PALEOCEANOGRAPHY, VOL. 16, NO. 4, PAGES 368-389, AUGUST 2001
Sedimentation rates in the Makarov Basin, central Arctic Ocean:
A paleomagneticand rock magnetic approach
Norbert R. Nowaczyk
GeoForschungsZentrum
Potsdam,Projektbereich
3.3, Laboratoryfor Paleo-and Rock Magnetism,Potsdam,Germany
Thomas W. Frederichs
FachbereichGeowissenschafien,
Universit[itBremen,Bremen,Germany
Heidi Kassens,Nils Norgaard-Pedersen,
and RobertF. Spielhagen
GEOMAR, Kiel, Germany
Riidiger Stein and Dominik Weiel
Alfred-Wegener-Institute
for Polar and Marine Research,Columbusstrasse,
D-27568 Bremerhaven,Germany
Abstract. Three long sedimentcoresfrom the Makarov Basinhave been subjectedto detailedpaleomagneticand rock
magneticanalyses.Investigatedsedimentsare dominatedby normalpolarityincludingshortreversalexcursions,indicating
thatmostof the sedimentsare of Brunhesage.In general,the recoveredsedimentsshowonly low to moderatevariabilityin
concentration
and grain sizeof the remanence-carrying
minerals.Estimationsof relativepaleointensity
variationsyieldeda
well-documentedsuccessionof pronouncedlows and highs that could be correlatedto publishedreference curves.
However,
together
withfiveaccelerator
massspectrometry
•4Cagesandanincomplete
løBerecord,
stilltwodifferent
interpretations
of thepaleomagnetic
dataarepossible,
withlong-term
sedimentation
ratesof either1.3or 4 cmkyr-•.
However,
bothmodels
implicate
highlyvariable
sedimentation
ratesof upto 10cmkyr-•, andabrupt
changes
in rock
magneticparametersmight even indicateseveralhiatuses.
1.
Introduction
Chronostratigraphic
investigationsof Arctic Ocean sediments
often suffer from the fact that the sedimentsare mostlybarrenof
biogenic relicts. Owing to low bioproductivityand additional
carbonatedissolution,foraminifersare rarely found,sothat neither
direct
dating
through
theaccelerator
mass
spectrometry
(AMS)•4C
methodnor oxygenisotopestratigraphycan be performed.On the
otherhand,the almostpurely lithogenicdepositsgenerallycarry a
strong magnetization.Thereforemagnetostratigraphic
investigations, i.e., determinationof the magnetizationdirectionsas well
as characterizationof the magnetic minerals by detailed rock
magneticanalyses,offer a powerful stratigraphictool. Depending
on the sedimentation
rate, the succession
of major reversals,such
as the Matuyama Brunhesreversal,or short-livedgeomagnetic
reversal excursions within the Brunhes Chron, such as the
relative paleointensityvariationsof the geomagneticfield [e.g.,
Tauxe and Valet, 1989; Tauxe, 1993]. A stack of 33 relative
paleointensityrecordswith different temporal resolution from
nearly all over the globe coveringthe time interval back to 800
ka createdby Guyodo and Valet [1999] proved that the Earth's
magneticfield intensitywas highly variable throughoutthe geologichistory.This mediumresolution"SINT800" stack,generally
characterizedby a successionof pronouncedlows and highs,
providesa new magnetochronostratigraphic
referencedatabasethat
is not based on the directionalbut intensity variations of the
geomagneticfield. Individual,high-resolutionrelative paleointensityrecords,suchasthe OceanDrilling Program(ODP) 983 record
[Channellet al., 1997], can evengive a muchmore detailedimage
of the geomagneticfield variationsthan the stackeddata and can
thereforeprovidean evenmoredetailedreferenceframe for dating
sedimentarysequences
of Brunhesage. However, our intentionis
not to providea furtherpaleointensity
datasetfor referencebut to
derivean agemodel of the Makarov Basinsedimentaryrecordsby
usingpaleointensityvariationsas a "global correlationtool," as
suggested
by, for example,Channellet al. [2000] or Stoneret al.
[2000].
Laschamp[Bonhommetand Babkine, 1967; Gillot et al., 1979]
or the Blake [Smithand Foster, 1969] excursions,
can,in principle,
providea moreor lessdetailedagemodel.Justtheseshortreversal
excursionswere frequently found in Arctic marine sediments:
Iceland Sea [Bleil and Gard, 1989; Nowaczyk and Frederichs,
1999; V'dlkeret al. [ 1999], GreenlandSea [Nowaczykand Antonow,
1997; Nowaczyk,1997], NorwegianSea [Bleil, 1989], and Fram
Strait, BarentsSea, and easternArctic Ocean [Lovlie et al., 1986; 2. Geological Settings
Nowaczykand Baumann,1992; Nowaczyket al., 1994; Schneider
The triangular-shaped
MakarovBasin,with a maximumdepthof
et al., 1996;Nowaczykand Knies,2000; Knieset al., 2000]. In this
paper we present the first high-resolutionmagnetostratigraphic •3950 m, is •500 km wide along the East Siberian Shelf and
resultson long recordsfrom the Makarov Basin, central Arctic narrowstowardEllesmereIsland.As partof the AmerasianBasinit
Ocean. Besidesa correlationof the rock magneticpropertiesand
paleomagneticdirectionswe also applied the determinationof
Copyright2001 by the AmericanGeophysicalUnion.
Papernumber2000PA000521.
0883 -8305/01/2000PA000521
$12.00
368
represents
one•of the majorbathymetric
featuresof the central
Arctic Ocean, consistingof the Wrangel and Siberia Abyssal
Plains,which are flankedby the Lomonosov,Alpha, and Mendeleev Ridges and borderedby the Siberianand CanadianShelves
[Weber and Sweeney,1990] (Figure 1). The Makarov Basin is
bisectedby the Marvin spur,a long,steepescarpment.
It is covered
by perennial sea ice of 2-3 rn thickness[Jokat et al., 1999;
NOWACZYK
ET AL.' MAKAROV
-150 ø
BAS1N MAGNETOSTRATIGRAPHY
180 ø
369
150 ø
Chukchi Sea
East Sibirian Sea
Beaufort Sea
Siberian
Islands
Canada
Basin
PS2180-2
PS2180-1
PS2178-3
PS2178-5
GPC
GKG
GPC
KAL
Severnaya
Zemlya
,
•
Kara Sea
Land
Barents
30 ø
0o
Scale:
1:11323951
at Latitude 90 ø
Figure 1. Coringsitesin the Arctic Ocean.
Rothrocket al., 1999] driven by the main drift patternsof the
BeaufortGyre and/orthe TranspolarDrift [Reimnitzet al., 1992].
The MakarovBasinprobablyevolvedparallelto the openingof
the CanadaBasinby eitherseafloorspreading
androtationalrifting
[Grantz et al., 1990] or crustalextensionprocesses
[Colesand
Table 1. AverageHoloceneSedimentation
Rates in the Arctic
Ocean
Sedimentation
Area
Rate,cmkyr-t
l•eference
a
Nansen Basin
Nansen Basin
0.7 - 0.8
2.1 - 16.9
1
2
GakkelRidge
GakkelRidge
0.6-1.3
0.7-10
1, 3, 4
2
Amundsen Basin
Amundsen Basin
0.5 to >2.0
0.7- 3.7
1
2
LomonosovRidge
LomonosovRidge
0.8-1.1
0.1- 3.0
1
2
Makarov Basin
Makarov Basin
0.4
1.4-2.1
1
2
Alpha-Mendeleev
Ridge
0.1
5
Canada Basin
0.1-0.2
6
aReferences:
1, Steinet al. [1994b];2, Gard [1993]; 3, K6hler [1992]' 4,
Mieneft et al. [1990]; 5, Darby et al. [1989]; 6, Scottet al. [1989].
Taylor, 1990 during Late Cretaceous(Hauterive) and earliest
Tertiary,i.e., between•--•120and 56 Ma. It experienced
tensional
faultingduringor shortlyafterthe formationbeforemostof the
overlyingsediments
were deposited[Weberand Sweeney,1990].
