Continental and marine influences expressed by deep-sea sedimentation off Japan (Kaiko project)

Palaeogeography, Palaeoclimatology, Palaeoecology, 71 (1989): 49-69

49

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

CONTINENTAL AND MARINE INFLUENCES EXPRESSED BY DEEP-SEA SEDIMENTATION OFF JAPAN (KAIKO PROJECT) HERVl~ C H A M L E Y and P I E R R E D E B R A B A N T Dynamique sddimentaire et structurale, UA 719 CNRS, Universitd de Lille I, 59655 Villeneuve d'Ascq Cedex (France)

(Received February 1, 1987; revised and accepted January 4, 1988)

Abstract Chamley, H. and Debrabant, P., 1989. Continental and marine influences expressed by deep-sea sedimentation off Japan (Kaiko Project). Palaeogeogr., Palaeoclimatol., Palaeoecol., 71: 49-69. A total of about 100 sediments and sedimentary rocks, composed of various clays to muddy siltstones of late Cenozoic age, and limestones and sandstones of early Cretaceous age, were sampled by the submarine Nautile during the Kaiko project at 3000 to 6000 m water depths in the trench areas South and East of Japan. A total of 70 samples were selected and studied mainly by optical and electronic microscopy, X-ray diffraction, atomic absorption spectrometry and microprobe analysis. The dominant terrigenous influences allow us to identify two main mineralogical provinces, to recognize the sedimentary expression of an early Pleistocene tectonic event southeast of Japan, and to propose an indirect stratigraphic use of clay assemblages in poorly fossiliferous deep-sea sediments. The Cretaceous sedimentary environments in Kashima Seamount area were submitted to various terrigenous and volcanogenic influences, with possible early to late diagenetic modifications. Only very minor post-sedimentary changes (oxidations, metallic coating, barite and zeolite formation, opal dissolution) affect most of the late Cenozoic deposits cropping out on the sea-floor, included those characterized by the development of deep-sea benthic communities (e.g. clams). Important early diagenetic changes occur only in volcanic-rich sediments of South Zenisu Ridge and South Kuril Trench. In those peculiar deposits very abundant smectites develop with various shapes and chemical compositions, pointing to the local peculiarities of volcanic glass morphology, chemistry and alteration, of permeability and of fluid migration processes.

Introduction One h u n d r e d sediments a n d s e d i m e n t a r y r o c k s h a v e been sampled by the submersible N a u t i l e d u r i n g the t h r e e K a i k o Legs accomplished in s u m m e r 1985, in t h e S o u t h a n d E a s t J a p a n b o r d e r i n g t r e n c h e s (Fig.l). These sedim e n t a r y m a t e r i a l s o r i g i n a t e from the b o t t o m surface, at w a t e r depths r a n g i n g b e t w e e n a b o u t 3100 a n d 5950m. T h e y comprise 24 samples of clay, mud, silty to s a n d y mud, 4 c l a y - p o o r sands o r gravels, 47 m o r e or less c o n s o l i d a t e d c l a y s t o n e s , m u d s t o n e s a n d siltstones with often oxide coatings, 6 s a n d s t o n e s or siliceous breccias, 13 b i o g e n i c l i m e s t o n e s 0031-0182/89]$03.50

issued from the D a i i c h i - K a s h i m a S e a m o u n t a r e a (Fig.l), and 6 pieces of pumice. The c o n s o l i d a t e d sediments a n d s e d i m e n t a r y r o c k s h a v e been sampled by the nippers of the N a u t i l e a r t i c u l a t e d arms, while soft sediments r e s u l t e i t h e r from n i p p e r sampling, tube coring, box c o r i n g or r e m o v a l of deposits a t t a c h e d on the submersible b o d y (Cadet et al., 1987; Le P i c h o n et al., 1987; P a u t o t et al., 1987). The s e d i m e n t a r y studies c a r r i e d o u t on K a i k o m a t e r i a l s c o n c e r n 20 of the 26 dives p e r f o r m e d (Fig.l), the 6 o t h e r dives h a v i n g provided no or only little r e p r e s e n t a t i v e samples (2-2, 2-4, 3-2, 3-3, 3-7, 3-8). Sixty-six samples h a v e been s u b m i t t e d to extended

© 1989 Elsevier Science Publishers B.V.

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Fig.1. Map of Kail¢o diving areas, and numbers of dives devoted to sedimentary studies. The first numeral represents the leg, the second one the serial number of dive in a given leg. The DSDP sites taken as references are also located.

sedimentological investigations. They include 16 soft sediments (clay, mud, silt), 40 claystones, mudstones and siltstones, 3 sandstones and 7 limestones (Table I). The other samples comprise mixtures of soft sediments, duplicated sediments of the same sampling location, coarse sand and gravel, and pumices, and were not or only preliminarily studied. The techniques applied to all the samples comprise microscopic observations on smear slides, X-ray diffraction on disoriented powders of finely grinded bulk material, and X-ray diffraction on oriented pastes of non-calcareous less than 2 I~m particles (i.e., clay fraction). They allow a precise lithological and mineralogical description. A large number of selected samples has been submitted to additional specific techniques: measurement of organic matter content with a Rock-Eval device (30

samples; analyses done at French Institute of Petroleum); transmission electron microscopic observations on the clay fraction of 25 samples, atomic absorption spectrometry in order to measure 13 major and trace elements of the bulk material (38 samples); microprobe measurements of the geochemistry of isolated clayey particles; micromorphological and geochemical observations of volcanic-rich sediments by scanning electron microscope coupled with an EDAX device (performed by A. Desprairies, Orsay University). Most of the analytical procedures are reported by Chamley and Debrabant (1984), and Debrabant et al. (1985).

Late Cenozoic sedimentary e n v i r o n m e n t In spite of the large variety of sedimentary facies encountered in a given diving area

51 TABLE I Areal d i s t r i b u t i o n of the studied s a m p l e s a Area

Clay to silt

Claystone to siltstone

Tenryu

l-l-T1. 1-3-T1. 1-5-BC. 1-5-T1. 1-7-BC. 1-7-T1.

1-3-1. 1-3-2. 1-7-R1.

Zenisu

1-2-BN. 1-4-4. 1-4-BC. 1-6-BC.

