24 



M.K. HOWARTH AND N.J. MORRIS 



limestones in the remaining 139 m up to a good contact with the 

 overlying Qishn Formation (Figs 14, 19, 20). Another important 

 section of the Mintaq Member is in the east cliff in Wadi Arus (Fig. 

 18), where it follows the Arus Member conformably, and consists of 

 85 m of thick limestones, with subsidiary marls and marly lime- 

 stones, the upper parts of which are well seen in the road gorge 

 leading south-eastwards up out of the wadi. It cannot be proved that 

 the base of the Mintaq Member at Mintaq correlates exactly with the 

 conformable contact between the Arus and Mintaq Members in the 

 east cliff of Wadi Arus, though the gypsum deposits in the Arus 

 Member at Wadi Arus suggests a general correlation with the 

 Sabatayn Formation at Mintaq (see Fig. 2). An even thicker develop- 

 ment occurs on Jebel Madbi, where Beydoun recorded 434 m of 

 beds that seem to belong to the Hajar Formation as here defined, and 

 most of that thickness is the Mintaq Member. 



BlOSTRATIGRAPHY. The age of the Hajar Formation is from the 

 base of the UpperTithonian up to about the middle of the Berriasian, 

 the latter date having been proved at Mintaq and Jebel Madbi. The 

 contact between the Arus and Mintaq Members is within the 

 Durangites Zone, probably in the low to middle part of that zone. 



1. The Arus Member. The base is well dated in Wadi Arus, where 

 38 ammonites were obtained from the microbialite boulders (Figs 

 16, 17) belonging to the genera Pseudoclambites, Baeticoceras, 

 Virgatosimoceras, Aulacosphinctes, Micracanthoceras, Himalayites, 

 Spiticeras, Virgatosphinctes, Berriasella, Riasanites and Blanfordi- 

 ceras. All these genera are confined to the Upper Tithonian or 

 younger, except Virgatosphinctes and Virgatosimoceras which also 

 occur in the Lower Tithonian. The date of the microbialite boulders 

 is Microcanthum Zone, Upper Tithonian. Baeticoceras morrisi sp. 

 nov. is most probably of basal Microcanthum Zone age, deduced 

 from its morphological features and probable relationships with 

 other species of the genus, but some of the other ammonites are 

 better placed higher in the Microcanthum Zone, suggesting that the 

 microbialite boulders might be a condensed horizon. Noteworthy 

 are two examples of the mainly Boreal speciesRiasanites rjasanensis 

 (Lahusen), and the rare ammonite Pseudoclambites which is poorly 

 known elsewhere. 



An ammonite fauna that is almost completely different from that 

 in the microbialite boulders in Wadi Arus occurs in the lower to 

 middle part of the Arus Member in eastern Jebel Billum (Fig. 12). 91 

 ammonites were obtained belonging to the genera Uhligites, 

 ?Aspidoceras, Spiticeras, Virgatosphinctes, Choicensisphinctes, 

 Berriasella, Substeueroceras and Malbosiceras, as well as 16 

 Laevaptychus (aptychi from Aspidoceratidae). The commonest ge- 

 nus is Berriasella (with 40 specimens collected), and the age is 

 Durangites Zone, Upper Tithonian, from the presence of 

 Malbosiceras andSubsteueroceras. This is slightly younger than the 

 date of the microbialite boulders in Wadi Arus. 



The only brachiopods seen in the Arus Member were two speci- 

 mens of an unidentified smooth terebratulid in the microbialite 

 boulders in Wadi Arus. Molluscs occur in the shell just below the 

 middle of the Arus Member in east Jebel Billum, especially the 

 astartid Neocrassina, and there are a few bivalves and gastropods 

 in the Coral Bed at the base of the Arus Member in the same 

 section. 



2. The Mintaq Member. The base is well exposed in eastern Jebel 

 Billum where 45 ammonites were collected in the basal 6 m (Fig. 

 12), belonging to the genera Uhligites, Virgatosphinctes, Choicensi- 

 sphinctes, Substeueroceras and Blanfordiceras. Although these are 

 only slightly different from the ammonites 40 m below in the Arus 

 Member in the same section, Substeueroceras makes up a higher 

 proportion of the total, and with Blanfordiceras, suggests a slightly 



higher horizon in the Durangites Zone for the base of the Mintaq 

 Member. 



