Magnetic properties of light and dark sediment layers from the japan sea: Diagenetic and paleoclimatic implications

Qurrrmcrn

Scirm r KP\iew.v. Vol. 16. pp. 1093-l

PII: SO277-3791(96)00118-7

MAGNETIC FROM

I 14, 1997.

C 1998 Elsevier Science I-id. All rights reserved. Printed in Great Britain.

Pergamon

0277-3791197

1332.00

PROPERTIES OF LIGHT AND DARK SEDIMENT LAYERS THE JAPAN SEA: DIAGENETIC AND PALEOCLIMATIC IMPLICATIONS

Istituto

di Geologia

Marina, {E-mail:

L. VIGLIOTTI CNR, Via P. Gohetti 101, 40129 Bologna, M~f#@hoigm2.igm.ho.cnr.it)

Abstract - Rock magnetic/paleoclimatic/diagenetic relationships of sediments spanning the last 0.78 Ma have been investigated using samples collected from light and dark layers recovered at ODP Sites 794 (Yamato Basin) and 795 (Japan Basin). Rock-magnetic parameters (K. Kfd, ARM. SIRM, S-ratio) are shown to reflect diagenetic processes and climate-related variations in the concentration, mineralogy and grain-size of the magnetic minerals contained within the sediments. The magnetic mineralogy is dominated by ferrimagnetic (magnetite-type) minerals with a small contribution made by hematite and iron sulphides such as pyrrhotite and/or greigite. Magnetic mineral concentration and grain size vary between light and dark layers with the former characterized by a higher magnetic content and a finer magnetic grain size. Magnetite dissolution, related to sulfate reduction due to bacterial degradation of organic matter, is the process responsible for the magnetic characteristics observed in the dark layers. testifying to the reducing conditions in the basin. Variations in the rock magnetic properties of the sediments are strongly correlated with global oxygen isotope fluctuations. with glacial stager, characterized by a lower magnetic tnineral content and a coarser magnetic grain size relative to interglacial stages. Major downcore changes in the magnetic properties observed at Site 794 can be related to changes in the oceanographic conditions of the basin associated with the flow of the warm Tsushima Current into the Japan Sea at about 0.35-0.40 Ma ago. Q 1998 Elsevier Science Ltd. All rightx reserved

INTRODUCTION Magnetic parameters provide a rapid and effective tool for monitoring the supply of terrigenous sediment to the

oceans in responseto climatic change, and for reconstructing the paleoenvironmental records of deep-sea sediments (Kent, 1982; Oldfield and Robinson, 1985; Doh et al., 1988; Bloemendal rf al., 1992; Sahota et ml., 1995). Rock-magnetic properties often vary with changes in the lithology of the sedimentsand these variations are in many casescontrolled by climate. Thus changesin the concentration, mineralogy and grain size of magnetic mineral assemblagesoften reflect climatically-induced variations within the lithogenic fraction of the sediment (Robinson, 1986; Bloemendal el al., 1988; Hall and King, 1989; Sagerand Hall, 1990; Robinsonrf ul., 1995). Gross downcore changes in the magnetic properties reflect physical changes in the sedimentary environment that may indicate paleoceanographicvariations and/or diagenetic processes. The aim of this paper is to investigate the rock magnetic/paleoclimatic/diagenetic relationships of the light-dark sedimentary cycles deposited during the BrunhesChron (Upper Quaternary, 0.78 Ma) in the Japan Sea at ODP Sites 794 and 795. 1093

Italy

QSR

Tada et al. (1992) found that variations in sediment composition are closely related to glacial-interglacial cycles expressed in the standard oxygen isotope curve (Imbrie et crl., 1984). The detrital fraction of the sediment tends to be enriched and the maximum grain size tendsto be larger during the glacial stages.Consideringthat often it is the terrigenous fraction of the sediment which contains magnetic minerals, the magnetic properties of the bulk sediment should exhibit distinct differences between glacial and interglacial horizons of the sequence.

GEOLOGIC

SETTING

The Japan Seais a semi-enclosedback-arc basinwith a distinctive physiographic configuration which is crucial to its oceanographicregime. Most of the basin exceedsa water depth of 2000-3000 m, but it is connected to outer seas only by shallow water sills: the Mamiya (I2 m), Soya (55 m). Tsugaru (130 m) and Tsushima (130 m) straits (Fig. I ). The oceanographicconditions of the basin are regulated by the precariousbalance of waters flowing through theseshallow sills. Therefore, glacio-eustatic sealevel change should play an important role in the oceanographic conditions of the basin, and it is

1094

I

I Sea of Japan

1.---l

0

300 km

I

FIG. I. Location map of the Japan Sea with sites drilled during ODP legs 127 (794-797) and 17-8 (798 and 799). This study focused on sediments recovered from Sites 794 and 795.

predictable that, as a responseto past climatic change, drastic paleoceanographicchangeshave occurred in the Japan Seaduring the Quaternary particularly with respect to bottom water oxygenation and detrital organic matter preservation level. Four sites were drilled in the Japan Sea during ODP leg 127: Sites 794 and 797 in the Yamato Basin and Sites 795 and 796 in the Japan Basin (Fig. 1). Fine-grained siliciclastic sediments with distinct darklight sedimentary cycles were recovered from the uppermost part of the sedimentary sequencesat all the sites. Volcaniclastic materials produced by explosive eruptions from the nearby volcanic islands were also recovered throughout the drilled intervals. Light-dark rhythms occur in the Upper Miocene to Pleistocene sediments.but they are most prominent and persistent in the Late Quaternary (Follmi et d.. 1992). The rhythmical alternation of these sediments suggests cyclic changes between oxic and anoxic conditions related to basin-wide paleoceanographicchanges which are likely to be linked to glacio-eustatic sea-level changes(Tada et al., 1992). On the basisof gray value (darkness) profiles, Tada et al. (1992) correlated the light and dark layers of Sites 794, 795 and 797 suggesting that the deposition of these cycles resulted from synchronous events. These cycles reflect highfrequency changes in the depositional environments of the basin with periodicities ranging between 100 ka and markedly less than 1000years. which is shorter than those in the Milankovitch band (Follmi et (II.. 1992).

SAMPLES AND METHODS For this study, 132 sampleswere selected from light and dark layers depositedduring the Brunhes Chron (last 0.78 Ma) at Site 794 (Yamato Basin) and 795 (Japan Basin). The sedimentconsistsof a rhythmical alternation of color-banded siliciclastic clay and silty-clay. Magnetostratigraphic data indicate that the time-interval examined in this study spans24.6 m at Site 794 and 35 m at Site 795 (Hamano et crl.. 1992). The number of samples studied retlects the difference in sedimentation rates between the two sites. Fifty-three sampleswere collected from Site 794 (26 dark and 27 light layers) and 79 samplesfrom Site 795 (38 dark and 31 light layers). The sampleswere collected by using paleomagneticcubes of constant volume (7 cc). Not all the horizons are clearly light or dark and the latter have been subdivided into dark and semidark sedimentsbasedon their relative darkness. In order to characterize the magnetic minerals in the sediment, detailed magnetic measurementswere carried out which determine the responseof the sedimentsto a variety of applied magnetic fields. This response is mainly determined by the mineralogy. concentration and grain size distribution

of the magnetic

phases.

The procedures used for the magnetic measurements were as follows.

( 1) Measurement of low-field volume magnetic susceptibility (K) at two different frequencies (0.47 and 4.7 kHz) using an MS2 Bartington susceptibility meter. The difference between the two MS values was used to calculate the frequency dependenceof

L. Vigliotti: Magnetic Properties of- Sediment Layers from the Japan Sea susceptibility (Kcd). This parameter reflects the presence within the sediment of very fine (CO.04 pm for magnetite) ferrimagnetic grains in the superparamagnetic state (SP). (2) Measurement of the natural remanent magnetization (NRM) after alternating-field (AF) demagnetization with peak fields of 20 millitesla (mT). The remanence was measured with a Jelinek Jr-4 spinner magnetometer (noise level: 4x 10 ’ A/m). (3) Acquisition of anhysteretic remanent magnetization (ARM) by subjecting the samples to an AF field of 100 mT biased by a 0.05 mT direct field, followed by progressive AF demagnetization in three steps (20, 30 and 40 mT). The ARM is expressed as anhysteretic susceptibility (KARM). obtained by dividing the ARM by the strength of the DC field. (4) Acquisition of isothermal remanent magnetization (IRM) in steps up to a maximum field of 1 tesla (T). The acquired IRM (referred to as saturation isothermal remanence; SIRM) was subsequently demagnetized in three steps (IS, 25 and 35 mT) and subjected to a reversed DC field up to 0.4 T (five steps). The latter measurements were used to calculate the coercivity of the isothermal remanence Bo(,.,, and the S-ratio (-IRMmo &SIRM) (Bloemendal, 1983). Low field ‘soft’ IRM (IRM20mT) was used to approximate the total concentration of remanence carrying ferrimagnets. (5) A composite IRM (1 .I.5 T along the Z-axis, 0.4 T in the Y-axis and 0.12 T in the X-axis) was given to a small collection of 16 samples (10 from Site 795 and six from Site 794) which were then subjected to progressive thermal demagnetization following the method proposed by Lowrie ( 1990). The light and dark layers were also characterized on the basis of sulfur content (S). total carbon (C,,,,) and organic carbon (C,,,) and the total nitrogen (N) content. These values, expressed as percentages, are given in Tables 1 and 2 together with the various magnetic parameters.

Time Control and Isotopic Stage Assignment The sediments considered in this study belong to the Late Quaternary. Unfortunately, within the Brunhes Chron (0.78 Ma) we have very poor time control for these sediments. A couple of biostratigraphic markers such as the last occurrence (LO) of the Pseudoemilima lacunosa (0.46 Ma; Thierstein ef al., 1977) and the LO of the Rhiznsolenia curvirostris (0.30 Ma; Koizumi. 1992) were identified at both the sites (Tada et al., 1992), but in intervals too large to be really significant. The only useful marker is the ash layer termed Aso- (0.86-0.90 Ma; Oba er al., 1991) identified at 3.86 mbsf at Site 794 and at 5.51 mbsf at Site 795 (Tada et al., 1992). Oxygen isotope (6’sO) data are not available for the sites studied. However, Tada et ul. (1992) used diatom abundance as a substitute for the 6’“O curve at Site 797. As stated above, these authors correlated the light-dark cycles of Site 797 with the cycles of Sites 794 and 795.

