Examensarbete vid Institutionen för geovetenskaper
Degree Project at the Department of Earth Sciences

ISSN 1650-6553 Nr 482

Anisotropy of Magnetic Susceptibility
and Remanent Magnetization Studies
in Sediments from the Ångermanälven
River Estuary (IODP Expedition 347,
Site M0061)
Studier av magnetisk anisotropi och remanens
i sediment från Ångermanälvens flodmynning(IODP Expedition 347, plats M0061)

Erneszt Samudovszky

INS TI TU TI ONE N F Ö R
GE O VE TE NS K A PE R
DEPARTMENT OF EARTH SCIENCES

Examensarbete vid Institutionen för geovetenskaper
Degree Project at the Department of Earth Sciences

ISSN 1650-6553 Nr 482

Anisotropy of Magnetic Susceptibility
and Remanent Magnetization Studies
in Sediments from the Ångermanälven
River Estuary (IODP Expedition 347,
Site M0061)
Studier av magnetisk anisotropi och remanens
i sediment från Ångermanälvens flodmynning(IODP Expedition 347, plats M0061)

Erneszt Samudovszky

ISSN 1650-6553
Copyright © Erneszt Samudovszky
Published at Department of Earth Sciences, Uppsala University (www.geo.uu.se), Uppsala, 2020

Abstract
This study presents the results of the magnetic properties of a sediment core from the Ångermanälven
River estuary (IODP site M0061). 37 samples were taken from the archived half of a 1 m long coresegment. The anisotropy of magnetic susceptibility (AMS) and the natural remanent magnetization(NRM) for the core material were measured. Alternating field (AF) demagnetization with fields
ranging from 5 to 80mT was used to demagnetize the samples and principal component analysis(PCA) applied to obtain the best-fit palaeomagnetic vectors.
For AMS the following results were observed: 1. A stereographic projection showing the principal
axes of susceptibility k max ≥k int ≥k min . It can be seen that k min plots along in the vertical axis, kint ismostly horizontally oriented with a tendency towards the west-east axis, kmax is oriented mainly
horizontally, along a north-south axis. The mean magnetic susceptibility K m ranges from 70 to 140[×10-6 SI]. The degree of anisotropy P j in general decreases as a function of increasing meansusceptibility, K m = ([k max + kint + k min ]/3). K m increases as a function of depth, although P j tends todecrease. The shape of the susceptibility ellipsoid, determined using the shape parameter T, isdominantly oblate. The shape parameter T did not change significantly as a function of depth.
Results for NRM and AF demagnetization are summarized as follows: (1) NRM ranges from around 1
to 25 mA/m; (2) AF demagnetization reveals that there is generally a single stable characteristic
remanent magnetization (ChRM) for all samples and (3) palaeomagnetic parameters change as afunction of depth as follows: (i) NRM intensity increases from the top to the bottom, whereas at thevery bottom part it drops almost to the top-most point in the section; (ii) inclination decreases slightly
with depth, (iii) maximum angular deviation (MAD) is relatively small (≤5°) in the uppermost part ofthe section and consistent with the depth, but in the deepest part it increases slightly (~10°) and (iv)the median destructive field (MDF) remains rather constant throughout the section, but is significantly
smaller at the bottom of the section.
Overall, comparing the current study results with the previous results collected from the working halfof the same core segment, magnetic properties have changed as a function of time. AMS parameters(K m , P j , T) from yearly comparisons show that the results for the current study (conducted in 2019)are placed somewhat in between previous measurements (performed from 2015 to 2017). NRM andpalaeomagnetic properties parameters (NRM intensity, Inclination and MDF) tend to follow the trendof the previous results, except at the deepest part of the core where all of them decrease noticeably.
Change in AMS and the decrease in intensity of the NRM most likely reflect the process of oxidationof the ferromagnetic iron sulphide, greigite. Such information when applied to magnetism in
sediments provide a deeper understanding of magnetic material history and be the study of the ancientmagnetic field in oceanic and lacustrine sediments.

KEYWORDS: Sediment, magnetic properties, anisotropy, magnetic susceptibility, remanent
magnetization

Degree Project D in Geophysics, 1GE038, 15 credits
Supervisor: Bjarne Almqvist
Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala(www.geo.uu.se)
ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, № 482, 2020

Populärvetenskaplig sammanfattning (svenska)
Denna studie handlar om magnetiska egenskaper i en sedimentkärna från Ångermanälven(IODP-plats
M0061). Anisotropin av magnetisk susceptibilitet (AMS) och den naturliga restmagnetiseringen(NRM) för kärnmaterialet mättes. Alternerande fältdemagnetisering med fält som sträckte sig från 5till 80 mT användes för att avmagnetisera proverna och PCA (principalkomponentanalys) tillämpas för
att erhålla paleomagnetiska vektorer.
För AMS uppnåddes följande resultat: 1. En stereografisk projektion som visar de huvudsakliga
axlarna för susceptilitet k max , k int och k min . Det kan ses som att k min är liggerlängs envertikal gaxel, k int
är för det mesta i öst-västerriktad i det horizontella planet, och k max ligger längs ennord-syd-riktning i
det horizontella planet. Medelvärdet för susceptibilitet (K m ) ligger i intervallet 70-140 [×10-6 SI],
graden av magnetisk anisotropi (P j ) i allmänhet minskar som en funktion av enökning iK m . Med
djupet i kärnanökar K m , medans P j minskar. Formen på susceptibilitetsellipsoiden(T) är till största deloblat. 2. Formparametern T förändrades inte noterbart som en funktion av djupet.
Resultat för NRM- och AF-demagnetisering har gett följande resultat: 1. NRM intensiteten sträcker sigfrån cirka 1 till 25 mA/m. 2. AF-avmagnetisering avslöjar att det finns en stabil karakteristisk
restmagnetisering (ChRM). 3. Palaomagnetiska parametrar ändras som en funktion av djupet enligt
följande: i) NRM-intensiteten ökar från toppen motbotten av kärnsektionen. I den djupaste delen av
kärnsektionensjunker

intensiteten

nästantillutgångspunkten(toppenav

kärnan);i)

