8. origin of the late cenozoic sediments of the ...sediments of all three units in hole 348 are...

8. ORIGIN OF THE LATE CENOZOIC SEDIMENTS OF THE ICELANDIC BASIN,DSDP SITE 348, LEG 38

M.P. Nesterova, F.A. Scherbakov, A.Ja. Shevchenko, N.W. Turanskaja, W.P. Kazakova,A.G. Samosudova, T.G. Kuzmina, and A.N. Rudakova, Analytical Laboratory,

P.P. Shirshov Institute of Oceanology, Academy of Sciences, USSR

INTRODUCTION

Site 348 attracted a great deal of interest because thehole was drilled within the Icelandic Basin, whichrepresents a large depression in the Icelandic Plateau.

Laboratory studies consisted of a determination of:sediment grain sizes, the mineralogic composition of thecoarse silt fraction (0.1 to 0.05 mm), and the chemicalcomposition and the composition of clay minerals in theless than 0.001 mm size fraction.

Data Presentation

The data obtained are listed in Tables 1-9. The data inTable 1 are average values that characterize thesediments and rocks of each of the three stratigraphicunits by the shipboard party (see Site Report, Chapter8 , this volume). The tables also present data on theterrigenous, biogenic, volcanogenic, and authigenicsediment components. The data on chemical composi-tion (Table 2) indicate the content of biogenic silica andCaCOa in the sediment. The iron content (FfcOa) (Table4) indicates the presence of both terrigenous andauthigenic material. Components in the separate grainsize fractions are grouped in such a manner so as tocharacterize most accurately the various components ofthe sediment. Table 3 also includes data on the quantityof particles with a size of less than 5 µm. It was assumedthat these particles consist almost entirely of clayminerals.

The data presented on the content of separateminerals in the 0.1-0.05 mm fraction (Table 1) concen-trate on a group of the most typical terrigenousminerals: quartz, potassium feldspars, hornblende, andweathered grains (chiefly rock debris, plagioclasefeldspars). For the volcanogenic sediments, the datashow the contents of varieties such as glass and varioustypes of more or less altered particles of volcanic ash.The authigenic group included pyrite and marcasite,iron hydroxides, glauconite, and zeolites which havebeen formed in the process of devitrification andpalagonitization of the primary volcanogenic ashmaterial. However, some zeolites probably have avolcanic origin.

From analysis of the data, it is apparent that each ofthe three lithologic units distinguished differ both incomposition and genesis. However, the interpretationson the composition and genesis of these sediments aresomewhat different from those of the shipboard party(see Site Report, Chapter 8 , this volume).

DISCUSSION

Based on the data available, it is concluded that thesediments of all three units in Hole 348 are essentiallyclay sediments. The average percentage of the clay con-tent calculated for the three units is over 70% (Table 3).The major bulk of these particles is represented by clayminerals, and a considerable portion of this claymaterial is authigenic. The material, which has beenaltered and converted into these clays, was probably of avolcanogenic origin and not terrigenous (see however,Site Report, Chapter 8 , this volume).

Biogenic Components (Carbonate and Silica)

Biogenic calcium carbonate has an extremely minorcontent in the Cenozoic sediments. Rarely, except inseparate interlayers, does the CaCθ3 content reach 15%.However, biogenic amorphous silica is far more impor-tant, although the Siθ2 content in the samples studiedhardly exceeds 8% (Table 2). A study of smear slides andthin sections of these sediments under the scanning elec-tron microscope shows a high content of siliceousskeletons. It is believed that although the skeletalvolume may be high, the mass contained in the skeletonsis low. On the other hand, the mass of clay material in asimilar volume is appreciably higher.

Volcanic Components

For the volcanic constituents, the predominant masshas been transported as ash particles to oceanic regions.The sediment contains particles of volcanic glass whosesize corresponds chiefly to silt and (partially) coarse clayfractions.

Volcanic glass, under certain conditions, will com-prise the major portion of such fractions; however, themain mass of volcanic glass appears to have been com-pletely altered and converted to clay.

Studies of Volcanic Components

Volcanic material in the coarse fraction consists ofheavy (specific weight 2.9 g/cc) and light (specific weightless than 2.9 g/cc) subfractions. The material includesvolcanic glass that contained both the basic (7V>1.54[dominant type]) and acid varieties (N<l.54). Frequent-ly, a significant portion of the volcanic material wasrepresented by devitrified and more or less altered glass,particularly the palagonitized variety. These can be con-sidered varieties of ash particles.

Also detected in the volcanogenic component of thecoarse silt (heavy subfraction) were monoclinic pyrox-

73

M. P. NESTEROVA ET AL.

TABLE 1Composition of Sediments Cored at Site 348

Age

Ple

isto

cen

eM

idd

le M

ioce

neto

P

lioce

ne

Olig

oce

ne

to

E.

Mio

cene

Q

65 m

N2

N!mc3

Nxmc2

N1mc1

527 m

Grain SizeD is t r i bu t ion {%)

> O . l

mm

- 1 5 - 7 9 •

22-25- 78 -

1-0.1

mm

1 5

4.3

2.5

-55-117-13-28

- 14.9 "

5.1

0.1-0.01

mm

3.3 .

6.4

2.7

2.7

<0005

mm

70.2

77.6

57.4

72.8

–̂ o

3 °föα> .= o

6.0

8.4

5.7

Clast ic Part 0.1-0.05 mm {%)

Terrigenous

Quartz

35.8

1.7

45.0

K-

Feldspar

13.1

1.0

13.0

Opaque

7.4

2.2

14.2

28.0

Horn-blendeGreen

6.9

0.4

6.2

Weath-eredFrag-ments

16.7

21.9

Volcanogenic

pyroxene

19.8

10.5

1.2

Volcanicash

heavy

46.7

80.0

t r

3.0

Vol-canic

ashl i g h t

9.0

35.3

t r

Volcanicglass

3.3

49.7

1.3

t r

Pyrite-marca-si te

0.5

4.9

55.9

70.8

30.6

enes (augite). However, some of the pyroxenes may havebeen transported (especially in Pleistocene times) asterrigenous components from Iceland.

Authigenic Components

Authigenic minerals formed by diagenesis includepyrite and marcasite (in the heavy subfraction of thecoarse silt fraction). These are grouped in Table 1 asiron sulfides (FeS2) and include iron hydroxides in theform of limonite and glauconite. These varieties,together with conspicuous zeolites, are commonly pres-ent in the thin bedded clay fractions. The zeolites wereobserved in the diffraction (X-ray) patterns of sedi-ments of the less than 1 µm fraction, however, it is be-lieved they are accessory minerals.

Clay Minerals

Important in the definition of sediment compositionand genesis is determining the composition of clayminerals. The study utilized the data from X-ray diffrac-tion and SEM microphotography. Detected were mont-morillonite and hydromica, as well as chlorite, zeolites,and mixed-layer clays of varying compositions.

Calculations of the quality of these minerals in the lessthan 1 µm fraction are based on the technique ofBrindley (1965).

Montmorillonite is among the clays which comprise amajor portion of the section. Moreover, montmoril-lonite, in pre-Pleistocene deposits, predominates andconstitutes, locally, up to 100% in the less than 1 µmfraction. It is believed that the main portion of thismontmorillonite is authigenic, formed as a result oftransformation of basic volcanic glass.

Thus, analysis of the clay fraction of the sedimentseems to provide substantial grounds that the majorportion of the pre-Pleistocene sediments in the IcelandicBasin is primarily volcanogenic. These volcanogeniccomponents have been subsequently transformed invarying degrees into authigenic components.

GENERAL CONCLUSIONS

Considerations of the data from the lithologic studiesof the core samples of Hole 348 permit some generalconclusions on the composition and genesis of thesedimentary material.

74

ORIGIN OF LATE CENOZOIC SEDIMENTS

TABLE 1 - Continued

Authigenie

Fe-hydrooxides

1.7

1.1

3.0

Glauco-nite

0.5

t r

1.6

Zeolite

t r

0.2-1.4

— 11.3 —

3 637.3

2.5-5.2

0.5-2.2

0.2-

-12.3-

Organic

CaCO3

51.7 ,17.4

- 29-36 -

- 6-85 -

Si l i c -eous

t r

C h e m i c a l C o m p o s i t i o n [%)

SiO2

(Amorph)

1.4

3.8

7.0

1.8

Fe203

9.1

9.9

13.9

8.6

CaC03

—15.0 —

30.4U -

— 39 —

3.23.5 —

— 1 5 - 4 1 -

— 32 —

1.6

OrganicCarbon

t r

0.2

0.9

0.8

C l a y m i n e r a l s <O .OO l mm {%)

m ite

50-60

30-60

10-30

t r

10-20

10

Mont-mori-

1 Ionite

10-40

25-60

60-80

%100

60-80

40

Chlorite

5-10

10

10-15

t r

10-20

20

Kaoli-nite

5-10

t r

t r

MixedLayer

Minerals

5-10

5-10

10

t r

Zeolite

t r

t r

10-20

30

Despite the homogeneous composition of clay in thesedimentary section, there are very minor variations inthe composition and content of accessory terrigenous,biogenic, volcanogenic, authigenic, and clay com-ponents. These variations support the division of thesediments into three stratigraphic units. There is also ageneral agreement of lithologic and stratigraphic bound-aries.

