OSL AND AMS 14C DATING ON MARINE AND TERRESTRIAL ORGANIC REMAINS FROM A CHAMPLAIN SEA BEACH NEAR COVEY HILL, QUÉBEC

The Champlain Sea dates are subject to numerous errors due to the presence of ancient carbon in the waters. The measured ages on carbon shells are thus subject to be older than the real ages that could be measured in terrestrial organic remains. Recently, studies based on varve chronology in New England and lake sediments (Lac Hertel) in the Champlain Sea basin has been indicating that shell-based Champlain Sea ages are about 1000 years older than the chronology of the region. In the vicinity of Covey Hill (Quebec, Canada), marine and terrestrial vegetal macro-rests have been found in one littoral deposit situated at elevation 92 m relative to actual sea level (the maximum elevation of the Champlain Sea is estimated at 160m in this area). The sediment consists of decimetric layers of well-sorted, quartzeous medium sand alternating with centimetric layers of organic matter containing Dryas leaves, carex grains, wood fragments, a well-preserved caribou horn, chitineous marine bryozoans and algae. This 3m sequence is underlain by shelly gravel and overlain by well-sorted and massive medium to fine sand resembling aeolian or littoral sand. The site provides a opportunity to cross-check and validate various chronological tools in the Champlain Sea basin. The site is particularly appropriate to verify the OSL (optically-stimulated luminescence) method applied to both quartz and feldspar grains in littoral and aeolian (?) settings. The contemporaneous deposit of layers of well-sorted sand and organic matter will pose a strong constraint on OSL dates, thus permitting to validate the range of application of these methods in the Champlain Sea environment. The 14C AMS dates that can be done in the sand/organic sequence include marine shells, caribou horns, terrestrial organic fragments and marine organic remains (chitineous bryozoans and algae), thus it is possible to assess the reservoir effect in the Champlain Sea at this elevation.