Successions of invertebrate microfossils and the late quaternary deglaciation of the central St Lawrence Lowland, Canada and United States

Abstract

Foraminiferal and ostracode assemblages in late glacial and early post-glacial sediments of the Central St Lawrence Lowland show that a proglacial lake (Glacial Lake St Lawrence) preceded the Champlain Sea in some parts of the lowland, and that the Champlain Sea was in contact with the Laurentide Ice Sheet during deglaciation of other parts of the lowland. Glaciolacustrine and glaciomarine environments were followed by marine environments with salinity as high as 24–34‰. The higher salinity water in the Champlain Sea was part of a salt water wedge extending from the Gulf of St Lawrence into the Central St Lawrence Lowland. The beginning of the Champlain Sea is placed between 11.4 and 11.6 ka BP on the basis of radiocarbon ages for the arrival of the salt water wedge in the Central St Lawrence Lowland. The distribution of rhythmites associated with Glacial Lake St Lawrence shows that subaqueous outwash fans in the Ottawa area were deposited in Glacial Lake St Lawrence rather than in the Champlain Sea.