Unit 3The "accessory" components in the silt portion of the

sediment section are almost exclusively "terrigenous" inthe lower portion of Unit 3 (Oligocene and earlyMiocene). Volcanogenic constituents are practically ab-sent in the silt fraction, however, there is a great deal ofquartz, weathered plagioclase, or other minerals. Thesilt is also characterized by the highest content of heavyore minerals (Table 1). Noteworthy is the low content ofbiogenic (S1O2, CaCOa) components. Interestingly,however, the sediments do have a high CWR content.

A direct correlation seems to exist with CWf and thepercentage of authigenic pyrite and marcasite in Unit 3.Less common is glauconite. In all probability, the high

Cora content present is the main factor that led to theorigin (via diagenesis) of these authigenic components.Also of interest is the fact that all these deposits are theoldest of those cored.

Although all sediment sections are characterized by agenerally low zeolite content in the silty sediments, Unit3 has a high content (Table 1). The distribution of thesezeolites in the coarse silts shows a tendency to increasein content from the top. An exception is the lowermostportion of Unit 3, where large zeolite crystals are abun-dant (Figures 1 and 2).

The clay component in Unit 3 has a quite differentcharacter. The less than 1 µm fraction is completelycomposed of montmorillonite, especially at the top ofthe unit (early-Miocene). X-ray diffraction fails to revealbut a trace of other minerals. An exception is the lower-most beds (late Oligocene) above basalts. Here, apartfrom the predominant montmorillonite, there is a con-siderable amount of chlorite, hydromica, and kaolinite.Zeolite is also conspicuous. The composition of theseclays provides grounds to indicate that this clay hasformed from ash material and basaltic lavas. Theabsence of the ash in larger size fractions indicates an

75

TABLE 2AResults of Immersion Minetalogical Analysis of the 0.1-0.5 mm Fraction Samples (Heavy Minerals) From Hole 348 DSDP Leg 38

Sample(Interval in cm)

1-1, 70-721-1, 70-721-3, 100-1041-3, 100-10414, 100-10214, 100-1021-5, 90-921-5,90-92l.CC1,CC2-1,98-1002-1, 98-1002-2,50-522-2, 50-5224,99-1012 4 , 99-1012, CC2,CC3-1, 99-1013-1,99-1013-3,99-1013-3, 99-1013-4, 99-10134, 99-1013-5,89-913-5, 89-913, CC3, CC4-1, 119-1214-1,119-1214-2, 99-1044-2, 99-1045-1, 99-1005-1, 99-1005-2, 139-1415-2, 193, 1415, CC5,CC6-1, 139-1416-1, 139-1416-2, 29-316-2, 29-316-4, 84-866-4, 84-866-5, 73-756-5, 73-756, CC6, CC7-1, 74-767-1, 74-767-3, 74-767-3, 74-767-4, 75-777-4, 75-777,CC7, CC8-2, 75-778-2, 75-778-3, 75-778-3, 75-779-1, 139-1409-1, 139-1409-2, 75-779-2, 75-779-5, 75-779-5, 75-779, CC9, CC11-1,80-8211-1,80-8211-2,80-8211-2,80-82114,70-72114,70-7212-2,60-6212-2,60-62124, 20-22124, 20-2213-1, 80-82

<u 433 2

I.SO S

266.6

7719.1

123.5

5313.9

14_

4910.25324.433987818.44313.53887174.551.161.320.4

122.8

122.6

214.4

194.0

122.3

102.0

112.5

19.040

6

[gne

tite

S

92.482.050.7

308.0

225.8

359.4

296.8

193.962.8

4513.2153.5

144.4

347830

8.2102.261.3

101.9

4310.140.971.551.1

142.961.461.551.1

306.3

133.2

142.650.971.340.9

132.761.4

203.840.961.34

rite

-ir

casi

te

82.151.2

10.3

10.5

30.8

91792.1

173.610.2

20.430.710.2

214.8

224.7

235.7

20.410.2

194.092.150.9

14431.340

8.5

drox

igeu

s

x £,

4104010.020.341.1

246.351.3

112.65_

377.7

125.5

133.8

153.561.992.0

1335

71.681.771.3

9121.2

71.561.3

112.140.840.840.9

112.830.7

132.841.050.940.850.9

224.730.661.461.1

9

ucox

ene

61.5

41.141.0

1_

51.052.351.530.7

:ath

erin

gig

men

ts

31.6

287.0

205.4

3

449.1

3114.3195.6

225.2

185.7

14132.1

51.0

102.171.3

met

ü

41.0

4010.0

10.171.9

112.910.220.51

377.7

136.0

185.3

358.272.2

102.371.940.910.251.010.2

40.810.210.2

10.2

<u <u

1 11 i l£ ox

236.1

4912.360.8

215.7

6116.3349.2

174.09

8918.2136.0

6820.0

2 870.5 20.6

6921.87116.23710.331

7.130.6

295.6

133.071.530.620.42.44.620.420.420.410.220.510.2

10.2

40.7

own

irnb

lend

e

30.4

184.8

113.051.1

174.610.2

30.7

10.2

10.2

salti

cir

nble

nde

51.320.5

10.2

20.420.951.510.2

10.2

itino

lite

emol

ite

< H

51.220.320.520.561.610.2

30.620.961.240.972.292.030.820.4

30.6

10.2

20.4

10.2

auco

phan

e

roxe

neim

b.)

δ a? w

20.5

1 60.2 1.5

40.510.3

184.741.110.2

1633

10.551.592.182.5

1023

41.130.710.210.2

10.210.2

10.220.4

10.2

10.21

(OU

Ol

9U9X

OI

123.1

348.5

375.1

9425.36817.87219.36415.014_8016.54821.07722.84510.69429.75211.89525.8

12327.611

2.361.1

204.7

265.7

163.4

224.7

295.571.6

377.7

153.4

123130

6.8157

34.035

8.640

7.335

6.536

6.7107

22.936

7.6184.2

7514.47516.339

8.326

<D

<

10.3

20.51_10.2

10.2

10.2

u

ifw ü

41.0

5814.381.1

6116.45113.44211.323

5.320

_6112.6188.3

339.8

7116.73611.44410.012

3.314

3.130.6

152.9

133.051.151.061.3

,30.620.461.2

10.261.410.220.520.440.8

10.2

4

otit

e

3

20.510.1

20.5

10.2

10.3

20.5

ilori

teag

men

ts

u n-

10.3

10.220.5

20.510.2

347.9

10.2

76



TABLE 2A - Continued

c

H

82.010.182.151.441.151.1

71.410.5

51.241.330.7164.310.2

10.4

lit

o

CΛ

10.2

10.2

13Pc0H

10.320.5

20.5

10.210.2

10.3

10.2

0.2

a0.aN

30.8133.220.320.520.520.510.21

71.473.282.3122.882.581.820.5

3.210.2

10.210.210.2

10.210.230.6

aj

<

10.3164.020.341.151.430.8

91.931.430.9143.320.651.161.6

30.6

20.4

o

3

30.7

20.5

10.21

10.2

20.510.3

e•>.

