Frasnian Stage

the lower stage of the Upper Devonian. The Frasnian stage was identified by the Belgian geologist J. Omalius d’Halloy in 1862. At the type locality, the stage is represented by coral-reef and other limestones and by clay shales. The stage is distinguished on the basis of brachiopods, ammo-noids, and other fossils. It is divided into three (in some places, two) substages and from two to five zones. In the USSR, limestones and shales—including bituminous shales containing ammonoids and tentaculites (domanic sediments)—predominate in the Frasnian stage. In addition, brightly colored continental deposits and volcanic rocks are widespread. In many basins, the rock sequence corresponds to a marine transgression. (SeeDEVONIAN SYSTEM [PERIOD].)