Pre-Cairnside Formation carbonate-rich sandstone: evidence for a Cambrian carbonate platform in southwestern Quebec?

Logging of cores drilled from the Unimin quarry, near St.-Canut, southwestern Quebec, revealed bioclastic, dolomitic sandstone lithofacies below the upper Cambrian Cairnside Formation, upper Potsdam Group. This lithofacies is distinctly different from any previously known lithology of the Covey Hill Formation (lower Potsdam Group). Preliminary local and regional lithostratigraphic correlations suggest that the pre-Cairnside Formation, mixed siliciclastic-carbonate unit extends eastward as far as the St. Croix village, about 50 km southeast of the Quebec City. Based on these correlations, two scenarios explaining possible regional depositional episodes and associated depositional systems tracts are also discussed. 1 Contribution to the Appalachian Foreland and St. Lawrence Platform Architectures in Quebec, New Brunswick and Newfoundland NATMAP Project 1 Resume : La description des carottes de forage provenant de la carriere Unimin, pres de Saint-Canut, dans le sud-ouest du Quebec, a revele la presence d’un lithofacies de gres dolomitique a texture bioclastique sous la Formation de Cairnside (partie superieure du Groupe de Potsdam) du Cambrien superieur. Ce lithofacies est totalement different de toute autre lithologie de la Formation de Covey Hill (partie inferieure du Groupe de Potsdam) decrite jusqu’a ce jour. Des correlations lithostratigraphiques preliminaires a l’echelle locale et a l’echelle regionale nous portent a croire que l’unite mixte silicoclastique-carbonatee qui est anterieure a la Formation de Cairnside s’etend aussi loin vers l’est qu’au village de Sainte-Croix, a environ 50 km au sud-est de la ville de Quebec. Sur la base de ces correlations, deux scenarios possibles d’evolution regionale des episodes de sedimentation et des corteges de facies associes sont presentes.