1-2-1a. 1-2-1c. 1-2-2a. 1-2-2b. 1-2-2c. 1-2-3. 1-2-4d. 1-2-5. 1-2-6. 1-4-1. 1-4-2. 1-4-3(g) 1-4-3(w)

Suruga

2-1.1.

Boso

Limestone

2-3-2. 3-9-5. 3-10-2.

2-3-3. 2.5.3. 2-5-6a. 2-5-6b. 3-9-1.3-9-2. 3-10-1.

2-8-1.2-9-1.2-9-3. 2-9-4.

Kashima

2-5-7. 2-6-2. 2~7-2.

2-5-5. 2-6-3/4. 2-7-1. 2-7-BC. 3-9-3. 3-9-T1.3-9-T2. 3-10-5.

N. Japan Trench

3-6-5b. 3-NHK.

3-1-1.3-1-5.3-6-1. 3-6-2. 3-6-6.

S. Kuril Trench

Sandstone

3-4-1.3-4-2. 3-4-3. 3-4-4. 3-4-5. 3-4-6. 3-4-6a. 3-5-1.3-5-2.

T = T u b e corer. B C = B o x corer. B N = s e d i m e n t a t t a c h e d on b o t t o m Nautile. ( g ) = g r a y - g r e e n . (w) = white to black. N H K = dive for J a p a n TV. aLegend: 3-4-1 --* Leg - - Dive of a given leg - - Sample of a given dive.

(Table I), some geographical trends can be identified from microscopic and geochemical investigations. The deposits from the inner wall of the Nankai Trench (Tenryu Canyon, accretionary prism) are characterized by relatively large amounts of silicon, and low amounts of iron, magnesium and manganese (Fig.2, Table II). These characters are caused by high terrigenous influx and sedimentation rates, responsible for the abundant supply of quartz and detrital feldspars (Table III), as well as for the dilution of Fe-Mg alkaline volcanic supply and for the fast burial which prevents Mn oxidation processes. The importance of the detrital supply off South Japan, emphasized by detailed investigations on sandy turbidites (De Rosa et al., 1986), is determined by the active filling of the Nankai Trench by materials directly provided by the

Fuji-Tokai river drainage system. Both Suruga and Boso diving areas, respectively located on the external part of the Nankai Trench and along the Sagami Trench (Fig.l), are also exposed to active terrigenous supply and burying, but somewhat less than in Tenryu area. Oxidized and semi-consolidated mudstones to siltstones crop frequently out on the sea-floor. They contain significant amounts of biogenic calcite (Tables II and III) preserved from dissolution because of the relatively moderate water-depth (> 3120 m). The Northern part of Japan Trench and Southern part of Kuril Trench diving areas show opposite trends of silica and iron-magnesium contents, like the Tenryu Canyon. But the opposition is much higher than in Tenryu area, and the cause is different. The abundance of silica is determined here by both siliceous

52 TENRYU ZENIZU

6,

SURUGA BOZO

KASHIMA

JAP. AND KUR. TR.

Siliceous influences 5

,L

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Ferro-Magnesian influences

0,5

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Fig.2. A v e r a g e geochemical t r e n d s of t h e s e d i m e n t a r y e n v i r o n m e n t (non-calcareous sediments).

microfossils (diatoms, radiolarians) and acid volcanic glass, the latter being also responsible for high amounts of aluminum relative to iron and magnesium (see for instance Fe203/ A1203, Fig.2). Calcite is usually absent. Dolomite occurs sometimes together with barite, and probably results from early diagenetic processes. The high values of Mn* index (and often of copper) (Fig.2) proceed from both volcanic activity and secondary oxidation impregnations. Feldspars are mostly potassic and sodic. Volcanic glass shows no or only little alteration patterns. The southern flank of Zenisu Ridge, that represents a topographic high between the Shikoku Basin and Nankai Trench, reveals geochemical trends intermediate between those of the near Tenryu Canyon and of the Japan-Kuril Trenches. The silica relative abundance is minimum and the iron-magnesium oxides show maximum values (Table II, Fig.2). This is determined both by a diminution of detrital influx from Japan over the Zenisu barrier (decrease of quartz abundance, Table III), and by a strong alkaline volcanic

activity (altered volcanic glass, plagioclases, pyroxenes, zeolites). The values of the Mn* index reflect strong oxidation processes. They result from the abundance of metallic coatings on muddy and silty sediments (Table I), favored by lower sedimentation rates, and by the diminution of terrigenous supply. The Daiichi-Kashima Seamount area, located southeast of Honshu Island in the South Japan Trench, displays a large variety of sedimentary facies (Tables I-III), expressed by the diversity of bulk mineralogy and geochemistry. The late Cenozoic muds to siltstones, generally devoid of carbonate fractions, depend on fairly strong terrigenous input, moderate volcanic influences and low oxidation processes (Fig.2). The Hauterivian to Apto-Albian limestone (Pascal, 1986) contain very few silicates (clay minerals, quartz, feldspars), are Sr-rich and sometimes include diagenetic phosphates (Tables II and III). All sediments contain low amounts of organic matter, which precludes measurements on its evolution stages. The total organic carbon ranges between less than 0.1% and 0.8%, the