109.5

On this basis, it has been possible to ‘tune’ the age of the sediments studied to the oxygen isotopic stages of Imbrie et [I/. (1984). According to this correlation, 20 samples from each site appear to belong to stratigraphic intervals deposited at the same time in the Japan and Yamato basins. In Fig. 2, the magnetic susceptibility (2a) and the sulfur content (2b) are plotted as an age function for these samples. The curves exhibit a good agreement between the two sites suggesting that the correlation is correct and that paleoceanographic processes in the Japan Sea are synchronous basin-wide events. Although the correlation can be considered correct, the assignment to the oxygen isotope stages is ambiguous with respect to glacial stage 8. The values observed in this stage, as discussed below, appear anomalous with respect to other glacial stages. Considering also that, at Site 797, this stage exhibited contrasting data (Tada et (I/., 1992 1. it is possible that the interval representing this stage has not been identified accurately. Evidence for this is given by the LO datum of the Rhi:osolmia curvirmtris. In the oxygen isotope assignment proposed by Tada et (11.( 1992) for Site 797, this datum falls in an interval belonging to stage 8. In fact, in the North Pacific, it has been tied to the oxygen isotope record at an age of 0.276 Ma (Morley et al., 1982). and it is only assumed to be time-correlative in the Japan Sea (Burckle et rll., 1992). However, at Site 798, it appears to fall in oxygen isotope stage 9 (Dunbar rt crl., I992), suggesting a diachronism for this datum. The intervals tied to the oxygen isotope stages X-9 should therefore be considered ambiguous. Furthermore the interval related to the oxygen isotope stage 8 at Site 794 corresponds to a small gap in the sedimentary record of the core (Tuda ct rd., 1992).

RESULTS Magnetic Mineralogy IRM acquisition experiments are helpful for a rough identification of the magnetic minerals present in a sample. Fig. 3 shows typical IRM acquisition curves for sediments from sites 794 and 795. Most of the IRM is acquired below 0.2 T suggesting that magnetite dominates the magnetic properties of these sediments. The highest IRM values correspond to light coloured samples, implying a higher ferrimagnetic mineral content for these layers. Nevertheless, S-ratio values (Table 1). which retlect the proportion of ferrimagnetic minerals to highcoercivity minerals such as hematite and/or goethite. indicate that the latter minerals are also present. For this reason a small subsample of 16 specimens (6 from Site 794 and IO from Site 795) were sub.jected to thermal demagnetization of orthogonal composite IRMs. This procedure reveals the unblocking temperatures of three different coercitivity fractions which correspond to different magnetic minerals (Lowrie, 1990). Four typical examples are shown in Fig. 4. Most of the IRM resides in the soft fraction (
0.78 0.85 2.04 2.70 3.1 I 3.71 3.90 4.60 5.18 5.82 6.1 I 6.29 6.47 6.98 7.35 7.71 7.94 8.69 Y.15 9.39 9.63 9.92 IO.19 10.4Y I I.13 I I .40 12.21 12.48 13.08 13.51 14.00 14.62 14.98 15.08 15.44 15.95 16.35

IH1-78 lH1-85 I H2-54 1H2-120 lH3-I I lH3-71 I H3-90 lH4-IO I H4-68 384-132 IHS-I I 1H5-29 I HS-47 2Hl-IX 2Hl-55 2H I-Y I 2HI-I I4 2H2-39 2H2-85 2H2- IO9 2H2-I33 2H3-I2 2H3-39 2H3-69 2H3-I33 2H4- IO 2H4-9 I 2H4-I IX 2H5-28 2H5-7 1 2H5- I20 2H6-32 2H6-68 2H6-78 2Hh-I I4 2H7-I5 2H7-55

D L L L L D L L L SD L D L SD SD L D L SD L D SD SD 1. D L D L L L D SD D L L SD D

Depth (m) Color

2.86 0.54 0.34 0.31 0.35 I.52 0.29 0.37 0.49 0.28 0.35 I.19 0.43 0.3 I I .os 0.4x I .73 0.3’) 0.64 0.48 I .03 0.44 0.9x 0.48 I .53 0.63 4.46 0.34 0.35 0.37 I .90 I .72 3.60 0.24 0.62 0.42 1.23

2.86 3.86 0.49 0.44 0.35 I.52 0.55 0.50 0.5 I 0.28 0.43 l.lY 0.43 0.44 I .os 0.x3 I .90 0.39 0.66 0.49 I.1 I 0.44 O.YX 0.48 I .64 0.78 4.47 0.35 0.35 0.37 I .90 7.49 3.60 0.27 0.64 0.42 1.27

0.40 0.18 0.14 0.09 0.34 0.27 0.15 0.15 0.22 0.22 0.17 2.92 0.98 0.18 0.27 0.20 I .2s 0.1 I 0.28 0.30 0.60 7.63 0.83 0.23 4.14 0. I2 3.04 0.40 0.13 0.22 5.13 2.24 3.47 0.61 0.3 I 0.25 0.57

0.30’) 0.072 0.079 0.074 0.060 0.170 0.073 0.078 0.08 1 0.04 I 0.077 0. I26 0.073 0.063 0. I43 0.101 0.171 0.063 0. IO6 0.080 0.121 0.090 0.1 I6 0.092 0.181 0. I02 0.444 0.063 0.087 0.070 0. I74 0.107 0.332 0.053 0.07 I 0.083 0.143

C,,,, (%) C,,,, (%‘I S,,,, (%:) N (%) 9.253 7.444 4.342 4.162 5.883 X.932 3.945 4.718 6.012 6.707 4.597 9.437 5.X22 4.937 7.322 4.713 10.10s 6.252 6.066 5.Y3X 8.54s 3.91 I X.448 5.272 8.425 6.206 10.054 5.413 4.057 5.243 10.908 16.075 10.840 4.52X 8.746 5.109 8.601

C/N 105.5 129.0 197.3 253.5 292.5 242.8 237.5 250.5 188.3 280.8 10x.0 62.8 124.3 191.3 156.8 142.8 193.5 332.0 185.8 216.0 201.0 160.3 134.5 103.5 56.3 182.3 35.x 90.0 74.X 58.5 51.3 19.2 33.5 6Y.X 53.3 32.7 44.7

K 1.66 I.41 1.27 1.38 1.45 2.52 2.00 1.26 1.73 I.16 I .23 3.46 2.31 1.57 I.59 I.23 0.52 0.X5 1.34 1.74 1.00 1.66 0.56 0.84 1.7X 0.55 0.70 I.11 1.78 1.93 0.98 3.16 2.83 1.13 2.35 1.37 1.78

2.48 I.51 0.87 0.65 0.92 I .72 I.55 2.17 5.29 1.35 1.76 0.08 0.20 I .os 2.95 0.82 4.13 0.57 1.33 0.63 0.72 0.32 0.57 0.42 0. I6 0.24 0.12 0. I x 0.26 0.1 I 0.06 0.07 0.13 0.34 0.12 0.15 0.05

Kfd (%) Q 26. I 19,s 17.2 16.4 26.9 41.8 36.7 54.4 99.6 37.x 19.0 0.5 2.5 20. I 46.3 II.7 79.8 18.8 24.x 13.7 13.5 5.1 7.7 4.3 0.‘) 4.4 0.4 I.7 1.9 0.6 0.3 0. I 0.4 2.4 0.6 0.5 0.2

NRM 117.3 140.2 Xi.6 117.1 I SO.4 273.9 174.3 174.0 2 IS.6 12X.1 30.4 7.X 15.3 23.8 46.2 30.0 262.7 70.6 23Y.Y 79.4 46.‘) 34.0 25.1 30.9 6.3 23.5 6.2 14.0 13.7 5.8 4.8 3.3 6.2 12.6 9.1 4.9 3.5

ARM 167.0 272.4 272.1 302.9 434.6 394.8 424.2 435.x 436.9 353.7 125.3 28.2 141.4 187.0 208.0 163.0 299.7 360.3 354.3 294.3 263.4 183.7 126.3 120.2 24.6 lh0.l 26.4 x2.0 57.3 24.1 IS.0 9.7 23.0 44.3 29.0 14.4 12.1

IRM,,,,, 2761.‘) 3901.8 3490.0 4638.4 5293.7 6619.0 5513.0 5615.6 4091.3 5419.8 1615.0 319.8 1094.2 1944. I 2523.2 2533. I 4529.0 5883.3 4097.5 3859.7 2708.2 201 I.6 1404.7 1335.0 294.6 I YS3.7 340.2 822.5 655.3 264.0 210.4 94.8 205.6 689.8 686.0 210.6 150.1

SIRM 26.1X 30.25 17.69 I X.3 18.1 27.27 23.21 22.42 21.73 19.3 14.95 5.1 X.81 10.17 16.1 17.74 23.4 I 17.72 22.06 17.87 13.47 12.55 10.44 12.Y 5.24 IO.71 9.52 9.14 x.77 4.51 4.1 I 4.95 6.14 9.88 12.86 6.44 3.36

SIRM/K 51.7 55.2 44.0 42.0 39.0 58.2 48.0 43.0 44.0 39.0 42.0 59.0 41 .o 39.0 41 .o 59.0 47.0 43.4 46.0 47.0 35.0 38.0 38.0 31 .o 56.0 46.0 73.0 59.0 56.0 59.0 73.0 54.0 Xi.0 61.0 90.3 75.1 67.0

0.92 0.96 0.89 0.94 0.92 0.96 0.92 0.95 0.94 0.97 0.8X 0.83 0.80 0.89 0.93 0.89 0.96 0.94 0.95 0.92 0.92 0.88 0.93 0.87 0.X6 0.8.5 0.76 0.73 0.79 0.72 0.85 0.90 0.88 0.x’) 0.81 0.76 0.80

B,., (mT) S-ratio 2.95 I .73 2.05 2.94 3.78 6.89 4.38 4.37 5.42 3.22 0.77 0.20 0.39 0.60 1.16 0.76 6.60 1.77 6.03 2.00 I.18 0.85 0.63 0.78 0.16 0.59 0. I6 0.35 0.35 0.15 0. I2 0.0x 0.16 0.32 0.23 0.12 0.09

KARM 27.95 13.44 10.40 I I.61 12.93 28.37 IX.45 17.46 28.79 I I .47 7.08 3.13 3.10 3.12 7.41 5.29 34.13 5.34 32.47 9.24 5.87 5.33 4.68 7.50 2.82 3.24 4.38 3.92 4.61 2.50 2.34 4.29 4.66 4.54 4.29 3.76 1.96

KARMlK

1. Organic carbon content (C,,,,). total carbon content (C,,,,), sulfur content (s), nitrogen content (N) and magnetic paramctcrs for samples from Site 794

Sample

TABLE

5.3 6.5 11.7 12.2 II.1 10.4 9.9 12.3 12.2 13.7 8.8 0.9 9.1 7.2 6.6 m-l.1 14.6 5.8 9.6 6.2 6.6 6.8 3.7 4.6 -0.7 6.1 -9.6 -2.6 I.7 -2.5 -5.3 -6.0 -4.2 -2.4 -17.7 -7.8 -6.7

ALF

o\

0W

16.76 17.35 17.63 18.27 18.57 18.84 19.54 20.05 20.36 20.63 2 I .08 21.27 21.66 22.47 22.85 23.50

parametera

381-46 3H1-105 3Hl-133 3H2-47 3H2-77 3H2- 104 383-24 3H3-75 3H3-IO6 3H3-I 33 3H4-28 3H4-47 3H4-X6 3H5-17 385-55 385-120

Magnetic

L D L D 1, L L D D D L L L SD SD SD

ARM.

