Discovery of Upper Devonian conodonts and event stratigraphy from the Eastern Jebilet, Morocco

Abstract

The Abichat section in the Eastern Jebilet, including allochthonous siltstones and sandy limestones rocks, revealed the presence of a Givetian and Early Frasnian conodont fauna. The Upper Devonian is discovered for the first time in Eastern Jebilet. A continuous biostratigraphic record could not be established, because of the gap that occurs in the Upper Givetian. However, six conodont Zones are recognized: rhenanus/varcus and ansatus to semialternans of Middle Givetian, Lower-Middle falsiovalis (MN1-2), Upper falsiovalis (MN3) and transitans (MN4) of Lower Frasnian. Notably, the conodont fauna contains particularly several species of Ancyrodella, Mesotaxis and Icriodus. Givetian conodonts show a polygnathid biofacies and Lower Frasnian conodonts reveal a mixed conodont biofacies with the Ancyrodella as dominating genus. Two anoxic global events are recognized for the first time in the Massif of Jebilet, the Upper Frasnes Event and the Timan Event. The Eastern Jebilet Devonian nappes have close links with the nappes of Azrou and Mrirt-Ziyar whose the sediments, characterized by stratigraphic gaps, were deposited along the disintegrated northern continental margin of Gondwana.