Late Quaternary vegetation and glacial history in the St. Lawrence Lowlands, Canada

This paper presents data of various kinds concerning the Quaternary geology of the St. Lawrence Lowlands: pollen diagrams, C14 dates, and diatom floras. These data show that the highest parts of the St. Lawrence Lowlands were already deglaciated more than 12,000 years ago, as appears from the existence of glacial lakes around some of the Monteregian Hills. The collected evidence seems to confirm the data concerning the age of the Champlain Sea: it lasted from approximately 11,400 years B.P. to somewhat before 9,500 years B.P. The data supply also evidence for a lowering of sea level during the Champlain Sea episode, related to the St. Narcisse readvance, followed by a sea level rise (indicated by deeper water) after the retreat of the St. Narcisse ice. As to the pollen diagrams presented here, they show that the New England pollen zonation can be applied to the lacustrine pollen sequence of the St. Lawrence Lowlands, and strongly suggest (together with C14 dates) that a correlation exists between the Younger Dryas of northwestern Europe, the St. Narcisse readvance, and the first part of the pollen zone A4 from New England as described by Davis and other workers. The diatom data of Lake Hertel appear to confirm the present elevation of the maximum marine limit (level) in the Montreal area as being approximately 570 feet or 171 meters. Finally the diatom floras supply information on the paleo-ecological conditions of the lakes studied.