MAGNETOSTRATIGRAPHY OF THE CALLOVIAN (UPPER MIDDLE JURASSIC) FROM OUTCROPS IN FRANCE, ENGLAND AND GERMANY AND CALIBRATION OF THE PACIFIC M-SEQUENCE OF MAGNETIC ANOMALIES

The application of magnetic stratigraphy as part of an integrated time scale, along with biostratigraphy and other stratigraphic methods, is a powerful tool for high-resolution global correlations. Over 350 oriented core samples collected from Callovian (upper Middle Jurassic) strata across stable Europe have yielded a nearly continuous composite geomagnetic polarity reference sequence. This compilation of sixteen outcrops from (1) the Burgundy carbonate ramp along the eastern Paris Basin, (2) the shallow shelf deposits in southern England and (3) the Swabian Alb in Southern Germany are dated and correlated through the application of ammonite and brachiopod biostratigraphy and sequence stratigraphy. The mean magnetic direction, paleomagnetic pole and paleolatitude of each sample were determined through the application of progressive thermal demagnetization at University of Michigan and at Oxford University. After the removal of secondary magnetic overprints, high-quality samples typically provided stable orientations of their remnant magnetization with decreasing intensity between 240°C and 350°C. The resulting virtual geomagnetic poles indicate that the sites were an average of 16° (σ=7°) further south during the Callovian than their current locations with a small post-Callovian clockwise rotation of approximately 5°. The pattern produced through the correlation of samples across outcrops results in a generally normal-dominated sequence within the Callovian, interrupted by three clusters of short reversed polarity zones. These clusters occur at the Upper Callovian (Quenstedtoceras lambent and Peltoceras athleta zones) continuing into the lowermost Oxfordian, at the top of the Lower Callovian (Sigaloceras calloviense and the uppermost Proplanulites koenigi zones), and at the Callovian-Bathonian boundary (lowermost Macrocephalites herveyi and the underlying Clydoniceras discus zones). This pattern mirrors that found in the pre-M25 magnetic sequence from the Pacific marine magnetic anomaly model. The Callovian-Oxfordian boundary correlates within anomaly M37n (tentatively within M37n.1n) and the Callovian-Bathonian boundary falling within M39n.