IRM,,,,,.

0.39 3.49 0.46 2.40 0.43 0.44 0.32 0.96 3.02 3.01 0.21 0.89 0.26 0.66 0.86 I.59 SIRM)

0.57 3.65 0.52 6.03 3.03 0.44 0.32 0.96 3.02 5.06 0.53 1.04 0.38 0.70 0.95 I .59 are exprc\\cd

0.23 4.98 0.23 2.23 0.43 0.26 0.27 3.77 6.33 3.05 0.39 0.29 0.49 0.43 1.19 0.42

Corg (‘%) C,,,, (%) S,,, (%)

in

6.459 I 1.046 4.742 12.345 6.X73 5.827 5.279 8.747 8.195 16.118 3.916 X.415 4.383 6.431 7.091 IO.587

C/N 56.5 30.9 38.5 9.6 39.1 42.1 38.4 55.3 29.7 14.6 64.4 58.3 93.3 43.8 65.0 60.1

K 1.47 0.81 0.49 1.57 1.53 1.78 2.77 0.67 1.78 7.04 1.47 1.72 0.54 1.28 0.96 2.08 (K)

values

0.06 0.06 0.13 0.17 0.08 0.25 0.14 0.08 0.08 0.12 0.09 0.08 0.20 0.08 0.04 0.07

Kfd (%) Q

mA/m. Magnrtic susceptitxlily

0.061 0.3 16 0.097 0.194 0.063 0.075 0.06 I 0.109 0.369 0.187 0.055 0.106 0.060 0.102 0.121 0. I so

N (%)

ARM 16.7 14.6 15.3 13.8 17.4 17.6 17.0 17.1 x.‘) 8.1 22.7 18.3 25.4 18.2 16.2 13.6

IRM,,rt 222.9 204.6 239.8 76.7 243.9 299.5 249.2 156.0 113.4 61.8 233.2 252.0 2459.0 222.0 195.1 164.3

SIRM

’ SI units (dimensionless).

6.0 3.x 5.4 2.9 5.5 7.0 5.2 5.2 3.3 2.2 6.6 6.6 13.9 6.1 7.0 5.3 are in 10

0.3 0.2 0.5 0.2 0.4 I.1 0.5 0.4 0.2 0.2 0.6 0.5 1.8 0.3 0.3 0.4

NRM 3.94 6.63 6.23 8.03 4.97 7.12 6.48 2.82 3.82 4.23 3.62 4.33 26.37 5.07 3 2.73

SIRM/K 71.0 66.0 73.0 41.0 73.0 72.0 78.0 70.3 68.0 53.0 50.9 70.0 74.0 66.0 56.0 61.0

0.79 0.89 0.86 0.95 0.87 0.86 0.86 0.91 0.88 O.Yl 0.95 0.87 0.98 0.86 0.92 0.88

B,, (mT) S-ratio

0.15 0.10 0.14 0.07 0.14 0.18 0.13 0. I3 0.08 0.05 0.17 0.17 0.35 0.15 0.18 0.13

KARM

2.69 3.08 3.55 7.74 2.79 4.21 3.40 2.38 2.82 3.72 2.58 2.84 3.75 3.48 2.71 2.21

KARM/K

1. Organic carbon content (C,,,,). total carbon content (C,,,). sulfur content (S). nitrogen content (N) and magnetic parameters for samules from Site 794

Color

(NRM.

Depth (m)

Sample

TABLE

-6.6 2.8 -5.4 -1.3 -7.8 -2.5 3.5 1.4 -4.3 -2.1 0.4 -6.1 1.0 -4.3 0.X -3.0

ALF

0.70 0.80 0.93 I .72 2.32 3.20 3.50 3.78 4.20 4.68 4.91 5.16 5.42 6.29 6.48 6.54 6.92 7.98 X.18 8.54 8.93 9.51 10.06 IO.45 IO.72 IO.85 1 I .46 I I .59 I I .77 12.52 12.84 13.20 13.46 14.04 14.45 14.71 15.10 ISSO 15.80 l6Sl

iHl-70 IHI-X0 lHl-93 I H2-22 182-82 I H3-20 I H3-50 I H3-78 I H3- I20 lH4-IS I H4-4 I I H4-66 1H4-02 185-29 I HS-48 I HS-54 I H5-92 I H6-4X 1H6-68 IHh-I04 186-143 2HI-21 2Hl-76 ZHI-I IS 2Hl-I42 2H2-5 2H2-66 2H2-79 2H2-97 2H3-22 2H3-54 2H3-90 2H3-I 16 2H4-24 2H4-65 2H4-Y I 2H4- I30 2H5-20 285-50 2HS-121

SD D D SD 1~ SD SD SD L SD L SD L SD L SD L D L D L SD SD SD D L D L SD D SD D L SD L D SD L L D

Depth (m) Color

I .93 2.26 I.91 I.15 0.48 I .85 I .oo 0.90 0.38 2.15 0.78 2.88 0.41 I.93 0.52 2.77 0.52 I .os 0.37 0.91 0.32 I.51 I.01 0.38 2.94 0.33 2.21 0.43 I .02 I .49 0.84 I.91 0.32 I s4 0.57 I .63 I .XY 0.47 0.49 I.75

I .Y3 2.26 I .99 I .20 0.43 2.02 1.00 I .Oh 0.38 2.30 0.81 I .54 0.47 2.06 0.5 I 2.77 3.15 I.12 0.43 0.90 0.89 0.68 I.19 0.50 2.94 0.36 I.I 331 0.4 I 0.85 I .49 0.93 2.49 0.32 I .57 0.57 1.77 1.89 0.57 0.85 I .76

Cc,,u (%,) C,,,, (%) 0.29 2.85 0.42 3.51 0.46 0.19 0.31 0.26 0.93 I.31 0.26 0.47 0.19 0.53 0.64 0.73 0.19 4.44 0.70 3.31 0.22 0.23 1.29 0.2x 3.60 0. I 3 0.38 0.21 0.22 3.1 I 0.46 4.18 0.3’) 0.52 0.12 0.71 0.76 0.10 0.09 0.34

0.210 0.223 0.196 0. I30 0.064 0.196 0.117 0.102 0.588 0.09 I 0.24X 0.143 0.076 0.200 0.08s 0.262 0.077 0. I2 I 0.067 0. IO2 0.080 0.06X 0.096 0.080 0.295 0.062 0.205 0.060 o.oxx 0.161 0. I07 0.131 0.063 0.162 0.085 0. I40 0.130 0.067 0.068 0. I66

S,,,, (o/c) N (%) 9.18 IO.12 9.77 X.88 7.50 9.45 X.56 8.78 0.65 23.63 3.13 20.13 5.37 9.66 6.16 10.5x 6.73 X.67 5.52 X.96 3.96 22.25 10.51 4.74 9.95 5.29 IO.79 7.13 I I.61 9.24 7.87 14.60 5.00 9.48 6.74 I I.65 14.54 6.97 7.24 IO.54

C/N 95.0 206.X 156.5 58.8 185.8 373.2 304.5 202.8 436.0 366.5 26X.3 166.0 328.8 182.X 189.3 24x.0 210.5 62.0 297.5 60.5 276.5 405.0 250.8 236.8 65.2 240.0 lYO.3 405.5 217.5 11X.5 257.5 54.5 212.8 355.3 356.8 303.5 304.8 375.8 587.x 593.5

K 0.61 2.06 2.45 2.77 1.43 1.36 I .40 2.10 2.05 0.95 2.12 2.91 2.05 1.46 1.06 I .x I 2.49 I .0x I.35 0.83 0.36 2.66 0.66 0.53 0.4x 1.35 I.31 I.17 I.38 I.01 I.36 1.38 0.91 1.30 0.42 I.15 I.31 1.24 1.52 2.15

Kfd(%)

NRM

0.58 5.5 2.36 48.8 1.75 27.3 0.18 I.1 0.34 6.3 0.96 35.9 0.54 16.4 I.13 23.0 0.46 20.2 1.27 46.5 I.14 30.7 2.29 3x.0 0.88 29.1 0.67 12.3 0.77 14.6 I .07 26.5 0.57 12.0 0.13 0.8 0.56 16.7 0.06 0.4 0.33 Y.2 0.45 IX.2 0.4x 12.0 0.28 6.7 0.16 I.1 0.24 s.7 0.79 IS.0 I.15 46.6 0.50 IO.8 0.73 x.7 3.74 122.0 0.27 I.5 0.46 9.8 I.10 39.0 1.48 53.0 0.99 30.0 0.65 IY.8 0.97 36.6 0.71 41.5 0.76 45.1

Q 24.8 196.6 15X.5 12.5 27.6 221.5 22 I .3 196.9 161.6 127.x 213.X I x0.0 201.7 x9.4 123.6 274.4 75.2 8.8 57.1 8.4 64.7 91.1 40.5 36.6 9.6 46.3 67.5 116.6 93.1 37.4 60.5 X.0 28.2 343.6 162.4 3 I I .6 2X1.2 168.7 244.‘) 435.3

ARM 163.4 382.6 279.X 52.2 192.6 517.3 427.3 289.4 604.3 453.0 43S.6 34 I .h 470.1 292.2 361.7 5 IS.5 251.5 40.6 321.0 44.1 395.0 372.6 2X2.7 281.6 78.5 303.Y 364.1 3x1.4 263.6 1x3.x 242.4 49.6 194.0 586.2 527.0 1075.3 612.2 717.1 963.2 725.0

IRM,,,,, 1550.8 5473.4 4154.1 763.9 4076.8 10597.0 10265.9 5014.x 8082.0 12152.3 7826.0 49X9.3 8476.0 4035.3 3591.5 7314.5 3704.4 414.5 55 16.0 397.4 4078.7 12136.6 3568.6 3033.3 648.3 3102.0 3486.7 25888.0 9215.9 2323.4 9500.0 414.5 2505.2 891 1.9 X797.0 8544.0 X005.6 7713.0 15306.0 2973 I .o

SIRM 16.32 26.47 26.54 13.00 2 I .9S 28.40 33.71 24.73 18.54 33.16 29. I7 30.06 25.78 22.08 IS.98 29.49 17.60 6.69 I x.54 6.57 14.75 29.97 14.23 12.x I 9.95 12.Y.3 18.33 63.84 42.37 19.61 36.89 7.61 11.7x 25.09 24.66 28. IS 26.27 20.53 26.04 50.09

SIRM/K 27.0 51.1 47.0 74.0 62.2 55.0 58.0 54.0 40.0 58.0 61.8 56.4 47.0 55.3 39.0 46.5 40.0 62.2 49.3 60.0 39.0 59.0 39.0 35.0 46.0 3x.0 39.0 72.6 65.0 39.0 67.0 57.0 43.0 46.8 60.0 S4.2 55.6 47.0 55.0 71.5