Inklinationenminskar något med djupet, iii) maximal vinkelavvikelse (MAD) minskar med djupettillsdet förblir nära konstant i djupare delar av kärnan (≤5°), för att slutligen öka något i botten av
kärnan (~10°), iv) Medianen av det avdemagnetiserande alternerande fältet (MDF) är relativt konstanti kärnmaterialet, men något lägre i den djupaste delen av kärnmaterialet.
Sammantaget när resultat från denna studie jämförs med de tidigare resultat som samlats in frånsamma kärna (representerande denmotsatta hälften), visar tydligt att de magnetiska egenskaperna
förändras som en funktion av tid. AMS-parametrar (K m , P j , T) från årlig jämförelse visar att resultaten
för denna studie (genomförd 2019) placeras någonstans emellan de tidigare mätningarna (utförda från2015 till 2017). Parametrarna för NRM och de palaeomagnetiska egenskaper (NRM-intensitet,
inklinationoch MDF) tenderar att följa trenden från den tidigare studien, förutom vid den djupastedelen av kärnan där alla ärbetydligt lägre än genomsnittet.

Table of content

1. Introduction ....................................................................................................................................1
2. Study area and samples ..................................................................................................................1
2.1 Sample preparation ...................................................................................................................3
3. Methodology ..................................................................................................................................4
3.1 AMS (Anisotropy of magnetic susceptibility)..............................................................................4
3.2 Natural Remanent Magnetization (NRM) ..................................................................................6
4. Devices ...........................................................................................................................................7
5. Results ............................................................................................................................................9
5.1 AMS results ..............................................................................................................................9
5.2 NRM and alternating field demagnetization results ................................................................. 11
6. Discussion ..................................................................................................................................... 15
6.1 AMS ........................................................................................................................................ 15
6.2 NRM and AF demagnetization ................................................................................................. 19
7. Conclusions ................................................................................................................................... 20
8. Acknowledgements....................................................................................................................... 21
9. References .................................................................................................................................... 21
10. Appendices ................................................................................................................................. 221. Introduction
This thesis demonstrates the importance of understanding the origin of the magnetic properties ofsediments. Such properties depend on the magnetic minerals, which can vary with origin area,
depositional setting and sediment type (Dekkers, 1978). One of the biggest purposes ofpalaeomagnetism is to reconstruct ancient geomagnetic fields. Continuous records of palaeomagnetic
measurements of sediments, are very valuable when investigating the ancient field behaviour.
Anisotropy of magnetic susceptibility (AMS) data have applications in determining such varied
parameters as palaeocurrent directions, directions of magma injection and tectonic strain. It is also a
useful method for correcting palaeomagnetic vectors (including intensity) for bias owing to anisotropic
remanence acquisition (Tauxe, 2019).
This thesis studied AMS and remanent magnetization of the Ångermanälven estuary sediments andobtained deeper understanding of their magnetic properties. The key conclusion from this study is thatmagnetic properties of these sediments change during laboratory storage, which is likely to havesignificant consequences for palaeomagnetism of these and similar types of sediments.

2. Study area and samples
The geographical location of the core section that was used in this study is in the Ångermanälven
River estuary, which is located near the western coast of the Bothnian Sea sector of the Baltic Sea(Snowball et al., 2019). A map of the study area and sampling locations is shown in Figure1. The river
stretches in length geographically for approximately 300 km, from the Swedish mountain range(Scandes) and exits into the Baltic Sea. The coastal zone has a mean annual temperature of
approximately 4 °C, and the annual rainfall at the estuarine site M0062 is 500–700 mm/year (1961–
2014, SMHI open access data). Pine and birch forests cover large areas in the surrounding area of theÅngermanälven River. The sediment core (Ref3) used for this project was taken from the Site M0061
in 2015 on board SV Ocean Surveyor using 6 m long Kullenberg piston corer. Its location can befound in Figure 1. The sampled core material was divided into two halves, one was investigated inprevious studies and the other one had been stored until May 2019, which served as the sample
material investigated in this thesis. The lithology log summary is presented in Figure 2 (Andren et al.,2013). The depth of the hole reaches almost 30 m, but the depth range for the core section used in thisstudy is from 4.88 m to 5.88 m. The graphic lithology of the site is illustrated in Figure 2.

1

Figure 1. Study location map that shows the location of the IODP sites M0061 and M0062 (redrawn from
Snowball et al., 2019). The drill sites M0061 and M0062 along the Ångermanälven River estuary are shown in
the inset figure on the right-hand side. The core used in this study was Ref3.