20.5

30.8

2

20.5

11 iU P3 U

c<

10.2

13 BUU

380

402

727

372

381

372

429

70

485

217

341

425

317

0

70-72

100-104

100-102

90-92

98-100

50-52

99-100

99-101

99-101

99-101

89-91

10.3

20.310.3718

20.5

30.6

10.230.7

20.5

20.510.3

10.2

91.9

20.5

27472.4

10.2

65189.6

3 1 2 610.8 0.3 0.5 16.3

3 400.8 10.5

1490.5 40.31 2 2 1 2500.2 0.5 0.5 0.2 58.3

1 1 10.2 0.2 0.2

10.5

439

1 1 3 98 369 119-1210.2 0.2 0.8 26.6

243 446 99-104545

430 470916

1 1 3 422 5220.2 0.4 0.2 0.6 80.71 1 1 188 4270.2 0.2 0.2 44.41 1 399 4590.2 0.2 86.91 1 415 4770.2 0.2 87.0

385 47281.5

3 1 426 5230.6 0.2 81.4

476 50594.0

409 48285.0

405 43593.2

356 38892.0

1 360 4390.2 82.0

2 234 4620.4 51.0

328 40581.0

2 475 5400.4 88.0

1 2 469 5220.2 0.4 90.0

1 48.1 1 5360.2 89.8 0.2

1 1 315 4690.2 0.2 67.1

1 401 4730.2 84.91 382 4230.2 90.5

413 52179.4

237 46151.3

1 382 4690.2 81.51

77


Sample^Interval in cm)

13-1, 80-8213-2, 20-2213-2,20-2213, CC13, CC14-1,20-2214-1, 20-2214-2, 20-2214-2, 20-2214^, 20-2214-4, 20-2214-5, 20-2214-5, 20-2214-6, 20-2214-6, 20-2214, CC14, CC15-1,60-6215-1, 60-6215-2, 60-6215-2, 60-6215, CC15, CC16-1,60-6216-1, 60-6216-3, 60-6216-3, 60-6216-5, 60-6216-5, 60-6216-6, 60-6215-6, 60-6216, CC16, CC19-1, 110-11219-1, 110-11219-3, 75-7719-3, 75-7719-4, 10-1219-4, 10-1219-6, 140-14219-6, 140-14219, CC19, CC20-1, 80-8220-1, 80-8220-2, 80-8220-2, 80-8220-4, 64-6620-4, 64-6620-6, 135-13720-6, 135-13720, CC20, CC21-1, 60-6221-1,60-6221-3, 100-10421-3, 100-10421-5,60-6221-5, 60-6221, CC21, CC22, CC22, CC23-1, 110-11223-1, 110-11223-3, 77-7923-3, 77-7923-5, 80-8223-5, 80-8223, CC23, CC24-1, 27-2924-1, 27-2924-2,49-5124-2, 49-5124-4, 2-424-4, 2-424-6, 60-6224-6, 60-62

>aq

ue

nera

ls

o i1.6

173.740.920.640.930.720.4

0.461.3

123.492.1

102.853.0

20.5

154.074.64

1

2

4

63.62

1

4

175.95

4112.631.0

286.2

10221.66916.3549.9

61.320.4

122.6

377.0

1S

1.171.5

51.430.771.530.640.930.730.9

51.35

14

30.9

4

6

1

2515.6

34

2

134.54

3310.231.0

194.3

408.4

204.781.5

51.1

162.8

rite

-ir

casi

te

123.4

5312.5185.9

336.4

9220.6184.0

7922.7

30066.7

71.8

20055.08853.6

26881.6

38493.7

21057.0

11374.380

45

38

12

6339.0

9

34

16

18062.810

13040.0

25584.1

31069.89820.6

18243.3

23543.1

42289.5

43189.6

40387.9

37470.5

'dro

xige

us

X fc

2.451.1

102.372.0

112.6

112.4

275.2

204.5

112.520.620.5

2.061.753.051.541.0

236.385.33

10

1

2

2

169.94

21

93.1

9629.6186.0

122.7

112.361.4

336.120.471.4

ucox

ene

20.420.420.4

10.210.2

;ath

erin

gag

men

ts

71.5

2

2

1

2

4

112.320.4

234.2

u

O

10.2

20.420.4

30.720.630.7

61.721.320.610.210.363.91

1

1

2

31.86

1

62.13

41.241.3

102.2

183.8

235.4

254.6

112.320.461.391.7

horl

onit

e

een

>rnb

lend

e

own

arnb

lend

e

£ ox £x

l0.210.2

51.120.4

41.120.520.541.163.710.320.551.410.7

1

2

3

2

1

849

1

1

124.24

20.631.0

173.8

7816.332

7.577

14.351.1

193.9

112.4

244.5

isal

ticD

rnbl

ende

:tin

olit

eem

olit

e

auco

phan

e

mX < H O

10.2

10.3

10.3

1

2 41.2 2.5

4

51.74

20.6

102.110.240.710.2

30.650.9

'rox

ene

Dm

b.)

0 - ^

0.310.210.2

10.6

'roxe

nelo

no)

C3

7.023

5.171.692.5

5613.45411.950

9.7255.661.3

236.5

4210.0143.6

8824.53320.23911.815

3.74411.953.31

2

1

1

2

6

53.1

2

2

31.0

41.220.761.310.2

30.681.751.0

sgir

ine

sido

tero

up

< w ü

1.120.420.510.310.230.730.620.420.561.750.582.0

154.2

169.882.4

41.1

106.54

1

2

3

3

2012.3

1

1 2

269.03

72.2

134.3

1 220.2 4.9

6814.2

1 490.2 11.5

6612.2132.7

162.351.3

397.3

iotit

e

llor

ite

ragm

ents

ffl U fc

10.2

51.7

10.2

10.2

10.2

20.410.2

78




"03 JI

U «

o S •a 2

0.3

1

0.2

1

0.2

10.2

10.2

10.3

20.5

20.610.610.310.210.3

20.6

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41.15

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87.640694.331589.8

297

344

75.339275.5

30267.639288.8

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21861.65918.3

34888.8175.0

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431

351

425

457

518

447

442

352

422

392

360

164

329

410

368

152

104

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163.740.710.230.620.471.3

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30.630.630.7

10.230.5

20.420.410.2

10.210.2

1

20.420.4

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31.03

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40.940.861.440.7

20.410.250.9

20.7

10.3

20.471.420.420.4

10.210.2

1

10.3

30.6

10.210.2

10.3

20.430.640.9

10.230.6

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24, CC24, CC25-1, 64-6625-1, 64-6625-3, 44-4625-3, 44-4625-4, 75-7725-4, 75-7725-6, 71-7325-6, 71-7325, CC25, CC26-1, 58-6026-1, 58-6026-3, 68-7026-3, 68-7026-4, 39-4126-4, 39-4126, CC26, CC27-1, 92-9627-1, 92-9627-2, 103-10527-2, 103-10527-3, 21-2327-3, 21-2328-1, 75-7728-1, 75-7728-2, 129-13128-2, 129-13128, CC28, CC29-2, 124-12629-2, 124-12629-3, 27-2929-3, 27-2929-4, 24-2629-4, 24-2629-5, 89-9129-5, 89-9129, CC29, CC30-1, 76-7830-1, 76-6830-2, 25-2730-2, 25-2730-3, 62-6430-3, 62-6430-5, 52-5430-5,52-5430-6, 18-2030-6, 18-2031-1,71-7331-1,71-7331-2, 72-7431-2, 72-7431-3, 62-6431-3, 62-6431-4,48-5031-4,48-5032-2, 82-8532-2, 82-85

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142.9

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almost complete alteration of the glass into mont-morillonite, and the absence of an admixture of acidvolcanogenic material. This results in a partial enrich-ment of the large size fractions by terrigenous compo-nents.

Unit 2

The sediments of Unit 2 (middle Miocene-Pliocene)are distinct in composition and in the content of variousgenetic components. Biogenic components in these

sediments show a remarkable increase in content. In-dividual thin interbeds are characterized by a sharppredominance of diatom skeletons. However, only inthese interbeds are they considered as a major sedimentcomponent (Figures 3 and 4). There is also a large in-crease in the quantity of carbonate biogenic material,mainly foraminifera tests.

The silt fractions in Unit 2 have a higher content ofvolcanogenic material as compared to Unit 1. The mainportion of this material is represented by devitrifiedvolcanic glass. However, there is also a considerable

80



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amount of unaltered glass present. It is predominantlybasic, but also includes acid glasses. The amount of acidglass increases regularly upward in Unit 2. The max-imum amount of the acid glass (up to a third of the totalbulk of glass) is recorded in Pliocene sediments.

Distribution of authigenic components in the silt frac-tion of Unit 2 is very irregular. At its lower portion (atthe boundary with early Miocene), the unit ischaracterized by a high content of iron sulfides andzeolites. The quantity of these components decreasessharply towards the upper boundary of Unit 2.

A common mineral in the clay fraction (less than 1µm) is montmorillonite. The content tends to generallydecrease in the upper layers of the unit. This can be ex-plained by the fact that in the younger sediments, a partof the volcanogenic ash material has not yet decom-posed, although it is nearly devitrified. Also, the acidglasses are not strongly altered. There is also a con-siderable decrease of finely dispersed zeolites in thesediments of Unit 2.