0.99 0.95 0.98 0.85 0.92 0.97 0.96 0.97 0.95 0.98 0.96 0.96 0.96 0.94 0.95 0.96 O.Y2 0.83 0.95 0.82 0.93 0.94 0.94 0.96 0.81 0.92 0.96 0.99 I .oo 0.95 I .OO 0.84 0.93 0.96 O.Y7 0.97 0.96 0.96 0.97 0.99

B,, (mT) S-ratio 0.62 4.94 3.99 0.32 0.69 5.57 5.56 4.95 4.06 3.21 5.37 4.53 5.07 2.25 3.1 I 6.90 I .XY 0.22 I .43 0.21 I .63 2.29 1.02 O.Y2 0.24 I.16 I .70 2.93 2.34 0.94 I .52 0.20 0.7 I 8.64 4.08 7.83 7.07 4.24 6.16 IO.94

KARM 6.56 23.91 25.46 5.37 3.74 14.92 18.27 24.42 9.32 8.76 20.04 27.26 15.43 12.30 16.42 27.82 X.99 3.56 4.82 3.47 5.88 5.65 4.06 3.88 3.70 4.85 x.91 7.23 IO.76 7.94 5.90 3.69 3.34 24.32 I I.45 25.8 I 23.20 I I .2Y IO.47 I x.44

KARM/K

2. Organic carbon content (C,,,,), total carbon content (C,,,,), sulfur content (S), nitrogen content (N) and magnetic parameters for samples from Site 795

Sample

TABLE

15.4 17.2 1.9 -5.X -0.5 10.2 9.8 17.4 8.9 2.4 3.5 10.0 6.X 6.x 13.2 16.0 7.6 -1.2 3.4 0.2 10.0 -2.6 6.7 8.1 6.9 7.6 10.7 -5.5 -3.3 7.9 2.0 0.4 4.8 15.6 3.3 IS.1 14.0 II.0 7.9 2.5

ALF

17.00 17.44 17.81 18.47 18.63 lY.04 19.77 20.4’) 20.94 21.46 21.62 21.98 22. I I 22.20 22.48 23.49 23.Yh 24.86 25.21 25.51 2S.Y4 26.80 27.30 27.62 28.16 28.35 2X.SO 29.20 29.47 30.00 30.24 30.95 3 1.50 3 I .98 32.25 32.47 32.9s 33.97 34.10

2H6-20 286-64 2H6-IO1 2H7-17 287-33 3Hl-24 3Hl-97 3H2-I9 3H2-64 3H2-I I6 382-132 3H3-1X 3H3-3 I 3H3-40 383-68 3H4- 19 3H4-66 3HS-6 3HS-4 I 3H5-77 3H5-I 14 3H6-SO 3Hh-IO0 3H6- I32 3H7-36 3H7-55 4H l-20 4H I-90 4Hl-I 17 4H2-20 4H2-44 4H2-I IS 4H3m20 4H3-68 4H3-95 4H3-I I7 4H4- I5 4H4-I I7 4H4-130

SD D D I. D L L D L D D D L

L

SD L SD L D L L SD D L L SD L D L SD SD SD I< D I> L SD SD D

Color

0.92 0.70 0.46 0.57 0.84 0.55 0.40 I .04 0.91 I .42 0.57 2.72 0.39 2.94 0.27 0.17 0.74 I .07 0.85 2.76 0.45 0.38 0.72 0.8X 2.63 0.41 0.37 0.65 1.72 0.27 ? ?6 -.0.25 0.3x 2.30 0.32 0.97 I .49 3.82 0.38

0.92 0.57 0.63 0.84 0.84 0.55 0.49 1.04 0.89 5.03 0.76 I.41 0.36 2.80 0.27 0.77 0.60 I .07 0.59 3.75 0.59 0.38 0.89 O.Y.7 2.60 0.42 0.36 0.62 1.72 0.92 3.64 0.25 3.00 2.30 0.39 0.99 I .38 3.82 0.38

Corf (%) C,,, (‘ir) 0.58 0.14 0.11 0.24 3.76 0.25 0.12 0.16 3.54 I .79 I .25 0.93 I .29 5.25 0.20 0.26 0.16 0.34 0. I7 3.7Y 0.22 0. IX 0.33 0.53 7.45 0.18 0.26 4.99 5.37 0.40 3.35 0.3 I 0.14 0.93 0.29 3.95 I .49 3.19 0.63

S,,, (%) 0.107 0.088 0.072 0.073 0.094 0.074 0.082 0.064 0.103 0.125 0.077 0.129 0.053 0.249 0.05 I 0.089 0.067 0.1 I.7 0.062 0.233 0.069 0.096 0.086 0.109 0.244 0.073 0.061 0.074 0. I40 0.057 0.223 0.057 0.064 0.217 0.072 0.11 I 0.139 0.322 0.077

N (%) 8.63 7.97 6.39 7.79 8.91 7.43 4.84 16.27 X.79 Il.39 7.3X 21.10 7.26 11.79 5.37 X.63 1 I .OO 0.50 13.71 11.x.3 6.45 3.YX 8.36 X.10 10.77 5.67 6.02 X.82 12.26 4.72 IO.1 4.32 5.94 10.60 4.50 8.74 IO.71 I I.85 4.88

C/N 186.8 171.5 103.2 134.7 75.3 212.8 3 17.0 247.8 57.9 63.0 118.3 65.3 56.4 29.6 ‘13.5 145.8 285.2 176.3 666.5 61.0 706.3 178.5 94.3 97.3 80.8 102.5 107.3 61.0 47.X 65.8 38.5 7X.5 52.2 56.0 103.8 57.X 139,s 47.6 113.0

K 0.98 2.19 0.87 0.62 0.66 1.73 2.05 1.61 1.47 0.92 1.27 2.54 0.20 1.31 0.39 1.03 1.60 0.57 0.90 I.64 0.73 0.98 0.84 1.29 1.02 I.71 I .S6 2.1s 2.25 2.01 3.02 1.48 2.86 1.04 1.93 1.73 1.07 0.64 1.33

Kfd(%) 0.77 0.40 0.37 1.84 0.28 1.26 0.75 0.69 0.08 0.06 0.39 0.06 0.07 0.08 0.30 0.x0 I.12 0.73 I.11 0.20 0.08 0.26 0.04 0.10 0.08 0. I I 0. IO 0.07 0.14 0.26 0. I2 0.23 0.27 0.13 0.17 0.08 0.26 0.05 0.26

Q 14.4 6.9 3.8 24.X 2.1 26.7 23.6 17.1 0.4 0.4 4.7 0.4 0.4 0.2 6.3 II.7 31.Y 12.9 13.7 I.2 I.6 4.6 0.4 I .o 0.6 I.1 I.1 0.4 0.7 I.7 0.5 1.x 1.4 0.7 I.7 0.5 3.7 0.3 3.0

NRM 47.4 42.7 15.4 17.5 x.4 180.9 229.0 129.7 6.7 5.X 20.5 7.9 6.1 4.6 29.S 128.5 251.5 243.1 194.9 I I.2 30.7 36.1 I I.2 17.4 IO.6 19.3 II.8 6.6 6.X 8.4 5.8 13.2 12.7 7.1 14.3 6.X 23.1 6.X 14.4

ARM 279.8 217.8 216.6 147.7 41.1 456.2 612.8 294.3 25.3 33.7 79.7 44.1 24.1 24.3 225.4 23x.9 528.6 289. I 384.0 46.7 253.9 237.5 64.8 Y9.S 70.8 118.3 x2.9 31.7 71.2 26.7 19.0 34. I 73.7 29.6 XI.5 23.6 95.5 32. I 107.2

IRM,,,,, 2819.7 2237.7 1019.9 1324.5 416.3 3793.6 6282.0 3977.3 304.9 281.7 3506.0 399.5 320.1 243.1 3X79.0 2730.0 5999. I 600 I .6 362 18.0 631.1 3347-.-1 ‘102.3 557.7 1028. I 6.50.6 ll3S.S 707.5 249.5 307.2 631.1 22 I .s 1744.2 627.5 402.2 1042.8 274.7 3 109.8 329.4 1011.0

SIRM IS.10 13.05 9.89 9.83 5.53 17.83 19.82 16.05 5.27 4.47 29.65 6.12 5.68 x.21 IX. I7 I x.73 21.04 34.05 54.34 IO.35 I I .36 1 I .78 5.91 IO.57 X.06 I I .0x 6.60 4.09 6.42 9.60 5.75 22.22 12.03 7.18 10.05 4.76 22.29 6.92 8.95

SIRM/K 37.0 37.0 39.0 37.0 59.0 37.0 37.0 40.0 60.0 55.0 70.0 45.0 68.0 53.0 61 .O 41 .o 4 I .o 63.0 61.8 71.4 39.0 37.0 40.0 41.0 44.0 43.0 36.0 63.0 73.0 75.4 64.0 75.8 64.0 62.0 62.0 64.0 61.0 56.0 42.0

0.94 0.88 0.83 0.88 0.79 0.93 0.96 0.93 0.86 0.82 0.98 0.87 0.79 0.86 0.92 O.YS 0.96 0.97 0.84 0.75 0.91 0.89 0.86 0.88 0.8 I 0.82 0.89 0.X7 0.86 0.93 0.87 0.98 0.82 0.x0 0.83 0.77 0.97 0.83 0.79

B,, (mT) S-ratio I.19 I .07 0.39 0.44 0.21 4.55 5.76 3.26 0. I 7 0.15 0.51 0.20 0.15 0.12 0.74 3.23 6.32 6.1 I 4.90 0.28 0.77 0.91 0.28 0.44 0.27 0.48 0.30 0.17 0. I7 0.21 0.15 0.33 0.32 0. IX 0.36 0.17 0.58 0. I7 0.36

KARM 6.38 6.25 3.74 3.27 2.79 21.38 18.16 13.16 2.93 2.31 4.35 3.06 2.72 3.92 3.48 22.17 22.17 34.67 7.35 4.63 3.74 5.08 2.99 4.49 3.30 4.73 2.76 2.71 3.57 3.20 3.80 4.24 6.10 3.20 3.46 2.96 4.16 3.60 3.21

KARM/K

2. Organic carbon content (C,,,,), total carbon content (C,,,,), sulfur content (S), nitrogen content (N) and magnetic parameters for samples from Site 795

Magnetic parameters (NRM. ARM. IRM,,,,,. SIRM) are exprersed in mA/m. MayneGc susceptibilq (K) values are in IO?’ SI units (dimensionless).

