Lithofacies, diagenesis and cyclicity of the 'Lower Member' of the Khuff Formation (Late Permian), Al Qasim Province, Saudi Arabia

Peritidal as well as subtidal cycles built-up the Lower Member of the Khuff Formation. The peritidal cycles consist of laminated lime mudstone or subtidal claystone, overlain by intertidal burrowed dolostone, which is capped in most cases by supratidal lithoclastic grainstone, and locally by subaerial caliche deposits. These cycles were probably formed by allocyclic mechanism due to the effect of sea level changes and intrabasinal tectonics. The subtidal cycles comprise laminated lime mudstone, claystone, foraminiferal wackestone, and ostracode wackestone, capped by intertidal burrowed dolostone or intraclastic wackestone. These cycles may be formed due to internal factors, e.g. carbonate production, changes in water circulation, salinity, depth, chemistry, energy, temperature and nutrient content. Diagenetic studies on the depositional cycles show that the basal part of cycle (subtidal zone) includes micrite cementation, micritization and silicification. The middle part (intertidal zone) was affected by early dolomitization, while the upper part (supratidal zone) was subjected to dedolomitization, aggrading neomorphism, sparry calcite cementation and evaporite-carbonate replacement.