Middle Devonian Orogeny in Western North America?: A Fish and Other Fossils

Abstract

Middle Devonian orogeny in western North America is suggested by unconformities in widely separated areas along the continental margin, and is consistent with a variety of geologic information. In the Shasta Lake region of northern California the Copley Greenstone and Balaklala Rhyolite, which contained an isolated arthrodire plate, are inferred to be of Eifel age. These units underlie the Late Eifel age Kennett Formation. An early Paleozoic sequence in the Gazelle-Callahan area to the north includes fossiliferous beds as young as the Ems to Middle Devonian. Age of metamorphism of rocks known a short distance to the west is about 380 m.y., which could represent an Eifel age event. An angular unconformity and orogenic interval is known at the northern end of the Sierra Nevada between fossiliferous Silurian and Mississippian age beds. In the southern Sierra Nevada, an unconformity exists between fossiliferous Late Devonian beds and unfossiliferous beds of older Paleozoic age. In the eastern Sierra Nevada, r...