Paleomagnetic Standards Measurements

Updated 2/19/20

Paleomagnetic standards were provided by Lisa Tauxe to confirm instrument measurements are correct. The standards were prepared specifically for the SRM although they can be used in the other instruments as well. These standards were prepared and measured at S10 in California. Standards are kept in a cardboard box (figure 1) and stored in the Pmag lab in the smaller MU metal shielding chamber (figure 2).

Figure 1 Paleomagnetic Standards     Figure 2 Standards Location

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. Intensity has been converted to A/m as this is the unit used by IODP instruments. The conversion used was 10^-1 A/m = 10^-3 emu. It is extremely important that these standards do not get demagnetized. Be sure to stress this to anyone who may use the standards.

Table 1 Paleomagnetic Standards Values

Standard Orientation

The Samples are oriented as if they were taken from an archive half. This can be confusing as most of the time, discrete samples would be collected from the working half. Be sure to keep this orientation in mind when loading into the instruments.  See Figure 3 for sample orientation arrows

Figure 3 Cube Orientation for Standards

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 archive half. For sample shape select Discrete J-Cube. Face orientation should be Top and the Arrow Orientation (-Z) should be set to Away. Be sure to select Archive Half under From Section. In Dimensions, set the sample area to 7.0 cm². Although this says sample area and the unit is an area unit, we are telling IMS what the volume of the J-cube is (i.e. 7.0 cm³). Name your measurement preset something useful such as Discrete Archive. More information on setting up a sample preset can be found in the SRM user guide.

Figure 4 Measurements Preset Editor for Archive Half J-Cube

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 up.

Figure 5 Loading Standards into Discrete Tray

In IMS, click start which will bring up the screen shown in Figure 6. Under sample type and orientation, select the measurement preset you set up for archive half discrete cubes. A diagram should appear in the lower left corner depicting how the sample should be oriented in the sample tray. Double check that the orientations match.

Figure 6 Entering Sample Information

This next step is very important!!! In the measurement sequence tab, select a measurement sequence that measures NRM only. Do not select a sequence that demagnetizes the samples first or they will be ruined and worthless. The Current Sequence box at the bottom of the screen should have a sequence such as NRM only.

Use the manual tab to enter the name of the standard cube, click use me, then double click on the tray position this cube is sitting in to assign their positions. Once all standards cubes are assigned to their position, click Measure.

When the measurements are complete, the data will go to the In folder. This data cannot be uploaded with MUT. Move the .dsc files out of the IN folder and save them in: V:\IODP_Share\PMAG_Documents\SRM\Pmag Standards

Open the .dsc file with a text editor. Under the Header <MULTI>, scroll to the far right. You are looking for the values inclination_w_bkgrd_w_drift, declination_w_bkgrd_w_drift, and intensity_w_bkgrd_w_drift. These are your background and drift corrected values that you can compare to the listed values of the standards. Record the values in the laboratory notebook.