High-resolution cyclostratigraphic analysis of magnetic susceptibility record from a Kimmeridgian alternating marl-limestone succession (La Méouge, Vocontian Basin, France)

• Autorzy: Boulila, S. , Galbrun, B. , Collin, P-Y. , Collin, P-Y. , Schnyder, J.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

The Kimmeridgian deep-water sediments of La Méouge section (South East Basin of France) show alternating marl-limestone successions. The limestone beds are mudstones or wackstones with benthic foraminifera, radiolarians and filaments which are characteristic of the pelagic realm (Colombié & Strasser 2003). We studied a 43 m thick well exposed interval of mainly Early Kimmeridgian (De Rafélis 2000). Cyclostratigraphic studies of marl-limestone alternations are commonly based on measuring the thickness of beds and bundles and counting their number to extract sedimentary cyclicities. By using high resolutions magnetic susceptibility (MS) measurements, we developed a methodology for detecting and quantifing sedimentary cyclicities recorded in this kind of facies. To perform high-resolution MS measurements, the sampling interval was fixed at nearly 7 cm. All the samples were measured with a Kappabridge KLY-2 susceptometer. The MS variations follow a net cyclic pattern (high and low frequencies). Spectral analysis of MS data show evidence of about all range of Milankovitch cyclicities (precession, obliquity, 100 ky and 400 ky-eccentricity) as demonstrated by the frequencies” ratios methodology and tuning technique. For this latter, we tuned MS data to 405 ky-eccentricity of astronomical solutions (Laskar et al. 2004). Moreover, we found highly significant periods of climatic precession not only in the original MS record but also in the tuned MS. Evolutive harmonic analysis (Maurer et al. 2004) was performed to examine the persistence of the Milankovitch properties throughout the whole section and the possible variations of sedimentation rate. Specifically, the two high peaks, seen in power spectra domain representing the short and the long precession, are characterized in amplitude spectrogram domain by obvious continuous lines, particularly the latter. This means that the precession cycles have much larger amplitudes than the other recognized cycles and are persistent too throughout the entire section. Furthermore, we noted that the long precession cycles show a sudden change in sedimentation rate occurring in the lower part of Lothari ammonite Subzone where the sedimentation rate shifted roughly from 2 to 3 cm/ky. This study proved that MS is a very useful tool for cyclostratigraphic analysis of Mesozoic sections, particularly in alternating marl-limestone successions, and it is also a powerful proxy to detect and estimate possible variations in sedimentation rate.

Słowa kluczowe

EN

cyclostratigraphy; magnetic susceptibility; Kimmeridgian; Vocontian Basin; France

• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 149-150
• Opis fizyczny: Bibliogr. 4 poz.

Twórcy

autor

Boulila, S.

autor

Galbrun, B.

autor

Collin, P-Y.

autor

Collin, P-Y.

autor

Schnyder, J.

• Université Pierre et Marie Curie, Laboratoire “CEPAGE” FR CNRS 32, case 117, 4 place Jussieu, 75252 Paris, cedex 05, France,

Bibliografia

• Colombié C. and Strasser A. 2003. Depositional sequences in the Kimmeridgian of the Vocontian Basin (France) controlled by carbonate export from shallow water platforms. Geobios, 36: 675-683.
• De Rafélis Saint-Sauveur M. 2000. Apport de l’étude de la spécification du mangan?se dans les carbonates pélagiques ? la compréhension du contrôle des séquences eustatiques de 3?me ordre. PhD. Thesis, Universite Pierre et Marie Curie, Paris, France, 214 pp.
• Laskar J., Robutel P., Joutel F., Gastineau M., Correia A. C. M. and Levrard B. 2004. A long-term numerical solution for the insolation quantities of the Earth. Astronomy & Astrophysics, 428: 261-285.
• Maurer F., Hinnov L. A. and Schlager W. 2004. Statistical time-series analysis and sedimentological tuning of bedding rhythms in a Triassic basinal succession (Southern Alps, Italy). Cyclostratigraphy: Approaches and Case Histories. SEPM Special Publicatio, 8: 83-99.