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

Abstract

The ‘Lower Member’ of the Khuff Formation, exposed along the western margin of the Arabian Basin (Al Qasim Province, Saudi Arabia) comprises seven carbonate and two siliciclastic lithofacies. The carbonate lithofacies include laminated lime mudstone, ostracode wackestone, foraminiferal wackestone, intraclastic wackestone, burrowed dolostone, lithoclastic grainstone and caliche. The clastic lithofacies are represented by claystone and quartzarenite. These lithofacies are arranged vertically into shallowing-upward or emergence cycles, the boundaries between which were delineated by field observations. 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.