Bernard Clavel

Répartition biostratigraphique des orbitolinidés dans la biozonation à ammonites (plate-forme urgonienne du Sud-Est de la France). Partie 1 : Hauterivien supérieur - Barrémien basal.

The proposed biostratigraphic distribution of orbitolinids from the Upper Hauterivian and the lowermost Barremian of SE France is correlated with the ammonite biozonation. It is based on the detailed study of eight sections which delivered orbitolinids intercalated with or capped by levels with ammonites and, in some cases, echinids and dasycladales. Among the 24 species of orbitolinids present during that period, 3 are restricted to the Late Hauterivian: Praedictyorbitolina busnardoi, Paleodictyoconus beckerae and Valserina primitiva.

Praedictyorbitolina carthusiana n. gen. n. sp., Orbitolinidé (Foraminiferida) de la limite Hauterivien-Barrémien des Alpes occidentales

Praedictyorbitolina carthusiana n. gen. n. sp. is described from the Early Barremian(@#@ hugiizone) of the Pas du Frou section (Chartreuse, western Alps). This new form very probably occurred already in the Late Hauterivian and is regarded as the direct ancestor ofDictyorbitolina ichnusae Cherchi & Schroeder.KurzfassungPraedictyorbitolina carthusiana n. gen. n. sp. wird aus dem Unteren Barrême(hugii- Zone) des Profils Pas du Frou (Chartreuse, Westalpen) beschrieben. Diese neue Form, welche sehr wahrscheinlich schon im Oberen Hauterive einsetzt, ist vermutlich der direkte Vorfahre vonDictyorbitolina ichnusae Cherchi & Schroeder.RésuméPraedictyorbitolina carthusiana n. gen. n. sp. est décrite du Barrémien basal (zone à Hugii) de la coupe du Pas du Frou (Chartreuse, Alpes occidentales). Cette forme nouvelle, qui apparaît très probablement dans l’Hauterivien supérieur, représente vraisemblablement l’ancêtre direct deDictyorbitolina ichnusae Cherchi & Schroeder.

Lithocodium and Bacinella signature of a late Hauterivian, local microbial event: the Urgonian limestone in South-East France

Sediment binding crusts of Lithocodium aggregatum and associated Bacinella irregularis abound in a shallow water limestone layer, in South-East France. The sudden appearance of these crusts denotes a local, conspicuous change in the otherwise balanced, open marine depositional environment. Based on regional correlations, the layer is Lower Hauterivian, Ligatus Zone, directly dated by an assemblage of orbitolinids, and indirectly by a specimen of ammonite. It is older than the Faraoni OAE (latest Hauterivian, Angulicostata auct. Zone), and presumably not linked with a global climate change. Two facies are recognized: (1) Lithocodium bindstone, with Bacinella, other microencrusters, and fluorescent automicrite of microbial origin; (2) floatstones containing numerous fragments of Lithocodium and accompanying biota. Coarse rhomboedral dolomite is locally present. Two modern analogues of microbial mediation are put forward to explain the Lithocodium event: (a) Lagoa Vermelha, in Brazil, along with anoxic, marginal marine conditions; (b) Highborne Cay, in the Bahamas, along with oxic, open marine conditions. A stack of four, Upper Hauterivian parasequences is described: Parasequence 1 ends with oolitic deposits; the somewhat deeper water Parasequence 2 occurs only in the south-eastern part of the study area, towards the direction of the Subalpine depotcenter; Parasequence 3 matches the layer with Lithocodium and Bacinella, with wide thickness variations (0.8 m - 11 m), resulting from a syn-sedimentary tectonic activity in the area of a major feature, the Vuache fault system. Parasequence 4 finally corresponds to the resumption of the normal, Urgonian carbonate factory.

The Cretaceous of the Swiss Jura Mountains: an improved lithostratigraphic scheme

