DEVELOPMENT OF GLACIAL EVENT-STRATIGRAPHY; SE QUEBEC AND N. NEW ENGLAND

Research that Perry Stewart and Paul MacClintock carried out in the 1950’s and 1960’s on Laurentide Ice Sheet deposits in northern New York and in Vermont led them to propose a three-event glacial stratigraphy, which was imported into the Quebec Appalachians by Barrie McDonald in 1964. He adapted their stratigraphy to his and others’ observations of many multi-till sections in Southern Quebec. The author and associates ultimately confirmed the basic validity of these models by careful quantitative study of sections in the Chaudiere River Valley and its tributaries, especially the critical Riviere des Plante sections. In the mid 1970’s, Robert Lamarche discovered that the end of the Lennoxville Glaciation was marked by a reversal of ice flow toward the north in the Quebec Appalachians. The Highland Front Moraine, originally described by Nelson Gadd, was deposited subsequently by an unnamed southerly readvance. Thus, Stewart and MacClintock’s Vermont stratigraphy eventually morphed into the Lennoxville Till/Gayhurst Formation/Chaudiere Till/Massawippi Formation/Johnville Till/Pre-Johnville sediments/Preglacial regolith stratigraphy that is presently established in Southern Quebec. It is the author’s opinion that the Lennoxville and Chaudiere Tills both represent deposition during Wisconsinan stades, separated by glaciolacustrine sediments of the Gayhurst interstade (~55ka). The non-glacial Massawippi Formation and at least part of the St. Pierre sequence are probably of Sangamon age, and the Johnville and Becancour Tills of Quebec and ‘older tills’ in Vermont are probably of Illinoian age; Pre-Johnville sediments (~181ka) are pre-Illinoian and are not clearly related to any identifiable glacial event. Extensive stratigraphic drilling and detailed examination of numerous sections in Southern Quebec, over many years, has revealed no evidence of any glacial deposits predating the Johnville Till; in fact, laminated lacustrine sediments, deposited by the advancing Johnville Glacier, lie directly on well-developed regolith with no components, mineral or otherwise, that could have been derived from the nearby Canadian Shield. This suggests that no ancestral Laurentide Ice Sheet covered this part of the Appalachians prior to deposition of the Johnville Till.