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

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

KEYWORDS:

• Ammonites
• Bouleiceratinae
• Nejdia
• Early Jurassic
• Toarcian
• Marrat formation
• Saudi Arabia

Acknowledgments

The author is grateful to Jacques LeBlanc for the discussion of the ideas presented in this paper and comments on Saudi Arabian Geology.

Many thanks to Dr. Mohamed Boukhary, for his wise review on Stratigraphy and Paleogeography.

I wish to thank Dr. Mohamed Bushnak and Dr. Ibraheem Bushnak, for their valuable observations, which highly contributed to this article.

I would like to thank Dr. Stefano Sassaroli and Dr. Jean Guex for their kind advice on Toarcian ammonites.

Finally, I would like to give special thanks to Dr. Louis Rulleau, for his precious recommendations on systematic description, which greatly improved this paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).