The MakarovBasinis incompletelyfilled with sedimentary
deposits of •--•3.5-6 km thicknessof well-definedhorizontallystratified,
unconsolidated
sediments.They were obviouslydepositedfrom
turbiditycurrentsthat flowedfromthe EastSiberianShelfacross
WrangelAbyssalPlainontothe SiberiaAbyssalPlain,wherethey
areinterspersed
with glacialmarinematerial[Weberand Sweeney,
1990; Sweeneyet al., 1990]. The long-termterrigenousinput
depends
on sediment
supplyfromtheborderingshelves,frequency
of turbidites,raftingof seaandglacialice, erosionandredeposition
of silt-andclay-sized
materialby currentactivity(winnowing),and
pelagicsedimentation
[Clark et al., 1980; Morris et al., 1985;
Jacksonet al., 1990;Schiiper,1994;Steinet al., 1994a;Steinet al.,
1994b;Jokat et al., 1999]. AverageHolocenesedimentation
rates
(Table1) indicatequitedifferentvaluesfor theindividualunitsof
the central Arctic Ocean.
3.
Material
and Methods
The coringsites(Table2) arelocatedin the MakarovBasinnear
the easternflank of the LomonsovRidge,•--•45km apart(Figure1).
The recovered sedimentsconsistof alternating light brownish
370
NOWACZYK
ET AL.:
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
Table 2. Location,Water Depth, Length of SedimentCoresand SampleSpacingof PaleomagneticSamplesPresentedin
This Study
Core
PS 2178-3
PS 2178-5
PS 2180-1
PS 2180-2
Latitude,
Longitude,
Water Depth,
Recovery,
SampleSpacing,
Typea
øN
øE
m
cm
cm
GPC
KAL
GKG
GPC
88ø00.3•
88ø01.5•
87037.6'
87ø38.6•
159ø10.1•
159ø42.2•
156040.5'
156ø58.3•
4009
4008
4005
3991
1372
831
48
1296
3
4
5
aGPC,giantpistoncorer(diameter
O of 10cm,25 m length);KAL, square
barrelKastenlot
corer(30 x 30 cm,12m length);GKG, large
box corerGrosskastengreifer
(50 x 50 cm, 0.6 m height).
monitor relative magnetic grain size changesof the magnetic
fraction.Additional rock magneticmethodswere appliedto samples from core PS 2180-2. Isothermalremanentmagnetizations
(IRM) were imprintedwith a pulsemagnetizerand measuredwith
a fluxgate spinnermagnetometer.Then 176 out of 251 samples
were stepwiseexposedto increasingpeak fields of up to 1500 mT
Therefore
nostable
oxygen
isot•?curve
could
bederived
from along their positive z axis in order to record complete IRM
the long cores.Only five AMS C agesare availablefor the box acquisitioncurves.The remainderof the samplecollectionwas
corer PS2180-1 for the upper 15 cm (Table 3).
exposedto a field of 1500mT only.The IRM acquiredat 1500mT
Thecores
weresampled
with6.2 cm3 plastic
cubes,
each3-5 is definedas "saturation"isothermalremanence(SIRM). Finally,
cm (Table 2), generallyavoiding sandy layers,yielding a total the intensityratio of ARM to SIRM was calculatedas another
collectionof nearly 900 samples.Magnetic volume (low field) estimateof relativemagneticgrainsizechanges.All samplesfrom
susceptibility
•LF of thepaleomagnetic
sampleswasmeasured
with corePS2180-2 were alsousedfor determinationof the anisotropy
a Kappabridge
KLY3S(sensitivity
of 1.2x 10-8 SI).A subcoreof magnetic susceptibilityusing the anisotropyoption of the
from the box corer taken at site PS2180 was logged with a KLY3S; that is, susceptibilityis numerouslymeasuredwhile the
Bartington MS2F sensorapplying the technique describedby sample is rotating around the x, y, and z axes, respectively.
Nowaczyk and Antonow [1997]. Measurementsof the natural Measurements
from the threeorthogonalplanesare combinedwith
remanentmagnetization(NRM) were performedwith three-axis one bulk measurementin order to createa completeanisotropy
cryogenicmagnetometers.
All sampleswere demagnetizedin 8tensor,represented
by the generalsusceptibilities
Kmax(maximum),
10 stepswith a maximum alternatingfield (AF) amplitudeof 100 rint (intermediate), and rmi n (minimum) and their respective
mT in order to remove viscous overprints. The characteristic orientation angles, declination,and inclination, with respectto
remanentmagnetization(ChRM) of each samplewas determined samplecoordinates.
Accordingto Nowaczyk[1997], estimationsof
by subjectingits demagnetization
resultsto principle component relativepaleointensity
variationswere calculatedby dividingNRM
analysis[Kirschvink,1980].
intensitiesafter 50 mT AF demagnetization
by (1) the low field
All samples were subjected to some basic rock magnetic magneticsusceptibility•LF, (2) the SIRM intensity,and (3) ARM
analyses.Anhystereticremanent magnetizations(ARM), as a intensities, also after demagnetizationwith 50 mT, and then
measureof concentrationof magneticminerals,were generated normalizingeachcurveto its average.
alongthe samples'positivez axiswith 0.05 mT staticfield and 100
mT AF amplitude.ARM were also measuredwith a cryogenic
Results
magnetometerand demagnetizedat the sameAF levels that were 4.
used for NRM demagnetization(up to 65 mT). The median 4.1. Paleomagnetism
destructivefield of the ARM (MDFARM) and the ratio •ARM/•LF
The coreswere recoveredcloseto the geographicNorth Pole.
(•AP• is anhystereticsusceptibility,ARM intensity,divided by
Here ChRM declinationsapparentlyshowa large scatterbecause
static field amplitudeof 0.05 mT) were determinedin order to
owing to the geomagneticsecularvariationthe geomagneticpole
canmigrateto positionssouthof the coringsitesevenduringstable
phasesof the geodynamo[e.g., Merril and McElhinny, 1983,
Table 3. Accelerator
MassSpectrometry
(AMS) 14CAges Figure 4.4]. Consequently,the paleomagneticresultsof the three
Determined for Core PS2180-1
cores are discussedmainly on basis of the ChRM inclinations
(Figure 2), the most significantpaleomagneticparameterat such
Age• ka
highlatitudes(88øN).ChRM directions
in therecoveredsediments
Depth•cm
Uncalibrated
Calibrated
a
are
clearly
dominated
by
normal
polarity,
i.e., steep positive
0.0
2.42
1.99b
inclinations,indicatinga Brunhesage for most of the sediments.
4.5
7.26
7.67b
However, six short intervals of steep negative inclinationsare
8.5
16.23
18.74b
documentedwithin the cores.Below the inclinationspike6 (Figure
12.5
35.02
38.60 c
14.5
37.35
40.85 c
2) the directionsin the lower •2 m of the pistoncoresexhibitonly
aRadiocarbon
ages,afterapplying
a constant
reservoir
effectof 440years a limited similarity,possiblycausedby the coringprocess.There
are also differencesin the inclinationpatternsbetweenthe Kas[Mangerudand Gulligsen,1975], were convertedto calendaragesby the
tenlot (KAL) and the pistoncore (GPC) from Site PS2178. Some
sandysiltsand light greenish-gray
silty clay. The contentof total
organic carbon (TOC) rangesfrom 0.1 to 0.5%. The carbonate
contentis generallyvery low (<0.2%), with somedistinctpeaks
reaching6% [Schubertand Stein, 1996]. However,below • 15 cm
biogeniccarbonate,coccolithsor foraminifersare rarely found in
the sedimentsrecoveredfrom the Makarov Basin [Gard, 1993].
CALIB 4.3 calibrationprogramby usingthe calibrationdatasetsof Stuiver
et al. [1998]andStuiver
andReimer
[1993]and,beyond
20.314Cka,by
applyingthe age shift determinedby I;6lkeret al. [1998].
intervals of the Kastenlot, below inclination events 1 and 3, show
scatteredshallow inclinationsthat are lesspronouncedwithin the
pistoncore (Figure 2). Another generaldifference,althoughboth
bCalibration
datasetsof Stuiver
et al. [1998]andStuiver
andReimer coresoriginatefrom the same site (in the limits of keeping the
[ 1993] were used.
CAgeshiftdetermined
by IGlkeret al. [1998] wasused.
ship'spositionwithin driftingseaice), is thatthe inclinationpattern
of the piston core is elongatedwith respect to the inclination
NOWACZYK
ET AL.'
