The SushiBar: An automated system for paleomagnetic investigations

Abstract

[1] We present a new, automated system based on a three-axis superconducting magnetometer and a custom-made coil designed to experiment on cylindrical specimens used in typical paleomagnetic investigations. The system, which resembles a sushi bar, facilitates stepwise alternating field demagnetization of up to 99 samples per loaded track. It also enables researchers to explore magnetic properties using an anhysteretic remanent magnetization (ARM) in any coercivity window up to peak alternating fields of 95 mT with direct current bias fields up to 0.17 mT. For example, partial ARM (pARM) spectra characterize magnetic grain size distributions in rocks, yet rarely are pARM spectra measured because the complete curve for one sample takes at least two hours to acquire manually. The SushiBar achieves 99 such curves in slightly less than 100 hours. Using the SushiBar, we measured the pARM sprectra, as well as the viscosity and anisotropy of ARM in three discrete switching field windows, of continental sediments from the Xishuigou section (western China). The average grain size remains constant along the 2200 m-thick section, yet magnetic viscosity varies systematically from bottom to top of the section; samples with high magnetic viscosities also have higher proportions of non-viscous material on average. Principal anisotropy axis directions from the lowest switching fields correlate well with principal axis directions from anisotropy of magnetic susceptibility. Principal axis directions defined at higher switching fields systematically deviate from those at lower switching fields, perhaps defining the fabric of the remanence-carrying grains.

Magnetotaxis and acquisition of detrital remanent magnetization by magnetotactic bacteria in natural sediment: First experimental results and theory

“…High‐resolution first‐order reversal curves (FORC) have been measured with 0.5 mT field increments using a Princeton MicroMag vibrating sample magnetometer at the Institute for Rock Magnetism (University of Minnesota, USA) and processed with the VARIFORC software of Egli []. Detailed AF demagnetization curves of anhysteretic remanent magnetization (ARM) acquired in 0.1 mT DC field and 90 mT peak AF field, and of isothermal remanent magnetization (IRM) acquired in a 0.2 T field produced by an electromagnet, have been measured with a vertical 2G cryogenic magnetometer equipped with an automatic sample handling and AF demagnetization system [ Wack and Gilder , ]. Coercivity analysis was performed on AF demagnetization curves according to procedures described in Egli [].…”

Automated paleomagnetic and rock magnetic data acquisition with an in-line horizontal “2G” system

“…Stepwise progressive demagnetization of natural or laboratory‐induced remanent magnetizations typically involve a substantial number of demagnetization steps, either by alternating fields of increasing strength, or by heating to increasingly elevated temperatures in dedicated field‐free furnaces. To reduce operator time and minimize handling differences between samples, several systems have recently been implemented that reach a variable level of automation [e.g., Frederichs et al ., ; Kirschvink et al ., ; Morris et al ., ; Wack and Gilder , ]. Here we report on two systems, based on a common software platform, that allow the fully automated processing of up to 96 samples attached to a horizontal “2G” SQUID magnetometer with in‐line alternating field (AF) demagnetization, acquisition of anhysteretic remanent magnetization (ARM) up to 150 (300) mT and acquisition of isothermal remanent magnetization (IRM) up to 700 mT.…”

Paleomagnetism of the Jurassic Transantarctic Mountains revisited — Evidence for large dispersion of apparent polar wander within less than 3 Myr

“…After cutting into standard~10 cc paleomagnetic cylinders, pilot samples were demagnetized both in alternating fields (AF) and by stepwise heating (TH) and subsequently measured using 2G Enterprises cryogenic SQUID magnetometers housed in a magnetically shielded room. AF demagnetization was carried out using the home-made automated system at the University of Munich (Wack & Gilder, 2012) with peak fields of 90 mT. Demagnetization results were plotted on orthogonal vector diagrams (Zijderveld, 1967) and analyzed using the least square method (Kirschvink, 1980) on linear portions of the demagnetization paths defined by at least four consecutive demagnetization steps.…”