Apart from the clay composition, Unit 2 differs fromUnit 3 by a gradual increase of hydromica and probable

81

TABLE 2BResults of Immersion Mineralogical Analysis of the 0.1-0.5 mm Fraction Samples (Light Minerals) From Hole 348 DSDP Leg 38


1-1, 70-721-1, 70-721-3, 100-1041-3, 100-1041-4, 100-1021-4, 100-1021-5, 90-921-5, 90-921, CC1, CC2-1, 98-1002-1, 98-1002-2, 50-522-2, 50-522-4, 99-1012-4, 99-1012, CC2, CC3-1, 99-1013-1, 99-1013-3, 99-1013-3, 99-1013-4,99-1013-4,99-1013-5, 89-913-5, 89-913, CC3, CC4-1, 119-1214-1, 119-1214-2,99-1044-2, 99-1045-1,99-1005-1, 99-1005-2, 139-1415-2, 139-1415, CC5, CC6-1, 139-1416-1, 139-1416-2,29-316-2,29-316-4, 84-866-4, 84-866-5, 73-756-5, 73-756, CC6, CC

N

o

6123.87534.38018.1

22054.576

29.2175

43.5134

36.57133.65827.47330.06630.27838.89442.26625.9

16745.2

13336.819

7.55726.53617.55120.3

93.9

124.3

L46.352.2

2 Vu δ

2610.25625.531

7.08521.52710.44812.04913.45224.62511.85723.34219.34220.84821.44818.755

14.84713.019

7.53013.83215.62610.6

31.3

124.341.841.7

•

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ε s10

3.920

9.115

3.411

2.719

7.313

3.2154.1

125.794.3

218.6

198.7

189.0

208.8

155.8

359.5

3710.2

20.8

73.493.620.910.420.9

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20.8

10.240.931.230.710.310.510.520.862.742.052.220.82

0.5195.283.241.821.052.041.7

114.031.431.3

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34.8104.5

227

51.3194.7

53

20.469

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124.7

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164.0

205.5

124.710.5

102.310.210.471.7

205.5

10.2

10.3

20.8

20.410.2

20.520.531.4

10.4

102.751.5

10742.38539.42512.37830.4

11548.8

11040.3

10547.89843.0

20.8

154.120.593.5

11512411.7

20.8

219.1

3914.219

8.6

10.5

41.141.1

8834.82712.42914.17329.17733.48631.07433.2

11650.5

10.220.552.4

10.4

40.96

15

123.071.9

0.2

10.3

10.3

4115.95123.3

368.9

4216.15313.28824.05325.1188.5

7832.07635.05326.45122.87529.57520.3

10629.1

4622.4

3814.6

10.3

7133.8

4417.3

20.9

256

219

443

404

260

402

366

211

211

244

218

201

224

255

370

362

253

216

205

252

233

275

221

229

HWJOO>

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to

7-1, 74-767-1, 74-767-3, 74-767-3, 74-767-4, 75-777-4, 75-777, CC7, CC8-2, 75-778-2, 75-778-3, 75-778-3, 75-779-1, 139-1409-1, 139-1409-2, 75-779-2, 75-779-5, 75-779-5, 75-779, CC9, CC11-1, 80-8211-1, 80-8211-2, 80-8211-2, 80-8211-4, 70-7211-4,70-7212-2, 60-6212-2, 60-6212-4, 20-2212-4, 20-2213-1, 80-8213-1, 80-8213-2, 20-2213-2, 20-2213, CC13, CC14-1, 20-2214-1, 20-2214-2, 20-2214-2, 20-2214-4, 20-2214-4, 20-2214-5, 20-2214-5, 20-2214-6, 20-2214-6, 20-2214, CC14, CC15-1,60-6215-1, 60-6215-2, 60-6215-2, 60-6215, CC15, CC16-1,60-6216-1, 60-6216-3, 60-6216-3, 60-6216-5, 60-6216-5, 60-6216-6, 60-62

7516.361.751.494.161.6

133.310.220.510.310.410.310.310.2

20.520.9

20.820.910.531031.010.431.262.083.310.493.883.610.42

224.841.430.841.820.541.010.210.2

20.9

20.910.4

20.910.410.4

51.720.810.4

10.510.41

132.851.451.431.420.520.561.251.420.5

20.630.910.2

10.2

10.4

81.761.712 13.4 0.231.4

133.6153.8193.9133.5

225.841.730.851.461.030.620.552.262.5125.020.920.951.851.752.0

51.711.731.141.731.483.33

20.410.230.8

41.010.220.530.8

30.810.310.210.2

31.4

10.4

10.4

1 20.4 0.8

20.8

1

40.920.5236.6

10.220.410.230.8

51.420.6

20.8

10.5

20.731.2

1 20.4 0.8

20.920.8

20.9

10.4

10.410.3

10.510.4

20.8

10.510.41

14531.315243.016045.75926.810829.517745.023849.416545.217947.64519.7

15343.015244.022841.019841.419546.09040.211247.39941.56128.790

4137929.012443.611546.06325.010536.0

2 1070.8 44.6

8731.38033.75826.311145.764

4610.0287.9

8624.78036.017648.110627.09920.6

12233.68021.49642.3329.0

4412.7122.0

275.6174.03113.82611.04317.93315.6188.2

3211.64114.4145.5124.81138135.431.1

4418.55424.5208.29

40.941.130.8

10.210.220.4

123.210.410.320.610.2

10.2

10.4

31.341.8

10022.014039.54312.24821.85815.86416.311323.55414.76417.05029.0

15543.13739.2

30655.0

24952.220848.69442.09038.08134.011052.010347.215055.011238.910944.512750.015352.49740.216761.09339.08840.09940.8131

10.2

10.5

20.410.2

10.261.5

10.271.8

10.2

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398.551.472.0

31.3

41.6

51.7

3

135.8

2410.5

10.4

134.7

460

354

351

221

367

394

482

366

376

228

356

347

557

478

426

224

237

239

212

218

273

286

248

253

292

241

275

238

220

243

21500

TABLE 2B - Continued

jt ,3

Sample(Interval in cm) a

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4.262.121.06

2.610.431.22

0.910.33

20.3

30.9

20.510.331.172.7

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10.2

10.310.2

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60.92.810.12713.0104.473.020.82712.392.94

40.741.282.241.210.282.272.4135.020.5

10.2

10.2

lalc

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ent!

U PL,

20.3

2810.8

20.520.510.252.0

10.261.9

irbo

nate

ù

8536.5

10.314

81.5

29185.3328.192.5

10.210.2

41.7

ilago

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erin

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£0 £ £1.4

4516.25928.68330.47231.02710.813259.95813.819

81.5

27678.0133.85313.3

2810.8

257.05414.85514.67931.75.3

26.1753276516.74213.680

icro

conc

ay F

ragi

S G

4716.8

187.7

12851.4

185.814

2424609228.4

9827.49536.319776.0

ilcu

late

dra

ins

278

206

228

233

249

220

308

90

529

325

355

341

397

356

262

259

356

363

377

248

203

230

390

309

232

15-6,60-6216, CC16, CC19-1, 110-11219-1, 110-11219-3, 75-7719-3, 75-7719-4, 10-1219-4, 10-1219-6, 140-14219-6, 140-14219, CC19, CC20-1, 80-8220-1, 80-8220-2, 80-8220-2, 80-8220-4, 64-6620-4, 64-6620-6, 135-13720-6, 135-13720, CC20, CC21-1, 60-6221-1, 60-6221-3, 100-10421-3, 100-10421-5, 60-6221-5, 60-6221, CC21, CC22, CC22, CC23-1, 110-11223-1, 110-11223-3, 77-7923-3, 77-7923-5, 80-8223-5, 80-8223, CC23, CC24-1, 27-2924-1, 27-2924-2, 49-5124-2, 49-5124-4, 2-424-4, 2-424-6, 60-6224-6, 60-6224, CC