In the course of the HARMOS project of the Swiss Geological Survey, the lithostratigraphic subdivisions of the Cretaceous sedimentary rocks outcropping in the Swiss Jura Mountains were revisited. New formation names are proposed where only inadequate facies terms existed so far. As in some cases outcrop conditions in the Swiss Jura do not allow for logging complete sections to characterise the formations, type localities in neighbouring France have been chosen. The following formations (Fm.) are defined to describe the Cretaceous lithological units (from bottom to top): Goldberg Fm., Pierre-Châtel Fm., Vions Fm., Chambotte Fm., Vuache Fm., Grand Essert Fm., Gorges de l’Orbe Fm., Vallorbe Fm., Perte du Rhône Fm., Narlay Fm. Dating of the formations is based on biostratigraphy (ammonites, echinids, dasycladalean algae, foraminifera, calpionellids, dinocysts, nannofossils). The fossils indicate Berriasian through to Coniacian ages. The lithostratigraphic units describe the general evolution from a shallow, peritidal platform to deeper-water shelf environments, then the installation of a carbonate platform, and finally the drowning of this platform followed by the predominance of pelagic conditions. The common lateral and vertical changes in facies and sedimentation rates as well as numerous hiatuses within the formations testify to a complex interplay of tectonics, climate, and sea level that controlled the Swiss Jura realm during the Cretaceous.RésuméDans le cadre du projet HARMOS du Service géologique suisse, les subdivisions lithostratigraphiques des roches sédimentaires crétacées du Jura suisse ont été nouvellement définies. De nouveaux noms de formation sont proposés pour remplacer quelques termes de faciès inadéquats. Dans certains cas, les conditions d’affleurement dans le Jura suisse ne permettent pas de lever des coupes complètes qui caractérisent les formations : des coupes en France voisine ont donc été choisies. Les formations (Fm.) suivantes sont définies pour décrire les unités lithologiques du Crétacé, de la base au sommet : Fm. du Goldberg, Fm. de Pierre-Châtel, Fm. de Vions, Fm. de la Chambotte, Fm. du Vuache, Fm. du Grand Essert, Fm. des Gorges de l’Orbe, Fm. de Vallorbe, Fm. de la Perte du Rhône, Fm. de Narlay. La datation des formations est basée sur la biostratigraphie (ammonites, échinides, algues dasycladales, foraminifères, calpionelles, dinocystes, nannofossiles). Ces fossiles indiquent des âges Berriasien à Coniacien. L’enchaînement des unités lithostratigraphiques résulte de l’évolution générale d’une plate-forme peu profonde, voire péritidale, vers des milieux d’eau plus profonde, suivie par l’installation d’une plate-forme carbonatée, et finalement l’ennoiement de cette plate-forme et la prédominance de conditions pélagiques. Des changements de faciès et de taux de sédimentation latéraux et verticaux ainsi que de nombreuses lacunes sont courants au sein des formations, ce qui indique une interaction complexe de changements tectoniques, climatiques et eustatiques qui contrôlaient l’évolution de la région du Jura suisse durant le Crétacé.

Praedictyorbitolina busnardoi n. sp. (Foraminiferida) et évolution de la lignéePraedictyorbitolina — Dictyorbitolina (Hauterivien supérieur — Barrémien basal)

KurzfassungDie Vertreter der Orbitoliniden-GattungenPraedictyorbitolinaSchroeder, Clavel &Charollais undDictyorbitolinaCherchi &Schroeder gehören einer einzigen, vom oberen Hauterive bis in das basale Barrême reichenden phylogenetischen Reihe an, die aus folgenden Arten zusammengesetzt ist (in stratigraphischer Reihenfolge):Praedictyorbitolina busnardoi n. sp. -P. claveliSchroeder -P. carthusianaSchroeder, Clavel &Charollais undDictyorbitolina ichnusaeCherchi &Schroeder. Die Aufstellung dieser Linie gründet sich — unter Berücksichtigung der stratigraphischen Position der einzelnen Arten — vor allem auf drei Entwicklungstendenzen: (1) Größenzunahme der Gehäuse und Veränderung der äußeren Form, (2) Verlagerung des Embryos und Komplizierung seiner Struktur und (3) Entwicklung des Septulen-Systems innerhalb der Marginalzone.-Praedictyorbitolina busnardoi n. sp. wird ausführlich beschrieben.SummaryThe representatives of the orbitolinid generaPraedictyorbitolinaSchroeder, Clavel &Charollais andDictyorbitolinaCherchi &Schroeder belong to a monophyletic lineage ranging from the late Hauterivian to the basal Barremian and comprising the following species (in stratigraphic order):Praedictyorbitolina busnardoi n. sp. -P. claveliSchroeder -P. carthusianaSchroeder, Clavel &Charollais andDictyorbitolina ichnusaeCherchi &Schroeder. Considering the stratigraphic range of the different species, the establishment of this lineage is based on three evolutionary trends: (1) increase of the size of the tests and change of their morphology, (2) shift of the embryo and development of a subepidermic cellular layer within the deuteroconch, and (3) evolution of the network of septula within the marginal zone.-Praedictyorbitolina busnardoi n. sp. is described in detail.RésuméLes représentants des genres d’OrbitolinidésPraedictyorbitolinaSchroeder, Clavel &Charollais etDictyorbitolinaCherchi &Schroeder appartiennent à une seule lignée phylétique d’âge Hauterivien supérieur — Barrémien basai, qui comprend les espèces suivantes (par ordre stratigraphique):Praedictyorbitolina busnardoi n. sp. -P. claveliSchroeder -P. carthusianaSchroeder, Clavel &Charollais etDictyorbitolina ichnusaeCherchi &Schroeder. L’établissement de cette lignée, examinée dans le cadre de sa répartition stratigraphique, se base sur trois tendances évolutives: (1) agrandissement du test et changement de leur forme extérieure, (2) déplacement de l’embryon et complication de sa structure, et (3) évolution du système de cloisonnettes dans la zone marginale.-Praedictyorbitolina busnardoi n. sp. est décrite en détail.

