14. geochemistry of deep sea sediments from the … · vation analysis. ten major elements and 24...

14. GEOCHEMISTRY OF DEEP SEA SEDIMENTS FROM THE NANKAI TROUGH, THE JAPANTRENCH, AND ADJACENT REGIONS1

Yoshitaka Minai, Department of Chemistry, Faculty of Science, University of TokyoRyo Matsumoto, Geological Institute, Faculty of Science, University of Tokyo

andTakeshi Tominaga, Department of Chemistry, Faculty of Science, University of Tokyo2

ABSTRACT

Sediments from Sites 582 (11 samples), 583 (19 samples), 584 (31 samples), 294 (1 sample), 296 (9 samples), 297 (3samples), 436 (11 samples), and 439 (3 samples) were analyzed by X-ray fluorescence and/or instrumental neutron acti-vation analysis. Ten major elements and 24 minor and trace elements (including 7 rare earth elements) were determinedwith these methods. Geochemistry varies systematically with both the site location and sediment age. Such variationsare explained in terms of changes in sedimentation processes caused by plate motion and changes in ocean currents.

INTRODUCTION

Geochemical data on deep-sea sediments have accu-mulated rapidly in the last 15 years, but at a slower pacethan data on lithology, geology, and geophysics. In par-ticular, the information concerning abundances of traceelements such as the rare earth elements (REE) is tooscarce to permit resolution of several problems in earthsciences. For the sediments collected by DSDP, even themajor element geochemistry has not been examined forall sites, and minor or trace element geochemistry hasbeen reported for only a few. Although the REEs areuseful for drawing inferences regarding the origin of con-stituent materials and for understanding processes andenvironments of sedimentation, their abundances in theDSDP sediment samples are reported in only a few pa-pers (e.g., Dymond et al., 1976; Bogdanov et al., 1976;Tarney and Donnellan, 1977).

In this chapter, we report concentrations of major,minor, and trace elements, including REEs, in sedimentsamples collected at Sites 582 and 583 (Nankai Trough)and Site 584 (Japan Trench) during Leg 87 (Table 1; Fig.1). For comparison, we have also analyzed deep-sea sed-iments from some nearby sites of other legs.

The objects of this study are the following:1. Elucidation of the history of sedimentation pro-

cesses by means of the depth profiles of major, minor,and trace element geochemistry. Concentrations of theseelements in deep-sea sediments reflect the origin of thosesediments and variations in sedimentation processes. Us-ing the depth profile of the concentration of each ele-ment, the variation of the sediment lithology with geo-logic event may be estimated, and the sedimentation his-tory can be read from the geochemistry.

2. Elucidation of regional differences between chem-ical constituents of deep-sea sediments of the Nankai

Table 1. Locations of Sites 294, 296, 297, 436, 439,582, 583, and 584.

Water Maximumdepth penetration

Site Latitude Longitude (m) (m)

294296297436439582583584

2229303940313140

°34.74'N°20.4 l'N°52.36'N°55.96'N°37.61'N°46.5'N°49.8'N°28.0'N

131133134145143133133143

°23.13'E°31.52'E°09.89'E°33.47'E°18.63'E°54.8'E°51.3'E°57.1'E

57842920448152401656487946344078

1181087679.5397.51157.5749.4450.0954.0

1 Kagami, H., Karig, D. E., Coulbourn, W. T., et al., Init. Repts. DSDP, 87: Washing-ton (U s Govt. Printing Office).

•2 Addresses: (Minai and Tominaga) Department of Chemistry, Faculty of Science, Uni-versity of Tokyo, Hongo, Tokyo 113, Japan; (Matsumoto) Geological Institute, Faculty ofScience, University of Tokyo, Hongo, Tokyo 113, Japan.

Trough and those of the Japan Trench, and the cause ofsuch differences. Chemical compositions of the deep-sea sediments near Japanese islands differ (Sugisaki,1978, 1979, 1980a, 1980b; Minai, 1982). Sugisaki stud-ied the geochemistry of modern deep-sea sediments inthe Japan Sea, Japan Trench, and Shikoku Basin, usingX-ray fluorescence (XRF). In this chapter, we hope toclarify the differences in geochemical characteristics (par-ticularly trace element—for example, REE—geochemis-try) between the deep-sea sediments of the Nankai Troughand those of the Japan Trench, and to discuss the fac-tors that govern such differences.

Because the analytical results from the deep-sea sedi-ments from three Leg 87 sites are not alone sufficient toinfer the origin of trench-fill and trench-slope sediments,we have also analyzed the sediment samples collectedduring the other legs in the West Philippine Basin (Site294), Shikoku Basin (Sites 296 and 297), and on the out-er slope of the Japan Trench (Site 436) and the terrace ofthe Japan Trench (Site 439) (Table 1; Fig. 1) (Sites 294-297: Karig, Ingle, et al., 1975; Sites 436, 439: ScientificParty, 1980).

METHODS

Samples consisting of about 10 ml of mud and mudstone werewashed with distilled water to remove contaminants from seawater inthe sediment column and then were dried moderately in air at ambienttemperature. Sand and sandstone were excluded. Air-dried samples

643

Y. MINAI, R. MATSUMOTO, T. TOMINAGA

40°N

25C

20° o O130°E 135° 140° 145° 150°

Figure 1. Locations of DSDP Sites 294, 296, 297, 436, 439, 582, 583,and 584.

were finely pulverized for chemical analysis. Thirty-four major, mi-nor, and trace elements in sediments were determined by means ofXRF and instrumental neutron activation analysis (INAA).

XRF Analytical Procedures

A small piece (1 g) of the pulverized sample was mixed with 5 g ofanhydrous lithium borate and melted to form a bead sample for deter-mination of 10 major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K,P). Another 5 g of the sediment were pressed without any binder toprepare a disk sample for determinations of minor and trace elements(Co, Cr, Cu, Ni, Rb, Sr, V, Zn, and Zr). The bead and disk sampleswere analyzed with a Rigaku IKF-3064 dispersive XRF spectrometer.The analytical conditions were 50 kV/40 mA (Cu tube) for major ele-ments and 70 kV/30 mA (W tube) for minor elements. More than 40geologic standard rock samples were analyzed to prepare calibrationcurves for each element; GSJ rock standard JB-1 (basalt) was ana-lyzed as a working standard to check analytical precision. The pre-cision and reproducibility were reported previously (Matsumoto andUrabe, 1980).

