CHRONOSTRATIGRAPHY AND HYDROCARBON PROSPECTS OF THE SAKAKA FORMATION, NORTHERN ARABIA

The age of the so-called Sakaka Sandstone exposed in the al-Jawf area, northern Saudi Arabia, has in the past been disputed. It is assigned here to the Middle- Late Devonian and middle Cretaceous. This age has been established from correlations of surface - subsurface sections utilising palynological and litholgical data, and also from the regional geological framework. The sequence is divided into two units. The lower unit, consisting of clastic and mixed fine-clastic and calcareous shoreline- shallow marine deposits, is considered to be part of the Middle Cretaceous Wasia Formation. The name “Sakaka Formation” is now restricted to the lower unit of the Middle - Upper Devonian sequence. This formation forms a well-exposed and lithologically-distinct mappable unit. The type section of the Formation can be designated from a traverse in the al- Jawf area, where a thickness of 215.5 m is exposed. The Sakaka Formation conforably overlies the Lower Devonian Jauf Formation, and uncomformably underlies the Middle Cretaceous Wasia Formation. At depth, in the subsurface, the sakaka Formation underlies conformably the Lower Carboniferous Berwath Formation. Reliable relative age-dating of the sakaka Formation has contributed to investigations of both the history of the Hail Arch, and the economic prospects of the area. This Arch extends throughout the al-Jawf area, and is probably of PreCambrian age: it was rejuvenated in pre Middle Devonian and pre-middle Cretaceous times. The Arch separates the Widyan Basin to the east from the Tabuk Basin to the west. The former basin is promising in terms of petroleum exploration owing to its great possible thickness, and the presence of favourable lateral facies changes, and potential source and reservoir rocks; moreover, tectonic activity has resulted in the generation of many traps, including stratigraphic traps. The Sakaka Formation and the overlying Berwath Formation could serve as potential reservoir rocks, capped uncomfortably by fine, argillaceous rocks of the Upper Carboniferous - Lower Permian Unayzah Formation.