Paleomagnetic Standards Measurements

Introduction

As part of the QAQC Paleomagnetism Standard Operating Procedure, the JR paleomagnetism laboratory uses sixteen standard cube samples. There are two sets of IODP standards that can be measured with either the SRM, the JR-6 or both.

It is extremely important that these standards DO NOT GET DEMAGNETIZED. Be sure to stress this to anyone who may use the standards.

The two sets of standards are kept in a cardboard box and stored in the Pmag lab in the smaller MU metal shielding chamber (Figure 1).

Scripps Institute for Oceanography Standards

Paleomagnetic standards (IODPSTD01 through IODPSTD12) were provided by Lisa Tauxe to confirm instrument measurements are correct. The standards were prepared specifically for the SRM. Do not measure them in the JR-6 spinner. These standards were prepared and measured at Scripps Institute for Oceanography in California.

Table 1 contains the values of the standards as they were measured in California before receipt by IODP. Note that the units of intensity in the provided values was in emu and the volume used was 1cc. Intensity has been converted to A/m as this is the unit used by IODP instruments and the intensity has also been listed if you assume a 7cc volume. The conversion used was 10^-1 A/m = 10^-3 emu.

Table 1 Paleomagnetic Standards Values from Scripps (November 2019)

Standard Orientation

The standard samples made by Scripps are oriented as if they were taken from an archive half. This means that the arrow etched into the cube points in the negative Z (i.e. towards the top of the core) on the ARCHIVE HALF SPLIT FACE (not the working half split face as a cube normally collected onboard would be). This can be confusing as most of the time, discrete samples would be collected from the working half.  The arrow on the orange dot sticker points in the positive X direction of the IODP coordinate system (Figure 2). Be sure to keep this orientation in mind when loading into the instruments. 

Open

The QAQC Text_ID created for IODPSTD01 through IODPSTD12 considers the samples as they were taken from the WORKING HALF. Put the sample upside down in the discrete tray, face X-Y on the bottom with +X arrow down and -Z arrow of the cube away from the SRM (Figure 3).

The Scripps Standards were measured with the SRM onboard the JR. Values are in the same range as the initial measurements conducted at Scripps. Samples with negative inclination in red in Table 2 show the largest variations, although they were measured with a sequence of 10 consecutive NRMs without removing the sample from the tray.

Table 2. IODP Standards created by Scripps measured with the SRM onboard the JR. Declination, inclination and intensity are corrected from background and drift (as of November 1, 2022). Volume is 7 cc.

Data used to create Table 2 are found here: QAQC SRM November 2022.xlsx

IODP created Standards

Because the standards provided by Lisa Tauxe at Scripps were not designed to be used in the JR-6, four new standards were created which can be used in the JR-6. A strip of magnetic tape was glued to a stick which is secured inside a J-cube. The standards were then given an IRM and measured in the JR-6 followed by the SRM. These standards are oriented as if they were collected from a working half with an assumed volume of 7cc . Each standard was measured 20 times with the JR-6. The process included inserting and removing the standard between each measurement. The mean intensity was calculated as well as Fischer stats for inclination and declination. The standards were also measured 10 times with the SRM. See Table 3 below.

Table 3. IODP standards, IODPSTD13 through IODPSTD16, measurements in JR-6 compared to measurements obtained with the SRM

Note: SRM data shown in Table 3 were measured on November 1, 2022.

Measuring in the SRM 

When measuring the standards in the SRM, install the discrete sample tray and set up your measurement preset to reflect a discrete J-Cube collected from the working half. This preset should appear in the list as "Discrete WTA". This means that the sample shape is Discrete J-Cube, the face orientation should be Top and the Arrow Orientation (-Z) should be set to Away (Figure 4). Be sure to select Working Half because the Text_ID of the standard samples are assigned to a working half. More information on setting up a sample preset can be found in the SRM User Guide.

Run a discrete tray background then load the standards into the discrete sample tray as shown in Figure 5. As with typical discrete measurements, load the first standard into the 13 cm offset position and leave a blank position between each standard cube (i.e. load standards into positions 13 cm, 33 cm, 53 cm…). The standard cube should be oriented so that the –Z arrow is pointing away from the SRM and the +X arrow is pointing down.

For more details on the sample position and the measurement with the SRM, please refer to QAQC Paleomagnetism Standard Operating Procedure.

When the measurements are complete, the data will go to the In folder and can then be uploaded to LORE with MUT2. See QAQC Paleomagnetism Standard Operating Procedure for details.

Measuring in the JR6

Do not measure the standards created at Scripps (IODPSTD01 through IODPSTD12) in the JR-6. Load the standard into the automatic sample holder with the up arrow that is etched into the cube body facing up and to the left, as shown in Figure 6. Be sure that sample type is set to cube in instrument configurations. Use a volume of 7cc. Use 0 for the azimuth and 90 for the dip. With these settings, you will look at the geographic inclination and declination (not specimen coordinates).

Viewing the Data 

All of the standards have been given a LIMS Text_ID so they can be scanned and the data uploaded to the database. The data can be viewed in LORE by selecting QAQC in the Expedition drop down menu, CORELAB as site, MAGNETICS for hole.

QAQC data can be seen with QCViewer for a quick assessment of the good quality of the data. Data can be downloaded with the "Measurements on Standards" web application.

See QAQC Paleomagnetism Standard Operating Procedure for details on viewing the data with QCViewer.

Archived Versions

• PaleomagneticStandards_X397T_SEP2022

• PaleomagneticStandards_exp378.pdf: PDF version of this wiki page as of 2020-02-24