Pseudopaleosecular variation due to remanence anisotropy in a pyroclastic flow succession

Abstract

In order to check the reliability of a paleosecular variation record in a sequence of pyroclastic rocks (Miocene, Sardinia), we measured various types of anisotropy: magnetic susceptibility (AMS), anhysteretic remanent magnetization (AARM) and thermoremanent magnetization (ATRM). The main magnetic carrier is pseudo-single domain titanomagnetite. No general relation appears between the degrees of AMS and AARM, while the degrees of AARM and ATRM are almost identical. Measuring the AARM thus provides a fast and reliable method to correct paleomagnetic deviation in volcanic rocks. Once corrected for anisotropy deviation the apparent scatter of the paleomagnetic directions, mostly on inclination, is drastically reduced.