Upper silurian and lower devonian conodonts from tafilalt, southeastern Morocco

Abstract

The conodont association from three Silurian-Lower Devonian sections (Bou Tchrafine N2, Atrous 3 and Atrous 7) in the Tafilalt (southeast Morocco) are presented. The sections are constituted by cephalopod rich limestones ("Orthoceras limestones") and by crinoidal limestones ("Scyphocrinites limestones") cropping out within thick shaley sequences. The association includes 29 taxa belonging to 13 genera (Ancyrodelloides, Belodella, Dvorakia, Icriodus, Kockelella, Lanea, Oulodus, Ozarkodina, Pelekysgnathus, Polygnathoides, Pseudooneotodus, Wurmiella, Zieglerodina). The conodont fauna allows the recognition of seven conodont zones: ploeckensis and siluricus in the Ludlow, eosteinhornensis s.l., Lower detortus and Upper detortus in the Pridoli, and hesperius and transitans in the Lochkovian. The age of the "Orthoceras limestones" is confirmed as middle Ludfordian (ploeckensis-siluricus zones), whereas it is stated that the "Scyphocrinites limestones" spans the Silurian/Devonian boundary. Some elements of the apparatus of Zieglerodina planilingua and the P2 element of Lanea omus are described. The phylogenetic relationships between genera Lanea and Ancyrodelloides are discussed.