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The Jurassic-Cretaceous is at an impasse: Why not go back to Oppel’s original and historic definition of the Tithonian (1865)?
Raymond Énay

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-05 10:20 AM – 10:50 AM
Last modified: 2018-11-23

Abstract


The questions of the highest Jurassic stage and that of the Jurassic-Cretaceous boundary were first discussed during two Jurassic Colloquia, Luxembourg 1 (1962) and Luxembourg 2 (1967), again in the Cretaceous Colloquium in Lyon (1963) and the Lyon-Neuchâtel (1973) Colloquium was devoted to the second item. Then, according to the ICS (International Commission on Stratigraphy) regulations the aim is to fix a boundary at a point in a section providing a well-defined standard. Such GSSP (Global Stratotype Sections and Points) being most commonly defined at a biostratigraphical marker point. Thus, only the International Subcommision of Cretaceous Stratigraphy (ISCS) and within this the Berriasian Working Group are competent for defining the lowest stage of the Cretaceous and the Jurassic-Cretaceous boundary. In 2007 the Group initiated a new phase of activity.

The Tithonian Stage defined by Oppel (1865) was accepted as the highest stage of the Standard Jurassic Time Scale in the International Congress of the ISJS in Poitiers (1991) and confirmed by the ICS. No GSSP has been selected as yet, however the lower boundary was accepted to be at the base of the Lithographicum/ Hybonotum Zone of the Tethyan Zonal scheme and equivalents in other provincial zonal schemes. The upper boundary will be at the base of the overlying unit. But what precisely is this unit and what is its position according to the Jurassic-Cretaceous boundary?

On the other hand the Jurassic-Cretaceous problem has been pending and awaiting a proposal likely to obtain a large acceptance. This issue persists in spite of new global data from multiple disciplines other than ammonite biostratigraphy: micropalaeontology, magnetostratigraphy, sequence stratigraphy (Wimbledon, 2008, 2017; Wimbledon et al., 2011).The reason for this impasse is the deep provincialism of the ammonite faunas and other groups between the Boreal and Tethyan Realms (also within them), which developed beginning in the Late Oxfordian onwards. This was also a time of connection with a large expanse of non-marine environments (e.g., Purbeck, Wealden).

Kilian scheme: Tithonian-Berriasian boundary is the Jurassic-Cretaceous boundary

From many decades definition of the Jurassic-Cretaceous boundary has been an age-old correlation enigma (Wimbledon, 2008); perhaps the reason is that it was defined loosely. Other criteria were possible (on which we shall come back to), but the issue dates back to the time when the stages were first defined. Only a few years separate the definitions of the Tithonian (Oppel, 1865) and Berriasian (Coquand, 1871) stages. In contrast to the other stages around the Jurassic-Cretaceous boundary (e.g., Portlandian, Volgian, Ryazanian, Purbeck, and Wealden), the Tithonian was not defined from a stratotype, but instead Oppel listed numerous localities in Central and Southern Europe, S Germany and SE France, with original ammonite faunas and other biota, which were published after Oppel’s death by his pupil, K. von Zittel (1868, 1870).

However, rock sequences in SE France were well-studied and as early as 1846 the Berrias Limestones were known by Malbos & Dumas and already classified as the earliest stage of the “Neocomian”. By 1868 Coquand noted the “Berriasian (ammonite) fauna”, which would be described by Pictet by 1867. Thus, in spite of Toucas (1888, 1889, 1890), Haug (1898) and Lapparent (1892), the prevailing scheme would be the Kilian one (1890, 1891, 1907, 1910), in which the Jurassic-Cretaceous boundary was identified with the Tithonian-Berriasian boundary. That scheme would be amplified by the Mazenot’s monograph (1939) on the Tithonian and Berriasian ammonites, Remane’s studies (1963, 1968) on calpionellids, and Le Hégarat’s (1968, 1973) exhaustive study of the Berriasian of SE France. But a quite different interpretation of the Jurassic-Cretaceous boundary and the age of the Berriasian stage is possible if the original definition of the Tithonian by Oppel (1865) is considered.

