POSTGLACIAL VEGETATION DYNAMICS AND ENVIRONMENTAL CHANGE RECORDED AT A SMALL SCOTSTOWN BOG LOCATED IN THE BASIN OF A FORMER PROGLACIAL LAKE, SOUTHERN QUÉBEC, CANADA

During the last glaciation, the buildup and retreat of the vast Laurentide ice sheet greatly influenced the geology and landscape of large regions of the Northeastern USA and Canada. At the onset of the late-glacial period, as the Laurentide ice sheet retreated from the area, the Rivière Saint-François valley in southern Québec (part of the Appalachian Upland), was covered by a large and deep proglacial lake impounded at the ice-margin. In this study we used a 6-m-long sediment core from Scotstown bog, in the limits of the former proglacial lake, to reveal the Late-glacial and Holocene paleoenvironmental conditions of the region. We aimed to describe the local vegetation development and changes in the sedimentary and aquatic environment using plant macrofossils, chironomids, and changes in sediment organic matter content. The clay bottom sediments of the Late-glacial period reveal a record of pioneer shrub vegetation on the (paleo)shore of a cold-water proglacial lake as reflected by the chironomid assemblages. A shift from clay to gyttja sediment suggests the lowering of the lake level and the isolation of the water body. This hypothesis is supported by the rise in sediment organic matter content and plant macrofossil composition that displays a variety of remains from aquatic species. The change in the composition of the plant macroremains also marks the start of the overgrowing of the lake and stepwise terrestrialization. The undisturbed Late-glacial and Holocene record of Scotstown bog is one of the few in the region studied for paleo-proxies and further research will give us valuable insights into the deglaciation processes and subsequent environmental dynamics in the Appalachian Upland in southern Québec.