22 



M.K. HOWARTH AND N.J. MORRIS 





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Quaternary 

 Basalt, Quaternary 

 Tertiary (Palaeocene, Eocene) 

 Cretaceous, post-Qishn Formation 

 Qishn Formation, U. Haut.-Aptian 

 Hajar Formation, Berriasian 

 Sabatayn Formation 

 Unmetalled roads 

 River in Wadi Hajar 

 "O- Hot spring 



Fig. 19 Geological Map of the Mintaq Salt Dome: X is the position of 

 the succession in Figs 14 and 20. 



Evidence for the age of the upper part of the Billum Member 

 comes from the large specimen of Crussoliceras cf. wegelei Enay 

 found in a limestone about 8 m below the top of the member in a 

 roadside cliff east of the Al Ma'abir road/river crossing (Fig. 3), 

 which is of Divisum Zone, Lower Kimmeridgian, date. 



The top bed of limestone of the Billum Member forms a pavement 

 below the west side cliff in Wadi Arus and many crushed Streblites 

 and indeterminate perisphinctids, some of which are probably 

 Torquatisphinctes, can be seen on the surface (Fig. 16). These are of 

 Eudoxus or Beckeri Zone, Upper Kimmeridgian, age. 



The abundant brachiopods in the Shuqra and Madbi Formations 

 disappear in the higher formations, except in the lower part of the 

 Billum Member where there are two 0.3 m thick marly limestones, 

 the "Microthyridina Beds', 4 m and 9.3 m above the base of the 

 member and well seen at the base of the Perisphinctid Cliff in east 

 Jebel Billum, that contain many large examples of Mkmthyridina 

 farquharsoni Muir-Wood, accompanied by a few Kallirhynchia and 

 Somali rhynchia. No brachiopods were found higher in the Billum 

 Member. 



Bivalves and gastropods are also much less common above the top 



of the Madbi Formation, though some occur in 'shell beds' and at a 

 few other horizons, such as the " Microthyridina Beds' in the bottom 

 4-9 m of the Billum Member. 



2. The Kilya Member. This member is dated as Beckeri Zone, 

 Upper Kimmeridgian, and Hybonotum Zone, Lower Tithonian. The 

 Beckeri Zone is represented by a very rich and mainly well-pre- 

 served ammonite fauna found in "Wadi Kilya, Naifa Cliff and Wadi 

 Arus. More than 250 anmionites of the following genera were 

 collected: Taramelliceras, Haploceras, Glochiceras, 

 Torquatisphinctes, Sutneria, Pachysphinctes, Idoceras, Nebrodites, 

 Aspidocems, Onhaspidoceras, Simaspidoceras and Lithacoceras, 

 and more than 75 Lamellaptychus (belonging to Taramelliceras) and 

 Laevaptychiis (from Aspidoceratidae). These ammonites occur at 

 the different horizons in the lower marly and middle limestone parts 

 of the Kilya Member that are shown in detail on Figs 3, 5 and 16, and 

 include well preserved specimens from the Breadloaf Concretions in 

 Wadi Arus. They are well dated as Beckeri Zone, Upper 

 Kimmeridgian. 



The upper marly part of the Kilya Member occurs only at Wadi 

 Kilya (Fig. 5), from where 72 ammonites were obtained, many of 

 them well-preserved, belonging to the genera Taramelliceras, 

 Katroliceras, Siibdichotomoceras, Pachysphinctes, Aspidoceras, 

 Onhaspidoceras, Simaspidoceras, Hybonoticeras andLithacoceras. 

 There are many species in common with the ammonites in the 

 Beckeri Zone below, but the presence of Katroliceras, Hybonoticeras 

 d. hybonotum and H. ornatum indicate the Hybonotum Zone, 

 Lower Tithonian. This is the date of the highest fauna in the Kilya 

 Member, and the disconformity between it and the Arus Member 

 consists of the remainder of the Hybonotum Zone (if any) and the 

 next four ammonite zones up to the top of the Lower Tithonian. 



Brachiopods are rare in the Kilya Member, with only a few 

 terebratulids (Ptyctothyris and ICererithyris) found in the middle 

 limestones and one Acanthothiris in the lower marls. An 'Astarte 

 Bed' with many Neocrassina occurs 0.3 m below the top of the lower 

 marly part of the Kilya Member in the east cliff in Wadi Arus. 



Hajar Formation 



LiTHOLOGY AND TYPE SECTIONS. The Hajar Formation is a new 

 name proposed here for the calcareous formation that is separated 

 from the underlying Naifa Formation by an unconformity. It is 

 named after Wadi Hajar, and the type section is in the cliffs on both 

 sides of Wadi Arus. It is essentially calcareous, and is divided into 

 two members, newly proposed here: a lower, thinner Arus Member, 

 consisting of marls, limestones, and concretions, and an upper, 

 much thicker Mintaq Member of more massive limestones. Both 

 members are well-developed and thick in Wadi Arus, but the Mintaq 

 Salt Dome and Jebel Madbi are important sections for the fullest 

 development of the Mintaq Member. 



The Arus Member is named after its type locality in a prominent 

 cliff' on the west side of Wadi Arus, where it has a clear contact with 

 the Kilya Member of the Naifa Formation, which it follows after an 

 unconformity that misses out the whole of the Lowo" Tithonian 

 except for part of its lowest zone (Figs 13, 15, 16). It consists of 

 marls with gypsum and scattered microbialite boulders, then a thick 

 bed of large microbialite boulders, followed by more marls and 

 limestones. The top is better seen in the opposite east cliff where the 

 complete thickness is 47.7 m. 



The Mintaq Member is named after the development at its type 

 locality in the south-west outcrop of the Mintaq Salt Dome, where 

 there is a good basal contact with the evaporites of the Sabatayn 

 Formation. It consists of 215.7 m of limestones, that are thick and 

 heavy for the lowest 77 m, then there are subsidiary marls and marly 