53 TABLE II

Example of bulk geochemistry data in samples of Kaiko diving areas Area

Tenryu

Zenizu

Suruga

Boso

Kashima

1-3-1

1-2-4d

2-1-1

2-9-1

2-3-3

2-5-5

2-6-2

N.Jap.Tr. S. Kuril Tr. 3-1-1 3-4-2 3-4-4

56.30 15.62 7.18 1.09 4.39 3.08 1.59 0.60

58.60 14.38 6.60 8.24 2.35 3.19 1.83 0.58

57.10 13.89 6.41 10.33 2.32 2.39 1.71 0.56

0.90 0.31 0.19 52.00 0.47 0.27 0.10 0.03

38.10 8.01 3.48 23.38 1.31 2.91 1.63 0.28

59.90 18.23 6.49 1.44 2.43 2.45 2.48 0.63

71.50 13.56 4.66 1.03 1.97 3.23 2.45 0.52

78.20 9.54 3.49 0.70 1.49 2.09 1.90 0.33

76.60 12.45 1.69 1.27 0.38 3.32 2.66 0.20

116 1967 205 41 55 11 15 29 31 40

342 805 263 40 23 23 22 49 28 160

368 736 189 43 26 43 24 52 27 150

137 147 379 0 21 12 16 5 34 10

842 468 447 17 30 21 15 31 33 40

126 778 310 100 44 78 21 21 50 80

79 1199 174 57 46 48 16 66 33 100

100 221 231 34 43 44 7 117 33 90

116 400 168 6 20 9 13 > 700 44

Major elements (%) SiO/ A120 3 F%O 3

CaO MgO Na20 K20 TiO2

63.70 15.52 6.06 2.16 2.48 2.84 2.41 0.60

Trace elements (p.p.m.) Sr Mn Zn Li Ni

Cr Co Cu Pb V

179 700 174 58 37 60 15 49 41 110

Geochemical parameters SiO2 A1:O3

4.10

3.60

4.08

4.11

2.90

4.76

3.29

5.27

8.20

6.15

Na:O K20

1.18

1.94

1.74

1.40

2.70

1.79

0.99

1.32

1.10

1.25

FeEO 3 + MgO AlzO3 A1 Al+Fe+Mn Mn*

0.55

0.74

0.62

0.63

2.13

0.60

0.49

0.49

0.52

0.17

0.66

0.61

0.62

0.62

0.63

0.68

0.68

0.67

0.84

0.10

0.48

0.13

0.10

0.17

0.12

0.45

-0.16

0.42

-

Mn* = Log [(Mn s a m p l e / M n shale)/(Fe sample/Fe shale)]. For detailed significance of geochemical parameters, see Debrabant and Foulon (1979).

highest amounts being observed in some muds and mudstones of Tenryu Canyon (1-3-T1: 0.7%; 1-5-Tl: 0.75%), of Boso Canyon (2-8-1: 0.8%; 2-9-3: 0.6%), and of Kashima Seamount (2-5-5: 0.8%; 3-9-3: 0.75%). Late Cenozoic mineralogical provinces, implications on sources and climatic expression The predominant terrigenous origin of marine clay assemblages in recent sediments ,'b

around the Japanese islands is widely demonstrated (e.g. Kobayashi et al., 1964; Aoki and Oinuma, 1974; Aoki et al., 1974; Huang and Chen, 1975; Murdmaa et al., 1977; Kolla et al., 1980). This allows us to interpret the different clay assemblages encountered in terms of different terrigenous sources. The middle to late Quaternary sediments, able to be biostratigraphically dated (Monjanel et al., 1986), show the existence of two major mineralogical provinces (Fig.3). The diving areas located south of Japan (Tenryu Canyon and Nankai

54 TABLE III Examples of bulk mineralogy data in samples of Ka~ko diving areas Area

Clay minerals

Calcite

Dolomite

Quartz

Feldspars

Pyroxenes Glass, opal

Tenryu l-l-T1 1-3-2

A RA

R

-

VA VA

A RA

-

Suruga 2-1-1

RA

RA

-

A

A

-

Boso 2-9-4

A

A

-

A

RA

-

Zenisu I-2-2C 1-2-6 1-4-3(g)

A A A

-

-

A RA R

RA RA A

R RA

Zeolites (clino./ heul.)

Biotite

RA

RA

-

A

-

RA

Barite

Apatite

Kashima 2-5-6

VR

VA

.

2-5-7

RA

RA

-

.

RA

A

-

2-7-1

RA

-

-

A

RA

-

3-10-2

VR

R

.

N Japan Trench 3-6-2 R 3-6-5b A

-

R -

R A

RA

-

R

S Kuril Trench 3-4-2 A 3-4-6 R 3-5-1 A

-

-

A A

RA RA RA

R -

A VA RA

.

.

.

.

A

.

A

RA

VA = very abundant. A = abundant. RA = common. R = rare. VR = very rare. Trough accretionary prism, Suruga Canyon, Boso Canyon, and to a lesser degree Zenisu Ridge), show relatively high amounts of illite, chlorite, quartz, feldspars and amphiboles (--"illite group"). They form a first province, widely extended toward the west and the south, according to data from DSDP and piston c o r e s ( K o l l a e t al., 1980; C h a m l e y e t al., 1985a; Y i n e t al., 1987). T h i s t y p i c a l l y d e t r i t a l a s s e m blage results from the abundance of plutonic, metamorphic and old sedimentary rocks outc r o p p i n g i n t h e s o u t h o f H o n s h u I s l a n d (e.g. M i n a t o e t al., 1965), a n d a c t i v e l y e r o d e d . T h e Z e n i s u a r e a is s o m e w h a t l e s s d e p e n d e n t o n t h i s South Japan terrigenous supply, because of morphological obstacles and local volcanic activity (see below). Nevertheless it belongs to the same province.

The Daiichi-Kashima and Japan to Kuril Trench diving areas constitute a second mineralogical province, characterized by abundant smectite at the expense of the illite group (except the feldspars). Also supported by DSDP data recorded elsewhere east of Japan (Mann a n d M f i l l e r , 1980; C h a m l e y e t al., 1985a), t h i s d o m a i n is m a i n l y d e t e r m i n e d b y t h e r e l a t i v e abundance of volcanoes in Eastern and N o r t h e r n H o n s h u ( M i n a t o e t al., 1965), t h e weathering of which provide large amounts of s m e c t i t e ( S u d o a n d S h i m o d a , 1978). T h e e r o s i o n o f J a p a n e s e T e r t i a r y s e d i m e n t a r y r o c k s is also responsible for the supply of smectite to the ocean. The subaerial alteration of volcanic r o c k s is v e r y f a s t a n d m o r e l i a b l e t o p r o v i d e large amounts of smectite to the common sediments than the submarine alteration. Such

55

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.0 Fig.3. Average mineralogical composition of the clay fraction in the late Quaternary sediments of Ka~ko diving areas. The total height of a clay log represents 100% . Associated non-clay minerals are plotted on an arbitrary scale.

active terrigenous reworking processes are consistent with the abundance of redepositional sedimentary structures (Ka~ko Shipboard Party, 1986) and with the presence of shallow-water and even of fresh-water reworked diatom debris (A.-L. Monjanel, pers. comm., 1986). The clay mineralogical successions attributed to Quaternary sediments do not clearly express climatic variations, related for instance to glacial/interglacial variations or to latest Cenozoic global changes (see Fig.5). This result differs from those obtained on diatoms and radiolarians, which express temperature changes of sea water (J.-P. Caulet and A.-L. Monjanel, pers. comm., 1986). The cause of this difference lies in the usually pedogenic origin of climate-shaped clays. M a n y Japanese soils are deeply dissected because of the subperman-

ent tectonic instability, and do not reach a real equilibrium stage with the climatic conditions. The tectonic effects on clay composition and shapes predominate over the climatic effects.