Depth (ml

Sample

TABLE

X.9 5.8 6.0 4.3 4.0 -2.1 6.5 -6.X -3.1 -0.2 -6.Y -3.6 -1.2 -1.3 0.1 3.4 5.4

1.9

8.3 6.0 4.9 7.6 2.5 12.2 13.4 16.6 0.5 0.4 2.7 2.8 -4.5 - 1.4 -2.6 10.9 17.0 2.5 I I.4 m-3.6 9.5

ALF

1100

Time

-0: 10 1 ;;3;’

~

5

7

‘X?~

9;

i 11 : 12 I 13

15

17 18:

Time FIG. 2. Sulphur content (%J) and magnetic susceptibility(K) (dimensionless, IO ’ SI Units) ‘tuned’ to the Oxygen Isotope Stages for samplesdepositedduringthe sametime interval in the YamatoBasin(Site 794; opensymbols)andthe Japan Basin (Site 795; full symbols) according to the correlation with Site 797 made by Tada PI al. (1992). The isotopic stage 8 boundaries are not well defined. and are thus drawn with a different (dashed) line.

66-68), which in some casesis coupled with a lower unblocking temperaturejust below 300°C (Fig. 4, samples 794 3H2 77-79 and 795 4H4 15-17). The medium coercivity fraction (0.12-0.4 T) has essentially the same unblocking temperatures which suggests a mixture of (titano)magnetite with higher coercivity minerals. Iron sulfides are present in these sediments(pyrite is common throughout the cores) and an iron-rich form of pyrrhotite (Fe9S,,,; Tc=260”C, O’Reilly, 1984; or Tc=29O”C. Thompson and Oldfield, 1986) may be the explanation for the low unblocking temperature ferrimagnetic phase present in the samples shown in Fig. 4. A similar interpretation hasbeengiven by Torii et al. ( 1992) for the magnetic mineralogy of the sedimentsrecovered at Site 797. However, it is possibleeven that greigite (Fe&) is represented in these sediments. This mineral is not common in deep sea sediments, but its occurrence is certainly underestimated(Verosub and Roberts, 1995). The hard IRM fraction (0.4-l. 1.5T) is a very small portion

of the total IRM

and it is difficult

to identify

unblocking temperaturesfrom the overall plots of Fig. 3. For this reason it is plotted separately in Fig. 5. This figure showsthat many samplesin this coercivity fraction have unblocking temperatures in excess of 58O”C,

indicating that hematite is alsopresentin thesesediments. The magnetic mineralogy of the sediments is dominated by magnetite. However, we should take into account that canted antiferromagnetic minerals such as hematite are two ordersof magnitude lessmagnetic than ferrimagnetic minerals.Therefore, even if the concentration of hematite is much greater than that of magnetite. it will not influence significantly the bulk magnetic properties of the sediment, which will be dominantly ferrimagnetic. The hematite observed in the samplescannot be a heating artifact because,if this were the case,it would have been oriented randomly rather than along the z-axis with highest coercivity. All these data suggestthat the magnetic mineralogy of the sedimentsat Sites 794 and 795 is characterized by a mixture of magnetic mineralsincluding (titano)magnetite, pyrrhotite and/or greigite, and hematite.

Carbon, Sulfur and Nitrogen Analyses The Cclrgcontent of the JapanSea sedimentsis variable, ranging between 0.26 and 7.63% at Site 794 (Fig. 6), and between 0.35 and 3.82% at Site 795 (Fig. 7). The sulphur

L. ViEliotti: Magnetic Properties of Sediment Layers from the Japan Sea

100 s 2 SITE 794 2

10

‘I

I

0

200

’

I

400

’

I

600 mT

’

I

800

I

’

I

1000 1200

10000

1000 g 3-

100

10

1 0

200

400

600 mT

800

deposited under anoxic conditions. Marine organic carbon enrichment may have been caused by increased surfacewater productivity or by increased preservation rate of organic matter under anoxic conditions. In general, these anoxic conditions occur during glacial stages (Figures 6 and 7). The glacial sea of Japan has been described as a poorly ventilated basin with low surface productivity (Ujiie and Ichikura. 1973), so anoxic deep-water conditions are the dominant mechanism controlling the preservation of the organic carbon. In spite of the low carbonate content of the sediments, a surprising inverse correlation exists between variations in magnetic susceptibility and C,,,, (Figures 9 and IO). Maximum values of both C<,rgand S were measuredbelow a depth of I I m (Six0 Stage IO) at Site 794. The carbon/nitrogen (C/N) ratio, (Tables 1 and 2), ranges between 4 and 16 at Site 794, and although, in general, the same range is spanned at Site 795, some spikesreach values above 20 at this site. The observed C/ N ratios suggest a mixed marine/terrigenous type of organic matter with the marine proportion dominant. The lower values of this ratio (generally below 8) belong to the light layers at both the sites. This parallels the minimum organic carbon content of these layers.

Differences in Magnetic Properties between Light and Dark Layers

SITE 795

E

I IO1

1000 1200

FIG. 3. Typical IRM acquisition plots for light (open symbols) and dark (full symbols) sediment layers from the Japan Sea. IRM intensity is expressed in mA/m.

content is also variable ranging between 0.09 and 5.13% at Site 794 (Fig. 6), and between 0.11 and 5.36% at Site 795 (Fig. 7). The observed ranges of Corg and sulfur are similar to those found by Tada et al. (1992) at Site 797 in the Yamato Basin. Fig. 8 shows the magnetic susceptibility plotted against the Corg and sulfur content at the two sites. Dark sediments, with very low susceptibility values exhibit the highest C,,., and sulfur content. Except in a very few cases, both Core and S content yield values above 1% only for the dark layers, suggesting that the presence of organic carbon contributes to the dark color (Tada, 1991). Corg and S content make the dark layers similar to the sapropelitic layers found in the Mediterranean Sea and the Black Sea (Rohling and Hilgen, 1991). The ratio between the Corf and the St<,, (C/S) can be used to distinguish euxinic from non-euxinic conditions (Berner and Raiswell, 1983). According to these authors the C/S ratio in modern non-euxinic marine environments is about 3. This means that most of the dark cycles were

Individually, magnetic parameterslike K, NRM, ARM and SIRM reflect the concentration of the ferrimagnetic minerals (i.e. magnetite-type) in the sediments,but also respond in different ways to variations in the average domain state (grain-size) of these minerals. In a mixed domain stateassemblage.K is more strongly influenced by coarser-grained ferrimagnets while SIRM, ARM and NRM are biased toward finer-grained ferrimagnets (Dankers, 1978; Harstra, 1982; King et al., 1982; Ozdemir and Banerjee, 1982). Thus relative changesin the ratio of coarserto finer grained ferrimagnets. aswell as in the total ferrimagnetic concentration. will influence these parameters. The presence of very fine-grained (<0.04 pm) ferrimagnets can be detected by the occurrence of significant frequency dependent susceptibility (e.g. Mullins and Tite, 1973; Thompson and Oldfield, 1986). The magnetic properties of the sedimentsat Sites 794 and 795 appear to discriminate between dark, semidark and light samples on the basis of their ferrimagnetic concentration. At both sitesthe dark sedimentsare usually characterized by lower values for concentration dependent magneticparameters,suggestinga lower magneticcontent for these layers. At Site 795, however, the minimum and maximum values of SIRM, ARM and K are found in the dark layers suggestinga wider variation in ferrimagnetic concentration within the dark sedimentsat this site. In most casesthe maximum values are observed in the dark layers depositedduring the interglacial stages. The modified Koenigsberger ratio (Q=NRM/K) provides a measure of magnetic stability as well as an indicator of changes in the magnetic properties. The

I 794 2HI

114-l

“.m

16

795

‘I

i

0.12 - O.?T

0

100

200

300

400

500

600

700

0

100

200

300

,

200-a

I

794

‘. ‘.

3000

,

2500 -

!

3H2 77-79

-

.1~

-

2000 E ;2 .g 1500-

0

100

200

300

400

500

600

700

795 4H4

4. Types

of thermal

600

700

500

600

700

demagnetization

15-17

“.,.’ 0.12 T

0

100

200

300

400 “C

curves

of composite

of the isothermal remanence Boc,,-, is indicative of the magnetic hardness of the sediment which is a function of both mineralogy and grain-size. Thompson and Oldfield (1986) gave a Boc,,-, of’ 33 mT for single domain (SD) magnetite, IS mT for multi domain (MD) magnetite and 700 mT for hematite. Histograms of Q and B,,(,,-, values (Fig. 11) show that the dark layers are characterized by lower Koenigsberger ratio values (generally below 0.2) and higher coercivity of remanence. Low Q values can be attributed to the presence of MD or SP magnetite grains, both of which contribute more strongly to susceptibility than to remanence. However, frequency dependent susceptibility is below 2% in most of the samplej (Table 1) which indicates that superparamagnetic grains are almost absent from these samples. so rhe results suggest that the dark layers are characterized by a larger grain size. This contradicts the observation that B,, values are higher in these layers. but this can be explained by a relative increase in the contribution of higher coercivity minerals.

coercivity

500

i

“C FIG.

400 “C

“C

250

2H2 66-68

orthogonal

IRMs.

IRM

values

are expressed

in mA/m

In order to check the domain state of the magnetic minerals we can compare the spectrum of coercivity of the ARM and IRM by applying a modified Lowrie-Fuller test (Johnson cv crl., 1975). To make a quantitative evaluation of this test Petersen et crl. (1986) introduced a parameter called ALF. that is the difference between the median destructive field (MDF) of the ARM and MDF of the IRM. Positive values of _1LF indicate a dominance of single domain magnetic grains, while negative values imply the presence of multi-domain grains. This parameter provides a numeric value for the Lowrie-Fuller test and is similar to the interparametric quotient AMDF (I -MDFSIKM/MDFARM) introduced by Dunlop (1953). Increasing values of AMDF suggest a change in the domain structure from multidomain (MD, negative values) to stable single domain (SSD. positive values) to a mixed assemblage of SSD+MD (higher values); the same changes in the domain structure can be predicted for ALF. This latter parameter is plotted against anhysteretic remanence. MDFIRbl and S-ratio for sites 794 and 795 in Fig. I? and Fig. 13. respectively. A positive correlation is

L. Vigliotti: Magnetic Properties of Sediment Layers from the Japan Sea

SITE 794

0

100 200 300 400 500 600 700 “C

,

\

0

100 200 300 400 500 600 700 “C

SITE 795

F

I

600

3 400 200 0

FIG. 5. Thermal demagnetizationcurves for the hard IRM fraction (0.4-1.15T). Open (closed)symbolsfor light (dark) sediments. IRM intensityin mA/m.