INAA Analytical Procedures

A portion (100 mg) of the pulverized sample was sealed in polyeth-ylene film. The sealed samples, together with standard rocks, were ir-radiated for neutron activation in the TRIGA-II nuclear reactor atRikkyo University. The irradiation conditions were as follows: thermalneutron flux, 1 × 1012 n/(cm2 s); irradiation time, 12-24 hr. Aftershorter-lived nuclides had decayed out, gamma-ray spectra were mea-sured with either a Ge(Li) detector at the Radioisotope Center, Univer-sity of Tokyo, or with an intrinsic pure Ge detector at the Laboratoryfor Earthquake Chemistry, University of Tokyo. On the basis of thespecific activity, estimated from the peak area of each nuclide, theconcentrations of 21 elements (Fe, Na, Ca, Ba, Co, Cr, Cs, Hf, Ni,Sb, Sc, Ta, Th, U, La, Ce, Sm, Eu, Tb, Yb, and Lu) were determined.The precision of each analysis was checked by analyzing the workingstandard at the same time. However, the precision was not always bet-ter than that obtained with XRF. Hence, XRF data are quoted in thisreport whenever ^determinations were made with both XRF and INAA.

RESULTS

Nankai TroughSite 582 is situated in the southern Nankai Trough,

about 135 km southeast of Shikoku. At Site 582, threeholes were drilled down to 749.4 m sub-bottom. Quater-nary sediments were collected down to 710 m, and up-per Pliocene sediments were found below 710 m. Thelithologic section was divided into two units accordingto the differences in sediment lithology (site chapter, Site582, this volume). Unit 1 (above 560 m) is composed ofthick alternations of turbiditic sand and mud, whereasUnit 2 (below 560 m) is composed of hemipelagite. Per-centages of major, minor, and trace elements in the sedi-ments are listed in Table 2.

At Site 583, eight holes were drilled near the trenchaxis of the Nankai Trough to the west of Site 582 (sitechapter, Site 583, this volume). Analyses by either XRFor INAA, or by both, were performed on 19 samplesfrom Holes 583, 583B, 583D, 583F, and 583G (Table 2).The depth profiles for selected chemical constituents atSites 582 and 583 are represented in Figure 2. The datafor some REEs (Ce, Sm, Eu, Tb, and Lu) are omittedbecause of the geochemical similarity among REEs.

Site 582

Major Element GeochemistryThe silica concentration in these sediments ranges from

62 to 69%, which is higher than the biogenic silica con-tent estimated by smear-slide observation and mineral-ogic studies (site chapter, Site 582, this volume). On thebasis of X-ray diffraction study, we have determined thatnonbiogenic silica components mainly represent quartzderived from terrigenous clastic sediment. The slight var-iation in silica concentration could be explained by vari-ation in the mineral composition and the grain-size dis-tribution of the sediments.

The chemical composition of deep-sea sediments atthis site is rather homogeneous with respect to sub-bot-tom depth, except for some components, such as CaO,Fe2O3 (total iron), and MnO (Fig. 2). The variation inthe CaO concentration could be explained by the varia-tion in the concentration of biogenic calcium carbonate.This explanation is supported by lithologic and mineral-ogic studies. The variation in Fe2O3 and MnO concen-trations could reflect changes in sediment lithology. Moregeochemical results, together with lithologic and miner-alogic data, are needed to clarify the factors that controlthese variations. Despite those slight changes, the chem-ical composition of turbiditic and hemipelagic mud isquite homogeneous.

Minor and Trace Element GeochemistryExcept for Sr, Ba, Co, Cr, Cu, and Ni, the concentra-

tions of minor and trace elements are similar through-out the sediment column (Fig. 2). Concentrations ofREEs such as La, a typical light REE (LREE), and Yb,a typical heavy REE, also remain nearly constant in Site582 sediment (Fig. 3). The major-element oxides CaO or

644

GEOCHEMISTRY

MnO or both are enriched at various depths, and the al-kaline earths, Sr and Ba, correlate with CaO, whereasthe other transition metals correlate with MnO. This re-lationship implies that heavier alkaline earths exist main-ly in biogenic carbonates, and that the other metals existin hydrogenous manganese hydroxides. The concentra-tions and elemental ratios (e.g., La/Yb, Fig. 2) vary on-ly slightly with sub-bottom depth.

Site 583The chemical compositions of sediments at this site

are almost homogeneous throughout the core, except forCaO and Sr concentrations (Table 2; Fig. 2). Fluctua-tions of these components are attributed primarily tovariation in the concentration of biogenic carbonate.

Chemical compositions of the mud and mudstone atSite 583 are similar to those at Site 582 (Fig. 3), implyingthat the Quaternary turbiditic mud from Sites 582 and583 as well as the upper Pliocene hemipelagite from Site582 have a common origin, despite their lithologicdifferences.

Philippine Sea and Shikoku BasinSite 294 is in the northern part of the western Philip-

pine Basin; Sites 296 and 297 are in the Shikoku Basinto the south of the Nankai Trough (Table 1; Fig. 1). Site297 is situated about 250 km north of Site 296. Onesample from Site 294 (typical pelagic red clay), 9 sam-ples from Site 296, and 3 samples from Site 297 were an-alyzed (Table 3; Figs. 4 and 5).

Site 294The chemical composition of the deep-sea sediment

collected from this site differs from that of the hemipe-lagic turbidite mud in the Nankai Trough. Concentra-tions of minor and trace elements are typical for pelag-ic sediments that have relatively high concentrations oftransition metals. The REE pattern shows LREE en-richment with respect to chondrite (Fig. 5). This pattern(Fig. 5) is similar to patterns of other sediments nearland (e.g., Fig. 3), except for the negative Ce anomaly.

The REE patterns are characteristic of various sedi-ments deposited in marine environments (e.g., Piper,1974). Shimizu and Masuda (1977) analyzed severalcherts from DSDP cores and from subaerial samples.The REE pattern of the pelagic chert shows a negativeCe anomaly, which does not appear in the REE patternsof on-land cherts. Steinberg and his co-workers (Stein-berg and Marin, 1978; Rangin et al., 1981; Steinberg etal., 1983) also discovered such a Ce anomaly in pelagicclays. These authors consider the Ce anomaly a finger-print characteristic of sedimentation in open-ocean en-vironments. Minai and his co-workers (Minai, 1982; Mi-nai et al., in prep.3) analyzed about 30 deep-sea surfacesediments in the Pacific Ocean. They showed that theCe anomaly in the REE pattern of several sediments maybe characteristic of pelagic sedimentation, and that the

Minai, Y., Tominaga, T , Nakamura, Y., and Wakita, H., in preparation. Geochemis-try of deep sea sediments in the Pacific.

magnitude of the Ce anomaly correlates well with thelatitude of the station and the distance from spreadingcenters. Considering Ce and Mn contents, as well as deep-sea sediment accumulation rates in the western PacificOcean, Matsumoto and others (in press) proposed a hy-drothermal origin of the Ce anomaly in pelagic sediments.

Our results on the sample from Site 294 agree withthe previous observations: the Ce anomaly of Site 294sediments can be attributed to the hydrothermal activityin the West Philippine Basin. We analyzed only one sam-ple from Site 294, however, and more extensive study isneeded to confirm the existence and magnitude of a Ceanomaly at that location.