Figure 2. Graphic lithology log summary, Site M0061 (Andren et al., 2013), where the Ref3 sediment core wastaken from2

2.1 Sample preparation
The sediment core half used for this study was kept in a plastic liner of approximately 1 meter length(488-588 cm river floor depth) in the cool storage since it was cored in 2015. Cubic plastic boxes (7cm3 of internal volume) were used for extracting and subsequently measuring the material. The
sampling procedure is divided into 3 main steps:
1. Plastic cubes preparation.
In order to place the sediment in the cubic boxes and avoid air trapping inside, holes were made on
one side of each cube (circa 1 mm diameter). The holes were drilled with a standard benchtop drillpress and cleaned afterwards.

2. Placing the material in the boxes
Cubes without lids were placed directly in the core (middle part of the core liner) and carefullypressed into the sediment until the cubes were filled. Afterwards they were taken out with a
special tool that allowed to cut the sediment at the bottom in order to release the cubic box andallow minimal disturbance of the sediment. Afterwards, the cubes were marked withcorresponding depths starting at the 488 cm depth point (most shallow) and until the deepest
sample 588 cm depth, with a sampling interval of approximately 2-3 cm.

3. Cleaning the cubes
The next step was to replace the additional amount of the core sediment of the cubic boxes inorder to close them with lids. A container with a wet tissue for the samples to keep moisture wasalso cleaned and prepared. The numbered plastic cubic boxes were placed in that container andstored in the cooling room before the experiment.

In total 37 samples were extracted and prepared for measurements.

33. Methodology
In this work two main methods of measurements were used: 1) anisotropy of magnetic susceptibility(AMS), and 2) natural remanent magnetization (NRM) measurements combined with alternating field(AF) demagnetization. A brief description of each of the methodologies is provided as follows.

3.1 Anisotropy of magnetic susceptibility (AMS)
Magnetic susceptibility is the ability to acquire induced magnetization or basically the ability of amaterial to become magnetized. Magnetic anisotropy is a directional variability of a certain magnetic
property, usually of magnetic susceptibility, which is referred to as Anisotropy of Magnetic
Susceptibility (AMS). Magnetic susceptibility is defined as kij = M i / H j , where H is the magnetic
field intensity and M is the magnetization (the bold lettering indicated that M and H are vector
quantities).

Magnetically isotropic material (Fig. 3) can be described by
M 1 = kH 1 , M 2 = kH 2 , M 3 = kH 3 (1),where M 1-3 is magnetization and H 1-3 is the applied field along the three unique axes
Magnetization of anisotropic materials (Fig. 3)
M 1 = k 11 H 1 + k12 H 2 + k 13 H 3
M 2 = k 21 H 1 + k 22 H 2 + k23 H 3 (2)M 3 = k31 H 1 + k 32 H2 + k 33 H 3
In general, magnetic susceptibility is described by a second rank tensor, that relate themagnetization of a material to the applied field, such that
𝑀𝑀1 = 𝑘𝑘11
�𝑀𝑀2 � = �𝑘𝑘21
𝑀𝑀3 = 𝑘𝑘31

𝑘𝑘12
𝑘𝑘22
𝑘𝑘32

𝑘𝑘13 𝐻𝐻1
𝑘𝑘23 � �𝐻𝐻2 � (3),𝑘𝑘33 𝐻𝐻3

𝑘𝑘11
𝑀𝑀1
where �𝑀𝑀2 � is the vector of magnetization, �𝑘𝑘21
𝑀𝑀3
𝑘𝑘31

the vector of the field intensity (Chadima, 2016).

𝑘𝑘12
𝑘𝑘22
𝑘𝑘32

4

𝑘𝑘13
𝐻𝐻1
𝑘𝑘23 � is the susceptibility tensor, and �𝐻𝐻2 � is
𝐻𝐻3
𝑘𝑘33

Figure 3. a) Magnetically isotropic material behaviour, where the magnetization is parallel to the applied field,b) magnetically anisotropic material behaviour, where the magnetization is generally not parallel to the appliedmagnetic field.

Figure 4. a) susceptibility ellipsoid, with axes of susceptibility k max , k int and k min , b) stereographic projection (orequal area net) to indicate the axes of susceptibility in spherical coordinates, where the square is k max , triangle is
k int and circle is k min . (Figure modified from Chadima, 2016). Note that k 1 = k max , k 2 = k int , k 3 = k min

5

Table 1. The summary of magnetic anisotropy parameters (Chadima, 2016)

Principal susceptibilities

k1 ≥ k2 ≥ k3

Mean susceptibilityk m = (k 1 + k 2 + k 3 ) / 3

Degree of anisotropy

P = k1 / k 3

Degree of magnetic lineation

L = k1 / k 2

Degree of magnetic foliation

F = k2 / k3

Shape parameter

T = (2η 2 – η 1 – η 3 ) / (η 1 – η 3 ), η 1 = ln k 1 , η 2 =ln k 2 , η 3 = ln k 3

Oblate (planar) fabric+1 > T > 0

Prolate (linear) fabric-1 < T < 0

Corrected degree of anisotropy

P j = Pa , a = √(1 + T2 /3)