MAKAROV
Makarov
PS2178-3
( GPC )
-90 ø -60 ø -30 ø
0ø
30 ø
BASIN
Basin
MAGNETOSTRATIGRAPHY
- ChRM
inclination
PS2178-5
( KAL )
60 ø
90 ø
-90 ø -60 ø -300
0ø
30 ø
371
PS2180-2
( GPC )
60 ø
90 ø
-90 ø -60 ø -30 ø
0ø
30 ø
60 ø
90 ø
lOO
IO0
200
200
300
300
400
400
500
500
600
600
7OO
700
8OO
800
90O
900
E
v
E
lOOO
1000
11oo
11oo
1200
1200
1300
1300
1400
1400
-90 ø -60 ø -30 ø
>,,
0o
30 ø
60 ø
90 ø
.90 o .60 o .30 ø
0o
30 ø
60 ø
90 ø
-900
-60 ø -30 ø
00
30 ø
60 ø
90 ø
30%
30% _
o
--
:::3 20%
20%
O'
I,,I.
s,,.
lO%
lO%
0% ..............................................
•"'i
'"'i'i i TM I
.90 ø .60 ø .30 ø
0o
30 ø
60 ø
90 ø
I , , I , , I , , i , , i , , i , ,'•::'•0%
I''1''1''i''1''1''1
_90 ø .60 ø .30 ø
0o
30 ø
60 ø
90 ø
.90 ø -60 ø .30 ø
0o
30 ø
60 ø
90 ø
Figure 2. Inclination of the characteristicremanentmagnetization(ChRM) of the three long cores from the
MakarovBasin.A subsetof correlationlevelsis indicatedby dashedlines.Trianglesat theleft depthaxisof eachcore
indicatecorebreaks.Circlednumbersmark intervalsof reversedmagnetizations
as discussed
in the text. Histograms
at the bottomshowthe frequencydistributionof the ChRM inclinations.
372
NOWACZYK
ET AL.:
MAKAROV
BASIN
ij
MAGNETOSTRATIGRAPHY
u•op
i
i
i
i
i
_
,
u,•op -
-
_
i
i
i
i
I
i
i
i
i
i
-
''
i
''""'1''''1''''1''
o
'7,
•,
•
,
i
i
I
i
i
i
I
i
i
i
i
i
i
i
i
I
i
_
i
_
_
_
.
•m
_
uMop
x
_
_
_
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o
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i
NOWACZYK ET AL.' MAKAROV BAS1N MAGNETOSTRATIGRAPHY
o
CD
T'
I,,,,I,,,,I,,,,I,,,,I,,,,I,,,
0
( •uo ) q:ldop •uo•oq-qns
t•ouonboJ-I 'lOJ
373
374
NOWACZYK
ET AL.:
MAKAROV
BASIN
patternof the Kastenlotby • 15%. This is causedby the suctionof
the piston. An alternativeinterpretationcould be that sediments
within the Kastenlotare compressedsinceit works like a gravity
corer. However, recovery of the PS2178 Kastenlot was •96%,
calculatedfrom penetrationand lengthof the recoveredcore. This
MAGNETOSTRATIGRAPHY
allows an estimationof a maximum compactionof 4%, so that the
differencebetween the two cores is more likely due to suction
effectsin the pistoncorer.
Correlationof the reversedintervals,supportedby information
on sedimentcolor and other physical/magneticproperties(see
Makarov Basin-JARM( mA m )
PS2178-3
( GPC )
lOO
•"
PS2178-5
( KAL )
200
300
0
100
PS2180-2
( GPC )
200
300
0
lOO
200
300
lOO
lOO
200
200
300
300
400
400
500
500
600
600
7OO
700
800
800
900
900
E
o
.,Q
1 ooo
lOOO
11oo
11oo
1200
1200
300
1300
1400
1400
0
,,,
30%
100
, I,
,,
200
, ! ,
,
,,
300
I
0
,,,
100
, I,
, ,
200
, I ,
300
0
,,,
100
,,,,
I,,,,
200
300
I , , , ,
-
.
30010
.
-
20%
-- 20%
.
-
_
.
_
lO%
lo%
.
-
.
0%
''''1''''1''''
o
I ' ' ' ' I ' ' ' ' I ' ' ''
!''''1''''1''''1
100
200
300
0
100
200
300
o
lOO
200
0%
300
Figure 5. (a) Correlationof down corevariationandrelativefrequenciesof ARM intensities-/ARMfor all threecores
from Makarov Basin (b) Correlationof down corevariationand relative frequenciesof MDFAmv[for Makarov Basin
cores.
NOWACZYK
ET AL.'
MAKAROV
BASIN
below), is indicatedby the dashedlinesin Figure 2. All histograms
includedin Figure 2 show a maximum at steeppositive inclinations. Nondipolar directions,i.e., shallow positive and negative
inclinations,are mainly due to samplesin transitionalintervals
between clearly normal (steep positive) and reversed (steep
negative) inclinations. However, totally reversed inclinations
375
Orthogonal diagrams of the demagnetization results of six
samplesfrom core PS2178-5 and six from core PS2180-2 are
shown in Figure 3, respectively.The plots are displayedin mA
m-• in orderto showthatthe sample's
intensity,
evenafter
maximum demagnetizationwith 100 mT AF amplitude, is still
highabovethemagnetometer's
noiselevel(0.005mA m-l). The
(700-90 ø) are alsoclearlypresent.
representative results were taken mainly from intervals with
Makarov Basin - MDFAR
M( mT )
PS2178-3
PS2178-5
( OPC )
2O
MAGNETOSTRATIGRAPHY
PS2180-2
( KAL )
30
40
20
( GPC )
30
40
20
3o
4o
lOO
lOO
200
200
300
300
400
4OO
500
500
600
600
7OO
700
800
800
900
900
lOOO
lOOO
11oo
11oo
1200
1200
1300
1300
1400
1400
20
30%
30
40
, , I , , , , I , , • i I
,
,,
20
I,,,,
30
I,,,,
40
I,
20
30
40
, , I , , , , I , , , • I
30%
.
•,..
2O%
20%
10%
10%
0% '''
I''''
20
I'
30
'•1
'
40
'
20
Figure 5.
'
'
'
I'
30
'
'
'
I
40
(continued).
,,,
i,
20
•,,
i,,,,
30
i
40
0%
376
NOWACZYK
ET AL.'
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
negativeChRM inclination,indicatinga reversedpolarity.Included
also are a few examplesof samplesexhibitinga shallow ChRM
inclination,indicativeof intermediatefield configurations,
andtwo
normal polarity samples.In general,despitetheir type of ChRM
inclination,shallow or steepnegative,all samplesdisplayedin
Figure3 are characterized
by a steepdownwarddirectedoverprint.
This viscouscomponentis parallel to the recentmagneticfield
direction,
with an expected
dipoleinclination
of 88.8ø. It couldbe
removedwithin the firsttwo to five demagnetization
steps,equalto
AF amplitudesof 20-50 mT. Consequently,mainly the last four
demagnetization
steps(50-100 mT) were usedfor determination
also characterizedby minimum grain size variationsof the magnetic minerals (Figure 4). Especially, the coercivity parameter
MDF^}•M is very narrow banded. This largely homogeneous
magnetomineralogy
is linked to pure silty clays. The remaining
intervals,with sand contentsof up to 30% and occasionalmud
clasts,show only moderatevariability in concentration
and grain
size,respectively,when comparedto the silty clay layers.
The dominantremanencecarder throughoutthe whole investigatedsedimentcolumnis (titano-)magnetite,as derivedfrom the
obtainedIRM acquisitioncurves,which all reachedsaturation
between 300 and 500 mT Results from all cores (J^mviand
of the ChRM direction.
MDF^mvi) together with some correlation lines are shown in
Figures5a and 5b, illustratingthat all threecorescomprisesimilar
variationsin rock magneticproperties,down core as well as in
4.2. Rock Magnetism
amplitude.Nearly all intervalsof steepnegativeChRM inclinaThe concentration
of magneticcardermineralsin corePS2180-2 tions in core PS2180-2 are parts of sectionscharacterizedby
as estimatedby magnetic susceptibility•LF, ARM, and SIRM extremelyhomogenousrock magneticparameters(Figure 4). On
intensitymeasurements
(Figure4) partly is extremelyconstant.For the other hand, intervals of larger variability of rock magnetic
•60% of the sedimentsinvestigated,the associatedparameters parameters,generallywith a higher sand content,do not show
varyjust by a factorof 2-3, whereasthe maximumvariationsdo anomalousdirections.A final proof that reverseddirectionsmost
reversalexcursions
is providedfrom
not exceedan order of magnitude.The homogenous
sectionsare likely documentgeomagnetic
0%
+ Kmax
I
ß Kint
330'
5%
10%
ooPS2180-2
1.05
i'"n.•,?n
....
i,,,.,i1.05
ß*
1.oo
• .•'' oblate
1.oo
30'
a)
b)
.. '.
