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Earth and Planetary Science Le
The magnetization of clay-rich rocks in sedimentary basins:
low-temperature experimental formation of magnetic
carriers in natural samples
M.G. Moreaua,*, M. Adera,1, R.J. Enkinb,2
aInstitut de Physique du Globe de Paris, FrancebPaleomagnetism, Geological Survey of Canada-Pacific, POB 6000, Sidney, B.C., Canada, V8L 4B2
Received 30 June 2004; received in revised form 15 November 2004; accepted 17 November 2004
Available online 4 January 2005
Editor: E. Bard
Abstract
Rocks are often magnetically altered during burial, thus providing a useful method to study their thermo-chemical history. In
order to improve the understanding of burial diagenetic magnetization, we experimentally synthesized magnetite in natural
samples. Lower Jurassic argillites from the Paris Basin were heated to 150 8C, under a confined atmosphere of argon. When a
magnetic field was applied during the heating, a chemical remanent magnetization was acquired. Rock magnetism studies reveal
that most of the newly formed magnetic carriers were magnetite. Using anhysteretic remanent magnetization as a measure of the
quantity of magnetite, an increase of up to 150% after heating was observed. Ferrimagnetic iron sulphide and hematite are
observed to have formed in samples composed of less than 3% calcite, and new magnetite is sometimes completely absent in
samples containing less than 0.5% calcite. Hysteresis measurements suggest that the new magnetite is in the pseudo-single
domain state. Scanning electron microscope studies indicate that the new magnetic carriers are associated with pre-existing
pyrite. The magnetic transformations during the experiments involved a fluid which reacted with iron-bearing and sulfur-
bearing minerals in ways depending on local redox conditions. This study shows that magnetite can be produced in argillaceous
sediments at the normal temperatures and pressures found in sedimentary basins, without any external supply from long-range
fluid flow.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Argillites; Burial remagnetization; Magnetite; Fluids
0012-821X/$ - s
doi:10.1016/j.ep
* Correspon
05; fax: +33 1 4
E-mail addr1 IPGP, T142 Tel.: +1 2
tters 230 (2005) 193–210
ee front matter D 2004 Elsevier B.V. All rights reserved.
sl.2004.11.013
ding author. IPGP, T14 Laboratoire de Paleomagnetisme, 4, Place Jussieu, 75252 Paris Cedex 05, France. Tel.: +33 1 44 27 26
4 27 74 63.
esses: moreau@ipgp.jussieu.fr (M.G. Moreau)8 ader@ipgp.jussieu.fr (M. Ader)8 renkin@nrcan.gc.ca (R.J. Enkin).
Laboratoire des Isotopes stables, 4, Place Jussieu, 75252 Paris Cedex 05, France. Tel.: +33 1 44 27 60 90; fax: +33 1 44 74 63.
50 363 6431; fax: +1 250 363 6565.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210194
1. Introduction
Paleomagnetists usually search for primary mag-
netizations, which are synchronous with the origin of
the rocks measured. Often, late magnetizations are
recognized but these can be difficult to interpret.
These remagnetizations may have been caused by
heating, which produces a thermo-viscous remanent
magnetization (TVRM), or by circulation of fluids,
which produces a chemical remanent magnetization
(CRM).
In the case of CRM, the magnetic carriers are
usually hematite (hydrated or not), magnetite, or
ferrimagnetic iron sulphide (FIS). Hematite can be
produced by remobilization of iron in an oxidizing
environment by the circulation of meteoric or oro-
genic fluids (e.g., [1]). The mechanisms leading to a
remagnetization carried by magnetite or FIS are more
difficult to explain. Magnetite formation may be
linked to hydrocarbon migration, with examples
found in North America [2,3] and Europe [4]. In
contrast, there are several cases in which secondary
magnetite exists where there is no evidence of fluid
circulation [5–7].
Fruit et al. [8] and Banerjee et al. [9] showed, for
the Belden Formation in Colorado, that magnetite is
formed by replacing pyrite. They observed that this
magnetite is spread throughout the rock matrix rather
than being concentrated near calcite-filled veins.
Furthermore, they observed that the magnetite was
absent in zones lacking organic matter. The age of the
remagnetization in four different tectonic settings
agrees well with the age of organic maturation at
between 2 and 3 km burial, for which Banerjee et al.
[9] speculate a causal connection. Brothers et al. [10]
have experimentally demonstrated that organic acids
can be responsible for magnetite crystallization, and
suggest that in sedimentary basins, organic acids
produced by maturation of organic matter are respon-
sible for remagnetization.
The transformation of clay minerals, in particular
from smectite to illite between 2 and 4 km depth may
also produce magnetite. Woods et al. [11] proposed
this model for Jurassic sediments from the Isle of
Skye (Scotland), as did Katz et al. [12,13] for Jurassic
and Cretaceous sediments from the Vocontian trough
(south-east of France). In the Mississippian Deseret
Basin, Blumstein et al. [14] found that remagnetiza-
tion occurred as the rocks were within the oil window,
whereas smectite-to-illite transformation apparently
predated both events. Whether the creation of magnet-
ite is linked to the transformation of organic matter or
clay minerals, it does not seem necessary to have
exterior contributions.
Late diagenetic magnetizations are often observed
in rocks rich in organic matter and pyrite, and authors
usually note the total absence of a primary component
of magnetization. Possibly these rocks contained no
primary magnetite of single or pseudo-single domain
grain size, capable of preserving a magnetic signal.
Alternately, the original single or pseudo-single
domain magnetite grains may have dissolved during
early diagenesis [15,16], with the iron precipitating as
pyrite—a paramagnetic mineral incapable of holding
a remanence. If there are no primary fine grains of
magnetite, then in the absence of subsequent dia-
genesis these sediments cannot hold a stable magnet-
ization. The key question concerns what happens to
such rocks when they are buried within a sedimentary
basin. Can burial, without any exterior contributions,
lead to the production of fine-grained magnetite and a
stable magnetization where there had not been one
before?
While researchers often note that a fluid is required
for the dissolution and reprecipitation of iron, in most
cases the origin of this fluid remains unknown [6,17–
21]. Long range transport of fluids has been invoked
to explain the broad regions which are observed to
have been remagnetized ahead of orogenic deforma-
tion fronts [22], however the hydrodynamic condi-
tions for this flow have been disputed.
