AMMONITES AND NAUTILOIDS OF WADI HAJAR 



species of Substeueroceras. they are probably slightly younger in 

 age in the Durangites Zone. 



Fauna 12. Upper Tithonian, upper Durangites Zone or lower 

 Berriasian, Euxinus Zone 



Few ammonites were found in the Mintaq Member inWadi Arus, but 

 a limestone in the upper half contains many crushtdSubsteueroceras 

 striatus sp. nov. (27 were collected) and Protacanthodiscus. sp. 

 indet. (4 were collected), and a large Aspidoceras sp. indet. was 

 photographed 15 m higher in the succession (Howarth & Morris. 

 1998: fig. 18). Possibly similar in age is the lowest ammonite in the 

 Mintaq succession, a single Substeueroceras striatum sp. nov., 25 m 

 above the base of the Mintaq Member, and about 70 m below the 

 main Berriasian ammonites at Mintaq. It is not possible to put a firm 

 date to these occurrences. They could be of upper Durangites Zone 

 age, slightly younger than the ammonites of fauna 1 1 , or they could 

 be of Euxinus Zone, lower Berriasian, age. 



Fauna 13. Berriasian, Occitanica Zone 



A rich Berriasian ammonite fauna occurs in the middle part of the 

 Mintaq Member at Mintaq, where the following were collected 

 (Howarth & Morris, 1998: figs 14, 20, beds 27-149): 



3 Haploceras umbilicatum sp. nov. 



2 Aspidoceras rogoznicense (Zejszner), with Laevaptyclms 

 attached 



4 Aspidoceras cf. taverai Checa, with Laevaptyclms attached 

 1 1 Laevaptychus 



1 Spiticeras (S.) spitiense (Blanford) 



2 Spiticeras (S.j subspitiense (Uhlig) 



2 Spiticeras (S.) indicum (Uhlig) 

 63 Spiticeras (S.) pricei sp. nov. 



4 Spiticeras sp. indet. 



3 Spiticeras (Negreliceras) cf. obliquenodosum (Retowski) 



1 Spiticeras (Negreliceras) paranegreli Djanelidze 



2 Berriasella (B.) chomeracensis (Toucas) 

 8 Berriasella spp. indet. 



2 Berriasella (Elenaella) sevenieri (Le Hegarat) 



1 Substeueroceras koeneni (Steuer) 



1 Malbosiceras sp. indet. 



1 ?Protacanthodiscus or Neocosmoceras sp. indet. 



1 Neocosmoceras sp. indet. 



2 Dalmasiceras sp. indet. 



1 Argentiniceras mutatum (Steuer) 



5 Argentiniceras mintaqi sp. nov. 

 1 ?Neocomites sp. indet. 



From the presence of the Berriasian genus Argentiniceras (which 

 has never been recorded in the Upper Tithonian) and such a rich and 

 varied fauna of Spiticeras. the age is certainly Berriasian rather than 

 UpperTithonian, and the species ofBerriasella indicate an Occitanica 

 Zone age, close to or just below the middle of the Berriasian. The 

 examples of Aspidoceras at Mintaq are amongst the youngest 

 Aspidoceratidae anywhere, perhaps even the youngest of all, if the 

 Berriasian occurrences in SE Spain are in the Euxinus Zone rather 

 than the Occitanica Zone (see above p. 65, and Checa et ai. 1986). 



Fauna 14. Berriasian, Occitanica Zone 



Two Tirnovella 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 ammonites in the 

 Mintaq Salt Dome section. 



103 



Fauna 15. Upper Hauterivian 



A single specimen of Crioceratiies (C) cf. villiersiamis (d'Orbigny) 

 found in the basal part of the Qishn Formation in eastern Jebel 

 Billum gives a date of Upper Hauterivian for the lower part of that 

 formation. The unconformity between the top of the Hajar Forma- 

 tion and the bottom of the Qishn cuts out an unknown amount at the 

 top of the Berriasian, the whole of the Valanginian and the Lower 

 Hauterivian. 



Fauna 16. Upper Aptian 



Ammonites found higher in the Qishn Formation at Wadi Masila, 

 220 km ENE of Makulla, are Cheloniceras (C.) cornuelianus 

 (d'Orbigny) (PI. 21, fig. 3), Cheloniceras (C.) sp. indet. (PI. 21, fig. 

 4) and another ^Cheloniceras (BMNH C.71676). These indicate an 

 Upper ApUan age at that level in the formation. 



COMPARISON WITH EAST AFRICA AND 

 INDIA 



The biostratigraphical distribution of those Yemen ammonites near 

 the Kimmeridgian-Tithonian boundary throws some light on the 

 distribution of ammonites described from East Africa. Upper Jurassic 

 ammonites from many areas in Ethiopia, Somalia, Kenya, Tanzania 

 and Cutch, India, were described in an extensive British, Italian, 

 German and French literature that was summarized up to the mid- 

 1950s by Arkell (1956). Most of the Callovian and Oxfordian 

 ammonites were collected from sequences that could be fairly well- 

 dated, but many of the East African Kimmeridgian and Tithonian 

 collections lacked good stratigraphical data, and their ages were not 

 well determined. Included amongst the latter are most of the exten- 

 sive faunas of Pachysphinctes and Aspidoceratids, especially those 

 from Ethiopia and Somalia. Better information was obtained from 

 Kenya by Verma & Westermann (1984), who were able to place 

 Pachysphinctes and the accompanyingAspidoceratids in the Beckeri 

 and Hybonotum Zones at the Kimmeridgian-Tithonian boundary 

 from the presence of good examples of Hybonoticeras. In Cutch, 

 India, Pachysphinctes, Katroliceras and many other ammonites 

 were referred to the same two zones by Spath ( 1 933: 79 1 ) and Arkell 

 (1956: 388), a dating that has been refined more recently by Krishna 

 & Pathak ( 1993), who described an evolving sequence of species of 

 Torquatisphinctes-Pachysphinctes-Katroliceras in several zones 

 across the Kimmeridgian-Tithonian boundary. 



Ethiopia and Somalia remain difficult areas, however, despite the 

 many Ethiopian ammonites described by Venzo (1959), who had 

 little detailed stratigraphy and lumped together into a single zone all 

 the Kimmeridgian below the Eudoxus Zone, and by Zeiss (1971), 

 who appeared to have better stratigraphical control, but did not 

 figure his ammonites. It also seems necessary to question the top 

 Oxfordian to basal Kimmeridgian dates given by Scott (1943) to 

 many of his Ethiopian ammonites, a dating that was accepted by 

 Arkell (1956: 314, 316). 



The biostratigraphical distribution of Pachysphinctes and 

 Katroliceras in Yemen confirms that their main occurrence is in the 

 Beckeri and Hybonotum Zones, as found by Verma & Westermann 

 (1984) and Krishna & Pathak (1993). This is one or two zones 

 younger than the date given by Arkell (1956: 332) to the large 

 collection of Pachysphinctes and Aspidoceras from the Mahokondo 

 stream in southern Tanzania described by Dietrich (1925), which 

 may have been placed too low. The large species of Idoceras 

 accompanying the Ethiopian Pachysphinctes described by Scott 

 (1943) are most probably of the same age, and they are not Upper 