Few ammonites were found in the Mintaq Member in Wadi Arus, 

 but a limestone in the upper half contains many crushed 

 Substeueroceras striatus sp. nov. and Protacanthodiscus. sp. indet., 

 and a large Aspidoceras sp. indet. was photographed nearer the top 

 of the member. These are either Durangites Zone, Upper Tithonian. 

 or Euxinus Zone, lower Berriasian, in age. This might also be the 

 date of the lowest ammonites (Substeueroceras and Dalmasiceras) 

 in beds 1 and 3 in the Mintaq Salt Dome (Fig. 20). 



The main evidence for the Berriasian age of much of the Mintaq 

 Member comes from rich ammonite fauna in the middle part of the 

 member at Mintaq (Fig. 20), where 108 specimens were collected of 

 the genera Haploceras, Aspidoceras, Spiticeras, Berriasella, 

 Substeueroceras, Malbosiceras, Neocosmoceras. Dalmasiceras, and 

 Argentiniceras, and 1 1 Laevaptychus. 



The presence of Argentiniceras. a rich and varied fauna of 

 Spiticeras including typical well-developed species, and two species 

 of Berriasella. B. (B.) chomeraciensis (Toucas) and B. (Elenaella) 

 sevenieri (Le Hegarat). give an Occitanica Zone age. close to or just 

 below the middle of the Berriasian. 



Finally, two Timovella occitanica (Pictet) collected by Dr John 

 Smewing from near the top of the Mintaq Member on the summit of 

 Jebel Madbi, are also of Occitanica Zone, mid-Berriasian, age, 

 though they might be slightly higher in that zone than the Mintaq 

 ammonites. The age of the top of the Hajar Formation on Jebel 

 Madbi is not known, but is likely to be in the upper part of the 

 Berriasian. 



No brachiopods or identifiable bivalves and gastropods were 

 found in the Mintaq Member, except for a few poorly preserved 

 bivalves in the base of the member in east Jebel Billum. 



Qishn Formation 



LiTHOLOGY AND TYPE SECTIONS. The type locality of the Qishn 

 Formation is at Ras Sharwayn, near Qishn, 290 km ENE of Mukalla. 

 where it is 41 1 m thick and consists of brecciated limestone at the 

 base, followed by limestones and marls, then hard crystalline lime- 

 stones containing Orbitolina in the upper half (Beydoun. 1968: 91). 

 A similar section in Wadi Masila, 70 km to the west, reaches a total 

 thickness of 498 m. In the Wadi Hajar and Mukalla areas the 

 formation is much thinner, being only 54.5 m thick in Beydoun's 

 reference section at Jabal al Rays, near Mukalla. where there is a 

 conglomerate at the base, then marls and sandstones, and the 

 Orbitolina Limestone is 17.5 m thick at the top. Two sections 

 measured by us in Wadi Hajar are in east Jebel Billum and at the 

 Mintaq Salt Dome. In east Jebel Billum the 31.9 m thick Qishn 

 Formation is at the top of the cliff immediately above the section 

 shown in Fig. 12; it consists of 5 mof shelly, cross-bedded, calcified 

 sandstones and silts, then 17.3 m of marls, mudstones and marly 

 limestones, up to the 9.6 m thick hard Orbitolina Limestone at the 

 top. In the whole of the Jebel Billum inlier, the red-brown basal beds 

 of the Qishn Formafion make an easily recognizable colour change 

 near the top of the cliffs of the grey Naifa and Hajar Formations. In 

 the Mintaq Salt Dome the Qishn Formation is 77.8 m thick: 0.8 m of 

 conglomeratic sandstone at the base, passes into sandstones, silts 

 and mudstones 69.4 m thick, including two oyster beds, up to the 

 massive Orbitolina Limestone 7.6 m thick at the top. 



BlOSTRATIGRAPHY. The main reason for including the Qishn For- 

 mafion in this description is to record the discovery of a single 

 example of the ammonite Crioceratites (C.) villiersianum 

 (d'Orbigny) in the east Jebel Billum section (Howarth, 1998: 98, pi. 

 23, fig. 2). Although found lying loose at the top of the Hajar 