In order to improve our understanding of the
mechanism controlling this magnetization we have
heated natural samples to investigate the magnetic
transformations that can occur during burial.
2. Choice of samples
For several years, we have been studying the
Lower Jurassic levels of an industrial bore-core
situated in the north-east of the Paris Basin in northern
France. Magnetostratigraphic studies of the Hettan-
gian-Sinemurian, between 1075 and 920 m depth,
where the proportion of calcite is almost always larger
than 40%, show that the primary paleomagnetic signal
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 195
is well-preserved [23]. Nevertheless, Moreau and
Ader [24] showed that, in clay-rich and organic-rich
layers (with less than 20% calcite), fine magnetite
grains are largely absent.
Higher up, in the Pliensbachian section of the
same core between 920 and 770 m depth, the
proportion of calcite decreases whereas that of clay
increases. In these rocks, the paleomagnetic signal is
less well preserved, and for 10% of the samples no
primary remanence was discernible [25]. For the
Toarcian (the target for this study), between 770 and
680 m depth, the proportion of calcite can decrease
below 1%, while that of clay occasionally reaches
clays
quartz
calcite
700
720
740
760
Dep
th(m
)
Major components Clay comp
chlor
kaoli
illite
smec
illite/
chlor
cumulative %0 100 0 cumulati
Fig. 1. Framework of the study, data obtained by X-ray analysis on po
composition and the depths of sampled levels in cumulative percentages;
increase in anhysteretic remanent magnetization (ARM) after heating of s
80%, and very little stable remanent magnetization
could be characterized in a reconnaissance study of
300 samples (unpublished). Mineralogical study of
this level (unpublished Agence nationale pour la
Gestion des dechets radioactifs (ANDRA) report by
Thiry and Schmidt, 1992, and [26]) has shown that
these rocks have not undergone any significant
transformation. Thus they provide interesting samples
for the study of authigenesis of magnetite during
burial diagenesis.
Fig. 1 shows the global composition as well as the
clay spectrum of the b2 Am fraction. The sediments
contain between 0.5% and 2% pyrite as isolated
onents ARM Gain
0 200
ite
nite
tite
smectite
ite/smectite
100ve % % gain
wdered samples every 5 m on average: Column 1—global rock
column 2—composition of the clay fraction (b2 Am); column 3—
ample at 150 8C for 1 week confined in a neutral atmosphere.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210196
crystals or framboidal clusters (unpublished report by
Thiry and Schmidt, 1992). The total organic carbon
varies between 1% and 6% [26].
Standard size paleomagnetic cores were drilled
perpendicular to core axis from the 11 cm diameter
bore-core, and samples are labeled after their depth
level in meters. Most samples were selected between
690 and 722 m depth where the reconnaissance study
showed that no stable remanent magnetization could
be characterized; the rest of the samples were selected
between 722 and 770 m deep where a weak primary
remanent magnetization was occasionally identified.
Obviously heterogeneous levels were avoided.
3. Experimental conditions for crystallization of
magnetic carriers
3.1. Methods
A suite of experiments was performed to determine
the conditions under which magnetic minerals could
be formed in the laboratory in these sedimentary
rocks. All measurements of remanent magnetization
were made using a 2G cryogenic magnetometer.
Monitoring several samples over 3 h showed that
viscous magnetic changes never observed after 15
min. Thus all samples were held in zero field for 15
min before remanence measurements were made.
We used the magnitude of anhysteretic remanent
magnetization (ARM) to quantify the amount of fine-
grain magnetite in the samples [27]. ARM acquisition
curves were determined using a continuous field of
0.1 mT and stepwise application of a parallel
alternating field (AF) with peak fields of 10 to 90
mT. While other measures, such as isothermal
remanent magnetization, have desirable properties
for quantifying the amount of magnetite, ARMs have
the advantage of being removable using AF demag-
netization. Before every ARM curve acquisition, the
samples were AF demagnetized at 90 mT, leaving a
residual magnetization always b2% of total ARM. In
this paper, total ARM refers to the magnetization
using a peak alternating field of 90 mT. By doing
these measurements before, ARM(I), and after,
ARM(II), each heating experiment, we could measure
the change in the quantity of newly formed magnetite.
Given the sources of noise and the experimental
reproducibility of these experiments, we find that
ARM gains can be considered significant when they
are greater than 10%.
3.2. Preliminary experiment
As a preliminary experiment to determine if it were
feasible to produce magnetite in natural sediments
subjected to burial conditions, we performed experi-
ments in an autoclave which was large enough for
samples which next required ARM measurements, but
which was unfortunately not well-adapted to holding a
constant temperature below 200 8C. Two samples
(699.76 and 700.45) were subjected to a 100 MPa
heating experiment to simulate the effects of ~3 km
burial. Samples (1.5 cm diameter, 1.5 cm long) were
wrapped in aluminum foil, and held at pressure under
argon gas at a temperature of 180F20 8C for 15 days,
using the apparatus at the Centre de Recherche sur la
Synthese et la Chimie des Mineraux in Orleans,
France. ARM acquisition curves before and after
treatment show an impressive increase of more than
3000% (Fig. 2a; Table 1 column 3).
3.3. Choice of experimental parameters for acquis-
ition of CRM
Having shown that formation of magnetic minerals
is possible under experimental conditions, we set out
to determine which experimental parameters control
the amount of this formation: the confining fluid, the
hydrostatic pressure, the duration, and temperature of
the experiment.
Since performing high pressure experiments with a
controlled magnetic field proved to be very difficult,
most trials were done at atmospheric pressure.
Samples were heated in a confined atmosphere by
placing them in Teflon air-tight containers. The
container manufacturer (Savillex) guarantees a good
seal at 150 8C up to 0.5 MPa. This maximum
temperature corresponds to a burial of about 5 km,
which is quite reasonable for a sedimentary basin.
