Determining Magnetic Field Intensity and Direction From the Anisotropy of Magnetic Remanence in Sediments

Anisotropy of magnetic remanence (AMR) holds promise for quantifying relative paleointensity values from sedimentary rocks. A proof of concept was established for applied fields that exceeded the intensity of the geomagnetic field. Under Earth‐like fields, large uncertainties necessitate the development of a new approach to improve the estimation of the anisotropy tensor. To this aim, we designed a numeral method that demonstrated the applicability and resolution needed to optimize the experimental protocol. Following this, we implemented a 30‐position procedure for AMR measurements and compared the numerical and experimental data with a typically used, 12‐position procedure. Redeposition experiments with sediments rich in single domain magnetite were carried out in fields with intensities of 0, 10, 50 and 100 μT; 25 individual samples were redeposited and measured at each field condition. The 30‐position protocol better facilitates the isolation and resolution of the field‐aligned prolate fabric (<3% of the total) from the oblate sedimentary fabric, and more so when applying tensor subtraction of the fabric obtained in a null field. Together with the high‐resolution protocol and tensor subtraction method, we demonstrate that an anisotropy‐based paleointensity deviates <10% relative to classical remanence based relative paleointensity in Earth‐like fields ranging from 10 to 100 μT. Using a synthetic subtraction method, we show that remanence‐based anisotropy precisely tracks the paleofield direction in rocks hosting detrital remanences, which is important when viscous or isothermal overprinting dominates the paleomagnetic vector.