E x p r e s s i o n o f Late Cenozoic t e c t o n i c activity In Tenryu, Suruga and Boso areas (= mineralogical province 1), the clay mineralogy of the various clayey to silty muds and mudstones sampled by the submersible shows two groups of compositions. One group is characterized by 60-75% illite plus chlorite, and by 10-25% smectite, in the <2 pm fraction. The other group contains 35-50% smectite, and only 40-50% illite plus chlorite. There is no intermediate clay composition. This distinction made on the sediments cropping out on the

56 sea floor strongly resembles the mineralogical change observed on the continuously cored sediments at Site 582 DSDP, located on the inner wall of the Nankai Trench, West of Tenryu-Suruga area (Fig.l). Somewhere in the early Pleistocene, the amount of illite plus chlorite suddenly increases at the expense of smectite abundance, whilst hemipelagites are replaced by turbiditic sediments (Fig.4). This fast change at Site 582 is attributed to a strong increase in the detrital supply of materials derived from Japanese rocks after the collision between Izu and Honshu islands provoked an uplift of Southeastern J a p a n (cf. Chamley et al., 1985; Taira and Niitsuma, 1986). The Ka~ko study area located between Tenryu and Boso canyons depends on Southeastern J a p a n detrital supply, in the same manner as Site 582 area (Taira and Niitsuma, 1986). It is thus suggested that each group of clay assemblages identified in surface sediments characterizes the depositional conditions existing either before (smectite) or after (illite group) the tectonic collision responsible for the formation of the Izu peninsula (Fig.5). As a result, the clay mineralogy of the sediments randomly sampled on the sea floor is able to express different tectonic conditions during recent geological times. Such a possibility of using mineralogical assemblages to identify a sedimentary expression of tectonic events does not exist in the

SITE 5 8 2 DSDP

CLAY

Kai'ko areas located East of J a p a n (= mineralogical province 2), where collision effects are recorded much earlier in past geological times (Chamley and Cadet, 1981; Von Huene et al., 1982).

Stratigraphic indications Because of the location of most Ka~ko sampling areas between 4500 and 6000 m, i.e. below the carbonate compensation depth, and because of the scarcity or sensitiveness of biosiliceous shells to dissolution, various samples are devoid of clearly recognizable fossils (Monjanel et al., 1986). Such a shortage of direct biostratigraphic markers occurs in various deep-sea pelagic or organic-rich sediments, and leads to the search for indirect stratigraphic indicators. The mineralogical zonation helps sometimes in such a way. South of Japan, in the Northern Philippine Sea, previous studies have shown a roughly progressive increase of smectite contents correlated with the increased age of sediments. In Shikoku Basin for instance, the smectite abundance increases from about 35 to 90% of the clay fraction, between the early-middle Pleistocene and the middle Miocene (Fig.6). This change is attributed to both more hydrolizing climate and more active volcanic activity before the latest Cenozoic (Chamley, 1980). When comparing the clay mineralogy with

MINERALS QUARTZ AMPHIBOLES FELDSpAR8

P

±

(~ ~- PLEISTOCENE /

/ (CORES ,, A,.., i--

!

1

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(20-35)

(8-17)

(25-40)

MIXED[~"/~LAYERB~]'n'~$MECTITE ~ : ; ~ K AOLINITE

RARE • FAIRLY COMMON O COMMON • VERY COMMON O

Fig.4. Site 582 DSDP, inner wall of Nankai Trench. Average clay fraction compositionof post- and pre-early Pleistocene sediments (after Chamleyet al., 1985a).

57

I TENRYU,SURUGA,E}OSO

EARLY TO LATE PLEISTOCENE SOFT SEDIMENTS

1-3-T1 ....~.....

1-5-BC 1-5-T1 1-7-BC I ¢-[

~1

AREAS ]

.,....,,,,.,.,..

Samples

1-7-T1 2-i-i

CONSOLIDATED SEDIMENTS 1-7-R1

LOWERMOST PLEISTOCENE AND OLDER Samples

m

SEDIMENTS CONSOLIDATED SEDIMENTS

1-3-1 1-3-2 2-9-1 2-9-3 2-9-4

. . . .

2-8-1 0 mchlorite

[:~illite,

50

100%

[~,--~ mixed-layers [T]-FI smectite y:EE~kaolinite

II

:':.:.:+:.:-

amphiboles

feldspars quartz

Fig.5. Tentative i n t e r p r e t a t i o n of South J a p a n Ka~ko samples (muds to siltstones) in terms of post- and pre-tectonic depositional groups, and of younger to older deposits, from clay mineralogical data (associated non-clay minerals on an arbitrary scale).

the biostratigraphic data in Ka~'ko bottom sediments where both are available, a proportional relation appears in the Tenryu canyon area. For instance the smectite abundance increases with increased age provided by radiolarians (J.-P. Caulet, pers. comm., 1986), in Late Pliocene to Pleistocene sediments (Fig.7). As a consequence, it is possible to propose relative stratigraphic positions for the different muds, mudstones and muddy siltstones cropping out on the sea-floor. An attempt is presented in Fig.5, for sediments of both pre- and post-tectonic depositional groups previously identified in the Tenryu, Suruga and Boso diving areas. The smectite increase in older sediments, the age of which is sometimes checked by biostratigraphy, corresponds to a downward decrease of the illite group and

associated minerals (quartz, amphiboles and part of feldspars). Comparable indirect deductions on the stratigraphic positions of sea-floor sediments and sedimentary rocks cannot arise from mineralogical investigations in other Ka~ko diving areas. South of Zenisu Ridge, the competition between the detrital input, the volcanic activity and the diagenetic processes (see below) results in a wide range of smectite contents within the sediments of a given biostratigraphical age (Fig.7). The mineralogical dispersion is still larger when considering the whole late Cenozoic time interval in this area (Fig.8). In Late Cenozoic sediments located close to the junction between the J a p a n and Kuril trenches, the smectite abundance does not significantly change with time. This is known