Since the preliminary experiment showed that no
additional fluids are needed to produce mineralogical
transformations, argon was chosen as the only
experimental fluid in order to avoid chemical reac-
tions with the sediments. The containers were placed
in a standard paleomagnetic furnace (Pyrox) for 1
150 II
I
a10
I
IIb5
I&II-75-100-125oC
II-150oCc
AR
M (
10-6
Am
2 /kg
)
0 100 0 0alternating field(mT) alternating field(mT)alternating field(mT) 100100
AR
M (
10-6
Am
2 /kg
)
AR
M (
10-6
Am
2 /kg
)
Fig. 2. Anhysteretic remanent magnetization (ARM) acquisition curves (using a bias field of 0.1 mT) for replicate specimens from level 699.76,
before (I) and after (II) heating confined in argon atmosphere. (a) 180 8C heating under 100 MPa pressure 2 weeks duration; (b) 150 8C heating
at atmospheric pressure, 1 week duration; (c) stepwise heatings at 75, 100, 125, and 150 8C.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 197
week. The ARM measurements (Table 1 column 4,
and Fig. 2b) show that magnetite growth occurred,
however the increases were far less than seen with the
preliminary high pressure experiment.
In order to determine the temperature at which the
transformation took place, samples from four levels
were heated in 25 8C steps of 7 days duration each,
from 75 8C to 150 8C. After each heating step, the air-
tight container was opened, the ARM acquisition
curve was measured, the sample was AF demagne-
tized at 90 mT, and then resealed with argon before
Table 1
Experimental conditions for acquisition of CRM
ARM(I) High pressure Atmospheric pressure,
confined
Step
180 8C 150 8C 75 8
Sample (10�6 Am2/kg) gain (%) gain (%) gain
693.74 4.3 0.0
697.67 4.3 155
699.12 3.5 67
699.76 4.5 3100 150 0.4
700.45 4.6 3500 95 0.2
739.48 3.5 19
754.53 2.8 58
759.83 4.0 15 0.2
762.91 3.9 28 0.0
766.02 3.1 17
769.15 3.4 14
Gain in ARM, measuring growth in magnetic carriers, after various experim
meters; column 2, ARM(I) is the ARM acquired before all experimentatio
were negligible. Columns 3–8, gain in ARM after heating confined in a con
8C during 15 days; column 4, under atmospheric pressure for 7 days at 1
successive temperature steps: 75 8C, 100 8C, 125 8C, and 150 8C; colum
being put in the furnace for the next week-long
heating step. A twin sample of each level was heated
directly to 150 8C for 7 days. The magnetic trans-
formation during this stepwise heating experiment
(Table 1 columns 5–8; Fig. 2c) was much smaller than
when a single heating at 150 8C was done (Table 1
column 4; Fig. 2b). For three samples, no significant
change was observed, while the fourth (699.76),
which saw the largest change during the single heating
(150%), saw only a 9% change and that only on the
final (150 8C) step.
wise heating at atmospheric pressure, confined Open air
C 100 8C 125 8C 150 8C 150 8C
(%) gain (%) gain (%) gain (%) gain (%)
�4.0
0.0
6.0
0.2 0.0 8.8
1.1 2.8 �2.7
1.0
�3.0
0.0 0.5 2.7
2.5 0.5 3.6
6.0
2.0
ental heatings. Column 1, sample identification refers to the depth in
n. Only one value is given as the variations among sister specimens
tainer filled with argon; column 3, under pressure of 100 Mpa at 180
50 8C; columns 5–8, heating confined in a container for 7 days at
n 9, gain in ARM after heating in open air for 7 days at 150 8C.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210198
Apparently breaking the confinement during the
heating limits the creation of magnetic carriers.
Following this observation, seven pairs of samples
were heated in argon under confinement and in open
air, respectively. The increase in ARM in samples
heated in open air was always negligible (below 6%,
see Table 1 column 9). This result compares well to
the usual paleomagnetic observation that standard
thermal demagnetization in open atmosphere to 150
8C or even 200 8C only removes a viscous present
field overprint and seldom leads to observable
magnetic mineralogical changes.
The implication from these experiments is that the
samples themselves produced fluids during the experi-
ments. These fluids are necessary for the mineralog-
ical transformations because when the atmosphere is
not strictly confined throughout the heating, there is
little or no transformation. Moreover, a deposit of
anhydrite (CaSO4) was usually observed on the
sample surfaces, uncorrelated to the increase in
ARM after heating experiments, whereas there was
little or no anhydrite deposit on the samples heated in
open air or the samples heated in steps. (Such deposits
had also formed on cracks after the core was brought
to the surface). These deposits indicate that fluid
circulations, which took place during the confined
heating experiments, mobilized calcium and sulfate
ions. The fluids have not been characterized in this
study.
Heatings done over 50 h, 7 days (168 h), and 1
month (720 h) on six sets of three samples from the
same level show irregular gains in ARM. The
variability is probably due to lateral heterogeneities
at the centimeter scale. A large part of the increase in
ARM was usually acquired in the first 50 h, however
the duration of 7 days was used for the following
experiments to allow the maximum amount of the
transformation in a reasonable experimental time.
The increases in ARM obtained by heating at 150
8C in a confined atmosphere for 7 days varied
between 0% and 155% (Table 1 column 4). In order
to understand this variability, experiments were done
on 10 more levels, with results shown in Fig. 1
column 3. These results show that in this type of
sediment, the creation of magnetic carriers is not
exceptional, and that almost all levels are susceptible
to remagnetization under these conditions. It appears
however that the lithology has an influence on the
degree of remagnetization: in the zone between 690
and 710 m (with b5% calcite) the gains in ARM vary
widely from zero up to 170%, while in the zone
around 760 m (with 10 to 30% calcite) the ARM gains
are generally weaker but never zero (5% to 60%).
4. Properties of the CRM
The preliminary experiments showed that most of
the Toarcian part of the core was susceptible to
acquisition of a CRM when heated in a confined
atmosphere. The next stage consisted therefore in
studying the properties of this CRM.
4.1. Experimental protocol
At 7 levels (3 around 700 m and 4 around 760 m)
sister specimens (1 cm long) were cut from 2.5 cm
diameter cores: specimens (a) and (b) were given
CRMs at atmospheric pressure, while specimen (c)
was left untreated as a control. When the sediments
were poorly consolidated (9 levels between 690 and
710 m) a single specimen (a) was collected. Before all
experiments, specimens were demagnetized by alter-
nating field (AF) with a peak field of 100 mT. Unused
rock went towards chemical analysis of carbonate
content.
