Illite crystallinity and organic matter reflectance techniques are applied to the evaluation of burial metamorphic conditions for lithostratigraphic groups accumulated during the post-Taconic stage of the Appalachian orogen in the southwestern Gaspé. The results of this work show that the metamorphic grade of the Paleozoic succession decreases upwards but is anomalously high in the youngest Fortin Group. A model is proposed in which the two parts of the succession were separately buried. The model envisages the lower part (Honorat, Matapedia, and Restigouche groups) being uplifted in the south whilst deposition of the Fortin Group continued in the north in a basin yoked by the Matapedia Fault. Burial is interpreted to have occurred under an average oceanic geothermal gradient in the early Paleozoic basin and under a high geothermal gradient in the Fortin basin.