3.2 Natural Remanent Magnetization (NRM)
Natural remanent magnetization (NRM) is the magnetization present in a rock sample before anylaboratory magnetic or thermal treatment. NRM depends on the geomagnetic field and geologicalprocesses that occurred during the formation of the rock and its subsequent geological history. NRM
typically consists of more than one component. The NRM component acquired during rock formation
is called primary NRM and is the component that attracts the most scientific attention (Butler, 2004).
Principal component analysis (PCA) is a linear transformation of the orthogonal coordinate axes to a
new orthogonal reference frame that corresponds to the geometry of the data set. The origin in the new
system corresponds to the ‘centre of mass’, while the new axes are positioned by least-squares to best
fit the data. Each axis in the new reference system has associated with it a measure of the variance (σ2)
about the mean in that particular direction; two of the axes are positioned to correspond to the
maximum and minimum direction of variance, while the other (in the three-dimensional case) isintermediate (Kirschvink, 1978).
In rock magnetic and palaeomagnetic research, the remanent coercive force H cr , and the median
destructive field (MDF) are frequently used to characterize the stability of the carriers of remanent
magnetization of rock specimens. Both parameters are an expression of the coercivity which is theability of a magnetization of magnetic material to resist reorienting forces (Dankers, 1981).
Progressive demagnetization techniques using alternating fields or heating experiments, and principal
component analysis (PCA), are universally used to recover directional information from individual6

samples and provide a measure of the error affecting the recovered direction, known as maximum
angular deviation (MAD) angles (Khokhlov, Hulot, 2015).

4. Devices
The measurements of susceptibility anisotropy were made with a MFK1-FA susceptibility bridge (Fig.
5) with Safyr 6.0 software. The Kappabridge device is fully equipped with an automatic sample
insertion mechanism and a semi-automatic rotator that spins the specimen during AMS measurements.

Figure 5. Multifunction Kappabridge (MFK1) device used for AMS measurements, Uppsala University.

7

The spinning specimen method uses a rotator for easy, rapid and precise AMS measurements, which
effectively over determines the AMS result by measuring many more positions than required toreconstruct the AMS tensor. The instrument is designed for measuring AMS and bulk magnetic
susceptibility in weak variable magnetic fields (field range from 2 A/m to 700 A/m, peak values).
For the NRM measurements a 2G-Enterprises 755 Superconducting Rock Magnetometer (SRM) within-house developed software to collect and plot the remanence data was used (Fig. 6). The
magnetometer uses liquid helium to keep the SQUID sensors at superconducting temperature,enabling very high sensitivity measurements. It also has a shielded area that holds alternating field(AF) coils, which allows demagnetization and measurements of the samples in a magnetically shieldedenvironment.

Figure 6. 2G-Enterprises 755 superconducting rock magnetometer (SRM) system used for the remanence fromthe Uppsala University palaeomagnetic laboratory.

85. Results
5.1 AMS
Such parameters as mean magnetic susceptibility K m , shape parameter T, and degree of anisotropy P j
were obtained. Figure 7 shows a summary of the principal axes of susceptibility in a stereographic
projection (stereonet). The minimum axis (k min ) is oriented vertically and the maximum andintermediate axes are parallel to the horizontal surface (Fig. 7). It should be mentioned that thegeographical directions of the horizontal axes are unknown, if 90 is East or 270 is West, for example,
because the azimuthal orientation of the core could not be determined after the core had been extracted
from the sediment. Figure 8 illustrates the dependence showing that P j is mostly within 1.03-1.08
range, proving our fabric is oblate and flattened (T ≈ 1).
Figure 9 describes the change of K m , P j and T with depth considering all the 37 samples. The meansusceptibility K m increases with depth, whereas the degree of anisotropy shows the opposite trend,with decreasing values. The shape parameter T remains quite constant with depth.

Figure 7. Complete AMS stereonet of all the 37 samples. The figure was generated with Anisoft software(www.agico.com)

9

Figure 8. a) Degree of anisotropy P j versus the mean susceptibility K m, b) shape parameter T plotted against P j

Figure 9. Depth dependence for: a) mean magnetic susceptibility K m , b) degree of anisotropy P j , c) shapeparameter T

10

5.2 NRM and alternating field demagnetization results
The natural remanent magnetization measurements provided vectors of relative declination(azimuthally unoriented cores) and inclination data for each sample. The overall range of NRM is
between approximately 1 and 25 mA/m. The AF steps were 5, 10, 15, 20, 30, 40, 60 and 80 mT.
Principal component analysis (PCA) was used to identify the best fit palaeomagnetic vectors(characteristic remanent magnetization, ChRM), and generally data from all demagnetization steps
were included in the analysis, with exception of the NRM (0 mT) and AF at 5 mT. All the data wasprocessed in the Puffinplot software (Lurcock et al., 2012). Also, the median destructive field (MDF)
was calculated from the AF demagnetization results.
Figure 10 and 11 show representative sample vector diagrams. A more detailed data set in table form
can be found in Appendix 1. The plots represent a single vector that demagnetizes to the origin.
Depth changes for parameters such as NRM Intensity, inclination, maximum angular deviation(MAD), and median destructive field (MDF)) are shown in Figure 12. It demonstrates how thoseparameters depend on depth, from sample to sample.

11

Figure 10. Four sample vector diagrams with PCA comparison (fitted blue lines) for each sample withcorresponding depths: a) 489.5 cm, b) 511.1 cm, c) 527.4 cm, d) 566.9 cm. Units of remanent magnetization are
in mA/m.