After the initial ARM curves were measured,
specimens (a) and (b) were confined in a Teflon
container purged with argon and heated at 150 8Cduring 7 days with a continuous 0.1 mT field applied
along the sample axis. The field was zeroed during the
cooling. The remanent magnetization was measured,
and then the specimens were heated a second time at
150 8C for 7 days, but this time in zero field and in
open atmosphere in order to demagnetize any
contribution due to thermo-viscous remanent magnet-
ization acquired during the first heating. The (a)
specimens were AF demagnetized and the (b) speci-
mens were thermally demagnetized to characterize the
nature of the magnetic carriers.
A fourth sister specimen (d) was heated at high
pressure (100 MPa) for 7 days, using an apparatus
specially designed and built at the Geology Labo-
ratory of the Ecole Normale Superieure de Paris (with
better temperature control than the one used in the
preliminary experiment). This new autoclave, sealed
Table 3
Chemical remanent magnetization (CRM) obtained in the laboratory
Sample CRM+TVRM CRM0 CRMRES
(10�6 Am2/kg) (10�6 Am2/kg) (%)
694.77a 4.41 3.4 22
700.28a 102 62 1.0
704.39a 47 31 5.5
759.90a 19 12 7.8
759.45a 21 12 2.0
762.58a 44 25 0.4
765.35a 1.7 1.0 2.5
694.77b 1.5 1.1 8.8
700.28b 1.3 0.8 7.5
704.39b 23 16 2.0
759.90b 2.1 1.5 10
759.45b 1.3 0.83 8.3
762.58b 2.8 1.6 5.3
765.35b 1.0 0.6 7.8
693.80a* 0.90 0.67 82
693.88a* 0.37 0.24 60
695.12a* 10.7 8.4 13
696.96a* 5.8 3.7 1.2
699.00a* 20.2 11.6 2.4
700.57a* 2.1 1.3 2.0
703.49a* 0.52 0.32 32
706.22a* 7.7 6.2 12
706.69a* 7.7 5.6 11
CRM+TVRM is magnetization measured after heating samples for
7 days at 150 8C with a continuous 0.1 mT field followed by
cooling in confined atmosphere and zero field; CRM0 is magnet-
ization measured after reheating samples in open air for the same
duration at the same temperature and zero field; CRMRES is
percentage of magnetization after demagnetization at 70–100 mT
alternating field for sample baQ or 500–570 8C for sample bbQ.Samples with asterisk are poorly consolidated.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 199
with a high-temperature Bridgman-type closure and
with argon as the pressure medium, was positioned
vertically in a topless furnace box. The temperature
was held at 150F5 8C, monitored with a Ni–NiCr
thermocouple placed 3 mm within the external
autoclave wall at the sample level. At the end of the
heatings, the pressure was reduced to atmospheric
pressure and the autoclave was removed from the
furnace box to cool at a rate of 100 8C/h. The
magnetic field unfortunately could not be controlled.
4.2. Results
4.2.1. Pressure effect
The increases in ARM in specimens heated under
high pressure are comparable to those observed in
sister specimens heated at atmospheric pressure
(Table 2). Apparently, the extremely large increases
observed in the preliminary experiments were caused
by the higher temperature and longer duration of the
heating rather than by the higher pressure of the first
autoclave. Since pressure does not greatly affect
formation of magnetite, we consider the atmospheric
pressure experiments to be representative of the
remagnetizations caused naturally by burial.
4.2.2. Demagnetization of CRM
The CRM intensities are listed in Table 3. The
difference between the remanence after the first
heating in a confined atmosphere and the second
heating in open air varies between 20% and 45%. This
difference is interpreted to be a TVRM since the
mineralogical study discussed below shows no evi-
dence of magnetic carriers with Curie temperature
b150 8C (e.g., goethite).
Table 2
Comparison of the acquisition of ARM in samples heated at atmospheric
Sample (a) ARM (I) ARM (II) ARM gain S
(10�6 Am2/kg) (10�6 Am2/kg) (%)
694.77a 3.18 5.30 67 6
700.28a 3.91 11.7 405 7
704.39a 3.50 46.1 1220 7
759.90a 4.04 20.1 397 7
759.45a 3.66 24.3 563 7
762.58a 4.08 41.2 910 7
765.35a 3.77 5.87 56 7
Samples from the same level heated at atmospheric pressure (sample baQ,ARM(I) is ARM before heating and ARM(II) is ARM after heating.
The thermal and AF demagnetization character-
istics of the CRMs separate the samples into two
categories. In the first, which includes almost all of
and high pressure
ample (d) ARM (I) ARM (II) ARM gain
(10�6 Am2/kg) (10�6 Am2/kg) (%)
94.77d 3.39 8.13 140
00.28d 3.88 11.7 201
04.39d 3.78 32.7 766
59.63d 3.94 4.37 11
60.54d 3.63 4.18 15
62.58d 4.00 40.5 910
65.35d 3.75 4.13 10
columns 1–4) and under high pressure (sample bdQ, Columns 5–8),
694.77(a)
90
694.77(b)
180
0
704.39(b)
90
0 200 400 600
704.39(a)
90
M/M
max
0
1.0
alternating field(mT)
temperature(ºC)
alternating field(mT)
540ºC
0 200 400 600
0 20 40 60 80 100
0 20 40 60 80 100
M/M
max
0
1.0
M/M
max
0
1.0
M/M
max
0
1.0
759.45(b)
90
540ºC
759.45(a)
90
0
703.49(a)
90
180
0
0 200 400 600
alternating field(mT)
alternating field(mT)
0 20 40 60 80 100
0 20 40 60 80 100
M/M
max
0
1.0
M/M
max
0
1.0M
/Mm
ax
0
1.0
90
temperature(ºC)
temperature(ºC)
Fig. 3. Representative intensity and stereograph plots of AF (a) and thermal (b) demagnetization of CRM acquired in 0.1 mT field along sample
axis with 1 week heating at 150 8C confined in an argon atmosphere. The samples were reheated in open air for the same duration at the same
temperature and zero field to eliminate thermo-viscous remanent magnetization that was concurrently acquired during the first heating.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210200
0
1
0 1
M/M
max
0 0
4010-4
0
1002*10-4
IRM
(A
m2 /
Kg)
0
702*10-3
0 0 0
20
3*10-5
0
a
b c
d e
Applied field (Tesla)
IRM
IRM
(A
m2 /
Kg)
IRM
(A
m2 /
Kg)
IRM
(A
m2 /
Kg)
susc
eptib
ility
(10
-5 S
I)
susc
eptib
ility
(10
-5 S
I)su
scep
tibili
ty (
10-5
SI)
susc
eptib
ility
(10
-5 S
I)
0 200 400 600temperature oC
694.77a696.96a
704.39a 703.49a
693.80694.77696.96703.49704.39759.45
0 200 400 600temperature oC
0 200 400 600temperature oC
0 200 400 600temperature oC
Fig. 4. IRM acquisition (a) and three-component IRM thermal demagnetization [27] and corresponding weak field susceptibility evolution (b–e)
for representative samples. IRM absolute intensities are listed Table 4, column 4. Solid circles indicate the soft component, 0.12 T field; open
squares indicate the medium component, 0.4 T field; small diamonds indicate the hard component, 1.2 T field, and black triangles indicate
susceptibility. In most specimens, the soft component shows unblocking temperatures around 580 8C, the Curie temperature of magnetite but
inflexions around 230–270 8C (c and d) suggest the presence of greigite and others FIS. Coexisting with magnetite and iron sulphide is a high
coercive component with unblocking temperatures of 680 8C, most likely hematite (c and e).
