AMMONITES AND NAUTILOIDS OF WADI HAJAR 



101 



BIOSTRATIGRAPHY 



The ammonites described here are referred to the 1 4 biostratigraphical 

 horizons ranging from the middle of the Callovian to the Berriasian 

 that are shown as numbered asterisks in Table 1, plus the Upper 

 Hauterivian and Upper Aptian ammonites in the Qishn Formation. 

 The scheme of ammonite zones used here is also shown in that table, 

 and it should be remembered that the Kimmeridgian Stage is the 

 Kimmeridgian of the Tethyan Province, being equivalent to only the 

 Lower Kimmeridgian of north-west Europe. The ammonites in each 

 biostratigraphical horizon and the evidence for their dating are 

 considered below. 



Fauna 1. Middle Callovian 



The discovery of three specimens of the ammonite Erymnoceras 

 (Pachyerymnoceras) jarryi (Douville) is important for dating the 

 Shuqra Formation. Two were found in the Upper Shuqra, 17 m 

 below the top of the formation, in central Jebel Billum and southeast 

 of Al Ma'abir respectively, while the third was in the top part of the 

 Middle Shuqra at the latter locality (Howarth & Morris, 1998: fig. 

 6). This dates most of the upper half of the Shuqra Formation to 

 Middle Callovian, Anceps Zone, or low Upper Callovian. A 0.5 m 

 thick bed of limestone 23 m below the top of the Shuqra Formation 

 in central Jebel Billum contains many large, solid, well-preserved 

 specimens of the nautiloid Paracenoceras meridionale Tintant. P. 

 calloviense (Oppel), indicative of the Callovian, occurs at a similar 

 horizon in the Al Ma'abir area. 



Fauna 2. Lower Oxfordian 



Ammonite evidence for the age of the Madbi Formation consists of 

 only the poorly preserved ammonites amongst the abundant 

 brachiopods and bivalves all banked-up together in the three Storm 

 Beds. The Lower Storm Bed is the basal bed of the formation and the 

 only cephalopod found is a single small Laevaptychus from an 

 Aspidoceratid ammonite, which does not provide much age infor- 

 mation, though it is probably Oxfordian rather than Callovian. Two 

 fragments of Perisphinctes sp. indet. and a Peltoceratoides sp. indet. 

 in the Middle Storm Bed are of Lower Oxfordian age. 



Fauna 3. Middle/Upper Oxfordian 



Eight fragments of perisphinctids obtained from the Upper Storm 

 Bed of the Madbi Formation are of the type of Perisphinctes which 

 are characteristic of the Plicatilis, Transversarium and Bifurcatum 

 Zones, Middle and Upper Oxfordian. 



Fauna 4. Upper Oxfordian, Bimammatum Zone 



Ammonites of the Bimammatum Zone occur low in the Billum 

 Member of the Naifa Formation. The following were obtained from 

 the basal 5 m of the Billum Member in the cliff south of the Wadi 

 Kilya section, and 7-8 m above the base of the member at the bottom 

 of the long eastern cliff in Jebel Billum (Howarth & Morris, 1998: 

 figs 5, 12): 



1 Ochetoceras sp. indet. 



2 Epimayaites sp. indet. 



3 Paryphoceras grayi (Spath) 



5 Larcheria gredingensis (Wegele) 

 39 Onhosphinctes polygyratus (Reinecke) 

 1 Euaspidoceras sp. indet. 



The Mayaitidae (Epimayaites and Paryphoceras) are Upper 

 Oxfordian ammonites, while the association of Larcheria greding- 

 ensis and Orthosphinctes polygyratus is characteristic of the 



Bimammatum Zone. A single Idoceras ahwarense sp. nov. was also 

 found loose at the base of the same Perisphinctid Cliff in eastern 

 Jebel Billum, but it is an Upper Kimmeridgian ammonite and must 

 have fallen from the Kilya Member. 



18-20 m above the base of the Billum Member in the road cutting 

 at the western entrance to Jebel Billum 5 Glochiceras (G. ) suhclausum 

 (Oppel) and 1 Orthosphinctes polygyratus (Reinecke) were col- 

 lected, which indicate the same Bimammatum Zone age. 



Fauna 5. Lower Kimmeridgian, Divisum Zone 



A large specimen of Cnissoliceras cf. wegelei Enay found in a 

 limestone about 8 m below the top of the Billum Member in a 

 roadside cliff east of the Al Ma' abir road/river crossing ( Howarth & 

 Morris, 1998: fig. 3), is characteristic of the Divisum Zone, at the top 

 of the Lower Kimmeridgian, and is the only Lower Kimmeridgian 

 ammonite found in Wadi Hajar. 



Fauna 6. Upper Kimmeridgian, Eudoxus or Beckeri Zone 



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

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

 plicodiscus (Waagen) and impressions of flattened perisphinctids, 

 some of which are probably Torquatisphinctes, can be seen on the 

 surface (Howarth & Morris, 1998: figs 13, 15, 16). That species of 

 Streblites probably ranges from the Eudoxus to Hybonotum Zones, 

 so its presence below a well-dated Beckeri Zone ammonite fauna 

 shows that this top bed of the Billum member is of Eudoxus or 

 Beckeri Zone, Upper Kimmeridgian, age. 



Fauna 7. Upper Kimmeridgian, Beckeri Zone 



The following very rich ammonite fauna occurs in the lower marly 

 and middle limestone parts of the Kilya Member in Wadi Kilya, 

 Naifa Cliff and Wadi Arus: 



5 Taramelliceras (T.) pseudoflexuosum (Favre) 



4 Taramelliceras (T.) cf. intersistens Holder 



4 Taramelliceras (T.) compsum (Oppel) 



5 Taramelliceras sp. indet. 

 20 Lamellaptychus 



8 Haploceras staszycii (Zejszner) 



4 Glochiceras (Lingulaticeras) pseudocarachteis (Favre) 



8 Torquatisphinctes naifaensis sp. nov. 

 7 Sutneria weidmanni Zeiss 



32 Pachysphinctes bathyplocus (Waagen) 



41 Pachysphinctes major Spath 



5 Pachysphinctes mahokondobeyrichi (Dietrich) 

 24 Pachysphinctes sp. indet. 



1 Idoceras ahwarense sp. nov. 



1 Idoceras cf. halderum (Oppel) 



1 Idoceras cf. hararinum Venzo 

 3 Nebrodites hospes (Neumayr) 



9 Aspidoceras longispimim (J. de C. Sowerby) 

 9 Aspidoceras apenninicum (Zittel) 



5 Aspidoceras sp. indet. 



5 Orthaspidoceras gortcmii (Venzo) 



16 Orthaspidoceras avellanum (Zittel) 



13 Simaspidoceras argobbae (Dacque) 



2 Simaspidoceras irregulare (Dacque) 

 56 Laevaptychus 



1 Lithacoceras (L.) cf. uhnense (Oppel) 

 38 Lithacoceras (Subplanites) momhassanum (Dacque) 



This list is a combination of the ammonites in five separate 

 horizons in the lower mariy and middle limestone parts of the Kilya 

 Member at Naifa Cliff (see Howarth & Morris, 1998: fig. 3). five 



