Paleoceanographic changes during the early Cretaceous (Valanginian–Hauterivian): evidence from oxygen and carbon stable isotopes

https://doi.org/10.1016/S0012-821X(00)00194-1Get rights and content

Abstract

We investigated Valanginian–Hauterivian bulk rock and belemnite samples from Vocontian Basin sections in southeastern France for their stable carbon and oxygen isotope signature. Firstly, because these sections permit calibration with high-resolution biostratigraphy based on ammonites and secondly because detailed isotope studies for the Hauterivian are lacking. The results show that δ13C values for bulk rock decrease during the late Valanginian–early Hauterivian with 1‰ and increase again during the late Hauterivian with 1‰. The δ18O signal for bulk rock samples is mostly disturbed by diagenesis. The belemnites show carbon and oxygen isotope values that are lower and higher than bulk rock samples respectively. We explain this as the result of the belemnites recording a deeper water signal with lighter δ13C values and heavier δ18O values, implicating colder water at greater depth. The overall preservation of the belemnites is very good and permits the construction of a paleo-temperature trend. This trend shows warm deeper water temperatures during the late early Valanginian (15°C) and progressively cooler temperatures during the late Valanginian and early Hauterivian (11°C). During the late Hauterivian temperatures increase again (13°C). We relate this cooling trend for deeper water to a second order sea level rise, which allowed for the exchange of cold Boreal and warm Tethyan water masses. The influx of cold nutrient rich water had a profound effect on carbonate producing biota along the northern margin of the Tethys during the Hauterivian leading to prolonged phases of condensation and platform destruction. During the early Hauterivian the carbonate system along the northern Tethyan margin shifted into a ‘green water’ mode of carbonate production. High rates of carbonate production under mesotrophic conditions, also observed in other parts of the world, meant that the global carbon cycle became buffered shown by the stable trends in carbon isotopes.

Introduction

During the late Jurassic and early Cretaceous, a carbonate platform of considerable extent developed along the northern Tethyan margin [1], [2]. The evolution of this platform system was punctuated by several phases of platform drowning, most notably during the late early Valanginian to early Hauterivian, and the Aptian. Within the sections preserved in the Helvetic Zone of the northern Alps, the drowning phases are documented by erosional surfaces, hiati, and condensed glauconitic and phosphatic beds, which have been described in numerous publications [1], [2], [3], [4], [5], [6], [7], [8], [9].

The large drowning unconformities formed during the late early Valanginian to early Hauterivian (D1 in [2]), the late early to early late Aptian (D4), and latestmost Aptian to earlymost Albian (D5) correspond in time to major positive excursions in the stable carbon isotope record [10], [11]. This correlation was used to propose a model for the development of the drowning unconformities, which includes major changes in the global carbon budget. In this model, the formation of the large flood basalt provinces at Paraña, Kerguelen, and especially Ontong Java is inferred to have led to major increases in atmospheric CO2 during the Valanginian and Aptian, thereby triggering a row of negative feedback mechanisms, which led to a decrease in atmospheric CO2 contents. These mechanisms include increases in rates of continental biogeochemical weathering, mobilization of nutrients and especially phosphorus, productivity and sedimentary burial of organic matter, whereas the rates of carbonate production were decreased leading to phases of widespread platform drowning and phosphogenesis [2], [11].

Since the publication of this model, new age models have been developed for several key areas and further detailed studies have been accomplished in the area of platform deposition [8], [12]. During these studies, the following subjects were shown to be critical and in need of further elaboration:

Section snippets

Correlation between the Helvetic realm and other regions

Whereas the drowning unconformities are well expressed in the Helvetic realm, they are less well traceable in more proximal areas, such as the Jura Mountains in western Switzerland and eastern France, and more distal areas, such as the Vocontian Trough. This is due to the prevalence of erosional processes during the drowning phases in the proximal areas and to the deposition of more complete, hemipelagic sections in the distal areas, beyond the platform margin (e.g., [1], [8]). Correlation of

The Hauterivian

The sections from which we sampled material for stable carbon and oxygen isotope analyses are exposed in southeastern France, in the region near Digne-les-Bains (Alpes de Haute Provence) and Nyons (Drôme, Fig. 1C). The sediments sampled for this stable isotope study were deposited along the western margin of the Tethys in a narrow inlet, known as the Vocontian Basin (Fig. 1A,B).