Site 296

Major Element GeochemistrySite 296 sediments are characterized by high CaO con-

centrations ranging from 15.9 to 36.3% (Table 3). CaOis present mainly in the biogenic-carbonate sediments.Considering the amounts of ignition loss, we estimatethat these samples contain about 10% or more CO2 ascarbonate.

The concentrations of major-element oxides TiO2,A12O3, Na2O, and K2O decrease gradually downhole, asdoes SiO2, after an abrupt decrease in the first 100 msub-bottom. In the upper part of the section, chemicalcompositions resemble those of terrestrial shales or near-shore sediments like those of Sites 582 and 583, whereasin the lower part of the stratigraphic section, composi-tions resemble those of pelagic sediments like those ofSite 294. These variations suggest that the contributionof terrigenous sediment is much higher in the upper zone.The Nankai Trough sediments (Sites 582 and 583) aresimilar in chemistry to shales and are classified as hemi-pelagites. The Shikoku Basin sediments are typical pe-lagic clay. The horizontal movement of Site 296 by platemotion probably explains the chemical variations. Thedeeper layer of the sediment column accumulated at asoutherly position within the pelagic sediment zone. Asthe Philippine Sea Plate moved to the north and Site 296reached the zone of hemipelagic sedimentation, the char-acter of the sediments changed gradually from pelagicto hemipelagic.

Minor and Trace Element GeochemistryBarium increases in the lower zone, where Hf, Ta,

and REEs decrease very slightly. Other elements showno clear change with depth.

The REE patterns change systematically with sub-bottom depth (Fig. 5). The REE patterns of the sedi-ments in the upper zone at Site 296 (Fig. 5) are similar tothose for Sites 582 and 583 (Fig. 3); LREE are enrichedand there is no Ce anomaly. REE patterns of the sedi-ments in the lower zone are similar to those of the pelag-ic sediment from Site 294; they show less enrichment ofLREE and a Ce anomaly. These relationships in REEpattern are attributed to plate motion.

Sample 296-13-3, 50-52 cm shows an exceptionallypositive Ce anomaly that could be explained by incorpo-ration of Mn hydroxides, because manganese nodules

645


Table 2. Sites 582 and 583: concentrations of major-element oxides (wt.%) and minor and trace elements (ppm) in deep-sea sedi-

ments.

Hole-Core-Section(interval in cm)

582-1-1, 52-54582B-2-2, 134-136582B3-2, 120-122582B-23-2, 40-42582B-26-2, 39-43582B-40-2, 40-42582B-52-3, 126-127582B-60-2, 38-39582B-62-3, 68-69582B-68-2, 39-41582B-71-1, 95-96583-1-1, 57-58583-4-4, 56-57583-7-1, 20-21583-11-1, 57-58583-17-1, 40-41583-23-1, 77-78583F-6-1, 27-29583F-8-1, 39-41583F-11-1, 112-114583F-15-1, 35-37583F-18-1, 78-79583F-22-1, 111-113583F-26-1, 124-125583F-29-1, 20-22583G-3-4, 47-48583G-10-3, 25-27583B-3-2, 33-34583D-14-3, 65-67583D-20-1, 38-40

Sub-bottomdepth (m)

0.5362.5570.61

262.61291.41424.51541.27615.99636.99693.10721.25

0.5828.0646.1174.08

107.41135.78198.98218.10247.73285.76314.99354.02392.75420.61330.88397.06

11.84175.66230.29

SiO 2

66.663.9

64.865.164.066.865.266.762.364.563.064.861.864.766.666.164.565.666.265.466.365.263.965.564.765.965.261.865.8

TiO 2

0.720.78

0.770.760.810.730.790.740.720.760.730.740.790.770.730.680.750.790.70.70.70.70.80.780.800.760.770.780.74

A12O3

16.617.4

17.316.518.116.117.417.217.017.516.216.517.817.116.415.517.117.415.916.716.617.117.016.717.117.116.617.916.5

F e 2 O 3

a

6.437.28

6.896.837.246.337.866.056.996.826.47.08.07.06.66.77.26.76.76.60.46.67.66.77.26.67.48.46.5

MnO

0.120.13

0.120.120.150.130.120.090.240.150.100.110.130.110.110.110.120.100.120.120.110.120.140.130.110.110.270.130.10

MgO

2.802.78

2.812.752.152.552.602.562.802.742.432.73.32.72.52.42.92.72.72.52.52.83.02.92.92.52.72.82.6

CaO

1.402.60

1.912.742.222.321.141.485.172.361.82.63.62.42.23.92.52.03.13.12.22.22.42.01.92.01.73.72.9

Na 2 O

2.191.95

2.132.071.722.241.651.991.631.712.42.61.92.01.92.02.01.82.12.22.12.22.02.31.91.72.41.82.4

K 2O

3.063.15

3.123.073.132.753.233.153.073.462.82.92.63.02.92.52.93.02.42.62.82.93.12.93.13.22.92.72.5

P2O5

0.060.09

0.120.080.080.090.050.030.120.060.040.060.060.060.040.070.060.050.090.040.030.050.050.040.420.310.080.120.09

Ba

584

524542

494569605

685

543553

430507

Co

1915

151517153213151613162017161314161317

1417131916

Cr

7385

8297

109839179829665796975948064866858

9592907681

Note: Blank: not analyzed.a Total iron as F e 2 θ 3

often show positive Ce anomalies (e.g., Piper, 1974).Another explanation relies on the selective partitioningand redistribution of Ce induced by the oxidation of Ceafter burial. Matsumoto and others (in press) have sug-gested that Ce depletion is an indicator for hydrother-mal interactions in the sediment layer, an anomaly pro-duced by oxidation of Ce3 + to Ce 4 + . In this case, Ce3 +

and Ce4 + would coexist in the sediment column in con-tact with hydrothermal water. Because the chemical prop-erties of Ce4 + are different from those of Ce3 + , hydro-thermal interaction through oxidation-partitioning maydifferentiate and redistribute Ce in the sediment column.

Site 297

Chemical compositions of Site 297 sediments are sim-ilar to those of the Nankai Trough sediments (Sites 582and 583) and to those of the upper Site 296 sediments,except that CaO concentrations at Site 296 are muchhigher. This similarity extends to the minor and trace el-ement geochemistry (compare the analytical results list-ed in Tables 2 and 3).

Summary: Geochemistry of Sediments from thePhilippine Sea to the Nankai Trough

The modern sediments at Site 294 are typical pelagicclay; their REE pattern shows a negative Ce anomaly,typical of pelagic sediment influenced by hydrothermalactivity. To the north, the character of the deep-sea sedi-ments changes from typical pelagic sediment at Site 294to the hemipelagite at Sites 582 and 583. Such regional

variations in geochemistry are also recognized in the ver-tical variation at Site 296. As for the REE geochemistry,the Ce anomaly diminishes with decreasing sub-bottomdepth, a variation explicable in terms of plate motion.The deeper layer of the sediment column accumulatedto the south of the present site, in a zone of pelagic sedi-mentation; and the upper layer accumulated near thepresent site, within the zone of hemipelagic sedimenta-tion. In contrast to Site 296 sediment, vertical variationof the Ce anomaly is not observed in Site 297 sediment.Site 297 is situated to the north of Site 296, and the ageof the recovered sediment column is younger than atSite 297. These facts suggest that the lithologic sectionrecovered at Site 297 is too short to reach layers accumu-lated earlier, beneath the zone of pelagic sedimentation.