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 201
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210202
the well-consolidated samples, at least 95% of the
remanence is demagnetized by heating to 570 8C or
by 50 mT AF (e.g., Fig. 3, samples 704.39 and
759.45). The dominant magnetic carrier is therefore
identified to be magnetite. The second category has
samples which do not demagnetize completely by 100
mT AF and thus include a significant quantity of high
coercivity magnetic carriers (e.g., Fig. 3, samples
694.77 and 703.49). Some of these samples, such as
694.77b were not entirely demagnetized by 570 8C,suggesting that the magnetic carrier is hematite. The
percentage of residual remanence after AF demagnet-
ization is tabulated in Table 3 (CRMRES). Type 1
sample 704.39b shows a magnetite unblocking
temperature spectrum between 500 and 580 8C.Chemical instabilities occurring during heating above
500 8C prevent a better characterization of the
magnetic carriers in many samples. For several
samples, a slight break in slope in the thermal
demagnetization curve around 300 8C suggests the
presence of FIS.
Table 4
Occurrence of the magnetic carriers and calcite content
Sample ARM (I) ARM (II) ARMgain
(10�6 Am2/kg) (10�6 Am2/kg) (%)
693.80a* 2.77 2.82 1.8
693.88a* 2.41 2.41 0.0
694.77a (694.77c) 3.18 5.30 67
695.12a* 3.12 10.4 230
696.56 4.22 8.90 110
696.96a* 4.19 10.6 150
699.00a* 3.80 21.6 470
700.28a (700.28c) 3.91 19.7 400
700.57a* 4.69 6.71 43
700.67 4.77 11.9 150
703.43 4.82 5.01 3.9
703.49a* 4.24 4.28 0.9
703.59 4.71 4.99 5.9
704.39a (704.39c) 3.50 46.1 1200
706.22a* 4.28 12.6 190
706.69a* 3.90 10.8 180
759.90a (759.90c) 4.04 20.1 400
759.45a (759.45c) 3.66 24.3 560
762.58a (762.58c) 4.08 41.2 910
765.35a (765.35c) 3.77 5.87 56
Column 1, samples bracketed (index c) are as control, samples without in
with asterisk are poorly consolidated. Column 2, ARM(I) is ARM before
ARMgain=(ARM(II)�ARM(I))/ARM(I)�100; Column 5, IRMMAX is IRM
T and 0.3 T; column 7, FISTEST =(IRM(230 8C)�IRM(320 8C))/IRM(320
content is obtained by quantification of CO2 released by phosphoric acid
Sample 700.28a broke after being demagnetized at
5 mT AF. The sample was reglued, however several
fragments could not be placed in their original
position. The magnetic moment of the sample
dropped from 6.5�10�7Am2 to 1.04�10�7Am2, a
drop of 80% while the sample only lost 6% of its
weight. We conclude that the poorly consolidated part
of the sample holds a high concentration of the
magnetic carriers. The unglued fragments were recu-
perated for further experiments, and this new sample
was called 700.28CHIPS.
4.2.3. Identification of the magnetic carriers
Isothermal remanent magnetization (IRM) acquis-
ition curves were measured for all the (a) specimens in
order to better characterize the magnetic carriers. For
most well-consolidated samples, 95% of IRM satu-
ration was acquired by 0.3 T, while for most of the
rest, saturation did not occur in applied fields up to
1.25 T (Fig. 4a). The ratio IRMHEM (defined as the
IRM acquired in 1.2 T over the IRM acquired at 0.3 T)
IRMMAX IRMHEM FISTEST CaCO3 F5% rel
(10�6 Am2/kg)
120 2.60 0.18 0.026
73.9 1.88 0.37 0.058
209 (56) 1.48 (1.06) 0.24 2.5
336 1.17 0.37 0.48
152 1.07 0.39 1.1
213 1.05 0.39 2.3
450 1.02 0.40 1.9
732 (52) 1.03 (1.06) 0.30 1.9
124 1.08 0.45 1.6
166 1.07 0.32 1.6
138 1.80 0.39 0.44
88.9 1.30 0.36 0.33
94.5 1.39 0.32 0.44
1682 (42) 1.01 (1.10) 0.29 0.77
328 1.28 0.33 0.77
383 1.09 0.41 0.34
386 (52) 1.03 (1.08) 0.29 10.0
319 (43) 1.02 (1.08) 0.29 14.6
653 (49) 1.01 (1.09) 0.32 12.2
96.3 (47) 1.05 (1.10) 0.33 12.9
dex where used for the choice of experimental parameters, samples
treatment; columns 3, ARM(II) is ARM after treatment; column 4,
acquired in 1.2 T; column 6, IRMHEM is ratio of IRM acquired in 1.2
8C) is used an indicator of the presence of FIS; column 8, calcite
. Precision for the calcite content is F5% of the calcite content.
