Cloridorme Formation is proposed as a new name to replace the time-stratigraphic usage of Normanskill Formation for the upper Middle Ordovician rocks of northern Gaspé Peninsula. Detailed physical stratigraphy in excellent exposures along the Gaspé coast permits subdivision of the formation, clarifies the structural pattern of the coastal belt, and delineates the source area of these rocks.

Graywacke, calcisiltite, calcareous wacke, and some carbonate rocks form thin interbeds in dark-gray argillite with an exposed thickness of about 7700 m. Valley-and-ridge folds were formed in the Taconic orogeny (Late Ordovician), accompanied by the formation of three structural blocks bounded by major faults. The stratigraphic sequence is recognizable within each block, but relations between blocks are uncertain. With a few exceptions the lithologies of the Cloridorme Formation recur in several units, but alternation of terrigenous clastic wedges with clastic carbonate-rich wedges permits the definition of 14 members.

Abundant sedimentary structures and reworked benthonic fossils among the pelagic autochthonous fauna indicate turbidity-current deposition of the graywacke, calcisiltite, and calcareous wacke. Current directions were longitudinal from the east except in the upper two members where they were reversed. The present limited extent and en echelon configuration of the members suggest that they are wedges built successively toward the west as the elongate trough was filled from the eastern end.

Fragments of serpentine, volcanic rocks, chert, argillaceous terrigenous rocks, and chromite indicate cannibalism of the adjacent Cambrian and Lower Ordovician eugeosynclinal rocks to the south, as the source of terrigenous material. The carbonate-rich rocks were supplied from a carbonate shelf whose exact location is unknown. It is inferred that the carbonate source was closer to the flysch basin than the terrigenous source and was only partly isolated from terrigenous material.

The Cloridorme Formation is age equivalent to the upper part of the type Normanskill Formation. Flysch of Early or Middle Ordovician age forms a narrow, nearly continuous belt from western Newfoundland to eastern Tennessee.