Oxiordian magnetostratigraphy of the Aguilón and Tosos sections (Iberian Range, Spain) and evidence of a pre-Oligocene overprint

A composite magnetic polarity sequence has been constructed for the middle and late Oxfordian (late Jurassic) from four overlapping sections situated in both limbs of an anticline. Two stable magnetisation components could be isolated in every sample analyzed. Both components pass the fold test: a low-temperature secondary component, with Dec. = 340.9°and Inc. = 44.9° (a 95 = 1.70), of pre-Oligocene age, showing always normal polarity, and a high-temperature primary component, with Dec. = 324.1°and Inc. = 40.6°(a95 = 2.9°).The latter shows both normal and reversed polarities and provides the geomagnetic record for the late Jurassic. The magnetostratigraphy of the four overlapping sections has given consistent results and indicates that a high frequency of reversals characterises the pattern of the geomagnetic field during the middle to upper Oxfordian. The corresponding Oxfordian paleopole is slat = 251.2°,P1ong = 55•90 (a95 = 3.1)