0.9279.7

3517.02310.2104.331.2

209.1154.913

15028.58325.520.692.6

21855.215644.04015.3186.9

21560.823364.321657.59839.99747.88637.2

24362.519663.5103

0.531.131.520.9

10.441.861.92

295.592.8

30.9

4110.3339.3155.831.2

3710.44713.06517.23212.83617.73615.75313.73812.534

10.510.4

10.4

10325

234.3103.1

20.6102.5154.251.931.2

102.8102.8164.220.842.083.5184.6154.83

1.4134.7188.8

229.662.610.4188.2

237.56

1426103.130.851.582.041.110.420.830.8

20.5

20.910.210.31

10.3

10.3

10.210.3

10.220.530.8

10.2

10.3

10.452.320.61

20.330.9

30.941.071.9

5314.992.592.4

20.5

10.5

10.2

30.91

30.772.2

0.59935.721.0

2611.3198.193.652.3

11437.33

254.7175.282.2102.982.010.310.4

20.5

10.520.9

72.5

5828.15323.2146.0

5016.26

173.2

5416.6

184.5236.5

10.451.451.492.4

2610.4104.9177.420.510.35

2329.47

32

10.2

3811.75816.2

3914.8135.0

52.0

0.5311

10.4

29.7

20.8

10.4

21.020.9

00H

m

o>wH>I-1

24, CC25-1, 64-6625-1, 64-6625-3, 44-4625-3, 44-4625-4, 75-7725-4, 75-7725-6, 71-7325-6, 71-7325, CC25, CC26-1, 58-6026-1, 58-6026-3, 68-7026-3, 68-7026-4,39-4126-4, 39-4126, CC26, CC27-1, 92-9627-1, 92-9627-2, 103-10527-2, 103-10527-3, 21-2327-3, 21-2328-1, 75-7728-1, 75-7728-2, 129-13128-2, 129-13128, CC28, CC29-2, 124-12629-2, 124-12629-3, 27-2929-3, 27-2929-4, 24-2629-4, 24-2629-5, 89-9129-5, 89-9129, CC29, C C30-1, 76-7830-1, 76-7830-2, 25-2730-2, 25-2730-3, 62-6430-3, 62-6430-5, 52-5430-5, 52-5430-6, 18-2030-6, 18-2031-1,71-7331-1,71-7331-2, 72-7431-2,72-7431-3,62-6431-3, 62-6431-4,48-5031-4,48-5032-2, 82-8535-2, 82-85

44.332049.9

22256.0

26466.517848.48142.29037.08537.39842.79742.410941.712849.111442.67739.38540.26027.35341.210444.211248.59644.29539.89211.59943.611448.79444.29344.59345.610545.410850.011155.59839.0

14.67912.36315.84310.84712.82915.25321.85021.94218.24620.15119.35320.44817.83417.34019.0135.91821.86125.83012.84621.25422.54018.05122.43012.83215.03215.33416.74519.53315.33819.03011.9

1.3233.6153.8

205.0

297.9126.3145.8146.1135.6

229.6197.2186.9186.7189.2146.7

7.4166.8125.2156.9166.7167.2187.9156.4115.2115.383.9156.562.863.0135.2

0.410.110.2

10.2

10.4

10.441.583.042.021.0

1

10.410.5

20.920.810.420.910.5

41.7

31.2

0.430.510.220.520.5

10.4

10.5

0.4

10.5

10.510.410.4

20.810.5

10.4

20.320.530.710.210.5

31.1

10.5

]0.5

10.531.3

10.520.8

10.110.210.2

10.5

10.5

10.420.910.510.4

30.541.041.041.1

52.452.2

72.720.8

21.010.5

20.9

31.341.7

10.520.8

10.520.8

10.1

20.5

21.0

6

31.2

3112.3

2.2355.4

235.782.0174.684.2125.0146.1146.1146.2135.083.151.942.062.983.683.362.573.062.772.9115.020.841.773.373.362.9

4 141.7 6.0

41.894.572.8

1.7 0.4 34.71 3 171 6430.1 0.5 26.6

3 2 62 3990.7 0.5 15.44 47 3981.0 11.8

1 7 82 3690.2 1.9 222

5 1 53 1922.6 0.5 27.5

5 63 2422.4 25.6

59 22826.063 23027.449 22821.759 26222.6

2 44 2600.8 17.0

75 26828.057 19629.2

2 58 2101.0 27.7

4 59 2201.8 26.7

63 24425.9

3 46 2361.3 19.4

1 69 2320.4 29.7

48 21722.1

7 60 2392.9 25.21 57 2210.5 259

52 22822.8

2 63 2340.9 27.0

5 62 2132.3 29.1

65 20931.351 20429.934 232

1471 2 57 216

0.5 0.9 26.43 30 2001.5 15-0

64 25225.2

oo


TABLE 3Chemical Composition of Sediments from Site 348 DSDP Leg 38

from X-Ray Fluorescent Analysis


1-3, 100-1041-5, 90-921, CC2-1, 98-1002-2, 50-522, CC3-1, 99-1013-4, 99-1013, CC4-1, 119-1215-1, 99-1006-5, 73-756, CC8-2, 77-798-3, 75-779-1, 138-14011-1, 80-8112-2, 60-6212-4, 20-2214-2, 20-2214-6, 20-2214, CC15-1, 60-6215-2, 60-6215, CC16-1, 60-6216-6, 60-6216, CC19-1, 110-11219-3, 75-7719-4, 10-1219-6, 140-14219, CC20-1, 80-8220-2, 80-8220-6, 135-13720, CC21-1, 60-6221-3, 100-10421-5, 60-6222, CC23-1, 110-11223-3, 77-7923-5, 80-8223, CC24-1, 27-2924-2,49-5124-4, 2-424-6, 60-6224, CC25-1, 64-6625-3, 44-4625-4, 75-7725-6,71-7825, CC26-1, 58-6026-3, 68-7026-4, 39-4126, CC27-1, 92-9627-2, 103-10527-3, 21-2328-1, 75-7728-2, 129-13128, CC

SiO2

58.854.250.752.245.454.554.756.256.557.154.437.447.653.553.748.452.254.552.652.651.753.254.454.855.556.956.655.253.548.751.046.047.046.047.640.446.750.951.854.451.852.755.254.658.356.054.956.054.255.055.655.254.656.556.155.656.856.858.557.556.458.256.554.659.8

TiO2

0.910.781.060.820.990.911.211.081.201.051.140.521.601.061.251.251.701.801.781.481.231.331.151.081.361.061.361.201.561.811.391.641.481.771.691.622.261.420.981.071.361.531.021.561.371.681.331.431.491.551.421.411.431.501.451.361.441.521.391.201.351.321.491.271.34

A12°3

15.114.713.613.512.014.715.113.914.814.815.18.45

10.013.712.512.011.59.55

10.710.710.310.411.711.111.611.810.311.411.010.610.79.67

10.49.40

10.27.809.17

10.612.411.712.913.313.714.014.014.214.113.414.9514.814.814.014.414.513.913.914.414.213.514.415.114.914.514.314.8

Fe

6.375.186.195.645.766.967.146.177.636.736.513.047.456.677.538.767.907.958.798.198.40

10.86.415.138.786.037.567.107.709.108.068.5412.410.19.808.40

11.58.957.536.238.747.406.466.726.604.736.836.556.237.486.426.877.275.267.596.886.677.207.206.086.526.176.717.906.99

MnO

0.220.140.150.190.130.140.100.530.120.130.110.280.160.080.080.100.110.110.110.120.120.150.070.050.100.010.130.030.060.070.080.250.090.200.080.380.170.060.050.030.070.060.040.040.040.050.050.040.040.050.050.040.040.060.020.050.050.040.020.040.040.040.050.040.02

Percentage

MgO

2.693.523.953.152.762.752.872.902.972.561.902.283.002.972.223.402.483.022.382.624.183.101.973.892.231.312.383.415.355.635.047.725.136.276.755.764.924.555.205.273.643.644.602.382.723.202.172.063.712.662.822.852.682.782.872.662.131.802.262.072.542.341.552.131.34

CaO

0.645.595.305.64

10.03.111.021.601.141.021.1020.310.61.912.022.013.684.053.873.864.366.302.782.545.073.04.381.902.062.482.134.872.984.052.33

11.34.682.001.641.441.711.111.521.541.381.361.221.251.241.471.191.561.251.431.551.421.561.531.831.451.491.421.401.621.43

K2O

2.553.202.693.122.783.003.243.263.073.053.090.671.432.682.622.271.521.331.481.621.440.931.891.871.592.201.181.981.911.221.670.880.920.721.150.830.841.412.212.622.252.382.242.492.352.212.262.182.262.622.482.202.502.342.472.112.142.472.422.392.452.152.472.252.42

Na2O

2.321.792.962.352.602.062.232.122.122.905.503.053.343.173.433.093.633.50

3.503.322.993.543.643.223.283.052.502.542.892.802.462.462.792.622.332.372.47

2.031.712.131.882.641.362.011.841.831.471.351.461.381.381.751.332.231.751.321.401.391.041.481.521.731.29

L.O.I.