.. prolate
300 ø
•
0.90 ' ' ' ' I ' ' ' '
&++ q
270 ø
o%
5%
0.90
lO%
90"
+•ßß
4-
4-
+
240
ø
4-
•-•
4-
•
0
20 ....
ß +ß ßß
I ....
C)
20
%
4-4-
ß 4- ß &ß
ßß
ßH-
ß+
120
ø
10-
lO •
•
_
210 ø
150 ø
o
•
0%
:::.;.....: .
=
60ø
.....
. ..
*
.
ß
ß. ß .
. '. ,. ß
o
i i ! , I ' i !
180 ø
e) d)
'.--,•'-.
60ø
ß
. * ß .. t- '
..:,::
0
105'o
5%
**
•*ß
60ø ¾
ß
*
0
._;
•'•
ii*l
*i 0ø' *'' ' I ' ' '
0ø'''•'1 •'•1 '1' ''1'''*'1'i*
_=
._;
.'
-90 ø
-60 ø
-30 ø
0ø
30 ø
Inclination(ChRM)
60 ø
90 ø
0%
100- (K•
5%
0ø
10%
- K.•.) I K.•
Figure 6. Resultsfrom determinations
of the anisotropyof magneticsusceptibility
performedon all samples(n =
Kint and Kmin,(b) shape(KmaxKmin/rint)
251)fromcorePS2180-2.
(a) Orientations
of theprinciple
axesKmax,
2 of
the anisotropyellipsoids,(c) relativemagneticgrainsizes,represented
by •^mvi/•LF,and (d) inclinationsof principle
axis mmin as a functionof degreeof anisotropy(100 (Kmax- Kmin)/r) and (e) ChRM inclinationsversusgmin
inclinations.The data indicate, in most cases,a flat-lying (oblate) ellipsoid, independentfrom rock magnetic
variations.Sampleswith a low degreeof anisotropyor nearly isotropicsamplesshow a randomorientationof
principleaxes.All transitional(shallow)and reversed(steepnegative)ChRM inclinationsare associated
with steep
gmin inclinations(Figure6e); that is, they are not associated
with an anomaloussedimentaryfabric.
NOWACZYK
ET AL.'
MAKAROV
BASIN
data of anisotropyof magneticsusceptibilitydeterminedon samplesfrom corePS2180-2.Figure6a displaysthe orientationof the
threeellipsoidaxesKmax,rint, andrmin. Generally,the Kmaxand
Kint axes,which aremoreor lessof the samelengththroughoutthe
MAGNETOSTRATIGRAPHY
377
whole core, are lying in the horizontalplane, and the rmin axes
have steepinclinations.The ratio 100 (Kmax- rmin)/Kmax,i.e., the
maximumdegreeof anisotropy,reachesvaluesof up to 10% and
increaseswith increasingsubbottomdepth,whereasthe shapeof
Makarov Basin- relative Paleointensity
PS2178-3
( GPC )
0
1
2
PS2178-5
( KAL )
3
4
0
1
2
PS2180-2
( GPC )
3
4
0
1
2
3
100
100
200
200
300
300
400
400
500
500
600
600
700
700
800
800
900
900
1000
-
-
1000
1100
1100
_ - -
JNRM(50mT)
1200
lC - -- --
•
1200
JNRM(50
mT)
JARM(50mT)
1300
1300
JNRM(50mT)
JiRM(1.5T)
1400
1400
0
I
2
3
4
0
I
2
3
4
0
I
2
3
4
Figure 7. Normalizedestimates
of relativepaleointensity
variation,asindicatedby the ratiosdefinedin themiddle
plot. The curveswere smoothedwith a weighted(triangular)three-pointrunningaverage.A subsetof correlation
levels is indicatedby dashedlines.
378
NOWACZYK
ET AL.: MAKAROV
BASIN MAGNETOSTRATIGRAPHY
Makarov
500
Basin - PS2180-2
-
a)
e)
400
300
200
.*
100
#
**%
-
_
_
_
0
''''1''''1''''1''''1''''1
0
40
'
80
120
160
200
J ARM
500
'
'
'
0%
I
'
'
'
'
I
5%
10%
100. ( K ;•x' K ;•. ) I K
ARM
/ l• LF
-
b)
d)
ß
400
• 4
ß'
0
,-C
300
I-
0
200
%
•
3
oblateprolate
*
*
*
ß
* ß •'*
•
2 *
•
0
**
-1
%***** ***[
lOO
0
''''1''''1''''
0
1
I''''1
2
J SIRM
3
'
4
'
I
0.00
'
'
'
0.05
'
I
0.10
,
I
0.9
J •.M I J
0.95
I
1.05
( K •.•' K .i. ) I K•i.•
Figure8. Reliability
testof paleDintensity
estimate
forcorePS2180-2.
Magnetic
susceptibility
(I•LF)versus
(a)
ARMintensity
JArMand(b)SIRMintensity
JSmM,
relative
paleDintensity
(JN}c•/JAP,•
(50mT))versus
magnetic
grainsizeindicative
parameters
(c) •A•M/•LFand(d)JA•M/JSmM,
andrelative
paleDintensity
versus
anisotropy
parameters
(e)100(Kma
x- rmin)/Kma
x(degree
ofanisotropy)
and(f)(Kmaxrmin)/ri2nt(shape
ofanisotropy
ellipsoid).
theellipsoid,
asestimated
bytheratio(KmaxKmin)/ri2nt,
isgenerally
Depth in Core PS2178-3 ( cm )
oblate,especially
for samples
witha stronger
anisotropy
(Figure
6b). Thereis no relationship
betweenmagnetic
grainsizevariationsandthedegree
of anisotropy,
asshown
by thediagram
•^•/
0
200
400
600
800
1000
1200
14oo
o
•LF versus100 (Kma
x - rmin)/Kma
x (Figure6c). The inclinationof
Kminis steepfor samples
withstronger
anisotropy,
whichis very
likelydueto simplecompaction
effects,
whereas
lowanisotropy
to
nearlyisotropic
samples
showrandomKmininclinations
(Figure
6d). However,this simplyreflectsthe factthatthe orientations
of
the threeprincipleaxesare lessdetermined
for samplesthat
approximate
an isotropic
status.Therefore,
in summary,
we take
200
200
o
400
400
•o I•
600
600
EE
o
a steepinclinationof Kmi. as a clear indicatorof an undisturbed
sediment
fabric.Sinceall intervals
withintermediate
(shallow)
and
steepnegativeChRM inclinations
are all linkedto steepinclinationsof therminaxis( Figure6e),i.e.,theyarenotassociated
with
a disturbedsedimentfabric,nonnormalChRM inclinationscan be
interpreted
as recordsof geomagnetic
field behavior,i.e., shorttermreversalexcursions,
comprising
dipolar(steeppositiveand
negative
inclinations)
andtransitional/nondipolar
directions
(shal-
PS21 78-5
Q' Q' 800
800
PS2180-2
• •'-1000
lOOO
200
12oo
low inclinations).
4.3. PaleDintensityEstimation
1400
1400
0
200
400
600
800
1000
1200
1400
Asdiscussed
in section
4.2,theconcentration
of magnetic
carder
minerals
in corePS2180-2varyby lessthana factorof 10 (e.g., Figure 9. Tie points of the correlationof coresPS2178-5 and
SIRM rangesfrom 0.42 to 3.50 A m-I), with mostof the PS2180-2to corePS2178-3, definedas mastercore.Correlationis
concentration
relatedparameters
just varyingby a factorof 2-3.
basedon low fieldmagnetic
susceptibility
•LF,ChRM inclination
Thisqualifiesthe investigated
sediments
asan appropriate
mate- (Figure2), ARM intensity(Figure5a), MDF^mvt(Figure5b),
rial for an estimation
of relativepaleDintensity
variations
of the estimates
of relativepaleDintensity
(JN• (50 mT)/J^rM(50 mT),
Earth'smagnetic
field [Tauxe,1993].Sincesecondary
overprints Figure 8), and sedimentcolors.
NOWACZYK
ET AL.'
MAKAROV
BASIN
of the ChRM directionshad to be eliminatedwith AF amplitudes
of up to 50 mT (Figure 3), we usedNRM intensitiesat this AF
level for paleointensitycalculations[see also Nowaczyk, 1997].