Deep-sea sediments can be classified into ridge sedi-ment, pelagic sediment, and offshore sediment, on thebasis of their Mn concentrations, sediment accumula-tion rates, and REE patterns (Matsumoto et al., in press).In that classification, the sediment at Site 294 is pelagic,and that at Sites 297, 582, and 583 is offshore. Drillingat Site 296 penetrated pelagic sediments at the lower lev-els and offshore sediments at the upper levels; this changein sedimentary environments was caused by plate motion.

Japan Trench

Site 584 is on the landward slope of the Japan Trenchoff Sanriku, northeastern Japan. A 954-m sediment col-umn was recovered from this site. Site 584 sediments arecomposed mainly of siliceous mud and mudstone with

646

GEOCHEMISTRY

Tkble 2. (Continued).

Cs

6.0

5.56.3

6.64.66.6

7.7

6.07.1

4.94.2

Cu

6854

8872364016585909535546344323652494251

5870399547

Hf

3.4

3.53.3

3.83.83.7

3.8

3.56.0

2.83.6

Ni

4555

526064439150665918322333372225372020

5064484847

Rb

110107

1041051169311911410712797967810410485951087985

1041171008081

Sb

0.51

0.270.38

0.460.37

0.67

0.460.50

0.340.27

Sc

15

1516

141515

16

1515

1915

Sr

150125

160181152192128149238165170179198175172228180165212220

183167146196210

Ta

0.52

0.520.52

0.670.450.60

0.63

0.620.61

0.410.45

Th

9.4

9.39.7

11.68.710.3

11.7

10.2 111.2 1

7.4 17.6 1

U

.4

.3

.4

.4

.2

.3

.5

.3

.3

.3

.1

V

95104

96103961001119196969898105104100891001049898

1051039899101

Zn

114105

1151061098911411411112610112311411216113210912012398

10815210010790

Zr

143133

140152155161145153131142164142118144159134137159131137

119148137115155

La

26.629.126.526.829.432.325.330.328.629.033.9

27.830.5

21.022.5

Ce

5154485158614856535259

5257

4243

Sm

5.045.574.925.265.525.895.045.425.035.305.77

5.225.37

4.784.53

Eu

1.05

1.051.08

1.141.091.06

1.18

1.091.16

1.091.01

Tb

0.590.770.570.600.800.700.540.640.780.740.73

0.850.98

0.740.77

Yb

3.24.02.93.53.53.53.33.33.13.83.4

2.83.2

2.92.9

Lu

0.510.570.440.520.500.520.490.470.470.500.52

0.530.48

0.520.45

sporadic thin interlayers of sand and ash. The age ofcores from this site ranges from the middle Miocene tothe Quaternary.

Site 584

Major Element GeochemistrySilica concentrations range from 67 to 88% (Table 4;

Fig. 6), higher than at Sites 582 and 583, and the varia-tion is somewhat larger than that in the sediments fromthe Nankai Trough. The high silica concentration reflectsthe sediment lithology, indicating that biogenic silicacontributes largely to the total silica component.

In the upper 530 m of the sediment column, silicaconcentration exceeds 75%, except in the Quaternarysandy mud at the top of the hole. Between 530 and 760m, silica concentration is lower. Farther downhole, con-centrations again increase to values comparable to thosein the upper, high-silica zone (Fig. 6). These changes cor-relate with the sediment accumulation rates. The accu-mulation rate is about 100 m/Ma in the upper, high-sili-ca zone, 20 m/Ma in the middle, low-silica zone, and100 m/Ma in the lower, high-silica zone (site chapter,Site 584, this volume). The incorporation of biogenicsilica into the sediment increases the silica content andthe accumulation rate. The biogenic silica component ishigh in the high-silica zones and low in the low-silicazones, where silica might be derived from terrigenouselastics. The fact that chemical compositions of the sed-iments in the low-silica zone are similar to those of tran-sitional shale supports this explanation.

Unlike the SiO2 concentration, the CaO concentra-tion varies randomly. Calcium is contained in terrige-nous elastics, such as feldspars and clay minerals, and inbiogenic carbonates. The concentrations of Na2O andK2O, which are contained mainly in feldspars and clayminerals, are nearly constant, indicating a constant con-tribution of terrigenous elastics throughout the core. Thus,the random fluctuation of CaO concentration could beexplained by the variable contribution of biogenic car-bonates.

Manganese, a sensitive indicator of the hydrogenouscontribution, is extremely enriched at some horizons inthe core (Matsumoto et al., in press).

Other major element abundances, except for total iron,are relatively constant throughout the core. Iron con-centration is, on the whole, negatively correlated withsilica concentration (Fig. 6), meaning that iron is notcontained in biogenic silica components, but is containedmainly in terrigenous elastics.

Minor and Trace Element GeochemistryStrontium concentration correlates excellently with

CaO concentration, implying that Sr is contained main-ly in CaO-bearing phases like biogenic calcium carbon-ate. The other alkaline earth, Ba, does not correlate witheither CaO or Sr. Barium concentrations are variable inthe zone from 30 to 120 m and enriched below 300 msub-bottom depth (Fig. 6). Because barium is a kind oflarge-ion lithophile (LIL), it does not always behave likeother lighter alkaline earths in geochemical processes.In volcanic rocks, Ba correlates with other LILs such as

647

Site 582


Figure 2. Depth profiles for concentrations of major, minor, and trace elements in deep-sea sediments from Sites 582 and 583.

GEOCHEMISTRY

100

50

100

10

• ^ ^

: 4i i

i

Site 582Hole 582 (1 sample)Hole 582B (10 samples)

Site 5831 583D-14-3, 65-67 cm2 583D-20-1, 38-40 cm

s. 3 583G-3-4, 47-48 cm* ^ s . 4 583G-10-3, 25-27 cm

1

La Ce Sm Eu Tb Yb Lu

Figure 3. Typical chondrite-normalized rare-earth-element patterns fordeep-sea sediments from Sites 582 and 583.

Cs, REEs, U, and Th. The LILs (Cs, Hf, Ta, Th, andREEs) are slightly enriched in the lower zone of the Site584 lithologic section (Table 4). In the zone below 300 m,barium would behave mainly as the other LILs, and wouldbe contained mainly in LIL-bearing phases. These LILsare not enriched in the upper, Ba-bearing zone, suggest-ing that Ba is contained in barite in this upper zone.Gurvich and others (1978) found an excellent correla-tion between Ba and barite concentration in pelagic sed-iments. In fact, barite nodules were found in several ho-rizons at shallow levels.

