The upper and lower Thvera sedimentary geomagnetic reversal records from southern Sicily

Abstract

Detailed paleomagnetic records of the upper and lower Thvera polarity transitions have been determined from Pliocenc marine marls in southern Sicily. The dominant magnetic mineral is fine grained magnetite. The two transitions have VGP paths following a great circle passing South America and the west coast of North America. There are strong indications that the VGP paths result from smoothing of the non-antipodal stable directions before and after the transitions. The upper Thvera transitional record is preceded by two excursions and followed by a third one. The first excursion is a sedimentary artefact caused by post-depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment. The upper Thvera transition from Sicily is compared with the record from Calabria, about 250 km away. The two records show similarities as well as differences: both transitions have identical VGP paths, but in Calabria the transition is recorded lower in the sediment, the first and third excursions have different characters and the second one is not present. Apparently the registration of transitions of the Earth's magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition.