Jurassic Gastropod Faunas of Central Saudi Arabia

Abstract

ABSTRACTMapping of Phanerozoic rocks at 1:250,000 scale by joint teams from the Saudi Arabian Deputy Ministry for Mineral Resources and the Bureau de Recherches Géologiques et Minières since 1980 has covered most of the Jurassic outcrops in central Saudi Arabia. Stratigraphic, sedimentologic and paleogeographic studies provided a precise framework for collected gastropod faunas that could be calibrated against ammonite zones and sequence-stratigraphic zones. Of more than 600 samples collected, about 440 gastropod specimens could be determined on at least a generic level. Their age range is from Bajocian to Oxfordian–Kimmeridgian. They correspond to 26 genera and 35 species from the Euomphalidae, Ataphridae, Pseudomelaniidae, Coelostylinidae, Procerithiidae, Nerineidae, Purpurinidae, Aporrhaidae, Naticidae, Acteonidae, Retusidae, and Akeridae families. Twelve species are new, and three (Kosmomphalus and Bifidobasis in the Euomphalidae, and Striatoonia in the Pseudomelaniidae) were proposed for new taxa of generic or subgeneric rank. Most of the identified species are of Middle Jurassic age, mainly Bathonian and Callovian and only six are Late Jurassic. All species are typical of an internal platform environment (upper infralittoral), in a lagoonal to back-reef setting, but some also colonized the external platform in the lower infralittoral fore-reef zone. Paleogeographically, most of the species are related to European and Sinai faunas; only seven are equivalent to North African or East African faunas, and one only was reported from Madagascar.