Geochemistry of LILs in deep-sea sediments providesan excellent key to the origin and diagenetic alterationof the sediments. As mentioned, most LILs are slightlyenriched in the lithologic section below about 400 m.The depth profile of U has almost no trend; it has onlya very slight enrichment in the upper few samples. Mostof the LILs in deep-sea sediments seem to be containedin silicates and in other accessory minerals derived fromterrigenous clastic sediments, and LIL concentrations areexpected to correlate positively with the total iron butnegatively with SiO2 (biogenic silica). These correla-tions were not observed in our data, perhaps becausethe changes were of such small magnitude. The REEscould be derived mainly from terrigenous elastics in thiscore, because the chondrite-normalized REE patternsshow an LREE enrichment as in shales (Fig. 7).

The difference in LIL concentrations between the up-per and lower zones suggests a change of sediment prov-enance. The LIL geochemistry changes in the upper-most Miocene sediments, a change also confirmed bythe other geochemical parameters, such as the ratios U/Th and La/Yb (Fig. 6). The La/Yb ratio represents theREE pattern. The ratio between elements was not af-fected by changing concentrations of other components.These ratios also change in the middle of the core, con-firming our previous explanation regarding the change

of LIL concentrations. The REE patterns also confirmthe change of the source for terrigenous elastics (Fig. 7);lighter REEs are more enriched in the lower zone.

Site 439Site 439 is situated on the deep-sea terrace near Site

584 (Fig. 1). Cretaceous black shale recovered at the bot-tom of the core might represent an open-ocean pelagicdeposit now accreted to the northeastern Japan arc inthe course of subduction of the Pacific Plate (von Hueneet al., 1982). The chemical compositions of these shales(Table 5), however, are quite similar to those of Mioceneto Pliocene hemipelagic mud at Site 584 (Table 4). Thissimilarity suggests that the black shale was not part ofthe accretionary prism but was also deposited in its pres-ent setting.

North Pacific Ocean

Site 436Site 436 is situated on the outer slope of the Japan

Trench about 150 km east of Site 584 (Scientific Party,1980). Site 436 sediments include Quaternary, Pliocene,and Miocene siliceous mud and mudstone, Oligocenebrown clay, and Cretaceous brown clay and chert. Theanalytical results are listed in Table 6 and are plotted inFigure 8.

Major Element GeochemistryIt is remarkable that concentrations of major elements

in the Quaternary, Pliocene, and upper Miocene sedi-ments at Site 436 are similar to those of Site 584 sedi-ments. Such a high degree of similarity may mean thattrench inner-slope and outer-slope sediments cannot bedistinguished by their geochemistry. Most of the Mio-cene, Oligocene, and Cretaceous sediments show ex-tremely high MnO concentrations.

Minor and Trace Element GeochemistryThe concentrations of LIL elements and their ratios

(like U/Th) change slightly at the Miocene/Plioceneboundary at this site and Site 584 (Figs. 6, 8). At bothlocations, LIL (except U) concentrations and Hf/Ta, U/Th, and La/Yb ratios increase in the lower sediments.This change suggests that the source of sediment sup-plied to the ocean margin near the Japan Trench changedat the Miocene/Pliocene boundary.

The REE patterns for Site 436 sediments (Fig. 9) showa negative Ce anomaly for the Cretaceous chert. TheseCe-depleted sediments always contain larger amounts ofCo, Cu, and other transition elements common in met-alliferous sediments near spreading centers, suggestingthat hydrothermal activity is responsible for the Ceanomaly in these sediments.

To summarize, the chemistry of the Quaternary, Plio-cene, and upper Miocene sediments at Site 436 resem-bles that of Site 584 sediments, whereas the chemistry ofthe middle Miocene to Cretaceous sediments at Site 436differs from that of overlying sediment at that site andfrom that of Site 584 sediments. The LIL concentra-tions, their ratios, and REE patterns appears to change

649


Table 3. Sites 294, 296, and 297: concentrations of major-element oxides (wt.%) and minor and trace elements (ppm) in deep-sea sed-

iments.


296-1-2, 117-119296-6-3, 50-52296-6-3, 78-80296-9-2, 50-52296-13-3, 50-52296-19-3, 28-30296-25-3, 39-41296-31-5, 100-102296-46-4, 105-107297-4-4, 69-71297-8-4, 30-32297-14-3, 50-52294-3-3, 30-32

Sub-bottomdepth (m)

2.6848.0148.2975.01

114.51171.29228.40289.01430.06

44.2110.31318.01

77.31

SiO 2

45.2941.9249.9335.4631.9035.0528.9129.3731.0563.564.763.5

TiO 2

0.490.350.360.340.230.320.210.190.210.750.760.79

A12O3

12.1710.0011.829.457.839.457.056.567.09

16.817.318.6

F e 2 O 3

a

4.993.653.943.692.713.732.552.774.006.296.738.02

MnO

0.120.130.110.120.120.100.170.260.360.230.210.18

MgO

2.051.261.321.310.651.460.630.631.242.813.032.91

CaO

17.9822.6215.9228.5934.2927.2736.2436.3334.20

4.492.080.67

Na 2 O

1.261.492.221.201.371.270.850.731.251.811.851.67

K 2 O

2.302.202.402.041.622.041.461.440.933.343.303.63

P2O5

0.040.010.020.030.050.080.040.060.070.040.04n.d.

Ba

538

9001065

250

Co

1158

1049

10148

152221

Cr

4225182723252115

7.88393

Note: Blank: not analyzed; n.d.: not detected.a Total iron as Fe 2 θ3

Table 4. Site 584: concentrations of major-element oxides (wt.%) and minor and trace elements (ppm) in deep-sea sediments.


584-1-2, 86-88584-2-3, 30-32584-4-1, 57-59584-4-2, 57-59b

584-5-2, 56-58b

584-11-1, 78-79584-11-2, 78-79584-14-1, 34-36584-20-1, 52-54584-22-2, 41-43584-24-1, 74-76584-27-1, 90-92584-29-1, 49-50584-32-1, 21-22584-36-1, 111-112584-40-3, 108-110584-46-1, 39-40584-48-1, 111-113584-49-4, 49-50584-53-3, 80-81584-56-1, 61-62584-60-3, 1-2584-67-2, 84-85584-70-1, 46-47584-76-2, 77-78584-80-1, 106-107584-86-1, 103-104584-90-2, 128-129584-94-1, 29-30584-96-2, 141-142C

584-97-1, 100-101

Sub-bottomdepth (m)

0.8713.6129.9831.4840.8796.7998.29

125.05183.33204.02223.55250.71269.30288.01336.72377.79431.90451.12465.10502.31527.72568.12634.45661.67721.38758.57816.53856.78893.10914.12922.81

