Gilbert Prichonnet

Alleghanian deformation in the eastern Gaspé Peninsula of Quebec, Canada

Juxtaposition of the Mississippian Risti- gouche and Cannes-de-Roches Basins, which are subbasins of the composite late Paleozoic Maritimes Basin, occurred through dextral movement along the north- west-striking PerceFault system in the east- ern GaspePeninsula of Quebec. The north- west-striking faults are truncated by small north-northwest-striking dextral strike-slip faults, which probably developed as region- al stress gradually rotated clockwise from north-northwest-south-southeast to north- east-southwest. This study provides the first evidence in eastern Quebec for significant post-Acadian block displacement other than normal faulting and indicates that Al- leghanian deformation extended much far- ther north than previously thought. Iden- tification of these structures formed during the Alleghanian orogeny but more than 1000 km away from areas of peak Allegh- anian metamorphism in the southeastern United States underlines the far-reaching effects of continental collisions. It also casts doubt on the age attribution of brittle strike-slip faults elsewhere in the Gaspe ´ Peninsula, away from Mississippian expo- sures. Such brittle faults were previously associated with late stages of the Acadian orogeny but could in fact be considerably younger.

Significance of paleosurfaces in interpreting the paleogeographic and stratigraphic evolution of the late Paleozoic Paspébiac graben, a recently identified basin in the southern Gaspé Peninsula of Quebec, Canada

The remote-sensing study of an exhumed upper Paleozoic surface in the southern Gaspe Peninsula of Quebec has provided indirect evidence for the presence of a previously unidentified post-Acadian (post–Middle Devonian orogeny) graben-fill unit. Subsequent work on stratigraphic sections in that area confirms that the graben-fill unit, the new Saint-Jules Formation, is indeed petrographically distinct and older than previously documented upper Paleozoic strata in that area, which were collectively assigned to the Visean (Upper Mississippian) Bonaventure Formation. Paleogeo-graphic reconstruction from sedimentary facies, paleocurrent, and provenance studies concurs with the geometric detail that was provided by the preliminary geomorphic study. The present paper therefore presents the case study of an upper Paleozoic stratigraphic unit that was first inferred by geomorphic constraints prior to being recognized in the field through the study of stratigraphic sections. The study underlines the stratigraphic relevance of analyzing exhumed paleosurfaces at the margins of ancient sedimentary basins.