LUMINESCENCE CHRONOLOGY OF PLEISTOCENE SEDIMENTS IN SOUTHERN QUEBEC: WHAT IMPLICATIONS FOR THE GLACIAL HISTORY OF NEW ENGLAND?

Over the last few decades, luminescence dating has gradually emerged as a new stratigraphic tool, even though difficulties inherent to its application to glaciarized environments have hampered its development. In order for the method to be effective, sediments need to be well exposed to sunlight before burial, limiting the applicability to a small number of sedimentary environments and facies, namely aeolian, lacustrine, and fluvial. Direct dating of glacially derived sediments, egoutwash or ice-contact drift, is of limited use as they yield grossly overestimated age. Quartz optically-stimulated luminescence is characterized by poor dose sensitivity and dimness, properties commonly encountered in quartz derived from glacierized landscape. Anomalous fading of feldspar luminescence has also severely hampered the elaboration of the regional chronostratigraphic framework until the development of reliable AF correction methods proposed by two Canadian laboratories (SFU in BC and UQAM in Qc). Feldspar is now the commonly-used dosimeter in the regional Quaternary stratigraphy because of its large dose range, allowing the dating of sediments of up to 500 ka in age.

A relatively coherent chronostratigraphic framework is now emerging for the Quaternary of Southern Québec, based on IRSL dating. Lithostratigraphy comprises three tills and at least three nonglacial sediment sequences, the oldest of these, described in the Grande Coulée section, is dated from the Middle Pleistocene, and may correspond to MIS 9. Sediments of the last interglacial would seem to span the Sangamonian sensu lato, from ca 130 to ca 80 ka. The age of interstadial sediments found below and above units associated to the Chaudière glaciation would suggest a MIS4 age assignment for this glacial event. The Gayhurst Formation is tentatively assigned to the earliest part of MIS3. Finally, the inception of the last glacial advance, formerly known as the Classical Wisconsinan, is tentatively dated at ca 35 to 45 ka, from a series of IRSL ages obtained for the aggradational facies of sub-Gentilly Till distal proglacial sand largely exposed in the St. Lawrence Lowlands. Correlation and possible synchronization of the New England Quaternary stratigraphy with that of Southern Québec will be discussed at the meeting.