Analysis of the early Jurassic geomagnetic data recorded at the Breggia Gorge (Ticino, Switzerland)

• Published in: Physics of the earth and planetary interiors Vol. 125; no. 1; pp. 19 - 29
• Main Authors: Vizán, Haroldo, Andrea Van Zele, Marı́a
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2001
• Subjects: Alps; Early Jurassic; Geomagnetism; Polarity reversals; Switzerland; Geomagnetism; Alps; Polarity reversals; Early Jurassic; Switzerland
• ISSN: 0031-9201; 1872-7395
• DOI: 10.1016/S0031-9201(01)00207-2

Geomagnetic directions recorded in a lower Jurassic stratigraphic sequence that outcrops at the Breggia Gorge are analyzed. A new method to identify directions suitable for calculating a time-averaged dipolar geomagnetic direction has been applied to calculate a hypothetical early Jurassic geocentric axial dipole. The data were separated to identify normal/reverse directions, corresponding to periods of stable field, and intermediate directions. From an analysis of the data in the palaeogeographic coordinates of the Breggia Gorge at the time of the acquisition of the remanence, it is suggested that polarity transitions in the early Jurassic behaved in a similar manner to that described for late Cenozoic reversals, with the VGPs preferentially following longitudinal paths. The preferred paths coincide with a time-averaged location of the Jurassic subduction area of Pangea. This agreement could indicate a connection between the geometry of the reversals and the subduction zones. An analysis to test whether both
N/
R and intermediate directions have similar preferred distributions suggests that the underlying structure of the early Jurassic geomagnetic field was similar to that observed for the late Cenozoic. The dispersion of directions with inclinations around 0° is higher than those belonging to
N/
R polarity directions, suggesting that there was an enhancement of fluctuations of the geomagnetic field during intermediate states in the early Jurassic.