58

SITE 4 4 4 - L E G 58 DSDP

CL-AY

MINERALOGY ASSOCIATED MINERALS • RARE 0 COMMON OABUNDANT N rt t~ t'r

CI

,,,,

LtJ

w

~

0

q~

qD

Fig.6. Mineralogy of the clay fraction in middle Miocene to Pleistocene sediments at Site 444 DSDP, Shikoku Basin (after Chamley, 1980). See the site location on Fig.1.

from DSDP Sites data (Mann and Miiller, 1980; Chamley et al., 1985a) and is confirmed for Ka~'ko sediments by comparison of data on clays and on radiolarians (Fig.7) and diatoms (Fig.9). A similar situation, with probable additional diagenetic modifications, characterizes the late Cenozoic sediments of the DaiichiKashima Seamount area (Figs.8 and 10). Indications on early Cretaceous environments

The study of the non-carbonate fraction of Valanginian to Apto-Albian limestones sampled on the subducting Daiichi-Kashima Seamount can provide complementary informations to those arising from paleoecological investigations (Pascal, 1986). A large range of

mineralogical assemblages is identified from X-ray diffraction analyses (Fig.8B). This indicates the existence of various possible origins. (1) Some limestones or marly mudstones contain abundant smectites (65-95%; e.g. 2-3-2, 2-33, 2-7-1), whose shape is flaky (Plate I, C), and the chemistry marked by an A1-Fe character (A1-Fe beidellites, Fig.llD; Table IV). These minerals, the morphology and composition of which resemble recent detrital smectites (Fig.llC, F) could result from the reworking of soils formed under a warm climate (e.g. Sudo and Shimoda, 1978). (2) A bioclastic neritic limestone shows kaolinite- and smectite-rich assemblages (2-5-3. Fig.8B; Plate I, D), the latter mineral consisting of Fe-beidellites marked by abundant Ti, Na and tetrahedral substitutions (Fig.liE; Table IV). Such a clay

59

RADIOLARIANS M.Y. 0

AGE

~

-f-

OIl|lilllllllilll|llll(~ll(~llllllllll

N

*

[]

10TENRYU CANYON S ZENISU RIDGE N E JAPAN

0

[]

m

O 0

I

10

I

20

I 30

4M0

I 50

I 60

L 70

8L 0

90%smectite

Fig.7. Radiolarians biostratigraphic ages (J.-P. Caulet, pers. comm., 1986) vs. smectite abundance, in three Ka~kodiving areas. composition suggests active weathering of rocks including volcanic components (probably the volcanic substrate), under warmhumid conditions. Kaolinite could also proceed diagenetically from acid water circulation in the porous limestone, but this is less probable in a submarine environment. (3) A third typical assemblage contains abundant illite (3-10-1: 60% of clay fraction), which could result either from erosion of crystalline substrates, or from early diagenetic changes (see Deconinck and Strasser, 1986) in the Gargasian intertidal environments described by Pascal (1986). (4) Other Cretaceous sedimentary rocks contain various clay minerals (e.g. 2-5-6, mixture of illite, chlorite, irregular mixed-layers, smectite, kaolinite). This suggests the probable influence of terrigenous non-volcanic sources for the small-sized silicate components of

Kashima Seamount sediments, especially during the Neocomian marked by platform environments. Competition between continental marine influences

and

(1) A stated above, most-fine-grained sediments deposited around the Japanese islands have a terrigenous origin, favored by the strong erosional processes linked to the tectonic instability (e.g., Kobayashi et al., 1964; Aoki et al., 1974; Mann and Miiller, 1980; Chamley et al., 1985a). This is peculiarly the case in the Nankai Trough and in the J a p a n to Kuril Trench areas, where important redeposition processes occur and are responsible for the abundant supply of typically detrital illites, chlorites and associated non-clay miner-

60

S O U T H Z E N I S U RIDGE LATE

i

CENOZOIC

A

MUD,MUDSTONE,SILTSTONE

N

o~

o

-fii

i

10 O i ,

• .-r/l~ll[l~

1-2-Bottorn

Naulile

1-2-2a,b,c

I - 6 - Box Core KASHIMA

1-4-4,Box

| , ,;---.i 1-2-1a,1c,4d,5 1-4-3

1-2-6 1-4-1,2

Core

SEAMOUNT

EARLY CRETACEOUS LIMESTONES

B

:::!i!

.'....:.[ .-.,~ ....r : '....•!

2o,1 '°o 1 3-10-1

2-5-6e

2-5-6

2-5-3

2-3-3

Fig.8. Mineralogical variations in the clay fraction of late Cenozoic muds to silty mudstones from Zenisu Ridge area (A), and of early Cretaceous limestones from Kashima Seamount (B),

als. The illites and chlorites often display sharp outlines and a fresh aspect (Plate I, A). The illites studied by microprobe analysis are potassium-rich, with the following average formula (Tenryu, 1-3-T1; Fig.10A): (8i3.2, Aloso) • (A11.37, Mgo.30, Feo.33, 3+ Ti0.o2) Ko.76, Nao.18, Cao.o4Olo(OH)2 Chlorites of the. same area are iron-rich (Fig.10B), with chemical formulas ranging between more and less magnesian types: type 1: (Si2.79, All.21 ) ( M g l . 3 6 , Fex.55, 2+ Tio.02)Ko.03, Nao.o5, Cao.olOlo(OH)2 (Alo.s9, Mgz.zT)(OH)6 type 2: (Si3.z5 , A10.75) (Fe2.72, 2+ Tio.02)Ko.15, Nao.z5, Cao.04Olo(OH)2 (Al1.21, Mg1.19, FeoZ.~7)(OH)6

(2) Most smectites are also exclusively terrigenous, as shown by their flaky and cloud-like aspect, their morphological independence with other clay and non-clay particles (Plate I, A, B), and their alumino-ferrous composition with low amounts of magnesium (e.g. Boso Canyon, sample 2-9-1; North Japan Trench, 3-6-6. Fig.llC, F; Table IV). These smectites are A1-Fe beidellites, typically developed on land by weathering processes under fairly hot climate, from non-volcanic or volcanic rocks. Note that the sediments in which deep-sea benthic communities develop (clams and other animals and bacteria) do not show any noticeable clay mineralogical peculiarity, which could be related to fluid migration at the subduction front (e.g., sample 1-5-T1). (3) In spite of the overwhelming terrigenous

61

M.Y. 0

D I A T O M S

AGE r

[] ¢1

0~ I

0 .J Q.