7.489.05

10.7510.0514.109.008.838.558.208.097.75

21.6811.9411.1611.3413.8412.0110.8512.2511.7011.176.33

13.1713.456.29

11.3410.0212.2811.4113.7013.4014.1511.2514.3613.9117.2012.7613.5813.1412.4012.2912.2011.2611.039.13

12.6312.3412.3811.839.53

10.8711.5911.4611.319.29

10.849.66

10.188.04

10.5310.5010.2010.4410.767.81

86


TABLE 3 - Continued


29-229-4, 24-2629, CC30-1,76-7830-2, 25-2730-3, 62-6430-5, 52-5430-6, 18-2031-1,71-7331-2, 72-7431-3, 61-6431-4, 48-5032-2, 82-85

SiO2

57.960.561.652.664.857.257.262.358.057.146.655.759.5

TiO2

1.331.541.281.561.461.321.511.381.381.552.241.621.61

A12°3

14.8513.813.715.713.313.115.013.814.915.819.117.015.2

Fe

5.736.646.187.483.277.336.473.946.306.127.905.546.06

Percentage

MnO

0.040.040.040.020.050.040.050.050.040.050.070.030.04

MgO

2.770.702.002.312.492.392.002.862.672.712.763.542.94

CaO

1.391.471.271.551.441.421.821.461.301.421.651.421.32

K2O

2.372.232.132.171.962.122.222.102.452.721.922.682.58

Na2O

1.571.231.561.511.57

1.521.381.412.540.771.21

L.O.I.

10.419.297.16

12.188.22

10.129.719.028.978.88

12.068.867.00

mixed-layered clays, mainly of the hydromica-mont-morillonitic composition. These components are prob-ably terrigenous, an indication of a gradual increase inthe supply of erosional material in the Pliocene.

Unit 1

A comparison of the Unit 1 (Pleistocene) depositswith the sediments of Unit 2 indicates many differences.There is a considerable decrease of biogenic material ex-pressed chiefly by a sharp decrease in the content ofamorphous silica and calcium carbonate. The content ofthese components is more characteristic for that in-dicated in Unit 3.

Analysis of the composition of the coarse silt fractionof Unit 1 shows a mixing of terrigenous andvolcanogenic components with some predominance ofthe volcanogenic. The terrigenous composition of thisfraction (quartz, potassium feldspars, hornblende,weathered minerals) is very similar to the composition

of the silts of lower units (Table 1). Volcanogenicmaterial (devitrified glass and palagonitized glass) ismore significant in the silts of Unit 1 than in Unit 3. Thisis probably caused by a smaller degree of alteration bydiagenesis.

An analysis of the silt composition also indicates asharp decrease in iron sulfide as compared with lowerunits. There is also an extremely low content ofglauconite and iron hydroxides. Only individual grainsof zeolite are present, which indicates a low degree ofdiagenesis of the Pleistocene sediments; this also cor-relates with the lower content of organic material (lessthan 0.1%) in these sediments.

A similar composition is characteristic for the (lessthan 1 µm) fraction of Unit 1. The mineral assemblage isvery rich, and many of the minerals are well crystallized.The predominance of hydromica and the presence ofconsiderable amounts of kaolinite and mixed-layeredvarieties of the hydromica-chlorite and montmorillonitepoints to a significant contribution by terrigenous com-ponents. However, montmorillonite, which is con-sidered to be authigenic and formed from volcanogenicmaterial, is also abundant. This is the second majorcomponent after hydromica in the clay fraction.

Figure 1. Less than 5 µm fraction of the sediments from adepth of 525-526.5 meters. Core 32. X9500 mag-nification.

Figure 2. Less than 5 µm fraction of sediments from adepth of 278-279.5 meters. Core 20. X2490 magnifi-cation.

87


TABLE 4Grain-Size Distribution of the Sediments from Site 348 Leg 38


1-1, 70-721-3, 100-1041-4, 100-1021-5, 90-921,CC2-1, 98-1002-2, 50-5224, 99-1012, CC3-1, 99-1013-3, 99-1013-4, 99-1013-5, 89-913, CC4-1,119-1214-2, 99-1015-1, 99-1015-2, 130-1445, CC6-1, 139-1416-2, 29-316-4, 84-866-5,73-756, CC7-1, 74-767-3, 74-7614, 75-777, CC8-2, 75-778-3; 75-779-1, 138-1409-2, 75-779-5, 75-779, CC11-1,80-8211-2,80-8111-4,70-7212-1, 85-8612-2,60-6212-4, 20-2213-1, 80-8213-2,20-2213, CC14-1, 20-2214-2, 20-2214^, 20-2214-5, 20-2214-6, 20-2214, CC15-1,60-6215-2, 60-6215, CC16-1, 60-6216-3, 60-6216-5, 60-6216-6, 60-6216, CC19-1,110-11219-3, 75-7719-4,10-1219-6, 140-14219, CC20-1, 80-8220-2, 80-8220^, 64-620-6, 135-13720, CC21-1, 60-6221-3,100-10421-5, 60-6221, CC22, CC23-1, 110-11223-3, 77-7923-5, 80-8223, CC24-1, 27-2924-2,49-5124-4, 20424-6, 60-6224, CC25-1, 64-6625-3, 44-4625-4, 75-7725-6,71-7325, CC

Weightof Samples

4.5713.254.817.58

18.555.106.336.15

11.608.039.938.43

11.2511.0011.43

8.2612.2613.586.936.61

12.1213.5710.6719.0213.11

8.208.95

18.469.378.817.369.53

12.1811.246.06

11.439.156.389.768.005.718.358.787.367.089.178.538.19

10.466.756.937.877.197.897.817.42

10.388.405.737.808.20

11.876.976.85

6.9511.056.379.097.038.758.347.036.375.29

13.5710.294.34

12.5911.3313.5111.2613.52

7.8511.1114.88

Wetness(%)

60.262.455.435.257.239.151.142.740.242.649.839.455.447.651.860.044.069.456.867.666.060.150.655.266.862.367.052.757.646.468.365.662.942.564.362.756.260.560.365.021.566.956.462.137.455.861.358.047.461.161.854.555.062.259.653.648.150.455.953.344.343.250.047.158.346.442.455.654..052.954.656.952.441.337.034.137.934.834.230.531.433.932.633.232.927.3

7-5

40.49

4.60

56.03

5-3

9.0218.01

7.199.14

8.80

3-2

2.9314.23

5.047.42

6.29

2-1 1-0.5

1.970.450.62

0.49

1.03

5.34

6.02

0.25

2.93 1.836.31 3.79

2.15

5.18 3.459.23 7.15

6.97 4.46

0.5-0.25

2.190.680.62

0.320.590.79

0.86

0.47

0.36

0.58

0.05

0.57

8.03

0.89

1.713.791.72

4.759.86

4.34

1.770.24

0.15

0.34

Fractions (%)

0.25-0.1

24.074.151.564.622.435.696.162.284.661.741.213.440.443.181.221.090.330.743.610.610.410.370.371.260.840.490.221.300.430.230.410.520.821.330.991.753.280.782.972.885.600.60

11.963.672.820.980.592.93

18.550.740.58

13.342.641.403.074.451.161.190.872.441.954.123.443.650.215.04

10.770.780.440.715.490.241.562.201.133.321.851.613.575.472.742.842.511.150.813.02

0.1-0.05

3.286.043.129.762.102.944.580.654.741.871.41

13.0010.445.911.221.212.371.255.340.760.740.370.484.100.380.980.441.630.530.340.680.731.311.961.652.014.921.882.561.881.751.80

15.481.632.680.760.591.71

10.610.590.58

10.170.970.641.411.211.450.240.350.260.120.170.290.150.210.293.620.160.100.141.140.240.281.571.515.530.872.301.912.211.112.581.111.780.902.35

0.05-0.01

0.883.772.083.560.811.763.630.652.070.500.720.590.443.091.311.210.820.592.020.450.410.290.482.370.310.490.220.540.430.460.410.310.410.441.491.312.622.353.480.881.750.365.810.410.560.220.230.493.350.590.582.030.700.380.641.350.480.240.170.260.120.420.150.580.110.290.450.320.100.140.570.240.280.160.570.370.190.410.400.620.370.180.150.510.450.34

0.01-0.005

0.8816.0819.866.47

35.6912.557.59

24.5515.7823.0422.5513.5724.3619.6518.5629.0621.6952.70

2.2328.5926.4922.2519.1037.2830.7325.0030.6117.9317.5923.0627.7220.7723.4128.3015.6726.4222.7319.4417.8322.5019.4524.54

