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Geological Society, London, Special Publications; 1995; v. 85; p. 143-164;
DOI: 10.1144/GSL.SP.1995.085.01.09
© 1995 Geological Society of London

Periodicities of carbonate cycles in the Valanginian of the Vocontian Trough: a strong obliquity control

F. Giraud1, L. Beaufort2 & P. Cotillon1

1 Centre des Sciences de la Terre, Université de Lyon, 27-43 Boulevard du 11 Novembre 69622 Villeurbanne Cedex, France
2 Laboratoire de Géologie du Quaternaire, CNRS Luminy case 907, 13288 Marseille Cedex 09, France

A high-resolution study of variations in carbonate productivity, quantified by CaCO3 content and by colour intensity (grey level) for a Valanginian rhythmic succession is presented in the Vocontian Trough. Spectral analysis techniques reveal the presence of strong CaCO3 cycles linked to cyclic variations in the Earth’s orbit. The results of the analysis suggest that obliquity cycle is the most clearly defined signal whereas the presence of CaCO3 cycles related to the precession signal is less distinct.

The transition from limestone-dominant alternations in the lower Valanginian to marl-dominant alternations in the upper Valanginian is characterized both by an increase of sedimentation rate and a change from the precession as the dominant forcing in the lower, calcareous part of the Valanginian, to obliquity as the dominant forcing for the upper marly part of the Valanginian.

An orbitally calibrated chronology is presented for the Valanginian based on the identification of the carbonate cycles. The application of band-pass filterings to the original carbonate record allows the extraction of 91 carbonate cycles related to precession and 137 cycles related to obliquity. The proposed duration for the Valanginian stage is 7.04 Ma.