2

z 10--

w

• '

0

\\\ "/ L _ . ~

1//

"o

KASHIMA

AREA

N E JAPAN

E

t 10

I 20

[ 30

40

I 60

50

I 70

t 80

90%

srnectite

Fig.9. D i a t o m s b i o s t r a t i g r a p h i c ages (Monjanel et al., 1986) vs. smectite a b u n d a n c e , in t h r e e Ka~ko diving areas. TABLE IV Chemical c o m p o s i t i o n and a p p r o x i m a t e chemical f o r m u l a s of Ka~ko s e d i m e n t a r y smectites, from m i c r o p r o b e a n a l y s e s Area

Zenizu

Boso

Kashima

Jap,Tr.

Kur.Tr.

Samples

1-2-1a

1-2-4d

1-2-5

1-2-6

1 - 4 - 2 1-4-3w

2-9-1

2-3-2

2-3-3

2-7-1

2-5-3

3-6-6

3-4-4

SiO 2 A120 3 MgO F%O 3 TiO2 K20 Na20 CaO

56.65 17.96 6.71 11.68 0.70 1.99 1.67 2.10

55.64 17.35 6.69 9.46 0.65 3.98 4.02 1.69

60.16 18.35 6.31 9.13 0.98 1.47 0.75 2.51

56.91 15.18 5.91 12.34 0.70 4.09 1.49 3.11

60.12 17.21 5.42 8.36 0.19 3.31 3.88 0.72

54.02 25.08 5.07 4.73 0.43 4.44 2.97 2.44

58.80 16.53 3.75 14.45 0.91 3.55 0.86 1.04

54.41 18.00 4.11 17.26 0.89 3.00 0.72 1.45

51.95 17.91 3.47 15.43 2.43 4.38 1.75 2.25

53.51 16.09 3.86 15.29 0.70 4.24 5.90 0.30

42.43 22.50 2.73 19.54 1.30 3.04 5.43 1.22

58.76 18.36 4.04 13.65 0.67 2.45 0.84 1.04

62.41 23.68 1.61 2.85 0.47 3.64 3.11 1.51

Tet. sheet Si 4+ A13 +

3.58 0.42

3.57 0.43

3.71 0.29

3.64 0.36

3.78 0.22

3.41 0.59

3.71 0.29

3.48 0.52

3.38 0.62

3.50 0.50

2.89 1.11

3.67 0.33

3.82 0.18

Oct. s h e e t A13 ÷ Mg 2 ÷ Fe 3 + Ti 4÷

0.91 0.64 0.55 0.03

0.88 0.64 0.45 0.03

1.04 0.58 0.42 0.05

0.79 0.57 0.60 0.03

1.05 0.50 0.40 0.01

1.28 0.48 0.22 0.02

0.94 0.35 0.69 0.04

0.84 0.39 0.84 0.04

0.76 0.34 0.76 0.12

0.74 0.38 0.75 0.03

0.70 0.28 1.00 0.07

1.03 0.38 0.64 0.03

1.53 0.15 0.13 0.02

Interlay K÷ Na ÷ Ca 2÷

0.16 0.20 0.14

0.30 0.50 0.11

0.12 0.09 0.17

0.33 0.18 0.21

0.26 0.47 0.05

0.35 0.36 0.17

0.29 0.11 0.07

0.25 0.09 0.10

0.36 0.22 0.16

0.35 0.75 0.02

0.27 0.72 0.09

0.20 0.10 0.07

0.28 0.36 0.09

No. of Meas. 29

13

27

21

28

28

12

24

24

Tet.sheet = t e t r a h e d r a l sheet. Oct.sheet = o c t a h e d r a l sheet. I n t e r l a y = i n t e r l a y e r sheet.

7

14

10

4

62

: -:..:,'. -..- : •

.

..-

,

:.:i)"::::.HONSH.U.:I:i.'.: .'!

Tenr, u:'/i'/,"~////I Suruga KYUSHU

582

®

Zenisu

,

philippine plate

m

Si 4+

a = illite 1-3-T1

AI 3+

b = Fe-chlorite 1-3-T1

Mg

[]]]~ Fe

2+ 2+

Fe 3+

C = s m e c t i t e 1-4-3w d = AI-chlorite 1-4-3w e = kaolinite 1-4-3w

Fig.10. Schematic geochemical composition of clay minerals in sediments rich either in illite and chlorite (Tenryu Canyon, 13-T1), or in biotite (South Zenisu Ridge, 1-4-3 w), from microprobe analyses. The different chemical elements are located in tetrahedral and octahedral sheets.

influence, some diagenetic processes occur. The less intense process corresponds to the growth of lathed structures, arranged in bundles oriented at 60 ° to each other, at the periphery of smectites but also of some other clay minerals (Plate II, A, B). The laths are sometimes absent, sometimes well developed and completely replacing the flaky smectites, all intermediate morphologies being observable. If one compares close sediments with and without lathed minerals, it is not possible to find noticeable differences in the clay mineral composition. These structures, already encountered elsewhere in the Western Pacific and in the Atlantic Oceans, are interpreted as the result of very early diagenetic processes,

occurring within little permeable microenvironments under stable mineralogical and geochemical conditions (Holtzapffel et al., 1985; Holtzapffel and Chamley, 1986; Chamley et al., 1985b). The environmental conditions favoring the growth of laths include mainly a little porous medium, a fairly low sedimentation rate and the scarcity of silica-rich diagenetic minerals (opal CT, clinoptilolite). (4) More extensive diagenetic influences occur in sediments containing abundant volcanic debris, whose clay fraction is formed by up to 100% smectite. These sediments consist of mudstones to muddy siltstones, located either in South Zenisu Ridge area (1-2-1a, 1-2lc, 1-2-4d, 1-2-5, 1-2-6, 1-4-3) or on the South

63

PLATE I

Electro-micrographs (bar = 1 ~m). A. Tenryu Canyon, recent gray mud (1-1-T1). Abundant well-outlined illite and chlorite, associated with fairly abundant flaky and cloud-like smectite, and irregular mixed-layered minerals. B. South Zenisu Ridge, gray-olive late Cenozoic muddy siltstone (1-2-3). Abundant flaky and cloud-like smectite particles, with few well-shaped illites and chlorites. C. Kashima Seamount outer wedge, white biogenic Cretaceous limestone (2-3-3). Very abundant (95% of clay) small-sized and flaky smectite, with low amount of small kaolinite hexagonal sheets. D. Kashima Seamount, whitish bioclastic Cretaceous limestone (2-5-3). Abundant large-sized hexagonal kaolinite, and flaky smectite.