-0.8
-1
110-3Am2/Kg
0.8T
-60
6010-3Am2/Kg
-0.8
-60
6010-3Am2/Kg
-0.8
a
b
e
fd
10-3Am2/Kg
-80
80
-0.8 0.8T
10-3Am2/Kg
-0.8
6
-6
g
h
40010-3Am2/Kg
-0.8
-400
10-3Am2/Kg 300
-300
15
-15
10-3Am2/Kg
-0.8 -0.8
c
Applied field(T) 0.8
Applied field(T) 0.8
Mag
netiz
atio
n
Mag
netiz
atio
n
Mag
netiz
atio
nM
agne
tizat
ion
Mag
netiz
atio
n
Mag
netiz
atio
n
Mag
netiz
atio
n
Mag
netiz
atio
n
Fig. 5. Hysteresis curves in fields up to 0.8 Tesla: total curve in (a), (c), (e), and (g), and with the paramagnetic component removed in (b), (d), (f), and (h). (a) and (b) for the unheated
sample 699.76; (c) and (d) for the sample 704.39 heated at 150 8C for 7 days confined in argon at atmospheric pressure; (e) and (f) for sample 699.76 heated at 180 8C for 2 weeks
under 100 MPa pressure; (g) and (h) for 700.28CHIPS.
M.G.Morea
uet
al./Earth
andPlaneta
ryScien
ceLetters
230(2005)193–210
203
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210204
has a large range from 1 to 2.6 in the (a) specimens,
while the unheated (c) specimens never have
IRMHEMN1.15 (Table 4, column 6). Thus carriers
with a large range of coercivity have been created by
the laboratory heatings.
Following the method of Lowrie [28], three
orthogonal IRMs (hard: 1.2 T, medium: 0.4 T, and
soft: 0.12 T) were applied to samples which were then
thermally demagnetized. Three different behaviors
were observed. For the first group (e.g., Fig. 4b), the
soft component is dominant, with unblocking temper-
atures up to 580 8C and a slight break in slope
observed between 230 and 330 8C typical of FIS
(ferrimagnetic iron sulphide). There is little medium
and hardly any hard component, and they demagnetize
by 600 8C. These samples, dominated by magnetite,
are the most consolidated of the samples with the
exception of sample 694.77. The second group (e.g.,
Fig. 4c and d) is similar to the first group except that
the remanence drops suddenly at 270 8C, principallyvisible in the soft component, and probably owing to
alteration of greigite [29,30]. The medium and hard
components are sometimes bigger than in the first
group, and they demagnetize between 630 and 690 8C,indicating the presence of hematite. This group
includes all the friable samples except for 693.80a.
The third group, consisting of samples 693.80a et
694.77a (Fig. 4e), hold hematite but show little
evidence for any FIS. The hard and medium compo-
nents are larger and they have unblocking temper-
atures up to 690 8C.Hysteresis curves were measured using a vibrating
sample magnetometer built by Maxime LeGoff
(Institut de Physique du Globe de Paris). Only
samples with relatively high magnetic concentrations
gave usable results, so we studied the two samples
Table 5
Hysteresis parameters
Sample JS(Am2/kg)
JRS(Am2/kg)
699.76 0.012 0.0041
700.45 0.038 0.012
704.39 0.0051 0.0018
700.28 CHIPS 0.256 0.116
Two samples heated to 180 8C with 100 MPa pressure argon, sample sho
heating experiments and 700.28CHIPS. JS: saturation magnetization; JRS:
coercivity of remanence.
heated to 180 8C under high pressure (from the
preliminary experiments, Fig. 5e and f) and their
unheated pairs (Fig. 5a and b), the sample showing the
greatest increase in ARM during the atmospheric
pressure heating experiments (Fig. 5c and d), plus the
700.28CHIPS sample (Fig. 5g and h). In the untreated
samples, magnetization at 0.8 T is N95% due to
paramagnetic minerals (Fig. 5a). On subtraction of the
paramagnetic component, the ferromagnetic magnet-
ization is seen to be weak and the curves are too noisy
to determine the hysteresis parameters (Fig. 5b). In
contrast, the heated samples have paramagnetic
magnetization below 75% of the total under an
applied field of 0.8 T (Fig. 5c, e, and g). The
ferromagnetic components offer noisy (Fig. 5d) or
well-defined hysteresis cycles (Fig. 5f and g) which
reach saturation by 0.3 T, indicating magnetite as the
dominant ferromagnetic mineral. The form of the
curve, without apparent inflections, suggests the grain
sizes are homogeneous [31]. The saturation magnet-
ization ( JS), saturation remanence ( JRS), coercive
field (HC), and coercive field of remanence (HCR) are
reported in Table 5. The ratios JRS/JS near 0.3 and
HCR/HC near 1.5 indicate the grains are in the single
to pseudo-single domain size range (around 0.1 Am,
by comparison with the data compiled by Dunlop
[32]). Since the hysteresis cycles shown in Figs. 5d, f,
and h are very similar, we propose that the magnetic
carriers are the same in these samples.
4.2.4. Occurrence of the magnetic carriers
The magnetic carriers of CRM apparently vary
according to the samples’ consolidation. As this
property seems to be related to the calcite content,
calcite was quantified in the levels of the studied
samples. The calcite content (Table 4, column 8) is
JS/JRS HCR
(mT)
HC
(mT)
HCR/HC
0.34 28 17 1.6
0.31 23 15 1.5
0.35 25 18 1.4
0.45 32 23 1.4
wing the greatest increase in ARM during the atmospheric pressure
remanence magnetization after saturation; HC: coercive force; HCR:
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 205
obtained by manometric quantification under vacuum
of the CO2 released from the powdered sample by
phosphoric acid at 25 8C for 4 h. Reproducibility is
better than F5% of the calcite content. Blanks are
negligible. The possible occurrence of dolomite was
checked by quantifying the subsequent CO2 released
at 100 8C for 2 h. Dolomite content was lower than
10% of the calcite content.