SiO 2

67.5

83.7

83.088.083.181.282.582.377.279.478.777.974.173.281.0

77.568.769.772.073.680.879.077.772.3

76.3

TiO 2

0.7

0.3

0.30.20.30.40.30.30.40.40.40.40.60.50.4

0.40.80.70.70.60.40.40.40.6

0.5

A12O3

15.2

7.5

7.95.06.78.57.27.98.59.69.79.7

12.312.39.4

11.414.614.213.612.59.79.7

10.213.0

11.6

F e 2 O 3

a

6.1

3.1

3.32.43.14.03.63.34.24.34.53.85.35.83.9

3.86.66.35.75.53.54.94.86.1

5.0

MnO

0.1

0.1

0.1n.d.0.10.060.060.060.10.10.10.10.10.640.1

0.070.10.10.10.10.10.10.50.6

0.1

MgO

2.3

1.1

1.30.8

:::

.3

.4

.3

.3

.8

.9

.8

.72.42.11.4

1.53.02.62.52.71.41.91.62.3

1.6

CaO

3.6

1.1

1.41.62.61.12.61.35.01.21.63.71.11.60.8

1.81.61.31.21.10.70.71.10.9

1.8

Na 2 O

2.6

1.8

1.61.11.51.91.42.21.51.51.51.82.01.81.2

1.72.22.51.91.81.51.51.62.0

1.5

K 2 O

1.9

1.8

1.20.9

.2

.4

.11.3.3.6.7.7

2.22.11.7

2.12.52.52.32.21.91.92.12.3

1.7

P2θ5

0.1

0.02

n.d.n.d.0.050.010.020.020.040.01n.d.0.040.040.050.02

0.03n.d.0.070.04n.d.n.d.0.010.030.03

0.03

Ba

250567605319439636

336255

183325680880

1062132810201180873

1065105210151059

793

767593357793

Co

12

6

9575

8111112141214

111215151615

242526

14

Cr

51

35

47183540

29466743387665

4440

12412011084

536876

39

Note: Blank: not analyzed; n.d.: not detected.a Total iron as Fe 2 θ3

Diatomaceous fraction of the sediment sample.c Volcanic ash fraction.

near the Miocene/Pliocene boundary. A negative Ceanomaly for the Cretaceous chert suggests a hydrother-mal origin.

COMPARISON OF GEOCHEMISTRY OF NANKAITROUGH AND JAPAN TRENCH DEEP-SEA

SEDIMENTS

Major and minor element geochemistry reveals thatsediments recovered from the Nankai Trough (Sites 582and 583) and the Shikoku Basin (Sites 296 and 297) aresimilar to one another, meaning that their source has

not changed appreciably throughout the interval fromthe late Miocene to the present. The geochemical char-acteristics of the Pliocene-Pleistocene sediments fromSites 584, 439, and 436, near the Japan Trench, are alsosimilar to each other, but different from those of theNankai Trough and the Shikoku Basin sediments (com-pare Tables 2, 3, 4, 5, and 6). For example, the SiO2 con-centration ranges from about 70 to 90% in the JapanTrench, but from 50 to 70% in the Nankai Trough andthe Shikoku Basin, a difference attributable to the abun-dance of biogenic silica.

650

GEOCHEMISTRY

Table 3. (Continued).

Cs

3.83.0

4.12.33.82.12.5

5.2

6.42.6

Cu

44243415194822772171 :58120 :

Hf

J.I£.1

1.91.4.7.1.3

5.6

).O>.l

Ni

39101112

171119

485556

Rb

725969543655333312117121135

Sb

0.48

0.23

0.33

0.65

0.49

0.99

Sc

10.0

6.9

8.45.88.15.55.9

11.9

13.7

19

Sr

5106775178119198101014

987809220147118

Ta

0.67

0.41

0.53

0.36

0.42

0.340.24

0.76

0.84

0.31

Th

6.35.5

6.43.76.13.74.6

8.2

9.84.9

U

1.1

0.80.8

0.7

V

65374537244129212398104122

Zn

1086575585661425239118120105

Zr

12614117411911811811310086151153138

La

22.9

19.6

24.4

16.2

23.617.5

20.6

25.5

31.6

36.0

Ce

4438

3743402924

55

6753

Sm

4.18

3.63

3.92

2.94

4.28

2.89

3.76

4.25

5.15

8.08

Eu

0.89

0.68

0.900.71

0.950.71

0.90

0.93

1.13

2.07

Tb

0.88

0.73

0.60

0.63

0.930.41

0.67

0.55

0.75

1.34

Yb

2.62.9

2.22.02.61.52.1

2.7

3.34.5

Lu

0.53

0.38

0.35

0.380.37

0.270.32

0.44

0.49

0.73

Table 4. (Continued).

Cs

2.81.62.41.01.72.31.61.42.2

2.22.23.53.23.24.34.03.3

3.74.85.35.2

3.5

4.36.2

4.1

Cu

56

53

85795058

705983807611353

936549528780

125101169

92

Hf

2.51.41.62.01.81.71.71.11.4

1.62.01.81.81.82.43.11.8

2.43.14.12.9

2.0

2.33.31.81.7

Ni

28

24

34313635

38434849554465

383756606854

7512390

52

Rb

51

44

44283943

43425757567465

616281837878

736989

64

Sb

0.54

0.46

0.690.77

0.64

0.64

0.59

0.44

0.53

0.52

0.59

0.77

0.56

0.54

0.63

0.860.57

0.55

0.51

0.41

0.30

0.42

0.70

0.890.95

0.77

0.88

Sc

176.87.74.44.69.38.65.28.3

7.59.710.2

9.510.0

11.8

139.0

9.414.5

1513.5

8.8

11.5135.512.6

Sr

237

108

120114144119

112221126137203157150

112140158150140140

104111110

135

Ta

0.30.180.21

0.22

0.22

0.27

0.13

0.19

0.14

0.24

0.32

0.28

0.280.41

0.47

0.27

0.32

0.49

0.63

0.49

0.34

0.47

0.66

0.77

0.33

Th

4.o :2.7 :

2.82.03.83.0 :2.71.72.8 :

2.63.03.93.8 :

4.3 :

5.05.74.0

4.96.36.56.0

u

1.7>.O.7.0

>.O

.2>.l

.4

.9

.8>.55.7.6.8.3.5.6.5.8.3

4.7 0.8

5.77.6 :

7.o :4.7

.3>.3>.4.2

V

100

42

61433844

445172746910085

686711812011597

736993

82

Zn

112

85

1048285100

8493103108115105125

10611394100110116

125155160

125

Zr

117

80

72416567

7980878485107100

78110129120116111

90106107

83

La

13.09.18.6

11.9

9.89.35.58.6

8.09.411.1

11.6

13.1

16.0

17.7

11.513.4

14.1

18.7

18. (17.5

14.2

18.618.4

19.3

12.9

13.9

Ce

281916

2320198.619

18162427293338233541593618

314242492733

Sm

3.21.88

1.9

2.18

1.91.91.21.8

1.82.152.22.42.62.83.72.22.68

2.93.63.93.4

2.63.93.43.73.96

2.8

Eu

0.86

0.40

0.47

0.58

0.53

0.39

0.33

0.45

0.40

0.47

0.59

0.60

0.65

0.73

0.86

0.56

0.43

0.74

0.83

0.93

0.85

0.65

0.880.78

0.78

0.250.71

Tb

0.62 :