1103

observed between ALF and ARM. but surprisingly a negative correlation is observed between ALF and MDFIKM (Figure 12 and 13). This contradicts theory by suggesting that coercivity (expressed by the MDFIRM) increaseswith increasinggrain size (expressedby ALF). An interpretation of this apparent contradiction is that the samples with larger magnetic grain size are also characterized by an increasingcontribution from minerals with higher coercivity. The positive correlation between ALF and S-ratio (Figure 12 and I3), as well asthe higher Bo,r,-, values observed in the dark layers, support this interpretation. For magnetic mineral assemblagesdominated by ferrimagnetic minerals. the ratios KARM/K and SlRM/K respond to changes in magnetic grain size within the magnetically stable fraction. K increasesthrough the SDPSD-MD range, while KAKM and SIRM show an opposite trend. sothat higher (lower) valuesof theseratios represent an increasing contribution from finer (coarser) magnetite grains (King et rrl., 1982).The resultswhich bestillustrate the changes in the magnetic properties within light and dark layers are representedby the samplescollected from Section 5 of Core 794- 1H and from Section 6 of Core 795 IH. These samples were collected in adjacent. well defined, light and dark horizons as can be seenin Fig. 14. In the samefigure are plotted the magnetic properties, as well asthe Corgand the S,cltmeasuredin the samples.The data show clearly that the change from light to dark layers is accompaniedby: (a) increasingsulfur and organic carbon content; (b) lower magnetic mineral content expressed by a decreasein the values of K. ARM and SIRM; (c) higher coercivity defined by higher Boc,,, and lower S-ratio values; (d) coarseningof the magnetic grain size expressedby a decrease in the ilLF values. as well as in the interparametric quotients K,,,,/K and SIRM/K.

SITE 974

T

l-

IO

IS Depth (mbsf)

FIG. 6. Downcore

profiles for Cr,rf (solid symbol)and S,,,, (opensymbol)contentfor Site 794. Ilashedlinesrepresent

boundaries of the Oxygen IsotopeStages.

1104

Qurrtrrnar~~

Science

Revievcs:

Volume 16

SITE 79.5 6

:7;

8?;

9

j II

13 ~ : : :

iI. i 17: : : : P/ ~

I5 20 Depth(mbsf) FIG. 7. Downcoreprofilesfor C,,,., (solid symbol)and S,,,,(opensymbol)contentfor Site 7%. Dashedlinesrepresent boundaries of the Oxygen IsotopeStages. Downcore Variations in Magnetic Properties

q

Q*

&& q* @SO& OcBBo I 0

4

10

10

100 K (IO-6 SI units)

400

100 K (lo-6 SI units)

1000

FIG. 8. Plots of magneticsusceptibility K (dimensionless) versussulfur content. Open (solid) symbolsfor light (dark) sediments, half-solidsymbolfor semidarksediments.

Downcore variations in rock magnetic parameters exhibit a significant difference between the two sites. Two major features characterize the magnetic profiles of Site 794. A significant drop in the values of all concentration-dependent bulk magnetic parameters (K, ARM, SIRM, NRM) occurs below 11 mbsf and at about 6 mbsf (Fig. 15). Downcore profiles of IRM,,,r, (indicative of ferrimagnetic mineral concentration) and of KARM/K (indicative of magneticgrain size) (Fig. 16) suggestthat, at these depths, the decreasein magnetic concentration is coupled with an increasein the grain size. Values for ALF alsosuggesta coarseningof magneticgrain size and a shift from SD to MD domain structures. Furthermore, the sediments exhibit an increase in magnetic hardness, testified to by lower S-ratio values and higher coercivities of IRM (Fig. IS). Higher values for Corg and sulfur measuredin these two intervals indicate a more anoxic environment at thesetimes. Covariations with shifts in the ‘“0 isotopic stagessuggesta correlation with the glacial stages6 (6 mbsf) and 10 ( 11 mbsf). At Site 795 there are not such well defined features in the profiles of magnetic parameters. Only KARM and IRM,,,r, (IRMZO,,,r) profiles (Fig. 17) exhibit a clear trend reflecting downcore variations in the concentration of SD magnetite. A significant decreasein the values of these parametersis observed below about 25 mbsf. Above this depth, high and low values of ARM and IRM,,,r, correspondto interglacial and glacial stages,respectively. The same glacial-interglacial signature is observed in grain size parametersALF and KARM/K (Fig. Ig), aswell as in magnetic hardnecs parameters S-ratio and Boc,,-, (Fig. 19). Maximum magnetic grain sizes and higher coercivities of IRM are typical of glacial stages, A general increase in magnetic hardness (lower S-ratio) seemsto occur below about I8 mbsf.

L. Vigliotti:

1105

Magnetic Properties of Sediment Layers from the Japan Sea

SITE 794 0,l

g

g

1,

c

10 10 1.5 Depth (mbsf! FIG. 9. Downcore

profiles of C,,, (open symbol) and K (solid symbol) for Site 794.

DISCUSSION Effects of Diagenesison the Magnetic Properties The magnetic properties of the Japan Sea sediments show that their magnetic mineralogy is dominated by ferrimagnetic (magnetite-type) componentswith a minor contribution made by iron sulfides (pyrrhotite and/or greigite) and canted-antiferromagnetic minerals (hematite). Iron sulfides such as greigite or pyrrhotite may be produced by magnetotactic bacteria in sedimentsrich in sulfide (Mann et al., 1990; Farina ef ul., 1990); however, their presence in these sediments is attributed to the reductive diagenesis of magnetite. Although a similar mineralogy is exhibited by both light and dark layers, a

significant difference exists between each layer in the content and grain size of the ferrimagnetic mineral present in the sediment. A lower concentration of magnetic minerals and a larger magnetic grain size are typical of the latter (Fig. 16). Sulfate reduction due to bacterial degradation of organic matter has been recognized in several suboxic/ anoxic environments (Karlin and Levi, 1983, 1985; Canfield and Berner, 1987; Channel1 and Hawthorne, 1990; Leslie et al., 1990; Karlin, 1990a, b). This process leads to the dissolution of the magnetic minerals and subsequenttransformation into iron sulfides. Pyrite is the most stable iron sulfide phaseunder reducing conditions (Berner, 1984), and this mineral has been observed

SITE 795

032

6,

0

5 FIG. 10. Downcore

10

15

20 Depth (mbsf)

25

30

35

profiles of C,,,, (open symbol) and K (solid symbol) for Site 795.

1106

I

I

I

I

I

III1

cI

+

l-4 I

I

I

I

IIII I I I I

I I I I

I I I

\9

” 3 -0

g”G

t 0

I

0

E2 5: M I

I I I

9

II I I I I

I I I I

l-7

I I I I

9 0 rz

90

I I I I

I I I

I I

a 0

I I I

!a I I I I

I

I I I I

I

I I I I

I

I I

I

I I

I

I

I I I

I I

I I

-t 5‘ 00

I I

3

I 1

I

I

I

I 1

I

I

I

I 1

I 1

1

I

z

8

22

s

%

gz

‘; b 0’

m

8

$

l-z cc

kmanbaq

I

2 d

I I

I I 1 Omw.+mo

I

I

I

I

I

I PI

dsuanb3.y

9 I I

R

I =

PI -

I I

I I

I I

I I

I ‘I’I’I’,‘I,

I

I

I

I

2

30

w

*

PI

A3uanba.g

- r9 3

L. Vigliotti:

Magnetic

1107

Properties of Sediment Layers from the Japan Sea SITE 794

““/

1

10 ARM

100 (mA/m)

1000

I

10

20

!

I

/

40

50

60

‘,

30 MDF-IRM

0.x S-ratlo

0.7

(mT)

0.9 (-0.3T)

FIG 12. Lowrie-Fuller test parameter ALF plotted versus ARM, MDF of IRM and S-ratio (-IRMP,,,,,/SIRM) Open (solid) symbols for light (dark) sediments, half-solid symbol for semidark sediments.

Paleoclimatic Implications Tem’genous Minerals

clearly in the sediments collected from the Japan Sea (Tamaki et al., 1990). The presenceof pyrite implies the

formation of intermediate ferrimagnetic iron sulfides such as pyrrhotite and greigite. In reducing environments, the reductive processproceeds through an initial dissolution of the finest magnetic fraction followed by the destruction of the remaining coarse grains (Karlin and Levi, 1983, 1985). This process can explain

the magnetic

I .(I

for Site 794.

and Origin

of the

Major changes in the magnetic parameters correlate with glacial-interglacial cycles suggesting that climate change is the principal mechanismdriving variations in magnetic properties of the Japan Sea sediments.Warm interglacial stagesare generally associatedwith a higher magnetic mineral content and a higher proportion of fine grained ferrimagnetic minerals. Cold glacial stageshave a lower magnetic mineral content and coarser assemblages of ferrimagnetic grains. Downcore variations in the magnetic properties of the sediments can be also related to changes in the paleoclimatic/paleoceanographicconditions of the basin. At site 794. a significant change in both magnetic

properties

observed in the sedimentsof the Japan Sea, in particular the differences betweenthe dark and light layers asshown in Fig. 11. All the samplesshowed very little frequency dependent susceptibility (generally ~2%) indicating that superparamagneticparticles (SP) constitute an insignificant fraction. Diagenetic dissolution of magnetite explains the lower magnetic concentration and the coarser magnetic grain-size observed in the dark layers.

SITE 795

-lO1..

loo0 ARM

(mA/m)

i!

101 10

/

30

20 MDF-IRM

40 (mT)

50

0.7

0.8

I).“,

IO

s (-0.3Tl

FIG. 13. Lowrie-Fuller test parameter ALF plotted versus ARM. MDF of IRM and S-ratio (-IRM ,, IT/SIRM) for Site 795 Open (solid) symbols for light (dark) sediments, half-solid symbol for semidark sediments.

1108

Quaternaq

Science Reviews: Volume 16

794-lH5 0

I BCK

20

*;\

\\

,? u; /’

E30 2 240 50

“P

F /

-

/

\\\ -

-

\\ & CEI

ARM

SNM/K

60 Arbitrary Units

7951H6 0

30

SIRMIK

60 -2 3 c E. 0” 90

120 / I I I

\

I, \

\ ', \

\ I

'KAk$K' 150 Arbitrary Units FIG. 14. Variations of physical and magnetic properties within light and dark sediments layers from two typical sections of the studied sites: 794-l H5 and 79%1H6. For units refer to Table I.

L. Vigliotti:

Magnetic

1109

Properties of Sediment Layers from the Japan Sea

SITE 974 500 t

g

100

2 c s

8 2 cc0 -0

E 10

5_ l 0

;3 i

Depth (mbsf)

5

f 1 3 2

3 co;; ro 1 091 i 0

10

15

20

25

Depth (mbsf) FIG. IS. Downcore profiles of B OCcr)(solid symbol) and S-ratio (-IRM_ (, 3T/SIRM) (open symbol) for sediments from Site 794. Dashed lines represent boundaries of the oxygen isotope stages.

SITE 794

,

/

I

I

/

,’ $

I,

,’ I

I

I,

10

1s

20

25

Depth (mbsf) FIG. 16. Downcore

profiles of IRMlof, and K A&K

for sediments from Site 794. Dashed lines represent boundaries of the oxygen isotope stages.

1110

Quatema?

