Abstract
This work proposes the application of magnetic surveying to the study of cyclicity in sedimentary basins. This application is favoured by the particular bed attitude/topography relationships found in the eastern sector of the Cretaceous Cameros Basin, N Spain. Both the measured total magnetic field (after diurnal correction) and the vertical magnetic gradient, provide a profile (14 cm separation between measurements, in average) of the short-wavelength magnetic anomalies associated with the sedimentary sequence. These anomalies depend on the magnetic susceptibility (dominant for low Koenigsberger ratios, a common scenario in sedimentary rocks), and the magnetic remanence (whose orientation is fairly constant in remagnetised basins) of the different sedimentary units. The comparison with direct measurements of magnetic susceptibility (in the field and in the laboratory) provided a successful double-check. The cyclostratigraphic analysis of magnetic profiles of this 6 km-thick series indicates the existence of cycles of 405 kyr (long eccentricity) and 100–125 kyr (short eccentricity), as well as other lower and higher frequency cycles. Cycles with similar, but slightly different, periodicities are the result of different sedimentation rates (mean of ∼0.2 mm/yr, with values ranging between ∼0.1 and ∼0.36 mm/yr). These results provide and indirect method for dating the basin fill, between the Tithonian–Berriasian boundary and the basalmost Albian (∼143.2–∼112.6 Ma), and impose new constraints for basin evolution. The results obtained open a promising field for quick and reliable determination of magnetic properties and cyclicity in thick sedimentary sequences.
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