In order to improve our understanding of the relationships between the late Hauterivian oceanic anoxic Faraoni event, contemporaneous platform drowning along the northern Tethyan margin and global environmental change in general, we established high-resolution δ 13 C and δ 18 O curves for the late Hauterivian and the entire Barremian stage. These data were obtained from whole-rock carbonate samples from the Veveyse de Châtel-Saint-Denis section (Switzerland), the Fiume-Bosso section and the nearby Gorgo a Cerbara section (central Italy), and the Angles section (Barremian stratotype, France).We observe an increase of 0.3‰ in mean δ 13 C values within sediments from the middle Hauterivian Subsaynella sayni ammonite zone to the Hauterivian-Barremian boundary; δ 13 C values remain essentially stable during the early Barremian. During the latest early Barremian and most of the late Barremian, δ 13 C values increase slowly (until the Imerites giraudi zone) and the latest Barremian is characterized by a negative trend in δ 13 C values, with minimal values at the Barremian-Aptian boundary. During the earliest Aptian, δ 13 C mean values start to rise again and attain + 2.25‰. We interpret the evolution of the δ 13 C record as resulting from the interaction between changes in the carbon cycle in the Tethyan basin and the adjacent platforms and continents. In particular, changes towards warmer and more humid conditions on the continent and coeval phases of platform drowning along the northern Tethyan margin may have contributed to enhance the oceanic dissolved inorganic carbon (DIC) reservoir which may have pushed the δ 13 C record towards more negative values and exerted a general attenuation on the δ 13 C record. From this may have come the general change from a heterozoan to a photozoan carbonate platform community, which influenced the evolution in δ 13 C values by increasing the export of aragonite and diminishing export of dissolved organic carbon into the basins.

The Altmann Member drowning episode 157 ABSTRACT During the Early Cretaceous, major palaeoceanographic changes are mirrored on the northern Tethyan carbonate platform by changes in the carbonate factory and by platform drowning. The Altmann Member of the central European, northern Alpine Helvetic thrust and fold belt, contains the sedimentary record of one of these drowning events which occurred during the Late Hauterivian -Early Barremian. It consists mainly of highly condensed beds, which are rich in glaucony and phosphates. The Altmann Member was hitherto only poorly dated. New ammonite findings and a re-evaluation of existing ammonite fauna allow to precisely date this drowning episode, starting in the Pseudothurmannia seitzi biozone (latest Hauterivian) and lasting until the Coronites darsi biozone (latest Early Barremian). These new age dates, coupled with sequence stratigraphic interpretations allow to better understand the unfolding of the drowning episode, which proceeded in two stages: The first stage consisted in an important phase of marine transgression during the latest Hauterivian, during which carbonate production was highly reduced; the second stage is recorded during the latest Early Barremian by an important sequence boundary, which is associated with a phosphatized hardground, followed by rapid sea-level rise and the deposition of outer ramp sediment associated with the backstepping of the platform. Almost the whole early Barremian is likely to be condensed in this phosphatized hardground, which is associated to a second order sea-level lowstand. The onset of the drowning event is linked to the Faraoni oceanic anoxic event, whereas during the Early Barremian, phosphatization might be the result of important winnowing during a period of highly eutrophic conditions. RESUME Durant le Crétacé inférieur, les changements paléoceanographiques sont enregistrés sur la marge nord-Téthysienne par des fluctuations du mode de production des carbonates ainsi que des épisodes d'ennoiement de plate-forme. Le Membre d'Altmann, qui affleure en Europe centrale, dans les nappes plissées et charriées du domaine Helvétique, est le résultat d'un de ces ennoiements de la plate-forme carbonatée se déroulant durant l'Hauterivien tardif et le Barrémien précoce. Principalement constitué de couches fortement condensées riches en glauconie et phosphate, le Membre d'Altmann, qui peut être relié à des changements paléocéanographiques majeurs durant le Crétacé infé-rieur, n'a pour l'instant été que faiblement daté. De nouvelles datations biostratigraphiques basées sur des ammonites nouvellement trouvées, ainsi que sur une réévaluation de celles précédemment publiées, permettent de précisé-ment dater cet épisode d'ennoiement de plate-forme. Celui-ci débute dans la zone d'ammonites à Pseudothurmannia seitzi (Hauterivien tardif) et se termine dans la zone à Coronites darsi (dernière zone du Barrémien inférieur). Ces nouvelles datations, couplées avec des interprétations en stratigraphie séquen-tielle, permettent de mieux appréh...