In order to examine the relation between calcite
content and the occurrence of different magnetic
calcite content (%)
150 105
1.15
2.5
IRM
HE
M
calcite con
1
10
100
1000
AR
M g
ain
(%)
0 1
a
b c
0
0
0
FIS t
est
0
Fig. 6. Occurrence of magnetic carriers as a function of the concentration o
the symbols used depend on the nature of the magnetic carriers identified in
the presence of FIS (ferrimagnetic iron sulphide), and a diamond marks t
shaded zone indicates the samples for which the ARM gain is below 1
significant growth of hematite or FIS. Above the 0.5% calcite threshold, th
and (c) FISTEST indicate the appearance of FIS and hematite below 3% c
carriers of CRM, we defined criteria for the recognition
of these carriers.
The gain in ARM acquired after heating [i.e.,
ARMgain=(ARM(II)�ARM(I))/ARM(I)] depends
mostly on the quantity of magnetite created (Table 4,
columns 2–4).
The IRM acquired above 0.3 mT is mostly held by
hematite. Thus we use IRMHEM=IRM(1.25 T)/
IRM(0.3 T) as a measure of the relative contribution
of hematite (Table 4, column 6).
tent (%)152 10
FIS
magnetitehematite
.15
.35
.45
calcite content (%)
150 105
.25
f calcite (Table 5). (a) ARMgain is plotted on a logarithmic scale and
the samples. A cross marks the presence of hematite, a circle marks
he presence of magnetite. In samples containing b0.5% calcite, the
0%, where formation of new magnetite is uncertain, but there is
ere is no apparent dependence on calcite concentration. (b) IRMHEM
alcite concentration.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210206
In the IRM thermal demagnetization curves, the
drop in intensity at 270 8C (Fig. 4) is distinctive and
typical of demagnetization or alteration of ferrimag-
netic iron sulphides, FIS. FIS Curie temperatures range
up to 320–330 8C, so we define FISTEST=(IRM(230
8C)�IRM(320 8C))/ IRM(320 8C). When there is an
observable inflection point in the thermal demagnet-
ization plots (e.g., Fig. 4, samples 696.96 and 706.49),
FISTEST is higher than 0.35, conversely when the drop
is not visible FISTEST is lower than 0.35 (Fig. 4, sample
704.39). Therefore, in this study the FISTEST is used as
an indicator of the presence of FIS (Table 4, column 7).
The relative quantity of magnetite created
(ARMgain, Fig. 6a), the relative contribution of he-
matite (IRMHEM, Fig. 6b), and the test of presence
of FIS (FISTEST, Fig. 6c) are plotted as a function of
the quantity of calcite. Magnetite is clearly present
when ARMgainN10%. FIS seems to be present when
FISTESTN0.35. There is new hematite when IRMHEMN
1.15, because the highest value of IRMHEM in unheated
samples is 1.14 (Table 4, column 6). Thus, Fig. 6a
shows that when there is less than 0.5% calcite, the
creation of magnetite is rare (2 of 7 samples). Above
0.5% calcite, magnetite is formed, however the
quantity bears little dependence on the percentage of
calcite. Figs. 6b and c show that FIS and hematite are
never present in samples with N10% calcite, but this
threshold might be as low as 3% since we have no data
between 3% and 10% calcite.
5. Microscope study of the magnetic minerals
Magnetic characterization of the newly formed
magnetic minerals was complemented by a scanning
electron microscope study to investigate their shapes,
sizes, growth habits, and composition. We performed
back scattered electron imaging using a Jeol
JSM840A, with semi-quantitative elemental compo-
sition measured by electron microprobe X-ray fluo-
rescence using energy dispersive spectrometry with a
Si–Li detector.
It is almost impossible to image single-domain or
pseudo-single-domain magnetite grains in sediments
because (1) the grain sizes are almost always smaller
than the best resolution of the SEM (~1 Am), and (2) the
quantity of magnetite is usually extremely low. Since
the saturation magnetization of magnetite at room
temperature is 92.4Am2/kg, the untreated samples with
saturation magnetizations below 10�3 Am2/kg (Fig. 5)
have magnetite concentrations below 1/100 000. The
hysteresis curves for the strong samples (the two
samples heated under high pressure at 180 8C during
the preliminary experiments, and residual sample
700.28CHIPS) display saturation magnetizations (Table
4; Fig. 5), which correspond to magnetite concen-
trations of 0.01% to 0.03% for the samples heated
under pressure and 0.3% for 700.28CHIPS.
These three samples were used for the microscope
study because of their relatively larger magnetite
concentrations. The largest piece of 700.28 CHIPS was
imaged directly. For both levels 699.76 and 700.45 we
looked at magnetic concentrates from 3 sister samples:
one untreated, one heated at 150 8C confined at
atmospheric pressure with argon, and one heated at
180 8C confined at 100 MPa by argon. These were
desegregated in distilled water with acetic acid to
dissolve the carbonate minerals. The pH of the
suspension was maintained above 4 to preserve the
iron minerals from dissolution. The powder was
sieved, and the coarse fraction was broken with
mortar and pestle until all could pass through a 50
Am mesh. The samples in suspension were circulated
through an apparatus similar to that described by
Hounslow and Maher [33], with which the magnetic
minerals are gathered on a glass sleeve containing a
permanent magnet.
No magnetic material was extracted from the
untreated sample using this method, so a strong rare
earth magnet held in a thin rubber sleeve was moved
through the suspension while it was agitated in an
ultrasonic bath. This method collected some material,
of which a small fraction was ferromagnetic. For the
three samples of each of the two levels 699.76 and
700.45, the extracted quantities (almost none for the
natural sample, a small amount for the sample heated
at atmospheric pressure, and about 10 times more for
the sample heated under high pressure) correlate well
with the ARM(II) (Table 1).
In the untreated sample, a few oxide and sulphide
grains were located among the mass of clays. The
magnetic grains, with sizes ranging from a few to
30 Am, have been identified as titanomagnetites and
ilmenites as well as one cuprite. The fine grains up
to 10 Am are isolated crystals or framboids of pyrite.
In the heated samples, there are also grains of
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 207
titanomagnetite or ilmenite and a few pyrite cubes.