Science

Reviews:

Volume 16

SITE 795 12

1

;3

/

,5

5

15

6

10

15

20

25

20

2s

Depth (mbsf)

15 Depth

(mbsf)

FIG. 17. Downcoreprofilesof KARMand IRM,,r, for sedimentsfrom Site 795. Dashed linesrepresentboundariesof the oxygenisotopestages.Open(solid)symbolsfor light (dark) sediments, half-solidsymbolfor semidarksediments. concentration and grain size occurs below a depth of 11 m, close to the boundary between glacial/interglacial stages IO/l 1. Possibleexplanations for this change may take into account a different source of magnetic material, or a possible change in oceanographic conditions. The lithological description of the sediments(Tamaki et al., 1990)doesnot support a possiblechange in sourcefor the magnetic material such as may be suggested by the occurrenceof ashlayers, or by differences in the biogenic content of the sediments.A possible explanation of this suddenchange in the magnetic properties may be related to oceanographic factors that caused changes in the paleoenvironmental conditions. Organic carbon and sulfur data suggest that anoxic conditions were more highly developed before 6”O stage IO. A significant paleoceanographic change, such as the inflow of the TsushimaCurrent into the Japan Sea, may be responsible for the observed variations. Site 794 is situated exactly within the flow of this warm current, while Site 795 is offset (Fig. I ). This may explain the differences in downcore magnetic properties between the two sites. Nevertheless,at Site 795, a decreasein coercivity can be seenbetween 17-20 m depth which largely corresponds to the sameisotope stage IO (Fig. 19). This may reinforce the evidence for an intensification of oceanic circulation in the Japan Sea since about 0.35-0.40 Ma. If this interpretation is correct. the sudden change in the

magnetic properties observed at a depth of about 6 m (glacial stage 6), may represent a major interval of lowered sea level and restricted circulation, with the Tsushima Current no longer flowing into the basin. At ODP Site 798 (Yamato Basin), the benthic foraminiferal ‘so values are lighter during this glacial stage than they are during the adjacent interglacials, suggesting an unusual warming and/or freshening of deep water (Dunbar et LZ~.,1992). At the same site. a planktonic foraminiferal assemblagerich in Globigerinu bulloides suggestsupwelling conditions, and increasedproductivity between 0.4 and 0. IX Ma (Kheradyar, 1992). Minimum abundance values for this species, coupled with a maximum in the occurrence of Neoglohoquarlrin~l pc~chylerma (sinistral) occur exactly in the interval corresponding to the 61h0 stage 6 providing evidence for variations in sea-surface temperature, surface-water masses,and circulation during this stage. The rock-magnetic/paleoclimatic relationships imply that climate is the main driving mechanismresponsible for changesin the magnetic content of the sediment.The data suggestthat both ferrimagnetic and canted-antiferromagnetic minerals contribute to the magnetic mineralogy of the sediments. Ferrimagnetic minerals may be of terrigenic, biogenic. volcanogenic. diagenetic or authigenie origin, while canted-antiferromagnetic mineralsare most probably of terrigenic origin. Among the potential

L. Vigliotti:

1111

Magnetic Properties of Sediment Layers from the Japan Sea SITE 195

20

/

!

15

20 Depth

2s

30

(mbsf)

:

1,

3j:5

6

1

I”“l”’ 5

0

7 10

‘X?’

9

: II

I”’ IS

13 I”“1 20

Depth

i

IS

17

15

/ 30

25

3.5

(mbsf)

FIG. 18. Downcore profiles of rock-magnetic parameters ALF and KARM/K for sediments from Site 795. Dashed lines represent boundaries of the Oxygen Isotope Stages. Open (solid) symbols for light (dark) sediments. half-solid symbol for semidark sediments.

SITE 795 I I9 >~

0,75

0,80 60 0,85 E 6 0,90 *

~

0,9s il L-J-

20 0

5

10

15 20 Depth (mbsf)

FIG. 19. Downcore profiles of Bo,,,-, (solid symbol) and S-ratio (-IRM 195.

2.5 (1+SIRM)

30

I,00 35

(open symbol) for sediments from Site

sources, a terrigenous origin is the one most likely to be influenced by climate as suggested by Robinson ( 1986). Accepting a terrigenous origin for the magnetic minerals of the Japan Sea implies an eolian or fluvial source. Even if the Yellow River is a potential source for the detrital minerals of the Japan Sea, several factors indicate that an eolian source is more likely, as has been suggested by a number of authors (Uematsu et trl., 1983: Mizota and Matsuhisa, 1984: Tada er al.. 1992). The presence of hematite supports an eolian origin. Hematite, which is not common in deep-sea sediments, is a typical component in the soils of arid regions, and thus an eolian origin may explain its presence in the Japan Sea sediments. Furthermore, the magnetic grain-size parameters (KARM/ K. ALF) exhibit a coarsening during the glacial stages (Fig. IS) similar to the maximum grain siLe observed by Tada et trl. (1992) in the detrital (probably of eolian origin) minerals at Site 797. The Japan Sea is situated along the dust trajectory of the prevailing westerly winds that s~~pply a high quantity of dust from the Mongolian and Chinese deserts. Wind-blown Asian dust is deposited as far away as the northwest Pacific Ocean (Hovan et trl., 1989) and it is one of the world’s most important eolian sources (Uematsu et ~1.. 1983). Atmospherically transported dust is considered to be the source of the paleoclimatic signal observed in the pelagic clay sequences of the North Pacific (Yamazaki and Katsura. 1990). The hematite observed within the Japan Sea sediments is strongly suggestive of an aeolian origin for at least one of the terrigenous components in the Japan Sea sediments, and this may be the reason for their paleoclimatological record.

CONCLUSIONS The magnetic properties of the light and dark layers from the Japan Sea are controlled by climatically-induced changes in oceanographic conditions in the Sea of Japan, leading to systematic changes in sediment (and magnetic mineral) diagenesis. The magnetic mineralogy of the sediments is dominated by ferrimagnetic (magnetite-type) minerals with a small contribution made by cantedantiferromagnetic minerals (hematite) and iron sulphides (pyrrhotite and/or greigite). Whilst mineralogically similar. differences exist between lighl and dark layers in terms of magnetic mineral concentration and grain size. Reductive diagenesis involving magnetite dissolution controls the magnetic properties of the dark layers. Sulfur and organic carbon content show that the euxinic conditions responsible for this process occur during glacial stages and are probably related to sea level changes. This strongly suggests that climate exerts ;I major control on the magnetic properties. Notwithstanding the difficulties involved in decoupling the climatic signal from the diagenetic overprint, the former is clearly dominating the magnetic properties as indicated by relationships between magnetic parameters and oxygen isotope stages. The oceanic circulation influenced by the arctic cold fronts system and cold sea current dominated

the climate of Japan through the Brunhes as recognked by palynological studies carried out by Fuji and Horowitz (1989) on lacustrine sediments from Lake Biwa. Wind-blown dust containing hematite, probably in the form of red coated desert quartz grains, and ferrimagnetic minerals probably of volcanogenic origin are the main contributors to the terrigenous input of the Japan Sea sediments. Grain-size dependent rock magnetic parameters (K,\&K: ALF) provide evidence for coarser ferrimagnetic grain size assemblages during glacial stages. During the Brunhes Chron more deeply developed anoxic conditions occurred in the Japan Sea before about 0.35-0.40 Ma when the warm Tsushima Current started to flow into the basin with the resulting development of more oxidizing conditions. Since that time the data imply that an interruption to this flow may also have occurred during Isotope Stage 6. The magnetic record of the Japan sea sediments parallel the magnetic signature of the Chinese loess and both match the SPECMAC oxygen isotope stack (Imbrie et (11.. 1984). Since very different factors such as the source of the sediments and the global storage of ice control these records. this implies that they respond to a global model of the atmospheric and oceanic circulation. Rock magnetic variations in Late Quaternary sediments from the Japan Sea can be used for paleoclimatic and paleoceanographic reconstructions, as tracers of a terrigenous component source and as indicators of reductive diagenetic processes related to anoxic conditions of the basin. Magnetic measurements provide a high-resolution constraint on the paleoclimatic/paleoceanographic conditions of the basin and confirm that at least during the Upper Quaternary. the Japan Sea behaved as a single sedimentary system responding to climatic changes. ACKNOWLEDGEMENTS The author thank\ Proi’eswr M.B. Cita for i‘inanclal support of this work, A. Boschrtti wd A. Ccwri for help during the experimentc He is xlw grateful to T. Rolph for critxal reading of the manuscript and to S. Robinson for hi\ helpful suggcstion~ to improve the paper. This is IGM pubhcntion N 1055.

REFERENCES Bcrner, R.A. (1984) Sedimentary pyrite formation: Grochimic~~

et Cos1~2/)(./litlli(,(l

Actcr

48.

605-6

An

update.

1S.

Berner, R.A. and Raiswell. R. ( 1983) Burial of’ organic carbon and pyrite sulfur in sediment\ over Phanerozoic time: A new theory. Grochi~uictr er Co.r,lroc,lzil)fi(.a Actu 47. 855-862. Bloemendal. .I. ( 1983) Paleo~nvironmental implications of the magnetic characteristics of sediments from Deep Sea Drilling Project Site 514. Southeast Argentine basin. 112:Ludwig. W.J.. Kra~heninikov. VA. PI rd. (eds), hitid Reports of’rh Dee/>

Sew

I>ritii0,q

Pwjccl.

71.

U.S.

Govt.

Printing

Office.

Washin_pton. Bloemendal. J., Lamb, J. and King. J.W. (198X) Palaecoenvironmental itnpllcation5 01’ rock-magnrlic properties of lateQuaternary cores from the eastern equatorial Atlantic. Prrlroi,earln,~rLij~ll!. Bloemendal, J.. King. Roth magnetism

3. 6 I-87. J.W..

Hall,

F.R.

and

Doh,

S.J.

(1992)

of late Neogene and Pleistocene deep-sea

L. Vigliotti:

sediments: Relationship to sediment source, diagenetic processes, and sediment lithology. ~OL~T& of Geo@,vsicrr/ Research 98, 4 199-42 19. Burckle, L.H., Sturz, A. and Emanuele, G. (I 992) Dissolution and preservation of diatoms in the sea of Japan and the effect on sediment thanatocoenosis. In: Proceedings of’ the Ckerrn Drilling Program, Scientific Re.sults, 1271128, Pt. I, 3(W 316. Canfield, D.E. and Berner. R.A. (1987) Dissolution and pyritization of magnetite in anoxic marine sediments. Geochimica

et Cosmochimica

Acta

51,

645-6.59.

Channel], J.E.T. and Hawthorne, T. (1990) Progressive dissolution of titanomagnetites at ODP Site 6.53 (Tyrrhenian Sea). Earth

& Plrmetuyy

Science

Letters

96,

469-480.