For the concentrationnormalization parameter we chose the
100
379
ARM intensity(also after demagnetizationwith 50 mT) because
the ARM mainly affectsfine-grainedmagnetiteparticlesthat are
also the main carder of the paleomagneticinformation,whereas
low field susceptibility•LF and saturatedisothermalremanent
J ^.M( mA m-'•)
0
MAGNETOSTRATIGRAPHY
MDF ^.M(mT )
200
300
20
30
4O
lOO
lOO
200
200
300
300
400
400
500
500
o 600
...................
600
'O 700
700
.m
o
800
E 8oo
o
900
900
__
1000
...................
_
1000
1100
1100
1200
1200
1300
......
_............................
1400
1300
PS2178-3
,,,
• ....
• ....
•
1400
PS2178-5
I
'
'
'
'
I
'
'
'
'
I
'
'
'
'
I
•
•
'
I
'
'
'
'
I
'
'
'
'
I
PS2180-2
I
0
'
'
'
'
I
100
'
'
'
'
I
200
'
'
'
'
I
300
'
'
'
I
20
'
'
'
'
I
30
'
'
'
'
I
40
Figure 10. (left) ARM intensity(dAm) and (right)mediandestructivefield (MDFAR•) aftertransformation
of the
depthaxesof corePS2178-5(middlecurvesin bothplots)andPS2180-2(fightcurvesin bothplots)to the depthaxis
of corePS2178-3(left curvesin bothplots),definedas compositedepth.Horizontallinesindicatevisiblechangesin
lithology.
380
NOWACZYK
ET AL.'
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
magnetization(SIRM) are also influencedby multidomainpar-
but only for core PS2180-2 (Figure 7). The morphologyof the
ticles that do not contribute to a stable NRM. Moreover, •Lv is
derived two or three curves are almost the same for each core,
also influencedby contributionsof the nonmagneticsediment independentof the method of normalization,with only little
matrix. However, we also calculated NRM normalizations with
amplitudenaloffsets within some depth intervals but with the
•I•V for all three cores, and we calculated SIRM normalizations samesuccession
of peaksand troughs For the majority of depth
Makarov
ChRM
-90 ø
-45 ø
inclination
0ø
Basin
rel. Paleointensity
Polarity
45 ø
90 ø
0
I
2
5
3
-
100
_
-
_
-
200-'
-:.••--.... •.'•,.-":
....................
'.11.L..,•--•.
-
200
_
:
1
.
300-_
......................
•..
_
-
.
-
300
_
_
-
_
.
400 -
:•-""'•':'J.............. ,,
.
-
400
_
.
-
_
.
500
-
-
-
500
-
_
_
_
600
............
................................................
..........................
;•..
:::::•..:.,
.,....:.:..:.:.r
..... ....
••
•
-
....
.....-..•
....
600
-
-
_
-
-
700
-
700
_
-
_
800........ ....;.......
.;•
-
-- 800
_
:.'.
.........
_
_
_
_
9•--
-- 900
_
_
_
_
................
-- 1000
1000
-
-
......
•
•: •..;•:.,:•,•.•,.•.
........ ...................
..........
:..:
.:.- ..:
-
.
_
_
.........
-
11
O0
•
_
-
1100
_
:... --•.,
-
....
....
_
..
12oo•
.....
•::..•,,%...:.:.•.
.................
-
.
-
•..C
1200
_
-
-_
-_
• .........
...::..
:•
.......................
;...•;..•.:•:.
...........................
;.....:.
.. •
-
1300
-
1300
-
-
;•... .
-
-
_
_
1400
1400
0
.90 ø
.45 ø
0ø
45 ø
I
2
3
4
5
90 ø
Figure 11. Stacksof the ChRM inclinations(see Figure 2) and relativepaleointensityestimates(d•R_U(50 mT)/
dAp,_u
(50 mT), seeFigure7) as a functionof compositedepthusingthe correlationfunctionsshownin Figure9. The
shadedareasunderlyingboth curvesindicatethe maximum deviationsof the individual recordsfrom the stacked
curves.Vertical lines in the middle indicatethe depth intervalscoveredby coresPS2178-3 (left line), PS2178-5,
(middleline), andPS2180-2(rightline). Accordingto the grayscalebar in thebottomleft, the inclinationpatternwas
convertedinto grayvalues,yieldingthe "polarity" patternin the middle.Numbersin boxesmark intervalsof reversed
magnetizationsas discussedin the text.
NOWACZYK
ET AL.'
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
381
AMDF ARM/AZ( mTcm -• )
all 3 cores
ChRMinclination -2
(stack)
-90 ø
100
-45 ø
0ø
I ....
45 ø
-1
• ....
0
• ....
1
I ....
90 ø
2 rel.Paleointensity
I
0
(stack)
1
2
3
-
- 100
-
--
-
--
-
-
200 -
--
200
-
-
--
__
300 -
400
- 300
-
.
.
-
-
- 400
-
.
-
.
-
.
500 -
- 500
.
600-
- 600
700
-
700
-
-
-
.
800
eo800900 -
900
-
-
_
-
1000
• ;•_/_
__•_•••-"=••-
1000
1100
11oo
1200
•
-
1200
.
1300
-
1300
_
1400
' ' I ' ' I ' ' I ' '
-90 ø
-45 ø
0ø
45 ø
1400
90 ø
0
1
2
3
4
I''''1''''1''''1''''1
-2
-1
o
I
2
Figure 12. (left) Stack of ChRM inclination,(middle) the ratio AMDFAmu/Az,and (fight) stack of relative
paleointensity.The stacksof ChRM inclination and relative paleointensityare plotted togetherwith the first
derivativesof the magneticgrainsizeindicativemediandestructive
field of the ARM (MDFAp,•) of all threecores,
approximated
by theratioAMDFAmu/Az.
The displayedAMDFAmu/Az
ratiosaverageovertwo successive
sampling
intervals.Ratiosthatareaboutequalzeroindicatehomogeneous
sections(compareFigure10). A singlespikewithin
the curves(e.g., at 800 cm) indicatesa suddenchangein magneticgrainsize,possiblya hiatus,whereassuccessions
of spikes(e.g., 190-380 cm) indicateshort-scale
magnetomineralogic/lithologic
variations.
382
NOWACZYK
ET AL.:
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
levels the ratios coincidewith one another,a basic requirement
for a reliable paleointensityestimation[Tauxe, 1993]. Dashed
lines in Figure 7 indicatethe correlationof the three coresbased
on the paleointensityestimates.In the following discussionthe
term relativepaleointensityrefersto the ratio JNRM(50 mT)/JARM
(50 mT). Additional testsof reliability of relative paleointensity
are shown in Figure 8. Magnetic susceptibilityH,LF exhibits a
fairly linear relationshipto the ARM intensityJARM(except for
•7% of the samples),and the SIRM intensityJSIRMis linearwith
•UF. There is no visible link betweenrelativepaleointensityand
magnetic grain size-indicativeparameters(Figures 8c and 8d),
and also, relative paleointensityvariationsare related to neither
the degree of anisotropy (Figure Be) nor the shape of the
anisotropyellipsoid (Figure 8f).
wheren denotesthe samplenumber.The calculationof the slopein
(1) averagesover two successivesamplingintervals,which was
done in order to achieve a slight smoothingeffect. The data
processingwas performedafter transformationto the composite
depthscale.The resultsof the individualcoresaresuperimposed
in
the middle of Figure 12 togetherwith the ChRM inclinationand
paleointensitystacks.Like in Figure 10, horizontallines indicate
lithologychangesderivedfrom inspectionof core photographs.
Intervalswherethe slopeis aboutzero (for longerintervals,suchas
from 40 to 190 cm, 390 to 510 cm, and 590 to 780 cm) represent
very homogeneous
sectionsin termsof magneticconcentration
and
grain size (see Figure 10) with no visible lithology change.A
single spike, such as at 800 cm, indicatesa suddenchangein
magnetic grain size, i.e., a change in type and/or rate of
sedimentation,possibly even a hiatus. Successionsof spikes
4.4. Core Correlation and Creation of Composite Profile
(e.g., 190-390 cm) indicate short-scalemagnetomineralogic
the overallvariationsare only
Data of ChRM inclinations (Figure 2), low field magnetic (lithologic)variations.Nevertheless,
susceptibilityH,LF, ARM intensity(Figure 5a), mediandestructive moderate(seeFigures4 and 5) and still clearlywithin a rangethat
[e.g., Tauxe,1993].
field of ARM (MDF^p,M,Figure 5b), estimatesof relativepaleo- allows a correctpaleointensityreconstruction
intensity (Figure 7), and additional informationfrom sediment Therefore the relative paleointensityrecord from the Makarov
color (core photographs)were used to correlatecoresPS2178-5 Basincanbe interpretedalsoacrosschangesin lithology.
and PS2180-2 to core PS2178-3, yielding the transfer functions
shown in Figure 9. Core PS2178-3 is defined as the mastercore 4.6. Radiometric Age Information
FiveAMS14Cagesareavailable
fromthelargeboxcorertaken
becauseit coversthe longesttime interval, and its depth scaleis
at Site PS2180 (Table 3 and Figure 13). First, a constantreservoir
referredto as "compositedepth" hereafter.
