Rayda Fm
Type Locality and Naming
The pelagic carbonates and marls of the Rayda Formation represent deep marine deposition following basin subsidence and drowning by a global sea level rise in the Early Cretaceou. Type section is Southeast Al Jabal Al Akhdar, alongside the road to the Saiq Plateau (E57°41 ́30”, N23°02 ́00”). Additional reference section is Dhulaima-4. Column: Oman Subsurface, Oman Outcrop
Synonym:
Lithology and Thickness
Siliceous limestone. "The Rayda Formation is a sequence of thin-bedded, dense, porcellanitic limestones (lime mudstones) and marls with fine argillaceous partings and/or levels of thin cherts. At the base, a variable bed of crinoidal debris may locally be present with synsedimentary fracture fills (‘neptunian dykes’) and very locally a ‘bone-bed’ with concentrated fish-teeth, belemnites, ammonites and bone fragments is found at outcrop in Al Jabal Al Akhdar. The lower part of the unit may be variably reddened, particularly along the argillaceous partings. Horizontal burrows are present on bedding planes. . . . An upper and lower division has been distinguished in the outcrop type section based on a facies change (Haan et al., 1990). The Lower unit of light grey-weathering, thin-bedded, lime mudstones with laminar and nodular cherts grades into an Upper unit of medium- to thin- bedded, olive to dark grey-weathering mud-/ wackestones. This has been interpreted as the onset of regression following initial drowning of the basin (Corbin and Mabillard, 1984)."
Relationships and Distribution
Lower contact
The lower boundary is a sharp contact with the carbonates of the Sahtan Gr, stepping down from the Jubaila Fm in the western subsurface to the Dhruma Fm in the Al Jabal Al Akhdar outcrops. Chart implies a hiatus of middle Tithonian below it.
Upper contact
Regional extent
The best development of the Rayda Fm (and Salil Fm) is in western North Oman in the Lekhwair and adjacent areas north of ca. 22°N. It thins and dies out to the west and southeast. In the Al Huwaisah area the presence of the Rayda Fm is questionable; the entire sequence is here assigned to the Salil and consists of limestone with lesser amounts of dolomite and marl. The Rayda Fm probably continues into the similar lithologies at the base of the upper Musandam Gr in Ruus al Jibal (Hudson and Chatton, 1959; Ricateau and Riché, 1980).
GeoJSON
Fossils
"Biozones F52 (lower part) and F51 (common large Calpionella alpina, C. elliptica and the presence of radiolaria). Simon Petroleum Technology (1995) recorded a basal Rayda Formation assemblage with Crassicollaria parvula and numerous Calpionella alpina, which they interpret to be Late Tithonian – Early Berriasian in age. . . . On the basis of the microfossil (calpionellid association) and macrofossil (ammonite) content, the Rayda Formation has been assigned to the uppermost Tithonian – Berriasian in Al Jabal Al Akhdar (Rousseau et al., 2005). Sharland et al. (2001) place their Early Berriasian K10 MFS within shales near the base of the Rayda Formation in well Dhulaima-4 and in the Wadi Al Muaydin outcrop. Interestingly they also illustrate a potential mid- Tithonian J110 MFS in Wadi Al Muaydin (their figure 4.53)."
Age
Depositional setting
The Rayda Fm sediments are characterized by deep marine pelagic fossils (radiolaria, tintinnids, crinoids, belemnites) and sediment surface ichnofossils. The depositional environment is well below wave-base, with slow sedimentation. The deep marine sediments are interpreted as the basinal facies associated with the rapidly prograding Lower Kahmah Gr shelf carbonates (Droste and Van Steenwinkel, 2004).);
Additional Information