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The Barremian Stage

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The Barremian Stage bulletin de l'institut royal des sciences naturelles de belgique sciences de la terre, 66-supp.: 25-30, 1996 bulletin van het koninklijk belgisch instituut voor natuurwetenschappen aardwetenschappen, 66-supp.: 25-30, 1996 The Barremian Stage by Peter F. RAWSON (compiler), with contributions from Emil Avram, Evgenij J. Baraboschkin, Fabrizio Cecca, Miguel Company, Gérard Delanoy, Philip J. Hoedemaeker, Mikhail Kakabadze, Elisso Kotetishvili, Han Leereveld, Jörg Mutterlose, Katharina von Salis, José Sandoval, José Maria Tavera and Zdenek Vasicek. Abstract npeflCTaBJlfleTCH B03MOXHOM B CBH3M c CHAbHOÜ ÖMOTMHeCKOÜ Au4ict>epeHUMaui/ieM, cytuecTByKJiueü Mexny pa3HbiMM o6nacTBMn, a TaiOKe B CB93M c OHeBMAHbiM HeflocTaTKOM èuocTpaTnrpacJjMHecKMX Inter-regional corrélation in the Barremian is impossible because of 3H3K0B, HeoöxoflMMbix A/ifl npaBH/ibHoro o6o3HaMeHust rpaHnq. strong biotic differentiation between realms coupled with a lack of no 3Toiï npnHMHe Mbi Bbiöpa/tu HaunyHiuyio M3 cyutecTByiournx obvious non-biostratigraphic markers to provide good boundaries. orpaHMHeHHbix B03M0>KH0CTeM Anti onpefleneHMH rpaHMLt oönacTM Thus we have chosen the best of the limited options available to define Teïuc. boundaries within the Tethyan Realm. M bi pexoMeHAyeM onpeAettBTb ocHOBaHne BappeMa no ocHOBaHwo We recommend that the base of the Barremian be placed at the base aMMOHMTOBOM 30Hbl Spitidiscus hugii, b pa3pe3e Rio Argos Ha of the Spitidiscus hugii ammonite Zone in the Rio Argos section, SE loro-BOCTOKe HcnaHMH. flonojiHMTeAbHaa HHtbopMauun 6yAeT Spain. Supplementary information will be compiled to fully document npeAOCTaBJteHa aah aoxyiviehtauhm AaHHoro Bbiöopa ao ero this choice before formai submission via the Cretaceous Subcommis¬ (JtopManbHoro npeACTaB/ieHMH CTpaTnrpact>MHecKOM Komhccmm, npn sion to the Commission on Stratigraphy. nocpeAHHuecTBe MenoBoü noAKOMMcenn. The base of the Upper Barremian should be defined by the first OcHOBaHne BepxHero Bappeiwa ao/dkho öbiTb onpeAeneHo ripn appearance of the ammonite Ancyloceras vandenheckei in one of the nepBOM noBBtieHnri aMMOHHTa Ancyloceras vandenheckei b Subbetic sections in SE Spain, probably section X.KV (Barrano de OAHoPi H3 npeAÖeTCKi/ix ceKU,nü Ha loro-Bocioxe HcnaHHM, BepotirHO Cavila, Caravaca). Other sections in the région require further docu¬ b pa3pe3e X.KV (Barrano de Cavila, Caravaca). flpyrite pa3pe3bi mentation before the final recommendation can be made. AaHHoro paüoHa TpeöyioT AonoriHMTe/tbHoro H3yHeHntt aah cftopMyJlMpOBKH KOHeHHblX peKOMeHAaUMÜ. Key-words: KnwHeBbie cnoBa: Barremian, Lower Cretaceous, biostratigraphy, magnetostratigraphy, BappeMCKnü npyc, hmxhhm Men, stratotypes. 6nocTpa™rpa(J)MB, MarHHTOCTpa™rpact>Mfl, cTpaTOTHnbi. Introduction Résumé: The Barremian Working Group has continued the work Pour le Barrémien, toute corrélation interrégionale est impossible à initiated cause d'une forte différentiation biotique entre les différents domaines by its predecessor, the pre-Albian Stages Work¬ combinée à un manque évident de marqueurs non biostratigraphiques ing Group, whose conclusions were presented at Munich pour indiquer de bonnes limites. C'est pourquoi nous avons choisi les in 1982 (Rawson, 1983) and Copenhagen in 1983 (Bir- meilleures parmi les options limitées existantes pour définir les limites kelund et dans le domaine téthysien. al., 1984). The preliminary proposals made at Nous recommandons de placer la base du Barrémien à la base de la the Subcommission's 1983 Copenhagen conference are a Zone de l'ammonite Spitidiscus hugii, dans la section du Rio Argos, necessary starting point for defining the base of the Espagne du S.-E. Des informations supplémentaires seront rassemblées Barremian. The Lower/Upper Barremian boundary was pour documenter ce choix avant de le soumettre formellement par l'intermédiaire de la Sous-commission du Crétacé à la Commission not considered at Copenhagen, but had been discussed de Stratigraphie. briefly at Munich. At both meetings debate centred La base du Barrémien supérieur devrait être définie par la première mainly on the ammonite sequence and little information apparition de l'ammonite Ancyloceras vandenheckei dans une des was offered on sections subbétiques (S.-E. de l'Espagne), probablement la section possible microfossil or other boundary X.KV (Barrano de Cavila, Caravaca). D'autres sections dans la région markers (Birkelund et al., 1984, pp. 7-8). The main doivent être étudiées de façon plus approfondie avant que l'on puisse obstacles to faire de recommandation définitive. making firm recommendations for stage and substage boundaries were recognised as: Mots-clefs: Barrémien, Crétacé inférieur, biostratigraphie, magnétostraigraphie, • a lack of detailed lithological, palaeontological, mag- stratotypes. netostratigraphic and chronostratigraphic logs for many key sections around the world (Rawson, 1983, p. 499). EappeMCKkift spyc. • provincialism in many fossil groups, rendering long- Pe3K>Me. distance corrélation very difficult (Birkelund et al., flnn BappeMCKoro npyca MexcperHOHattbHaa KoppennuMB He 1984). 