Original Tithonian definition and two schemes of the Jurassic-Cretaceous boundary

Oppel defined the Tithonian (1865, p. 535) as “… a particular formation group located between the stage of Kimmeridge and the deepest Neocomian layers, which I call this Tithonian Stage, in order to indicate the relationship of this group of layers to the Cretaceous formations that begin immediately above”. This definition of the lower boundary of the Tithonian is ambiguous because of two later meanings of the Kimmeridgian Stage (sensu anglico vs sensu gallico). However the quoted faunas are undoubtedly those of the highest zone of the Kimmeridgian Stage. But definition of the upper boundary, which is the overlying marls with pyritic fossils of Valanginian age in SE France, is not ambiguous.

Coquand’s Berriasian (1871) is not defined any better. The Berriasian name was derived from a locality at Berrias, and it is based on the “Calcaires de Berrias” Formation, which already was assumed to be part of the Neocomian Stage (Malbos & Dumas, 1846). Its fauna was described by Pictet (1867) and was named the “Berriasian Fauna” by Coquand (1869). Thus the question of the position of the Berriasian was posed early.

  • On one side are those who considered the Berriasian to be part of the Jurassic (Haug, 1898; Lapparent, 1892a, b; and particularly Toucas, 1889, 1890, 1908), and divided the Tithonian into three substages, lower, middle (= Ardescian Toucas, 1890) and upper Tithonian or Berriasian.
  • On the other side, according to Malbos & Dumas (1846) and Coquand (1869, 1871), are those who accepted the Berriasian as the first Cretaceous stage (or substage within the Valanginian Stage), particularly Kilian (1890-1891, 1907, 1910) the scheme of which was confirmed by Mazenot (1939, 1957), Busnardo et al. (1963), Barbier & Thieuloy (1963, Remane (1963, 1968), Le Hégarat & Remane (1968), Le Hégarat (1965, 1973), Donze & Le Hégarat (1965, 1966, 1972), and Barthel et al. (1973).

Brief review of the Toucas scheme and the Lyon-Neuchâtel Colloquium (1973)

The Toucas proposal re-appeared in 1967 (Wiedmann, 1967, 1968, 1971) and at the Lyon-Neuchâtel Colloqium (1973) on the Jurassic-Cretaceous boundary (Wiedmann, 1974, 1980; Druschichts, 1969, 1975; Geyer, 1983). At the same time the Ardescian Stage was resurrected, but Wiedmann and Druschichts did not agree exactly on the original meaning. A modern revision of the Ardescian stratotype was presented later (Énay, 1980; Cecca, 1986; Cecca et al., 1988; Énay et al., 1989a, b; Jan du Chêne et al., 1993), but the Ardescian was considered only as part of the Tithonian s.l., the Berriasian being included as well.

However, this return to the Toucas scheme had little impact save the motions submitted during the Lyon-Neuchâtel Symposium on the Jurassic-Cretaceous boundary, which included Motion III by J. Flandrin, R. Énay, J.-P. Thieuloy, G. Le Hégarat and V. Druschichts and motion XII by A. Zeiss (Mémoire du B.R.G.M., 86, p. 388-389).

Motion III, with three proposals: (i) the Tithonian-Berriasian boundary at the base of the Jacobi/Grandis Zone and the Calpionellids B Zone; (ii) Berriasian-Valanginian boundary at the base of the Pertransiens Zone; (iii) The Jurassic-Cretaceous boundary situated at the base of the Valanginian.

Motion XII: Tithonian is the upper stage of the Jurassic system and is divided into four substages: Danubian (Hybonotum-Palatinum zones), Neuburgian (Bavaricum zone s.l. = Semiforme-Ponti zones), Ardescian (Microcanthum-Durangites zones*= Transitorius zone s.l.; Calpionellid A zone) and Berriasian (Jacobi-Boissieri zones; B-D Calpionellids zones” (*Presently: Andreaei zone).