After transformationto composite depth, the concentration correctionof 440 yearswas appliedto the radiocarbonagesafter
andGulliksen
[1975].However,
weexpect
thatthe•4C
(J^RM) and grain size (MDF^RM) variations of the magnetic Mangerud
minerals match nearly perfectly (Figure 10). Horizontal lines reservoir effect of seawaterhas been considerablylarger and
indicatelithologychangesderivedfrom inspectionof corephoto- variableduringperiodsof oxygenisotopestages2 and 3 [V6lker
graphs.The datasetsof ChRM inclinationandrelativepaleointen- et al., 1998]. Radiocarbonageswere convertedto calendaragesby
sitywere alsotransformedto compositedepth(PS2178-3)but were the CALIB 4.3 calibrationprogramby usingthe calibrationdata
then resampledin intervalsof 0.5 cm, stacked,and subsequently setsof Stuiveret al. [1998] and Stuiver and Reimer [1993] and,
20.314Cka,byapplying
theageshiftdetermined
byVb'lker
smoothedwith a weighted(triangular)movingaveragewindow of beyond
5.5 cm length (Figure 11). Thick vertical lines in Figure 11 et al. [ 1998].
Theresults
indicate
lowsedimentation
ratesof •0.4 cmkyr-•
indicatethe lengthsof the individualcoresversuscompositedepth.
Since only three coreswere stacked,with 30% of the composite for the last •40 kyr with slightlyhigherratesin the Holocene(0.6
extrapolation
would
yielda depth
of •310 cm
coveredby only two cores,we showthe minimumand maximum cmkyr-•).A linear
deviationof the individual resultsfrom the stack, indicatedby for the Matuyama Brunhes reversal (780 ka). Obviously, the
inclination pattern of the Makarov Basin compositeexhibits
shadedareas,insteadof giving the standarddeviation.
normalpolaritydownto at least970 cm.According
The stackedChRM inclinationswere also transformedto gray predominantly
performedon the corespresentedin this
valuesaccordingto the gray scalebar in the lowerleft of Figure 11. to nannofossilstratigraphy
The resultingpseudopolarity
patternshownin the middleof Figure
11 clearly indicatesthat at leastthe upper •10 m are of Brunhes
PS2180-1
PS2180-2
age. The resultingminimum mean sedimentationrate thus calcu( GKG )
latesto • 1.3cmkyr-•.
( ka BP)
4.5. Quantification of Sediment Variability
The rockmagneticparameters
ARM intensity(J^RM),representing the concentrationof magnetic particles,and the coercivity
parametermediandestructivefield of ARM (MDF^RM) as a proxy
of their relativegrain size, show significantpatterns.Intervalsof
constantconcentrationand constantmagneticgrain size alternate
with intervalswherebothparametersshowlargerfluctuations,e.g.,
in the top half of the compositeprofile (Figure 10), or sudden
changesfrom one constantlevel to a differentconstantlevel, e.g.,
at 1140 and 1305 cm compositedepth.All thesefluctuationsare
linked to lithology changesexpressedby sedimentcolor and/or
texture.In orderto quantifythe effectof thesevariationswe chose
the magneticgrain size-relatedparameterMDF^p,Mand calculated
the slopeof its down corevariationwith the formula
0
ß
1.99
ß
7.67
150
10 ©18.74
• 40.85
38.60
•' •,o
•..
( GPC )
KLF( 10'6,SI)
AMS•nCage
200
i
KLF( 10-6,SI)
150
i
200
0
,10
20 E
-
30
•
40-
40
50
i
50
(" - 51
[z(.)
- M(n
AMDFA.•M
([MDFAP,
M(n)
-- z(.
MDFAP,
-1)]
+ [MDFARM(,
[z(.+
- z(.)]
+1)
-MDFAP,
M(,)]
)' (1)
Figure13. AMS 14Cagesof corePS2180-1
(GKGis thebox
corer)and correlationwith core PS2180-2by meansof low field
magneticsusceptibility
•LF.The symbolsizesareproportional
to the
paleomagnetic
samplesize (PS2180-2) and the intervalintegrated
duringspotreadingmeasurement
(PS2180-1),respectively.
NOWACZYK
ET AL.: MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
383
ii
,,
( tuo ) qldep el!sodmoo
384
NOWACZYK
ET AL.:
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
paper [seeGard, 1993, p. 229], "in the Makarov Basin Holocene sedimentationrate event in the Makarov Basin, providing a
sedimentsare about10 cm deep."Unfortunately,no furtherprecise high-resolutionrecord of the geomagneticfield behavior,i.e.,
data,e.g., a plot of theraw data,are givenby Gard [1993], excepta the field intensity decay startingat •50 ka, followed by the
listedsedimentation
rateof •1.4 cmkyr-1. Thisdoesnotdirectly normal-reversed
(N-R) transitionof the Laschampreversalexcurcontradict
the resultsfromAMS 14Cdatingsincecoccolithssion. Its abrupttermination(R-N transition)is obviouslycaused
stratigraphy
is a moreconceptualdatingtechniquebasedon several by a drasticdecreasein sedimentation
rate or, more likely, a hiatus
assumptions.
since sedimentproperties,especiallythe sand content,change
Takingthe correlationof the box corerto the pistoncorerfrom quite drasticallyabove the interval of reversedinclinations(e.g.,
Site PS2180, the topmostinterval of reversedChRM inclination Figure 14). A similar conclusion can be drawn at least for
can be identifiedas the Laschampgeomagneticreversalexcursion excursions2 and 3 at •400 and 600 cm composite depth,
[Bonhommet and Babkine, 1967; Gillot et al., 1979]. The respectively,
becausethey are also situatedin the top of homogeLaschampexcursionhas been frequentlyfound in Arctic marine neoussedimentsequences,
overlainby depositswith more hetersedimentsas a pronouncedpaleomagneticfeature,i.e., with thick- ogeneous properties (Figures 12 and 14). According to the
nessesbetween 30 and 60 cm, clearly reversedinclinations, (tentative)correlationshown in Figure 15, excursions2-4 can
extremelylow relativepaleointensities
for transitionaldirections, be relatedto the Blake (118 ka), Jamaica(190 ka), and Pringle
and a field strengthrecovery during its reversedphase [e.g., Falls excursions(220 ka), respectively.
As alreadypointedout by
Nowaczykand Baumann,1992;Nowaczyket al., 1994;Nowaczyk, Nowaczyk and Frederichs [1999] and Channell [1999], the
1997;NowaczykandKnies,2000]. Anothercandidatewouldbe the PringleFalls excursionis not coincideritwith the "Jamaica
Mono Lake excursion[Denham and Cox, 1971; Liddicoat and excursion"(or IcelandSea excursion)as concludedby Langereis
Coe, 1979]. However, detailed studies could not detect a field et al. [1997]. Finally, excursion5 would be relatedto the Biwa II/
recoveryfor this excursion[e.g., Nowaczyk,1997; Nowaczykand Fram Strait excursion(260 ka [Langereiset al., 1997]). From
Knies, 2000], as was found for the topmostexcursionin Makarov •1170 cm (compositedepth) downward,no clear correlationof
Basin sediments(Figure 11). With an age of •40 ka [Laj et al., the paleointensityrecordto ODP Site 983 can be achieved.This
2000] and a maximumdurationof •5-6 kyr, it is spreadover 30 sectionis characterized
by oscillatingflat positive and negative
cm in corePS2180-2(Figure2), yieldingsedimentation
ratesof at inclinations.Accordingto the correlationshownin Figure 15, an
least5 cm kyr-1, 5-10 timeshigherthanfor the overlying age of •350-400 ka can be estimatedfor the bottom of the
sediments,
whentaking
theAMS 14Cdata.Obviously,
thedepo- Makarov
Basin
composite
record,
resulting
linamean
sedimentasitionalconditionsat the coting sitesin the Makarov Basin were
highly
variable
during
thelast
•50kyr.[1994]forcorePS2178A øBerecord
isestablished
bySchi•)ver
5 (Figure 14) down to 760 cm compositedepth(equivalentto 640
tion rate in the range of 3-4 cm kyr-. However, temporal
sedimentationratesrange from 0.4 to •5, perhapseven 10, cm
Similar to the results from the Iceland and Greenland Seas,
cmin corePS2178-5;
totallengthis 831cm).TheløBeconcen- geomagneticexcursionsrecordedin Makarov Basin sedimentsare
tration obviouslyis stronglyinfluencedby lithologicalchanges
sinceits morphology(roughly)parallelsthe morphologiesof the
dry bulk density(DBD) and the magneticsusceptibilityrecords,
respectively(Figure 14). Intervalsthat are composedof silty clays,
with little changesin lithology,i.e., whereDBD, susceptibility,
and
AMDF^mvt/ZXz
are constant,are characterized
by only a slightand
associated
with a recoveryin relativepaleointensity(Figure 15).
