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Jurassic-Cretaceous Boundary by Viktor A bulletin de l'institut royal des sciences naturelles de belgique sciences de la terre, 66-supp.: 7-10, 1996 bulletin van het koninklijk belgisch instituut voor natuurwetenschappen aardwetenschappen, 66-supp.: 7-10, 1996 The Berriasian Stage and the Jurassic-Cretaceous boundary by Viktor A. ZAKHAROV, Paul BOWN and Peter F. RAWSON Abstract Jurassic-Cretaceous boundary Working Group is respon- sible for defining the base of the Berriasian stage and of It is recommended that the base of the Berriasian Stage be placed its subdivisions, as well as for determining the base of the either at the base of the Berriasella jacobi Zone or at the base of the Cretaceous. It should be stressed that some authors (e.g. Tirnovella subalpina Subzone. The choice of stratotype section will Wiedmann, 1980; Rawson, dépend on the choice of zone, but will be in SE France or SE Spain. 1990; Remane, 1990) have Subdivision of the Berriasian Stage into 2 or 3 substages will again indicated that the latter boundary could usefully be placed dépend on which level is chosen to define the base of the stage. above the Berriasian, at the base of the Valanginian. As no draft Key-words: Berriasian, Lower Cretaceous, biostratigraphy, ammo¬ paper had been prepared for Working nites, calpionellids. Group members prior to the Brussels meeting, this short contribution is based on notes from the Brussels meeting compiled by Viktor A. Zakharov (W.G. Chairman 1992- Résumé 1995) and edited by Paul Bown (Acting Secretary), with additional material by Peter Rawson. Il est recommandé de placer la base de l'étage Berriasien soit à la base de la zone à Berriasella jacobi, soit à la base de la sous-zone à Tirnovella subalpina. Le choix du stratotype dépendra du choix de la zone, mais il sera situé dans le SE de la France ou dans le SE de The l'Espagne. La subdivision de l'étage Berriasien en 2 ou en 3 sous- Jurassic-Cretaceous boundary étages dépendra également du niveau choisi pour définir la base de l'étage. Définition of the Jurassic-Cretaceous boundary re¬ mains an intractable Mots-clefs: Berriasien, Crétacé inférieur, biostratigraphie, ammonites, problem despite some 30 years of calpionellides. debate, over a dozen international conferences and a Working Group dedicated to the issue since 1974 (Casey et al., 1975). The problem hinges on the need to define a BeppnacKMÜ npyc m lOpcKO-MenoBan rpaHviua. boundary that can be correlated over as wide an area as possible and ideally from Tethyan to Boréal Pe3toMe. realms. OcHOBaHue EeppnacKoro upyca peKOMeHflyeTCfl onpeflennTb nnôo no ocHOBaHnio 30Hbi Berriasella jacobi, nn6o no The issues were discussed ocHOBaHUK) nofl30Hbl Tirnovella subalpina. Bblôop by Jürgen Remane, Chairman CTpaTOTuna öyfleT 3aBiiceTb ot Bbiôopa 3ohw, ho b nio6oM of the Working Group from 1982 to 1992, in a paper c/iynae cTpaTOTun ôynei pacnonoxeH Ha toro-BOCTOKe given at an international field meeting on "The Jurassic- OpaHuun v\m HcnaHMM. Pa3flejieHMe EeppuacKoro stpyca Ha 2 Cretaceous Boundary in the Northern Caucasus" in 1987 nnn 3 noAtnpyca 6yaeT Taioxe 3aBttceTb ot ypoBHH, BbiöpaHHoro anti onpefleneHHH ocHOBaHMH npyca. (Remane, 1990). An English language version of this paper was circulated to Working Group members with KniOHeBbie c/ioBa: BeppnacKuû npyc, huxhmm Men, Newsletter 9 in October 1988, while a modified (English) 6nocTpaTMrpa<t)hh, aMMOHUTbi, Calpionellida. version was published by Cretaceous Research in 1991. Remane (1990, 1991) pointed out that the problems appear due largely to: Introduction ( 1 ) a lack of significant faunal turnovers at the base of Because the base of the Cretaceous is generally placed at the Berriasian, however defined (though some ammonite the base of the Berriasian stage, définition of the base of changes are discussed below); the Berriasian has been linked inextricably with the de- finition of the Jurassic-Cretaceous boundary. Thus the (2) the effects of the "Purbeckian régression". 8 Viktor A. ZAKHAROV, Paul BOWN and Peter F. RAWSON The "Purbeckian régression" marked a major global fall (3) If this boundary level cannot be correlated from the in sea-level that led to an interval of high faunal and floral Tethyan to the Boreal realm, a level close to it should be endemism and extreme facies across differentiation the selected [the base of the occitanica Zone might be a good Eurasian région. This in turn renders corrélation extre- solution (Hoedemaeker, 1987)]. mely difficult. Remane (1990, 1991) also recalled the recommenda- (4) Until a final décision is made on the Jurassic-Creta- tions made by the Working Group at the 27th IGC in ceous boundary, the Berriasian should be placed in the Moscow in 1984: Cretaceous. ( 1 ) The Jurassic/Cretaceous boundary should be defined Although Remane concentrated on biochronology, he in the Tethyan Realm. mentioned the possible role of magnetostratigraphy in future efforts to define the boundary. At the same (2) The first candidate for the boundary