Safiq Gr
Type Locality and Naming
The Safiq Group consists of open marine to restricted/marine sediments stacked into a number of transgressive-regressive cycles. Named by Winkler and Rácz (1978), see also Hughes Clarke (1988), upgraded to Group status by Priebe and Kapellos (1993), see also Droste (1997). Composite sections from formational type wells that provide a Group ‘type’ overview are Sahmah-1 in Central Oman (Figure 12.3), Hasirah-1 in Central Oman and Saih Nihayda-24 in North Oman. Upward succession of the Saih Nihayda Fm, Hasirah Fm and Sahmah Fm. For additional subsurface reference sections, see those individual formations. Column: Oman Subsurface
Synonym:
Lithology and Thickness
"Fine-grained to coarse-grained, variably micaceous quartz and slightly arkosic sandstones, with lesser argillaceous sands, silts and shales. … The Safiq Group is a mainly marine clastic sequence with facies and age indications derived from acritarch and chitinozoan assemblages. The range of recovery from barren sands to shales with rich and diverse assemblages indicates a general interplay of regressive to transgressive cycles in an overall marginal to at times fully marine setting. … The shale-to-sand sequences show gross coarsening- upward cycles, and the shalier units may be organic-rich and yield marine palynomorphs and chitinozoa." Upward succession of the Saih Nihayda Fm, Hasirah Fm and Sahmah Fm.
Relationships and Distribution
Lower contact
Onlapping onto the eroded surface of the Ghudun Fm. "The lower boundary is not always a marked lithological change. South of latitude 20°, the Safiq lies upon various continental clastic units of the Haima Supergroup Gr. The base of the Safiq has previously been defined as the lowest evidence of marine influence, but there are significant marine intervals in the Ghudun Fm,
Upper contact
"The upper boundary is formed by the top Haima hiatus or unconformity overlain by the Haushi Gr; although the next younger regional unit is the Misfar Gr. Haushi clastics lying upon Safiq clastics may not provide a marked lithological change, and confirmation by palynological dating may be necessary. Care should be taken as reworking may confuse the palynological signature at this boundary, notably the Upper Ghudun, and this no longer strictly applies. Recognition of the usually distinctive log character of the Ghudun Fm helps make a more reliable boundary pick. To the north, the Safiq lies upon the older formations of the Andam Gr, which comprises very similar marginal- marine clastics. The boundary is often formed by the base of a transgressive-marine shale overlying sands. Palynological dating can assist in ambiguous cases. There is palynological evidence for a hiatus between Andam Gr and Safiq Gr marine sedimentation (Booth, 2009). … The youngest intervals are found in wells near Oman’s western border. Biostratigraphic data from the Amdeh Fm outcrops in the Saih Hatat of the Al Hajar Mountains, originally documented by Lovelock et al. (1981) indicate that the ‘Upper Siltstone Member’ (Amdeh Unit 5, after Le Métour et al., 1986) is time equivalent to the Saih Nihayda Fm (see also Sansom et al., 2009 and Rickards et al., 2010)."
Regional extent
The Safiq Group is only fully preserved in western parts of Interior Oman, and is interpreted to have transgressed from north to south and from the center of the Rub’ Al-Khali Basin to its flanks between middle Ordovician and early Silurian. Lithologically the formations of the Safiq are similar and it is impossible to differentiate between the Sahmah Fm, Hasirah Fm and Saih Nihayda Fm on lithology alone. Recognition of the three Palynozones 1003, 1005 and 1098 is often the only way to confidently differentiate between them.
GeoJSON
Fossils
The three formations within the Safiq Group are each characterised by conspicuously different palynological assemblages, which define the PDO Palynozones 1003, 1005 and 1098, equating to the Sahmah, Hasirah and Saih Nihayda formations respectively (Mohiuddin et al., 2007 and Booth, 2009). Subdivision is possible within these Palynozones and the most useful data is derived from the study of marine palynomorphs (acritarchs and chitinozoa). Consequently, biozonal resolution is at its best when sedimentation was in the marine realm. If sampling is sufficiently detailed many transgressive and regressive events can be observed through the study of variation in acritarch diversity. Work on chitinozoa has been fundamental in assigning more robust ages to the acritarch zones in these Middle Ordovician – early Silurian sections (Paris, 2002, 2005 and 2006).
Age
Depositional setting
"The Safiq Group consists of open marine to restricted/marine sediments stacked into a number of transgressive-regressive cycles. An unconformity occurs above the Hasirah Fm, associated with the sudden influx of fluvial to deltaic sands in a deeper-marine setting, suggesting significant drops in sea-level. This has been tentatively correlated with major continental glaciations that have been reported from the Katian?/Hirnantian to ?Rhuddanian of Saudi Arabia (Droste, 1997). However, Miller and Al-Ruwaili (2007) restrict glacially-influenced sedimentation in Saudi Arabia to the Hirnantian. Oman was positioned at the margin of this glacial realm and it should be noted that to date glacial sediments have not been reported in Oman. Large-scale canyons seen on seismic of North Oman are filled with Katian sediments and are therefore considered to pre-date any proven glacial period in the region. The potentially glacial-induced regression and subsequent transgression was followed by a rapid flooding of the Gondwana platforms with widespread accumulation of marine anoxic organic-rich mudrocks of the Sahmah Fm (Svendsen, 2004). The organic-rich beds represent the eastern extension of a thick interval of rich marine source rocks in the Silurian Qalibah Fm (Qusaiba Member) of Saudi Arabia, whose origin is linked to widespread anoxic conditions and high organic productivity, possibly as the result of the flooding of extensive shelf areas."
Additional Information