatic significance of late Pleistocene ice-wedge casts in Southern Quebec, Canada
Abstract Ice-wedge casts in southern Quebec are exclusive to deposits pertaining to two ice front positions during the retreat of the Laurentides ice sheet: the Highland front morainic system located at the southern margin of the St. Lawrence lowlands, and the St. Narcisse front morainic system located at the southern margin of the Laurentides highlands. Wedge casts filled with sand and gravel are relic of true ice wedges and give evidence of former permafrost conditions in the ground during the retreat of the ice sheet in that area, between 13 000 and 11 000 years B.P. Mean annual air temperature was lower than −6°C, a difference of 8–12° with the present-day temperature. Humidity was high enough to allow the growth of ice wedges in the permafrost. These rigorous climatic conditions prevailed during a few centuries only. There is no positive evidence of tundra conditions in southern Quebec young than 11 000 years ago.