Toarcian ammonites of the Polymorphum Zone, Amellago area (eastern central High Atlas), Morocco, with a discussion on ammonite turnover events

In the Amellago area (central High Atlas), the widely distributed Toarcian succession consists of marls and marly limestones of the Tagoudite and Agoudim formations. We here describe, for the first time, the ammonites of the Polymorphum Zone from the Tagoudite Formation, including Canavaria cf. rosenbergi Fucini, C. aff. zancleana (Fucini), Dactylioceras (Eodactylites) mirabile (Fucini), D. (E.) aff. Meneghini, Neolioceratoides cf. hoffmanni (Gemmellaro) and Praepolyplectus sp. This ammonite assemblage is closely correlated with those reported from the Polymorphum Zone of several basins of the Tethyan margins and the Northwest European Subboreal Realm, indicating marine communications between the different Moroccan Jurassic basins and the central Atlantic trough. The overlying Agoudim Formation yields ammonites of the Levisoni Zone in its base and rare ammonites of the Bifrons Zone in the middle part. Four significant changes in the ammonite assemblages during the early-middle Toarcian and their probable causes are also discussed.& COPY; 2022 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.

Automated summary

This study describes the Toarcian strata in the Amellago area of the central High Atlas, including the Tagoudite and Agoudim formations. Ammonites from the Polymorphum Zone of the Tagoudite Formation, such as Canavaria cf. rosenbergi, C. aff. zancleana, Dactylioceras (Eodactylites) mirabile, D. (E.) aff. Meneghini, Neolioceratoides cf. hoffmanni, and Praepolyplectus are described for the first time. The presence of similar ammonite assemblages in other Tethyan basins and the Northwest European Subboreal Realm suggests marine connections between the Moroccan Jurassic basins and the central Atlantic trough. The ammonite assemblages in the overlying Agoudim Formation from the Levisoni and Bifrons zones are also discussed, along with the potential causes for four significant changes in the early-middle Toarcian ammonite fauna.