0.34

0.37

0.30

0.37

0.43

0.25

0.29

0.42

0.51

0.39

0.44 :

0.46 :

0.34

Yb

5.7.3.6

.9

.4

.3

.0

.3

.5

.5

.7>.3>.l.6

0.83 2.4

0.31

0.44

.2

.80.49 2.4

0.52 ;..80.61 2.4

0.57 2.2

0.45

0.44 ;

.9>.5

0.51 2.2

0.55 2.0

0.98 :.80.59 2.0

Lu

0.52

0.27

0.29

0.31

0.23

0.22

0.19

0.29

0.29

0.33

0.30

0.43

0.39

0.31

0.44

0.27

0.34

0.42

0.400.44

0.37

0.330.34

0.37

0.43

0.60

0.33

The LILs are more enriched in the sediments in theNankai Trough and the Shikoku Basin than in the JapanTrench, a trend observed not only in major-element ox-ides, such as Na2O and K2O, but also in trace elements,such as La and Yb. These differences imply that the sed-iments in these regions differ not only in the ratio of bi-ogenic silica to terrigenous elastics but also in the chem-ical characteristics of terrigenous suites. The LILs aremore concentrated in the Miocene than in the Pliocenesediment. In other words, the LIL concentrations of theMiocene sediments in the Japan Trench are like the Plio-cene to Recent sediments in the Nankai Trough region.The similarity is confirmed by comparing not only theLILs but also the La/Yb, U/Th, and Na2O/K2O ratios.

During the Miocene, sediments of similar chemicalcomposition may have been supplied to the Japan Trench,the Nankai Trough, and the Shikoku Basin. Changes ofocean currents might explain variations in their presentgeochemistry (Fig. 10). During the Miocene, the Kuro-shio flowed from the Shikoku Basin toward the shore ofnortheastern Japan and carried huge amounts of terrig-enous sediments off the Japanese islands along its path.In the Pliocene, the current shifted to a more easterlycourse and did not reach the Japan Trench region. Finegrains suspended in the open ocean can travel more than1000 km in strong ocean current (Reed et al., 1975).Such transport of suspended particles by the Kuroshiomay possibly account for the sedimentation of geochem-

651


I °AI2O3 (%) αCaO (%) TiO2 (%)

f ? . • 4° °Fe2O3(%) N a 2 0 ( % ) o M n 0 ( o / o )g j c SiO2(%) •MgO(%)

Site 2 9 7 2,5 . 65 o 8 o ' 4 oo

P2O5

Ba Co Cr Cs Cu Hf Ni Rb Sb Sc Sr( p p m ) (ppm)(ppm)(ppm)(ppm)(ppm)(ppm) (ppm)(ppm)(ppm)(ppm)

4 0 1200 0 50 0 100 010 0 200 0 5 0100 0 200 0 1 0 20 0 1000

100-

200-

300-

Pleist.

Plio.

\

I f !

Site 296

E2 0 0 -

O

•? 3 0 0 -

400-

Pleist.

Plio.

Mio.

Oligo.

5 / i f

Ta Th U V Zn Zr La Yb(ppm)(ppm)(ppm)(ppm)(ppm)(ppm) (ppm) (ppm)

Site 2970

100-

200-

300-

Pleist.

Plio.

010 0 2

T

200 0 200 0 200 0_l_

4 0 0

U/Th La/Yb Hf/Ta(log) (log) (log)

0.1 0.35 10153 5 10

I !Site 2960

c 100-

I2'n 300-

Pleist.

Plio.

Mio.

Oligo.

)

Figure 4. Depth profiles for concentrations of major, minor, and trace elements in deep-sea sediments from Sites 294, 296, and 297.

ically similar materials in very wide regions offshore ofthe Japanese islands.

CONCLUSIONS

The following conclusions are drawn from chemicalanalysis of the deep-sea sediments in the Nankai Troughand the Japan Trench:

1. Sources of the Pliocene to Quaternary sedimentswere similar in the Nankai Trough and the northern partof the Shikoku Basin.

2. The REE pattern varies in the Miocene to Qua-ternary sediments at Site 296. The change reflects themotion of the Philippine Sea Plate, which is migratingnorthward toward the islands of Japan.

3. The source supplying sediment to the Japan Trenchchanged near the boundary between the Pliocene andthe Miocene.

4. During the Miocene, geochemically similar terrig-enous sediments were supplied to a large area of the Pa-cific Ocean side of the Japanese islands, including theShikoku Basin, the Nankai Trough, and the Japan Trench.This supply might have been caused by the Kuroshioflowing northeast along the Japanese islands.

5. Negative cerium anomalies in sediments are an in-dicator of the hydrothermal activity.

ACKNOWLEDGMENTS

We are indebted to Professors N. Nasu and H. Kagami for givingus an opportunity to study these sediments, and to Professor A. Iijimafor his interest. Thanks are also due Professor H. Wakita and Dr. Y.Nakamura for generously permitting us to use their facility. We wouldlike to express sincere thanks to Professors A. Masuda and H. Wakitafor their valuable suggestions and critical reading of this manuscript.This work was supported in part by a grant from Ito Science Founda-tion.

652

GEOCHEMISTRY

100

50

100

50

100

50

100

10

Site 2971 297-4-4, 69-71 cm2 297-14-3, 50-52 cm

2, 117 — 119 cm3, 50—52 cm

Site 2941 294-3-3, 30-32 cm

- 2

; 1

1 296-9-2, 50-52 cm2 296-13-3, 50-52 cm3 296-19-3, 28-30 cm4 296-25-3, 39-41 cm5 296-31-5, 100-102 cm

3


Figure 5. Typical chondrite-normalized rare-earth-element patterns fordeep-sea sediments from Sites 294, 296, and 297.

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Steinberg, M., Bonnot-Courtois, C , and Tlig, S., 1983. Geochemicalcontribution to the understanding of bedded cherts. In Iijima, A.,Hein, J. R., and Siever, R. (Eds.), Siliceous Deposits in Pacific Re-gion: Amsterdam (Elsevier), pp. 193-210.

Steinberg, M., and Marin, C. M., 1978. Classification géochimiquedes radiolarites et des sediments silicieux océaniques, significationpaleo-océanographique. Oceanol. Acta, 1:359-367.

Sugisaki R., 1978. Chemical composition of argillaceous sediments onthe Pacific margin of southeast Japan. Geol. Surv. Japan CruiseRept., 6:65-73.