64 EURO-ASIAN '.:": " ~ D "PLATE : ~ "::::'.":.'y/ •

.

. . : . ¢ .

C'x.f"

I

.

\

/ / /~'I L/ )

',./2 / I

~/ ' v / /,~I f/

/

/

/ ,..) /

.

.

:.,.':-..~_ AMERICAN PLATE :." ":.".":..~?:XJ:--..."

/i

/,

. i

)

INA (

"I

.

• hbk'KAii~dY ~"

~.

JAPAN

SEA /~

F') I

(/ 1 (

/

f/~'

al Kashima PACIFIC PLATE

KYUSHU

'.enisu

b

Average 1 - 2 - le 1-2-4d 1-2-5 1-2-6 1-4-2

: 1-4-3w

C : 2-9-1

Average

d

'~ 5hikoku basin

--

g

study area

~

Si

r=l

A,

3+ 2+

subduction I

Mg

zone

Fe 3 +

~

e: f g:

t 2-3-2 2-3-3 2-7-1

2-5-3 : 3-6-6 3-4-4

PHILIPPINE PLATE

Fig.ll. Schematic geochemical composition of smectites, from microprobe analyses. The different chemical elements are located in tetrahedral and octahedral sites.

Kuril Trench inner wall (3-4-4, 3-4-6). In Zenisu area, the in situ formation of smectites is responsible for large differences in late Cenozoic clay assemblages (Fig.8A). In this area, smectites develop at the expense of small-sized, altered and somewhat porous volcanic glass (SEM observations, A. Desprairies, pers. comm., 1986). They form ruffled hair-like structures, more or less developed on the external parts of glass hards, and sometimes replacing completely the volcanic debris (Plate II, C, D). Analyzed by microprobe, these smectites are both magnesium- and iron-rich, with moderate amounts of aluminum (Fig.llA; Table IV). The average chemical composition indicates the presence of F e - M g montmorillonite, either more siliceous:

Si4(A1H4 ' Mgo.35 ' Feo.44, 3+ Tio.03)Ko.06, Nao.04, Cao.17Ozo(OH)2,

or more alumino-ferrous: 3+ (Si3.49, Alo.51) (Alo.61, Mgo.62, Feo.73, Tio.o3)Ko.37, Nao.19 Cao.2sOlo(OH)2.

These smectites certainly represent the re: sult of the submarine alteration of volcanic glass, marked by a calco-alkaline character (abundance of plagioclases). (5) The volcaniclastic and biotite-rich sandy mudstone sampled in Zenisu area during dive 4 (1-4-3) contains ruffled smectites and also layered clay minerals developed at the expense of micas (Plate III, A). The microprobe analysis shows the presence of various clay minerals:

65

PLATE II

Electro-micrographs ( b a r = 1 ~ra). A. South Zenisu Ridge, greenish muddy siltstone (1-2-2a). Development of 60 ° oriented laths system at the periphery of detrital clay minerals. Laths peculiarly develop at cloudy-like smectites expense, but also round the other clay species. B. Kashima Seamount, gray semi-indurated silty clay (2-5-7). Growth of laths round a detrital illite, as a system oriented at 60 ° angles. Note the absence of morphological relations with the partly dissolved adjacent biosiliceous debris (left side). C. South Zenisu Ridge, bioturbated and light gray volcaniclastic clayey siltstone (1-2-4d). Homogeneous black particles of volcanic glass with some cavity-like features at the periphery. Growths of ruffled hair-like smectites at the expense of smaller glass particles (right side). D. South Zenisu Ridge, bioturbated whitish to blackish volcaniclastic and micaceous sandy mudstone (1-4-3 w). Ruffled hairlike smectite h a v i n g entirely replaced altered volcanic glass.

66 mainly aluminum-rich Mg-beidellites, but also dioctahedral (Al-rich) chlorite or pseudo-chlorites, and kaolinite (Fig.10C, D, E; Fig.llB; Table IV). These various minerals probably PLATE III

developed within the biotite particles under acidic conditions, and evolved chemically with mutual connections, as shown elsewhere by Weaver and Pollard (1973) and Velde (1985).

67 (6) The light-colored v o l c a n i c l a s t i c silty m u d s t o n e s o u t c r o p p i n g on the i n n e r wall of the S o u t h K u r i l t r e n c h r e v e a l the exclusive develo p m e n t of a n o t h e r and p e c u l i a r type of smectite. T h e clay m i n e r a l c o n s t i t u t e s filmy and t r a n s p a r e n t veils r o u n d the fresh and massive r h y o l i t i c glass p a r t i c l e s (Plate III, B, C), and does not develop on the N a - K feldspars also p r e s e n t in the sediment (A. Desprairies, pers. comm., 1986). T h e m i c r o p r o b e a n a l y s e s point.to the f o r m a t i o n of d i o c t a h e d r a l smectites, v e r y rich in silica (no t e t r a h e d r a l s u b s t i t u t i o n ) and in aluminum, and depleted in m a g n e s i u m ( F i g . l l G ; T a b l e IV). Those p e c u l i a r a u t h i g e n i c clay minerals, observed in p o r o u s volcaniclastic r o c k s showing friction s t r u c t u r e s , could r e p r e s e n t the only witnesses of silicate c h a n g e s linked to s o l u t i o n p r e s s u r e and fluid m i g r a t i o n d u r i n g the s u b d u c t i o n of the Pacific plate b e n e a t h J a p a n . It is difficult to test such a h y p o t h e s i s by now, b e c a u s e the r a r e examples of clay d e v e l o p m e n t a t t r i b u t e d to the r e s u l t of s u b d u c t i o n o v e r t h r u s t s seem r a t h e r m a r k e d by the p r e s e n c e of m a g n e s i u m smectite in n o n - v o l c a n o c l a s t i c sediments (Schoonmaker, 1986). N o t e t h a t in all cases the s u b m a r i n e g r o w t h of smectite does not o c c u r on biosiliceous debris, even if the tests show s t r o n g dissolution figures (Plate III, D).

