Microbial-sponge and microbial-metazoan buildups in the Late Viséan basin-fill sequence of the Jerada Massif (Carboniferous, NE Morocco)

Three distinctive Late Viséan buildup intervals are differentiated on the southern limb of the Jerada Synclinorium. The oldest buildups (BI‐1) are preserved as olistoliths in the Oued El Koriche Formation (Fm). They were located on a southern platform prior to reworking. The younger Koudiat Es‐Senn Fm contains two autochthonous buildup intervals (BI‐2 to BI‐3). BI‐1 and BI‐2 buildups are large microbial‐sponge buildups, BI‐3 are small microbial‐metazoan buildups in the capping bed succession above BI‐2. All buildups are characterized by a rigid non‐skeletal microbial framework. Growth of the largest BI‐2 buildups started in aphotic to dysphotic conditions in a water depth significantly less than 100 m and continued into agitated shallow‐water. Smaller BI‐2 buildups and all BI‐3 buildups are encased in grainy shallow‐water carbonates. In contrast to a mostly homogeneous microbial‐sponge facies below, the uppermost part of the BI‐2 buildups and all BI‐3 buildups consist of heterogeneous boundstones with differing frame builders. BI‐1 to BI‐3 buildups represent different stages within a Viséan basin‐fill sequence. Carbonate sedimentation ended with the deposition of peritidal oncolitic floatstones below the unconformably overlying Namurian shales. The Jerada buildups have many features commonly associated with ‘reefs’. Comparison with contemporaneous buildups shows considerable similarities to buildups from Algeria, the Eastern Moroccan Anti‐Atlas and the British Isles. Copyright © 2008 John Wiley & Sons, Ltd.