BrunhesChronreversalexcursionsare not presentin the majority
of other paleointensityrecords,which are, unfortunately,often
basedon u channelmeasurements,
which sufferfrom smoothing
owing to the broad sensorcharacteristics
of whole-coremagnetometers.In addition,paleointensityestimatesare frequentlydetersmooth
decayin the løBecurve,whereas
intervals
of variable mined on demagnetizationlevels of 20 or 30 mT, which are, at
lithology
exhibitlargedistortions
in the 1øBecurve.Especiallyleastin the caseof Arctic marinesediments,probablytoo low to
withinintervals
of increased
sandcontent
(>63 txm),the løBe really resolvethe primarymagnetization,i.e., the real paleointencontent
is strongly
reduced.
Thisisnormal
sinceløBeisadsorbedsity variation, in detail. Relative paleointensitycurvesfor sediby clayminerals.
Fittinganexponential
decaycurveto theløBe mentsfrom the GreenlandSeawouldyield a singleminimumwhen
record of PS2178-5, a maximum mean sedimentationrate of 1.1 cm basedon 20 mT data,which is split into two muchlowerminima,
kyr-1 (corrected
to composite
depth)wasestimated
by Schi•)verwith a significantmaximum in between,when basedon 50 mT
[ 1994],assuminga constantdeposition.
However,thiscanbe onlya data [seeNowaczyk,1997].
roughestimatesincethe sedimentation
wasnot constant(seeabove)
5.2. Age Model 2
both in termsof rate andtype of materialdeposited.
An alternativeinterpretationof the Makarov Basin magnetostratigraphicrecord,correlatedto ODP Site 1010 in the northeast
Pacific [Hayashida et al., 1999], is shown in Figure 16. The
5. Discussionof Age Models
polarity transitionbetween 1000 and 970 cm is now related to
5.1. Age Model 1
the Matuyama Brunhesreversal(780 ka). The normal intervals
On the basis of the identification
of excursion
1 as the
from 1135 to 1070 and 1050 to 1040 cm compositedepthcanbe
Laschampexcursion(Figure 11) we correlatedthe magnetostrati- related to the Jaramillo and Kamikatsura events, respectively.
graphic results (relative paleointensityand polarity) from the Overall, the Makarov Basin record matchesquite well with the
Makarov Basin to comparabledata sets from the Nordic Seas ODP Site 1010 recordbetween•840 and 1150 cm. Especially,the
and the North Atlantic (Figure 15). From thesereferencedata sets patternwithin the 200 cm abovethe inferredMatuyamaBrunhes
and the "SINT800" paleointensitystack [Guyodo and Valet, reversalwith its strongincreaseafter the R-N transitionappearsto
1999] it is known that the intensity minimum in the SINT800 be convincing.In light of this alternativeinterpretation,there
linked to the Laschampexcursionat •40 ka is precededby a shouldbe a clearpreferencefor reverseddirectionsfor the lowerbroad high between45 and 60 ka, with a maximum at 50 ka. most •2 m of the ChRM inclinationstackof the Makarov Basin,
Comparingthe morphologies
of the paleointensity
records,sucha as one would expectfor pre-Jaramillo(mid-Matuyama)sediments
maximum is presentat •200-230 cm compositedepth in the (Figure 16; see also Figure 11). Instead, inclinationsare very
Makarov Basin record,yielding very high sedimentation
rateson scattered.So, also in age model 2, no unequivocalcorrelationto
the order of 10 cm kyr-. The interval from 200 to 30 cm the chosenreferencedata set is possiblefor this sectionof the
(compositedepth) of homogeneoussedimentsreflects a high compositeprofile.
NOWACZYK
ET AL.'
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
385
Age( ka )
0
50
100
150
3
200
I
I
I
I
i
I
I
i
I
I
250
300
350
ODP Site 983
North Atlantic
I
I
I
I
I
I
300
3
350
Iceland
I
o
I
I
I
I
I
I
I
I
I
I
I
I
Sea
I
I
I
I
I
Polarity
o
',sO ',
,'
•0o
I
3
I
, ,
I I
',
Greenland
Sea
I
I
o
I
I
i
350
I I
I
I I
Polarity
/ /
I i
I
I
/ t5o
130o
I •
I
I
I I
f
I
350
I
0
Polarity
Lithology
boundaries
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
Composite depth ( cm )
Figure 15. Age model 1: correlationof the magnetostratigraphic
resultsfrom the Makarov Basin, Arctic Ocean,
plottedversuscompositedepth,to otherrecordsfrom the GreenlandSea [afterNowaczyk,1997], the Iceland Sea
[Nowaczykand Frederichs,1999], and the North Atlantic, Site ODP 983 [Channellet al., 1997], all plottedversus
age. Names in the North Atlantic graph indicate geomagneticexcursions;NGS is Norwegian Greenland Sea
excursion.Numbersin boxesin the MakarovBasingraphmark intervalsof reversedmagnetizations
as discussed
in
the text (see also Figure 2).
386
NOWACZYK
ET AL.: MAKAROV
BAS1N MAGNETOSTRATIGRAPHY
NOWACZYK
ET AL.:
MAKAROV
BASIN
Accordingto age model 2, four BrunhesChron reversalexcursionsarepresentin the MakarovBasinrecord.Their identification
is not straightforwardsinceLangereiset al. [1997] discussthe
presenceof 11 and Lund et al. [1998] postulateeven 14 reversal
excursionsduring the BrunhesChron. From the available AMS
MAGNETOSTRATIGRAPHY
387
Mudie, 1985] andcomparemoreto paleomagnetic
resultsfrom the
easternArctic Ocean,e.g., the NansenBasin(Table 1, minimumof
1 cm kyr-1) [Nowaczyk
andBaumann,
1992;Schneider
et al.,
1996],ortheYermak
Plateau
(3-10 cmkyr-1) [Nowaczyk
et al.,
1994; Schneideret al., 1996; Nowaczykand Knies, 2000].
Dating of long sedimentcoresfrom the neighboringLomonois a record of the Laschampreversalexcursionat 40 ka. The sov Ridge is of similar difficulty since here the paleomagnetic
paleointensitymaximum at •210 cm compositedepth shouldbe resultsalso allow alternativeinterpretations.Below •3 m subrelatedto an age of •50 ka (Figure 13). The identificationof the bottom depth a complexpatternof steeppositive and negative
threeotherreversalexcursions
(2-4) mustbe left astentativesince inclinationsbut withouta clearpreferencefor reversedor normal
sedimentationrates in the Makarov Basin must be recognizedas polarity was found as well. Dependingon where the Matuyama/
highly variable,or even noncontinuous,
resultingin compression, Brunhes reversal was set, minimum sedimentationrates can be
elongation,or missingof partsof thepaleointensity
patterns.So,in estimatedto be either in the range of 0.2 [Spielhagenet al.,
et al., 2000].A thirdage
age model 2, excursion2 now might relate to the Biwa II/Fram 1997]or 0.7 cm kyr-1 [dakobsson
Strait excursion(255-265 ka [Langereiset al., 1997; Nowaczyk model with interpretationof reversedinclinationsas being solely
and Frederichs,1999]). The identificationof excursion3 (470 ka?) records of short reversal excursion within the Brunhes Chron
is not clear,whereasexcursion4 with an inferredage of •615 ka yieldssedimentation
ratesof theorderof 1.4 cmkyr-1 [Fredmight be relatedto the La Palmaexcursion,recentlydescribedby erichs, 1995]. Sedimentaryconditionson top of the Lomonosov
Ridge are different from that of the Makarov Basin since
Quidelleuret al. [1999].
winnowingdue to water currentspassingthe crestof this oceanic
5.3. Comparison of Age Models
ridge shouldlead to reducedsedimentation.Fine-grainedmaterial
The age-depthrelationships
of theMakarovBasinrecordfor age not depositedon top of the ridge shouldaccumulateelsewhere,
model 1, based on correlationto ODP Site 983 and other Nordic e.g., in the Makarov Basin, so that comparablyhigh sedimentaSeasrecords(Figure 15), and agemodel2, basedon correlationto tion ratescan be foundhere. Both age modelsof this studyagree
ODP Site 1010 in the northeastPacific (Figure 16), are shownin with this.
