The Late Jurassic (Kimmeridgian) Arab-D member consists of complex facies associations and clinoform units that make up the intrashelf Arabian basin and associated platform. A ramp borders the Arabian basin and extended >300 km from Abu Safah and Berri fields (offshore) in the north to the interior of Saudi Arabia. This basin encloses the largest field in the world (Ghawar) as well as several other supergiant fields (Qatif, Abqaiq and Khurais) fields, all of which produce from the Arab-D member.
From bottom to top, the Arab-D member consists of predominantly mud/intraclast-, organic-, and grain-dominated facies associations, which generally record an overall shallowing upward history and a long-term base-level fall. However, we recognize numerous high-frequency sequences on the basis of facies stacking patterns and regional correlations. Lime mudstones, which are common in the lower Arab-D, represent a sub-wave base (~100 ft), outer ramp setting. Interbedded intraclastic and oncolitic rudstones represent storm-dominated tidal channel and algal bank environments. Thick, amalgamated rudstones record base-level fall and storm-wave erosion of the firmground substrates. The upper Arab-D reservoir mainly consists of open-marine low-relief biohermal and biostromal limestones succeeded by skeletal/peloidal and oolitic grainstones. Coral-stromatoroid facies have accumulated as sheets and local buildups (10-20 ft of relief) during a major base-level rise that culminated with a bank margin centered in Abqaiq and northern Ghawar fields.
These organic-rich facies were laid down as backstepping, northward thickening buildups. Subsequent base-level fall led to the deposition of several seaward stepping (southward), skeletal, peloid, and ooid grain shoal complexes, which have shingled or clinoform geometry. The youngest clinoforms stepped southward as base level fell and were followed by lowstand to transgressive, onlapping anhydrite units that formed in a subqueous to desiccated salina, which extended across the remnant Arabian basin and provide a regional seal.