Discussion of the paper by Godet et al. 2011, entitled “Reconciling strontium-isotope and K–Ar ages with biostratigraphy: the case of the Urgonian platform, Early Cretaceous of the Jura Mountains, Western Switzerland” (Swiss Journal of Geosciences, 104, 147–160)

For decades, the age of the Urgonian deposits, in Switzerland and in the southeast of France in particular, has been addressed and disputed in several articles, by authors belonging to two opposing groups of researchers. For Arnaud-Vanneau and Arnaud (1990) and a number of other workers (e.g. Adatte et al. 2005; Godet et al. 2010, 2011, 2012, and references therein), the Urgonian deposits found in the Canton Vaud, in the western part of the Swiss Jura, and the lower member of the Urgonian limestones, in the French Subalpine Chains, are Late Barremian in age. These authors rely on a certain approach to sequence stratigraphy, combined with chemostratigraphical and geochronological data and selected palaeontological data (rejecting or neglecting some fossil groups that might support alternative interpretations). For instance, Godet et al. (2012) state that ‘‘The orbitolinid biostratigraphy fide Conrad et al. (2012) is questionable’’. This is in contrast to Clavel et al. (1987) and a number of other researchers, such as the present authors (see Clavel et al. 2007; Conrad et al. 2012 and references therein) who maintain that foraminifers provide reliable biostratigraphical information, particularly in depositional environments where the classical markers such as ammonites, planktonic foraminifers, and nannofossils are lacking. In our stratigraphical interpretation, all Urgonian deposits are Late Hauterivian in age in the western Swiss Jura, whereas in the French Subalpine Chains the lower member of the Urgonian limestones dates from the Late Hauterivian, the Early Barremian or the Late Barremian, depending on its paleogeographic location (Clavel et al. 2012). This interpretation relies on a wider set of palaeontological data and different approach to sequence stratigraphy. However, according to Godet et al. (2012), ‘‘The sequence-stratigraphic interpretation forwarded by Conrad et al. (2012) is not consistent with modern sequence-stratigraphic interpretation of platform carbonates’’. Since we understand from this statement that there will be no agreement on the best practice in sequence stratigraphy, we will not discuss the topic further. We focus here of the western Swiss Jura and on the difference in age between the interpretation of the first group (represented by the paper by Godet et al. 2011) and our interpretation. The difference between these two interpretations is significant, because it covers a full stage, with implications that go far beyond the study area, referring to the whole of the northwestern Tethyan domain. In particular it is whether, Editorial handling: A. G. Milnes.

Comments on "Estimating the impact of early diagenesis on isotope records in shallow-marine carbonates: A case study from the Urgonian platform in western Swiss Jura" by A. Godet et al. [Palaeogeography Palaeoclimatology Palaeoecology 454 (2016) 125-138]

A recent paper by Godet et al. on Urgonian carbonates from the Swiss Jura concluded that diagenesis may hinder chemostratigraphic correlations of deep- to shallow-water facies. Although we agree with this conclusion we question their arguments and interpretations. These authors correctly identified diagenesis as the key factor, but we question the timing of events in their paragenetic sequence. In particular, they reported the leaching of originally calcitic oolitic cortices but failed to discuss this puzzling feature properly. In addition, the backbone of their argument is the stratigraphic correlation of a specific sequence from three dominantly shallow-water sections together with a basinal reference section. However, a reliable alternative biostratigraphic framework shows that this attempt of long-distance correlation might be erroneous.

Refining Urgonian Biostratigraphy: A Key Section at L’Estellon, Drôme, France

In a basinal section of the Vocontian Trough, “freshly” reworked shallow-water assemblages (orbitolinids and dasycladales) can be calibrated directly with ammonite zones. The section documents, for instance, the oldest record of Palorbitolina lenticularis and those of the so-called “typical early Aptian” representatives of the genus Orbitolinopsis in lower Barremian strata.