New data on the Devonian of Bou Khadra-Bou Trou (eastern part of Western Meseta)

The Devonian succession of the Bou Khadra–Bou Trou area, southwest of Azrou, belongs to a supposedly autochthonous block of the eastern Western Meseta and differs stratigraphically and facies-wise from both the Azrou and Mrirt nappes. Above the Silurian Bou Trou quartzite, the new Aït Ben Alla Formation records a moderately deep, poorly oxygenated outer shelf receiving fine siliciclastics from a prodelta around the Silurian–Devonian transition. This was followed by shallowing and increasing aridity, producing the reddish, bioturbated sandstones and siltstones of the Al Aççama Member, likely linked to the Lochkovian–Pragian regression. The overlying Bou A’ar Member consists of thick, cross-bedded, calcareous fine sandstones that indicate renewed transgression during the Pragian. Higher in the section, limestones and shales tentatively assigned to the Bouechot Formation reflect open deep-neritic conditions with dacryoconarids and restricted conodont faunas. Its three members document a progression from lenticular wackestones to griotte-like limestones, and finally to shales, with bioclastic limestones containing mixed pelagic-neritic faunas. The presence of Caudicriodus celtibericus shows that the upper part of this unit is top-Pragian in age, making it older than similar nodular limestones at Jebel Ben Arab and Azrou but equivalent to the lower Anajdam Member of Mrirt. Previously reported Upper Devonian ages for local limestones could not be confirmed. The only Middle Devonian conodonts are reworked specimens found in a conglomerate at the base of the Carboniferous, which overlies the Devonian with angular unconformity. Overall, the Bou Khadra–Bou Trou succession is intermediate between Azrou and Mrirt, but it is distinguished by a much stronger regional silt-sand input rather than sediment supply from the distant Gondwanan shoreline.