26 Peter F. RAWSON Since the Copenhagen meeting much new information within the angulicostata Zone based on the first appear- has been published, especially on various European sé¬ ance of the desmoceratid ammonites Raspailiceras and quences. Some important palaeomagnetic data are now Barremites. The Copenhagen meeting recommended that available and sequence stratigraphy has given new in- the Hauterivian/Barremian boundary should be placed sights. However, this new information has highlighted the difficulty of correlating the better-known West Te- thyan (Spain to the Caucasus) sequences with Barremian successions elsewhere. Even within Europe, the increas- o ö CN m ing endemicity of many fossil taxa by the beginning of ^ z w £ § S 2 S the Barremian makes it difficult to correlate the West Si O u u O O Tethyan faunas/floras with those of the NW European "Boréal" area. Conversely, the stratigraphy of some of the rich ammonite faunas of the Americas is poorly known. We are therefore taking the pragmatic view that as I a truly global corrélation of Barremian rocks is still h •3 « an unachieved ideal which C/5 C/5 may never be fully satis- •S fied, it is better not to delay making our recommenda- ÖË "S S tions on the §■ s ^ boundary levels. Although there are différ¬ § w o . Q 05 Q ences of opinion and emphasis within our working group, which will be elaborated O O O upon below, the consensus is u, J fa that the boundaries should be defined in the Western \ Tethys and based primarily on the ammonite sequence there. It proved impossible to find good, reliable micro- fossil markers of any wide applicability, but we have indicated those useful biological (and non-biological) events &0 that coincide closely with the ammonite bound¬ s; o aries. O O Définition of the Barremian Stage \ Busnardo (1965) noted that although Coquand's (1861) original définition of the Barremian was not very précisé, it embraced both the Upper Hauterivian and Barremian of current usage. The pre-Albian Stages Working Group s agreed with Busnardo that "despite historical priority it is best in the interests of stability" to follow Kilian's more o (1888) limited interprétation of the Barremian öo (Rawson, 1983, p. 497). Kilian had included the zone O ei of Pseudothurmannia angulicostata in the Hauterivian, O O —I Urn and that is the view taken by the majority of, though not all, wolkers since (see discussion below). \ \ \ The base of the Barremian During the preliminary exchange of ideas among Work¬ ing Group members, it became apparent that there were no obvious microfossil or non-biostratigraphic markers •73 that could convincingly supplant the ammonites as a ao ao § a primary tooi for defining the base of the Barremian. Thus -c § debate has centred primarily on which ammonite level Fig. 1 — Lower Barremian and lower Upper Barremian Te¬ would provide the best boundary. thyan (Mediterranean) ammonite zones, microfossil At Copenhagen is was noted that while some workers events and magnetic polarity chrons. placed the base of the Barremian at the base of the The solid line beneath the hugii Zone represents the Pseudothurmannia angulicostata Zone (i.e. base of the recommended base of the Barremian and that be¬ Pseudothurmannia beds) others put it above that zone neath the vandenheckei Zone the recommended while Busnardo (in Rawson, 1983, p. 498) drew it high base of the Upper Barremian. The Barremian Stage 27 either below or above the Pseudothurmannia beds and are separated by some levels very rich in Desmoceratidae that a boundary within them should be avoided (Birke- (Barremites, Raspailiceras). These desmoceratids do lund et al, 1984, p. 8). not appear to be of a very refined stratigraphie usage, Three possible horizons for the base of the Barremian and their local abundance is perhaps due to particular were discussed at Brussels: ecological conditions. Vasicek (personal communica¬ tion) also points out that as desmoceratids are rather • base of the Spitidiscus hugii Zone (i.e. above the difficult to determine and are mostly not very well pre- Pseudothurmannia beds) served, it is unrealistic to use them for defining the boundary. • middle of the Pseudothurmannia beds Cecca et al. (1994) suggest that the base of the hugii Zone lies somewhat above the last occurrence of the • base of the Pseudothurmannia beds nannofossil Lithraphidites bollii. However, von Salis (personal communication) notes that in général the nan- nofossils show little
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