In contrast, the most numerous grains were pyrite
framboids. These framboids form almost the entire
collection of grains extracted from the sample heated
at high pressure. Pyrite in its pure state is para-
magnetic, with a susceptibility 104 times weaker
than that of magnetite. In the low fields produced by
the permanent magnet used for magnetic extraction,
no pyrite should have been isolated. Both the fact
that pyrite was isolated and that the amounts of
pyrite extracted magnetically correlate with the
amounts of magnetite determined independently,
suggest that these pyrite framboids have been partly
oxidized to magnetite. Magnetite couldn’t be iden-
tified using the electron microprobe (~1 Am)
Fig. 7. Scanning electron microscope images of sample 700.28CHIPS. (a) P
pyrites are bright; (b) detail of a zone with concentrated pyrites; (c) rhom
probably because they are too small to be resolved by
this technique. However the amount of pyrite extracted
apparently reflects the amount of newly formed
magnetite.
A piece of 700.28CHIPS was examined as a whole
in order to study the environment in which magnetite
has the greatest probability of crystallizing. The
images show that, as well as a groundmass of clay
(Fig. 7a), there is a large concentration of pyrite
(approximately 20% as opposed to the 0.5 to 2%
estimated from the other samples; Fig. 7b). These
pyrites are found both in the form of rhombohedra
(Fig. 7c) and framboids (Fig. 7d). This observation
confirms that the formation of magnetite is intimately
associated with the pyrite in these samples.
hoto of the largest piece. The clay minerals are imaged dark and the
bohedric pyrite, (d) framboidal pyrite.
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210208
6. Discussion
The results outlined above show that magnetic
minerals, mostly magnetite, are formed at temperatures
as low as 150 8C in these argillaceous sedimentary
rocks when they are confined in an inert gas at
atmospheric pressure. This study shows that (i)
magnetic carrier formation involves a fluid produced
by the sample, (ii) magnetic carriers are closely
associated to pyrite, and (iii) the mineralogy of the
new magnetic carriers is linked to the abundance of
calcite in the sample.
Occurrences of secondary magnetite grown at the
expense of pyrite have already been observed
[8,9,17]. In the case of the Belden formation
(Colorado) the magnetite is present as a rim in
replacement of the pyrite in some coprolites con-
stituting a reducing micro-environment. In an exper-
imental study undertaken to explain the replacement
of pyrite by magnetite in the Belden formation,
Brothers et al. [10] have experimentally demonstra-
ted that organic acids when complexed to ferric
(Fe3+) ions, allow the oxidation of pyrite. They
further propose that the neutralization of the acidity
generated by this oxidation by carbonate dissolution
would allow dissolved ferrous iron to precipitate as
magnetite. A process of this type may account for
the formation of new magnetic minerals in our
samples.
The samples studied here are mainly composed of
clay minerals, contain organic matter (between 1% and
6% [26]) and have never been buried below 1 km or
heated above 50 8C throughout their geological history
[26]. Heated at 150 8C, they are expected to produce
water by dehydration of clays [34] and organic
molecules (organic acids and/or hydrocarbons) by the
maturation of organic matter [35–40]. Such a mixture
of water and organic molecules with iron or sulfur
bearingminerals is expected to produce redox reactions
[41,42]. The source of ferric ions, necessary for the
proposed process [10], could be the clay transformation
of smectite to illite [43,44]. The formation of magnetite
only in samples containing more than 0.5% calcite
suggests that the acidity was buffered by calcite
dissolution as suggested by Brothers et al. [10]. When
there was insufficient calcite to neutralize the acidity,
only FIS could precipitate [45]. Such a precipitation of
FIS was not observed by Brothers et al. [10] because
the experimental conditions were too basic and too
oxidizing for FIS formation. During their experimental
magnetite formation stage, the presence of nitrate in the
solution they used increased the pH.
The coexistence of hematite and FIS is more
surprising. From a thermodynamic point of view they
should not be present together. Two hypotheses could
account for this observation: an oxidation of iron
sulphides during the heating step in open air at 150 8Cfollowing the experiment (designed to remove any
thermo-viscous remanent magnetization), or, local
heterogeneous control on the formation of the iron-
and/or sulphide-bearing minerals during the experi-
ment. Since the samples containing hematite are
unconsolidated, and are therefore highly permeable
to air, hematite formation could be due to some air
remaining in the porosity of the sample at the
beginning of the experiment or to the recrystallization
of oxidized phases formed during the 12 years
between core extraction and these experiments.
7. Conclusion
In summary, the major results obtained in this
experimental study are
1. magnetic carriers are produced at temperatures as
low as 150 8C in these argillaceous sedimentary
rocks when they are heated while being confined
in an inert gas,
2. fluids generated by sample heating are necessary
to the synthesis of the magnetic carriers,
3. the location and amount of newly formed
magnetic carriers are highly heterogeneous and
physically associated with pyrite crystals,
4. the calcite content controls the nature of the
newly formed magnetic carriers.
Even if the exact hydrothermal conditions of burial
have not been reproduced in these laboratory experi-
ments, and if the samples had been altered since their
coring, these observations can be used to improve the
understanding of some cases of remagnetization. Our
experiments suggest that sedimentary rocks can be
remagnetized during burial diagenesis with fluids
produced in situ during burial. In this hypothesis,
both organic matter maturation and clay transforma-
M.G. Moreau et al. / Earth and Planetary Science Letters 230 (2005) 193–210 209
tion appear to be key elements for such a remagne-
tization. The new magnetic carriers form locally in
micro-environments inherited from early diagenesis,
probably where organic matter and pyrite are con-
centrated; the nature of the newly formed magnetic
carriers being controlled by lithologic parameters.
Characterization of (i) the chemistry of the fluid
produced, (ii) the claymineral transformations, and (iii)
the organic matter maturation during the experiments
would help in understanding the processes associated
with the formation of new magnetic carriers in our
laboratory experiments and in sedimentary basins.
Acknowledgments
Core samples and unpublished reports were gen-
erously made available by ANDRA. High pressure
preliminary experiments were performed by J. Roux at
the Centre de Recherche sur la Synthese et la Chimie
desMineraux in Orleans (France). We are grateful to G.
Marolleau for his help with the high pressure experi-
ments in the Laboratoire de Geologie at Ecole Normale
Superieure de Paris. Fruitful discussions with F.
Brunet, V. Courtillot, M. Thiry, J. Trichet and B. Velde
were much appreciated. The manuscript was much
improved due to the careful reviews done by Mark
Dekkers andMaria Cioppa. This is a IPGP contribution
No. 2020 and G.S.C. publication 2002260.
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