Givetian Stage

Givetian Stage

      uppermost of the two standard worldwide divisions of Middle Devonian (Devonian Period) rocks and time. Givetian time spans the interval between 391.8 million and 385.3 million years ago. It was named for exposures studied near Givet in the Ardennes region of northern France and is characterized by a zone (a smaller subdivision of geologic time) whose rocks include the ammonite (ammonoid) genus Maenioceras.

      In the Ardennes, limestones (limestone) predominate and form escarpments about the town of Givet. Their rich fossil invertebrate fauna is characterized by the coral genus Favosites as well as gastropods (gastropod) and brachiopods (lamp shells) (lamp shells). Important Givetian sections also occur in Great Britain, where limestones and gray, slaty goniatite-bearing rocks predominate; in Germany and Russia, where limestones and shales include fossils of the widely distributed brachiopod genus Stringocephalus; in northeastern North America, where the richly fossiliferous limestones and shales include the upper formations of the Hamilton Group; and in Australia. As formally ratified in 1994 under the authority of the International Commission on Stratigraphy, the Global Stratotype Section and Point (GSSP) identifying the lower boundary of this stage is located at Jebel Mech Irdane ridge, 12 km (about 7 miles) southwest of Rissani, Morocco. The Givetian Stage is overlain by the Frasnian Stage of the Upper Devonian Series and underlain by the Eifelian Stage of the Middle Devonian Series.

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