Figure 17. Both age modelshave in commonthat sedimentation
ratesarehighlyvariable,andthey arenearlyidenticalfor aboutthe
•4Cagesit isclearthatthereversed
section
between
35and63cm
top2 m sincehereAMS •4Cagesandtheinterpretation
of the
paleomagnetic
resultsare the same.Below •2 m compositedepth
6.
Conclusions
Intervalsof steepnegativeinclinationspresentin theinvestigated
Makarov Basin sedimentsare interpretedas recordsof geomagkyr-• foragemodel
2. Ononehand,
thedecay
oftheløBecontent netic field behavior,i.e., shortreversalexcursions[Gubbins,1999]
inferslowsedimentation
ratesontheorderof 1 cmkyr-•;thatis, and/or major reversalsof the Earth's magneticfield. Reversed
this data setfavorsage model 2. On the otherhand,the lowermost inclinationsare mainly found in intervalsof homogeneous
sedi2 m of the compositeexhibittoo muchnormalpolaritydirections. mentsin termsof rock magneticand sedimentological
properties.
This interval should be characterizedby clearly dominating The overallmoderatelyvariableto nearly constantrock magnetic
reversed field polarity since it is of middle Matuyama age, propertiesprovidesuitableconditionsfor reconstruction
of relative
accordingto age model 2. The presenceof a high amount of paleointensityvariationsand their correlationto dated reference
normalpolaritydatamightbe an indicationthatmodel 1 shouldbe curves. In the recovered Makarov Basin, sediments' relative
paleointensitiesare lowest during polarity transitions,with a
favored,
resulting
inages
ally•ounger
than
theMatuyama
Brunhes
reversal
(780ka).Sincethe øBerecord
is incomplete,
no final recoveryin amplitudeduringthe reversedstateof the geomagnetic
interpretation
canbe drawn.Nevertheless,the new resultsfrom the field. Highest valuesare always linked to clear normal polarity
MakarovBasinclearlyindicatehigherlong-termmeansedimenta- phases.This patternof high normal polarity field strength,low
tionthanattheAlphaRidge(0.1cmkyr-•) (Table1) [Aksu
and transitionalfield strength,and (slight) recovery during clearly
reversedpolarity of the excursionshas been found also in other
both
agemodels
result
incomp?etely
different
long-term
mean
sedimentation
rates:•5 cm kyr- for age model 1 and only 1 cm
detailed studies on sediment cores from the Greenland
Age ( ka )
200
o
•
400
600
800
1000
1200
200
- 200
E
_
_
e- -•
400
54oo
_
• •0.600
ß=
o
I..•
•
_
• 600
•-• 800
•
:•
•
•
Age Model2
_
correlated
toSite •
_
_
•
ODP1010
800
_
_
_
• •ooo '
_
•
1000
E
o
• 1200
•
. Age model
correlated
toSite
ODP 983
Noah
1400
_
_
5 1200
_
_
Atlantic
.... I .... I .... I .... I .... I .... I .... I .... I .... I .... I .... I ....
o
200
400
600
800
1000
-
1400
1200
Figure 17. Age-depthcurvesof the two agemodelsbasedon the
correlationsshownin Figures15 and 16, respectively.
and Iceland
Seas[Nowaczyk,1997; Nowaczykand Frederichs,1999] and the
Arctic Ocean [Nowaczykand Knies, 2000]. However, in these
recordsthe transitionalfield intervalswith low relativepaleointensity amplitudeswere much shorterwith a more or less instantaneous change from normal to reversed inclinationsand back.
Comparedto this, the onsetsof the excursionsare spreadover
quite a long interval characterizedby a broad low in relative
paleointensitywith ChRM inclinations oscillating rather than
switchinginstantaneously
from normal to reversed.The terminations of the excursionsare often quite sharp.They coincidein
generalwith changesin lithology,i.e., changesin type of sediment
and rate of deposition,or even hiatuses.Obviously, the asymmetricalpatternof the directionalas well as amplitudinalbehavior
of the paleomagnetic
signalis rathercausedby a highly variable
sedimentationthan by geomagneticfield behavior.This has to be
takeninto accountwhencorrelatingthe paleomagnetic
resultsfrom
Makarov Basin to referencedata setssincethe fairly well established patterns of relative paleointensityrecord, such as the
SINT800 stack, should be largely elongated or compressed
depending on the current sedimentationrate. Correlations to
available referencecurves allow two different interpretationsof
388
NOWACZYK
ET AL.:
MAKAROV
BASIN
MAGNETOSTRATIGRAPHY
intensityJ•p,•; ChRM inclinationand declination;low field susceptibility •LF; ARM intensityJAm; MDFAp,•; •AP,•/•LF; J•P•
(50 mT)/•rF, same with 3 point weightedrunning average;and
J•p• (50 mT)/JAp,•(50 mT), samewith 3 pointweightedrunning
meansedimentation
ratein therangeof4 cmkyr-1andanageof average.Additional data are available for core PS2180-2 only:
•400 ka for thebottomof the compositesection(agemodel 1). An SIRM intensity(JSIRM);JNRM(50 mT)/JsiRM,samewith 3 point
alternativeinterpretation
yields a mean sedimentation
rate in the weightedrunning average;mean susceptibilitydeterminedfrom
rangeof 1.3cmkyr-1, anageof atleast•1.2 Ma,forthebottom anisotropyellipsoidplus standarderror;principleanisotropyaxes
of the Makarov Basinrecord.The available,unfortunatelyincom- Kmax,Kint,andKmin;inclinationand declinationof Kmax,Kint,Kmin;
the Makarov Basin paleomagnetism,
i.e., inclinationand relative
paleointensityrecord.Both modelsresult in highly variablesedimentationratesbut with differentmaximumvalues.Interpreting
all documented
reverseddirectionsas excursionalfeaturesyieldsa
plete,1øBe
record
favors
thelowsedimentation
interpretation,
but anddegree
(100(Kma
x - Kmin)/Kmax)
andshape
(KmaxKmin/K•n)
of
the low amountof clearlyreverseddirectionin the bottomof the
sectiondoesthe opposite.Thusunlessno furtherhigh-qualitylong
coresexceedingthe presentMakarov Basin recordare available,
this questionmustbe left open.
anisotropyellipsoid. Color photographsof core PS2178-3 are
available as a pdf file. Data for Makarov Basin stack comprise
ChRM inclinationandpaleointensity
basedonJ•p,• (50 mT)/J^mv•
(50 mT).
7.
Acknowledgments. We thankthe captainand the crew of R/V Polarstern for cooperationduring expeditionARK VIII/3. L. Brick and C.
Miiller helped during laboratorywork in Bremenand Potsdam.We also
would like to thank Y. Guyodo, J. E. T. Channell,and A. Hayashidafor
providingtheirpaleointensity
datasets.JohnKing andtwo otherambitious
reviewersare acknowledged
for their constructive
commentson the manuscript. This study was partly financed by the Bundesministeriumftir
Forschungund Technologie,Germany.
Data Availability
Paleomagnetic
and rock magneticdata are accessible
at http://
www. pangaea.de/PangaVista.Enter search option Nowaczyk
+2001 +Makarov (with a spacebeforeeachplus).The datafrom
coresPS2178-3,PS2178-5,andPS2180-2 comprisedepth;compositedepth(PS2178-3); agesaccordingto agemodels1 and2; NRM
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(ReceivedMarch 3, 2000;
revisedFebruary20, 2001;
acceptedMarch 26, 2001.)