12

Figure 11. Four sample vector diagrams with PCA comparison (fitted blue lines) for each sample withcorresponding depths: a) 530.2 cm, b) 546.2 cm, c) 554.2 cm, d) 561.8 cm. Units of remanent magnetization are
in mA/m.

13

Figure 12. Depth dependences for parameters of: a) NRM intensity, b) Inclination, c) MAD, and d) MDF

14

6. Discussion
This chapter is dedicated towards comparing the results of previous measurements with those thathave been achieved in this study. The earlier measurement results were obtained from the working halfof the split sediment core. AMS measurements took place in March 2016, June 2016, and June 2017.
The NRM measurements were made previously in the palaeomagnetic laboratory at Lund University
in 2016.
From the previous studies of the sedimentary magnetic properties, it has been indicated that magnetiteand greigite are the likely remanence bearing ferromagnetic minerals (Snowball et al., 2019; Snowball,
unpublished data). Other studies have shown the presence of greigite (Fe 3 S 4 ) in water basin bottom
sediments (Roberts et al., 1996) so it is a well-known contributor to magnetization of sediments foraround 30 years. Greigite is an iron sulphide mineral with a spinel structure, which typically occur inreducing environments. Two types of greigite are known: 1) authigenic greigite, and 2) greigite
biosynthesized by magnetotactic bacteria (MTB) (Reinholdsson et al., 2013). Like the related oxide
magnetite (Fe 3 O 4 ), greigite is ferrimagnetic and makes for an important contributor to the recording of
the Earth magnetic field. Greigite is, however, unstable at atmospheric (typical laboratory) conditions
and tends to oxidize (Snowball and Thompson, 1988). Such oxidation will likely lead to changes in themagnetic properties of sediments.

6.1 AMS
Figure 13 shows how the mean susceptibility K m of the previously sampled half of the core haschanged over the years, from2016 to 2017 (Snowball, unpublished data), in comparison with themeasurements of the currently investigated core half (in 2019). Figure 14 illustrates the same trend of
analogy for the degree of anisotropy Pj. Figure 15 summarizes the collation of K m , P j and T atdifferent measurement times. As shown, K m in the 2019 results are similar to previous years and agreewith similar results from the measurements made in 2016 and 2017. P j in the meantime shows asimilar trend with exception of some spikes at the top and the bottom of the core.

15

Figure 13. Comparison of the mean susceptibility K m results depending on the year: a) 2015, b) 2016, c) 2017,d) 2019. Note that d) measurements were made on the working core half

16

Figure 14. Comparison of the mean susceptibility P j results depending on the year: a) 2015, b) 2016, c) 2017, d)
2019. Note that d) measurements were made on the working core half17

Figure 15. Comparative illustration for K m, P j and T in different years: a) K m, b) P j , c) T. The results indicatethat the archived half will not have oxidized in the same way as the material that was measured repeatedly for 3
times.

18

6.2 NRM and AF demagnetization
The currently measured data and Lund University data are used for comparison in this section. Two
different sediment material depth dependence behaviours are shown in Figure 16. It illustrates
parameters of NRM intensity, inclination, MAD, MDF change with depth in two different split core
halves.

Figure 16. Comparison plots with the working half-core measurements made in Lund for: a) Inclination, b)
MAD, c) NRM intensity, d) MDF

It is worth to mention that there is a trend of decreasing NRM intensity, inclination and MDF withdepth. Previous measurements, made shortly after the sediment core was sampled, show different
results in terms of remanence magnetic properties. The loss of NRM intensity in the 2019
measurements (particularly towards the bottom of the core) has apparently caused inclination to
decrease with storage time. Changes in magnetic properties must relate to a remanence bearing
mineral, likely greigite and/or magnetite. Magnetite is quite stable at atmospheric conditions and does
not easily break down because of oxidation. Greigite, on the other hand, is unstable and likely to break19

down during oxidizing conditions, and thus likely responsible for the decrease in remanence with time
and the apparent inclination shallowing.

7. Conclusions
The outcome for AMS parameters such as the mean susceptibility K m , the degree of anisotropy P j , andthe shape parameter T show similar behaviour in comparison with previous results. It seems that the 1m long core has a lower mean magnetic susceptibility at the core ends, which is likely because that iswhere the air enters the storage tube. P j seems to increase in the sections of the core that have lost
NRM intensity and magnetic susceptibility, so those parts of the cores have become more anisotropic
over time.
NRM and AF demagnetization results show a reduction in remanence parameters as a function of
depth, in comparison with earlier palaeomagnetic measurements. A probable reason for this is theoxidation of the iron sulphide greigite (Fe 3 S 4 ), which that is part of this sediment. Greigite is one of
the remanence bearing minerals that makes the core material carry a remanent magnetization. It
becomes oxidized while in contact with air and therefore, bringing the sediment from the bottom of
the river up to the surface starts the oxidation process. The results hence indicate that the material islosing its magnetic properties gradually with time. An addition to the hypothesis would be that that the
NRM acquired by biosynthesized greigite was acquired later than the NRM carried by the inorganic
greigite.
The results presented here bring an important consequence for studies of sediments in different
settings of ocean, seas and lakes, where metastable greigite is present. Oxidation of the greigite, whichmust carry a steeper component of mixed, intermediate NRM, reveals the shallower component
carried by iron oxides. Long-term storage of greigite bearing sediments may give unreliable
palaeomagnetic data, and the breakdown of greigite needs to be acknowledged when working withthese sediments for reconstruction of the Earth’s magnetic field.

