Sonoma orogeny Sonoma orogeny The Sonoma orogeny was a period of mountain building in western North America. The exact age and structure of the Sonoma orogeny is controversial. The orogeny is generally thought to have occurred during the Permian / Triassic transition, around 250 million years ago, following the Late Devonian Antler orogeny. The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent. Evidence of this event has been reported throughout western North America, but most distinctly in
Cadomian Orogeny typical structure. After the orogeny, continental sediments were washed on top of the deformed Cadomian rocks. They include conglomerate and sandstone in Brittany, Jersey and Alderney. The Cap Frehel red beds are dated at . These post orogeny deposits were dumped from braided stream channels. The basins for these sediments followed the structural grain in the Cadomian Orogeny. There are two overall models for the formation of the Cadomian Orogeny. Firstly by Jean-Pierre Brun & P. Bale that compression to the south west of a volcanic arc and back arc basin onto the edge of the continent at the St