Nejdia Arkell, 1952, an Early Jurassic (Toarcian) ammonite from the Marrat formation, Central Saudi Arabia

Abstract

ABSTRACT The present article describes the ammonite fauna from the genus Nejdia, pertaining to the Early Jurassic (Toarcian) deposits of the upper Marrat Formation, exposed in the southwest of Riyadh, capital city of Saudi Arabia, Nejd region. The fossiliferous zone is spread within an area of circa 40 km long, consisting of: light-brown limestone, including interbedded lime-mud at the lower part, yellow and red, clayish limestone at the middle part, cream, dense limestone at the upper part. The cliff forming Marrat Formation contains ammonites Nejdia and Parahildaites belonging to the upper member as well as Bouleiceras and Protogrammoceras in the lower member. At least four species of ammonites from Nejdia genus have been identified. They can be essentially distinguished through the differences in suture line shapes and the whorl section. The associated fauna contains mainly: brachiopods Calyptoria, echinoids Acrosalenia, bivalves. http://zoobank.org/References/7b33f54f-599a-4394-8f2f-95d3c2c631d9