Fish assemblage and palaeoenvironment of Early Cretaceous (Barremian) neap-spring tidal rhythmites from Sidi Aïch Formation of the Chotts basin (Southern Tunisia)

Sedimentary facies of the Sidi Aïch Formation, which encompasses the KABBS include channel intraformational clasts, cross-bedded sandstones with mud drapes, herringbone cross-bedding; and sigmoidal cross-bedding suggesting strong tidal influences. Tidal facies together with paucity of bioturbation and mixed freshwater to marine fossils indicate that sedimentation took place mainly in restricted tidal flat ponds. The clayey varved facies, which dominates the KABBS corresponds to dark organic-rich and white organic-poor laminae interpreted as cyclic rhythmites reflecting neap-spring tidal cycles interrupted by flood events. Excellent preservation biota within KABBS and like-varved facies suggest deposition in low-energy restricted environments like mixed marine and fresh-water ponds along the tidal flats of the tidal meandering channel. Organic geochemistry analysis supported the idea of rapid burial associated with short-period sub-anoxic condition.