MIDWISCONSINAN HISTORY OF THE SOUTHEASTERN SECTOR OF THE LAURENTIDE ICE SHEET AND THE LATE QUATERNARY STRATIGRAPHIC RECORD OF SOUTHEASTERN QUÉBEC

The southeastern sector of the Laurentide Ice Sheet experienced an important episode of ice volume reduction during transition from marine isotope stage 4 to 3, which led to the development of a large glacial lake in the northward-flowing Chaudière and St-Francois River valleys (Québec). This episode is associated with glacial Lake Gayhurst and is reflected by locally thick deposits of glaciolacustrine sediments. Our chronology assigns this interstadial event to a period between ca. 60 to 35 ka. The objectives of this study are to: 1) characterize the sediments and the stratigraphic architecture of the Gayhurst Formation, 2) define the physical lateral extension of the Gayhurst Formation; 3) present a new IRSL chronology of this glaciolacutrine sequence, and 4) bring additional precision to the paleogeographic reconstruction through the interpretation of the ice volume of the LIS and the evaluation of different meltwater routing scenarios through New-Brunswick, Maine and Vermont. Recent field and stratigraphic data that were acquired in the course of a groundwater/Quaternary geology mapping project in the Chaudière.