In the uppermost Hauterivian sediments of the western Tethys, a short-lived anoxic event (Faraoni event) is documented both in the form of an interval enriched in organic matter (pelagic realm) and in a condensed interval enriched in glauconite and phosphate (shelf realm). This latter interval represents the onset of a drowning episode on the Helvetic carbonate platform along the northern tethyan margin that lasted throughout the early Barremian. This drowning episode marks a turning point in the way the platform carbonate factory functioned: during the Hauterivian carbonate production was dominated by heterozoans, whereas during the late Barremian a photozoan assemblage developed that is preserved in the so-called Urgonian limestone. The late Hauterivian Faraoni oceanic anoxic event is of particular interest because it is not accompanied by a major positive shift in y 13 C unlike other oceanic anoxic events during the Cretaceous (Valanginian, early Aptian, Cenomanian-Turonian boundary).We have analyzed four (hemi-)pelagic sections with regards to their phosphorus content to better understand the palaeoceanographic conditions related to this anoxic event and the associated changes in the shallow-water carbonate factory. The sections are located in Angles (SE France), Fiume-Bosso and Gorgo a Cerbara (central Italy), and Veveyse de Châtel-St. Denis (west Switzerland). We calculated phosphorus mass accumulation rates by using a cyclostratigraphic approach in order to obtain an adequate age model. We observe a comparable and correlatable long-term trend for the four sections, which suggests that the phosphorus mass accumulation rates and temporal changes therein are representative for the western tethyan pelagic realm. The Faraoni event is marked by a minimum in phosphorus accumulation and a positive shift in the C org /P tot ratios, which is interpreted as a reflection of the decreased capacity of storing and preserving phosphorus in oxygen-depleted sediments. Moreover, the onset in the decrease in phosphorus accumulation coincides with a sea level rise, while the Faraoni level itself corresponds to a maximum flooding interval. This phase of sea-level rise may have been important in the establishment of marine connections between the boreal and tethyan realms and, as such, in the exchange of nutrient-enriched waters. The model for the origin of the Faraoni oceanic anoxic event proposed here incorporates these aspects together with a positive feedback loop generated by phosphorus regeneration and a negative feedback loop related to changes in the ocean oxygen cycle.The subsequent long-term changes in phosphorus burial rates during the Barremian suggest that the Faraoni event marks the onset of a long period of environmental instability with regards to platform growth, leading to periodic phases of eutrophication * Corresponding author. Tel.: +41 32 718 26 05; fax: +41 32 718 26 01.E-mail address: stephane.bodin@unine.ch (S. Bodin).and drowning of the northern tethyan carbonate platform. This environmental cr...

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The Faraoni Level is a short-lived oxygendeficient event that took place during the latest Hauterivian. In order to improve our understanding of the palaeoenvironmental conditions that occurred during this event, we have analysed the contents of several redox-sensitive trace elements (U, V, Mo, As, Co, Cd, Cu, Zn, Ni, Pb, Cr) from bulk limestone samples of late Hauterivian-early Barremian age from three reference sections. U, V, Mo and As show consistent and significant enrichments during the Faraoni event whereas the other redox-sensitive trace elements analysed here are not systematically enriched. In order to explain this discrepant behaviour, we propose that the Faraoni Level was deposited during a period of anoxic conditions near the sediment-water interface. The distinctive peaks in U, V, Mo and As contents are traceable throughout the three studied sections and represent a good correlation tool which helps to identify the Faraoni Level and its equivalents in the western Tethyan realm and outside of the Tethys. For example, a peak in U contents in upper Hauterivian sediments of the northwestern Pacific realm (ODP leg 185, site 1149) may well be an expression of the Faraoni event in this particular basin.

The Chopf Member is a glauconitic, phosphate-bearing succession that occurs in the distal part of the Helvetic Alps (eastern Switzerland). The recent discovery of age-diagnostic ammonites within this horizon allows for its attribution to the lower part of the Gerhardtia sartousiana zone (middle Late Barremian). This new age corresponds to a maximal age for the onset of the Schrattenkalk Fm. in this area, and is coeval with the onset of the Urgonian facies in other parts of the western Tethyan realm. This new age allows also for a more precise dating of Late Barremian δ 13 C curves. RésuméDonnées nouvelles sur la datation de l'installation des calcaires urgoniens le long de la marge nord-téthysienne : biostratigraphie du membre du Chopf (nappes Helvétiques, Suisse orientale). Le membre du Chopf correspond à un horizon glauconieux déposé dans la partie distale de la plate-forme helvétique. La découverte récente d'ammonites permet de dater pré-cisément cet horizon de la partie inférieure de la zone à Gerhardtia sartousiana (Barrémien supérieur moyen). Cette nouvelle datation permet de donner un âge maximal à la formation du Schrattenkalk dans cette région. Cet âge est cohérent avec ceux qui sont obtenus dans les autres parties de la Téthys occidentale pour l'installation des faciès urgoniens. Cette nouvelle datation permet aussi d'apporter des précisions sur la calibration des courbes du δ 13 C du Barrémien supérieur.

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