, 1979. Chemical composition of argillaceous sedimentsaround the Yamato Bank in the Japan Sea. Geol. Surv. JapanCruise Rept., 13:75-88.

_, 1980a. Major-element chemistry of argillaceous sediments,at Deep Sea Drilling Project Sites 442, 443, and 444, Shikoku Ba-sin. In Klein, G. deV., Kobayashi, K., et al., Init. Repts. DSDP,58: Washington (U.S. Govt. Printing Office), 719-735.

., 1980b. Major element chemistry of the Japan Trench sedi-ments, Legs 56 and 57. In Scientific Party, Init. Repts. DSDP, 56,57, Pt. 2: Washington (U.S. Govt. Printing Office), 1233-1249.

Tarney, J., and Donnellan, N. C. B., 1977. Minor element geochemis-try of sediments at Site 328, Falkland Outer Basin and Site 329,Falkland Plateau, Leg 36, Deep Sea Drilling Project. In Barker, P.F., Dalziel, I. W. D., et al., Init. Repts. DSDP, 36: Washington(U.S. Govt. Printing Office), 929-939.

von Huene, R., Langseth, M., Nasu, N., and Okada, H., 1982. Asummary of Cenozoic tectonic history along the IPOD Japan Trenchtransect. Geol. Soc. Am. Bull., 93:829-846.

Date of Initial Receipt: 4 January 1984Date of Acceptance: 8 May 1985

653


on A. π to/\ TiO9 (%)o AI2Oo (%) *

£ 0 25 θ F e 2 O 3 ( % ) . N a o

g •MgO(%) N a 2 °| _ SiO2(%) α C a0(%) o K 2 O ( 1

i: 'c 65 90 0 7 0CO 3

(m)

j -

"Q.Φ

-bot

tom

nCO

100-

200-

300-

400-

500-

600-

700-

800-

900-

Φ^ CΦ Φ

low

Plio

cjp

pe

rio

cen

eM

o.

E

:%) oMnO (%)

'o) p 2 ° 5 (%)4 0 0.7

Ba Co Cr Cs Cu Hf Ni(ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

1400'0 50 0 150'0 10 0 200 0 5 0 200

Rb Sb Sc Sr Ta Th U V Zn Zr La Yb U/Th La/Yb(ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (log) (log)0100 0 1 0 50 0 300 0 1 0 10 0 5 0 200 0 200 0 200 0 20 0 0.4 0.1 0.5

Hf/Ta(log)

10 2 5 10 20

E

Φ•σ

1co

0 -

100-

200-

300-

400-

500-

600-

700-

800-

900-

Φ

O

upp

er

ΦCΦ

O

E

CD

Wo

ce

nA\

o.

^~

E \ M \Figure 6. Depth profiles for concentrations of major, minor, and trace elements in deep-sea sediments from Site 584.

50

CO

CO

6

584-1-2, 86-88 cm584-14-1, 34-36 cm584-27-1, 90-92 cm584-36-1, 111-1 12 cm

584-49-4, 49-50 cm584-60-3, 1-2 cm


Figure 7. Chondrite-normalized rare-earth-element patterns for sev-eral deep-sea sediments from Site 584.

654

GEOCHEMISTRY

Table 5. Site 439: concentrations of major-element oxides (wt.%) in deep-sea sediments.


439-37-1, 96-98439-38-1, 107-109439-39-1, 32-34

Sub-bottomdepth (m)

1144.971149.081153.83

SiO2

68.767.065.5

TiO2

0.530.830.85

A12O3

17.318.219.0

Fe 2O 3a

5.65.96.5

MnO

0.060.060.06

MgO

1.562.012.07

CaO

1.070.420.38

Na2O

2.142.051.80

K2O

3.113.483.74

P2O5

0.010.060.05

a Total iron as Fe2C>3.

Table 6. Site 436: INAA results (in ppm) for deep-sea sediments.


436-3-1, 60-62436-12-2, 60-62436-19-3, 140-142436-23-4, 70-72436-31-3, 130-132436-34-2, 74-75436-38-5, 34-36436-39-5, 42-43436-41-1, 43-45a

436-41-1, 43-45b

436-41-1, 46-48

Sub-bottomdepth (m)

18.10105.11173.91212.71287.81314.25356.35365.93378.94378.94378.97

Cs

3.82.62.64.33.65.46.16.80.390.260.93

Hf

2.41.61.82.52.12.42.53.70.210.160.53

Sb

0.740.650.420.670.690.720.561.160.340.130.27

Sc

1414121312141521

2.11.33.6

Ta

0.600.350.390.500.500.600.660.910.050.030.13

Th

5.94.14.46.35.87.99.7

15.50.30.21.5

U

19.91.71.91.0

La

17.513.613.119.520.324.326.041.8

2.31.8

15.2

Ce

4029313944

5.369

1365.43.4

13

Sm

4.473.543.413.833.864.385.229.580.830.603.58

Eu

0.830.850.720.870.860.961.222.310.200.140.81

Tb

0.880.690.730.600.630.640.871.700.120.110.55

Yb

2.72.42.22.62.42.63.05.80.300.221.8

Lu

0.460.560.470.520.440.420.580.970.100.100.32

Note: INAA: instrumental neutron activation analysis; blank: not analyzed.a Reddish brown fraction of the chert sample.

Noncolored white fraction of the chert sample.

655


°MnO(%)°K2O(%) P2O5

7 0 4 0 0.5

(ppm) (ppm) (ppm) (ppmMppm) (ppm)

Figure 8. Depth profiles for concentrations of major, minor, and traceelements in deep-sea sediments from Site 436. Major element depthprofiles were drawn from Sugisaki (1980b). The samples repre-sented in the major element depth profiles are as follows (all fromHole 436, expressed in core-section, interval in cm): 3-3, 100-104;12-2, 36-40; 19-4, 86-90; 23-5, 35-39; 31-4, 40-44; 34-2, 60-64;38-2, 66-70; 39-6, 60-64; 40-4, 50-54.

100

10 -

- j ^ % ^ N^ 3

^ 5 ^ . 5

^ ^ < * \ 6

(436-3-1, 60-62 cm| 436-1 2-2, 60-62 cm(436-19-3, 140-142 cm

(436-23-4, 70-72 cm| 436-31-3, 130-132 cm

• [436-34-2, 74-75 cm

5 3 2i i i

100

oo 10

1 -

_ 436-41-1, 4 6 - 4 8 cm

La Ce Sm Eu TB Yb Lu

Figure 9. Typical chondrite-normalized rare-earth-element patterns ofdeep-sea sediments from Site 436.

656

GEOCHEMISTRY

45°N

30c

25°

East Asia

130° 135C 140c 145°E

Figure 10. The proposed model for the sedimentation process in thesouth of the Japan islands from the Miocene to the Quaternary.

657

14. geochemistry of deep sea sediments from the … · vation analysis. ten major elements and 24...

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