20

8. Acknowledgements
Many thanks to Bjarne Almqvist for helping and advising with the study, Steffen Wiers for theassistance with the instruments and the measurements. Also, special gratitude to Ian Snowball forreviewing the thesis.

9. References
Andrén T., Jørgensen B.B., Cotterill C., Green S., Andrén E., Ash J., Bauersachs T., Cragg B., Fanget
A.-S., Fehr A., Granoszewski W., Groeneveld J., Hardisty D., Herrero-Bervera E., Hyttinen O.,
Jensen, J.B. Johnson S., Kenzler M., Kotilainen A., Kotthoff U., Marshall I.P.G., Martin E., Obrochta
S., Passchier S., Quintana Krupinski N., Riedinger N., Slomp C., Snowball I., Stepanova A., Strano S.,
Torti A., Warnock J., Xiao N., and Zhang R., (2013), Scientific report on core Site M0061
Butler R.F., (2004) Paleomagnetism: Magnetic Domains to Geologic Terranes
Chadima M. (2016) Magnetic anisotropy of rocks, Lecture notes, Slides 9,12,14
Dankers P., (1981) Relationship between median destructive field and remanent coercive forces fordispersed natural magnetite, titanomagnetite and hematite, Geophys. J. R. astr. SOC. 64,447-461
Dekkers M.J. (1978) Magnetic properties of sediments. In: Sedimentology. Encyclopedia of Earth
Science. Springer, Berlin, Heidelberg
Khokhlov A., Hulot G., (2015), Principal component analysis of palaeomagnetic directions:converting a Maximum Angular Deviation (MAD) into an α95 angle, Geophysical JournalInternational, Volume 204, Issue 1, January, 2016, Pages 274–291
Kirschvink J. L. (1978) The least-squares line and plane and the analysis of palaeomagnetic data
Lurcock P. C. and G. S. Wilson (2012), PuffinPlot: A versatile, user-friendly program forpaleomagnetic
analysis,Geochemistry,
Geophysics,
Geosystems,
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Q06Z45,
doi:10.1029/2012GC004098.
Reinholdsson M., Snowball I., Zillen L., Lenz C., Conley D.J., (2013), Magnetic enhancement of
Baltic Sea sapropels by greigite magnetofossils
Robers A.P., Reynolds R.L., Verosub K.L., and Adam D.P. (1996) Environmental magnetic
implications of greigite (Fe 3 S 4 ) formation in a 3 m.y. lake sediment record from Butte Valley,
northern California
Snowball I., Almqvist B., Lougheed B.C, Wiers S., Obrochta S. and Herrero-Bervera E. (2019) Coring
induced sediment fabrics at IODP Expedition 347 Sites M0061 and M0062 identified by anisotropy ofmagnetic susceptibility (AMS): criteria for accepting palaeomagnetic data
Tauxe, L, Banerjee, S.K., Butler, R.F. and van der Voo R, Essentials of Paleomagnetism, 5th Web
Edition, 2018.

21

10. AppendicesA1. AMSAMS appendix part consists of one big table of all the data for the measurements.
Table A1.

A2. Remanent magnetization
The NRM appendix consists of the table with the results and vector diagrams with PCA for all thesamples. Table A2, Figures 17-21.

