Reconstruction of the position of the continents at 255 Ma

Between the end of the Ordovician to the Quaternary, a geological record of deposition is absent. During that period much of the Precambrian and Ordovician rock formations were eroded, tith as much as 1000 metres of rock removed in some areas. During that time, the Grenvillian depositional shelf was deformed by the Appalachian orogeny, showned by numerous faults and vertical displacement of Paleozoic and Precambrian blocks ( Maps - GeoServ ). The general smoothness of the modern surface between fault blocks, as indicated by the smooth bedrock topography ( Maps - GeoServ ), bears witness to erosional levelling since the Ordovician period.

Following the Ordovician Period, several marine invasions are recorded in rock formations along the St Lawrence Valley, but there is no evidence that they affected the western Ottawa Embayment. Both Precambrian and Paleozoic formations were also subjected to several igneous intrusions mainly during the Cretaceous Period, but these are too small in the NCA to appear on a regional compilation of bedrock geology.

During the ~185 million year interval separating the Ordovician and Middle-Permian, Florida and Avalonia continued to drift toward the Laurentian craton to become part of North America. During the same period of time, continents collided together to form the Paleozoic-Mesozoic Pangea, that lasted for nearly 120 million years, from the late Carboniferous to Early Jurassic. A reconstruction of the position of continents indicates that the supercontinent started to break apart at the end of the Triassic to Early Jurassic periods, and the plates drifted to their modern position forming continents as presently known. North America slowly migrated to higher latitudes bringing changes in the climate, fauna, flora and geological processes that shaped the surface of the Continent. (Bally, 1989; Bally et al.,1989; Hoffman, 1985; Johnson et al.,1992; McLennan, 1992; Rast,1989; Williams, 1991; Hogarth, 1962)