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Late Neoproterozoic to Early Cambrian carbonates of the Ara Group form important intra-salt 'stringer' reservoirs in the South Oman Salt Basin. Differential loading of thick continental clastics above the six carbonate to evaporite cycles of the Ara Group led to the formation of salt diapirs, encasing a predominantly self-charging hydrocarbon system within partly highly overpressured carbonate bodies ('stringers'). These carbonates underwent a complex diagenetic evolution, with one stage of halite cementation in a shallow (early) and another in a deep (late) burial environment. Early and late halite cements are defined by their microstructural relationship with solid bitumen. The early phase of halite cementation is post-dated by solid reservoir bitumen. This phase is most pervasive towards the top of carbonate stringers, where it plugs nearly all available porosity in facies with initially favourable poroperm characteristics. Bromine geochemistry revealed significantly higher bromine contents (up to 280 p.p.m.) in the early halite compared with the late halite (173 p.p.m.). The distribution patterns and the (high) bromine contents of early halite are consistent with precipitation caused by seepage reflux of highly saturated brines during deposition of the overlying rock salt interval. Later in burial history, relatively small quantities of early halite were dissolved locally and re-precipitated as indicated by inclusions of streaky solid bitumen within the late halite cements. Late halite cement also seals fractures which show evidence for repeated reopening. Initially, these fractures formed during a period of hydrothermal activity and were later reopened by a crack-seal mechanism caused by high fluid overpressures. Porosity plugging by early halite cements affects the poroperm characteristics of the Ara carbonates much more than the volumetrically less important late halite cement. The formation mechanisms and distribution patterns of halite cementation processes in the South Oman Salt Basin can be generalized to other petroliferous evaporite basins.

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In the South Oman Salt Basin (SOSB), the Ara carbonates form an extensively cored, deeply buried intra-salt hydrocarbon play. Six surface-piercing salt domes in the Ghaba Salt Basin (northern Oman) provide the only outcrop equivalents for carbonates and evaporites of the Ediacaran – Early Cambrian Ara Group (upper Huqf Supergroup). Based on fieldwork, satellite images and isotope analysis it is concluded that most of the carbonate bodies (so-called stringers) in the Ghaba salt domes are time-equivalent to the stratigraphically uppermost stringer intervals in the SOSB (A5–A6). Maturity analyses demonstrate that the carbonate stringers in the salt domes were transported with the rising Ara Salt from burial depths of c. 6 to 10 km to the surface. Petrographic and stable-isotope data show that their diagenetic evolution during shallow and deep burial was very similar to the Ara carbonate stringer play in the SOSB. However, during the retrograde pathway of salt diapir evolution, the carbonate stringers were exposed to strong deformation in the diapir stem and diagenetic alterations related to dedolomitisation. As the salt domes contain facies that are in all aspects identical to the deeply buried Ara play in the SOSB, this study provides substantial additional information for hydrocarbon exploration in southern Oman. Moreover, our work has implications for the hydrocarbon prospectivity of the Ghaba Salt Basin and possibly of other Ediacaran – Lower Cambrian evaporite basins in the Middle East, such as for the time-equivalent Hormuz salt basins.