ABSTRACT: Donnees complementaires sur la Transgression laurentienne, à Montmagny (Québec), à partir d'une coupe dans lat partie arrière de la terrasse de 8-10 mètres [ Additional data on the Laurentide Transgression at Montmagny, Québec, from a section into the back area of the 8-10 m terrace].

CGRG Bibliography of Canadian Geomorphology
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Abstract

A recent 6-m deep excavation into the 8-10 m terrace revealed the lithostratigraphic units at the back of the low coastal terrace between Montmagny and Cap-Saint-Ignance. Only 3 units have been observed compared to the 5 units exposed in the active cliff located in front of the airport stripe. The 2 missing units are the subtidal silt-clay units dated to 8 to 7 ka and the terrestrial organic layer containing logs and stumps dated to 7 to 6 ka. At the back of the 8-10 m terrace, the Goldthwait Sea clay surface is 4 m higher than at the base of the cliff. This unit is overlaid by a sand and grave layer about 30 cm in thickness. A piece of wood at the summit of this unit has been dated at 5970+/-70 BP (UL-2737). The coarse grained unit, which is absent in the cliff, is covered by a sandy silt intertidal unit about 3 m tick; it contains abundant in situ, aquatic plant remains, that were dated at 5460+/-70 BP (UL-2719), whereas two pieces of wood collected at the base of the unit were dated at 5680+/-80 BP (UL-2740) on peat and at 5020+/-70 BP (Ul-2737) on a stump of larch (Laris sp.). This vertical section confirms the extent and the altitude reached by the mid-Holocene transgression in the area between Riviere du Sud, at Montmagny, and Cap-Saint-Ignance.

Bibliography of Canadian Geomorphology