JURASSIC AND LOWER CRETACEOUS OF WADI HAJAR 



208). Little (1925: pis 24, 26) drew vertical sections of the outcrop 

 of the Naifa Formation in Naifa Cliff and in the east cliff in Wadi 

 Arus, and suggested that oil shales of similar appearance in both 

 sections were outcrops of the same bed. He was basically correct in 

 making this correlation, though it is not now possible to interpret his 

 more general section (Little, 1925: pi. 25) of the succession on the 

 west side of Wadi Arus. 



Beydoun, 1964 



The exposures in Wadi Hajar formed a major part of Beydoun's 

 (1964) description of the Jurassic over a much wider area in the 

 south-eastern half of Yemen. This was based on field work by Z.R. 

 Beydoun and E.K. Elliott in 1954-58, and resulted in the geological 

 maps accompanying the published report (Beydoun, 1964: maps 1, 

 2) and the much more detailed unpublished reports held by British 

 Petroleum Pic. Beydoun used four formation names for the Jurassic 

 in Wadi Hajar - Kohlan Formation (oldest), Shuqra Formation, 

 Madbi Formation, Naifa Formation (youngest) - though there are 

 some difficulties in their interpetation because the type sections of 

 the four formations are in widely separated parts of Yemen. Never- 

 theless, it is quite clear to which rocks Beydoun applied the formation 

 names in Wadi Hajar, and our own work would not have been 

 possible without the basic work done by Beydoun (1964: 30^6), in 

 which he gave detailed lithological descriptions and long lists of 

 fossils. 



Lexique Stratigraphique International (Beydoun & 

 Greenwood, 1968) 



Formal definitions of the Kohlan, Shuqra, Madbi and Naifa Forma- 

 tions were given in the volume of the Lexicon that covered the 

 southern Yemen area, from which it is clear that only the Naifa 

 Formation has its type area in Wadi Hajar, though the type area of the 

 Madbi Formation on nearby Jebel Madbi is only 20 km south-west 

 of Wadi Hajar. On the other hand, the type area of the Shuqra 

 Formation is at Shuqra, 80 km north-east of Aden, and 300 km 

 south-west of Wadi Hajar, while the Kohlan Formation ought to have 

 its type section in the Kohlan area north-west of Sana'a, though 

 Beydoun (1968: 64) described his 'reference' section from its devel- 

 opment at Al Ma'abir in Wadi Hajar. 



Later mapping of the Wadi Hajar area 



After the political changes in 1968-71, integrated geological map- 

 ping and exploration of southern Yemen was done in cooperation 

 with geologists from three eastern European countries. The eastern- 

 most area extending as far as Mukalla was the province of geologists 

 of the then German Democratic Republic, and this included maps 

 for the area that contains Wadi Hajar. Maps were published in Aden 

 by the Ministry of Energy and Minerals, Department of Geology and 

 Mineral Exploration, of the then People's Democratic Republic of 

 Yemen, on a scale of 1 : 100,000. The three sheets that have been used 

 by us are D-39-49 (Jawl Ba Hawa), D-39-61/73 (BirAli/Balhaf) and 

 D-39-62 (Mayfa Hajr), which we were able to consult through the 

 kindness of BP Exploration. These maps have been of much value in 

 locating the positions and extent of the sections we studied. They 

 were prepared after some reconnaisance on the ground, followed by 

 tracing geological boundaries and inserting detail from aerial photo- 

 graphs. The lithostratigraphical nomenclature used is largely that 

 due to Beydoun, and some of the outcrops have to be interpreted with 

 care, bearing in mind the errors and difficulties in his interpretation 

 that are described below. One of these is the Madbi Formation on the 

 Bir Ali/Balhaf map (D-39-61/73), from Jebel Madbi eastwards to 



the large area of outcrop around Jebel Timurah, which also includes 

 the whole of the Naifa Formation as defined at its type locality at 

 Naifa Cliff on the Mayfa Hajr map (D-39-62), where it is correctly 

 mapped as Naifa Formation. 



CORRELATION AND 

 LITHOSTRATIGRAPHICAL NOMENCLATURE 



On our first visit in November 1991 , it became apparent that there 

 was a significant unconformity within the 'Naifa Formation' in its 

 outcrop at the eastern end of Jebel Billum. From beds above the 

 unconformity some good UpperTithonian ammonites were obtained, 

 including some crushed top Tithonian berriasellids only 5 m below 

 the base of the Qishn Formation (Upper Hauterivian-Barremian), 

 which are much younger than the Upper Oxfordian to Upper 

 Kimmeridgian ammonites that had been found lower in the Naifa 

 Formation by Beydoun and other early collectors. The splendid new 

 Berriasian ammonite fauna collected from the 'Naifa Formation' at 

 Mintaq on the same visit was younger still. 



Work in 1994 on all the sections (Al Ma'abir/Naifa CliffAVadi 

 Kilya, Jebel Billum, Wadi Arus, Mintaq) led us to the conclusion that 

 there are two different limestone formations in Wadi Hajar, sepa- 

 rated by a series of marls, limestones and concrefions, in the middle 

 of which is a major unconformity or disconformity, where the whole 

 of the Lower Tithonian is missing except for part of its basal zone 

 (Fig. 2). Beydoun had correlated these two limestones, believing 

 them to be separate outcrops of the same Naifa Formation, the 

 consequences of which have had such a profound effect on all later 

 work on the lithostrafigraphy and biostratigraphy of the Jurassic in 

 Yemen, that it is important to understand the origin of these errors. 



The Naifa Formation is named from the development of lime- 

 stones and marls at the type locality in Naifa Cliff, which is a river 

 cliff about 2 km upstream from the road/river crossing at Al Ma'abir 

 in Wadi Hajar. The top of the section at Naifa Cliff is overlain by 

 recent river deposits, but at a nearby exposure in Wadi Kilya the 

 Naifa Formafion extends slightly higher into the base of the Lower 

 Tithonian before being overlain by the Qishn Formation of Upper 

 Hauterivian to Barremian age. Beydoun collected large perisphinctid 

 ammonites from a horizon high in the Naifa Cliff section, which 

 were determined by Dr W.J. Arkell as of Lower Kimmeridgian age. 

 It is important to realise that Arkell was using 'Lower Kimmeridgian' 

 in the north-western European sense, where it is equivalent to the 

 whole of the Tethyan Kimmeridgian; this relationship is still valid 

 today (ie. the Tethyan Kimmeridgian, divided into Lower 

 Kimmeridgian and Upper Kimmeridgian, is equivalent to the Lower 

 Kimmeridgian only of Britain), but this was not entirely clear in the 

 mid- 1 950s when Arkell made these determinations, and the different 

 north-western European and Tethyan divisions of the Kimmeridgian 

 were not used consistently by Arkell (1956) in his Jurassic Geology 

 of the World. Beydoun also collected some crushed ammonites from 

 an horizon that is now known to be low in the sequence near Naifa 

 Cliff, which were determined by Dr L.F Spath as perisphinctids of 

 top Oxfordian or basal Kimmeridgian age. Both sets of ammonites 

 have been seen and redetermined by us, and there is no doubt that 

 Arkell's and Spath's determinations and dating were basically cor- 

 rect (in fact, the higher Naifa Cliff ammonites are from the Becked 

 Zone at the top of the Tethyan Upper Kimmeridgian, which is 

 approximately equivalent to the top of the north-western European 

 Lower Kimmeridgian). So the Naifa Formation at its type locality at 

 Naifa Cliff extends from the top part of the Oxfordian up to the top 

 of the (Tethyan) Kimmeridgian, and we now have further evidence 



