26 



M.K. HOWARTH AND N.J. MORRIS 



formations, both mainly non-marine and difficult to date, though 

 both probably range from late Triassic (Adigrat Sandstone) or 

 Lower Jurassic (Kohlan Formation) to Middle Jurassic (probably 

 Bathonian). 



The Shuqra Formation and Biben Limestone contain rich, near- 

 identical faunas of brachiopods, molluscs and some echinoids, but 

 rare mid-Callovian ammonites occur in the Shuqra Formation, and a 

 loose Upper Bathonian Paracenoceras and a loose Upper Callovian 

 or Lower Oxfordian Pachyceras are probably both from the Bihen 

 Limestone. 



The Madbi Formation and Gahodleh Shales are both argillaceous 

 formations of Oxfordian age. though excluding the highest part of 

 that stage, as deduced from the poor ammonites in the Madbi and the 

 ages of the adjacent formations in both areas. Both formations 

 contain many of the same brachiopods and molluscs. 



The Naifa Formation, Billum Member, and the Wanderer Lime- 

 stone contain several similar or identical ammonites. There are 

 many difficult-to-determine crushed perisphinctids of Upper 

 Oxfordian or lowest Kimmeridgian appearance in the Wanderer 

 Limestone, but the presence of Orthosphinctes polygyratus 

 (Reinecke) and a ILarcheria dates at least part of it to the 

 Bimammatum Zone, Upper Oxfordian, as in the lowest part of the 

 Billum Member Other ammonites in the Wanderer Limestone might 

 be higher in the Kimmeridgian, but there is nothing that is definitely 

 determinable as being of the same age as the Eudoxus or Beckeri 

 Zone ammonites at the top of the Billum Member 



The Kilya Member and the Daghani Shales both contain ammo- 

 nites from the Beckeri Zone at the top of the Kimmeridgian. Others 

 in the Daghani Shales could be lower in the Kimmeridgian 

 {Torquatisphinctes, Idoceras, Sutneria and some aspidoceratids), 

 while it cannot be proved that the Daghani Shales extends up into the 

 Lower Tithonian, like the Kilya Member. Nevertheless, the two 

 formations are similar in age, and better preserved ammonites would 

 be needed from Somalia to make a more exact comparison. 



The Hajar Formation and the Gawan Limestone represent a return 

 to more calcareous conditions of deposition in both areas. The two 

 formations might be similar in age, and Spath's (1935: 206) 

 determinations of the poorly-preserved ammonites in the Gawan 

 Limestone as Aulacosphinctes. Anavirgatites, Pseudovirgatites, 

 Sublithacoceras and Simoceras certainly indicate a Tithonian age, 

 though they could be Lower Tithonian, so it is not possible to show 

 an exact equivalence with the Hajar Formation. The disconformity 

 that excludes most of the Lower Tithonian in Wadi Hajar in Yemen 

 might be absent, or it might be present at a lower biostratigraphical 

 horizon, in Somalia, and the absence of any ammonites in the top 

 142 m of the Gawan Limestone means that neither the Upper 

 Tithonian nor the Berriasian can be proved to be present in that 

 formation. The correlation of the Hajar Formation and the Gawan 

 Limestone is still tentative, and further progress also requires better 

 ammonites from Somalia. 



Acknowledgements. We wish to thank Dr Ashley Price and Dr Mark 

 Eller, of British Petroleum Pic, who sent us the first ammonites and. together 

 with Mairead Rutherford, took us on our visit to Wadi Hajar and the 

 surrounding area in November 1991. Also, we would like to thank Dr John 

 Smewing for presenting us with ammonites for determination from newly 

 discovered faunas, and for discussion on the interpretation of the succession 

 and its correlation. Our visit to Wadi Hajar in January 1994 was made 

 possible by generous support from Clyde Petroleum Pic. We have had other 

 discussions with Professor Z.R. Beydoun, of the American University, Bei- 

 rut, and Dr M.D. Simmons, Aberdeen University. Mrs Diana Clements 

 helped considerably with the compilation of the appendix. 



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1968. In, Beydoun. Z.R. & Greenwood. J.E.G.W. 1968. See below. 



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APPENDIX 



Macrofossils collected in Wadi Hajar. Ammonites identified by 

 M.K. Howarth, brachiopods by Dr E.F. Owen, echinoderms by Dr 

 Andrew Smith, and bivalves and gastropods by N.J. Morris. The bed 

 numbers listed for the Mintaq section refer to those in the vertical 

 section of Fig. 20. Numbers in square brackets are the number of 

 specimens collected. 



Naifa Cliff (N 14° 16'38" E48°32'52") 



Naifa Formation, Kilya Member: 



Marly limestone, 41.5 m above base. Ammonites: Pachysphinctes 

 spp. indet. [15], Aspidoceras longispinum (J. de C.Sowerby) [2]. 



Limestone and marl, 0.4 m thick, 22.0-22.4 m above base; the 

 main ammonite bed in Naifa Cliff. Ammonites: Taramelliceras 

 sp. indet. [2], Lamellaptychiis [6], Pachysphinctes bathyplocus 

 (Waagen) [21], Pachysphinctes major Spath [23], Pachysphinctes 

 mahokondobeyrichi (Dietrich) [5], Idoceras cf. hararinum Venzo 

 [ \], Aspidoceras longispinum (J. de C. Sowerby ) [i], Aspidoceras 

 or Orthaspidoceras sp. indet. [1], Simaspidoceras argobbae 

 (Dacque) [1], Laevaptychus [7], Lithacoceras (L.) cf. ulmense 

 (Oppel) [1], Lithacoceras (Subplanites) mombassanum (Dacque) 

 [4]. Bivalves: Palaeonucula sp. [14]. 



Limestone 19 m above base. Ammonites: Orthaspidoceras gortanii 

 (Venzo) [5]. 