22

Table A1
№

Field

Fre
q

Km

L

F

P

Pj

T

U

K 1dec

K 1incK 2decK 2incK 3dec

K 3inc

K 11

K 22

K 33

K 12

K 23

K 13

1.5

200

F1

84.02179

1.003

1.08

1.083

1.095

0.92

0.917

359.3

1.9

269.2

4.7

111

84.9

1.02738

1.023650.948960.00016-0.00628

0.00251

4.2

200

F1

78.6759

1.004

1.057

1.061

1.069

0.86

0.856

216.3

2.4

306.3

0.6

51.3

87.5

1.01959

1.01830.962110.00197-0.00194-0.00161

7.0

200

F1

70.38136

1.003

1.057

1.06

1.068

0.901

0.898

183.4

1.1

273.4

0.5

28.5

88.8

1.02026

1.01734

0.962390.00017-0.00057-0.0011

9.6

200

F1

73.98455

1.003

1.062

1.065

1.074

0.893

0.89

185

1.2

95

0.1

357.8

88.8

1.02196

1.01858

0.959460.00030.00004-0.00127

12.3

200

F1

71.80271

1.005

1.061

1.066

1.074

0.856

0.851

178.5

0.5

268.5

0.8

57.4

89.1

1.022641.01794

0.95942-0.00013-0.00079-0.00055

14.9

200

F1

85.58895

1.003

1.051

1.054

1.061

0.9

0.898

5.2

0.2

275.2

1

107.3

89

1.01818

1.01555

0.966270.00024-0.0008

0.00026

17.7

200

F1

102.7309

1.002

1.047

1.049

1.055

0.918

0.916

6.5

0.8

276.5

0.8

143.8

88.9

1.016391.01447

0.969140.00023-0.00053

0.00075

20.4

200

F1

105.4435

1.001

1.044

1.045

1.051

0.951

0.95

193.9

0.3

283.9

0.6

76.5

89.3

1.01476

1.01379

0.971450.00025-0.00052-0.00013

23.1

200

F1

116.4717

1.002

1.116

1.118

1.136

0.964

0.962

356.9

2

86.9

0.2

182.3

88

1.03709

1.035170.92775-0.00012

0.00015

0.00389

25.7

200

F1

89.86324

1.002

1.051

1.053

1.06

0.923

0.921

153.5

1.2

243.6

0.7

4.1

88.6

1.017311.016120.96657-0.00081-0.00007-0.00123

28.5

200

F1

107.6635

1.001

1.042

1.042

1.049

0.974

0.973

309.6

2.4

39.7

1.9

169.1

86.9

1.01346

1.01367

0.97287-0.00025-0.00043

0.00214

31.2

200

F1

105.6051

1.001

1.044

1.045

1.052

0.975

0.975

359.3

1.9

89.3

0.2

184.5

88.1

1.01466

1.01416

0.97118-0.00001

0.000120.00148

34

200

F1

107.2655

1.001

1.042

1.044

1.05

0.941

0.94

356.1

1.9

86.1

0.2

181.4

88.1

1.014541.01333

0.97214-0.00009

0.000030.00143

35.7

200

F1

113.4495

1.002

1.037

1.038

1.043

0.917

0.915

5.5

1.3

275.5

0.8

154.3

88.4

1.012931.0114

0.975670.00016-0.00042

0.00092

39.4

200

F1

114.3883

1.003

1.043

1.046

1.052

0.858

0.855

160.3

0.2

250.3

0.6

55.4

89.4

1.015621.01311

0.97127-0.00103-0.00037-0.00027

42.2

200

F1

105.0106

1.001

1.042

1.043

1.049

0.97

0.969

313.7

0.1

223.7

0.6

54

89.4

1.01377

1.01379

0.97244-0.00032-0.00037-0.00027

44.7

200

F1

101.1457

1.002

1.049

1.051

1.058

0.917

0.915

193.9

0.4

103.9

0.5

320.2

89.3

1.01696

1.0151

0.967940.000490.00035-0.00044

47.6

200

F1

113.3194

1.001

1.038

1.039

1.044

0.945

0.944

189.6

1.4

99.5

1.9

316.7

87.7

1.01286

1.01187

0.975260.00020.00102-0.00112

50.1

200

F1

105.1969

1.003

1.049

1.052

1.058

0.876

0.873

338.8

0.9

68.8

0.8

199.2

88.8

1.01741.015070.96753-0.001080.000320.00101

52.8

200

F1

117.0232

1.001

1.035

1.036

1.041

0.924

0.923

198.9

0.5

108.9

1.1

311.1

88.8

1.01211.01102

0.97688

0.000420.00053-0.00047

55.4

200

F1

132.128
6

1

1.026

1.027

1.031

0.966

0.966

8.2

0.8

98.2

0.5

217.9

89

1.00895

1.00851

0.982540.00006

0.000270.00035

58.2

200

F1

110.531
6

1.001

1.036

1.037

1.042

0.951

0.95

344.8

0.2

74.8

1.8

248

88.2

1.01223

1.011440.97634-0.00024

0.00104

0.00043

60.8

200

F1

118.591
1

1.001

1.037

1.038

1.043

0.93

0.928

355.1

1.1

85.1

0.3

190.9

88.9

1.01284

1.011540.97562-0.00012

0.000130.00073

63.5

200

F1

110.598
3

1.002

1.037

1.039

1.044

0.905

0.903

359.7

2.6

89.7

1.2

205.1

87.2

1.01316

1.01138

0.97546-0.00004

0.000750.00169

66.2

200

F1

108.014
6

1.001

1.039

1.04

1.046

0.938

0.937

359.1

2.6

89.2

1.2

204.6

87.1

1.01336

1.012180.97446-0.00005

0.000790.00178

68.9

200

F1

122.311
4

1.002

1.035

1.037

1.042

0.88

0.878

345.1

1.9

255.1

0.4

153.1

88.1

1.012761.01084

0.97639-0.00054-0.00054

0.00109

71.3

200

F1

115.416
8

1.001

1.028

1.029

1.033

0.953

0.952

328.1

0.5

238.1

0.5

103.9

89.4

1.009541.00924

0.98122-0.0003-0.00031

0.00008

73.8

200

F1

110.144
5

1.001

