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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).

Figure 1. Sets of IODP Standards: (1) IODPSTD01 through IODPSTD12 (for SRM only) and (2) IODPSTD13 through IODPSTD16 (for SRM and JR-6) in a cardboard box stored in the MU container

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)

Sample Name

Text ID

Declination (°)

Inclination (°)

Intensity (A/m) as provided (assumes 1cc)

Recalculated Intensity (A/m) assuming 7cc volume

standard deviation

IODPSTD01

CUBE11242251

217.4

33.9

3.17E-01

4.529E-02

0.9

IODPSTD02

CUBE11242261

134.2

35.5

8.48E-02

1.211E-02

0.8

IODPSTD03

CUBE11242271

143.5

-29.1

9.40E-02

1.343E-02

1.3

IODPSTD04

CUBE11242281

227.5

-22

6.36E-02

9.086E-03

0.1

IODPSTD05

CUBE11242291

18.9

-24.9

9.09E-02

1.299E-02

0.4

IODPSTD06

CUBE11242301

137.6

28.2

4.20E-01

6.00E-01

0.5

IODPSTD07

CUBE11242311

326

34

5.86E-01

8.371E-02

0.7

IODPSTD08

CUBE11242321

221.8

-12.2

7.82E-02

1.117E-02

0.6

IODPSTD09

CUBE11242331

34.7

-28.4

1.13E-01

1.614E-02

1

IODPSTD10

CUBE11242341

316.2

-19.8

6.39E-02

9.129E-03

0.4

IODPSTD11

CUBE11242351

333.3

24.3

9.78E-02

1.40E-02

1

IODPSTD12

CUBE11242361

28.4

40.2

1.96E-01

2.80E-02

0.4

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. 

Figure 2. Coordinate system for the Scripps Standards

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).

Figure 3. Position of the Scripps Standards into the discrete tray


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.

Sample NameText IDDeclination (°)Inclination (°)Intensity (A/m) assuming 7 cc volumeNumber of measurements
IODPSTD01CUBE11242251212.6 ± 0.634.6 ± 2.64.35E-02 ± 0.1414
IODPSTD02CUBE11242261128.5 ± 1.039.3 ± 7.81.23E-02 ± 0.1715
IODPSTD03CUBE11242271137.8 ± 0.9-13.5 ± 11.61.29E-02 ± 0.0315
IODPSTD04CUBE11242281217.8 ± 0.9-13.3 ± 16.98.62E-02 ± 0.0215
IODPSTD05CUBE1124229112.8 ± 0.7-18.5 ± 12.01.18E-02 ± 0.0715
IODPSTD06CUBE11242301136.3 ± 1.129.1 ± 2.15.94E-02 ± 0.1215
IODPSTD07CUBE11242311320.1 ± 0.734.2 ± 1.87.96E-02 ± 0.1415
IODPSTD08CUBE11242321213.9 ± 0.4-4.3 ± 13.51.00E-02 ± 0.0213
IODPSTD09CUBE1124233130.5 ± 0.5-24.9 ± 8.81.48E-02 ± 0.0913
IODPSTD10CUBE11242341312.7 ± 0.4-12.1 ± 16.78.52E-03 ± 0.0113
IODPSTD11CUBE11242351324.7 ± 0.526.0 ± 8.01.42E-02 ± 0.1313
IODPSTD12CUBE1124236121.4 ± 1.543.8 ± 3.62.80E-02 ± 0.1713

Data used to create Table 2 are found here: QAQC SRM discrete 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


JR-6

SRM

Sample Name

TextID

Int (x10-3 A/m)

Stdev (x10-3 A/m)

Geo Dec (°)

Geo Inc (°)

κ

α95 (°)

Intensity (x10-3 A/m)

Inclination (°)

Declination (°) 

IODPSTD13

CUBE11242371

41.41

0.05

309.4

-11.1

1197

0.9

38.2E-3 ± 0.6

-12.7 ± 3.8

301.8 ± 0.2

IODPSTD14

CUBE11242381

47.75

0.06

329.0

-33.0

565

1.4

44.1 ± -1.6

-37.5 ± -2.8

329.4 ± 0.3

IODPSTD15

CUBE11242391

27.43

0.04

263.2

31.5

354

1.8

27.3 ± 1.2

23.8 ± 4.9

261.2 ± 0.3

IODPSTD16

CUBE11242401

14.91

0.03

274.0

34.6

4062

0.5

14.9 ± 1.6

31.4 ± 8.0

268.0 ± 0.3

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.

Figure 4. Measurements Preset Editor for the Discrete WTA preset


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.

Figure 5 Loading Standards into Discrete Tray


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).

Figure 6. Standard loading position for JR-6 automatic sample holder

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.

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