ADDITIONAL EVIDENCE FOR THE LAURENTIAN TR ANSGRESSION ON THE SOUTH SHORE OF THE MIDDLE ST-LAWRENCE ESTUARY, QUEBEC

Additional evidence for the Laurentian transgression on the south shor e of the middle St. Lawrence estuary, Quebec. A vertical section in th e 10-12 m terrace at the mouth of Ruisseau Bellechasse, near Berthier- sur-Mer, on the south shore of the middle St. Lawrence estuary, provid es evidence for a 12-m maximum level for the middle Holocene Laurentia n transgression, This level is two meters higher than suggested in the past. The 4-m thick intertidal unit deposited during the transgressio n overlies an erosion surface cut into a stratified silt and clay depo sit (rhythmites), poorly fossiliferous and dated circa 10 ka. Radiocar bon dates on wood and on aquatic and intertidal plant debris in situ r eleased ages BP between 5.4 and 6 ka (N-8). This chronology is slightl y older than at Montmagny - Cap-Saint-Ignace reference sites, located approximately 30 km downstream. The Anse de Bellechasse section does n ot present the full sequence of Holocene events observed at Montmagny. However, there are a few fluvial terraces related to the St. Lawrence water level; one was built up circa 1.4 ka, two other between 0.5 and 0.7 ka suggesting minor fluctuations of the base level during the las t two millenia.