is the Tithonian/ (1987) conference, Rawson (1990) suggested the need Berriasian boundary, which corresponds to the base of the to consider the applicability of non-biological "events", combined jacobi-grandis Zone [following the recommen- while at Brussels Erba (1995) challenged palaeontolo- dation of the 1973 Lyons Colloquium (Flandrin et al gists to consider the role of magnetostratigraphy, chemo- 1975, p. 392)]. stratigraphy, sequence stratigraphy and cyclostratigraphy Table 1. Relationship between the Mediterranean ammonite and calpionellid zones, and possible corrélation of the Boreal ammonite zones with the Mediterranean "standard". ka <ü ka ka <D O sp Mediterranean ka -4-» région Northern Siberia a> sp ka $ -4-» jo ka sp C/3 3 +-» C/3 C/3 ammonites calpionellids ammonites C/3 'C •21 Tirnovella alpillensis D3 Tollia tolli }r> t-H O O <5 Picteticeras D2 picteti Bojarkia mesezhnikowi <D O £ CX Surites analogus P Malbosiceras paramimounum D1 .1 ka l Surit Surites es analogus subquadratus 2 S—< O .SJ Surites CQ SU praeanalogus Dalmasiceras daim asi cd <D 'o Borealites constans S—> § O O C kochi 'i CQ '5 -S Hectoroceras kochi SU Betriasella Hectoroc U privasensis Middh >> Lowei m O Chetaites sibiricus S t-H Tirnovella subalpina Praetollia maynci Chetaites sibiricus O Chetaites chetae O Pseudosubplanites grandis s Craspedites taimyrensis <D -S B É SU C. O originalis h-l S ■15 "a 5 Uppei s Berriasella SI s jacobi « C. okensis o S ® > O C. exoticus A Durangites spp. Tithon. Upper (pars) Epivii'gatttes variabilis Middle note: The single and double question marks indicate degrees of uncertainty in corrélation of the boreal sequences with the two candidate boundaries for the base of the Berriasian. The Berriasian Stage 9 in defining Cretaceous stage boundaries. Despite this, significant ammonite turnover, and has good corrélation debate has continued to concentrate on the biostrati- potential. The level is coïncident with, or approximates graphic aspects. to, the base of the Praetollia maynci/Runctonia runctoni ammonite Zone and the Buchia okensis buchiid Zone in the Boreal area. The base of the Berriasian Stage At the Brussels meeting, the Working Group discussed a Stratotype Section number of proposals for boundary points and sections. The conclusions are summarised below. The choice of boundary stratotype section is dépendent upon the final choice of the defining event. The base of the jacobi ammonite Zone is well represented in the Boundary Criteria Puerto Escano section (Prov. Cordoba, Spain). The base of the subalpina ammonite Subzone may be best defined It was agreed that the base of the Berriasian should at La Faurie, Ravin de Dreymien (Alpes-de-Provence, be defined on the appearance of a new fossil taxon, France) or Section Z, Berrancode de Tollo (Rio Argos, and that the stratotype section should be in the Mediter- Caravaca, Prov. Murcia, Spain). ranean région. Two possible faunal events were pro- posed: • base of the jacobi ammonite Zone Substage définitions • base of the subalpina ammonite Subzone (occitanica Ammonite Zone) Substage définitions are dépendent on the final stage- boundary event décision. If the base of the jacobi Zone base of the jacobi Zone is chosen, then the base of the Middle Berriasian may be This is essentially the level suggested at the 1973 Lyons defined by the base of the subalpina Subzone, and the Colloquium, as adopted by the Lower Cretaceous Cepha- Upper Berriasian by the base of the boissieri ammonite lopod Working Group of IGCP Project 262 (Hoedemae- Zone. If the base of the subalpina Subzone is chosen as ker & Bulot, 1990; Hoedemaeker, Company et al., the base of the stage, then an Upper Berriasian substage 1993). According to Hoedemaeker & Bulot (1990), can be defined by the base of the boissieri Zone, and no middle the index species first appears at the base of the zone - substage should be retained. a level that corresponds to a major event in ammonite évolution, i.e. at the family level. It is also closely ap- proximated by an important calpionellid event, marking Recommendations the base of the B Calpionellid Zone (Table 1). However, the jacobi Zone is virtually impossible to correlate with The working group concluded that further documentation boreal areas. of these potential stratotype sections is required and interdisciplinary teams should investigate the corrélation base of the subalpina Subzone potential of the biostratigraphic events proposed. To im- The subzone is dominated by the abundance of Timovella prove Tethyan/Boreal corrélation, such teams should in¬ subalpina, which first appears at the base of the subzone vestigate sections in northern California and northern (Le Hégarat, 1973, table 12, p. 176). This level marks a Siberia. References Casey, R., Allen, P., Dörhöfer, G., Gramann, F., Hughes, Hoedemaeker, P. !.. 1987. Corrélation possibilities around the N. F., Kemper, E., Rawson, P. F. & Surlyk, F., 1975. Strati- Jurassic-Cretaceous boundary. Scripta Geologica, 84: 1-55.
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