9.3515.2221.0635.0023.0920.51

6.2121.9318.329.03

21.5618.8023.8413.4836.4224.7621.4719.2315.49

1.6816.0726.4222.01

6.472.45

32.6523.4626.470.66

20.8731.7221.3517.2017.6727.2217.8012.9425.8635.6813.4119.9013.2427.1816.47

0.005-0.001

20.7921.1327.4424.9331.3714.9023.8524.8819.5724.6624.9715.0725.9622.3633.0727.6030.8332.1824.8228.7431.1938.0335.4329.8133.8727.6827.6238.8936.2934.2635.1938.5131.0325.2724.9225.0333,0123.6736.5835.8726.4431.7419.3630.8429.3832.9331.8927.72

9.0837.7827.2716.7726.2936.2731.5035.7129.7631.5523.0429.1027.68

2.3624.3927.5938.4113.678.60

32.9731.2426.88

1.1434.0533.0037.3639.7027.8625.7526.0427.0122.5030.6326.8225.1524.0824.7625.40

<O.OOl

37.2047.7044.7050.6626.7961.5753.4046.9951.2948.1949.1453.8648.3645.4544.6239.8343.9632.5449.0640.8540.7638.6944.1425.1333.8744.7640.8930.7144.9341.6535.5939.1643.0242.7055.2843.4833.4451.8836.5835.9945.0140.9637.4748.2943.5030.1143.6146.6438.1538.3752.6747.5247.8441.5139.4443.8030.7342.0254.1048.7136.224.63

51.7941.6139.0544.0331.3133.1244.6645.66

4.1144.3633.1637.3639.8943.4844.1251.8454.1743.3429.3254.1751.L859.2445.9052.08

88


TABLE 4 - Continued


26-1, 58-6026-3, 68-7026-4, 39-4126, CC27-1, 92-9627-2, 103-10527-3, 21-2328-1, 75-7728-2, 129-13128, CC29-2, 124-12629-3, 25-2729-4, 24-2629-5, 89-9129, CC30-1, 76-6830-2, 25-2730-3, 62-6430-5, 52-5430-6, 18-2031-1,71-7331-2, 72-7431-3, 62-6431-4, 48-5032-2, 82-85

Weightof samples

5.846.03

11.1114.9314.2912.17

9.3212.1110.4116.2811.2910.698.97

11.0815.69

9.6810.15

6.297.44

12.059.81

10.2214.5012.6810.92

Wetness(%)

18.028.228.528.934.229.733.527.631.218.831.628.230.463.421.931.223.524.513.435.121.524.424.219.020.3

7-5

18.93

5-3

3.82

3-2

0.64

2-1

0.64

2.20

1-0.5

5.90

0.322.48

0.88

0.55

0.5-0.25

1.00

3.81

3.124.65

1.86

3.11

Fractions (%)

0.25-0.1

2.572.993.155.695.870.412.042.066.15

11.363.724.776.022.268.86

11.477.001.10

5.386.147.545.281.106.628.79

0.1-0.05

3.251.991.714.024.483.042.041.572.696.392.754.122.451.905.422.385.524.786.052.493.363.910.554.26

10.53

0.05-0.01

0.860.830.360.330.280.160.540.741.630.840.800.471.110.450.320.410.890.791.340.830.921.960.340.790.64

0.01-0.005

12.1518.7421.3426.5317.2919.9719.3127.3310.4710.7821.2518.0518.4022.8210.1923.3513.9822.7419.6223.22

7.6517.9131.2512.4611.54

0.005-0.001

25.8625.0424.4825.3223.7931.0620.2823.3825.4624.9223.4721.2323.9723.9215.8117.5618.6224.0122.8523.5727.0123.0926.0729.8119.05

<O.OOl

55.3150.4148.9637.1148.2945.3655.7944.9253.6036.0048.0151.3648.0548.6531.9337.7053.9946.5844.7643.7553.5245.1140.6946.0643.59

TABLE 5, Tiθ2, and MnO Content in Sediments

from Site 348, DSDP, Leg 38

Core

5777

1113131416202129

Section

234CC41CC554CC3

Interval(cm)

139-14174-7675-77

70-7280-82

20-2760-6264-66

25-27

Fe2θ3 (%)

7.879.609.718.59

11.049.31

11.367.267.058.88

12.267.32

Tiθ2 (%)

0.961.561.381.181.861.361.520.860.961.101.341.16

MnO (%)

0.060.090.090.060.100.090.110.070.060.040.050.06

CONCLUSIONS

The origin of the late Cenozoic sediments in theIcelandic Basin represents a series of sedimentationstages characteristic for the North Atlantic. The contactbetween the sediments and underlying basalts issedimentary. The approximately 20-meter-thick layer ofOligocene(?) sediments, which overlies the basalts, hasbeen formed, to a considerable degree, as a result of sub-marine weathering of these variolitic basalts, and/orerosion from adjacent uplifted sections of the oceanicfloor. This is further supported by the presence ofbasaltic gravels in the lowermost layers. The high degreeof zeolitization indicates the importance of the altera-tion products from the basalts. Zeolites of the analcitegroup may also be present.

The accumulation of the late Oligocene-earlyMiocene deposits occurred concurrently with effusivesurface and submarine volcanism. The supply of thevolcanogenic ash material increases upward in the sec-tion, attaining a maximum at the.end of early Miocene,particularly at the boundary with middle Miocene.

Probably, the ash material consisted almost entirely ofbasic glass. Subsequently, this glass was altered to mont-morillonite and zeolite.

The supply of the terrigenous material was very low,probably, lower than in the Pleistocene and Holocene.The factor affecting the supply of terrigenous materialwas probably glaciation, but may have been lessoperative at this time. The similarity of the Oligocene-early Miocene deposits with contemporary sediments isdisplayed by the low content of biogenic componentswhich may be indicative of a severe climate similar tothe present.

The latter comment seems contradictory because thesediments of the lower stratigraphic horizon are largelyenriched in organic matter. However, the level of this"enrichment" is significantly low, and it can be detectedonly by comparison with the "poorer" organic carboncontent in the sediments of the overlying units (1 and 2).The relatively higher content of organic matter in thesediments of Unit 3, as well as the evidence of iron sul-fidization, evidently points to a somewhat higher con-tent of hydrogen sulfide in benthonic depths of the basinat that time. If this is the case, there are reasons tosuggest the existence of a relatively low content of freeoxygen in bottom waters. These would be associatedwith a slow circulation of water masses in the basin andexistence of a chalistatic zone in this water. Another fac-tor leading to stagnant water masses of the basin in theOligocene-early Miocene times may be the steeptopography of the peripheres (i.e., the Jan-Mayen Ridgesystem).

These conditions were favorable for the preservationof the organic matter which appeared to change its com-position mainly by diagenesis. At the same time, itshould be added that these conditions stimulated thedissolution of carbonate skeletons, and to some degree,the silica varieties, both of which are unstable in analkaline environment.

Sedimentation in the middle and upper Miocene andin Pliocene (Unit 2) shows an increase in the supply of

89


TABLE 6P2O5 Content in Sedimentsfrom Site 348 DSDP Leg 38

TABLE 6 - Continued

Core

1111222333333455666789

111213141414141515151616161919191919202020202021212122232323242525252526262627272828292930

Section

335CC12CC1124CCCC1125CCCCCC3112CC26CCCC12CC1661346CC1146CC13CCCC1CCCCCC466CC13CC121CC3CC1

Interval(cm)

100-104100-10490-92

98-10050-52

99-10199-10175-7799-101

119-12199-100

134-14173-75

75-77138-14080-8660-62

20-2220-22

60-6260-62

60-6260-6260-62

110-11275-7710-12

140-142

80-8280-8264-66

135-137

60-62108-109

110-112

75-7771-7371-73

58-6068-70

92-96103-10575-77

25-27

76-78

P2O5 (%)

0.240.230.120.170.180.220.180.160.180.080.160.110.130.160.120.100.200.190.180.130.110.100.150.170.130.140.130.120.110.140.180.080.140.130.100.110.090.080.380.050.140.110.090.240.160.090.080.030.270.220.130.130.090.100.110.100.100.160.130.140.140.200.130.180.110.090.16

Core

3030303031

Section

23561

Interval(cm)

25-2762-6452-5418-2071-73

P2O5 (%)

0.120.100.140.120.10

Figure 3. Less than 1 µm fraction of sediments from adepth of 400-401.5 meters. Core 26. ×4900 magnifi-cation.

Figure 4. Less than 1 µm fraction of sediments from adepth of 160.5-161 meters. Core 11, CC. X4900 magni-fication.

