The Lower Ordovician Upton Group is part of the Cambrian–Ordovician external domain of the Appalachian Orogen of southern Quebec. It is a mixed carbonate–siliciclastic–volcanic succession occurring within flyschoid sediment of the Lower Cambrian Granby Nappe. The bulk of the Upton Group is a grey, massive, recrystallized limestone of probable peritidal and shallow subtidal origin. Associated siliciclastic lithofacies are typical of peritidal and outer-shelf settings. The proposed peritidal paleoenvironmental model differs from previous interpretations and indicates that it is unlikely that the Upton Group is a slab derived from the Ordovician continental margin which has slid into the Granby Nappe.