WENLOCK SERIES

the second of four main divisions (in ascending order) in the Silurian System, representing all those rocks on a global basis deposited during the Wenlock Epoch (428421 million years ago). Its name is derived from the type district at Wenlock Edge, a prominent escarpment that stretches for about 29 km (18 miles) southwest from the town of Much Wenlock in Shropshire, Eng. The ridge is formed by fossiliferous limestones (Wenlock Limestone) with a maximum thickness of 29 m (95 feet), but broadly underlain by siltstones and mudstones up to 292 m (960 feet) thick. By international agreement, the base of the Wenlock Series is defined with a global stratotype section and point (GSSP) on the north bank of Hughley Brook near Hughley Church at Ape Dale, Shropshire. The boundary point coincides with the base of the Buildwas Formation and closely corresponds to the first occurrence of the graptolite species Cyrtograptus centrifugus. The base of the Wenlock Series is also marked by the fossil disappearance of the conodont Pterospathodus amorphognathoides. The Wenlock Limestone is one of the best-studied Silurian formations of the world and is noted for its abounding variety of excellently preserved fossils: brachiopods, corals, trilobites, clams, bryozoans, and crinoids. Similarly rich Wenlock fossil assemblages occur on the Swedish island of Gotland and in the Great Lakes region of North America. The Wenlock Series is overlain by the Ludlow Series and is divided into two worldwide stages: the Sheinwoodian and Homerian stages.