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M.K. HOWARTH 



horizons in the same parts of the Kilya Member in Wadi Kilya 

 (Howarth & Morris, 1998: fig. 5), and from the Breadloaf Concre- 

 tions in the lower marly part of the Kilya Member in the east cliff of 

 Wadi Arus (Howarth & Morris, 1998: fig. 16). They are listed 

 separately on those three figures, and those from the Wadi Arus 

 Breadloaf Concretions are of especial interest There are many 

 indications that the whole fauna is from the Beckeri Zone and not 

 lower in the Kimmeridgian, and the date is limited above by the 

 Hybonotum Zone ammonites in the immediately overlying beds in 

 Wadi Kilya. Of the 22 identified species, 12 are well-dated as 

 occurring mainly in the Beckeri Zone in other areas in East Africa, 

 Cutch and Europe. These include Pachysphinctes major, 

 Orthaspidoceras avellanum and Lithacoceras ulmense, which have 

 not been recorded below the Beckeri Zone elsewhere, and so give a 

 lower age limit to the fauna (Haploceras staszycii first occurs in the 

 top of the Eudoxus Zone, but is commoner in the Beckeri Zone). 

 Also included is the genus Simaspidoceras. which is not dated 

 accurately anywhere else in its range (Ethiopia, Somalia andYemen) 

 The presence of Nebrodites in the Beckeri Zone appears to be the 

 highest record of this genus. 



Fauna 8. Lower Tithonian, Hybonotum Zone 



Lower Tithonian ammonites were obtained from the upper marly 

 part of the Kilya Member, which occurs only in Wadi Kilya, from 

 where the following were obtained (Howarth & Morris, 1998: fig. 5, 

 upper marls): 



9 Taramelliceras (Metahaploceras) subsidens (Fontannes) 



32 Katroliceras formosum Spath 



1 Katroliceras pottingeri (J. de C. Sowerby) 



7 Katroliceras sp. indet. 



1 Subdichotomoceras ?latissimum (Zwierzycki) 

 5 Pachysphinctes bathyplocus (Waagen) 



5 Pachysphinctes major Spath 



3 Aspidoceras longispinum (J. de C. Sowerby) 



2 Orthaspidoceras avellanum (Zittel) 

 1 Simaspidoceras argobbae (Dacque) 

 1 Simaspidoceras irregulare (Dacque) 



1 Laevaptychus 



2 Hybonoticeras omatum (Spath) 



1 Hybonoticeras cf. hybonotum (Oppel) 

 1 Lithacoceras (L.) cf ulmense (Oppel) 



1 Lithacoceras (Subplanites) mombassanum (Dacque) 



There are many species in common with the underlying Beckeri 

 Zone fauna, but the presence of Hybonoticeras cf. hybonotum 

 (Oppel) and the many examples of Katroliceras (which is dated as 

 Hybonotum Zone in Cutch, Kenya and Madagascar) is sufficient to 

 show that the age is Hybonotum Zone. This is the date of the highest 

 fauna in the Kilya Member, and the disconformity between it and the 

 Arus Member of the Hajar Formation consists of the remainder (if 

 any) of the Hybonotum Zone and the next four ammonite zones up 

 to the top of the Lower Tithonian. 



Fauna 9. Upper Tithonian, basal Microcanthum Zone 



The lowest Microcanthum Zone fauna consists of the following 

 ammonites obtained from the microbialite boulders from both west 

 and east side cliffs in Wadi Arus (Howarth & Morris, 1998: fig. 16): 



18 Pseudoclambites araense sp. nov. 



2 Baeticoceras morrisi sp. nov. 



1 Virgatosimoceras broilii (Schneid) 



1 Aulacosphinctes spitiensis (Uhlig) 



2 Aulacosphinctes natricoides (Uhlig) 



1 Micracanthoceras fraudator (Zittel) 



1 Himalayites sp. indet. 



1 Spiticeras gregoryi (Spath) 



1 Virgatosphinctes cf. broilii (Uhlig) 



7 Berriasella (B.) cf. oxycostata Mazenot 



2 Riasanites rjasanensis (Lahusen) 

 1 Blanfordiceras wallichi (Gray) 



This is clearly an Upper Tithonian fauna because none of these 

 ammonites occur in the Lower Tithonian, except Virgatosphinctes 

 and Virgatosimoceras. A Microcanthum Zone date is given by the 

 presence of Micracanthoceras and Baeticoceras, and the new spe- 

 cies of the latter genus is morphologically the oldest species of 

 Baeticoceras, indicating a basal Microcanthum Zone age for this 

 species at least. If the microbialite boulders in Wadi Arus represent 

 a condensed bed, then it is possible that they also contain higher 

 horizons in the Microcanthum Zone, to which Spiticeras gregoryi, 

 Berriasella (B.) cf. oxycostata and Riasanites rjasanensis could be 

 referred. This would ease the difficulty of claiming that those species 

 are as old as basal Microcanthum Zone. 



Fauna 10. Upper Tithonian, lower Durangites Zone 



An ammonite fauna that is almost completely different from that in 

 the microbialite boulders of Wadi Arus occurs in the Arus Member 

 in eastern Jebel Billum (Howarth & Morris, 1998: fig. 12). Of lower 

 Durangites Zone age, it is slightly younger that the Wadi Arus fauna. 

 The following were collected: 



1 Uhligites kraffti (Uhlig) 



3 ?Aspidoceras sp. indet. 

 1 6 Laevaptychus 



1 Spiticeras sp. indet. 



22 Virgatosphinctes cf. broilii (Uhlig) 



8 Choicensisphinctes limitis (Burckhardt) 

 18 Berriasella (B.) oppeli (Kilian) 



22 Berriasella sp indet. 

 8 Substeueroceras koeneni (Steuer) 



8 Malbosiceras cf. aizyensis Mazenot 



This fauna has to be dated as Durangites Zone from the presence 

 of Berriasella (B. ) oppeli, Substeueroceras koeneni andMalbosiceras 

 cf. aizyensis, none of which occur below that zone elsewhere. 

 Spiticeras does not occur below the UpperTithonian. while Uhligites, 

 Aspidoceras and Virgatosphinctes occur throughout the Tithonian. 

 This leaves the Lower Tithonian genus Choicensisphinctes as the 

 only anomoly, for which this is the first recorded Upper Tithonian 

 occurrence. C. limitis is probably the most advanced species of the 

 genus, and persisted for longer than the earlier, less advanced 

 species. 



Fauna 11. Upper Tithonian, Durangites Zone 



The base of the Mintaq Member is exposed in eastern Jebel Billum 

 where the following ammonites were collected in the basal 6 m 

 (Howarth & Morris, 1998: fig. 12): 



2 Uhligites kraffti (Uhlig) 



13 Virgatosphinctes cf. broilii (Uhlig) 



9 Choicensisphinctes limitis (Burckhardt) 



14 Substeueroceras koeneni (Steuer) 

 6 Substeueroceras striatum sp. nov. 

 1 Blanfordiceras wallichi (Gray) 



Although they are only slightly different from the lower Durangites 

 Zone ammonites 40 m below in theArus Member in the same section 

 in eastern Jebel Billum, from the presence of Blanfordiceras and two 