The lithology consists of alternations of hemipelagic calcareous marlstones and micritic limestones. In addition to

Methods

Stable carbon and oxygen isotope analyses were performed on bulk rock samples from the limestone intervals and on belemnites mostly from the marly intervals for all four sections. The whole rock samples were taken from fresh outcrops; powder was drilled out of the micritic matrix, avoiding bioturbation fabrics. The belemnites were cleaned in 1% HCl and cut along the alveolic line if their size allowed for this. Powder was drilled avoiding the outside laminae and the alveolus, because it has

Carbon and oxygen stable isotopes

The data obtained by Hennig et al. [12] for the Vocontian Basin show that the Valanginian positive carbon isotope excursion commences in the Campylotoxus Zone, and reaches its maximum in the earliest late Valanginian (Verrucosum Zone, +2.5‰). During the late Valanginian δ13C values gradually decrease. Our study indicates that δ13C values derived from bulk rock material decrease further to reach a minimum at the early-late Hauterivian boundary (Nodosoplicatum Zone, +0.59‰), after which they

Conclusions

It seems that every phase of platform drowning has to be viewed in the light of its own set of paleo-environmental controls. The model established for the Valanginian and Aptian platform drowning events [2], [11] does not necessarily apply to the Hauterivian and Albian. The early Valanginian carbonate platforms suffered from widespread regression and the shedding of siliciclastics onto the shelf. Organic carbon was stored in coastal and continental settings. The transgression that followed

Acknowledgements

We are greatly indebted to Thierry Adatte for fruitful discussion and improvement of the manuscript. We also would like to thank Sebastian Ryser of the University of Neuchâtel for performing the AAS analyses. Jan Veizer and Gregory Price are thanked for reviewing this paper and for making useful comments.[AH]

References (47)

  • A. Heim, O. Seitz, Die mittlere Kreide in den Helvetischen Alpen von Rheintal und Vorarlberg und das Problem der...
  • K.B. Föllmi et al.

    Garschella-Formation und Goetzis-Schichten (Aptian–Coniacian); neue stratigraphische Daten aus dem Helvetikum der Ostschweiz und der Vorarlbergs

    Eclogae Geol. Helvet.

    (1987)
  • K.B. Föllmi, Die Garschella- und Seewerkalk-Formation (Aptian–Santonian) im Vorarlberger Helvetikum und...
  • P. Haldimann, Sedimentologische Entwicklung der Schichten an einer Zyklengrenze der Helvetischen Unterkreide, in:...
  • O. Kuhn, Der Einfluss von Verwitterung auf die Paläozeanographie zu Beginn des Kreide-Treibhausklimas (Valanginian und...
  • G.W. Wyssling

    Der frühkretazische helvetische Schelf im Vorarlberg und Allgäu

    Jahrb. Geol. Bundesanst. Vienna

    (1986)
  • A. Lini et al.

    The Valanginian carbon isotope event; a first episode of greenhouse climate conditions during the Cretaceous

    Terra Nova

    (1992)
  • S. Hennig et al.

    C-Isotope stratigraphy, a calibration tool between ammonite- and magnetostratigraphy: the Valanginian–Hauterivian transition

    Geolog. Carpath.

    (1999)
  • L.G. Bulot et al.

    Le cadre stratigraphique du Valanginien superieur et de l’Hauterivien du Sud-Est de la France; definition des biochronozones et caracterisation de nouveaux biohorizons

    Geol. Alp.

    (1992)
  • G. Saelen

    Diagenesis and construction of the belemnite rostrum

    Palaeontology

    (1989)
  • G. Saelen et al.

    Chemical signatures of belemnites

    Neues Jahrb. Geol. Palaeontol. Abh.

    (1989)
  • H.C. Jenkyns et al.

    Carbon- and oxygen-isotope stratigraphy of the English Chalk and Italian Scaglia and its palaeoclimatic significance

    Geol. Mag.

    (1994)
  • J.A. Haggerty, J.E. van Hinte, S.W. Wise, Jr., B.N.M. Biart, J.M. Covington, D.A. Dunn, et al., Petrology and carbon...
  • Cited by (138)

    View all citing articles on Scopus
    View full text