The Zini Formation (Floian, Early Ordovician) outcrops in the central Anti-Atlas of Morocco (Zagora area) and is interpreted as a wave dominated ridge and runnel intertidal zone (Vaucher et al., 2017). (A) The sandstones of the Zini Formation consist of an alternation of beds dominated by symmetrical and slightly asymmetrical oscillatory sedimentary structures of various sizes (red part) sandwiched between more massive beds, which mainly exhibit low-angle- or plane-parallel stratifications (yellow part). White arrow points to the limited lateral extension of oscillatory structures dominated interval. Red-to-yellow arrow shows the lateral transition from oscillatory structures dominated interval to low-angle or plane-parallel stratifications dominated interval. (B) Detailed section of the Zini Formation showing the transition between sedimentary structures characterizing the ridge part (Upper Stage Plane Beds) and the runnel part (2D Symmetrical Ripples, 3D Asymmetrical Ripples and 2D/3D Symmetrical Dunes). Scale: hammer is 32 cm long.