Revising the lithostratigraphic framework of the Ediacaran succession of the Anti-Atlas belt: correlation across the Cadomian domain of the West African Craton

In the northern margin of the West African Craton (WAC), Ediacaran terranes crop out in the Anti-Atlas and the peri-Gondwanan terranes of the Meseta and the Ossa-Morena Zone of Western Europe. In the latter, the ca. 640-530 Ma Cadomian evolution is well understood, whereas geodynamic events effected terranes in Morocco remain debated, partly due to imprecise lithostratigraphic units and their ages. In this study, we integrate new field surveys with available geochronological and isotopic data to refine the lithostratigraphy of the Anti-Atlas and establish an across-orogen correlation with the Meseta and the Ossa Morena Zone (Spain).

The lithostratigraphic revision suggests that the Ediacaran succession of the Anti-Atlas can be subdivided into the early Ediacaran Saghro Group (640–600 Ma) and the late Ediacaran Ouarzazate Supergroup (580–538 Ma), separated by a 20-million-year (Ma) sedimentary gap. The Ouarzazate Supergroup is further subdivided into three groups: M'Gouna, Lower Ouarzazate, and Upper Ouarzazate, each characterized by distinct isotopic signatures and separated by two angular unconformities.

This new lithostratigraphic framework shows that the Eastern-Central Anti-Atlas (ECAA) and Meseta preserve an early Ediacaran sedimentary and volcano-plutonic infill of a subsiding back-arc basin that developed between 640 and 600 Ma. This early Ediacaran back-arc succession is also present in Ossa Morena Zone but is absent in the western Anti-Atlas, which remained tectonically stable during this period. The closure of this basin was marked by tectonic-metamorphic and magmatic activity, as evidenced by the deformation of the Saghro Group in the ECAA and Meseta and the Montemolín Formation in Ossa Morena, accompanied by the emplacement of adakitic and magmatism with high Sr/Y signature. Throughout the Anti-Atlas and the Meseta area, this phase was followed by a magmatic and sedimentary gap of approximately 10 Myr and 20 Myr, respectively. After these hiatuses, sedimentation transitioned to a subaerial continental environment with deposition of the M'gouna Group between 580 and 570 Ma with sedimentary and magmatic rocks characterized by negative εNd values indicative of West African Craton (WAC) continental crust recycling. The Lower Ouarzazate Group (LOG, 569–567 Ma) was deposited over ∼2 Ma across the entire Anti-Atlas and Meseta, coinciding with a shift toward a more juvenile magma source. The Upper Ouarzazate Group (UOG, 567–540 Ma) is dominated by sedimentary, epiclastic deposits with exclusively juvenile magma.

This revised lithostratigraphic framework highlights a similar evolutionary history between the CEAA, Meseta, and Ossa-Morena Zone and sheds new light on the effects of the Cadomian orogeny on the Gondwana mainland.