Neptunian dykes in the Devonian carbonate buildup Aferdou El Mrakib (eastern Anti-Atlas, Morocco) and implications for its growth

Aferdou El Mrakib is the largest single carbonate buildup in the eastern Anti-Atlas, Morocco. Its sediments are intersected by several Neptunian dykes. Herein, we compare their facies, spatial arrangement and the associated fauna to that of Neptunian dykes from other mound localities in Morocco and elsewhere in order to assess their origin as well as that of the mound. One of the studied dykes is filled with pisoids. Its facies suggests some kind of seep origin, but the carbon and oxygen isotopic values have only slightly negative signatures, which might be diagenetic, thus prohibiting further interpretation. Nevertheless, the unique occurrence of pisoids at a depth of c. 50 metres below the mound surface within a dyke is herein interpreted as supporting the presence of a source with a considerable discharge.