Conclusions The sediments and s e d i m e n t a r y r o c k s sampled by the Nautile on the sea-floor of t r e n c h

areas s u r r o u n d i n g the J a p a n e s e island express v a r i o u s influences on d e p o s i t i o n a l and d i a g e w etic conditions. T h e lithotogy, bulk m i n e r a l o g y and bulk g e o c h e m i s t r y of late Cenozoic m u d / m u d s t o n e s to m u d d y silt/siltstones point to the overw h e l m i n g i m p o r t a n c e of t e r r i g e n o u s supply, only locally completed by s u b m a r i n e volcanic a c t i v i t y (south of Zenisu Ridge, some o u t c r o p s on the S o u t h K u r i l T r e n c h i n n e r wall), early d i a g e n e t i c c h a n g e s (barite, clinoptilolite . . . . ) and o x i d a t i o n processes (metallic coatings and indurations). No m i n e r a l o g i c a l peculiarities are observed in the s e d i m e n t a r y e n v i r o n m e n t s m a r k e d by the d e v e l o p m e n t of deep-sea b e n t h i c c o m m u n i t i e s (clams, etc.). The clay m i n e r a l o g y data allow us to identify two m a j o r s e d i m e n t a r y provinces, to the s o u t h of J a p a n ( a b u n d a n c e of illite, chlorite, quartz, amphiboles, feldspars) and to the east of J a p a n (relative a b u n d a n c e of smectite and feldspars). These mineralogical provinces characterize the t e r r i g e n o u s sources, which largely depend on the d i r e c t erosion of r o c k s instead of soils. T h e fairly w e a k supply of evolved soil-derived m i n e r a l s results from the sloped m o r p h o l o g y and t e c t o n i c instability of J a p a n , p r e c l u d i n g an a c c u r a t e climatic expression of s e d i m e n t a r y clays. Two m a j o r clay assemblages c h a r a c t e r i z e the late Cenozoic surface sediments sampled in N a n k a i T r e n c h and Boso C a n y o n diving areas ( S o u t h Japan). A c o m p a r i s o n done with n e a r b y D S D P Site 582 d a t a shows t h a t these assemblages r e s p e c t i v e l y c o r r e s p o n d to pre- and post-

PLATE III Electro-micrographs (bar = 1 ~tm). A. South Zenisu Ridge, bioturbated whitish to blackish volcaniclastic and micaceous sandy mudstone (1-4-3 w). Development of clay layers at the expense of an altered biotite grain (see microprobe analysis data). The ground shows numerous hair-like smectites issued from porous volcanic glass alteration processes. B. Kuril Trench inner wall, very light gray volcaniclastic silty mudstone (3-4-1). Non-porous fresh volcanic glass particles (e.g., center, right), with a more or less development of filmy transparent clay, which consists of exclusive smectite. C. Kuril Trench inner wall, white-greenish tuffaceous volcaniclastic mudstone (3-4-4). Filmy and transparent smectite developed at the expense of non porous volcanic glass. D. Japan Trench inner wall, siliceous to siltstone (3-6-6).Abundant smectite (70% of clay fraction) with a shape intermediate between ruffled and filmy volcano-derived clays (see Plate II, C, D, and Plate III, B, C). Note the lack of morphological relations between the diagenetic smectite and the partly dissolved diatom debris. Illite and chlorite well-outlined sheets are also recognizable.

68 tectonic early Pleistocene sedimentation. The collision between Izu and Honshu islands determined a tectonic r e j u v e n a t i o n of Central J a p a n river basins, which is clearly expressed by the clay mineralogy of sediments randomly cropping out on the sea-floor. The progressive decrease of smectite abundance in N o r t h Phillipine Sea sediments since the Miocene (e.g. DSDP Sites of Leg 58) allows a t e n t ativ e use of mineralogical assemblages for stratigraphic estimations. A comparison between clay mineralogy and biostratigraphic data done on South J a p a n Ka~ko sediments points to the interest of such an indirect and relative stratigraphic tool, especially in deepsea deposits marked by a poor biostratigraphic record. The shallow-water limestones deposited during the early Cretaceous in the DaiichiKashima S eamo u n t area contain few amounts of phyllosilicates, whose composition varies largely according to the samples, between smectite-rich, kaolinite-rich and illite-rich endmembers. Some indications are provided on Cretaceous environments, especially on various terrigenous and volcanic influences, and on the existence of warm climatic conditions on emerged areas. In spite of the predominant influence of J a p a n es e detrital supply, the late Cenozoic muds to muddy siltstones sampled by Nautile express some diagenetic modifications, particularly identified by electromicroscopic and microprobe investigations. A near l y iso-miner alogical and iso-geochemical growth of laths is observed in some common deposits at the periphery of smectites and some ot he r clay species in some common deposits. The main diagenetic changes are located in sediments containing ab u n d an t volcanic debris, in which very well crystallized smectites often represent the exclusive clays. South of Zenisu Ridge, small and altered ashes give way to ruffled Fe-Mg-smectites, with local development of Mg-beidellites and Al-chloritic minerals at the expense of biotite particles. On the inner wall of the South Kuril Trench, fresh and rhyolitic glass particles are bordered by t r a n s p a r e n t

veils of Si-A1 smectites, which could result from pressure solution and fluid migration in the subduction context.

Acknowledgments We gratefully acknowledge the French-Japanese Kaiko scientific committee, and especially X. Le Pichon, J. T. Iiyama, G. Pautot, K. Nakamura, J.-P. Cadet, K. Kobayashi, for committing to our care the responsibility of dispatching Ka~ko sedimentary materials and their sedimentological study. We benefited by J.-P. Herbin's Rock-Eval measurements on organic m a t t e r (French Institute of Petroleum, Rueil), and by A. Desprairies's SEM/EDAX investigations on micromorphology and particles geochemisty (Orsay University). The technical support in Lille was provided by P. R~court, M. Bocquet, J. Carpentier, F. Dujardin, D, Le Maguer. The financial support was provided by Ka~'ko ASP, CNRS, France.

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