1.034

1.035

1.04

0.94

0.939

349.9

0.6

79.9

0.3

197.1

89.3

1.01175

1.01077

0.97748-0.00018

0.000120.00041

76.3

200

F1

128.081
5

1

1.032

1.032

1.037

0.975

0.975

127.6

0.7

217.6

1

0.9

88.8

1.010451.01057

0.97898-0.00019-0.00001-0.00065

78.9

200

F1

140.065
3

1.001

1.026

1.027

1.031

0.96

0.959

68

2.8

337.8

3.2

199.1

85.8

1.008411.00891

0.982680.000140.000650.0018

81.5

200

F1

136.035
8

1.007

1.03

1.037

1.039

0.612

0.606

227.9

3

137.7

4.7

350.9

84.4

1.01023

1.011210.97856

0.00357

0.00016-0.00302

84.1

200

F1

131.953
7

1.001

1.036

1.037

1.042

0.957

0.957

347.4

1.5

77.4

0.6

191

88.4

1.012221.01154

0.97624-0.00017

0.000180.00099

86.6

200

F1

106.944
8

1.001

1.034

1.035

1.04

0.924

0.923

180.2

5.2

90.1

1.4

345.3

84.6

1.011531.010480.977990.00008

0.00078-0.0031

89.5

200

F1

125.755
2

1.002

1.041

1.043

1.049

0.927

0.926

175.5

0.3

85.5

3.3

270.7

86.7

1.01438

1.01272

0.9729-0.00012

0.00228-0.00004

92.2

200

F1

108.803

1.002

1.06

1.063

1.072

0.926

0.924

195.1

1.1

105.1

1.7

318.5

88

1.02071

1.01872

0.96057

0.000620.00132-0.00155

94.8

200

F1

96.5819

1.001

1.061

1.062

1.071

0.953

0.952

7.7

0.8

277.7

0.2

174.2

89.2

1.02039

1.019020.960590.00019-0.00008

0.00082

97.6

200

F1

97.7699
7

1.002

1.058

1.06

1.069

0.924

0.922

352.7

1.6

262.7

0.7

147.8

88.3

1.02

1.01782

0.96218-0.00026-0.00091

0.0015

Table A2

Depth,mm
15
42
70
96
123
149
177
204
231
257
285
312
340
357
394
422
447
476
501
528
554
582
608
635
662
689

Total depth, cm
489.5
492.2
495
497.6
500.3
502.9
505.7
508.4
511.1
513.7
516.5
519.2
522
523.7
527.4
530.2
532.7
535.6
538.1
540.8
543.4
546.2
548.8
551.5
554.2
556.9

Declination,degrees
8.61
331.55
3.43
22.35
14.37
3.64
5.28
4.9
357.83353.85358.350.42
4.74
355.050.05
354.711.29
354.18351.71
347.19358.89353.414.12
358.68359.78
6.35

Inclination, degrees
65.69
63.7
64.42
68.75
70.87
69.62
73.76
68.93
72.58
69.65
74.18
73.98
73.07
71.4
71.43
68.66
69.45
68.57
69.03
69.1
69.04
70.05
68.5
70.56
70.94
65.8

Mad1, degrees
19.85
26.3
33.52
22.66
5.67
10.95
16.57
18.92
27.44
40.84
25.84
16.97
27.9
25.97
22.97
41.85
35.18
21.32
37.34
3.22
16.58
10.35
27.21
6.62
32.09
13.9

Mad3, degrees
16.11
11.82
7
6.79
10.47
3.99
4.72
1.71
2.04
2.27
2.44
2.61
2.38
2.32
1.64
3.62
1.34
1.7
4.07
12.39
1.82
1.84
1.99
2.64
1.59
2.3

NRM intensity,
mA/m
2.07
3.35
3.98
1.86
2.56
8.41
12.7
14.8
19.3
9.58
17.4
15.5
16.6
21.7
18.9
17.6
13.2
23
13.5
25.3
34.6
24.9
20.9
19.4
20.4
29.2

MDF,mT
25.22
18.91
19.34
18.37
17.37
20.73
23.12
23.43
22.96
22.52
23.46
23.65
24.17
23.81
24.3
23.73
23.85
23.81
24.73
26.07
25.41
25.51
24.45
24.01
24.34
24.07

713
738
763
789
815
841
866
895
922
948
976

559.3
561.8
564.3
566.9
569.5
572.1
574.6
577.5
580.2
582.8
585.6

1.06
3.19
6.8
7.19
13.07
5.77
348.76
16.44
41.67
11.08
18.31

63.41
66.94
63.15
68.76
62.44
68.68
61.81
65.05
54.49
63.26
61.17

21.98
28.22
26.77
28.54
12.21
27.46
12.27
23.48
17.37
30.97
23.07

1.53
1.48
1.57
1.8
2.18
1.7
2.87
2.92
10.74
10.99
11.56

24.4
0.79
27.4
25.4
27.2
23.4
13.3
12.2
5.14
4.07
4.02

22.66
25.24
23.52
23.62
23.53
23
18.94
15.19
12.93
14.24

Figure 17. Nine sample vector diagram with PCA comparison (fitted blue lines) for corresponding depths: a)
489.5cm, b) 492.2cm, c) 495cm, d) 497.6cm, e) 500.3cm, f) 502.9cm, g) 505.7cm, h) 508.4cm, i) 511.1cm

Figure 18. Nine sample vector diagram with PCA (fitted blue lines) for corresponding depths: a) 513.7cm, b)
516.5cm, c) 519.2cm, d) 522cm, e) 523.7cm, f) 527.4cm, g) 530.2cm, h) 532.7cm, i) 535.6cm

Figure 19. Nine sample vector diagram with PCA comparison (fitted blue lines) for corresponding depths: a)538.1cm, b) 540.8cm, c) 543.4cm, d) 546.2cm, e) 548.8cm, f) 551.5cm, g) 554.2cm, h) 556.9cm, i) 559.3cm

Figure 20. Nine sample vector diagram with PCA comparison (fitted blue lines) for corresponding depths: a)
561.8cm, b) 564.3cm, c) 566.9cm, d) 569.5cm, e) 572.1cm, f) 574.6cm, g) 577.5cm, h)580.2cm, i) 582.8cm

Figure 21. The last and final sample vector diagram with PCA comparison (fitted blue lines) for thecorresponding depth of 585.6cm

Examensarbete vid Institutionen för geovetenskaper
ISSN 1650-6553