32 



M.K. HOWARTH AND N.J. MORRIS 



Bed 31 (1.2 m brown, marly, rubbly limestone; 87.9 m above 



base): Spiticeras (S.) spitiense (Blanford) [1], Spiticeras (S.) 

 indicum (Uhlig) [2], Spiticeras (Negreliceras) paranegreli 

 Djanelidze [1], Indet ?Spiticeratinid [1]. 



Bed 30 (0.3 m grey-brown, marly, nodular limestone; 87.6 m 

 above base). Ammonites: Aspidoceras cf. taverai Checa [1]; 

 Laevaptychus [6]; Spiticeras pricei sp. nov. [2]; Spiticeras 

 (Negreliceras) cf. obliquenodosum (Retowski) [1]; indet. 

 berriasellid [1]. 



Bed 29 (0.8 m brown, marly limestone; 86.8 m above base). 

 Ammonites: Spiticeras pricei sp. nov. [1], Spiticeras 

 (Negreliceras) obliquenodosum (Retowski) [1], Laevaptychus 

 [5], Berriasella (Picteticeras) chomeracensis (Toucas) [1], 

 BerriaseUa spp. indet. [1]. 



Bed 27 (1.3 m Grey-brown, fine-grained limestone; 85.1 m above 

 base). Ammonites: Spiticeras (S.) pricei sp. nov. [3]. 



Bed 21 (0.4 m grey-brown, fine-grained limestone; 81.0 m above 

 base). Ammonites: indet. ?berriasellids [3]. 



Bed 13 (0.3 m thinly laminated limestone; 60.7 m above base). 

 Ammonites: indet. ?berriasellid [1]. 



Bed 3 (3.8 m grey, fine-grained, thin-bedded limestones, with 

 marly partings; 27.5 m above base), 1 m above base. Ammo- 

 nite: IDalmasiceras sp. indet. [1]. 



Bed 1 (25 m buff-grey, fine-grained limestones in beds 0.2-0.7 m 

 thick), 0.4 m below top. Ammonite: Substeueroceras striatum 

 sp. nov. [1]. 



Jebel Madbi (N14°21'20" E48°01') 



Hajar Formation, Mintaq Member: 



In upper part of member, on summit of Jebel Madbi. Ammonite: 



Tirvonella occitanica (Pictet) [2]. 



NOTE ADDED IN PROOF 



After this paper had gone to print, a paper was pubHshed by Beydoun 

 (1997, Introduction to the revised Mesozoic stratigraphy and no- 

 menclature for Yemen, Marine and Petroleum Geology, 14 (6): 

 617-629) which made many revisions to the lithostratigraphical 

 nomenclature of the Jurassic ofYemen. These are to be formalized in 

 a new edition of the Yemen volume of the Lexique Stratigraphique 

 International (Paris), scheduled for publication in 1997, but which 

 we have not seen. 



The most far-reaching change is to the Upper Oxfordian to lowest 

 Tithonian Naifa Formation, whose type locality is at Naifa Cliff, 

 Ma'abir. Beydoun proposed to alter the type locality to the Mintaq 

 Salt Dome, 65km to the north-west, where the rocks are Upper 

 Tithonian and Berriasian in age. This is to be done because of past 

 mis-correlation and misinterpretation of the age. However, such 

 wholesale alteration of the type section of a formation is not permit- 

 ted under Article 22 (c) of the North American Stratigraphic Code 

 (NASC) which maintains: 



'Type section never changed. - The definition and name of a 

 stratigraphic unit are established at a type section (or locality) that, 

 once specified, must not be changed' (NASC, 1983, Bulletin Ameri- 

 can Association Petroleum Geologists, 67: 856). 



We fully support the NASC's aim of achieving reasonable stabil- 

 ity in lithostratigraphical nomenclature. In advancing such stability 

 for the Jurassic rocks of Wadi Hajar and Yemen, we would make the 

 following points: 



1. An important purpose of lithostratigraphical nomenclature at 

 Formation level is to name rocks units that are lithologically 

 distinct, and are easily separable on the ground as mappable 

 units. In Wadi Hajar the formafions we use have widely different 

 lithologies, and are based on those originally proposed by 

 Beydoun (1964). Thus the Kohlan, Shuqra, Madbi, Naifa and 

 Hajar Formations consist of markedly different arenaceous, cal- 

 careous, argillaceous, calcareous and calcareous rocks 

 respectively, the latter two being separated by an unconformity 

 and by detailed lithological differences. Such clear division of 

 the Jurassic is abandoned by Beydoun's new proposals. 



2. The Madbi Formation is argillaceous at its type locality on Jebel 

 Madbi, and the term was used for the same rock division in Wadi 

 Hajar by Beydoun (1964). Its extension upwards to include the 

 heavily calcareous 'Madbi Forcellanites' (= our Billum Member; 

 = Ma'abir Member newly proposed by Beydoun), then a calcar- 

 eous 'Upper Madbi Shales' (= our Kilya Member) places widely 

 differing lithologies in the Madbi Formation. The overlying 

 Billum Member makes such a marked contrast to the argillaceous 

 Madbi Formation that it needs a different formation name, for 

 which Naifa Formation is available, as originally defined with its 

 type locality at Naifa Cliff, near Ma'abir. Billum Member (or 

 Ma'abir Member if this is held to have priority) is the name for 

 the heavily calcified lower half, and Kilya Member for the 

 calcareous upper half. A 'Madbi Formation' for all the rocks from 

 the bottom of the Madbi to the top of the Naifa Formation as used 

 by us, embraces too many markedly different lithologies, over 

 too large an age range from the bottom of the Oxfordian to the 

 bottom zone of the Tithonian. 



3. Beydoun ( 1 964) was already in possession of ammonite evidence 

 that the date of the Naifa Formation at its type locality was Upper 

 Oxfordian/Lower Kimmeridgian, and collections of ammonites 

 giving good dating evidence can be obtained in abundance in 

 Wadi Hajar, as the present paper shows. Miscorrelation from 

 Naifa Cliff to Wadi Arus then Mintaq (where microfossil evi- 

 dence showed that the date of the wrongly identified 'Naifa' 

 Formation was Upper Tithonian/Berriasian) cannot be used as a 

 reason for the illegal alteration of the type locality of the Naifa 

 Formation. 



4. Nor is the subsequent misuse of the term 'Naifa Formation" 

 (many in unpublished company reports) sufficient reason to alter 

 its type locality and age to the Mintaq Salt Dome and Upper 

 Tithonian to Berriasian. The rocks at Mintaq are similar in 

 lithology to those of the Naifa Formation at Naifa Cliff, but they 

 are wholly different in age and are separated from the latter by an 

 unconformity and intermediate beds (our Arus Member) that are 

 lithologically different. Our new division, the Mintaq Member, 

 Hajar Formation, is available for the Mintaq rocks. 



5. For reasons of priority, clear lithological differentiation and 

 inviolability of the type section, Beydoun's original nomencla- 

 ture and usage, as interpreted and refined with age dating in our 

 paper, should be retained in preference to the extension of the 

 Madbi Formation upwards to include rocks of entirely different 

 lithology, and the alteration of the age and type locality of the 

 Naifa Formation. The subsurface data now available from many 

 parts of Yemen does not invalidate the lithostratigraphical no- 

 menclature used for Wadi Hajar. If rocks of different lithology 

 and/or intermediate age are present in the subsurface, they can be 

 given new formation names applicable to the local conditions. It 

 seems, however, that age dafing for the subsurface rocks may not 

 be known in sufficient detail to make good comparisons with the 

 rocks in Wadi Hajar. 