90


TABLE 7Siθ2 Content from Soda Extraction in

Sediments at Site 348 DSDP Leg 38

TABLE 8CO2 and C Organic Content (by Knopp's

Method) in Sediments at Hole 348 DSDP Leg 38

Core

1123356777889

111313141414141414151516161616161919192020202020212121212223232324252525262626272728282929303030303031

Section

3CC11CC2CC34CC23CC41CC12456CC121356CC46CC1246CC135CCCC13CCCC46CC13CC121CC3CC123561

Interval(cm)

100-101

98-10099-101

139-141

74-7675-77

75-7775-77

70-7280-82

20-2220-2220-2220-2220-22

60-6260-6260-6260-6260-6260-62

10-12140-142

80-8280-8264-66

135-137

60-62100-104

60-62

110-11277-79

75-7771-73

58-6068-70

92-96103-105

75-77

25-27

96-9825-2962-6452-5418-2071-73

SiO 2 (%)

1.101.441.201.281.241.704.565.002.563.263.283.503.507.046.145.267.867.766.005.947.265.308.147.846.308.048.608.062.022.201.300.761.561.351.981.301.201.661.721.701.281.202.681.361.461.181.441.180.701.321.101.101.361.501.420.861.342.001.141.281.241.341.321.32

Core

113679

131314161619202122232425262829

Section

3CCCCCCCCCCCCCCCC1CCCCCCCCCCCCCCCCCCCCCC

Contents inInterval Dry

(cm) CO2

100-104 1.042.860.164.200.051.880.100.110.06

67-69 0.130.100.231.250.135.800.140.060.050.180.134.44

Sample

COrg

0.270.310.320.330.360.230.100.110.311.470.570.110.100.220.050.420.650.840.950.910.62

ash. A substantially high amount of this material is pres-ent in the lower portions of Unit 2, particularly at theboundary with the early Miocene. The highest contents

of montmorillonite in the clay and zeolite in the silt frac-tion are present in the lower portions of the middleMiocene. Thus, the early/middle Miocene in the Icelan-dic Basin was a time of accumulation of essentiallyvolcanogenic sediments.

Upward within Unit 2, the volcanogenic constituentsdecrease, giving way to an increase in terrigenous com-ponents. This is especially noticeable in the composi-tion of the clay fraction where hydromicas and mont-morillonites are sediment components. These changesare clearly seen in sediments of Unit 2, of late Plioceneage. This may indicate active glaciation with ice raftingbeing the main source of terrigenous material by latePliocene times.

A distinctive feature of the volcanogenic sediment ofUnit 2, when compared with the sediment of Unit 3, isthe high degree of preservation of silt-sized ash material.A considerable portion of the glass is not yet devitrified.They may be explained by the relative young age of thesediments and the low content of organic matter. This,together with a sharp decrease of iron sulfidization, mayindicate that in the middle, especially, upper Miocene areconstruction of the water mass characteristics was oc-curring in the Icelandic Basin. This reconstruction maybe a result of an increased influence of North Atlanticwaters in the Norwegian-Greenland Sea due to a sub-sidence of barriers (Iceland-Faeroe Ridge).

Possibly, during the accumulation of Unit 2 there wasa change in volcanic activity. This seems indicated by anincrease of acid products upwards in Unit 2, with a max-imum supply in the Pliocene.

Sedimentation in the Icelandic Basin during themiddle-upper Miocene and Pliocene was taking placeunder climatic conditions that differed from those dur-ing the deposition of Units 3 and 1. In all probability,the climate was "mild" which resulted in a minimaleffect by glaciation and/or ice-rafting. The temperatureregime of the water masses became favorable, which, in

91


TABLE 9Ca and Mg Content in Carbonates inSediments at Site 348 DSDP Leg 38

Core

112335677788

1113131414141414151516161616161919\92020202020212121212223232324252525262626272728282929303030303031

Section

3CC11CC2CC34CC2341CC1246CC121356CC46CC1246CC135CCCC13CCCC46CC13CC122CC3CC123561

Interval(cm)

100-104

98-10099-101

134-142

74-7675-77

75-7775-7770-7280-82

20-2220-2220-2220-22

60-6260-6260-6260-6260-6260-62

10-12140-142

80-8280-8264-66

135-137

60-62100-10460-62

110-11277-79

75-7771-73

58-6068-70

92-96103-10575-77

25-27

76-7825-2762-6452-5418-2071-73

CaO (%)

2.004.348.340.720.721.427.202.581.681.081.081.522.181.181.721.841.921.822.241.961.922.281.921.241.962.241.561.767.101.643.242.001.08

17.163.201.881.362.201.808.760.741.361.161.281.021.403.480.841.161.521.141.120.881.360.967.481.020.780.941.041.061.04

MgO (%)

1.471.411.481.371.042.321.371.191.121.020.891.121.210.751.191.151.020.981.211.060.951.051.090.780.880.961.283.156.036.025.414.921.284.185.333.401.281.444.872.860.450.950.891.270.830.961.370.940.970.980.790.810.960.750.780.810.800.610.760.970.890.70

combination with an active circulation, led to increasedproductivity. This is reflected by the increase of biogeniccomponents in the sediments of Unit 2. Thepredominance of diatoms indicates the increase of

temperature was not sufficient to exclude this area fromthe subtropical climatic zone.

The Pleistocene stage (Unit 1) of sedimentation in theIcelandic Basin is characterized by a sharp increase inthe supply of terrigenous material. This material becamethe predominant sediment component in the Unit 1sediments. Thus, the sediments can be considered to bevolcanogenic-terrigenous.

The increase in the terrigenous components isassociated with increased glaciation resulting fromPleistocene on Greenland and the Scandinavian Penin-sula. The transport of ice-rafted terrigenous materialhad already been recorded in the upper Pliocene(Laughton, Berggren, et al., 1972). This cooling wasresponsible for a decrease in water mass temperatures inthe North Atlantic, for a change of climatic conditionsto "Arctic" types for the Norwegian-Greenland Sea,and for a certain reduction of primary productivity. ThePleistocene was notable only for rare local increases inproductivity, expressed by a sharp increase of biogeniccalcium carbonate and foraminiferal fragments inseparate interlayers. Most of these maxima are mostlikely confined to the Holocene.

Since the change of the composition of the Pleistocenesediments was brought about by the increase in thesupply of terrigenous material, it is difficult to establishwhether there was a change in the rates of supply ofvolcanogenic material to the area. A decrease in thepercentage of volcanogenic components in the Pleisto-cene sediments is caused primarily from dilution by ter-rigenous material. However, some indirect data indicatethat during the Pleistocene, there was a decrease in therate of supply of volcanogenic (mainly ash) material.This is testified by a sharp drop of the percentage of(fresh) volcanic glass in the silty fractions of these sedi-ments.

Devitrificated glass (its quantity remains always high)is not a sufficiently exact indicator, inasmuch as part ofthis glass, in the form of terrigenous material, is suppliedfrom the continental extrusive sources.

SUMMARY1. Dominant volcanogenic sources were active during

almost the entire period of late Oligocene, Miocene, andPliocene. The main component is explosive material of abasic composition. The maximum influx corresponds tothe boundary between early and middle Miocene. At thebase of this primarily volcanogenic sequence, a basalsediment sequence exists whose composition indicatesderivation by weathering of underlying basalts.

2. The major portion of the volcanogenic materialhas been subjected to reworking and alteration to mont-morillonite clay. These changes are most vividlymanifested in older late Oligocene and early Miocenesediments.

3. Pleistocene sediments represent mixed volcano-genic-terrigenous sources. This can be explained byclimatic change (cooling) and by a decrease of volcanicactivity.

4. Biogenic component (silica, calcium carbonate) inthe late Cenozoic sediments is subordinate. The max-imum accumulation was during the middle and lateMiocene and in early Pliocene.

92


ACKNOWLEDGMENTS REFERENCES

All analyses on the sediments from Site 348 were performedat the Analytical Laboratory of the P.P. Shirshov Institute of Brindley, G. V., 1965. Quantitative analysis of mixtures ofOceanology, Academy of Sciences, USSR. The analyses were clay minerals: Bull. X-Ray Methods for Study of Clayperformed by A.G. Samosudova, N.P. Tolmacheva, M.B. Minerals: Moscow (Mir Publishers).Chermashenzeva, N.W. Turanskaya, T.G. Kuzmina, L.I.Streljanova, S.N. Koptilkina, W.P. Kasakova, A.N. Laughton, A. S., Berggren, W. A., etal., 1972. Initial ReportsRudakova, A.Ja. Shevchenko, E.A. Marketov, W.A. Karlov, of the Deep Sea Drilling Project, Volume 12: Washingtonand O.S. Dimitrenko. (U.S. Government Printing Office), p. 1-1243.

93

8. origin of the late cenozoic sediments of the ...sediments of all three units in hole 348 are...

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