Long discussion at the end of the Symposium resulted in the submission of 12 motions too numerous to be discussed during the session. Thus an inquiry was decided and organized after the meeting on (i) the motions and (ii) on the Jurassic-Cretaceous boundary.

Of the 120 questionnaires sent around, the Jurassic-Cretaceous boundary gathered 84 votes, but only 70 concerned the motions. The results concerning motion III were:

  • Motion III itself: 22 favorable votes;
  • Proposal 1 (Tithonian-Berriasian boundary): 52 favorable votes;
  • Proposal 2 (Berriasian-Valanginian boundary): 73 favorable votes;
  • Proposal 3 (Jurassic-Cretaceous boundary): 18 favorable votes (facing 33 favorable to the boundary at the base of the Jacobi/Grandis Zone).

Since the 1973 Lyon-Neuchâtel Symposium progress has been made but until now no decision has been taken and no GSSP has been fixed. Thus it is time to recall some evidences and advantages to place the Jurassic-Cretaceous boundary at the bottom of the Valanginian Stage (i.e., the Pertransiens zone).

Why the Jurassic-Cretaceous boundary should not be at the base of the Valanginian Stage?

First when concluding his monograph and about the Berriasian and the Jurassic-Cretaceous boundaries, Le Hégarat himself (1973, p. 297) stated emphatically that « aucun renouvellement important de faune ne se produit à la limite Tithonique-Berriasien. Seules s’observent des fluctuations au sein des genres et des espèces ». Likewise the calpionellids are only impoverished, without any major change across the boundary, which is placed in the middle of the Calpionella Zone (Zone B). So, concerning both the ammonites and the calpionellids, « Le passage Tithonique- Berriasien est mal caractérisé paléontologiquement car aucun changement fondamental ne se produit à son niveau » and further « il est cependant certain que les faunes du Tithonien terminal et les faunes du Berriasien sont intimement liées »

In revising the Ardescian type-section Cecca (1986) and Cecca et al. (1988, 1989a, b) proposed that a new definition of its stratigraphic range should correspond to the Microcanthum and Durangites (recte Andreaei) zones, i.e., Upper Tithonian, based on recent studies of the Le Chouët section in the Vocontian basin ( Wimbledon et al., 2013; Bulot et al., 2014). These authors agree that the change between highest Tithonian Andreaei Zone and the lowest Berriasian Jacobi/Grandis Zone is of a usual level for consecutive zones, i.e., without sharp break.

In contrast, Le Hégarat (1973, p. 297) wrote that “contradistinction is strikingly with what it is noted at the Berriasian-Valanginian boundary”. According to Le Hégarat (1973, p. 295), the boundary between the highest Berriasian zone and subzone (Boissieri Zone, Callisto Subzone) and the lowest Valanginian zone and subzone (Roubaudi Zone, Pertransiens Subzone) is “a well-marked discontinuity between Berriasian and Valanginian”,  and further “the changes in the faunas are rude”. He suggested that external events would have strengthened the efficiency of that change, but it is asserted that “these are added to deep and irreversible biological changes: nearly all the Tithonian and Berriasian ammonite genera have disappeared above the Berriasian-Valanginian boundary”. As noted by Blanc et al. (1994), many authors (e.g., Le Hégarat & Remane, 1968; Hoedemaeker, 1982; Busnardo & Thieuloy, 1979) have underlined that the Berriasian-Valanginian boundary is disturbed by sedimentological events (gap, slumps), but they did not use the same zonal scheme. The proposal by Bulot et al. (1993) to place the Berriasian-Valanginian boundary at the base of the Pertransiens Zone would be strengthened by the first occurrence at about the same level of Calpionellites darderi (= base of the Calpionellites Zone).

To conclude, a decision to use the Berriasian-Valanginian boundary as the Jurassic-Cretaceous boundary (i) would end decades of as yet unsuccesseful discussions, (ii) would provide easier and larger possibilities for world-wide correlation and (iii) would be in better agreement with the original and historic definition of Oppel’s definition of the Tithonian Stage, while the concept of a Berriasian Stage as a normal integral part of the Tithonian of Oppel is preserved.