Dankers, P.H. (1978) Magnetic properties of dispersed natural iron-oxides of known grainsizes. Ph.D. thesis. I42 pp.. Univ. of Utrecht, Utrecht, The Netherlands. Doh, S.J., King, J.W. and Leinen, M. (1988) A rock-magnetic study of Giant Piston Core LL44-GPC from the Central North Pacific and its paleoceanographic significance. Pa/eowtrmgraphp 3, 89-l 1 I. Dunbar, R.B., deMenocal, P.B. and Burckle. L. ( lYY2) Late Pliocene-Quaternary bioxiliceous sedimentation at Site 798. Japan Sea. In: Proceedings of the Owtrr~ Drilling Prqrrou, Scierdjic Results, 127/128, Pt. 1, 5439-5455. Dunlop, D.J. (1983) Determination of domain structure in igneous rocks by alternating field and other methods. Earth & Planetap Science Letter.! 63. 353-367. Farina, M.. Esquivel. D.M.S. and Lins de Barros. H.G.P. ( 1990) Magnetic iron-sulphur crystals from a magnetotactic microorganism. Nature 343, 256-258. Follmi. K.B., Cramp, A., Folhni, K.E., Alexandrovich, J.M.. Brunner, C., Burckle, L.H., Casey, M.. dehlenocal. P., Dunbar, R.B.. Grimm, K.A., Holler. P.. Inple Jr.. J.C., Kheradyar, T., McEvoy, J.. Nobes, D.C., Stein. R.. Tada. Ii., von Breymann. M.T. and White. L. (1992) Dark-light rhythms in the sediments of the Japan Sea: preliminary results from Site 798, with some additional results from Sites 797 and 799. In: Proceedings of the Ocecrn Drilling Progruttl, Sc.ient@c Results, 127/128, Pt. 1. 559-576. Fuji, N. and Horowitz, A. (1989) Brunhes Epoch paleoclimates of Japan and Israel. P~ll~rc,ogeoRrtr/,h~. Ptrltrc,oc~lin7trt~)lf~,~~, Palrteoecolog~

72,

1113

Magnetic Properties of Sediment Layers from the Japan Sea

79-88.

Hall, F.R. and Kmg. J.W. (I 989) Rock-magnetic stratigraphy of Site 645 (Baffin Bay) from ODP leg 105. Proceedin~~s of the Ocean Drilling Program. Scient(fic Results 105, 843-859. Harstra, R.L. (1982) Grain-size dependence of initial susceptibility and saturation magnetization-related parameter\ of four natural magnetites in the PSD-MD range. Geopkwi[cr/ Journal of’ the Rowl A.strotwnictrl Society 171, 377~395. Hamano. Y., Krumiiek, K.A.O., Vigliotti, L. and Wippern, J. (1992) Plio-Pleistocene magnetostratigraphy of sediment cores from the Japan Sea. In: Proc,erding.\ of’ the O~~etm Drilling Program, Sc.ierltifc Re.su1t.s. 127/12X, Pt. 2, 969984. Hovan, S.A.. Rea. D.K., Pisias. N.G. and Shackleton. N.J. (1989) A direct link between the China loess and marine delta “0 records: aeolian flux to the North Pacific. Nurture 340. 296-298. Imbrie. J.. Hays, J.D., Martinson, D.G., McIntyre. A.. Mix. A.C., Morley. J.J., Pisias. N.G.. Prell. W.L. and Shackleton N.J. (1984) The orbital theory of Pleistocene climate: support from a revised chronology of the marine delta “0 record, 1~1: Berger. A.L. et ~11.(eds), Miltrnkovitch rend C’limrrtr, Purt I. pp. 169-305. Reidel, Boston. Johnson. H.P.. Lowrie, W. and Kent, D.V. (1975) Stability of anhysteretic remanent magnetization in fine and coarse magnetite and maghemitc particles. Geopl~ysic~nl Journal of the Ro!d A.stronomiurl Soc.ir!\* 41, I- 10. Karlin, R. (lY90) Magnetic diagenesis in suboxic sediments at Bettis Site W-S. NE Pacific Ocean. Journrtl of’ Grophy.\icn/ Resmrch 9.5, 447 14436.

Karlin, R. (1990) Magnetite diagenesis in marine sediments from the Oregon continental margin. Journal of Geophysicd Rasecrrch 95, 430544 I Y. Karlin, R. and Levi, S. (1983) Diagenesis of magnetic minerals in recent hemipelagic sediments. Nutl4r.e 303, 327-330. Karlin. R. and Levi, S. (1985) Geochemical and sedimentological control of the magnetic properties of hemipelagic sediments. Jortrmrl of’ Geophyictrl Reserrrch 90. 1037% 10392. Kent. D.V. ( 1982) Apparent correlation of paleomagnetic intensity and climatic records in deep-sea sediments. Nrrtrrre 299. 53X-539. Kheradyar, T. (1992) Pleistocene planktonic foraminiferal assemblages and paleotemperature fluctuations in Japan SW. Site 7Y8. III: Procecding.c of the Ocean DrillirlS Program, Sccient~~i’c Re.sults. 127/128. 457370. King, J.W.. Banerjee, S., Marvin, J. and Ozdemir, 0. (1982) A comparison at different magnetic methods for determining the relative grain size of magnetite in natural materials: some results from lake srdiments. Etrrth & Pkmettrr! Sckm.e Letters

59.

4043

19.

KoiLumi. I. ( 1992) Diatom bmstratigraphy 127.

III:

Proc~eerlingv

of’

the

(kerrtr

of the Japan Sea: leg Drilling

Progrrlm,

127/128, 249-789. Leslie, B.W.. Lund, S.P. and Hammond, D.E. (1990) Rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the California Continental Borderland. Jourmrl of‘ Geophysicrrl S&wt(/i’c

Re.sd/s.

Rr.tetrrc~h

95,

44373451.

Lowrie. W. ( 1990) Identification of ferromagnetic minerals in a rock by coercitivity and unblocking temperature properties. Groph~~.siurl Resenrc~h Letters 17, 159- 162. Mann. S.. Sparks. N.H.C.. Frankel, R.B.. Bazilinsky, D.A. and Jannasch, H.W. (1090) Biominerali~ation of ferrimagnetic greigite (Fe&) and iron pyrite (I-‘&,) in a magnetotactic bacterium. Ntrtrrre 343, 25X---261. Mirota, C. and Matsuhisa, Y. ( 1984) Eolian dust-mainly based on analyhi$ of core KH-79.3.C3. C’/liX!.~r Monthly 6. 5S3SS7. (in Japanese) Morley. J.J., Hays, J.D. and Robertson. J.H. (1982) Stratigraphic framework for the late Pleistocene in the northwest Pacific Ocean. Dc,epSecc Resetrr(fr. Ptrrt A 29. l485- 1499. Mullins, C.E. and Tite, MS. (IY73) Magnetic viscosity, quadrature susceptibility. and frequency dependence of susceptibility in single-domain assemblies of magnetite and maghemitc. ./nrrrrltr/ oJ’ Ge~~ph,vskrr/ Rewtrrch 78, 804-809, Oba, T.. Kato, .M.. Kitazato, H., Koizumi. 1.. Omura. A., Sakai, T. and Takayama. T. (IVY I I Palcocnvironlnental changes in the Japan Sea during the lai;t X5,000 years. Prr/eoc,etrnognrph? 6. 49Y-5 IX. Oldfield. F. and Robinson. S. ( 19X5) Geomagnetism and palcoclimate. In: Tooley. M.J. and Sheail, G.M. (eds). The Climrrtic. &II<,. pp. 186-205. Allen and Unwin, Winchester, Mass. O’Reilly. W. ( 1984) Rock rlrlrl Mirwrd Mqqneti.sm. Blackie, Gla5gow. 220 pp. Ozdemir. 0. and Banerjee. S.K. (1982) A preliminary magnetic study of soil samples from west-central Minnesota. Earth & Plrmetrrr~

Sc,ieuce

Letter.5

59.

393-303.

Petersen. N.. van Dobeneck. T. and Vali, H. (1986) Fossil bacterial magnetite in deep-sea sediments from the South Atlantic Ocean. Mrture 320. 61 I-615. Robinson. S.G. ( 1Y86) The Late Pleistocene paleoclimatic record of North .Atlantic deep-sea sediments revealed by miner&magnetic measurements. Ph?,,sic~.t of the Ecrrth curd P/trmto/~~

Interior.s

42.

7’747.

Robinson, S.G.. Maslin. M.A. and McCave, I.N. (199.5) Magnetic susceptibility variations in Upper Pleistocene deep-sea sediments of the NE Atlantic: implications for ice rafting and paleocirculation of the last glacial maximum. Ptr/~~oc~~‘fl/20,~/~~1/~/1~’ lO(2). 12 1-350.

1114

Quuternnr~

Science

Rohling, E.J. and Hilgen, F.J. (1991) The eastern Mediterranean climate at times of sapropel formations: a review. Geologic en Mijnbouw

70.

253-264.

Sager, W.W. and Hall, S.A. (1990) Magnetic properties of black mud turbidites from ODP leg 116. distal Bengal fan, Indian Ocean. Proceedings of the Oceun Drilling Program. Scientijic Results 116. 317-335. Sahota, J.T.S., Robinson, S.G. and Oldfield, F. (I 995) Magnetic measurements used to identify paleoxidation fronts in deepsea sediments from the Madeira Abyssal Plain. Geophwical Reseurch Letters 22, 196 I - 1964. Tada. R. (1991) Origin of rhythmical bedding in middle Miocene siliceous rocks of the Onnagawa Formation, northem Japan. Journal of Sedimentary Petrology 61, I 123-l 145. Tada. R.. Koizumi, I., Cramp, A. and Rahman, A. ( IYY2) Correlation of dark and light layers, and the origin of their cyclicity in the Quaternary sediments from the Japan Sea. In: Proceedings Results,

of’

the

Oceun

Drilling

Progrtrm.

127/128, Pt. 1, 577-601. Tamaki, K., Pisciotto, K., Allan, J. et cl/. (1990) ings

of

the

Oretrn

Drilling

Program.

Initial

Sc,ient(ii’c In: ProceedReports. 127,

776 pp. Thierstein, H.R., Geltzenhauer, K.R.. Molfino. B. and Shackleton. N.J. (1977) Global synchroneity of late Quaternary

Rel&vs:

Volume

I6

coccolith datum levels: validation by oxygen isotopes. Geolo
Proceedings R~wlts,

of

the

Oceun

Drilling

Pro,g’rum,

127028, Pt. 2. 947-957. Uematsu, M., Duce, R.. Prospero, J.M.. Chen, L., Merril, J.T. and McDonald, R.L. (I Y83) Transport of mineral aerosol from Asia over the North Pacific Ocean. Journnl r!f Geophysirtrl

Reseurch

88.

5343-5352.

Ujiie. H. and Ichikura. M. (1973) Holocene to uppermost Pleistocene planktonic foraminifers in a piston core from off San’ district. Sea of Japan. Trunsuctions und Proceedings of the PLllnc~onrolo,~i~clI so(.iPt~’ of’ Jupun 91. l37- I so. Verosub, K.L. and Roherts, A.P. (1995) Environmental magnetism: Past, present and future. Journul qf Geoph?‘.sicu/ Krserrrch 100. 2175-2192. Yamaiaki, T. and Katsura. I. (1990) Magnetic grain size and viscous remanent magnetization of pelagic clay. Journul of Grt~phvsicul

Re.veurch

9.5. 4373-4382.