Analyse cyclostratigraphique des variations de la susceptibilité magnétique des argilites callovo-oxfordiennes de l' Est du Bassin de Paris (application à la recherche de hiatus sédimentaires)

Une approche cyclostratigraphique a été utilisée pour étudier la série argileuse callovo-oxfordienne de l Est du Bassin de Paris, et plus particulièrement pour y détecter des hiatus sédimentaires. L analyse s est basée sur l étude des fluctuations du gamma ray (GR) et de la susceptibilité magnétique (SM). Leurs évolutions à long terme, similaires à l échelle du bassin, reflètent les variations du niveau marin relatif, et ont été interprétées en terme de cycle transgressif/régressif. L analyse des variations haute fréquence de la SM a démontré le contrôle astro-climatique. La reconnaissance des cycles d excentricité a permis de proposer des estimations de durée minimales, en particulier pour la zone à Mariae estimée à 2.6 +-0.3 Ma. 2 hiatus ont été observés : le premier à la limite Callovien moyen/>, d'une durée minimale de 150 ka. Le deuxième, à la base de l'Oxfordien < dans la zone à Mariae, correspond à la MFS de 2nd ordre et se traduit par une condensation d'une durée de 300 ka.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Magnetic Viscosity for Cyclostratigraphic Logging of Argillaceous Sediment

Magnetic susceptibility (MS) is currently used as a directly representative proxy for the study of climatic variations, and for cyclostratigraphic studies. It depends on the concentration of magnetic minerals in the rocks, but does not allow identifying the magnetic minerals. In the case of argillaceous sediments, the paramagnetism of clay particles often plays a major role in determining the magnitude of their magnetic susceptibility, while the presence of ferrimagnetic iron oxides or sulfides cannot be assessedusing susceptibility measurements alone. Among the different methods that can be used to detect ferrimagnetic particles magnetic viscosity (MV) characterizing the delay corresponding to the acquisition or loss of induced magnetization, has the same advantages as MS. Itsmeasurement is direct, rapid and has been proven to be very efficient in detecting the presence of secondary ferrimagnetic minerals in soils. A MV measurement technique was tested on cores taken from a borehole, in Callovian-Oxfordian formations in the eastern Paris Basin (France) (Fig. 1). Although the MV values are very small, they have cyclic variations of which strongest values are found at the base of the Lower Oxfordian. These values, when correlated to MS,Gamma Ray (GR) and a sequential interpretation of a borehole drilled close-by are found to be associated with the maximum clay fraction in the core samples, a MS maximum, and a major transgression event. Consequently, a significant increase in ferrimagnetic minerals can be associated with this event

Improvement of cyclostratigraphic studies by processing of high-resolution magnetic susceptibility logging: Example of PEP1002 borehole (Bure, Meuse, France)

International audienc

(Appendix 4) Grey level values obtained for ODP Hole 122-762C

International audienceAn integrated framework of magnetostratigraphy, calcareous microfossil bio-events, cyclostratigraphy and δ13C stratigraphy is established for the upper Campanian–Maastrichtian of ODP Hole 762C (Exmouth Plateau, Northwestern Australian margin). Bulk-carbonate δ13C events and nannofossil bio-events have been recorded and plotted against magnetostratigraphy, and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the Maastrichtian. Thirteen carbon-isotope events and 40 nannofossil bio-events are recognized and calibrated with cyclostratigraphy, as well as 14 previously published foraminifer events, thus constituting a solid basis for large-scale correlations. Results show that this site is characterized by a nearly continuous sedimentation from the upper Campanian to the K-Pg boundary, except for a 500 kyr gap in magnetochron C31n. Correlation of the age-calibrated δ13C profile of ODP Hole 762C to the δ13C profile of the Tercis les Bains section, Global Stratotype Section and Point of the Campanian–Maastrichtian boundary (CMB), allowed a precise recognition and dating of this stage boundary at 72.15 ± 0.05 Ma. This accounts for a total duration of 6.15 ± 0.05 Ma for the Maastrichtian stage. Correlation of the boundary level with northwest Germany shows that the CMB as defined at the GSSP is ~ 800 kyr younger than the CMB as defined by Belemnite zonation in the Boreal realm. ODP Hole 762C is the first section to bear at the same time an excellent recovery of sediments throughout the upper Campanian–Maastrichtian, a precise and well-defined magnetostratigraphy, a high-resolution record of carbon isotope events and calcareous plankton biostratigraphy, and a cyclostratigraphic study tied to the La2010a astronomical solution. This section is thus proposed as an excellent reference for the upper Campanian–Maastrichtian in the Indian Ocean